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Before I start I would like to offer the obvious solution is to use some sort of sled, like a crosscut, that would give the perpendicular fence that would allow the cut. The problem with that is I was making my first sled so I was was stuck staring at my table saw trying to think of a solution.

Since it was my first sled I was allowing for some irregularity since the saw is not the best to begin with. I had this odd contraption using clamps and a long level that I knew was straight. I figure there has to be a better way (for when I make a better one).

Assuming I am working on a sheet (sheeted goods but not a full 4x8) or something where a mitre saw would not help what can I do with my table saw to have two side meet at a right angle? I can make 2 opposite sides parallel but I don't know how to get my 90 degrees.

Or perhaps this was not meant to be done with the table saw?

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    Are you looking for ways to produce 90-degree cuts in general on the table saw, or are you specifically looking for how to break down full-size sheet goods on a table saw? – rob Aug 31 '15 at 3:25
  • Can you elaborate on your problem? Are you specifically asking about squaring the edges on sheet goods? – Daniel B. Aug 31 '15 at 4:30
  • Before I propose an answer can I assume your table saw has a track of some kind in the bed? – Graphus supports Monica Aug 31 '15 at 6:19
  • Why do you need to cut a 90 degree angle for a sled? What part is it for? – Pubby Aug 31 '15 at 10:07
  • I am cutting smaller sections of plywood mostly. @rob Not full sheets. I pick up left overs from people in town and make them into other things like bat boxes. Most recent on was approximately 1x8 – Matt Aug 31 '15 at 11:29
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As you mentioned in your question, using a crosscut sled is an easy and reliable method of making perfect 90 degree cuts on a table saw.

If you don't have a sled but your blade is properly aligned parallel to the miter slots, you can use a miter gauge. Most saws include a miter gauge, although some are better than others at locking in their settings without wobbling during a cut.

It's common practice to screw a longer wooden fence onto a miter gauge using the slots on either side of the miter gauge's face, as shown below. Some commercial miter gauges include aluminum fences that serve the same purpose--namely, providing better support for your workpiece close to the blade.

miter gauge with fence

(Source)

Since it was my first sled I was allowing for some irregularity

Your sled itself doesn't need to be any particular shape, and the base doesn't even need to be square with the rails. It only needs to have a back fence which is adjusted perpendicular to the blade (in the case of a crosscut sled) or whatever angle you need (in the case of a miter sled).

Assuming I am working on a sheet or something where a mitre saw would not help...

Usually the factory-cut edges are straight and square, so you can put one factory-cut edge up against your table saw's fence, make the cut, then rotate the workpiece so the adjacent factory-cut edge is against the fence.

That said, the table saw is not my first choice for breaking down full-size (8'x4') sheet goods. Usually I'd rather lay the sheet down on a piece of foam on the ground and use a circular saw with a zero-clearance straightedge guide (or a track saw) to cut the sheet down to rough dimensions, then trim to final dimensions on the table saw if necessary. You can also use a parallel edge guide like the Kreg Rip-Cut along with your circular saw, using factory edge as your reference surface rather than using a straightedge or track saw that runs slightly longer than the length of your workpiece.

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    Usually the factory-cut edges are straight and square - straight, yes, square, no. Test with the 3-4-5 rule and be surprised, even for high quality Baltic birch plywood. – Eli Iser Aug 31 '15 at 6:16
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Since you have tracks available I would suggest making a crosscutting sled, probably the most basic of table saw jigs/appliances. Large piece of plywood or MDF for the base, scrap of plywood or suitable plastic for the runner (or buy commercial track material), a few additional scraps of ply for the fences and that's all the material you need. The width of material you can saw is only limited by the front-to-back measurement of the sled so size it as generously as your tablesaw's bed will allow.

Although it would be nice if the whole thing ends up entirely square, you actually don't have to be particularly careful about many aspects of the construction. The runner doesn't need to be square to the leading or trailing edges of the ply base, the two main 'fences' (braces more accurately) fore and aft don't need to be perfectly parallel, even the ply base itself doesn't have to be square. The reason being that none of these parts or edges are used as references in the finished appliance.

The one and only thing that needs to be attached accurately is the fence the workpieces will ride against, this must be square to the saw kerf created when you first run the sled through the saw.

Crosscut sled

Here's the construction sequence:

  • Nail or screw your runner to your plywood base, approximately square or dead-on square doesn't matter.
  • Flip it over and attach your front and rear braces, again approximately square is good enough. Glue these on, so that you don't have to worry about the placement of nails or screws in relation to the saw kerf. See note 1.
  • After the glue has hardened fit the runner into its slot and run the sled through the table saw with the blade raised. See note 2.
  • Now is the one and only time you need to be accurate — the actual reference fence is now attached, making sure it is perfectly square to the sawn kerf. Use a large square you know to be true, or rely on the 3-4-5 rule to ensure it is at a perfect 90.
  • Run once more through the saw and your sled is ready to use.

Note 1: braces need to be high enough that they exceed the maximum thickness of material you expect to cut; if you do a cut with the blade raised higher than this you'll saw the sled into two pieces!

Note 2: the saw should be fitted with the same blade you expect to use the sled with.

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    I've been using a miter gauge when I really ought to be using a crosscut sled for some time ... I think it's probably time I finally got around to making one. – Daniel B. Sep 1 '15 at 3:07
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This YouTube video depicts an extremely clever method for setting a right angle when making a cross-cut sled. It is a so-called five-cut method that depends on precision thickness readings and feeler gauges plus a little arithmetic. It does not rely upon the use of an existing right angle square or triangle.

The video shows the entire process for making a "perfect sled" from making and sizing the miter slot runners to making and attaching blade guards

I was totally enthralled by the video and watched for the full thirty-seven minutes without realizing the passage of time. (Probably a slow day.)

Since the OP asked for how to make a right angle, I'll attempt to describe the method:

original drawings and explanation

enter image description here

The measurement process shown below is different from the method shown in the video. Instead of using a micrometer and feeler gauges, you need no more than a ruler or a tape measure.

enter image description here

The video suggests that to get a more accurate right angle, you can repeat the process, however if the your original placement of the fence is within about 2 degrees of exact (you can eyeball it to that accuracy) you will gain no appreciable increase of precision by doing so.

  • Origami techniques applied to woodworking; interesting. I don't have time to work thru the geometry, but it's at least plausible. I need a proper sled; may have to try this. (I hope whoever invented it has already submitted it to the various woodworking magazine tip contests and gotten a suitable prize for it.) – keshlam Jan 26 '16 at 1:28

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