Question on Wood to UHDP Friction Reduction

[Tom Banes]

I built a small ripping sled from baltic birtch ply. It slips over my rip fence (Jet Xacta type) which has UHDP panels on the sides. The sled tends to stick a bit when moved fore and aft and the inside sides that contact the UHDP build up sort of caked on particles that inhibit free movement. THe particles are easily scrubbed off with afingernail or steel wool substitute. They act like wax that has "melted" and re-hardened.

I finished the sled with a 1# cut of shellac, more as a protectorant than a finish. Just wiped on 3 or 4 coats, let it cure for 24 hours, then waxed with Johnsons wax, rubbed out with the grey substitute for

000 steel wool and buffed. THe wood feels slicker than s*** but drags on the UHDP after a few passes.

Any suggestions? I want the sled to fit firmly to the fence (i.e. no slop side-to-side), but slide easily. Obviously, I don't want to grease or lube the inside of the sled as I still use the fence by itself with wood sliding on it.

Regards.

Tom

[BobS]

Tom,

I'll bet a nickel that the sides of your jig and fence are neither parallel to each other nor are they really flat surfaces. The "zero-tolerance" you're trying to achieve can be tough. Take a dial gauge jig and slide it along your miter slot and measure the face of your fence. Unless you have done some shimming and flattening of the surface plus critically aligning it so its perpendicular (both sides) then you will not achieve what you're trying to do - easily anyway.

Look at the faces on your fence and jig - any small ripples? If so - there's a problem and they can be a bear to get perfectly smooth and flat. I ran mine through a planner mounted on a carrier bed to insure no snipe (divots on the ends) and finished them on a Performax sander using 180 grit to get rid of the planner blade ripples. Overkill but it worked to get the faces of my tablesaw fence flat. Jet sent me 3 replacements and none were better than the original faces.

The grunge I think you're seeing is wax that you've applied to the fence or jig and it's probably trapping some sawdust and being rubbed into the wax. No place for the dust impregnated wax to go except - peel off. Try cleaning the UHDP with some mineral spirits to take off all the wax. Work on getting the faces flat and parallel - then I think you'll be close enough to perfection that you won't need any lubricant on the UHDP.

Bob S.

[BillyBob]

Why make it fit the fence so tightly? Even UHDP will have some movement with moisture and temperature changes, which would make your fit vary. I would think you could have a very effective sled if you made it looser and just held it against the fence while ripping. It ought to slide more consistently and easier, too.

Bob

[Tom Banes]

Thanks BobS and BillyBob.

Yup, the jig is probably tighter than it needs to be.

Yup, the UHDP fences faces are not smooth. They are, however, reasonably flat to eye and to a machinists rule, ignoring the lack of smooth. A bit of smoothing is in order. 24" long MDF hunk with some

320 grit glued to it is the plan. I'll lap those puppies like I would the sole of a plane, after cleaning with mineral spirits. I'll also dewax the inside of the jig with MS and trust to the smooth wood.

The face parallelism issue I can'y really check until they're smooth as the DI jumps all over the place on the roughness. I did check the inside sides of the jig though, and those faces are parallel to within .005, so I have hope that the UHDP faces are close since the jig was built on them.

Regards.