holding flatness in nylon plates

[Oppiz]

Recently we've been making boards made out of 1/2" nylon 6/6. The plates are 16" x 24". We squared them up then machine a series pockets in 1 side.

They just added a parallelism and flatness within .005 . We all know how unstable this type of part can be. What processes in machining do you recommend that will allow me to maintain this tolerance? Possible there are some better materials that I could recommend to the designers???

[Guest]

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Possible there are some better materials that I could recommend to the designers???

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Depends on the design intent and the reason for using Nylon.

 

in the end, it will have to be cut in as "free" a state as possible.

[Dave.L]

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They just added a parallelism and flatness within .005

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Good Luck.

 

Acetal would probably be better. As John stated, you need to hold these parts without distorting them while machining.

 

The trick is to get a face cut to make a very flat side, then use that side to clamp down and all should be good (unless the material springs)

[jeff]

Make sure you rough them out and let them set overnight.

They WILL change on you.

I'll never forget about 15yrs ago we had a big UHMW job that I turned up, all nice and pretty with close tolerances.. .the boss came in the next day and reamed my a$$ telling me that I didn't inspect them when they came out of the machine.

ran them again, he checked them, next day they were scrap again.

I'm still waiting for his apology

[taperlength]

Rough out the parts and have them stress relieved before finish machining.

 

http://www.boedeker.com/anneal.htm

[BrianP.]

Double stick tape to hold parts for finish. Nice light cut parts should come out nice and flat. Have done this before and works well. As free a state as you can get as John said.

[Newbeeee™]

The trouble with Nylon is that it absorbs water (moisture) so can change quite dramatically.

Acetal or Delrin will be better from a machining point of view.

 

I'd ask the drafty boys if flatness is really an issue?

If you use a vac fixture, both sides will be parallel to eachother, and as the plates are only 1/2" thick, they will 'bend' more than 5 thou quite easily on assy.

What I mean is they will clamp flat very easily, clamping out any 'bend' within them, negating any drawing flatness requirement.

Ask what the application is.

[Oppiz]

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I'd ask the drafty boys if flatness is really an issue?

If you use a vac fixture, both sides will be parallel to eachother, and as the plates are only 1/2" thick, they will 'bend' more than 5 thou quite easily on assy.

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Theres fixtures I'm making are use to hold parts for an engraving operating in a production environment. The fixture sits in its natural state with only locating pins. The "designers" claimed they researched and did testing on nylon and found it to be the best material for this application, I'm going to make some suggestions for different material and possible a design change. Wish me luck.

Thanks for all the input.

[MACHINEMASTERG]

double disc grind it to size first it cuts equal amounts off both sides in the free state we have this done for some of our plastic jobs that need to be flat www.precisiondiscgrinding.com

[Chris Parish]

Jeff:

 

i feel your pain... I absolutely had the same thing happen

UHMW ... poor mans nylon

[left coast lefty]

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Rough out the parts and have them stress relieved before finish machining.

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This solution has worked for us.