Tamming Warp

Magnum

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OK, I have designed parts for the Space Station and other critical applications and generally I have passed on my parts to a stress engineer and they will come back and tell me that during machining no more than XXX in pounds of force can be used to hold the parts during machining. The reasons are varied, but this weekend I can kick myself for not checking this first.

I made some parts which I was hoping would eliminate some vibration in the final application. I machined all 5 parts out and then flipped the parts one by one into my vise to machine the back side off. There was a little bit of chatter as the parts were about 2IN long and maybe .5IN wide and could only be held on the ends... Result was I clamped a couple too tight and they bowed slightly leaving a concave (is that right) surface once the tension was released.

Needless to say I can't drill the secondary ops holes in the sides as they are now too close to the material edge.

Darn it! How do you hold small parts securely for secondary operations? If I used a soft jaw I could grab more surface area but still too much force would bow the parts. really no effect way to bolt the parts down, there are no through holes except for a bearing hole on one end.
 
i've used 3M double sided tape on small aluminum and uhmw parts..
 
author=brucer link=topic=3696.msg26992#msg26992 date=1316963790
i've used 3M double sided tape on small aluminum and uhmw parts..

I have heard that, I am not a fan of tape. The cleanup is a big issue for me... While I have 5 parts in this run, they are prototype and test parts. Next batch is 20-30 parts and I don't want to have to clean that many parts:)

If I went the tape route, I might consider using my vacuum table. Would be a little more time to setup and cost more for shop material, but would probably work.
 
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Can you re-order the ops to allow the drilled holes to be done before the backside is milled? Or devise a fixture to hold them stress free?
 
Not really I cut the parts out of .25IN plate. 4 at a time. Then have 2 holes each side to drill on 3 sides..

Good news is it looks like the parts MAY work except for one. Won't know till they are mating and tested, but they are in tolerance.

The stress free fixture is probably the best way to go. I can probably mill an offset pattern where there is a boss sticking up through the bearing holes and the open slots and that would prevent any warp.

Then again, I could face mill the .25IN plate on both sides down to 5mm. That might be a pain, but the better option.
 
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