Micrographs

With a bit of help from my workmates, I’ve got my hands on some interesting metal samples which I’ve etched and taken some photos of through my microscope.

Below are some photos of a Martensitic high chromium white cast iron that show evidence of heat checking (cracking due to thermal fatigue, IE, hot grinding)

I’m not 100% sure on what the microstructure is but from what I’ve read (ASM Specialty Handbook: Cast Irons), but what I think I’m seeing below is dendrites of Austenite-Martensite in a matrix of Cementite. The Austenite apparently doesnt 100% convert to Martensite on quenching, though sub-zero heat treatment does get most of it to convert. These samples have had such treatment.

White Cast Iron

White Cast Iron

White Cast Iron

White Cast Iron

You can see the dendrite formation in these two photos.

White Cast Iron

White Cast Iron

White Cast Iron

White Cast Iron

Below are photos of pieces of Austenetic Manganese Steel that have been fillet welded together using some various techniques. The first is with mild steel filler wire, air cooled, no preheat. There is some porosity present as the welder’s gas solenoid started to play up mid weld.These samples were all initially etched with hydrochloric acid (from a pool shop). Since the hydrochloric didn’t etch the stainless samples shown later, I also tried sulphuric (car battery) oxalic acid, phosphoric acid (rust converter), hydrochloric acid + methanol, hydrochloric acid + some other solvent (brick cleaner), boric acid (borax) and garlic salt (I didn’t have any normal salt). I’d really like to try some Nital or Picral but I can’t seem to find anywhere in Melbourne that even knows what it is.

The upper and lower sections with visible grains are the manganese steel. The porours right hand side is the mild steel filler. The shiny bit on the left is a stainless steel tack weld.

Austenitic Manganese Steel welded with mild steel filler, air cooled. Holes are from welding porosity.

Austenitic Manganese Steel welded with mild steel filler, air cooled. Holes are from welding porosity.

Austenitic Manganese Steel welded with mild steel filler, air cooled. Holes are from welding porosity.

Austenitic Manganese Steel welded with mild steel filler, air cooled. Holes are from welding porosity.

The big stain in the middle is a crack. The phosphoric acid really brought that out.

Austenitic Manganese Steel welded with mild steel filler, air cooled.

Austenitic Manganese Steel welded with mild steel filler, air cooled.

Austenitic Manganese Steel welded with mild steel filler, air cooled. Holes are from welding porosity.

Austenitic Manganese Steel welded with mild steel filler, air cooled. Holes are from welding porosity.

Austenitic Manganese Steel welded with mild steel filler, air cooled. Holes are from welding porosity.

Austenitic Manganese Steel welded with mild steel filler, air cooled. Holes are from welding porosity.

Next is the same thing, but quenched in water after welding. Normally, quenching a weld is a big no-no but manganese steel is different. It’s got lots of manganese in it (11-14% or so) which stops carbides from precipitating from the Austenite. The result of this is that it can be quenched, resulting in an Austenitic structure at room temp. It’s soft but work hardens a lot and very quickly. According to the (super awesome) webpage: George’s Basement, the mechanism behind this is something along the lines of this material forms very long stacking faults that interfere with each other and kind of bind up. I think.
Anyway, quenching Mang is OK but the mild steel filler has probably gone Martensitic. Unfortunately, this microscope doesn’t have the magnification to see Martensite’s structure. I might need to get my hands on my old scope which is currently in service looking at dead fish. True story.

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

There appears to be a third kind of metal in here. Damned if I know how. Did the stainless and the mild steel alloy together?

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

You can see here that the quenched sample cracked also.

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

DSC02197

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

Austenitic Manganese Steel welded with mild steel filler, quenched

Next is stainless filler, air cooled. You can see on this one that there is some kinda cross-alloying taking place at the border between the weld and the mang.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Austenitic Manganese Steel welded with stainless steel filler, air cooled.

Finally we have the same thing, quenched. I can’t see any discernible difference between them except I did a particularly bad job of polishing this sample.

Austenitic Manganese Steel welded with stainless steel filler, quenched.

Austenitic Manganese Steel welded with stainless steel filler, quenched.

Austenitic Manganese Steel welded with stainless steel filler, quenched.

Austenitic Manganese Steel welded with stainless steel filler, quenched.

You can really see the grains of the manganese steel in this photo.

Austenitic Manganese Steel welded with stainless steel filler, quenched.

Austenitic Manganese Steel welded with stainless steel filler, quenched.

OK, so that’s all the shots I have that are worth showing. Next, I’m going to try to etch them with Hydrofluoric acid and then try to figure out a way of putting a measurable load on the samples to see how strong they all are. I’ll post more pics then.

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Safe Machine Design: A Mechanical Engineer’s Guide to, uh, Electrical Engineering.

