Table saw fence flatness

[Michael J Evans]

I just got a UNI-T fence from Peachtree woodworking. I set it up, tried to get It parallel and noticed ever time I fed a long length of wood (30" or so) that the back end (operater side) of the board would pull away just before the blade and through the cut. I repeated four more rips and same scenario (even with board buddies). I whipped out the digital calipers to measure test pieces and was getting a narrower measurement at the front of the board than rear (or maybe I have it backwards) either way I'm not getting parallel rips.

I decided to take a 24" framing square and test the UHMW fence face for flatness. I put one edge of the framing square just before the beginning of the blade. I was able to see a gap at the front edge of the fence and also able to rock the framing square back and forth. I didn't measure the gap, but from aligning the fence to fence to miter slot with a dial indicator I was getting a hump in the middle of the fence from .008-.013 (8 to 13 lines on the dial indicator, if I didn't list the decimals correctly). When I moved the dial indicator to the very back of the fence (rear of table) it would right itself / zero out.

Peachtree list that UHMW varies in thickness and that the UHMW may not be perfectly flat with the top part of the aluminum extrusion. But they do not list anything about the UHMW face not being flat along it's length.

1) Is too much deviation in the middle of the fence? (The OEM unifence extrusion has some slight deviation along it's length but only like .002-.003 at most)

2)if yes to above and Peachtree doesn't see it as a issue, how could I accurately shim behind the UHMW to get the fence flat along it's 43" length or should I make a new face out of hardwood?

Thanks in advance
Michael

[Bruce Wrenn]

If there are no exposed fasteners, could you face joint the whole assembly?

[Lee Schierer]

Hmm, 13 thousands isn't a lot and the fact that the far end of the fence goes back to zero. Are you seeing any burning on the sides of the cut? The hump in the middle should also be causing some burning on the side of the cut next to the blade on the fence side. Have you checked your blade alignment to the miter slot recently? An angled blade will give you the same type of problem you have noticed with almost no burning.

[Lisa Starr]

UHMW and most other plastic sheet goods have a huge tolerance on thickness/flatness so I'm surprised you're only seeing .013". The industry standard for most plastic sheet is +/-10% of thickness, so a 1/2" thick piece of plastic facing can be "acceptable" if it measures .450 to .550" (.100" variation). Plastic is machinable if you can avoid melting issues, but I'd probably just make a hardwood face and move on.

[Wes Grass]

Shimming it would be a good start. You already know how much you need, somewhere between 2 and 4 thicknesses of paper.

I'd worry about hitting the extrusion if you tried to joint it. And I have no idea how it work going thru a planer. Some of these plastics are difficult to get a good finish on. Some you can just forget about sanding.

[Michael J Evans]

If there are no exposed fasteners, could you face joint the whole assembly?

There are three removable Phillips in the face. It would have to be machined down removed from the extrusion

[Michael J Evans]

Hmm, 13 thousands isn't a lot and the fact that the far end of the fence goes back to zero. Are you seeing any burning on the sides of the cut? The hump in the middle should also be causing some burning on the side of the cut next to the blade on the fence side. Have you checked your blade alignment to the miter slot recently? An angled blade will give you the same type of problem you have noticed with almost no burning.

Hi Lee
No burning, but I was only cutting 1/2 spruce.i did noticed crosshatching / teeth marks on the back end of the board.
I did just do the blade to miter slot and got it within .001, but I did that with a think kerf blade and have now switched to a full kerf.

It may be worth double checking the blade alignment.

[Michael J Evans]

UHMW and most other plastic sheet goods have a huge tolerance on thickness/flatness so I'm surprised you're only seeing .013". The industry standard for most plastic sheet is +/-10% of thickness, so a 1/2" thick piece of plastic facing can be "acceptable" if it measures .450 to .550" (.100" variation). Plastic is machinable if you can avoid melting issues, but I'd probably just make a hardwood face and move on.

Wow good to know.
I think your right and I'll just make a hardwood face. I have some nice sapele and other tropical pieces that I could use.

[Michael J Evans]

Shimming it would be a good start. You already know how much you need, somewhere between 2 and 4 thicknesses of paper.

I'd worry about hitting the extrusion if you tried to joint it. And I have no idea how it work going thru a planer. Some of these plastics are difficult to get a good finish on. Some you can just forget about sanding.

