Far From Square Miter Cuts

  • Advertise with us

« back to Jigs & Fixtures forum

Forum topic by squarehippo posted 06-12-2013 03:54 AM 980 views 0 times favorited 6 replies Add to Favorites Watch
View squarehippo's profile


16 posts in 2031 days

06-12-2013 03:54 AM

Topic tags/keywords: square miter cuts miter sled question table saw

I made a few cuts with simple miter sled and got some curious results. Here is the sled:

And here is the problem in pictures:

As you can see, I am not getting square cuts. But even worse, I’m not getting consistently crooked cuts either. A consistent problem I could fix, probably with a simple fence adjustment.
Here’s what I know:

1. The blade is square to the miter slot.
2. The blade is cheap, but it’s flat and there is no visible wobble as it winds down.
3. The fence on the sled is square to the blade.
4. The sled does not wobble.
5. The board is 5” long and the width is 2.42” on one end and 2.49” on the other. Far from perfect, but not nearly enough to cause so much of a problem…is it?

I’m pretty new to all of this…surely I’m missing something basic.

6 replies so far

View patron's profile


13606 posts in 3364 days

#1 posted 06-12-2013 03:58 AM

maybe the board is creeping slightly
as it goes thru the cut
or is lifting slightly
from the blade

a hold down clamp
or some sandpaper glued to the fence face
might help with that

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View Loren's profile


10476 posts in 3671 days

#2 posted 06-12-2013 04:00 AM

Are you clamping the work?

Using a stop block?

View squarehippo's profile


16 posts in 2031 days

#3 posted 06-12-2013 04:52 AM

I just tried adding a hold down clamp to the sled. It does make cutting the increasingly smaller pieces much safer, however, the cuts are still just as crooked. I should mention that even though the cuts are crooked in different directions, they are consistently crooked. That is, the left side of the board always slopes to the left, and the right side always slopes to the right. (Just to prove to myself that I wasn’t crazy, I pivoted the fence on the sled about ten degrees and, as I expected, both sides of the board sloped to the right. Different amounts naturally, but at least they were crooked in the same direction!)

View Loren's profile


10476 posts in 3671 days

#4 posted 06-12-2013 05:03 AM

Assuming the blade isn’t healing, the sled
surface may not be riding at consistent depth
in relation to the table.

In a 90 degree cut, such variations are irrelevant –
but with each degree the compound error
becomes more pronounced and the thin
edge of the miter reveals it.

Contractor saws typically heal when tilted
due to the pull of the motor’s weight. This
is a real problem. If you are using a contractor
saw I suspect your blade is healing when
tilted. This will not show up if you
measure blade/miter slot parallelism at
90 degrees.

The solution is to not tilt the blade at all, but
make a jig to hold the work at the desired

View squarehippo's profile


16 posts in 2031 days

#5 posted 06-12-2013 06:13 AM

I checked the blade at 45 and you are right, it is out of alignment! Go figure. (Not that it matters, but it’s an R4512.) I read an article that explains how to shim the trunnion mounts to fix the problem. The procedure for figuring out how much of which one to shim is going to be interesting since I don’t have precise measuring tools. But at least there’s hope!

Anyway, thank you very much! I’ll post again when the problem is fixed.

View squarehippo's profile


16 posts in 2031 days

#6 posted 06-12-2013 07:34 PM

Success!! Using calipers I was able to figure out the shim amount and a few minutes later the blade was square at forty-five degrees! (A few minutes plus an hour or two to figure out the math.) I re-squared the fence, made my cuts and…no improvement whatsoever. #!$???

And then, in an unusual moment of clarity, I checked the bottom of the miter cut. It was perfectly square. Only the top edge of the board was crooked. You might have noticed that I’ve been working with maple and walnut glued together. What you didn’t know is that I don’t have a planer yet and that I sanded these “flat” with a belt sander. I use quotation marks because they were far, far, far from being flat…which…naturally, resulted in crooked top edges.

So, I learned the importance of flat and I now have saw that cuts square at forty-five degrees. But even so…Jiminy Cricket!

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics