Difficulty Squaring DeWalt DHS790 Double Bevel Sliding Compound Miter Saw - Router Forums
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post #1 of 29 (permalink) Old 01-30-2020, 01:34 AM Thread Starter
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Default Difficulty Squaring DeWalt DHS790 Double Bevel Sliding Compound Miter Saw

I mentioned in my thread about the fort ladder that I'd discovered my miter saw was not cutting square. I had some time today to try to square it up and ran into a can of worms. I am having trouble comprehending what is going on and I think I'll have difficulty explaining it, but I need to try.

The saw is cutting square front to back (miter direction?). It is in the vertical (bevel) direction that the difficulty is occurring. When I first got the saw 18 mos. ago, I checked to see if it (the blade) was square vertically, according to the manual's directions, using a square on the table looking for light cracks up & down the vertical leg, which was up against the blade. It was already square as I do not recall having to do anything to it. That squaring procedure is part of this mystery, more on that as I go.

Today, I checked it with the square, but also used one of my angle cubes (another recent thread here). It indicated the blade was not square to a readout of the cube to 0.00º, even though the square seemed to show it was. But, test cuts showed that the cuts being made on a 2x6 were NOT square - vertically. So, I figured out what the procedure is for squaring the saw and dove in to it. Setting the angle cube to 0.00º resulted in the cuts being further out of square than before. Huh?

Through quite a lot of test cuts and adjustments, I determined that - when I get the cuts to turn out square vertically, the blade is actually angled off of square by about 1º. In examining the saw more closely, it is quite evident that the blade, is angled, but seems to be coming down vertically. That is, the blade is not square to the table, but the vertical travel of the whole moving assembly is coming down squarely. A confirmatory bit of info is that the black writing on a yellow background on one side of the saw, all that is smeared, as though it is rubbing against the fixed wood section of the 2x6. Further, black writing (but no yellow background on the other side of the blade is not smeared at all.

This is where I'm having difficulty understanding what is going on. I don't understand how the blade can be canted at an angle and coming down vertically and the saw cuts are coming out square. And there is no sign of the blade rubbing on the fresh cut ends. I'm baffled and it is too late tonight for me to think about it any more tonight. I plan on calling DeWalt support tomorrow. If anyone has any thoughts on what this could be, I'm eager to hear them.

Rick

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post #2 of 29 (permalink) Old 01-30-2020, 02:10 AM
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conquer one thing at a time..

put away the cube... it maybe telling you your blade is bent/warped or what not...
mechanically square the blade to the table...
check it in the up position, halfway and all the way down...
run a test cut...
check the end of the cut for squareness to the face of the 2x...
fiddle w/ it till it's perfect..
can't get it???
change the blade...
start all over...
how we doing so far???
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post #3 of 29 (permalink) Old 01-30-2020, 07:31 AM
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Yeah, with everything mechanically being square it could be the blade - you got another one you can mount and remeasure with? Always wondered if we could run into a bent blade at some point. Now I’ve got to recheck mine...hope you get it resolved. This sort of thing can keep you up at night!

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post #4 of 29 (permalink) Old 01-30-2020, 07:52 AM
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Likely what you have is the blade arbor is not exactly parallel to the table. Probably due to the motor mounting to its housing.

Can you confirm that the arm travels perpendicular to the table at 90deg...? Check that as Stick described...

If the arm travels perpendicular and the saw blade is not then the arbor is not parallel. This will bring the blade down at an angle which would leave one side of the blade label clean and the other side worn.

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post #5 of 29 (permalink) Old 01-30-2020, 08:10 AM
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Hope not to muddy the waters but do yourself a favor and test that cube on the table saw. I've seen where sitting flat on the table saw and the blade square it reads fine but raise the blade, set an angle and then check, say 45 degrees. Start by setting the cube against the blade and flat on the table. Make sure it's zeroed out. Raise the blade and set it for say 45 degrees. Remove the cube and then try putting it back on. Any rotation will change the reading, at least that's my finding.

