I’m building my version of the router table fence in the April issue.
Biggest difference is I’m making it bigger, so I can put a full four inch hose into it, and tie it into the dust collection. That way, I can add yet more spaghetti to my dust collection system.
I got a good deal on some UHMW plastic at onlinemetals.com, (a source, by the way, that I highly recommend, particularly if you live here in Seattle) but it’s bent. Not flat. Un-flat. Without flatness, curved, un-straight.
I’ve put a picture here, the pieces I’m working with are 3/4 thick, 6″ wide and about 24″ long.
If they were wood, I’d joint them. If they were cast iron, I’d force them flat, whack them, and shock them straight.
I suppose I could try heating them, but on occasion, Bad Things Happen when I just fire up the torch and point it at something without understanding what I’m doing.
Jointing them (UHMW works very easily, like mahogany or cedar without the grain) would probably take them down to 1/2″, and that seems like a shame.
Any UHMW experts here? Any suggestions on straightening out errant UHMW?
Replies
I don't even know what UMHW is... it sounds like some kind of labor union, but I love the idea of firing up the old torch and pointing it at something. If you think heat might be the answer why not try a heat gun or hair dryer ?
uhmw
Jammersix,
If you're putting it in a dado, it should straighten out and fit right in as you insert it. It comes all gollywampus, but then I've never needed a piece longer than 2 feet. If it doesn' work, send it back. Then there's always that torch idea, Yeah.
Steve
No Dado
Nope, it's going to be the bearing surface of the fence.
Un-flat UHMW
"Any suggestions on straightening out errant UHMW?"
Nails? ;-)
Although I may be talking through my hat here, my impression is that UHMW is fairly flexible, and thus subject to bending when stored in a manner that it can become un-flat, un-straight, or otherwise malformed. It should, however, be amenable to "training" - that is, being bent into the proper position, and held there with the appropriate attachment devices (e.g. screws). Gently heating it with a heat gun or hair drier might help in that regard. I don't believe that UHMW is intended to be structural in the usual sense, like Melamine or phenolic ply.
UHMW
Perhaps you could attach the Ultra High Molecular Weight plastic straight to a sub-fence assembly using counter sunk screws or counter bored bolts of some kind. It would end up as straight as what it's attached to. Seems like the plastic is intended as a slick wear surface and not so much a precision component.
-Paul
I would counter-sink / screw it onto your fence, the run it over the jointer.
Aah Google Rocks
The following info suggests that heating on something flat in your oven might do the trick - under some weight of course.
View Image
Many applications require Gar-Dur® UHMW plastic rod, bar or sheet to conform to a specified contour surface or to bend around corners. Shaping thin (<1/8" thick) sheet over large (<10") diameter contours can be accomplished simply by forcing the sheet against the surface and mechanically fastening them together. To form more difficult contours, heavier cross sections, or sharp edges, however, the sheet must be heated and shaped.
Unlike most thermoplastics, UHMW plastic does not become a liquid when it is heated above its "melting point". Because of its high melt strength, it can be handled and shaped above its crystalline melting temperature of 265° F (129° C). Although UHMW plastic can also be shaped below the crystalline melting point, this causes residual stress in the part.
Heating
Optimum forming temperatures for Gar-Dur® plastic sheet, rod or bar are 280 to 300° F (138 to 149° C). At these temperatures, the plastic is translucent and newsprint can be easily read through thin sections.
Methods for heating Gar-Dur® plastic include air-circulating ovens, conventional ovens (similar to those in the home), heat lamps, radiant heating panels and oil baths. The most reliable ones are the air-circulating oven and the oil bath, since these heat most uniformly. With other methods, it is difficult to control temperature accurately and uniformly. Colors can also affect radiant energy heating.
A conventional fryer can be used as an oil bath for heating small parts. Most units for use in homes will hold temperatures with sufficient accuracy for the forming processes. Recommended heating oils are glycerin, silicone oil and commercial automobile antifreeze (ethylene glycol).
Forming
Forming is a simple process. After being heated to the recommended temperature, Gar-Dur® plastic sheet, rod or bar is forced to conform to a contoured surface and is then held in place. It is important to clamp the workpiece to the contoured surface until it is completely cooled.
Use a less thermally conductive material, such as wood, for the molding form. If a metal surface is used for a molding form, the metal may draw heat from the Gar-Dur® plastic piece before the forming process is complete. If it becomes too cold, it will be difficult to form and will have residual built-in stresses.
High residual stresses occur because of rapid cooling of the formed part. This is most likely when forming thick (<1/2") parts. Residual stress is minimized if the formed part is cooled slowly by covering it with an insulated cover or blanket.
Thanks, Gang!
Thanks, guys!
I was, in fact, hoping that thicker (3/4") would be semi-structural, at least stiff enough to form the sliding portions of the fence without a sub assembly, but perhaps not. The UHMW on my saw fence is, in fact, screwed to the fence.
Thanks, Jerry, for the complete answer! I appreciate it!
Now, of course, I have other issues-- I do, in fact, have some 1/8" UHMW, left over from god-knows-what, and it occurs to me that if it bends politely, I could bend some nice, smooth baffles to change the hard, right angle corners inside the box to nice, smooth, dust-collection curves...
Pictures
A picture for you: the general plan is on page 14 of the April 2010 issue.
I haven't figured out how to add more than one picture to a post, but I'm pretty sure the problem is on my end, not Taunton's.
The change orders are these:
1. The size has been increased. The bottom is 6" wide, the height is 5". This is to accommodate a 4" pipe for dust collection, rather than a shop vac.
2. The dust collection is stubbed out the bottom of one end of the fence.
3. The tracks have been replaced by slots in both sides (actually all three) sides.
4. The bearing surface fastenings will be long carriage bolts, counter sunk into the bearing surface, running through the fence, and fastened with knobs on the back of the fence.
5. I've never used hold downs or feather boards with a router table, and have not made any provisions for them.
6. Chamfer added to port.
7. Interior supports added to long end of fence.
Now, of course, looking back at the plan, I see that he used HDPE, not UHMW.
I've used UHMW before, and that error is mine. I read HDPE, and thought "oh, UHMW. I know what that is, and I know exactly where to get it."
Read once, measure twice, cut once, re-read, discover error, start over.
Repeat process, throw hands in the air, leave for vacation.
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