Radial Arm Saw Blade Coming Loose

[Yonak Hawkins]

I have a DeWalt radial arm saw with a brake. Every week or so the blade will spin loose after turning off the saw. I have a large lock washer to hold it on but that fails. Since the nut is a reverse thread I have modified the lock washer to accommodate it. Does anyone else have this problem and I wonder what the solution is.

[Rick Potter]

It should tighten, not loosen. That is weird.

[John TenEyck]

It happens during braking. The blade wants to keep rotating, the brake doesn't, so the blade tries to take the nut with it. It sometimes wins because it has a lot of mass and angular momentum compared to the nut. I've found it can happen if there is any little bit of dirt, sawdust, etc. on any of the mating surfaces, or if one of the components isn't truly flat. If anything isn't truly flat replace it. After that if everything is clean, and I tighten the nut very well using both the arbor and nut wrench it doesn't happen. Using a lock washer may actually be a bad idea. You want contact area to increase the friction between the components. Adding a lock washer will decrease contact area.

John

[Mike Schuch]

All of my radial arm saws have always taken forever to spin down. Is the brake on your saw electronic? Can you reduce its braking force by swapping in a smaller resistor? Could you put a really thin rubber washer between the blade and the collar on the arbor to lock the two together better without messing up the blade alignment? I have never seen a lock washer on a RAS arbor. Iassume the lock washer is between the blade and the retaining nut? It seems like the lock washer should be between the blade and the collar on the arbor because to keep those from slipping. I would worry about anything between the blade and the collar throwing off the alignment of the blade and making it wobble but a bit of expermenting might help find a solution.

[jack forsberg]

Saws with breaking in the EU usually have a pin drive keeps the blade from spining the nut off on breaking . the way to Remedy this on American saws is just like a spindle molder does . double nut it

[Don Sundberg]

I've had that happen a couple times on my Unisaw, and it doesn't have a braking resistor (it's only 1 phase). Does the spindle on the RAS have a flat / key way / or other feature that a like shaped washer could be used between the nut and the blade. The washer cant rotate because it has a non round hole. This is what my circular saw, miter saws and my Bosch portable table saw use.

If all else fails Jack's suggestion to double nut should alleviate the problem.

[Yonak Hawkins]

I put the lock washer on after the first few times the blade spun loose. It is between the retaining collar and the nut.

Everything seems to be flat and aligned. I tighten the nut very tight until the lock washer is flat.

I don't know if it's an electronic brake but I can't figure how it could be anything else. It works automatically. I'm afraid a rubber washer would allow too much movement and actually exascerbate the problem, but it's worth a try.

[Yonak Hawkins]

There is no flat or keyway on the arbor. That would have been a good feature.

[Yonak Hawkins]

the way to Remedy this on American saws is just like a spindle molder does . double nut it

This seems like the most likely solution.

Thanks, everyone, for your responses.

[Peter Quinn]

I've had that happen a couple times on my Unisaw, and it doesn't have a braking resistor (it's only 1 phase). Does the spindle on the RAS have a flat / key way / or other feature that a like shaped washer could be used between the nut and the blade. The washer cant rotate because it has a non round hole. This is what my circular saw, miter saws and my Bosch portable table saw use.

If all else fails Jack's suggestion to double nut should alleviate the problem.

Thats how most shapers operate too, a single or double key way washer, but I've never seen such on a RAS. The newer original saw models have brakes, anyone know how they keep the blades on?

[mark kosse]

You don't say a model but I had that happen on mine. It's a mid 80's 7790. Mine has a hex wrench machined on the end of the arbor shaft. Using an Allen wrench while tightening the blade nut solved the problem.

[John TenEyck]

This seems like the most likely solution.

Thanks, everyone, for your responses.


The saw was designed to operate safely without having to add anything. The blade is coming loose because something is wrong. If you find the root cause and fix it it will run as intended.

John

[Ronald Blue]

I agree with John. Something is wrong if it isn't staying tight. I would inspect everything closely. Have you always had this issue or did it just start? I have had my Dewalt for nearly 30 years and have never had the blade loosen.

[jack forsberg]

Thats how most shapers operate too, a single or double key way washer, but I've never seen such on a RAS. The newer original saw models have brakes, anyone know how they keep the blades on?