I’ve had to do a bit of learning on the fly at work and so thought I’d write down some of my thoughts to make things easier if I forget bits and pieces. Then I thought I’d publish it so all 3 of my subscribers can reap the benefits of my frustration.

Disclaimer: I’m not a safety authority or an electrical engineer and this article is not a substitute for an up-to-date safety standard.

Standards

As an engineer in Australia, you’ll need to be aware of three standards of safety of machinery:

AS 4024.1-2014

This standard uses Safety Categories- CAT B, CAT 1, CAT 2, CAT 3, and CAT 4 to designate what kind of architecture you’ll need to use for your safety related circuits. So, once you’ve done a hazard analysis to determine what could go wrong and determined what safeguards are required to protect from those hazards, you then need to do a risk assessment to determine what safety category those safeguards must be.

The image below shows the basic risk analysis from NHP’s website.

http://www.nhp.com.au/Products/Products-and-Services/safety/Safety-Standards

safety_categories_01

NHP’s website also has a really good rundown of the safety categories at the link below. They range from “Don’t do anything stupid” (CAT B) to double redundancy with constant self-checking (CAT 4).

http://www.nhp.com.au/files/editor_upload/File/Safety/Safety-Category-Assessment-Summary.pdf

Most of the machinery I can think of is going to end up as Category 2 which means a safety relay is needed or Category 3 which means dual channel interlocks/estops as well as the safety relay.

Unfortunately, this method of determining machine safety is on the way out. It’s based on EN954-1 which has been superseded by ISO 13849-1. AS 4024 was recently updated to accept either EN954-1’s method or ISO 13849-1’s method with the intent that people will transition to the latter over time and the former can eventually be disallowed. In order to future-proof your processes, it’s best to use the ISO 13849-1 method.

EN/ISO 13849-1

This standard takes the above approach and adds to it a Mean Time To Failure (MTTF) calculation, a Diagnostic Coverage (DC) fudge factor and a check for Common Cause Failure (CCF).

Eaton have a good manual on how do do this here:

http://www.eaton.dk/ecm/groups/public/@pub/@sweden/documents/content/pct_399695.pdf

MTTF:

You calculate the Mean Time To Failure based on B10d specs you get from manufacturer’s websites (like Schneider have here: http://www.schneider-electric.co.uk/documents/legislation/machine-safety-technical-update.pdf). Then you calculate the MTTF of the whole system based on those numbers using a few equations given in the standard (and explained pretty well in the above links).

DC:

If you’re using a PLe or SIL 3 safety relay (check the manufacturer’s website), dual channel safety circuits with cross checking (more on this later) and redundant contactors of a reputable brand, you can assume 99% DC. These three elements are pretty much industry standard so you only really need to worry about diagnostic coverage if you’re deviating from the norm.

CCF:

Common Cause Failure is checked by scoring the safety system against table F.1 from ISO 13849-1 which I unfortunately don’t have a link to but again- it’s explained pretty well in the Eaton manual linked above. It’s not factored into the calculation at all and is a bit subjective to be honest. The circuit itself should cause no issues if properly designed but this check might prompt you to think about problems that might take out two or more parts of the system at once… like metal dust taking out both a magnetic and optical sensor.

So once you have the CAT, MTTF and DC, you can determine the PL from the chart below (again, it’s from Eaton’s manual). There’s a more precise calculation in the standard.

plr1

You might at this point be thinking about how much of a pain all this is- and you’d be right! Fortunately, most suppliers have done the work for you and sell packages that have the calcs already done. Eaton, Phoenix Contact, Omron all do this and the others probably do, too. Sometimes the best thing to do is just call these guys and tell them what you’re trying to do- While regulatory bodies often seem to want to make your life as difficult as possible, the suppliers of these electronics will take a lot of load off your shoulders if it means a sale.

IEC 62061

SIL is a little bit like PL (Diagnostic Coverage, Common Cause Failure) but uses a dangerous failure rate rather than a Mean Time To Failure. It also factors in the diagnostic test interval and fraction of safe failures. Because of these two elements, you might have a machine reach a higher or lower standard of safety by using this or ISO 13849.

I’ve yet to use this standard and don’t really plan to in the future so I won’t write more about it. It’s covered in Eaton’s safety manual.

Explanation of some Components/Terms

I thought I’d throw this section in because I didn’t know any of this stuff when I started doing electrics.

