Bandsaw motor repair or replacement
I have an older model (1970) Craftsman 12″ bandsaw. The tool is good and reliable, and in very good condition. However, as of a couple of days ago, when I hit the switch the motor just hums and won’t start. I have tried rotating the shaft — which moes freely, and I whacked it a couple of times, but nothing but hum.
This is a detached motor hung beneath the table and connected by belt, so access is reasonable easy. It is a Sears-branded motor, of unknown make.
So, two questions:
1) Any idea what the problem might be and if it can be repaired at a reasonable cost?
2) If irrepairable, or expensive to repair, can I safely replace it with one of my orphan washing machine or a/c blower motors (for a squirel cage blower)? Would there be any risks in that?
Replies
Joe ,
You can use one of your orphan motors , the main concern is the rpms or the speed of the motor .Make sure you use the same pulley ratio to maintain the correct blade speed or feet per minute .
Obviously the hp should also be adequate or at least close to the same .
It's hard to say what exactly is wrong , if a capacitor start type motor that could be the problem , just a guess .
good luck dusty
Dusty:What I worried about was that my orphans might have an inherently faster speed -- and how would I know? On the other hand, if they all run at about the sale speed,I can just trade out the pully or get one of the same diameter.
I know zilch about motors.
But I just had one go south, and one of the things I learned was to check the capacitor if the machine has trouble starting. The capacitor is located on the outside of the motor, and is covered with a housing that is easy to take off. If it is "bad," I was told it will generally be discolored and/or leaking. If that is the case, apparently you can easily get a replacement (it will have a number printed on it) from anybody that fixes motors.
Otherwise, if the machine is worth saving, I would simply take the motor off, and carry it in to a motor repair place.
********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
Sounds like the start capacitor is gone..... Assuming it is single phase. A cheap fix
Come on Joe, forget about "orphans" until you have established some basic facts:
Obviously there is power reaching the motor from the switch.
A) If you have no knowledge of motor electrics at all either find someone who has or remove the motor and take it to a qualified person.
B) If you are keen and can establish that the motor uses a centrifugal start mechanism you can decide if you want to go further i.e check out that part-if it is stuck this could be the problem. Sometimes one can manipulate that mechanism without removing an end cover. Try blowing dust out if it an open type. If not decide if you want to take off that cover.Those switches can stick or their contacts can be burned.
B) It may be a capacitor start and run type- no mechanical switch. Then the capacitor(s) need checking by someone with instrument and knowledge- often there is no outward evidence of failure. Check obvious things first , such as connections to capacitor. Beware of capacitors that are not fully discharged- they bite.
Seems to me that if you took option A)you could fix it and get some knowledge at the same time.
Hope that is helpful.
NIkkiwood, Philip:
I am a well-versed layman in electricity, but don't know much about motors beyond the theoretical (magnetic flux -- that sort of thing). Also used to build radios in my pre-microcircuit youth, so understand what a capacitor is. No problem removing the motor or even opening it.
However, just as a theoretical knowledge of internal combustion does not help much when you try to tune up a specific engine, I don't know what to look for in actual electric motors when they go Hummmmm.
I will take a look, and if nothing jumps out, I'll call or go into a motor shop, but these days, the repair can at times outrun the cost of a fractional horsepower motor. If that unhappily proves true--IF it proves true, I'd prefer to just substitute one of my "orphans," if that can safely be done. However, at least the first one I looked at a former house a/c blower motor, has no nameplate, and hence, I have no way of knowing how fast it goes.
BTW, Philip -- in my near angelic youth, we found an entertaining way to put capacitor "bite" to work. We would take big "can" type capacitors out of the television sets of the day, and tape up half the "can with electrical tape. We would then run a bare wire from the terminals around the tape. The next step was to buy a rectifying diode and solder it to a piece of lamp cord so as to provide a mobile source of DC to charge the capacitor. We cold plug this in to any outlet. We would take the devive to school, say, chare it up, and either toss it to people, or leave it on their desks. WHen they caught it or picked it up they would usually complete the circuit and get a discharge through their hands. Seemed like very big fun to us as 15 and 16 year olds.
We also tried to figure a good way to wire urinals, but never perfected the technology.
Joe,
Older motors are worth getting rewound if they were good motors to begin with. You will have a much better motor when you are finished. That being said , the price may make it cost prohibitive. It all depends on the motor shop. I wouldn't even think about using one of your old appliance motors. They were designed for a completely different application and I doubt if you would be happy with their performance. Most motors, other than Baldor and Marathon are built offshore so you are at the mercy of your supplier for a warranty.
Terry
Thanks, Terry.
Actually, the original Sears saw motor dates to the 1970s, as do the orphan appliance motors. There wouldn't be any warranty in any event, and if they burn out, they burn out. Right now, the orphans are just collecting dust on a shelf, except for one which I use to spin polishing disks. I'd like to have some use for them as I am too thrifty to throw them away.
The way the saw is set up, the motor is a separate item that is hung below the table that supprts the saw. It is about 5 minutes work to take it off or put it on.
Is there a potential safety issue to using one of them?
