I thought I had a good idea, but clearly there is something in cutting aluminum that I don’t understand.
I started with square I purchased from home depot. Just needed to trim it down so it would fit on a laser cutters hex grid. But after cutting it down, both parts of the square decided to not be square anymore.
The cut seemed to do really well, 36ipm, 18000 rpm, 0.01 dpp. The material did not feel hot, so I’m assuming this isn’t a failure in the cutting process, just a failure to understand the material.
you released the internal stresses in a stamped part, will adams post sort of covers it but more basically you need to stress relieve the part which may in itself cause minor warping especially if not done right.
which brings us to the next point you’re probably unsure of the grade of aluminum used for example 6061 is reccomended 343C for 1 hour but 7075 has results at 413c for 2 1/2 hours
Then technically you would rough it, leave it for 2 weeks then run a light pass with your final so that any new internal stresses aren’t freed, assuming your final pass isn’t going to open the pocket up like the picture above in which case im sure there are even more workarounds required.
I once bought a new Johnson steel square at Lowes that was not square. As long as the square is straight but not square you can fix it. You use a center punch and make a series of strikes and it will slightly adjust the squareness of a square. If your arms are not straight this wont work. If you punch 3 strikes on one side do the same on the other side.
To test a square for squareness put one arm on a known straight edge like a piece of plywood. Draw a line down the other arm. Then turn the square over 180 degrees and put it close to the pencil line and not over it. Draw another line. If the lines diverge the square is not square. If the two lines are parallel your square is square.
Here is a drawing as an example. The drawing only has two circles but you would put your center punch and make 5-10 strikes. Checking after each strike to see if the square has been brought to square.
Metal stresses are tough to deal with sometimes. Hate it but it happens. Working in machine shops, I have come across this crap many times over the years. A lot of times we had issues like this come up and we would have to send the parts out to stress relief, because waiting on a part to sit and then be ready to finish machining weeks later isn’t feasible.
Releasing stress on metal is the same as releasing stress on wood when cutting it on a table saw. Been there, done that. Have started a rip down a board and watch the cut gap come together as it clears the riving knife on my saw and make pushing the board thru harder. Usually means that the board is not going to work now unless I can cut it down and cut most of the stress away.
So metal is the same way, basically ripping down metal where stress within the metal may be, will release the stress and strength of the material and cause it to bend out of control.
Aluminum can warp and the thicker, the worse it can be. Casting and heat treatment can induce stresses in the material that relieve as you remove material. One part I troubleshot in aerosoace took a couple of roughing operations to release stress before the actual to size machining. But that was 16" x 16" X 3.5" material and one feature had 0.005" positional tolerance. And that meant it couldn’t be off more than ~0.001" on any dimension.
I would think that one solution for cutting a square and still getting it square after it warps is cut the material away further over from the actual size you want the part to be made. Then you would have to machine both sides of the square at smaller depths of cut from the sides until you brought it to size by machining. The one issue I see with machining both sides is holding the square down without the holders being in the way. You could use double sided tape and that might work. By making smaller passes, something like .010" or ever .015", would work by cutting out warpage because the smaller cuts would reduce, if not eliminate, warpage on the aluminum. Maybe this would work for you, but I am sure you don’t want to keep buying squares to try to figure this out, so why not just use the whole square and call it a day?
I don’t know if you are trying to use both parts that you separated, but with my solution, you will only get one cut out, which might not be worth cutting apart in the first place, unless you have to have the square smaller in width regardless.
