Help! > Mistakes, muckups, and dangerous behaviour

Can this part be saved? Internal stress

(1/4) > >>

matthew-s:
I could use some wisdom and experience here. I’m rather internally stressed about this internal stress. :(

This is the radius rod from a 3/4 scale Kozo A3 (Kim’s build for reference).  There are other similar parts I’ve machined, and this did not happen …

The material is annealed 303 stainless.

You can see after cutting the part from the block with a slitting saw, it bowed by 0.020 over its span.

Can it be saved?
My current thoughts are:
1. Attempt to bend it back … somehow. Clearly I’d have to support it to keep it from twisting.
2. See what happens when I machine the taper, try to favor one side or another? Technically only the dimensions between the three to-be-completed holes matter. That may not work, and/or look like junk.
3. I guess I could anneal it, but I don’t think that would return it to a different dimension, it might just freeze it as is? OTOH, maybe that would make option (1) easier / more feasible?

For the next part(s) …
There is still the rough second rod that has not been sliced from the block yet. Should try to anneal this in the kitchen oven ( O:-) )  before using the slitting saw to separate it from the block? Any other advice?

Thanks in advance!

uuu:
Although it seems to be a sledgehammer to crack a nut, I have found the fly press to be a very effective tool for straightening things.  Guided by my friend John, who definitely has a knack for this, it's possible to use a vee-block and blade to tap the part back into shape.

You can build up a feel just bouncing the tool along the part, within the elastic limit, so it stays as it is.  Then little by little you increase the bounce until you just, and only just, take it past the limit, and the magic happens.  It's amazing how sensitive it is.

Wilf

PS - but I've not done it on stainless, where there's clearly a risk of hardening.

crueby:
If it had been milled on one side from a flat bar, then milling the same amount from the other would have it straighten out again - if done in a couple shallower cuts, alternating sides. But, if I read it right, this was cut off the side of a wider block. In that case, machining the side away from the slitting saw cut will likely not have it change the bow. But, if the part is thick enough to trim some more, you could mill one side flat, then take the other side down parallel to that. If its not thick enough to do that, then bending it could work, 303 will take small bends without cracking. Support the ends, then press down on the center, past straight and see where it returns to. If you dont have a press, a wide vise would work too, tape blocks at either end of one jaw and one in the middle of the other jaw to get the supports needed. Worst case is to make a new part from flat bar, and mill alternately from either side to get it down to thickness without warping.

matthew-s:
Thanks to the input so far. People are converging on bending it.

As an aside. I did mill equal amount off either side of the block to get it from .250 to .200 thick.

The problem here is the part itself is not symmetrical. The long thin part is offset from the centerline, aligned with the “back” of the part.

Anyone ever try to anneal 303 at home? What happened?

crueby:
I'm not sure  I understand  how it was cut from the bar. The offset on one 3nd would warp from stresses to the side towards the fork, but it seems to have warped in the other axis?

Navigation

[0] Message Index

[#] Next page