Interlock

Click for a link to the part on my local supplier's website

Click for a link to the part on my local supplier’s website

Interlocks are what you should use in your safety circuit to check door, gate or guard closure. Note that there’s quite a few different types available, not just the key type shown above- you can get hinges with interlocks built in, pin type ones suitable for gates and so on (as well as a myriad of other safety devices like light curtains, pullwires and so on but that’s well beyond the scope of this article). Anyway, you should use them instead of cheaper, more conventional switches/sensors because

  1. They usually use a switching method that is difficult for an operator to bypass such as a key, a magnetic signal or a switch internal to a hinge that is inaccessible.
  2. They usually have two more more contacts which you’ll need to run dual channel safety circuits

If you can cut power to your machine and have it reach a safe state reliably before an operator can access the dangerous bits, that’s all you need… but if they can put them self into harm’s way before the machine will shut down, you’ll need a locking interlock, of which there are two types that I am familiar with:

Click for a link to the part on my local supplier's website

Click for a link to the part on my local supplier’s website

The first is the key type locking interlock- Very similar to the key interlock shown above but a few hundred dollars more expensive and it will lock the key in place so the guard/door/whatever can’t be opened when the machine is in a dangerous state. These are the cheaper alternative (though you might not realise that when you’re paying for them) but have two disadvantages that I’ve encountered: They are sensitive to alignment between the key and the lock and they can be broken by heavy handed operators, misalignment, overslam or just plain heavy equipment.

Click for a link to the part on my local supplier's website

Click for a link to the part on my local supplier’s website

The second type is the magnetic type- They use super strong electromagnets to hold your whatsit closed. They’re a couple hundred more expensive than the key type but are a hell of a lot more difficult to break and aren’t as sensitive to alignment. Once you’ve broken a key type interlock, you’ll wish you bought one of these.

Safety Relay

Click on the picture for a link to the part on Omron's website. I'm not being paid to say this but hopefully the referral will discourage them from suing me for ripping off their stock image.

Click on the picture for a link to the part on Omron’s website. I’m not being paid to say this but hopefully the referral will discourage them from suing me for ripping off their stock image.

These things are called a safety relay by most but are more of a safety controller. Their functions are fourfold:

  1. They monitor a dual channel safety circuit to detect things like activation of E-stops, interlocks and so on.
  2. They check the circuit mentioned above for any cross talk between the two channels (this is to check that the circuit hasn’t failed closed… more on this later)
  3. They periodically check a feedback circuit through all the contactors to detect any welded contacts
  4. Based on the results of the checks above, they will activate one or more relay contacts.

Dual channels and cross checking

Let’s start with the most basic circuit we can think of. I pulled an example circuit from Omron’s manual, modified it and highlighted the part we’re talking about.

Don't do this

Don’t do this

This is a basic, single Estop circuit. It’s normally closed, then when you hit the button it opens the circuit and the relay turns off the machine as a result. That’s all well and good, but what if someone drops a heavy piece of steel on the cable and crushes both those wires together? Or what if the Estop box is left out in the rain and fills with water? In both those cases, it might short together and the next time someone hits the Estop, the machine won’t stop! It only detects open circuit failures. If you changed the circuit to have a normally open contact but then you run into the same problem in reverse- the circuit will only detect closed circuit failures. You need to change it so that closed circuit failures are caught.

You could do this by having two circuits- one normally open and one normally closed- but this doesn’t work so well with multiple Estops. It would require wiring all the normally open circuits in parallel and all the normally closed circuits in series. A better solution is shown below- it’s the industry standard system.

Dual channel Estop circuit

Dual channel Estop circuit

There’s two circuits with normally closed contacts in the Estop. The safety relay monitors both these circuits for cross-talk, which means if you bridge the two circuits together anywhere (fill the Estop box with water, crush and short the wires, etc), it will trip the relay and shut down the machine. This is called cross checking.

Feedback/Monitoring

So, by having dual channels and cross checking the system is now fairly redundant and safe on the input side, but how about the outputs? You run into a similar problem to the Estop circuit: The simplest solution is to have a single contactor controlling the motor (or device) but if that contactor fails to cut the power (welded contacts are a common failure mode), the safety relay can’t do anything to stop the machine.

So you install a second contactor and run the two in series. For a while this works great. Both contactors turn on and off as required until one of them welds shut… and the machine continues to operate as normal, except only one of the contactors is now switching. This could continue for a long time until the second contactor welds, rendering the safety circuit useless. In order to do this, the safety relay needs to check that when both contactors are “off,” they really are both off. To do this, you put an auxiliary contact on each contactor and wire them into a feedback circuit with a reset switch as shown below.

Contactor feedback circuit

Contactor feedback circuit

Now, the machine has two contactors in series controlling the motor and these contactors are both checked for welded contacts any time the machine is reset. This makes for a pretty safe system but note that it assumes that the contactors all have positively guided contacts. If the contacts are not positively guided, the reset circuit will reset the machine ready for operation, even if one of the contactors has welded shut.

Eaton's XT series contactors are all positively guided.

Eaton’s XT series contactors are all positively guided.

