[Crashmaster]

Hi guys, I machined the following fixture; 1020 Steel; 19 inches long, 6 inches wide and about .625" thick. As you can see from the pictures, over time the table begins to bow upwards in the middle. We have tried the same table 1" thick and the same problem still arises. I am at a loss as to what is causing this, any thoughts would be appreciated. I should mention that it is being held between two 6" kurt vises set 4" apart.

Thanks;

CM

[mactec54]

Crashmaster

Stress relieving the steel before you mill it will help, also the type of cutter you are using to cut it, you can get/buy the steel already in a stress relieved state

This is normal for steel & other materials that have stress in it from the manufacturing process, to warp & move around when being cut

[txcncman]

As mentioned, stress relieve the material before machining. Also, machine equal amounts of material off both sides.

[Crashmaster]

Thanks for the info guys. Is there anyway to stress relieve steel without heating it or is that generally the only way to do it?

[rowbare]

Cutting the same pattern on the bottom of the plate might suffice since it would somewhat balance the stresses.

Could you get away with using different material for the fixture? Cast aluminum tooling plate comes to mind.

bob

[Geof]

6" wide and finished at about 5/8"; you should be able to make this out of a piece of 6" x 1" hot rolled steel which will solve your warping problems.

[txcncman]

Thanks for the info guys. Is there anyway to stress relieve steel without heating it or is that generally the only way to do it?

There are also processes to stress relieve material with vibratory stress relief and with shot peening. These seem to be only effective in materials with smaller cross sections.

[Crashmaster]

I think aluminum tooling plate maybe on the high side of cost for us for this part. We are getting pricing now. Geof, we have only dealt with cold rolled here, is there any machining issues with hot rolled? Generally doesn't hot rolled have a bit of carbon scale on it?

[DareBee]

I think aluminum tooling plate maybe on the high side of cost for us for this part. We are getting pricing now. Geof, we have only dealt with cold rolled here, is there any machining issues with hot rolled? Generally doesn't hot rolled have a bit of carbon scale on it?

Yes it does.
That is why you start with 1".
Needs 100% machined and should have equal amounts taken off each side.
Even with HR, perfection would dictate a rough machine - stress relieve - finish machine process, but even with just straight machining will be much better that CR

[Crashmaster]

Great. Thanks to everyone who responded. Learn something new every hour!

[tacdriver]

My two cents, by the time you rough, stress relieve, and finish, you might as well have bought aluminum. We use a lot of fixture plates with the Jergens clamps / bushing system. They work great. We just put in a cheap overhead electric hoist and trolley so now we can lift the pair of double vises (about 250+ lbs) / switch to a pair of single vises / switch to fixture plates without compressing a disk in our backs. Works great.

The cost of the cast aluminum plate (can't recall the number off the top of my head right now) is not that bad. It's already finished to .005" so we just run a face mill where things are going to be sitting.

[diyengineer]

3/4" Alcoa Mic 6 tooling plate 12"x48" off ebay is about $279 and 33 to ship. You can get a shorter piece for a lot cheaper. Many different sizes. I'd check it out.

Mic 6 Cast Tooling Aluminum Plate 3 4" x 12" x 48" | eBay