UHMW Tables saw top

[Karl Brogger]

To avoid hijacking the granite top thread. Why not offer a UHMW top? I see the benifit to stone top, but I worry that using jigs, or T-squares would scratch the surface eventually. There' plenty of scratches in my top from who knows what, but they aren't deep enough to be an issue. I realise that UHMW would be a wear item, as it is on my fence, but if it was a 1/4" thick bolted to a cast top it would be easily replaceable and slippery. Corrosion wouldn't be an issue either.

What got me thinking about this is for the shaper that I use for cutting stick & rail material I have the feeder pushing away from the cutterhead to another fence. I don't get any snipe this way, or have to worry about alignment of the fences. I've been planning on having a better fence built that would just use thumb screws to change the settings. Right now I have to measure the distance, and have a piece of plywood clamped down to the table to change settings. Which is a royal pain. I had a ton of trouble with pieces "sticking" in the shaper when it was just running on the metal. I took a 1/4 thick piece of UHMW about 4" wide running the length of the bed and have barely had to lube it up at all. Wear has actually been less than I expected, but I've only ran probably 2000' with this setup, so time will tell.

Thoughts?

[Lee Koepke]

I like the flatness of cast iron. I would think uhmw would not stay flat enough.

couple of coats of wax and my cast iron is slick ...

[Doug Shepard]

The UHMW distorts pretty easily under screw pressure. I used it for some sled runners and 1/8 of a turn too tight with the screws caused it to bulge enough it would no longer slide in miter slots. The idea does have some merit but I'm thinking the very thin adhesive-backed Slik-Tape might be better than trying to screw it down.

[Cliff Rohrabacher]

Or 1" thick jig plate aluminum that's been hard coat anodized.

[Matt Meiser]

Ice--cheap and virtually friction free. Get a mini zamboni to refresh the top. Summer might be rough though. :D

I have UHMW ZCI's for my saw. It would need some kind of support as most plastics would tend to sag over time. I think the thin stick on sheet over CI has merit. When it gets bad, just tear it off and replace.

[Tom Esh]

Or 1" thick jig plate aluminum that's been hard coat anodized.

Indeed. Like the stuff Kreg uses on their tracks. That stuff is hard, and not just the coating. I had the opportunity to cut some recently and it dang near wore me out. I had no idea aluminum could be made that hard. I swear I could hack through 1/8" steel faster. I suspect a machined aluminum top of that grade (assuming anyone could afford it) would hold its own against CI.

[Jim Becker]

Karl...in a word, lack of...mass...would preclude using the plastic product. Both cast iron and the granite have tremendous mass for the given size and that is very meaningful relative to tool performance, vibration, etc.

[Rob Will]

I would say that the coefficient of expansion for most any plastic is too high for use in machine tools. Precision surfaces such as a miter slot would become unuseable with temperature changes.

Here is how much some common materials expand and contract with temperature changes: (inches per inch per degree F x 10*-6)

Somebody check me on this.

UHMW 80 -125
ABS Plastic 55
CPVC 34
Aluminum 12.3
Steel 7.3
Marble 6.5
Cast Iron 6.0
Porcelain 1.7
Wood (oak across grain) 3.0

Rob

[Karl Brogger]

Karl...in a word, lack of...mass...would preclude using the plastic product. Both cast iron and the granite have tremendous mass for the given size and that is very meaningful relative to tool performance, vibration, etc.


What I was thinking is that you'd still have the cast iron below, just something more slippery above. The thin peel 'N' stick sheet idea definatly has merit.

[Doug Shepard]

FWIW I googled yesterday after posting to see how wide you could get the stuff. PIecing it together from 3-4" stuff available at WW suppliers would be a real pain. Looks like you can get this clear out to 24" though I have no idea what it costs.
http://www.industrialgeneralstore.com/Slick%20Surface%20Tape.asp

[Russ Filtz]

UHMW, while slick, is relatively soft. You will end up scratching it all over, then gunk will fill the scratches, then the gunk will either scratch your work piece, or end up stickier than the bare top. Stick with cast iron, wax it or use some SlipIt spray like I do. Protect with Boeshield T-9.

[scott spencer]

Ice--cheap and virtually friction free. Get a mini zamboni to refresh the top. Summer might be rough though. :D



I think Bosch has a portable Zamboni that would be perfect for this Matt! ;)

As for UHMW plastic...I agree with those that have said it's too soft and too unstable for a horizontal reference surface. I wonder if Corian on a substraight would work for extensions? We've had a good size square as a cutting board on our countertop for 7 or 8 years and it's still going strong.

[Greg Cole]

I would say that the coefficient of expansion for most any plastic is too high for use in machine tools. Precision surfaces such as a miter slot would become unuseable with temperature changes.

Here is how much some common materials expand and contract with temperature changes: (inches per inch per degree F x 10*-6)

Somebody check me on this.

UHMW 80 -125
ABS Plastic 55
CPVC 34
Aluminum 12.3
Steel 7.3
Marble 6.5
Cast Iron 6.0
Porcelain 1.7
Wood (oak across grain) 3.0

Rob

Rob,
I have first hand experience with some UHMW pieces for die tooling sets that will NOT fit on a humid day in the summer. 10 minutes in the freezer and that same part will drop in place (usually less than 1/2 millimeter clearance for a proper fit). No factual #'s on expansion etc, but UHMW would be my last plastic compound choice, but there are 10,000,000 other types of this sort of material now.
All the other comments are spot on @ being easlit scratched, not dense enough etc etc etc...

Greg

[Ben Cadotte]

A problem with having it over the cast iron top is you will get corrosion unless you seal all the way around it. And had it very clean before sealing them together. Would be very hard to keep corrosion at bay underneath it. Could use a corrosion inhibitor like LPS or something. But whats the advantage of using the HDPE if you have to work on the top continiously. Might as well just spend the time on the cast top from the start.

[Chris Padilla]

Karl...in a word, lack of...mass...would preclude using the plastic product. Both cast iron and the granite have tremendous mass for the given size and that is very meaningful relative to tool performance, vibration, etc.

I think density is the word you are looking for, Jim. :)

Some quick looks on the www find:

Cast Iron: 7300 kg/m^3
Solid Granite: 2700 kg/m^3
UHMW: 940 kg/m^3