You might also see something like what is shown below referred to as a safety relay:

Relay with positive guided contacts

Relay with positive guided contacts

This is simply a relay with positively guided contacts- No monitoring or anything like that. I use these as an auxiliary relay to the safety controller if I want to control more NO and/or NC contacts than is available.

Well, that’s all I’mma write for now. This was originally just going to be about how to satisfy AS4024 but snowballed somewhat. Hope it helps someone out there.

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Safety Culture.

I was nerding out and browsing some random tech reports from Los Alamos National Laboratory (Interesting if you’re into nuclear stuff though I won’t lie- most of it went over my head) and happened to come across a safety manual. I was interested to see what kind of safeguards they had in place and started reading but was somewhat surprised by the introduction:

“Safety is an accept balance of risk against benefit; it is meaningless as a concept isolated from other goals. It follows that safety should be considered one of the goals of design and operation instead of something superimposed. Although experience has shown that criticality hazards are no more serious than other industrial hazards, controls for balancing criticality risk against benefit are somewhat more stringent than is usual in nonnuclear industry. It is reasonable that there be some allowance for the uneasiness naturally associated with this new type of hazard. But the extreme concept of risk elimination (as implied by any claim that certain controls “assure” safety or “ensure” safety) is dangerously misleading. Dismissing risk as nonexistent can detract from the
continuing job of maintaining an acceptably low risk level.”

Pow. The whole document is here by the way:  http://library.sciencemadness.org/lanl2_a/lib-www/la-pubs/00194221.pdf

Anyway, it stood out because usually the guy that writes the safety manual is the “safety at all costs type” that is becoming ubiquitous these days. This guy, though, held a very down to earth and common sense approach. It got me thinking to the kinds of experiences I’ve had with OH&S types and whether they really increased the safety of a workplace.

Safety without common sense often leads to unsafe situations. I remember once seeing a guy using a grinder. He was wearing gloves because it’s “more safe.” (Note to the uninitiated, it most definitely isn’t- you can lose a finger that way or with high power equipment like large lathes and mills, a limb or even your life). Someone pointed this out so he held the piece with pliers as well as using the gloves.

I remember once when I was involved with FSAE I bought my personal welder in to university so that we could have two people welding at the same time in order to get more work done. I left to take a nap (which is to say I didn’t leave, I just found somewhere inconspicuous and slept there) and woke up to find that my welder had been decommissioned because it wasn’t “tested and tagged.” This isn’t a legal requirement in Victoria, by the way, it’s just enforced in some workplaces. I took it home and placed it among the hundreds of commercial electronics equipment that people operate every day without ever testing and tagging. Televisions, air conditioners, ovens, electric blankets, lights… That welder still gets a lot of use, incidentally. Currently it’s a current source for an electrolysis tank.

I’m not the only one who’s getting a bit uneasy by safety culture and where it’s headed. Mike Rowe (presenter of Dirty Jobs and pretty fuckin’ awesome dude in general) has been saying similar things, too. Here’s a choice quote:

“In the jobs I have seen thus far, I can tell you with certainty, that safety, while always a major consideration, is never the priority.

Never.
Never, ever.
Not even once.

Is it important? Of course. But is it more important than getting the job done? No. Not even close. Making money is more important than safety – always – and it’s very dangerous in my opinion to ignore that. When we start to believe that someone else is more concerned about our own safety than we are, we become complacent, and then, we get careless. When a business tells you that they are more concerned with your safety than anything else, beware. They are not being honest. They are hedging their own bets, and following the advice of lawyers hired to protect them from lawsuits arising from accidents.”

Full article is here: http://profoundlydisconnected.com/the-only-one-responsible-for-my-own-safety-is-me/

Anyway that’s it for now- just a brief bitching session. In the next week or so, I’ve got an article planned on machine safety- what’s required- particularly the control system that comes at this from the opposite angle. I just thought I’d preface it with a little bit of common sense and cynicism.

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A quick experiment in hydroforming.

I had some spare time over the holidays so I decided to play around with something I saw on youtube some time ago. The idea is that you can weld together two pieces of metal, pump them up with a high pressure hose and basically inflate the shape like a balloon.

I took off the high pressure hose nozzle and turned up a piece of steel to match it.

P1016122-1600

P1016121-1600

Then welded together these bits of steel and welded on the bung I just made. I just plasma cut the steel pieces and didn’t bother to clean them up so the welds are pretty crappy.

P1016124-1600

You can see I forgot to do something in this photo which I addressed with the one below it.

P1016125-1600

The explosion guard! Safety third, guys.

Just kidding- The idea with this is that since the water is relatively non-compressible, when the welds yield, the part will just crack and leak. It won’t explode.

P1016127-1600

Here’s two photos of a misshapen… thing. All up, it’s made from 6 pieces of 1.6mm mild steel. There’s a long list of things that I could have done to make it inflate more… better fitup (less weld), thinner steel, less pieces, better welds (that won’t crack so readily) but I was just playing.

P1016129-1600

P1016133-1600

Anyway, to answer my question, “can you really use an ordinary high pressure hose to form steel?” is a surprising “yes!”

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Engineering language, pain and beards

One of the things that makes engineering a bit inaccessible to newbs is the language that is always used but rarely explained. It differentiates the young from the old like a weathered beard, a list of expensive mistakes or a drawer full of wires too short to ever actually use.

Cutting and stashing wires is easy enough, fucking up and costing someone money is even easier and growing a beard is a little tricky… I should note here that engineers don’t crop their beards; An engineering beard is a product of laziness, not fashion. Though I had a fitter suggest to me that engineers like to grow beards because they need something to hide behind…

…But the language, in absence of any form of engineering jargon dictionary takes a lot longer to pick up. So, I got bored the other day and wrote an article with 10 engineering terms that should give you at least as much cred as a dirty mustache. Enjoy and add a few more in the comments section if you feel so inclined.

Chamfer

From middle english, meaning to break the corner

When you make a part that has a sharp corner on it, gouge your hand on it, get angry with it and take an angle grinder to it in order to remove the corner. After you knock the corner off, the small 45 degree angled section with a burr on it to to cut yourself on rather than a sharp corner to gouge yourself on is called a chamfer. If you cut yourself on burr you left on the chamfer, get an angle grinder again and chamfer the chamfer. Objects in high traffic areas tend to become spherical over time. It’s common practice to chamfer hard corners on turned parts to avoid cutting your hands on them and also so you can slip a bearing on without catching it on the edge. When I was in FSAE, we had a rule of thumb wherein if the thought of rubbing a turned part on your genitals makes you flinch, you probably should have chamfered it.

Spigot

This is a tough one to find a proper source on as all online dictionaries refer to a spigot as a tap or a plug. Maybe this is American. Anyway, in English/Australian mechanical engineering, a spigot is a short cylindrical projection that inserts into a bore of some kind. I think this one may have come about because before spigot came to mean a tap, it was used to mean a plug/cork.

spigot

Trunnion

A pair of bosses on a thing perpendicular to its main axis. Those cannons you see in old war movies are mounted on trunnions so that they can be aimed up or down. We obviously don’t do this anymore, but it’s a common way to mid-mount pneumatic cylinders so that they can pivot.

trunnion1trunnion2

Gusset

A triangular stiffener used to stiffen a joint between two members. If you stand up straight and hold one arm out horizontal, you’d get tired after a while. If you put a triangular brace between your waist, your elbow and your armpit, you’d look stupid but be less tired. This brace would be a gusset. I know that was a bit of a weird example but I used it for a reason: If you happened to be wearing a shirt or jacket with diamond shaped expansion sewn in at the armpit, that would also be called a gusset. The word is shared between engineers, armourers and habidashers. So here’s an engineering gusset.

397-1600

Here’s the other type of gusset. If you run afowl of Chuck, it’s probably the last gusset you’re ever going to see.

norris gussetnorriscrotch

Jig/Fixture

A jig is a piece of equipment used to hold a tool in an operation. It’s different to a fixture. A fixture holds the workpiece where a jig holds the tool. If you drill some holes in something and then drill through that something into another thing using those holes as a guide, that’s a jig because you’re holding the tool (the drill bit). If you make a device that clamps and locates the workpiece, then it’s a fixture.

Hungry Board

When you put a backboard around a bin of some kind to prevent spillage, it’s sometimes referred to as a hungry board.

Hardface

The practice of welding a hard material on top of a soft one to produce a hard face. I’ve heard of this being done to axe heads and digging equipment back in the old days. These days, we just weld a plate of something hard on top because welding labour is costly. Also it’s something I find myself doing when I’m working through a dodgy suburb at night.

Gib

An adjustable spacer that is designed into a machine way in order to take up any slack. Sometimes, these have a slight taper to them  so that you can slide them in or out a little bit in order to adjust them. Sometimes there are screws pressing against them that can be tightened. There’s a picture below of each type. Overtightening the gibs tends to make the mechanism too stiff to operate. Conversely, having them too lose may result in unpredicted or unwanted movement. Thus, a person who talks a lot without thinking could be said to have his brain gib too tight, and jaw gib too loose.

You can see a gib here in the vertical way of my Deckel FP1. It’s the parallelogram shape at the top-middle.

gib

I also used gibs here in my English wheel. This is a low tech way of doing it. They’re straight, not tapered and tensioned by the allen keys.

gib2

Sheave

Part of a pulley. Specifically, the rollery pulleyish round part of a pulley. A sheave plus an axle and two side plates is a pulley.

