Machining flat 304 stainless

[charkmandler]

I will be machining some front fork top links for a vintage motorcycle the will come out finished size at .340" x .766" x 4". The material will be 304 stainless steel.
Initially I skimmed some stock that I had to remove the stresses and let it rest, this did not work as the warp did not leave me enough metal to finish to size.
Is there a recommended way to remove the stresses before finishing to size and is there a way to determine the warp so that I can order material near to size but not have too much material to remove.
Thanks

[NP317]

Two ways I know about to remove inherent stresses in metal:
- Heat soak with slow cool-down cycle (a 2+ day process);
- Machining of material from both sides in several steps to limit warping.

I've done both processes with success. Neither was quick.
RussN

[Rich_Carlstedt]

+ 1 with Russ's comment .
I have also used "Shock" at work
As soon as possible after machining , you shock the metal . sometimes dropping it on a hard floor is enough
Also drop it before you machine it . The Molecular structure rearranges ( partially ) in the shock process and while the metal moves, it releases stress.
The greater the internal stress, the more movement you get
This works as well with "rolled" metal fabrications
In some shops, they attach air powered vibrators to steel to relieve the stress instead of dropping the parts

Just as with normal steel bar, if it is cold finished (cold rolled) it has lots more stress, than hot finished steel products ( Hot Roll)
There is no way to predict the amount of stress and movement other than experience with a product
Rich

[charkmandler]

Thanks Russ and Rich, several skims, shock treatment and buy with plenty of spare metal. Really interesting about the shock treatment, I'll do some reading about that.
Thanks, Mark.

[Harold_V]

One thing to remember. The stresses are generally well balanced, side to side. By removing a small amount of metal from one side, then doing the same for the other side, repeatedly, you can keep a piece quite straight. The amount of movement is limited, then offset when the second side is machined. Repeat as necessary. Assuming you will end up removing about the same amount from each side, you need not start with excessively oversized material, as that isn't really a solution, and it costs a lot more.

I speak often about roughing before finishing, but I get the idea that my words fall on blind eyes. However, once one has experienced what you've described, maybe it will sink in. Learn to rough parts, leaving a reasonable amount for finish cuts. If the material is super active, as you described, do light roughing cuts, followed by semi-finishing cuts, then finish cuts. Movement due to stress can be controlled quite nicely if you make it your objective.

One caveat. As RussN suggested, this all adds considerable time to a project, so think accordingly.

H

[charkmandler]

Thanks Harold.