De Walt miter problem

[Barry Bruner]

I have a DW705 model miter saw and I have had it repaired 3 times in about 5 years. The repair man said that they really do not have a brake and that the motor reverses direction. The saw is fine when it works but it is getting expensive and the repair man has it as much as I do. So, should I need to buy another saw, or get it fixed again? Barry Bruner

[Bruce Wrenn]

I've had two DeWalt 705's for several years, and never had a problem with either of them. The 708 uses the same motor, if memory serves me correct. Is the switch the part that is failing? The reason I ask is when B&D brought out the Super Saw Cat back in the seventies, the switches didn't last. Same basic motor as the 705. Also are repairs being done at a Dewalt Service Center?

[Mike Henderson]

What failures are you experiencing?

It's highly unlikely that DeWalt would reverse the motor in order to do a brake function. When you let go of the switch, the motor could be reversed, but there's no action after letting go of the switch - so if the motor was reversed, it would start running backwards instead of stopping.

When an electronic brake is used, a common way of implementing it is to treat the universal motor as a generator when the switch is released and then dump the generated current into some low Ohm resistors. The motor (acting like a generator) absorbs the kinetic energy of the rotating blade and converts it to electricity, which is then dissipated in the resistors. This stops the blade pretty quickly.

Since the motor/generator is designed to handle the braking function, it should last a long time. After all, it's no worse than starting the blade (it's just the inverse).

I would expect that most miter saws with brakes implement the braking function in a similar manner so DeWalt's implementation should be about the same as any other brand.

The electronic brake is better than a mechanical brake because the mechanical brake will eventually wear out, while the electronic brake does not have any parts that will wear out - beyond the motor itself.

Mike

[Barry Bruner]

I want to thank both of you for your help. I can pull the trigger on it and it sounds fine and cuts fine, when I take my finger off the trigger I get a little viberation and a fair bit of noise. The switch has not been the problem. And I was thinking along the lines Mike was talking about. If the motor is reversing like the repairman said, then it should start to go backwards after some point. I do use it a lot, I cut 500 wooden shear pins for work and that is 1000 cuts a year, plus a lot of not too fantastic woodworking during the year. I think I will get it fixed because I like the saw and I have made extensions on my miter table which would not work on another saw. Since they all have similar breaking systems, it would not help to switch brands. Thinking, it might be better to buy me a rather cheap backup saw to use while this one is being fixed. Does anyone have any ideas? Thanks again. BARRY BRUNER

[Jason White]

Check the brushes.




I have a DW705 model miter saw and I have had it repaired 3 times in about 5 years. The repair man said that they really do not have a brake and that the motor reverses direction. The saw is fine when it works but it is getting expensive and the repair man has it as much as I do. So, should I need to buy another saw, or get it fixed again? Barry Bruner

[Steve Griffin]

I want to thank both of you for your help. I can pull the trigger on it and it sounds fine and cuts fine, when I take my finger off the trigger I get a little viberation and a fair bit of noise. The switch has not been the problem. And I was thinking along the lines Mike was talking about. If the motor is reversing like the repairman said, then it should start to go backwards after some point. I do use it a lot, I cut 500 wooden shear pins for work and that is 1000 cuts a year, plus a lot of not too fantastic woodworking during the year. I think I will get it fixed because I like the saw and I have made extensions on my miter table which would not work on another saw. Since they all have similar breaking systems, it would not help to switch brands. Thinking, it might be better to buy me a rather cheap backup saw to use while this one is being fixed. Does anyone have any ideas? Thanks again. BARRY BRUNER


I've owned 4 of these. One has been used hard for 8 years and runs like a champ. One burned up in a year and when I replaced it, lasted 1.5 years or so and it ran like yours only worse--sounded like it was filled with gravel. Brushes were fine. Of course in my shop we use them daily and hard.

So I gave up on the brand and with much reading replaced it with a Hitachi 12", which I'm happy with so far. My only complaint is that it is the loudest tool of any kind I have owned. Don't use it around small furry animals or they will be killed by the shriek!

-Steve

[Barry Bruner]

I checked my brushes and they look fine. The description of the sound Steve gave is more accurate than what I gave. I will keep the Hatachi 12 inch miter saw in mind and go with the best deal, unless it is another De Walt. At least I will have something to compare it to this way. Barry Bruner

[Joe Scharle]

I think your saw may use a braking winding in the motor. If so, what happens is when you let go of the trigger the braking winding has a path through the switch and acts as a reverse inductance to the collapsing primary windings. All this relies on good brush contact and of course, the trigger switch itself.