Rise/Run/Going

When you’re designing ladders or stair cases, the rise is the vertical height between steps/rungs. The run or the going is the horizontal distance between steps or rungs. A guy I work with told me a story about an ex-employee who was adamant that the Australian standards for the rise and going of a staircase was specifically calculated so that a woman could walk up it without her tampon falling out. I’m not even kidding, he really did think that.

 

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11 Mechanic’s tricks your dad (hopefully) taught you

I usually find out the easiest way to do something right after I’ve just done it the hard way. I also love learning new mechanical tricks and shortcuts but sources of this stuff are hard to find so here’s a few of my favourite tricks that I’ve learned (mostly from my old man, hence the title). If any readers out there have a good trick to add, leave a comment.

(I’ve amended this article with a few ideas that friends suggested to me via Facebook)

Removing a spigot bush from the end of your crankshaft. Or pretty much any bearing from a blind bore:

HYDRAULIC TRICKHYDRAULIC TRICK 2

  1. Put some thick grease in there.
  2. Get a shaft that fits snugly in the bush and, uh, put it in there.
  3. Hit the shaft with a hammer. The hydraulic pressure will force the bush out.
  4. Wipe your face clean. The grease comes out with the bush.

When you’re drilling a big hole and the drill bit just keeps throwing the workpiece around and cutting Reuleaux triangle shaped holes

  1. Check your drill bit
  2. Slow down the spindle speed a bit
  3. Engage the drill until it juuuust touches the part enough to centre it
  4. Clamp it down
  5. Drill firmly through a business card.

When you just can’t get enough torque to undo that nut…

  • Try slipping a pipe over the socket wrench.
  • If you’re using a ring/open spanner, use the ring end on the tricky nut/bolt and interlock the ring end of another spanner on the open end of the spanner you’re using. Your double spanner is now twice as long. This isn’t really that good for your spanners but sometimes you need to get things done.
  • If you don’t have room for the extra leverage because something is in the way, sometimes you can use a pinch bar or a big screw driver to lever the spanner or wrench off of that something.
  • Screaming helps.
  • Buy an impact driver. This was just the excuse you were looking for. If that bolt gets the better of you for a day then once you factor in your daily wage then you can’t afford *not* to buy one. It’ll pay for itself. Now that you dropped a couple hundred on the wrench and Li-ion batteries, you should probably get the matching drill and grinder, right? The savings keep rolling in! Also beer. It’ll relax you and help prevent mistakes.

A few extra from Luke:

Step 1: Pipe on end of wrench
Okay so now you might be getting that engineer-sense/tingling sensation that you’re about to twist off the end of the bolt..
Step 2: Whack the end of the bolt with a hammer a couple of times If it’s still stuck… (Impact screwdrivers are great for this too)
Step 3: Bust out the oxy and heat the area up.
Step 4: Rush around trying to find something to put out all the grease and oil you have just ignited because you’re too lazy to clean the area beforehand.

Are you bashing a male thread with a hammer?

Put a nut on it first so you don’t trash the thread!

Thread burnishing by turning and tapping with a hammer:

Sometimes you cut a large thread (almost) correctly and the first time you put it together, it seizes. When it does seize, tap the assembly lightly with a hammer. This burnishes the threads to match. You’ll find that the nut will loosen as you do this so tighten it a bit more and tap it again. Repeat this a few more times and you’ll have a nice, free-running threaded assembly.

Locking two nuts together for various reasons:

The easiest way to tighten a stud or a piece of allthread is to tighten two nuts against each other on it. This locks them and the allthread/stud to each other so that you can turn it. Also, double nutting is a good way to prevent nuts from loosening under a varying load.

Do you need to hold that threaded thing in a vice?

Cut a slot into a nut with a hack saw. Now thread it on and clamp the nut in the vice. As the vice tightens, it’ll clamp up the nut and hold the thread tight, too.

My Phillips head screw is mangled and I can’t get it out

  1. Penetrant oil. Do this before anything. It probably won’t help but it does boost your confidence.
  2. Get an impact driver and try that, they’re like $30 now.
  3. Vice grips around the head of the screw.
  4. Vice grips in combination with a screwdriver. Vice grips are like red wine, they go with anything and anyone who says otherwise is lying to you.
  5. Try cutting a slot with a hacksaw or dremel and undoing it with a flat head screwdriver.
  6. Try welding something to it.

From Autopilot: “For mangled screw heads, you can get a bigger Phillips head driver and a patient ball peen hammer to re forge the head. Usually works and your screw even looks presentable afterwards”

OK now it’s broken, now what?

