Motor help

Questions about tools and jigs you want to buy/build/modify.

Motor help

Postby Bryan Bear » Sun Sep 15, 2019 12:30 am

I have an old craftsman radial arm saw that I almost never use. I keep it around mostly because I can use it as a deep reach drill press and a drum sander. I used it a couple months ago and everything operated perfectly. Tonight I went to use it to build some basement storage shelves. This is the first time I have used it since the movers brought it to the new house. When I turned it on, all the lights on that circuit dimmed to almost nothing. The saw turned but with low power and tripped the breaker as Soon as the blade came into contact with the sacrificial fence.

One time, years ago, the motor would not start and it tripped the breaker. I vacuumed out the dust from the motor and it worked fine. I never thought of the issue again until tonight. I’ll try that soon (I don’t currently have access to the shop vac).

Does anyone have a guess as to what is wrong? Could it have been damaged in the move? Something else?
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Re: Motor help

Postby Bob Francis » Sun Sep 15, 2019 9:15 am

With it unplugged can you spin the motor/blade by hand?
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Re: Motor help

Postby Bryan Bear » Sun Sep 15, 2019 11:12 am

I went back down this morning and did a quick blow out of the dust in the motor vents. Now the lights dim for about 1/2 a second while the motor spoils up to speed and everything runs fine. Obviously something is up but not sure what. Am I doing damage to the motor?
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Re: Motor help

Postby Bob Gramann » Sun Sep 15, 2019 12:53 pm

There might be some kind of centrifugal switch and a starting capacitor in the motor starter circuit. If the switch contacts are dirty or smoked, it may not be working correctly. To test the capacitor, it needs to come out of the circuit and be shorted to completely discharge it. Then, put a needle type Volt-ohm meter across it. The needle will jump to little or no resistance while it charges and then sink to infinite when the capacitor is charged from the battery in the VOM. If it won’t jump or if it never settles, the capacitor needs to be replaced.

The dimming of the lights when starting the motor could be an artifact of the size of the circuit rather than a problem with the motor. Motors draw a lot of current when they start.
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Re: Motor help

Postby Bob Francis » Sun Sep 15, 2019 7:47 pm

What Bob says.
Is that circuit heavily loaded with goodies? i.e. freezer, fridge, etc.?
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Re: Motor help

Postby Jim McConkey » Sun Sep 15, 2019 9:16 pm

Sounds like something is shorting out, or maybe the capacitor is shot. If it ever becomes more trouble than it's worth, there is a recall out on most of those old Craftsman radial arm saws and they will pay you $100 to take back the motor. Take the check and buy a new sander.
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Re: Motor help

Postby David King » Mon Sep 16, 2019 4:58 pm

Could it be the grease in the ball bearings that's turned to very old and dried parmesan rind? Once that grease starts to warm up it will spin normally.
Most of these saw motors are "universal" AC-DC and don't use a starting capacitor and circuit. If the RPM stated is 3450-3600 then it's going to be an induction motor.
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Re: Motor help

Postby Bryan Bear » Tue Sep 17, 2019 7:26 pm

Update:

I’m still not sure where my meter is so I couldn’t really test the start capacitor but I did open up the case to see if it was bulging or anything. With it open, I blew out any dust I could and lubed the centrifugal switch. After I put it all back together it snapped to life right away. So, I guess problem solved. . . For now. . .
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Re: Motor help

Postby Bob Gramann » Tue Sep 17, 2019 9:47 pm

Now that it works, be very careful. I owned one of those Craftsman radial arm saws for a couple of weeks long ago (I bought it used). I bought it thinking it might be a good way to cut fret slots. It had way too much slop for any precision work. Besides that, it really scared me. I couldn’t figure out how I was going to keep all of my fingers. I sold it, with a warning, for what I paid.
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Re: Motor help

Postby Bryan Bear » Tue Sep 17, 2019 10:18 pm

Yeah they are pretty dangerous. I only very rarely use it for crosscuts. Mostly I use the other end of the motor. I have a drill chuck on it. Sometimes I will use it as a drill press when the throat on my drill press is too shallow. Every now and then I’ll use it like a pin router. And of course, the sanding drum is convenient; that is what I use it the most for.

I considered using it for fret slots for a few seconds then came to my senses.

This was the first woodworking tool I ever got. I got it for free when I decided I wanted to give woodworking a try. For a while, it was my workbench and only power tool. I was making everything up as I went along and am lucky I didn’t get injured. One time I was using it to cut a bunch of kerfs of uniform depth so I could thin a board. I neglected to remove the sanding drum before I put a blade on. I was going holding the work against the fence with my right ha d and pulling the handle with my left. Everything was going fine until I sanded my knuckles on my right hand.
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Re: Motor help

Postby Bob Hammond » Wed Sep 18, 2019 8:59 am

There are no safe machines - only cautious and mindful operators.

