Why are my miter open with my Kapex?

[Toller]

I have had a Kapex for about a year now and have been happy with it.
Last week I made a mitered picture frame.  None of the corners were closed at the outside; which I presume meant they were slightly less than 45 degrees.  I mixed up some filler and the gaps disappeared so all is well, but it is annoying to screw up with a $1,300 saw.

Today I did the 4 cut test 3 times and got -.04*, .01* and -.02*.  According to Rick's guide the target is .16*; so I presume my saw is essentially perfect, the variations are a bit of human error.

I cut some more miters and they they don't close either.

Could the saw be perfect at 90* but off at 45*?
What else could I be doing wrong?

 

[bobbobbob]

Did your stock have parallel edges?  Was the same reference face used when cutting mitres?

 

[Rick Christopherson]

Yes, the saw could be perfect at 90 but off at 45. I did not document how to calibrate the saw at 45 because it is much more complicated.

Because your miters are open at the tips, it means your cuts are less than 45 degrees and the miter gauge plate needs to be moved slightly toward the rear of the saw. Important: Remember that the error you are seeing is being compounded eight times, so what looks like a huge error in the finished cut is actually very, very tiny at the blade.

Before you even attempt to calibrate the saw, make sure you eliminate all possible causes for operator error. I don't mean that as an insult, but with an 8x-compounded error, it would take very little from the operator to induce the error. Make sure the workpieces are firmly clamped down and not held by hand. Make smooth, steady cuts, paying special attention to any possible side-to-side bias you might introduce to the saw head.

Before making any adjustment, it is important to know whether the same error is present for both right-hand and left-hand miter angles. If the same error exists for both sides, then slide the miter gauge straight back. If the error exists on only one side, then you will need to slide only that side back.

Because your saw is accurate at 90 degrees, you need to make sure the middle of the gauge stays the same (but can slide in and out without changing the angle). To do this, place the saw at 90 degrees before loosening the screws on the gauge. The miter detent must be engaged at 90, but you can't set the miter lock, as this locks down to the miter gauge that you need to reposition. The detent should help keep the center of the gauge at its original 90 degrees.

If you need to slide the gauge straight back (both right and left errors are equal) then you need to loosen all three screws. If you need to move only one side, then leave the other side tight, but loosen the other two screws.

 

[Toller]

First, let me tell you where I stand.  After fixing the bevel adjustment I cut some more miters.  They are open enough to force a piece of paper in at the very end.  I then cut a few with the saw set at -45*.  They were perfect.  So I guess I leave that side screwed tight, but push the other side in, right?  How much are we talking about 0.001"?  0.01?"  0.1"?

OTOH, I figure that .003" (the thickness of a sheet of paper) is only 0.1* over 1.5" (the width of my miter.  That means the saw is only off 0.05*, which seems pretty good.

Am I expecting too much out of the saw?  Am I likely to make it worse if I try to fix it?

The big question...  how tight a miter joint is "good"?

(and do I just cut my miters at -45* now, however awkward that is, because it is exactly on?)

 

[Rick Christopherson]

After fixing the bevel adjustment I cut some more miters.  They are open enough to force a piece of paper in at the very end. 
...........
OTOH, I figure that .003" (the thickness of a sheet of paper) is only 0.1* over 1.5" (the width of my miter.  That means the saw is only off 0.05*, which seems pretty good.

Yes, your miters are off by less than 0.05 degrees. If your miters are off by only 0.003" over 1.5", which is 2x the error for a single joint, and 8x the error for a full 360 degree assembly, your saw is performing so close to perfect that you would be foolish to even attempt to make it better.

If you really, really wanted to push the envelope, make sure that BOTH of the other screws are very tight, and loosen only the one screw near the incorrect miter side, and force the miter gauge to deform to reach the desired angle. The change is so trivial that you could accomplish the desired angle just by this imperceptible deformation of the aluminum plate.

Otherwise, I would not even consider adjusting this saw.

 

[Holzhacker]

Getting the chop saw just right takes effort. Even when it is just rights sometimes the cut may be slightly off for various reasons. I keep a rasp and file nearby. For the variance you are talking about, a couple of swipes along the backside of the material is usually enough to get the joint to close up.

 

[Toller]

Yes, your miters are off by less than 0.05 degrees. If your miters are off by only 0.003" over 1.5", which is 2x the error for a single joint, and 8x the error for a full 360 degree assembly, your saw is performing so close to perfect that you would be foolish to even attempt to make it better.

No, that was 0.003 per corner.  I made a full frame and the "bad" corner was off by about 0.015".

I loosened the one bolt and pushed in while tightening it.  No change.  I tried again, tapping it with a hammer.  Again no change.  I am reluctant to do more than tap with a hammer.  Any suggestions?

BUT...  I put two thicknesses of masking tape on the fence to change the angle a hair.  The resultant cuts were good.
I took the tape off and tried on the other side.  They were still good.
So, I seem to have a work around; but a $1,300 saw ought to not need masking tape shims.