  1. If you can, sometimes tapping with a small centre punch in the loosening direction works. This has worked for m a couple of times.
  2. If it’s soft, you can try drilling it and using an easy out.
  3. Once the easy out has broken, you might want to try welding to it
  4. If it’s recessed deep, welding gets tricky but here’s a last resort to consider: Wrap an arc welding electrode in a couple of layers of masking tape so it’s only “live” at the tip. Then insert it in the hole, strike an arc on your broken bolt and then jam the electrode down and unclip the stick holder. Wait for it to cool.

From Graham: “Easy outs, junk, all they do is ease money out of your wallet. Drill the hole and hammer a torx bit into it. Preferably a Mac or Snap-On the odd chance it breaks you can get a new one for free. Works like a hot dam and way better than any easy out system I have ever tried !!”

From Tuddaz: “Get some left handed drill bits for removing stuck screws before you reach for the easy out. It’ll probably just come out with the drilling (or you’ll snap the drill bit off) before you reach the point of needing to use the easy out. I’ve been told you can just keep drilling larger and swap to a reamer when you get close to the diameter of the thread, but I’ve never tried that to know if it works.”

Unbolting your steering wheel:

Leave the nut on loose until you’ve yanked it loose off the spline. Otherwise, it’s highly likely that you’ll hit yourself in the face with it when it comes off.

Removing CV’s with a particularly stiff snap ring that doesn’t want to yank out:

From Aaron: “Camry Haynes manual said “Step 15: Grip CV drive shaft with hands, and pull to remove. Step 16:….”

Good luck.

I got a spare bench vice, camped it to the shaft and hammered the vice to get the CV shaft out.”

On Patience:

One of the big things I took away from a brief period where I did some work in a panel shop was from sanding small fiddly areas of panels. We’d undercoat and then spray on a mist of “guidecoat” which was just some black pressure pack rubbish paint. It’s look sort of peppered. Then you’d just sand with 180 grit until all the black specks were gone. At that point, you know you’ve sanded everything to the same level- no scratches. Anyway, when you’re doing a panel with lots of edges, you have to screw around for ages with a little bit of sandpaper and it feels like you’re getting nowhere for two hours and then suddenly, you’re almost done. It’s weird how it sneaks up on you. Anyway the point I’m making here is that building a car is the same, any large project really is like that. The trick is to stick with it until you realise you’re done.

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Saving money with laser cutting.

Laser cutting has been around for a long time and has been embraced by industry for the most part but I still do see some instances of designs that don’t really take advantage of all the things you can do with it. So I’ve come up with a list of a few tricks I’ve learned that you can do to save time, money and manufacturing effort. Maybe you’ll take away a new trick from this article and if you have one I didn’t mention, please leave a comment below. 🙂

One of the first big time savers I learned with laser cutting is the relative ease with which you can cut a thin rectangular hole in a part to correspond with a tongue on another part. Not only does it eliminate the need to measure out the position of the part but it also holds the parts together while they are being welded. I picked up this trick in my early days of FSAE from the chief engineer at the time.

The clearance around the tongue should vary depending on the application and thickness but I’ve found that in 90% of situations (mild steel between 1mm and 10mm), a 0.25mm gap all around the tongue works. If you’re dealing with material over 10mm, you might want to increase this a little bit. Also, if you’re using obscure stuff, you might find that the 6mm plate is actually 6.35 (1/4″) so double check. The depth of the tongue is another parameter that requires a little thought. If you’re going to fillet weld the parts together and you have clearance on the back side of the slotted part, you can make the tongue long so it protrudes through (The example on the right in the below picture). A long tongue holds the part together better and makes assembly nice and easy. Alternatively, you might want to make the tongue short (half the part thickness) so that you can plug weld in the slot. (The left hand example). This results in a weld that can be ground flat without losing (much) strength.

tongue

Below is a photo of a machine part with this trick done in 6mm thick mild steel. In the foreground you can see the bent part which has the tongues mated against the flat part that has the grooves cut into it. In the background, you can see the same assembly from the other side. Those lines of weld which are filled into the back of the groove.

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Here’s an image of the dxf file I sent out for laser cutting in 2009. It’s 1mm thick 4130. The two pairs of grooves cut in the panel second in from the bottom left correspond with the tongues cut in the bit at the top right as well as with another gusset (not pictured). This part actually features a couple of other tricks that I’ll be talking about later.

lasercut

Another use for tongue and grooves is controlling warp. If you’re having long strips cut, you may find that they come back from the cutter with a significant bend in them. This can be alleviated with good design. See the picture below for an example. It’s a quick sketch showing a long warped piece with tongues cut in it being retained in a big sheet with grooves cut into it.

