Warped plywood in middle of crosscut sled

[Jeff Skory]

Help!

The crosscut saw that I just finished (slides incredibly well :) ) has a slight problem. The plywood base seems a little warped in the middle of the kerf. The kerf at both fence ends are even but in the middle of the sled one side sits up 1/32-1/16 (I haven't actually measured it).

Should I be concerned? Is there anything that can be done about it?

Thanks in advance for you suggestions or your humor. Either one or both are welcomed. :D

[Ken Wright]

problem with my sled ...... right side stands proud about 1/32 of the left side.

Good ply .. 2x5x24" chunks of walnut at each end ..... good finish. No idea why it happened. No problem so far with the cuts so I just keep on knowing at some point I'll have to replace it.

[Todd Burch]

Jeff, how thick is the plywood, and how rigid is the warp?

A couple considerations.

First, when your sled is flat on the tablesaw, will your stock that you are cutting be enough weight to cause the ply to lay flat? If so, I wouldn't worry much about it.

Second, is the warp proud enough and/or rigid enough that will cause headaches when sliding work sideways on the sled? If it will be grabbing or creates enough of a ledge to hang material up, that could be a real pain.

To make the plywood sled base more flexible so that it lays flat, you could always kerf the top or bottom of the ply. (See my thread about how to do this here: http://www.sawmillcreek.org/showthread.php?threadid=5559&highlight=cupped+wood) You could fill the kerf if you wanted or thought it necessary.

Finally, remember that (ply)wood will bend. You could wet it and create a reverse bow with some cauls, clamp it for a day or so, and try that.

Todd

[Todd Burch]

Another thought - could you flip the warped ½ of the plywood sled over and cause the warp to face down? You've already cut it in two, and, the other side should hold everything square during the process.

[Fred Voorhees]

The first crosscut sled that I built a few years ago was made from plywood and within a day or two, the darned thing warped on me. It ended up in the crap pile. I went with 3/4" MDF and I have had nothing but good luck with that since then. I wouldn't consider anything else for the base material for a sled now.

[Donnie Raines]

I have gotten away from useing ply(of any type) for jigs and the like. I use 3/4 mdf....very, very stable....and cost is lower. Ply, for the most part, still has bits of solid wood in it.....and it still needs to move...not to the extent regulare lumber does, but move non the less.

...you could always try it and see what happens....

DonnieR

[Jeff Skory]

Good suggestions everyone. Here are my thoughts on them.

>> cut kerfs in the top or bottom:
I couldn't do that to such a pretty sled. :eek:

>> wet the plywood and clamp it for a day:
I applied a healthy dose of paste wax to both the top and bottom of the sled. Not sure how I would go about wetting it.

>> flipping over the offending half of the base:
It's screwed AND glued to the fences, and the rail is also screwed and glued. And the screws for the rails are covered with dowel plugs. :D Not much chance of re-architecting this baby.

The difference does not seem to affect how the sled works (other than maybe catching wood if you slide it sideways). So I guess I'll live with it for now till I build the next one.

I may use MDF for just the base. I will not however build another one completely out of MDF. Darn near got a hernia moving that one around. ;)

Thanks again for the suggestions guys.