small annoying vent

[Justin Rapp]

I am building a new sled for my sawstop and I built a pretty cool looking fence which is two 9 ply 3/4 maple ply laminated together and bordered with some poplar for a clean look. Well today is is slightly bowed, and even if I force it flat, there is no way in hell I am getting it square to the blade. I got it close, about 89.5 but that isn't cutting it. Oh well. I'll build a new fence out of hardwood. I have poplar and hickory sitting around that is spare or I dig into the nicer stuff. Hickory will just make the sled 10 tons.

Flat plywood is a thing of the past!!!

[Richard Coers]

You put a bunch of water between the two layers with glue. Did you let it lay on a bench after laminating? No air got to the outside of one layer if you did, so uneven drying. Not the plywood problem, a gluing and drying problem. Also no way do you need 1 1/2" of plywood as a base to a sled!

[Bob Cooper]

i think his 1 1/2 is the fence...not the base.

[mreza Salav]

Want flat and stable? Use mdf.

[Maurice Mcmurry]

I have made good sleds that need to be thin with 1/4 inch baltic birch covered on both sides with formica. I do the lamination on the table saw top with gorilla glue (do not wet), do doth sides of the glue up at the same time, use a full-size pice of MDF as a caul and load the sandwich with weight. The result is very flat and stays flat. And you have plenty of blade height left.

(I thought this was going to be about the neighbors bathroom fan)

[Jason Evans]

Want flat and stable? Use mdf.

I disagree. Mdf absorbs too much moisture and changes thickness.

[Rich Engelhardt]

I disagree. Mdf absorbs too much moisture and changes thickness.
I get around that by using a solvent based adhesive - such as the Original Contact Cement - or shellac.
3# cut orange shellac (now called Amber) makes a wonderful fast dry adhesive.

[Maurice Mcmurry]

Flat plywood is a thing of the past!!!

I am not quite visualizing what you are making.

Flat plywood is all about balance. Lumber yard and home store plywood is seldom balanced, unless you can find a product like Baltic Birch. I sometimes glue two layers of 3/8 Radiata together back to back to create balanced 3/4. Titebond works, polyurethane without wetting, or epoxy is better.

[Dave Sabo]

I disagree. Mdf absorbs too much moisture and changes thickness.


If the edges aren't sealed - otherwise it's very stable and doesn't seasonally expand and contract like say..........hardwood.

[al ladd]

I think quartersawn hardwood is an easy superior alternative to laminated plywood.
For a really superior fence use 2040 or 2060 aluminum extrusion. Many possibilities for auxiallary faces, sacrificial tips, hold-down clamp and stop mounting etc. Relatively inexpensive (for 2040) in matched pairs on Amazon, and you can make a quick disconnect extension from the two pieces. Way stronger and more stable than any wood product and only uses 20 mm of your sled surface.

[Justin Rapp]

You put a bunch of water between the two layers with glue. Did you let it lay on a bench after laminating? No air got to the outside of one layer if you did, so uneven drying. Not the plywood problem, a gluing and drying problem. Also no way do you need 1 1/2" of plywood as a base to a sled!

1 1/2 of fence, not the base. The base is just 1 layer of 3/4. Where do you get the water from, the glue? Just a pair of 4" x 48" x 3/4 ply face glued, clamped every 4 to 5 inches. 1 hour later I glued on the 1 1/2 x 3/4 hardwood on all 4 edged, clamped for 1 hour. Let dry for a few hours, flush trimmed the hardwood to the plywood. Flat/square fence. Next morning after sitting on the edge on my bench it was slightly bowed. Oh well.

[Justin Rapp]

Want flat and stable? Use mdf.

I was thinking about MDF for the base but I added t-track for hold downs and other jigs that are in the plan. Unless I used through bolt with a screw & nut since I don't trust mdf to hold the very short wood screws. To do this, i'd have to go with a much thicker (and heavier) base to hold the through-bolt. My last sled was melamine, it was flat as can be but weighed a ton.