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There are some pitfalls associated with doing this. The more obvious ones are the tongues and grooves just plain not lining up due to design changes in one part not following through to the other part or just not being the right size. Some less obvious ways to screw this up occur when dealing with symmetrical or near-symmetrical parts. Below, a slightly asymmetrical part is shown with symmetrical tongues. It can be assembled either way. If you drawing is super clear, this may not cause any issues but a clear drawing and knowing you weren’t “technically” wrong is small consolation when you need to cut a machine apart to fix a mistake.

tongue 4

Incidentally, with the image above, another approach you can take is to make the part symmetric by mirroring that hole so that it doesn’t matter if the part is assembled the right way or not. Sometimes one way is better than the other. With CAD these days, it’s often easier to constrain your model so that the tongues and grooves are equispaced rather than to dimension them individually so I often find myself trying to preserve symmetry. Inevitably, though, a mounting hole is going to go in at the last minute and you may well forget to un-equispace those tongues and grooves. As such, I’m currently trying to get into the habit of making all of my tongue and grooves non-symmetric to avoid this happening.

Another pitfall arises when parts are being folded. Laser cutting is usually a 2D process, so the part you cut can usually be folded the “right” way or the “wrong” way, which would result in a mirror-image part. You can get around this by ensuring that the part is symmetric. Which brings us again to the conundrum I mentioned above- to symmetry or not? It’s very easy for your folder to misread a drawing and bend something the wrong way. I make an exception for folded parts. We’re engineers. We compromise.

tongue 3

Sometimes you need to butt weld two parts together. This can happen because of limitations in the size of the sheet. Also, some laser cutters will quote material cost based on the smallest rectangle that can contain the part- so a very large “L” shape part made from two rectangular parts butt welded together can save you a lot of money when your material cost is high. In this case, you might want to cut dovetails into the part. If you’re just doing this to roughly locate the part then a 0.25mm clearance is fine. If you’re trying to use this to fully align the parts, though, you might want to cut that clearance down because you can get quite a large angular misalignment from a relatively small clearance. Also, bear in mind that your boilermaker is going to grind a chamfer all around that with an angle grinder (unless you do some trick 3rd axis laser cutting which is probably going to be too expensive) so it just might be cheaper in the long run to have a straight line joint and align the parts another way.

DOVETAIL

Now, back to that upright piece I showed earlier. I’ve shown it below again so you don’t have to scroll. You can see the two long edges at each end of the net have some zig-zag kind of pattern cut into them. The idea of this was for them to lock together to make assembly easier- and it did- but bear in mind your weld will have a slight zig-zag to it. I’ve had boilermakers complain that I didn’t do this and I’ve had boilermakers tell me not to do it because they don’t like their welds to look crooked. So I guess what I’m saying here is, your mileage might vary. You might want to put in just a couple of locking tabs at each corner that can be ground off after tack welding but before seam welding.

lasercut

Finally, you can see the stitches cut in between each section. These are so the part can be easily bent into shape by hand. There are situations where a part can’t be bent by a brake press or a folder, so this is a way around that.

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On the topic of folding, most software will automatically put in fold lines when you export a part so you can etch them in to make your folder happy. Another trick to reduce folding cost is shown below. I don’t know what the proper term is but I call it scotch fingering because the parts break apart like scotch finger biscuits and because it sounds amusingly lewd. Some folders will charge per part so sometimes it might be a good idea to join several parts together so they can all be folded in one hit and broken apart afterwards.

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Now I’ll put in a few random ones. Corner breaks. It used to be common practise for engineers to put a chamfer on every exposed corner so you don’t get a sharp edge that will cut or gouge unsuspecting operators. We used chamfers because they were easy to cut, grind, punch or shear. Straight lines were easier. Nowadays it’s just as easy to laser cut a curve but I still see a lot of chamfers laser cut into parts and to me it makes them look dated and lazily designed. It’s not any cheaper than putting in a nice looking radius so why do it?.

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Below is a photo of a few parts that I was worried about tolerance stack on. So I slotted the mounting holes to give myself some wiggle room. Slotted holes are a brilliant arse-covering technique and I do it pretty often.

Edit: After a friend commented, I realised that I didn’t really write enough about this the first time. The part you can see is mounted by the slotted mounts you can see but is located by other, nonstructural parts (In this case, a pair of screw conveyor troughs). If position is important and your structure is not positively located in anyway, putting slots in everything just might make your workshop foreman/fitters want to kill you. Getting a few hundred kilos of steel in the right place with a crane and podgy bars is not easy. I guess what I’m saying here is that there’s a time and a place for doing this kind of thing.

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Most laser cutters can’t cut a hold that’s a smaller diameter than the sheet thickness so you’ll just have to drill it. Make it easy for yourself, though, and laser-etch the hole centre.

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Also, the cost added to etch on the part number is very little.

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Another quick way of locating two parts:

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Slots aren’t just good for covering your potential mistakes. You can also use them to standardise your parts. Below is a photo of a standard torque arm. It’s slotted so that it will fit any size gearmotor.

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