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DeWalt Compound Miter Saw Screech at Start-Up

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Forum topic by Steve posted 02-16-2018 04:25 PM 504 views 0 times favorited 7 replies Add to Favorites Watch
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Steve

66 posts in 1032 days


02-16-2018 04:25 PM

Topic tags/keywords: question miter saw

I have a DeWalt DWS780 compound sliding miter saw that just about three years old. This last week, it started making an ear-piercing screech at start-up. It’s a grating noise, but brief, so it’s hard to tell exactly where it’s coming from. Once the saw gets up to speed, the noise goes away.

Here’s a photo of the saw:

I blew the dust off the saw, took a look at the belt (seems nominal, if a little tighter than the manual says it ought to be) and pulled the motor brushes (still withing tolerance). According to the manual, all the bearings are sealed and meant to last the life of the saw. I contacted DeWalt and the best they could offer was a service center about 50 miles north of me.

I’m wondering if anyone else has had issues like this and knows where else I might look for the trouble? I search on the web found a few items, but all with different brand, lower end saws that were close to the end of their service life. I would really like to repair this rather than replace—I’ve already had a couple of tool failures this year and can ill afford another.

-- ~Steve


7 replies so far

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Ripper70

1020 posts in 930 days


#1 posted 02-16-2018 05:52 PM

I think you may need to start an exploratory disassembly of the saw and start checking things like the armature bearing or the belt pulley and the gear that engages the arbor, etc. While you’re at it, blow the dust out and lubricate anything that moves. I’m skeptical of bearings made to “last the life of the saw”. Who’s to say whether DeWalt believes that life isn’t any more than 3 years?

If replacement parts are necessary, it’ll cost you the small price for the parts and whatever your time is worth. Bringing to a service center for out of warrantee repairs will probably cost half as much, if not more, of the price of a new saw.

-- "You know, I'm such a great driver, it's incomprehensible that they took my license away." --Vince Ricardo

View John Smith's profile

John Smith

989 posts in 184 days


#2 posted 02-16-2018 06:21 PM

remove the blade – clean the bolt and female threads and all the washers
with a solvent and brass brush – get everything squeaky clean.
reassemble and see if that works. (I used turpentine and then the aerosol Brake Cleaner).

-- Graduated Valedictorian from the University of HardKnocks --

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Steve

66 posts in 1032 days


#3 posted 02-17-2018 05:31 PM

Thanks for the tips. I’ll start pulling the saw apart on Monday and see what I see. I believe the saw is just barely within the 3-year (limited) warranty period, but although I’m normally pretty good saving receipts, naturally, this one has vanished. (I bought the saw in the middle of a move. That’s my excuse and I’m sticking with it.)

I’ve replaced bearings on both an old Grizzly table saw and my long-in-the-tooth Ridgid sander, and my experience has been that the results are better, but not quite up to factory original. Those tools were near the end of their life, though; hoping for better results here. Stay tuned.

~Steve

-- ~Steve

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jbay

2331 posts in 921 days


#4 posted 02-17-2018 05:37 PM

1st thing I would try is to take off the belt and see if it still makes noise. If it still does, that at least eliminates the arbor bearing.

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runswithscissors

2762 posts in 2047 days


#5 posted 02-18-2018 12:30 AM

I bought a 12” Bosch Glide miter saw 2 years ago off CL. It had one troublesome issue, and that was a ticking sound it made, like maybe there was a cracked cog on a gear, or something. So I stripped it down to get at the bearings, gears, and belts, but found nothing that I could identify. So I put it back together, and the noise was gone. Guess that makes me some sort of genius (though not necessarily a stable one).

Sometimes machinery does heal itself.

By the way, I have found the saw to be very accurate and stable. I like it.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View Steve's profile

Steve

66 posts in 1032 days


#6 posted 02-19-2018 07:29 PM

To avoid suspense, I got this resolved and it is a failing/slipping belt

Here’s the journey:
I removed the blade. Seemed like the bolt was looser than I’d like and there was more grease around the arbor than I would expect:

There were four screws holding the gear housing in place. Inside, it was pretty well lubed, though a lot of the grease had just been thrown into nooks and crannies where it was doing no good. I smeared it around a bit and removed a little of the excess.

The gears were in good shape. I couldn’t detect any roughness or looseness in the bearings. Sorry, the photo is a little blurry.

I did run the saw without the belt and couldn’t hear the screech. It occured to me, though, that a bad bearing in the motor might not make noise if there was no load.

I reassembled the saw and set the belt tension to the specifications outlined in the manual, which say that when pinched in the middle, the belt should almost touch. The factory setting was much tauter than that, but when I ran it sans blade, the noise was gone. I did note on reinstallation that the belt was a little frayed:

Once I put the blade (newly cleaned!) back on, the screech came back. I had the belt cover still off and could see the belt was jumping around at start up. I tightened it up further and the noise, even under the load of the blade, disappeared. The manual warns that an overly tight belt could lead to premature motor failure, so I’m going to get a new belt and see if that will let it run quietly under less tension.

Thanks, everyone, for the tips and assistance.

~Steve

-- ~Steve

View Ripper70's profile

Ripper70

1020 posts in 930 days


#7 posted 02-19-2018 10:08 PM

Nice job Steve. I think you just saved yourself at least $300 bucks!

-- "You know, I'm such a great driver, it's incomprehensible that they took my license away." --Vince Ricardo

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