# Difficulty Squaring DeWalt DHS790 Double Bevel Sliding Compound Miter Saw



## RickKr (Dec 30, 2018)

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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## Stick486 (Jan 4, 2013)

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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## Bstrom (Jan 2, 2020)

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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## Nickp (Dec 4, 2012)

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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## sreilly (May 22, 2018)

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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## Cherryville Chuck (Sep 28, 2010)

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/sho...and-measuring/squares/32601-engineers-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.


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## Nickp (Dec 4, 2012)

Cherryville Chuck said:


> 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/sho...and-measuring/squares/32601-engineers-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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## Stick486 (Jan 4, 2013)

reset/change the stop to rotate the CL axis of the arbor/motor..


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## DesertRatTom (Jul 3, 2012)

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.


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## RickKr (Dec 30, 2018)

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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## rmark (Feb 11, 2009)

Lots of good information here guys! You all are way above my pay grade. There is so much I wished I knew. I had a 12” Rigid miter saw and it wouldn’t cut straight. On an 8” board, it was 1/8” out of square. Come to find out, the radial arms were parallel, factory defect on many of the Rigid saws that year and Rigid would do NOTHING to fix their mess up. A $599 saw that was totally worthless! I was able to sell it for $350 to someone who wanted it for rough cut lumber only. I applied that $$$ to a Dewalt that I still have.


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## Cherryville Chuck (Sep 28, 2010)

Nickp said:


> 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...


Yes, correct. The knuckle joint might be lined up perfectly but the motor could be angled. If left to right on the table is X, and Y is forward and back then the motor would not be perpendicular to the Y axis since it should be possible to correct any deviation in the Z axis (vertical up and down) by adjusting the bevel function. This is all of course if the arbor is moving perfectly up and down the Z axis. The only solution would be if you could shim the motor true to the swivel frame.

I did have a cheap SCMS that didn't line up with the detents properly. There was a steel plate under it with holes drilled in it where a spring loaded ball bearing would fit into them. I had to move the steel plate until the detents were in the right spots but this problem doesn't sound like that because my blade still cut true, just not at the angle it was supposed to when using the detents.

Rick if your blade is crooked to the cut then I would expect to see a lot of splintering on one side and more on one than the other if both sides are splintering.


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## Stick486 (Jan 4, 2013)

@RickKr...
ummmmmm, Rick..... 
was your square square???..

*Test it:*
Align the arm on the straight edge of something (sheet goods, bench top, etc) and draw a line down the body. Then flip the arm over along the edge, and draw another line down the blade in the same place. If the lines are parallel, the square is true, but if they make a narrow X or V, it's off....

*The fix:*
You do this by punching at the corner where the arm and body meet.

If the square is less than 90°, punch near the inside corner. This spreads the legs out. 
If the square is greater than 90° you punch near the outside corner, this pushes the legs in toward each other.

*Note: *
This repair only works with very small errors. 
If the square is more than 1/16” off at the end of the long blade, consider it junk and replace it.....
or cut/separate the arm and body to make a pair of rulers/straight edges out of it...


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## Stick486 (Jan 4, 2013)

a picture works more gooder...

,


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## RickKr (Dec 30, 2018)

The blade is no longer crooked to the cut. It is perpendicular to the table. Cuts are clean and square with virtually no splintering. 

There is no longer any issue.


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## Nickp (Dec 4, 2012)

RickKr said:


> The blade is no longer crooked to the cut. It is perpendicular to the table. Cuts are clean and square with virtually no splintering.
> 
> There is no longer any issue.


glad you got it straightened out...


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## RickKr (Dec 30, 2018)

Stick486 said:


> a picture works more gooder...


Nice trick. Thanks. _I didn't use that large framing square on this project_, but it is good to know about. (Edit: oops, I did use that square... My bad. Nonetheless, it got me close and the subsequent step dialed it in.)

I have two such squares, the second, a Starrett, was purchased recently. It is powder coated and I see now the edges are also powder coated and I wonder how much that affects its squareness. I'll have to check. 

The first one I've had for probably 40 yrs, Sears, is plated (satin chrome I think) but the edges are clean and sharp. But I felt it was not so square and got the Starrett thinking "it has to be square". I recently heard of a method of checking where the base leg is aligned with a known straight edge of stock and a line drawn up the short arm, flip the square over and to the same and compare the lines. If parallel, it is square, if not, it isn't. I need to pull out a long enough piece of clean MDF to do this test. 

Rick


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## RickKr (Dec 30, 2018)

Nickp said:


> ...and the fix was...?


Did you not read my post on that, just yesterday, with all the photos of the indicators and such... ? Basically, doing a proper alignment. 

Rick


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## Nickp (Dec 4, 2012)

RickKr said:


> Did you not read my post on that, just yesterday, with all the photos of the indicators and such... ? Basically, doing a proper alignment.
> 
> Rick


I saw your post after I posted...went back and edited it...


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## Nickp (Dec 4, 2012)

RickKr said:


> Nice trick. Thanks. _I didn't use that large framing square on this project_, but it is good to know about. (Edit: oops, I did use that square... My bad. Nonetheless, it got me close and the subsequent step dialed it in.)
> 
> I have two such squares, the second, a Starrett, was purchased recently. It is powder coated and I see now the edges are also powder coated and I wonder how much that affects its squareness. I'll have to check.
> 
> ...


