How rigid is UHMW plastic?

[Dan McGonigle]

Hey guys, I make a lot of picture frames. That means cutting mat and glass. I’ve been thinking up some plans to make a mat cutting jig and a glass cutting jig. Basically a shop made version of a Logan mat cutter, if anyone’s familiar. I’m looking at UHMW plastic for the “fence” material - the fence that the mat cutter or glass cutter will ride against. I’ve never used it, so I’m wondering how rigid it is. Basically, would a 1/8” thick 3” wide piece of UHMW plastic sag in the middle over a span of 4 feet?

[Jim Becker]

Yes, it would sag on its own...UHMW is pretty flexible, especially something thin like that. But these kind of things are normally used on a solid surface, so that adds back stiffness from that support. IE...the design of your jig matters.

[Frank Pratt]

Even thick UHMW will sag & flex. It needs something rigid to back it up.

[Dan McGonigle]

Is HDPE plastic similar? I was thinking of going with aluminum flat bar, but wanted something softer. I could still make the UHMW work, just have to rethink my plan.

[roger wiegand]

This is probably more than anyone ever needed to know about the flexibility of plastics-- it's all there:

https://omnexus.specialchem.com/poly...ties/stiffness

[Frank Pratt]

Is HDPE plastic similar? I was thinking of going with aluminum flat bar, but wanted something softer. I could still make the UHMW work, just have to rethink my plan.

Yes, UHMW plastic is HDPE.

[Alex Zeller]

If I was doing a lot of frames I think I would look into something like a used Fletcher 3100 multi-material cutter. I often see them used for around $1000. I've only used one for cutting glass but with it, once set up, cutting glass is about as easy as it can get. The best thing about them is that once they depreciate from the price of new they hold their value very well. I've seen the Fletcher brand ones that are over 50 years old in frame shops going strong. Fletcher is the best known brand but there are several others. If you're just looking for a straight edge then something like a simple glass cutting square and a hard surface is all you need.

[Erik Loza]

I did a stint in plastics machining. As others have said, UHMW and HDPE will sag badly. OP, what if you got some aluminum 20/20 channel and just faced it with a strip of UHMW? Basically, a table saw fence. Or, what about a strip of phenolic-faced ply? Just thinking out loud.

Erik

[Derek Cohen]

Even thick UHMW will sag & flex. It needs something rigid to back it up.

I learned this the hard way. I built a great drill press table out of UHMW ...

It warped!



In the end it needed to be supported by steel sections. That seems to have done the trick, but I am still tossing up whether I should just build another table out of ply ...



Regards from Perth

Derek

[Jim Matthews]

I learned this the hard way. I built a great drill press table out of UHMW ...

It warped!




Regards from Perth

Derek

What, only three degrees of freedom?
How 20th century...

https://www.julesbartow.com/Controls...RoboticArm.png

[Derek Cohen]

Don't confuse me now, Jim. Too many settings and I get a tension headache

I must tell you, however, that I was using the Nova to drill mortices for three Wharton Esherick stools I am building (as you are aware), and I set up a sub table for 10 degrees slope (with a Wixey) and then 0 degrees axis (the latter using a laser), and then proceeded to zoom in on the precise position with laser cross hairs .... oh, soooo easy!










Regards from Perth

Derek

[Zac wingert]

Very rigid