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In particular the fence. The other day I got my sled nicely calibrated and on final screw up it lost its accuracy. I was only using a 18 mm MDF strip for the fence. I was worried it's flex was the problem. So can anyone tell me.

  1. The best wood to use for the sled.
  2. The best wood for the fence if different
  3. Minimum recommended thicknesses for the fence.
  • Thanks for the answers. Re my technique for squaring. Basically I put one screw in, moved it until it was square with a framing square to the kerf line. Then I put another screw in to fix it. I then did the 5 cut method and used feeler gauges to move the fence the last 0.039 mm. I wondered about gluing it. I just wondered if I would be quick enough to adjust it before it set. – GavGee Oct 29 '15 at 7:19
  • See this meta post on the word "best." – grfrazee Oct 29 '15 at 18:09
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    I was very fond of my sled that had a big honkin' chunk of 2x maple for a fence. Total overkill, but really nice to hold onto. Rosebud! – Aloysius Defenestrate Oct 30 '15 at 23:23
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This is probably largely personal preference, but I like to use baltic birch plywood for my jigs -- including my cross cut sled. Like MDF, plywood is dimensionally stable. But I find plywood holds up better over time.

5

As a rule there is no one best material for anything, although for jigs it's almost universal that plywood or MDF are recommended these days for the major elements, but they are not the only options. Also note that not all ply or MDF is created equal, and the storage conditions where they were bought is a factor too (whether stored dead flat being the main one).

Overall I would prefer to use plywood for something like this myself for a couple of reasons, primarily because a mid-range ply is stronger and more resilient than MDF. But that said, many many jigs for table saws have been successfully made from MDF and given reliable service for years after.

on final screw up it lost its accuracy

I wonder if you weren't using clamps here (or enough of them) to hold the fence firmly in position while the screws were being driver. An additional aid worth considering is a couple of square clamping guides of one kind or another, e.g. something like this:

Right-angle clamping jig

I was only using a 18 mm MDF strip for the fence.

That would usually be plenty thick enough. The overall size of the piece could have been a factor, and/or the quality of the MDF.

If in doubt laminate it with something to stiffen it up (doesn't have to be another piece of the 18mm MDF, but you can't go too stiff here and the added bulk of another 18mm of thickness on the fence wouldn't normally be a hindrance during use).

From your Comment underneath the main Question:

I wondered about gluing it. I just wondered if I would be quick enough to adjust it before it set

A tip to help with this is to drill clearance and pilot holes for your positioning screws for the fence, with the fence firmly clamped in place and checked for accuracy, then drive all screws home, check for square and then withdraw the screws.

This will allow for a very quick (and hopefully still very accurate) fixing of the fence once glue has been applied, with little if any problem of it moving out of alignment due to the lubrication provided by the glue.


In case it helps, a previous Answer has some details on how you might construct one of these, requiring minimal work on keeping things square.

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    What a perceptive response. You have predicted many things right from the detail you extracted from my question. Some very important points that has helped me get back to a much more sturdy solution. Thanks immensely, it didn't quite go down like you tube suggested and this helped a lot. – GavGee Oct 31 '15 at 0:08
  • I am having problems with both MDF and plywood as a base material. With plywood I'm lucky of I can even find a piece that isn't already warped or twisted. Is this because of the quality of wood I am buying? With MDF it consistently temporarily warps when the humidity changes. E.g. when a wet day dries out, the side of the MDF facing up dries faster and it curves as its drying. It is frustrating. Is there another material? Or some way to keep things stable? I considered delrin but it is $$$ and I don't have the tools to machine it. – Jason C Nov 14 '15 at 22:17
  • @JasonC, "Is this because of the quality of wood I am buying?" Very likely part of it, how it's stored would be another factor of course. I'm pretty amazed at the problems you're having with MDF, I've never experienced anything like that (at least as far as I've noticed, I've never made a jig this large from it). That too may indicate the MDF is not of the best quality, it can vary quite a bit. "Or some way to keep things stable?" shellac or varnish the MDF. Just as in furniture this will slow moisture transfer. – Graphus Nov 15 '15 at 10:32
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I use MDF for the base, and either MDF, Ply or Tri for the fence (depending on what's lying around).

I don't think it hugely matters what wood you use, but MDF is nice and flat and smooth - a decent quality plywood would probably be the same.

18m is plenty thick enough - you shouldn't see much flexing. Particularly once you've managed to get it glued to the base.

What technique are you using when you try and square it? I like to glue, screw in one end, nail at the other, quickly make a few cuts to test (and adjust the nail end via hammer). Once it's square, leave it for 30 minutes to dry and then drive in a few more screws.

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