Since the OEM motor has the right mount, it's probably going to be easier to just take it in and have it repaired. The speed will be correct, it'll be fresh and the right one for the saw. Maybe the place doing the work would take an orphan in as partial payment. If you want to check the starting capacitor, remove the motor from the saw, remove the cover on the capacitor and disconnect one wire. Then, connect the two wires through a resistor (if there are two) and that will discharge the stored voltage (if you have one- 1 meg will do). If it has only one wire, use a needle nose pliers to connect the terminal on the wire to the case of the capacitor. If you have a multi-meter, set it to OHMS and take a reading from the wire to the case. You shouldn't see continuity but may see a brief drop in resistance, then it will go back to 'open' or infinite resistance, depending on whether the meter has a needle or is digital. Then, reverse the leads and check for continuity again. If you see continuity with either polarity of the meter, the cap is bad. This test won't tell you if the cap is actually good (meeting capacitance spec) but it will tell you if it's shorted. It could also be that dust is caked between the brushes and the armature's commutator. Using compressed air to blow this out may get it to work again. Bad brushes can cause problems and the motor being 30+ years old makes this a possibility. Brushes are cheap- the motor may have a pair of caps that unscrew at opposite sides of the motor- usually, unscrewing these caps will allow removal and replacement.
"I cut this piece four times and it's still too short."
Thanks. I'll have a look.
"could also be that dust is caked between the brushes and the armature's commutator. "
OK. Here it is again. A reference to brushes and commutator when discussing what is clearly an induction motor. I'm no motor-head, but I've never seen an induction motor with brushes and commutator. In my experience, those are exclusively in the domain of universal motors. What have I missed in life -- is this a reference to some sort of hybrid?
Always lookin' to learn sumpin.
Mike HennessyPittsburgh, PA
Why is it "clearly an induction motor"? The fact that it hums? I don't think so. The fact that it's from the '70s? I don't think so. NOTHING shows that it's an induction motor, going form the posts.I'm throwing ideas out, trying to be helpful and you want to come in and crap on my pancakes. Nice. Thanks a lot.
"I cut this piece four times and it's still too short."
Nope. Not trying to flavor your pancakes in any fashion (tho' I do like the phrase). Just trying to learn something. I assumed you knew more than I did (which I still assume is true) since I've seen several threads recently -- besides yours -- mentioning capacitor starting and brushes in the same breath. I still don't know if those two are mutually exclusive and it would be enlightening to find out.
Mike HennessyPittsburgh, PA
Joe,It sounds like the bandsaw you have may be the same one I have; the Model Number on mine is 113.24201. If so, the motor is most likely a 113.12550. You can Google up Sears Parts and plug in the model number to see the parts diagram and parts list. If your motor is a different model number it probably doesn't matter. For purposes of illustration they're all pretty much the same.Bottom line is, there's no commutator and no brushes. But there is a centrifugal switch for the capacitor start, and I think my first shot would be to take Phillip's advice: get out the air hose and blast the heck out of that end of the motor. If you've got someone who can manually give the motor enough of a spin to open the contacts while you're doing that it might help. Wind a string around the pulley and give it a yank.The second shot would be to take Highfigh's advice on the capacitor, except for one thing: if you look at the parts diagram you will see that there are no wires on the capacitor, only terminals that the wires connect to. So connecting the resistor between the wires would do nothing and you could still have a charged capacitor waiting to zap you. Not his fault, he didn't have the diagram. Anyway, I'd just connect the resistor across the terminals and let the capacitor discharge before disconnecting the wires.The third shot would be to pull the end off the motor and see if the centrifugal switch contacts are clean and that it's working properly. If none of that works, then might be the time to drag out Plan B, but I wouldn't do it until then.Hope this helps,
Dan
Lacking wires, the terminals should be the obvious place to connect the resistor since he's trying to verify the capacitor's integrity, right?
"I cut this piece four times and it's still too short."
Sure, no problem. I almost didn't mention the wire issue at all. I knew you didn't need any help checking capacitors and figured most likely Joe didn't either. But then it crossed my mind that later on someone might come across this thread and connect the resistor between the disconnected wire and the other, and miss the capacitor completely. If I didn't have several Sears motors my basement, it wouldn't have occurred to me that that could happen.Dan
My bandsaw motor quit (a Steel City 16 inch saw). I took the motor to a local shop and had it rewound - I don't recall what it cost, but it was very inexpensive.
Joe,
The motor is probably an induction motor, since most universal motors are quite small and usually attached directly to the machine, not mounted separately driving a belt. While a capacitor failure is possible, at least 95% of the time the problem is that the starter switch has gotten caked up with sawdust and/or the switch's contact points are burned.
In either case, the motor can be repaired by simply disassembling it and giving it a good cleaning, the points can usually be salvaged with a light filing. I have done this many times with complete success.
Band saws require quite a bit of starting torque, you will need a replacement motor with a capacitor start, to supply the need starting torque, if you decide to replace the motor. In most instances, the Craftsman motors were 3,600 RPM models, the motor's spec plate should, in any case, tell you it's speed.
John White, Shop Manager, Fine Woodworking Magazine
Edited 3/9/2007 12:18 pm ET by JohnWW
This sounds like a bad start capacitor. If your motor is a "Cap start" motor and utilizes a start capacitor it will state "CAP START" on the nameplate on the motor. I just replaced the start capacitor in mine. They are available on Walmart.com for less than $10.00.
His motor died almost 15 years ago, he's probably figured it by now.
This forum post is now archived. Commenting has been disabled