CMS Brake

[Dennis McDonaugh]

Can you adjust the brake on a CMS. I looked in the instruction book but didn't see anything.

[John Miliunas]

Dennis, not to the best of my knowledge. If I'm not mistaken, the "braking action" is actually done electrically. :) :cool:

[Dennis McDonaugh]

That's what I thought John. I knew they were some type of dynamic or regenerative brake. I thought there might be some sort of electronic adjustment. I wonder if there is a replacable part inside I can identify.

[Dennis McDonaugh]

Well, it looks like the motor is sold as a complete unit for $188. A that price I'll be looking for a replacement instead of repairing this one.

Before I give up is there anything else that could cause the blade not to stop when you release the trigger? It spins for several second even unplugged.

[John Miliunas]

Dennis, I've heard of someone else having a similar issue. As I recall, the advice given at that time was to check the brushes on the motor and that it could possibly be the trigger switch itself. I believe there are multiple points on the switch, which engage the circuit for the brake. Could be those points are shot. Switch replacement might be a "gamble" but, should only run you about a ten-spot or so. Might fix it...:) :cool:

[Russ Massery]

My old miter saw brake stopped working it was the brushes. At the repair station where I get parts they told me 9 times out of 10 it's the brushes.
Hope it helps.

[Ian Barley]

I'm not sure on something like a CMS but on big machines braking comes from "injecting" a dose af DC current into the AC motor. Therefore if the machine is unplugged it will definitely run on because there is no current availanle to do this.

I had this on one of mine and solved it with maintenance step number one. Which is take the cover off and give the insides a good going over with a compressed air gun. Not sure which bit of micro crud was causing the problem but it got solved anyway. Always worth a try.

[Richard Wolf]

I second it on the brushes. I use Dewalt SCMSs and I always know when the brushes have to be replaced. No brake. The brushes last me about two years, your milage may differ. I use mine every day.

Richard

[Jim Becker]

Checking the brushes was the advice I was given on the same question not long ago...as John appears to remember. ;)

[Dennis McDonaugh]

Okay, the old brushes are 3/4" long and don't appear to be worn out. I don't know how long they are supposed to be since I didn't look at them when new. They are only making contact with about half the surface area--half is shiney and half is rough. I wonder if they are too short for the springs to provide good contact with the commutator? I'll order a set and see what happens. In the meantime I'll take the switch apart and blow it out.

[John Miliunas]

Sounds like a good plan, Dennis. Keep us posted as this may be good info for the next person!:) :cool:

[Richard Wolf]

3/4 sounds like they are shot. It's not always the lenght that is left but the spring tension and wear on the old brushes.

Richard

[tod evans]

brushes will cause the brake to fail, sometimes removing them and cleaning the crud from the track they ride in then reinstalling the brushes and running the motor for several minutes non-stop will cure the problem temporarily (6-months for me) but you`ll need new ones down the road. tod

[Gene Collison]

Dennis,

Typically the brake on a series type motor as used in power tools with brushes works like this. The trigger switch is a four pole switch, when the saw is running power is connected to the brushes and field coils of the motor. When you release the switch, a high wattage resistor is connected across the brushes of the motor putting a load on the motor, the motor is now acting as a generator, being shorted by the resistor brings the saw to a quick stop. So you should be looking for a bad switch, brushes or a burned out resistor. The brake circuit is open when you let off on the trigger instead of connecting to the resistor, that's the problem.

Gene

[Tyler Howell]

Is this the Delta 10" CMS???

Had one with the only symptom being no breaks:eek: . Turned out to be the internal drive belt was loose and pully screw stripped.
Replace both with 5 more years of great sevice.

[Dennis McDonaugh]

Tyler, it's a 12" model 36-235. Are you saying your 10" didn't have a direct drive motor?

[Tyler Howell]

Tyler, it's a 12" model 36-235. Are you saying your 10" didn't have a direct drive motor?
That is correct sir, heavy son of a gun too!

[Rick Haigh]

This is a silly question, but is your blade securely fastened? I have found that my miter saw blade has worked its way loose a few times in its life and it behaves exactly the same as if the brake no longer works.

Rick

[Dennis McDonaugh]

This is a silly question, but is your blade securely fastened? I have found that my miter saw blade has worked its way loose a few times in its life and it behaves exactly the same as if the brake no longer works.

Rick

Rick, I haven't checked that, but will do that right now!

[Kirk (KC) Constable]

This is a silly question, but is your blade securely fastened? I have found that my miter saw blade has worked its way loose a few times in its life and it behaves exactly the same as if the brake no longer works.

Rick

DeWalt had a TSB on this very problem a few years back. Although I didn't have the very specific model identified, I did ruin a basically brand new $100 Freud Ultimate Cutoff blade when mine loosened up. :mad:

KC

[Dennis McDonaugh]

This is a silly question, but is your blade securely fastened? I have found that my miter saw blade has worked its way loose a few times in its life and it behaves exactly the same as if the brake no longer works.

Rick

Rick, I checked and its tight. I ordered brushes and as soon as I have a chance I'll clean the switch. I can probably ohm it out and see if it's working properly too.

[Steve Clardy]

One of my Dewalt 705's did that some time back. No brake part of the time. I removed and blew out the dust in the switch. Fixed it.