Miter saw blade coming loose

[Doug B]

My DW 708 SCMS has had the blade loosen on me a couple times now. I replaced the blade recently and thought I tightened it up properly, but it somehow worked loose after a short time of using it. I tightened it up again and it worked for a while but loosened again.

Thinking it was a bad blade, I put the old blade back on and everything seemed fine. Until today...when it loosened up again with the old blade.

What the heck is going on with this saw? I have had it several years and have replaced the blade several times before with no problems. Any ideas?

Thanks for your help.

[triplefreak]

Does it have a washer that goes on under the nut itself, next to the blade?
Check the owner's manual & see if it's supposed to have one.
Or, you might be putting the nut on backwards.
My saw has a blade nut that's flat on one side, rounded over on the other.
The flat side goes against the blade on my saw.
Hope this helps.

[TDHofstetter]

That's got the big Allen screw that holds the outer arbor washer in place? Got a blade brake, too, true?

I'm pretty sure the blade brake is the culprit here - it's slamming the blade to a stop so fast that the Allen screw (socket head cap screw) is backing out & loosening the blade.

There might be a little oil or wax on that screw - that'll make it easier for it to back out. You didn't oil it, did you? Ever? Gotta' be DRY DRY DRY, and clean. If ya oiled it, clean it out with mineral spirits, liberally applied. Acetone, even. Gotta' get that oil OUT so the screw is metal-on-metal again.

...or just look to the blade brake. Does the saw seem to be stopping more quickly now than it used to? Ya might need to tweak that brake a little, or replace the brake pad / band.

[Doug B]

It's just a left hand thread hex head screw holding the blade on and I really think I have the inner washer and the outer "clamp" washers and placed correctly - I even took them off and cleaned everything up, including the new blade.

Tim, I wondered if it might be the blade brake, but it has not seemed different lately. I have had this saw for several years and use it almost daily and have changed the blade several times before.

How can I check the blade brake? My manual is less than helpful

[TDHofstetter]

Well... it SHOULD NOT stop the blade within a couple of second, I wouldn't think. It SHOULD take a four or five seconds to wind down. If it stops faster than that, it's probably time to replace the electric brake.

Here's another thought. Does that arbor shaft (or adaptor) have a pair of flats that engage the outer arbor washer? Is it possible the outer washer isn't engaging those flats, so it can turn freely?

Also... if it's just got a round point of engagement with no flats, did you happen to use a blade with a Teflon coating, or one that's been waxed? If the arbor washer is trying to grip the blade through a slick material like that, it may slip when the blade brake kicks in. Going back to the old blade (no coating) may have carried a thin film of Teflon or wax back to that blade, too, and so the problem would persist.

If you think there's wax between the washer(s) and blade, try cleaning up all those surfaces with mineral spirits & a small (toothbrush-sized) wire brush. A brass brush would probably be best. Teflon is harder to remove, if that transferred over... that might take a scrubbing session with steel wool.

[rrich]

You are using the arbor locking button when tightening the blade, right?

The surface of the arbor, washer and both sides of the blade are free of sawdust, right?

And, lastly, you are using the washer, right?

[Doug B]

OK, here are a few pics. While you guys digest these pics I'll go give everything a good cleaning.

I did not notice the shiny ring on the old blade when I put it back on...I've got this funny feeling that you figured it out Tim...something might have been transferred from the other new blade that is now making the old one behave the same way.

Just before removing the blade...


Blade, both "clamping" washers, and the center washer that fits in the blade.


Where all the pieces need to go back onto...

[fredbelknap]

Looks like the blade has been slipping on the washer. It may be wore down to much to tighten correctly. Might have to get a new washer or some kind of spacer. Cleaning like Tim said might fix it.

[Doug B]

I cleaned all the parts with some acetone and a toothbrush. Put it back together and made 3 or 4 cuts and it is still tight so far. Hopefully it will stay that way.