I have made good sleds that need to be thin with 1/4 inch baltic birch covered on both sides with formica. I do the lamination on the table saw top with gorilla glue (do not wet), do doth sides of the glue up at the same time, use a full-size pice of MDF as a caul and load the sandwich with weight. The result is very flat and stays flat. And you have plenty of blade height left.

(I thought this was going to be about the neighbors bathroom fan)

Too thin to mount the recessed hold downs. And if I could find baltic birch these days around here i'd be pretty happy.


I am not quite visualizing what you are making.

Flat plywood is all about balance. Lumber yard and home store plywood is seldom balanced, unless you can find a product like Baltic Birch. I sometimes glue two layers of 3/8 Radiata together back to back to create balanced 3/4. Titebond works, polyurethane without wetting, or epoxy is better.

Was just making a 1 1/2x4x48 fence for a sled. The Radiata is just another ply. I used a semi-decent plywood, it just didn't stay flat on me. And no Baltic Birch to find local. I tried.


I think quartersawn hardwood is an easy superior alternative to laminated plywood.
For a really superior fence use 2040 or 2060 aluminum extrusion. Many possibilities for auxiallary faces, sacrificial tips, hold-down clamp and stop mounting etc. Relatively inexpensive (for 2040) in matched pairs on Amazon, and you can make a quick disconnect extension from the two pieces. Way stronger and more stable than any wood product and only uses 20 mm of your sled surface.

I was thinking of using extruded aluminum. Most likely would have gone with a pair of 2080 and figure out an extension to keep them together/flush with a gap for the blade. Maybe the next sled gets it.

[mreza Salav]

I was thinking about MDF for the base but I added t-track for hold downs and other jigs that are in the plan. Unless I used through bolt with a screw & nut since I don't trust mdf to hold the very short wood screws. To do this, i'd have to go with a much thicker (and heavier) base to hold the through-bolt. My last sled was melamine, it was flat as can be but weighed a ton.


My big honky sled is MDF base with T-track to accept hold-downs. Used epoxy to secure them. Working fine over 12 years now....

490773

[Jason Evans]

If the edges aren't sealed - otherwise it's very stable and doesn't seasonally expand and contract like say..........hardwood.

The edges on the bed of my cnc router are sealed. I still have to surface it flat every so often because of expansion in different areas making it not flat. this wouldn’t work well for a sled fence imo.

[Justin Rapp]

My big honky sled is MDF base with T-track to accept hold-downs. Used epoxy to secure them. Working fine over 12 years now....

490773

Mreza Thanks good to know for my next sled. I have a small parts MDF sled that I build and my clamp screws pulled right out (as I was kind of expecting them to). Epoxy sounds like a great idea.

[Justin Rapp]

Now i have a dead flat (hope it stays that way) poplar fence. I took two flat poplar boards and face glue them. Once dried I re-milled it on the jointer and planner to make sure it was once again flat, and to the thickness I wanted. Well see if it stays.

[Paul F Franklin]

When I made the fence for my sled, I first milled a piece of 12/4 red oak longer than the fence, as flat as I could get it. Then I glued up the two 3/4 plywood fence pieces and clamped them to the piece of oak. The two plywood pieces had some bow, and I arranged them so they both bowed out in the middle, in opposite directions, so there was a fair gap between them until it was all clamped. I left it clamped for 2 days. It came out flat and has stayed flat. The advantage of using the piece of oak is that you can put many clamps all around the fence pieces. It's harder to clamp something like that as well to a bench top or table saw top.

[John TenEyck]

I used a solid piece of 6/4 poplar when I made mine about 30 years. I never expected it would stay perfectly flat and straight, but it has. That said, 3 layers of 3/4" plywood is another option. I used that approach for a fence on my original router table. And one featuring just such a fence is in the latest version of FWW for anyone who cares to take a look.

John

[Frank Pratt]

I built my sled fence from 2 layers of 18mm Baltic birch and clamped it to my bench to ensure is stayed flat until the glue cured. It came out dead flat and has stayed that way.

[Warren Lake]

laminations are always odd numbers. my sled was one layer 1/2 baltic birch and could cross cut a 4 x 8. It fine for many years.

