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UHMW Binding - how to resolve?

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Forum topic by Paul D posted 08-19-2014 01:09 AM 1440 views 0 times favorited 16 replies Add to Favorites Watch
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Paul D

2130 posts in 3210 days


08-19-2014 01:09 AM

Topic tags/keywords: tablesaw sled uhmw binding

I’m in the process of building the Eagle Woodworking Super Sled. The UHMW I bought works great and slides perfectly in the miter slots by itself. When I screw this to the 1/2” plywood base it binds so terribly that the sled barely moves and is unusable. I’ve tried #8-1/2” FH and #6-5/8” FH screws and the result is the same. I’ve never used UHMW before and was assuming (maybe incorrectly) that I would not have to do any fiddling with it to get a smooth running sled and so I opted not to make hardwood runners.

What should I do to resolve this?

-- Paul D - Lawrenceville, Georgia


16 replies so far

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NoThanks

798 posts in 991 days


#1 posted 08-19-2014 01:13 AM

Is it possible that the screws are bulging out the UHMW ?

-- Because I'm gone, that's why!

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bondogaposis

4024 posts in 1813 days


#2 posted 08-19-2014 01:21 AM

That is my guess too, when you tighten the screws it adds lateral pressure to the sides of the strips. Put a straight edge on it and see if you’re getting bulges at the screw locations. Try backing off the screws and see if it slides easily. You may have re-flatten the sides w/ some sand paper to bring it back to straight.

-- Bondo Gaposis

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Paul D

2130 posts in 3210 days


#3 posted 08-19-2014 01:42 AM

I tried a test. I put the runners in the miter slots and attached it to the plywood with double-sided tape. The sled glides across the table quite well. A bit of paste wax on the table and the underside of the sled would make it nearly perfect. Screwing the UHMW is definitely causing the problem. Backing out the screws helps but still not as good as no screws at all. Can I take a 32nd off the UHMW on the jointer to see if that helps?

-- Paul D - Lawrenceville, Georgia

View Loren's profile

Loren

8301 posts in 3110 days


#4 posted 08-19-2014 01:42 AM

UHMW is quite flexible in smaller sections and it will certainly
bulge. You may be able to simply drill the screw hole
a little larger so the threads clear. You can also, if the
screw is threaded all the way, file the threads to a smaller
diameter where the go through the plastic.

I think I tried jointing it once and it didn’t work very well…
very choppy cut. It may hand plane but I don’t remember.
It can definitely be scraped with a razor blade or card
scraper. You can tape sandpaper to your jointer table
and use that as a sanding board. It’s slower going but
you’ll be assured of not messing up the material with
a sanding board.

I have a piece of belt sander paper glued to a 6” x 24”
piece of MDF and I use it often. I’m well equipped
otherwise too. I learned about sanding boards while
building guitars.

View TheFridge's profile

TheFridge

5765 posts in 948 days


#5 posted 08-19-2014 01:48 AM

What about using a forstner bit to countersink a screw with a flat or wafer head on it. With the hole going through it a little larger than the threads to give some play for adjustment.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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Loren

8301 posts in 3110 days


#6 posted 08-19-2014 01:53 AM

.... What ^^^ said, if you have forstners. It can be done
with a plunge router too but the question there is whether
you want to fuss with setting it up.

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Loren

8301 posts in 3110 days


#7 posted 08-19-2014 01:55 AM

You can leave the screws as the are. Tape some sandpaper
to a bubble level and “joint” the runner in place

View Crank50's profile

Crank50

173 posts in 1038 days


#8 posted 08-19-2014 02:05 AM

The best you can do is to counter bore holes for the mounting screws. Make the bore holes almost the same size as the width of the runners, say 5/8 diameter for a 3/4 runner and 3/16 deep for a 3/8 thick runner.
Then place a washer of the same diameter as the counter bore under the screw head. File the screw head thinner if you need to to prevent dragging the bottom of the miter slot.

If you have the time, space and materials it is better to have more mounting screws with less torque on each, than a few that are really tightened.

This should relieve the spreading of the UHMW runner. In the future it is better to use HMW polyethylene instead of UHMW because it is slightly more rigid and has a little better compression strength.

If you still have an interference fit it is possible the runners have become permanently deformed. You could help this situation by shaving a tad off the sides of the runners with a shoulder plane. Done carefully this will only shave off the high spots and stilll leave you with a good fit in the slot, overall. f you don’t have a shoulder plane you could use Lorens trick and make a sanding board to do almost the same thing.

View Chris208's profile

Chris208

237 posts in 1732 days


#9 posted 08-19-2014 03:06 AM

I used 1/4 inch thick oak runners on mine, and had the same problem. I just hit the runners with a card scraper where they were binding. Honestly it still binds a tiny bit in spots, but I figure it will loosen up with use.

Good luck.

View Lumberpunk's profile

Lumberpunk

323 posts in 1799 days


#10 posted 08-19-2014 05:42 AM

I had the same problem, I used a shoulder plane set to a very thin cut to plane off the high spots after the UHMW was screwed down, checking often for fit.

-- If someone tells you you have enough tools and don't need any more, stop talking to them, you don't need that kind of negativity in your life.

View timbertailor's profile

timbertailor

1591 posts in 886 days


#11 posted 08-19-2014 12:35 PM

Yeah, try drilling out the polyethelyne to clear the screw threads.

-- Brad, Texas, https://www.youtube.com/user/tonkatoytruck/feed

View Sarit's profile

Sarit

514 posts in 2602 days


#12 posted 08-19-2014 06:22 PM

Just shave a little off the edges next to the screws with a utility knife. The areas you didn’t shave should still be a perfect fit so there’s no need to make your shaving absolutely perfect.

View DrDirt's profile

DrDirt

4167 posts in 3204 days


#13 posted 08-19-2014 06:48 PM

Sarit nailed it.

I would shave right next to the screws… NOT joint the entire edge

I would take the piece and clamp it in a vise and use a card scraper 2 strokes for about 1 inch right where each screw will go, just to compensate for the bulge that will form.

Alternatively – you can go to making a counterbore (flat bottom recess) to accommodate a flathead/pan head screw instead of the cone shape screw head acting as a wedge in a standard countersink.

-- 'Political correctness is fascism pretending to be manners' ~George Carlin

View Paul D's profile

Paul D

2130 posts in 3210 days


#14 posted 08-20-2014 12:20 AM

Thanks for the help everyone. I ended up drilling out to clear the screw threads as Brad suggested. I also hand tightened the screws. I found that one of my runners was off the miter slot a little bit and I made the needed adjustment. After thoroughly cleaning and waxing the saw table and lightly sanding then waxing the underside of the sled it slides nicely.

-- Paul D - Lawrenceville, Georgia

View splatman's profile

splatman

558 posts in 861 days


#15 posted 08-20-2014 01:56 AM

Instead of screws, cut dadoes into the bottom of the sled, and slot the UHMW strips into the dadoes. The thickness of the strips will need to be the miter slot depth + dado depth – a fuzz. Cut the dadoes a few .001” narrower than the strips, for an interference fit, and use double-stick tape in the bottom of the dadoes, to make sure the strips say put.

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