P.S. Does this count as my shop picture? ;D

[woodmannie]

Had that same ring on my 4 1/2" grinder. the locking washer (one against the blade) was worn. Put on a new one and had no problem. Wasn't so much the nut got loose, just didn't get tight enough, even though it was tightened the same as always.
I'd try a new set of washers, front and rear. Cheap fix, maybe.

Tom

[TDHofstetter]

Ya know, Tom's on something there, too.

Doug, next time you haul a blade off that saw, put back the washers & all WITHOUT THE BLADE, but otherwise fully assembled the way it's s'posed to go. The washers may seat against each other, or there may be a small gap between 'em, a little slimmer than the body of the blade. If that gap is too large, it'll be impossible for the washers to grip the blade as they should. In that case, it's time either to replace one or the other arbor washer (whichever seems more worn) or install a slim blade stabilizer to take up some space. The stabilizer will need the same size arbor hole as the blade, o'course. Or even just a thin shim with the same size center hole. Ten thou thick, maybe.

Or just a heavier-bodied blade.

[woodmannie]

Actually Timmer, Think Fred hit it first.

Tom

[Joe Lyddon]

As soon as I saw that worn ring on the blade, I thought the same thing... ;D ;D

I've never seen that happen before... must have "bound" in wood a few times...

Fred & I think alike... ;D

[TDHofstetter]

Don't mind me. I'm feeble.

[Doug B]

Well, I'm still not too sure about this...why did this only happen when I put a new blade on? And why after years of service with not a single problem? Wouldn't there be some kind of indication? There was no "ring" left on the new blade at all.

I really thought it was a bad blade and returned it, so I cannot do any testing with it...not that I'd want to anyway because it is very uncomfortable to have a 12" miter saw blade spinning freely for a while and you just hoping the guard works like it is supposed to and does not let the screw come all the way off and release that spinning Tasmanian Devil into the shop to bounce around chopping off random limbs as it careens from one end of the shop to the other and back several times.

I suspect the blade for one (possibly good) reason...I saw the blade at Harbor Freight and it was cheap! It was so cheap that I figured I could not go wrong even if all I used it for was for rough cuts. Now I wonder if that was a bad decision. I think it may have transferred something to the old blade as well. I'm thinking the bright ring on the old blade was caused when the blade loosened up and spent over a minute free spinning against that clamping washer...maybe.

I think from now on I'll stick to blades I more sure of even though they cost a lot more.

If the old blade comes loose again, I'll look into replacing the clamping washers, but they really look fine to me.

I'm tempted to blame it all on that cheap-a$$ saw blade from HF.

[fredbelknap]

Doug I hope you are right and the blade fixes it. I remember a year or so ago someone was killed by a blade coming off a CMS. Be careful.

[TDHofstetter]

It was an HF sawblade? You put a HARBOR FREIGHT sawblade on a high-ticket saw like that???

I'm thinking the HF had some sorta' crap on it that wiped off onto the washer & started the whole shebang. That or it had too thin a body and an abrasive surface... and so ground the surface of the washer. Or both & all of the above.

Do check the space between the washers next time you have it apart. If that gap is too large, there's no way it can clamp a decent-thickness blade.

[lexrex]

Just be careful man. There was a true story a few years back of a guy using a miter and the blade came off and cut his arm deep enough to sever an artery. He did not survive.

[Doug B]

The blade guard on the DW708 works. I wish I did not have to know that. It is not a good experience to go through. I can see how that would be a very nasty thing to have come off. I had some major puckering going on

I know Tim...one of those things that seemed like a good idea at the time...I never used a HF blade before...and never will again

[rrich]

Going along the thinking of Tim and Fred...

Clean the INSIDE of the threads on the arbor. I'm thinking that something is in there and not allowing you fully tighten the blade in the saw. Also you could try filing any lip or burrs off of the end of the bolt that holds blade in place. I'm thinking that the bolt is bottoming out and not tightening fully.