Table Saw Cutting Out of Square when Set on the Bevel

A little help with the problem of a table saw that cuts out of square, but only when the blade is tilted over to 45 degrees. November 16, 2010

I recently made a crosscut sled for my table saw, which worked great when the blade is set at 90 degrees. When I tilted the arbor to 45 degrees, the saw would no longer cut the panel square. It was off by about 1/8" in 20". The saw is an older model Delta Unisaw. I adjusted the table to the blade as the owner’s manual suggested, but it still won't cut square at 45 degrees. Can anyone tell me why the saw will cut square when the arbor is set at 90 degrees, but won't cut square when the arbor is set at 45 degrees? Any help is appreciated.

Forum Responses
(Furniture Making Forum)
From contributor L:
It sounds like the arbor is twisting. Back off the 45 degree stop. See if that helps. If I miter panels like that, I use the rip fence. But your saw might be a right-tilt. If so, using the fence doesn't work so well.

From contributor J:
Check the condition of your blade arbor, the arbor gear and or the arbor worm gear. It's possible that one of the castings is incorrect or worn causing the blade to track differently as you move the arbor.

From contributor O:
Check that the bottom of the sled is dead flat, and that it sits tightly against the table across the full depth of the sled. If it's cupped even a little bit, then pressing down on the near edge (where you push from) will lift the far edge. On a 45 degree tilt, if the far side of the sled is 1/8" off the table then that end of the cut will move over 1/8".

From contributor L:
Also make sure your blade is sharp and cuts freely. At 45°, the cutting action pulls the stock sideways into the blade.

From contributor F:
If the issue is not related to the piece rising as others have already pointed out, you might look at the trunnion and its slides, maybe something loose or misaligned there. Set the blade at ninety, mark a tooth and measure from the miter slot to the tooth rotated to the front and then rear, flush with the table top, then set the blade at 45 and repeat to see if they agree.

Assuming the saw is a right tilt, using the fence instead of a sled is an excellent way to rip miters. Simply cut your parts square edge to net size. Attach a sacrificial fence to your saw fence, hold one of your parts or a scrap piece of the same material flat against the table with its edge against the fence and scribe a line on the fence using the top of the piece as a guide, with the blade set at 45 degrees and running, manipulate the blade height and fence until the outside edge of the cutting circle hits the scribed line, the top of the kerf will be entering the sacrificial fence right at the top of the panel. Run the blade using the height adj. into the fence about the length of the tip. Using your setup piece again clamp a featherboard to the fence to hold the panel flat against the top of the saw. At this point run the edges you want to miter against the fence for a perfect cut, the saw will cut cleaner and with no burning as the fragile long point is not trapped between the blade and table. A word of caution, you must either have a helper on the outfeed side hold the falloff to the panel so it exits the blade with the panel, or if the pieces are too small or if you work alone you must use a push stick at the end of the cut to push the falloff clear as it exits, otherwise a nasty kickback can occur. As with any other operation stay out of the line of fire as well.

From the original questioner:
Thanks for all of the responses. The sled base is made of 3/4" MDF, and is flat, as well as the panels, I'm sure they're not lifting. Also, the blades are sharp (one fairly new and one re-sharpened). The saw is a right tilt model, and I probably would have used the rip fence, however, the panels are 50" long, and my fence is only 48" long. I suspect the issue is with the trunnion twisting, which may come from too much pressure on the stop, or worn bushings. I didn't know how common worn bushings where on Unisaws. I appreciate all of the insight and tips.

From contributor E:
It sounds like your table is not squared to the arbor. Shimming either that back or the front of the table, (depending on the cut), will allow you to set the table square to the arbor. If the cut is narrow at the beginning and wider at the end of the cut, shim the front table bolt mounts, and if the cut is wider at front and narrower at end of cut, shim the back bolt mounts. A lot of trial and error in checking square at 90 and 45 deg is required. It'll test your patience for sure.

From contributor L:
All of the above are likely causes of your problem and good solutions. It's awfully difficult to check that the blade is running parallel to the miter slots when angled at 45 degrees. To comment on Rob's points, it's just as important and just as difficult to check that the blade is running parallel to the cut with a portable saw as it is with a stationary one (see below). What I do is miter a piece of MDF on the saw, clamped in place on the sled, then check the blade front and back as he suggests using a feeler gauge.

Two alternatives to consider:

First, perhaps this is the excuse you needed for a new table saw. I've pounded my pulpit for years about the advantages of left-tilting table saws. I cut miters like those you're working with on a regular basis using just the rip fence. In that regard, I'll second the importance of keeping the piece flat on the table. I usually also set the angle just past 45 so that the outside of the miter joint touches before the inside; that is if only the outside shows.

Secondly, I use my Festool circular saw sometimes. Today I have some panels to miter that are about 12 inches by about 45 inches with the miters on the short dimension. I'll be setting up the Festool at a 45 (more likely about 46 degrees), then using the straight edge guide to cut the miters. I could use a sled on the table saw, of course, but sometimes it's easier to move the saw than to move the piece.

From contributor K:
When the front to back axis of the tilt is not parallel to the table, you will get this. You didn't mention which way the blade tilts, and which way it runs out, which makes it hard to tell you whether to raise the front of the table or the back. If you examine the tooth marks made by the back of the blade on the parts after sawing, you should get a pretty good idea. However a blade which is dull on one side, or not properly sharpened will give the same results.