I think this will be my first plan of attack. I can remove the screws holding the UHMW on and try sticking sheets of paper behind it to see. Thanks

[Matthew Curtis]

Hmm, 13 thousands isn't a lot and the fact that the far end of the fence goes back to zero. Are you seeing any burning on the sides of the cut? The hump in the middle should also be causing some burning on the side of the cut next to the blade on the fence side. Have you checked your blade alignment to the miter slot recently? An angled blade will give you the same type of problem you have noticed with almost no burning.

I would bet that some table saw blades deflect more than what you are seeing in your fence.

[johnny means]

You can joint the face.

[Robert Engel]

It does wear. I replaced it with a piece of ply with laminate.

[michael langman]

I have used a hand plane to plane uhmw if you own a hannd plane.

[glenn bradley]

I too have hand planed UHMW but, for your task I wold be more inclined to put sand paper on a flat surface and rub it back and forth a bit. If your reference surface is good you should be able to gt much closer than you are. BTW, the problem you describe is what kept me from getting a UNI-T fence many years ago. I would not hesitate today having gained some skill in making things "un-crooked". ;-)

[Derek Cohen]

Michael, if this was mine, I’d first call Peachtree and report the issue. They may sort it out for you.

If I set out to fix it myself, I would mark the high spots on the fence, and plane those down with a block plane.

Only if this failed would I replace the face with something else. Probably not hardwood — this moves. Waxed MDF?

Regards from Perth

Derek

[Dave VanDewerker]

This happened to my PM fence. The UHMW face on the fence wore right around blade (.006). It was enough to cause burning whenever I was ripping. I replaced it with a piece or extruded aluminum.

[Meryl Logue]

I have an old 1984 PM66. It was in a custom furniture shop. They had to replace the original face at some point with a type of synthetic. They flipped that. I had to flip it back... it was less trashed. But I did buy a new UHDP or whatever it’s called. It screwed it on using their original holes. I then shimmed it with slips of paper or card stock. Last task was to glue scraps of an old health card under one of the stabilizer wings of the fence to square it to the table. Huge difference. No more burning or hanging up. They used it to break down miles of sheet goods. They were on the second feeder when I got it.

[Michael J Evans]

I too have hand planed UHMW but, for your task I wold be more inclined to put sand paper on a flat surface and rub it back and forth a bit. If your reference surface is good you should be able to gt much closer than you are. BTW, the problem you describe is what kept me from getting a UNI-T fence many years ago. I would not hesitate today having gained some skill in making things "un-crooked". ;-)

Hi Glen the UHMW strip is only maybe 2" wide x approx 1/2" think x 43" long. I am afraid even just slight uneven pressure would cause more damage than it current has. Plusy float glass is only 48" long.

[Michael J Evans]

Michael, if this was mine, I’d first call Peachtree and report the issue. They may sort it out for you.

If I set out to fix it myself, I would mark the high spots on the fence, and plane those down with a block plane.

Only if this failed would I replace the face with something else. Probably not hardwood — this moves. Waxed MDF?

Regards from Perth

Derek

I may do that Monday just to get their thoughts before doing anything. Thanks.

[Michael J Evans]

Hi everyone. Hope all doing well.

Just wanted to update this thread. I received some zero slop adjustable miter bars and made a new jig to hold my dial indicator.

Spent way to many hours fiddling with my setup. Got my original unisaw fence dialed in, but then just couldn't help myself and took one more stab at the new UNI-T fence.

I layed a 12" framing square across the UNI-T fence while it was off the actual unifence carrier thing. It was not dead flat as in zero light shining thru but overall it was really flat and I couldn't replicate the rocking I had while it was on the unifence carrier or whatever that's called. So I stuck it back on the saw and only lightly tightened the bolts that hold the fence to the saw. Instead of killing myself with the dial indicator to start, I ended up setting the fence parallel to slot using my finger tip. Then I broke out the dial indicator and only measured the front and back, it was within 1 thou and I decided good enough.

I just bought a 1/2 sheet of MDF for my micro jig splitter setup and ripped a 48" length to 4.5".

The front of the piece was 4.5095
The rear of the piece was 4.5075 and everything in between was within 2-3 thou depending on how hard I pushed.

That seems pretty good to me, right?

I'm wondering if when I originally tightened the fence to the saw, if I over tightened the front bolt and that somehow bowed the extrusion? I feel that's highly unlikely as it's pretty damn stiff. Either that or my original miter gauge had more slop throughout the slop then I thought?

Either way I'm pretty happy with the setup now (convincing myself, because I feel like it should be dead on) unless someone says otherwise 😂

Thanks for reading