If I'm setting the table saw to any angle I always zero it that way and check with a good known square. Once set at 0 I don't touch the cube till I'm done. Setting the cube this way even if the miter saw is at a slight angle will register as 0 degrees and then the blade should also be at 90 if the blade is square to the table which you can check by a known good square. As for a bent blade I know how to check on a table saw but with now miter channel on the miter saw I'm not really sure. I usually rough size my lumber on the miter saw and make final cuts on the table saw.
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post #6 of 29 (permalink) Old 01-30-2020, 09:27 AM
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I agree with what Stick said about putting the cube away for now. This job is not what it was designed to do. This tool is the one designed for that job: https://www.leevalley.com/en-us/shop...ineers-squares

Nick may have the problem right. One way to check is to put the square up against the end of the arbor and raise and lower and see if the gap between the square and arbor stays the same. Then check for squareness of the blade to the table. If the arbor is moving vertically but the blade isn't vertical then you have the problem he described and you need to return the saw to DeWalt.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #7 of 29 (permalink) Old 01-30-2020, 10:59 AM
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Quote:
Originally Posted by Cherryville Chuck View Post
I agree with what Stick said about putting the cube away for now. This job is not what it was designed to do. This tool is the one designed for that job: https://www.leevalley.com/en-us/shop...ineers-squares

Nick may have the problem right. One way to check is to put the square up against the end of the arbor and raise and lower and see if the gap between the square and arbor stays the same. Then check for squareness of the blade to the table. If the arbor is moving vertically but the blade isn't vertical then you have the problem he described and you need to return the saw to DeWalt.
Yes...but the arbor may still travel exactly perpendicular but it may still not be parallel to the table...that the blade is cutting on one side would almost say the motor is not mounted square. I'm thinking also it's a return to Dewalt...unless the motor mount screws are loose and just need tightening...
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post #8 of 29 (permalink) Old 01-30-2020, 11:09 AM
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reset/change the stop to rotate the CL axis of the arbor/motor..

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #9 of 29 (permalink) Old 01-30-2020, 12:19 PM
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The arbor not being parallel is worth checking, however, I had a 12 inch deWalt and it was impossible to set perfectly because the blade delected during the cut. I sold it and went back to a 10 inch compound miter saw (Bosch), and started using only full kerf blades. After very careful vertical setup, it cut perfectly and the angles (90 and 45) were perfect.

I find it hard to judge accuracy using an engineers square. I just can't see that well, so I rely on the Wixey and comparing edges of cuts. Mitered cuts for picture frames require perfect cuts, even slight blade deflections ruin the cut. For perfect miters, I rely on a Lyon style sliding guillotine for the final cut.

In short, I suspect the blade isn't flat, or deflecting as it cuts, particularly if it is thin kerf. No arguments with the information from others' posts.

The more I do, the less I accomplish.
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post #10 of 29 (permalink) Old 01-30-2020, 06:38 PM Thread Starter
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Thanks for the feedback. I think I have figured it out. I did put aside the angle cube, at least for this.

I went to my precision "physical" measuring instruments. I first took the blade off the saw and mounted it on my Monarch 10EE metal lathe with the unpainted back side facing outward and made some measurements of runout, both radially and laterally.

TIR around the circumference was about 0.008", measured by setting up a test dial indicator (TDI) against the side of the blade near the outside diameter and rotating the blade 360º.


To measure extent the to which the blade was "flat", I ran the TDI inward from the OD to as close as I could get to the center.



The TDI barely moved and ended up the same as at the OD, so 0.000", so it is flat, more so than I expected. I'm glad, as I don't have another blade to install and do not want to shell out the dough for another.

I think someone said to determine whether the arbor was parallel to the bed, or something like that. I could not figure out how to do that, as the arbor is only about 1/2-5/8" long. Moving on, I measured the vertical travel deviation of the arbor, from its top to bottom positions, in the same manner as a cut would be made. I made these measurements by clamping a large square to the bed/fence and measuring the gap between the arbor and square at the top and bottom positions, using a digital caliper. It started out at 0.091". I worked on adjusting the bevel adjusting screw until I got it to 0.000", but thinking that precision is not real given the form of the measurements as I have no idea just how square that large square really is. Additionally, the square is powder coated, so who knows how much off it is for that reason alone. I feel is was darn close, at least.


After re-installing the blade back on the saw, I made a cut and checked it for being square. It wasn't. I set a travel dial indicator against the blade and made adjustments to the bevel adjustment screw. It took only a couple changes to get the cut to be essentially perfectly square. The square touches on each side of the cut but there is a very faint line of light in the middle. I doubt there is anything I can do about that and I doubt it matters, so I consider this resolved and done.


Thanks for the help.

Rick
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