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Squaring Crosscut Sled & Making Hold Downs?

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12K views 16 replies 13 participants last post by  Marty5965  
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#1 · (Edited by Moderator)
Anyone have tips on either?

I just finished a crosscut sled for my Bosch 4100. I cant tell if its perfectly square thought. I've tried the 5 cut method BUT I don't have any pieces of wood that are square to start out with. I used a square and it seems good but still cant tell for sure.

Also, any idea on making hold down clamps for the t slots? Dont want to by yet. I was thinking just to make a block with a 1/4" bolt and handle to keep the work piece against the fence.

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#2 ·
Take a piece of plywood that has two parallel edges put one of the parallel edges against the fence of the cross cut sled trim one end now flip the piece over keeping the same parallel edge against the fence now make a cross cut on the opposite end measure from corner to corner both directions on this piece if both edges ar equal the fence is square.
 
#3 ·
Or you can use the 3-4-5 method if you have a triangle that is 3x whatever number you choose on one edge, 4x the same number on the other edge, if the number from 3x to the 4x points and that number is 5x the same number you have square 90% corner. So say you measure up the kerf of your sled 12" from the fence on one edge of the kerf, now measure over 16" from the point of the kerf, and the fence, now the distance between theese two points should be 20" if the fence is square your multiplier would be 4".
 
#4 ·
I like using these hold downs from Peachtree on my sleds. You want the small ones for most T tracks; the large are sized for Peachtree's heavy duty T track.

My favorite method of squaring a sled is to clamp a precision square against the fence and clamp a dial indicator to the table saw so that it contacts the blade of the square. If your fence is perfect the dial indicator should not deflect in either direction as you move the sled as if making the cut. I use one of these . You can also use a good quality plastic drafting square so long as you clamp it with a block underneath to raise it up. Because these are so thin it takes some care to keep the dial indicator touching the square edge. Since your sled spans both sides of the blade you would probably want to mount the dial indicator on the splitter.
 
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#5 ·
Patrick:
A simple way to test for squareness is to cut a piece of 1×4. Flip one side of the cutoff over and butt it up against the other piece that was just cut off. If there is no gap, your cut is square. If there is a gap at the saw cut, you need to make an adjustment.

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#6 ·
The 5 cut method doesn't depend on starting with a square. It only depends on starting with a reasonably straight edge.

The sled cuts with the fence 90 degrees to the blade, and you are trying to determine if it's exactly 90. You start by cutting with the straight edge against the fence. This gets you another straight edge 90 degrees (we hope) from the first edge. It doesn't matter if the original board had a 90 degree angle, we cut a new one. You rotate so the new cut edge against the fence, and do it again. And again it doesn't matter what the original angle is. You do that 4 times. In theory, you now have a board that has four 90 degree angles.

Then you cut a strip off that board. In theory, it's rectangular, because in theory it too has four ninety degree angles.

If it doesn't, then what happens is that one edge is a different width than the other. If they were exactly four 90s, then it would always be the same width top and bottom.

The thing is that the angle of the fence doesn't change on each cut. So, if it was originally, say 91 degrees, you would have four 91 degree corners, and, of course, that means the top and bottom wouldn't be the same width.

That 5th cut isn't really necessary, but it lets you have a board bigger than your measuring tool, which is good. You cut off a strip narrow enough to measure with a caliper or micrometer. And, of course the error is 5X the actual error, because you compound the error 5x.
 
#7 · (Edited by Moderator)
I just built the Super Sled, acquiring the plan from Eagle Lake Woodworking. I did everything the way they did it and it turned out great. The only real changes I made were to inset t-track in the sled for holddowns and I also inset a 2"-wide, 1/4" -deep dado to hold a sacrificial ply throat plate.

Watch the videos and see how he does the squaring up. Nifty.

Super Sled instructions and videos
 
#9 ·
I think the others above have answered your question. I just want to add that you have made one sweet looking sled. Love all the features you built in. Did you use a metal t-track on your fence? Or did you just route it out? Just curious since I plan on doing this on my next sled.
 
#13 ·
Lots of great advice here. Sounds like you could use an engineers square, or at the very least, a decent combination square. These things are a must have tools to get anything done with precision, including tool and cut setups. I also recently picked up a digital angle gauge thingy that I use on my table saw and mitre saw blades for dead accurate mitres. There's a Wixey brand that gets recommended a lot but I picked up an iGauge at Rockler on sale and it works just fine and uses regular batteries instead of watch batteries.
 
#15 · (Edited by Moderator)
"Wow, I guess I'm old-school. I just use a framing square and hold it up to the light."
Now I agee with pintodeluxe if you have a framing square that you trust, or what ever square or device everyone should know that nothing is perfect it just what tolerances is good enough .01" / .001" / .001", or is everyone trying to get to the nearest molecule. It seems to me you get the squareness of your fence as close to square as you possibly can useing what you have without breaking the bank if you have a $20 square that is close enough to your particular tolerances cut a piece of wood and check that sucker with your $20/$500 square, and call it a day.
 
#16 · (Edited by Moderator)
Matt, sorry for the delay in responding to your request. I had to deal with the flu for a few days.

Below is a photo of my sled. You can see the replaceable throat plate there. It's held in place by a couple of screws and can slip in/out through a slot in the back fence. Right now, that little piece is made from scrap 1/4" ply. Depending on how it does, I may ultimately replace it with something else-maybe plastic. But, right now I have only cut a thin kerf slot in the table and it's no big deal. As soon as I (unfortunately) widen that slot with my dado set, that sacrificial plate will really come in handy when using my regular blades.

A couple more photos can be seen here.

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#17 ·
The error on the sled is calculated by the difference in width of the fifth cut times the length of the cut piece. Then you need to calculate the length of the front fence to determine the amount you need to swing your fence to true it up. Google 5 cuts to the perfect sled to see a great video.
 
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