Most of the cost of bending is setup
Once you have a bend on your laser cut part, its cost has increased significantly. Adding one or two more bends to it often doesn’t increase it much more- The majority of the cost is in setup. So with that said, say you are making an end stop. You might design that to be a single 90 degree bend with holes on one side like the image on the left below If having a relatively compliant part is what you’re after then this is fine- But if you want a bit more stiffness and less weight, add two more bends and make it like show on the right. Now it has two shear planes resisting the load, making it far stiffer.
Spring washers don’t resist loosening (but do have their uses)
Spring washers do not lock a bolted connection together. They are marketed as being able to do so but they do not. The only use of spring washers is to make it easy to identify if a bolted connection has been left finger tight or not. You don’t need to take my word for it. Try these sources:
Don’t spec a threaded hole full depth
The machinist making your part doesn’t know the application of your part. Maybe the part was drawn that way because the threaded depth was calculated based on minimum pullout force and also the part carries a bending load so the hole depth was minimised for strength. Maybe you just let CAD make a “full depth” thread by default. There is no way for them to tell. The result is that the machinist will tap the hole full depth with a conventional tap. Then tap it full depth with a plug tap. Then they’ll blow out the swarf with compressed air and run in the plug tap again. Then they’ll charge you for all that time. Or if they are running a CNC machine, they’ll smash 3 taps trying to get the depth and make a mental note to charge you more next time.
Tapping laser cut pilot holes
Modern laser cutting on relatively thin sheet metal (3mm or lower) is clean enough that you can laser cut directly to pilot drill size for tapped holes and then just tap them. I’ve tapped hundreds of holes this way, usually with the tap in a hand drill. Don’t use straight flute taps like this if you can avoid it- Use spiral flute taps for blind holes or spiral point taps for through holes as well as cutting lube.
Thread burnishing
If you’ve had a male and female thread machined by separate workshops, particularly if they are large, they might be tight when you try to fit them. Yes, ideally they should be done by the same person so they can check but life doesn’t always work that way. Don’t panic. It’s pretty normal. Put them together by hand – finger tight only- until they get tight and then tap with a hammer. This burnishes the two threads against each other. They will come loose again. Now tighten a bit more and tap. Repeat until you’re all the way. If you just wound them together hard with a wrench, they’d gall up, seize and you’d end up in an argument with your two machinists over two wrong parts that were actually perfectly fine.
Calculating anything more than once is a waste of time.
I made an excel spreadsheet called the Mentaculus about a decade ago. In it, I keep saved tables of material standard sizes, what sizes of SHS/NB pipe telescope inside each other, simply supported beam equations (parameterised for easy changes), floor plate deflections, euler buckling equations, hertzian stress calcs, fastener torque specs, etc, etc. Once you build yours, you’ll be able to do a fast, first order check of your bread-and-butter kinds of jobs while the slowpoke next to you is still trying to remember how to manually draw a bending moment equation. Though even that guy will look like a genius compared to the guy two seats down who at the end of the day is still trying to apply a 3-D FEA mesh to his cantilevered I-beam.
Properly tensioning big bolts is no trivial matter.
If you are designing for very large fasteners (M24+) and tension is critical (if it isn’t, why are you using such large fasteners?), you need to think about how you are actually going to properly tension them. So, options are big fuckin’ torque wrench (probably not big enough for something like M30 and will require a breaker bar, too), torque indicating washers (super easy to use but make sure you have enough room under the head of the fastener to use them) or a hydraulic torque wrench. If you are using a hydraulic, you need to react the torque against something. Google image search it and you’ll understand. The point I’m making is applying more than 1,000Nm to a fastener is no trivial matter and your life will be easier if you figure out how to do it before you’re on site staring at it surrounded by tradesmen calling you a fuck stick.
Hyllest 