That said, I would say that your motor needs some maintenance. It's likely that it starts slowly or not at all because the starter windings are not energized due to gumming up of the centrifugal switch, which disengages after the motor has come up to full speed. The switch is stuck in the 'open' running position. The bearings could be dried out as well. It's not likely but possible that the capacitor is shot (about $10 for that). I had one of RAS motors rebuilt - cleaned, bearing, etc. for $100 at a competent motor shop.

I've got two RAS from the late 1950s, which are much better built than later saws built after 1962 or so. They were never abused - and had the original table boards on them when I bought them. The 1959 DeWalt 925H is quite precise, for cut after cut. The key point for radial saw operation is proper alignment, and having a saw that will hold the settings. You might look at my post that's in the library:

https://www.mimf.com/old-lib/hammond_ra ... w_jigs.htm

When you read the article section about alignment, you'll see the part about placing a magnet on the blade - I no longer do that. I use the disc from a discarded computer hard drive, which is a perfect front surface mirror. Somewhere I have a picture of the DeWalt running at 5000 rpm with a computer disc on it - you can read the finest graduations of a machinist's ruler in the reflection from the disc, and it runs whisper-quiet.
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Re: Motor help

Postby Bob Francis » Wed Sep 18, 2019 10:55 am

Bob Hammond wrote:There are no safe machines - only cautious and mindful operators.

That said, I would say that your motor needs some maintenance. It's likely that it starts slowly or not at all because the starter windings are not energized due to gumming up of the centrifugal switch, which disengages after the motor has come up to full speed. The switch is stuck in the 'open' running position. The bearings could be dried out as well. It's not likely but possible that the capacitor is shot (about $10 for that). I had one of RAS motors rebuilt - cleaned, bearing, etc. for $100 at a competent motor shop.

I've got two RAS from the late 1950s, which are much better built than later saws built after 1962 or so. They were never abused - and had the original table boards on them when I bought them. The 1959 DeWalt 925H is quite precise, for cut after cut. The key point for radial saw operation is proper alignment, and having a saw that will hold the settings. You might look at my post that's in the library:

https://www.mimf.com/old-lib/hammond_ra ... w_jigs.htm

When you read the article section about alignment, you'll see the part about placing a magnet on the blade - I no longer do that. I use the disc from a discarded computer hard drive, which is a perfect front surface mirror. Somewhere I have a picture of the DeWalt running at 5000 rpm with a computer disc on it - you can read the finest graduations of a machinist's ruler in the reflection from the disc, and it runs whisper-quiet.


That is an awesome thread and full of great ideas.
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Re: Motor help

Postby Bob Hammond » Wed Sep 18, 2019 7:08 pm

Bob Francis - I wrote that up as an article, and it was provisionally accepted for a major woodworking magazine in 1990, and i was told that a certain plaid-shirted carpenter liked it. Unfortunately, the mag hired a new editor, who thought that was of little interest because no one used RAS anymore because they were 'dangerous' and couldn't be used for precision world. He canceled the publication. Well, I guess he never heard of Wally Kunkel, the grandmaster of DeWalt RA saws.

Oh, and a good overall blade choice is a thin kerf sliding compound miter saw blade, such as a Freud TK604. Under no circumstance should you put a table saw blade on an RAS, they're too aggressive.
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Re: Motor help

Postby Clay Schaeffer » Wed Sep 18, 2019 9:39 pm

When I built my house I used a RAS to cut all the framing lumber (joists, studs, and rafters). It wasn't a high precision tool, but accurate enough for the work. It was no more dangerous then a 12 inch sliding miter saw (and probably no less). A moment of inattention can give a lifetime of disability.
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Re: Motor help

Postby Daryl Kosinski » Tue Oct 08, 2019 1:02 pm

Craftsman is not a very good Radial Arm Saw. I have one from the 60's.

The motor burnt out some 30 years ago. I looked into getting it rewound. Slightly less than a replacement motor and more than the poorly built modern whole saws.

I went for the rewind, the motor shop assured me it would be better than new, It was.

The built in circuit breaker went bad and could not be replaced, I ended up eliminating the built in breaker and replacing the on off switch with a motor start switch rated for the motor ( it has a built in breaker so I'm safety covered )

With lots of tweaking and set up it still is a pretty good saw, I use it daily.
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