Shim material--runner alignment


Ken Smith:
Recently someone asked for some shim material.  I had some in my box, and gladly provided it. 

What do you use this stuff for?  Runner edges in glued-to-the-plank chocks need to be parallel.  [I prefer glued chocks.  There is enough to do on the ice so I avoid aligning chocks there.  I align and glue the chocks to the plank in the warmth of the shop.]  I have spent considerable time getting the runners sanded and/or shimmed so the edges are parallel.  Prior to shimming, the edges are sometimes just a little out of line with the sharp edge.  So shim material is placed on the runner body to set the runner body in the chocks with the sharp edges parallel.  In fact, all my runners are now set up so any runner can be put on any side of the plank, and it will be parallel with any runner in the other chock.  Sometimes shims on one side and sanding on the opposite side is required to keep the runner body fitting the chock properly.  Shimming and sanding is required to achieve perfect alignment.

[Jane, that is why the starboard runner can go on the port side.  It no longer matters.  That is what engineers do!]

So what can be used for shim material?

The economy package is high-density urethane adhesive-backed tape.  It comes with a paper over the adhesive and it comes in various sizes and thicknesses.  Some years back, I googled the product and found a source.  I ordered a 50 foot roll in 0.010 and 0.003 inch thicknesses.  Search for "UHMW tape"  The thirty dollar investment is still doing service...  I use some annually on one side inside my Jablonski chocks so they are tight on the runners.  It is goon anti friction tape and I use it on sliding surfaces, like the inside surface of my one-car boom track.  I still have a few runners with this tape as shim tape.  [But not for long, if lack of ice continues!]  It is sold as an anti-friction, anti-wear tape for such things as production machinery, the leading edges of ailerons and flaps on home-built aircraft, etc., and for abrasion resistance on leading edges of lots of stuff in the air.  I se the thin stuff on my bike to keep the paint from being chipped on the rear stays.
The advantages:  Low cost, easy installation, easy replacement, smooth low friction abrasion resistant surfaces. 
The disadvantages:  It wears and extrudes under high pressure, and gets thinner over time.  The glue gets gooey when oil and grease gets to it, over a year's time or so. The edges fold over in tight fits.

Premium materials:  If you can find a source, there is a very good material available.  The layers between printed circuit boards comes in flat, uniform and various thicknesses of resin cured fiberglass.  It works great.  Use it dry in your chocks to figure out the thickness needed, and then super-glue a 1.5 x 2 inch strip on the runner body near the edges of the chocks.
Advantages:  Wears better than UHMW tape, so it lasts longer.  Like forever.
Disadvantages:  Slightly abrasive, so use grease in the chocks!  Hard to find a source.  Care required in gluing to runner bodies.

Compromise:  Make fiberglass or carbon shim material yourself.  I just made a batch of 0.010 in material as follows:  Cover two flat boards with wax paper, or use waxed plexiglass, to make a smooth surface at least twice as wide as the tape being used.  Wet out some 0.010 inch thick fiberglass tape with epoxy, lay it on one of the flat surfaces.  Lay the other surface on top of the tape.  Clamp tightly to put the tape under pressure until the epoxy sets up.  The pressure will push out epoxy, so trim the excess off with scissors.  Super-glue the shims as with the bought glass.  Other thicknesses of materials make other thickness of shims.
Advantages:  Easy to make with scrap materials...  Good wear properties.  Less abrasive than bought materials.
Disadvantages:  Not as uniform in thickness as bought materials.  Glue carefully.

Good alignment is the master genesis of good boat speed!   ;D


Geoff Sobering:
Quote from: Ken Smith on January 25, 2007, 10:30:30 PM

Compromise:  Make fiberglass or carbon shim material yourself.  I just made a batch of 0.010 in material as follows [...]

I just finished shimming all my runners using DIY fiberglass sheet like Ken describes above. 

It worked great. 

I was initially a bit concerned about the variability in the material.  I made a number of 4"x36" sheets with 6 oz. glass fabric and WEST epoxy using the tooling we have for making runner-body reenforcement sheets.  The thickness came out nominally 0.010", but ranged between 0.005" and 0.015".

The process I used to shim was:
Determine where I needed extra thickness and approximately how much was neededClean the runner surfaces with Acetone and optionally roughen them with 80-grit sandpaperRoughen the glue-side of the shim patch with 80-grit sandpaperSuperglue piece(s) of shim material just thicker than required to the runner Once the glue had cured, flood superglue around the perimeter of the shim material (esp. where there were obvious glueless areas).  Capillary-action will wick the glue under the shim anyplace it's not glued down, this also seal the edges so it's harder for stuff to get under the edge of the shim.  I also used some accelerator to cure the glue quickly.Wipe off excess accelerator (also a double check that there's no uncured glue around - don't want to glue the runner into the test-chock!)Recheck alignment and verify expected overcorrectionSand down the shim material with 220 grit sandpaperRecheck alignment and repeat sanding as necessary
I found that after doing a couple of runners the sand-check-sand... process went very quickly.

One older insert runner I have required more than 0.010" of shimming, and I just glued two sheets on top of each other to get the required thickness.

I've had this kind of shimming on one set of runners of over a season, and there was no sign of any ungluing when I removed the shims to re-do them earlier this year (removal hint: plastic scraper, Acetone, and maybe some MEK).


Geoff S.


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