UHMW vs. Delrin

[mxrethoret]

I am currently designing a mill fixture. The application of the component that I'm making this particular material selection for will be to hold the flange of a part during a drill operation. It slides up to the flange after the part is loaded onto the fixture, and is then held into place by three 3/4" bolts. Dimensions are 1" X 5" x 59".

Must be:
1) Lightweight so that 1 person can lift and bolt into place
2) Resistant to vibration fatigue
3) Easily machinable
4) Cheap
5) Since it will be on shop floor, it must not break if something bangs up against it.

I've narrowed down my options to UHMW Polyethylene and Delrin and wanted to get some input from people that have worked with both. Is the high cost of delrin worth it? What are some advantages/disadvantages of each?

Thanks in advance.

-Rich

 

[MintJulep]

You've given essentially no quantifiable information for anyone to base any recommendation on.

How did you manage to narrow down the options to UHMW or Delrin?

Neither of those materials are particularly well suited for machining fixtures. They are hydroscopic, and will thus change dimensionally with changes in moisture.

They both have relatively high coefficients of thermal expansion.

Neither are particularly rigid.

 

[hydromarine]

Prefer to work with Delrin and for both you will need very sharp drills, milling cutters etc have you considered Tufnol a superb material to machine Tufnol.com

 

[mxrethoret]

Mint.. Thank you for your insight into the properties of these materials. I have narrowed down the choices to UHMW and Delrin because they have low friction coefficients (so that it can slide up and down a guide), and was also told that they have good moisture resistance.. which seems to be the opposite of what you're telling me..? Thermal effects are negligible in this particular application. The mill simply drills pilot holes through a 1/4" aluminum flange, and this part is there to reduce vibration and deflection. There are no quantifiable requirements for this design, simply a need to use a material that will do a good job of supporting the flange through multiple uses.

How do the impact resistances of these materials compare?

 

[MintJulep]

Plywood.

 

[KENAT]

A classic approach might be to build the fixture from steel or aluminum and just face the sliding surfaces with your low friction material.

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[mxrethoret]

The fixture itself is made of steel. This part of the fixture only supports the flange. Metal is not an option because the flange support has to be lifted up into its locked position by one person. Given the dimensions, this would be way too heavy.

 

[Occupant]

I have used them both. They are not particularly hydroscopic compared to e.g. Nylon. Delrin is dimensionally more stable and easier to machine, but if you just have to supply a sliding surface UHMW is plenty good and a lot cheaper.

 

[MECH8T4]

Not sure on all the details, but in the past we have worked with nylon which is easil machinable, unbreakabe, and I think affordable

 

[drawoh]

mxrethoret,

When I want plastic, I usually specify Delrin because our machinists like it. I figure I get a cheaper part. I only specify other plastics when the requirement is tricky, and I need high performance of some sort.

JHG