Starrett's are reliable...good thing you didn't go for a Chappell...:smile:


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## Cherryville Chuck (Sep 28, 2010)

RickKr said:


> Nice trick. Thanks. _I didn't use that large framing square on this project_, but it is good to know about. (Edit: oops, I did use that square... My bad. Nonetheless, it got me close and the subsequent step dialed it in.)
> 
> I have two such squares, the second, a Starrett, was purchased recently. It is powder coated and I see now the edges are also powder coated and I wonder how much that affects its squareness. I'll have to check.
> 
> ...


I like checking a square using Stick's described method but you could draw a line down both legs in the middle of the sheet and then flip the square over and line up the short arm with the mark made on the first step and draw another line down the long leg. If a long straight edge doesn't line up with both lines from the long edge then it's not square.

You can check your saw to see if it really is 90* too the same way. Take two boards at least 2' long and mark the face that is going to be up and cut them to the 90* setting. Then butt them together and see if they edges line up. Then flip one over and see if they still line up along the edges. If they do you're square and if they only line up with one face up and the other down you're not square.


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## RickKr (Dec 30, 2018)

Cherryville Chuck said:


> I like checking a square using Stick's described method but you could draw a line down both legs in the middle of the sheet and then flip the square over and line up the short arm with the mark made on the first step and draw another line down the long leg. If a long straight edge doesn't line up with both lines from the long edge then it's not square....snip...


That is essentially what I thought I was describing...


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## Stick486 (Jan 4, 2013)

- Seemed like a good idea at the time.

- All you have to do is...

- This should work.

- Hey, y'all, hold my beer and watch this.....................


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## DesertRatTom (Jul 3, 2012)

Finally looked up that model and it is a 12 inch saw. The same as the one I got rid of many years ago. Worse, it came with a think kerf blade, so it deflected like mad and I could never get a great cut. One thing that does help defeat deflection is to start your cut behind the workpiece and slide it forward making a light cut. This also channels sawdust backward when you make the return cut. Only thing I miss about that saw was being able to cut big, fat lumber. You can also buy a blade stiffener for narrow kerf (thin) blades, but it limits your depth of cut. It's like a BIG fender washer made of good steel.


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## Nickp (Dec 4, 2012)

DesertRatTom said:


> Finally looked up that model and it is a 12 inch saw. The same as the one I got rid of many years ago. Worse, it came with a think kerf blade, so it deflected like mad and I could never get a great cut. One thing that does help defeat deflection is to start your cut behind the workpiece and slide it forward making a light cut. This also channels sawdust backward when you make the return cut. Only thing I miss about that saw was being able to cut big, fat lumber. You can also buy a blade stiffener for narrow kerf (thin) blades, but it limits your depth of cut. It's like a BIG fender washer made of good steel.



Tom...one should never pull cut with SCMS. If the blade catches the wood it will climb up on the wood and fling the saw back at the operator before they have a chance to react...not a good idea...it's as bad as kickback on a table saw...

If one has a proper blade (negative hook, for example) it might be considered a bit safer but a SCMS should never be pull cut...

I understand your experiences with a thin kerf blade on a 12"er but it's really dependent on how one handles the arm. Done properly, there is no deflection with a quality blade. Not sure why one would buy a 12" saw and then reduce their cutting depth with a blade stiffener.


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## Stick486 (Jan 4, 2013)

nickp said:


> tom...one should never pull cut with scms. If the blade catches the wood it will climb up on the wood and fling the saw back at the operator before they have a chance to react...not a good idea...it's as bad as kickback on a table saw...
> 
> If one has a proper blade (negative hook, for example) it might be considered a bit safer but a scms should never be pull cut...
> 
> I understand your experiences with a thin kerf blade on a 12"er but it's really dependent on how one handles the arm. Done properly, there is no deflection with a quality blade. Not sure why one would buy a 12" saw and then reduce their cutting depth with a blade stiffener.


agreed...


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## DesertRatTom (Jul 3, 2012)

Thank you for the heads up. Been doing it that way for a number of years. My pull cut is always very shallow, no more than 1/8th inch, which is probably why I get away with it.


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## Stick486 (Jan 4, 2013)

DesertRatTom said:


> Thank you for the heads up. Been doing it that way for a number of years. My pull cut is always very shallow, no more than 1/8th inch, *which is probably why I get away with it.*


luck is more likely...


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## Nickp (Dec 4, 2012)

DesertRatTom said:


> Thank you for the heads up. Been doing it that way for a number of years. My pull cut is always very shallow, no more than 1/8th inch, which is probably why I get away with it.



Comfort can lead to accidents..."always done it that way" doesn't make it right...

Maybe when you make the recommendation to pull-cut with a SCMS you could at least add the warning of the possibility of climbing if not done properly...just sayin'...shouldn't you at least also recommend a shallow cut...? And how to make it as safely as you do...?

There's a lot of folks out there that are just starting...would you still make that recommendation without a warning...? And what will you say when your saw climbs on you...I just pray it doesn't hurt you when it does...

Submitted for your consideration...

BTW...take a gander at the thread I just started on SCMS Safety...worth a watch to be reminded of better practices...


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