Peter most likely with a longer brake time and a nut sufficiently tight. I fitted my Delta 40C with a VFD and on breaking of less than 8 sec it will spin the nut off. My Wadkin 18" cross cut does have a Keyed spindle pin drive and the double nut and came with a hand brake.


http://i284.photobucket.com/albums/ll29/oldtool1/locknut4_zpsciv1osip.jpg (http://s284.photobucket.com/user/oldtool1/media/locknut4_zpsciv1osip.jpg.html)

short spindle motor with pin and lock nuts

http://i284.photobucket.com/albums/ll29/oldtool1/lock%20nut_zpsipnaahhd.jpg (http://s284.photobucket.com/user/oldtool1/media/lock%20nut_zpsipnaahhd.jpg.html)

I have the long spindle for trenching heads and key drive.

http://i284.photobucket.com/albums/ll29/oldtool1/locknut%201_zpslkhg7uxm.jpg (http://s284.photobucket.com/user/oldtool1/media/locknut%201_zpslkhg7uxm.jpg.html)

http://i284.photobucket.com/albums/ll29/oldtool1/locknut2_zpsgebmrjmv.jpg (http://s284.photobucket.com/user/oldtool1/media/locknut2_zpsgebmrjmv.jpg.html)

here you can see that the trenching head locks on the key way without a nut on this expanding head.

http://i284.photobucket.com/albums/ll29/oldtool1/locknut3_zpsmahtuyub.jpg (http://s284.photobucket.com/user/oldtool1/media/locknut3_zpsmahtuyub.jpg.html)

there now you can say you see one.:cool:

[Yonak Hawkins]

I agree with John. Something is wrong if it isn't staying tight. I would inspect everything closely. Have you always had this issue or did it just start? I have had my Dewalt for nearly 30 years and have never had the blade loosen.

I don't know what to look for. Everything seems to be square and flush. The threads look good. It takes 7 seconds for the blade to slow down to a complete stop. Is that an excessively aggressive brake ?

I've had the saw for 3 or 4 years. I can't remember when the problem started but it doesn't seem to be getting more frequent. Usually, I don't even know the blade has come loose until I turn it on the next time and I hear a terrible screeching noise. Ronald, does your DeWalt have a brake ? Could you tell me how long it takes to come to a stop ?

Mine is designed to be held with an allen wrench in the end of the shaft and I tighten it down pretty well.

[jack forsberg]

I don't know what to look for. Everything seems to be square and flush. The threads look good. It takes 7 seconds for the blade to slow down to a complete stop. Is that an excessively aggressive brake ?

I've had the saw for 3 or 4 years. I can't remember when the problem started but it doesn't seem to be getting more frequent. Usually, I don't even know the blade has come loose until I turn it on the next time and I hear a terrible screeching noise. Ronald, does your DeWalt have a brake ? Could you tell me how long it takes to come to a stop ?

Mine is designed to be held with an allen wrench in the end of the shaft and I tighten it down pretty well.
Regs in the EU are 10 sec for braking . Is this a single phase with DC braking?

[Erik Loza]

Try a fresh arbor nut?

Erik

[John TenEyck]

An Allen wrench in the end of the shaft? Never seen that. Can you post a photo of how it looks with the blade on and another of all the components that go on the arbor?

John

[Yonak Hawkins]

Yes, single phase. I don't know if it's DC. It's a DeWalt 7790 with "Lectrostop", serial number : 80230355. I'll have to look it up later this evening.

[Matt Day]

I had that saw for about 4 years, sold it a month or so ago after I restored a delta. Mine was the B&D vintage, with the same Allen key design. Never had a problem and it had probably the same spin down time. You have the arbor washers on right? Have you simply tried tightening the arbor nut more?

[Rick Potter]

Mine is a 1980, type 7, Dewalt 7790. It has the Allen wrench hole in the end of the shaft. The Allen wrench holds the shaft from turning while you tighten the bolt. There is an arbor flange (thick washer) between the nut and the blade.

I just timed it, and the electric brake (Lectrostop) takes 13 or 14 seconds to come to a complete stop. Someone on this site told me that 30 seconds is within spec.

No problems with the blade coming loose. I do have a 4" blade stabilizer on the machine, but I never had a problem, with or without it.

Hope this helps.

[Yonak Hawkins]

Thanks, Rick. Any idea how to adjust the timing of the brake ?

[David Eisenhauer]

I bought a new early-mid 1980's 10" saw (Model 7770? 7700?) that says "Lectrostop" on the side so I guess it is electric braked. It does not use a lock washer, just the collar and the brass looking arbor nut. It uses the Allen wrench in the arbor as already described. I have never had a slip in all the time I have owned it.

[Rick Potter]

Sorry, no idea how to adjust it. I don't think there is anything I the manual, but I will check.

[michael langman]

It could be possible there is something wrong with the blade. Warped, out of balance, just enough to cause the nut to vibrate loose when blade is slowing down. An accident with the blade?
If the saw uses a domed washer I would replace it, and the nut as recommended above.
Bearings could be going in the motor or vibration from the saw itself.
Not an expert but just some thoughts.

[Matt Day]

Good thought on the bearings. If the bearings are going bad and getting crunchy, they would cause more friction and make the blade spin down faster.

[David Eisenhauer]

Assume you have confirmed that the arbor nut and washer are flat, correct? Maybe a little rub on a stone for them? Then look at the makeup of the blade face to the domed washer face (as in plane iron back to cap iron) to confirm flat makeup.