[Myk Rian]

Panels will have a bow to them. Inspect each panel and glue the convex sides together. Like this ) (.
Clamp overnight and done.

[Justin Rapp]

Folks,

I do appreciate all the ideas and comments. Glue up of 3 layers of 1/2 inch might have been better than two 3/4 layers to get it to stay flat.

In any event I have a dead flat poplar fence, at least to the milled surface of my sawstop and 2nd check against a a strait edge rule. I used the the 5 cut method and the fence was 0.029 inches off from end to end. After resetting the fence with a 0.029 feeler gauge, I did another 5 cut test and my cut-off exactly the same on both ends at 0.7370 of an inch, and the remaining piece was square on all four corners to a woodpecker square. That felt good. Ask me again in a year if it's still square :)

For all those that keep saying they used baltic birch, it is pretty much a dried up resource right now. The product was from Russia and there is no more coming in. And honestly, even if it was, I wouldn't buy it now.

Hopefully Finland starts producing enough to make it down to those of us who don't buy a container of it for their furniture business. We'll see where the plywood market goes in the next year.

Justin

[Bruce Page]

I built my sled using 3/4” particle board faced with melamine on both sides. Other than being too darn heavy, it has remained stable & accurate for 20+ years.

[Justin Rapp]

I built my sled using 3/4” particle board faced with melamine on both sides. Other than being too darn heavy, it has remained stable & accurate for 20+ years.

My previous sled was Melamine and it really was a heavy beast but stable for about 15 years.

[Jared Sankovich]

You can just use some dry construction lumber. Careful looking will get cvg fir. 490871

[Maurice Mcmurry]

My MDF jigs, fixtures, and sleds that need to stay spot on have been finished with several coats of Watco Danish oil. The edges will soak Watco up like crazy. It stabilizes and hardens MDF in a very beneficial way. I am also careful about how I store them.

[Prashun Patel]

Plywood isn't always perfect, but I think we overstate the frequency of warping. I still use plenty of BORG plywood, and for the most part can be relied on to be flat and straight. I think to make a blanket statements about qshw or mdf being superior all the time unfairly overstates it.

[Wes Grass]

I've glued a number of pieces of plywood together,, baltic birch included, 'back to back', and had *NONE* of them come out flat. Even when clamped to a granite surface plate while the glue dried.

Next time will involve epoxy and carbon fiber cloth between the layers. And I'm not particularly optimistic.

[Maurice Mcmurry]

Creating balanced plywood and stiffening with formica has served me well. Very flat, very stable, very accurate.

491102

[Mel Fulks]

I get around that by using a solvent based adhesive - such as the Original Contact Cement - or shellac.
3# cut orange shellac (now called Amber) makes a wonderful fast dry adhesive.

Yes, and Orange Shellac flakes have some WAX in them , unless it’s marked “dewaxed”.

[Charlie Jones]

I am building a new sled for my sawstop and I built a pretty cool looking fence which is two 9 ply 3/4 maple ply laminated together and bordered with some poplar for a clean look. Well today is is slightly bowed, and even if I force it flat, there is no way in hell I am getting it square to the blade. I got it close, about 89.5 but that isn't cutting it. Oh well. I'll build a new fence out of hardwood. I have poplar and hickory sitting around that is spare or I dig into the nicer stuff. Hickory will just make the sled 10 tons.

Flat plywood is a thing of the past!!!

Just run the hardwood face through your jointer. Check it again after a couple of days.

[Justin Rapp]

Just run the hardwood face through your jointer. Check it again after a couple of days.

yup - my hardwood (well, poplar - using it up from another project) is still flat after it was face jointed and my sled was used a ton today so it's all good :)

[glenn bradley]

Now i have a dead flat (hope it stays that way) poplar fence. I took two flat poplar boards and face glue them. Once dried I re-milled it on the jointer and planner to make sure it was once again flat, and to the thickness I wanted. Well see if it stays.

I imagine you'll be OK. I have a couple of sleds with vertical grained fir fences that have been stable for many years. I have also used laminated 3/4" BB ply on a couple but I drum sand (read mill) the blanks after laminating and before cutting to final dimension. these have remained stable for years as well.