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Volts Disappearing

06/08/2010 7:53 PM

I'm losing volts somewhere between plug end and motor winding on a radial arm saw. Doesn't sound complicated but its a Craftsman digital saw and disassembly promises to be a 3 hour nightmare in re-mounting and recalibrating all those digital position sensors. Spare parts no longer available. I have verified continuity from plug blade to motor terminals. Power switch has continuity and contact resistance so low my meter cannot read it. Nearest town to get a replacement cord is round trip of 100 miles(160Km ). Any suggestions for finding exactly where the volts are leaking out. I get some volts at motor but not enough to turn new motor. Cords does not look damaged being mostly internal conduit in saw frame. Hence the prolonged job to remove and inspect it. Saw does not trip a GFCI breaker. If I have to go to town again, hopefully its only once to get the right part.

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#1

Re: Volts disappearing

06/08/2010 8:51 PM

Two ideas. Neither of them great but hopefully one will be helpful.

1) You refer to the motor as "new". What went wrong with the previous motor? Are you sure that the new motor is a correct replacement? Even if the new motor is correct are there terminals under a cover plate that allow the motor to be configured for 115V/230V operation? Could whatever caused you to replace the motor have caused more damage than just the motor? Could you either be connected to the wrong terminals or to terminals that are not appropriate for your 115V/230V configuration? Is the "new" motor just "new to you" and it may have been sitting in your friend's garage for years and is actually bad?

2) Sometimes putting the details on paper is helpful. I don't know how much you know about electricity and I don't want to insult you. You need to try to collect as much information as possible. If the motor is not turning and IF IT IS SAFE to turn the switch on for a few seconds then you need to try to measure across as many items in the circuit as possible. If the power outlet is a duplex (two outlets in one) then try to SAFELY measure from one outlet to the blades of the plug. You expect good contact and almost no voltage drop. If by chance the power cord has screw terminals then, IF IT IS SAFE TO DO SO then measure the voltage from the plug's screw terminals to the switch's terminals. Keep doing this across as many items as possible, especially the switch. Where you get large voltage readings you know you are across large resistances. If you have access to a number of measurement points then this should be helpful. If you don't have much access then this is a worthless good idea.

The key point is to try to measure across items to allow you to know the voltage drop for that item.

Collect and organize as much information as possible. Make notes of what can not be collected and why. Add all of this to this CR4 thread. With the information you have provided some people can make some suggestions but the help will be limited. The more information you provide the better the chances that someone can help.

Just to add two more "silly ideas":

1) Does the saw have a shaft lock? Could it be in the locked position?

2) Is the power actually good going to the saw? Are you plugged into the same outlet as before? Could you have pulled the fuse or tripped the breaker and the circuit it actually "dead" but your high input impedance meter is picking up readings due to the voltage coupled onto the wires?

Bruce

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#2

Re: Volts Disappearing

06/08/2010 9:03 PM

Volts don't get "lost", they either don't get there or they leak to ground. If you have a GFCI and it is not tripping, it's not likely to be leaking to ground. So something is interrupting the flow of power from your cord to your motor windings.

When you say "I get some volts at motor but not enough to turn new motor." I get very concerned. What do you mean by "some volts"? How are you measuring that?

The problem with "digital" things like saws is that there are a myriad of "digital" things that can go wrong, and most likely the say has a controlling device that is not engaging because one of those digital devices is either malfunctioning or detecting something that you are not aware of. If you are reading a few volts at the motor, that is most likely "leakage" through a solid state switching device, the thing that is interrupting the power flow. That part would be normal, the reason it is not allowing the motor to run is the problem. Troubleshooting to find that may be very challenging and time consuming. Good luck.

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#5
In reply to #2

Re: Volts Disappearing

06/08/2010 10:38 PM

Jraef I realize volts don't get lost . But this is so obviously a stupid oversight on my part I figured I would use very plain language hoping somebody woud set me straight about my stupidity. And I was hoping I did not have to dismante this beast to replace the cordset.

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#3

Re: Volts Disappearing

06/08/2010 9:07 PM

If it is only a power problem: a regular motor (induction or universal)on the saw, and your steering is the digital part you should check the whole loop from your plug or connection box to the end.

Measure the voltage at the connector or box:

1. with the switch off 2. with the switch on. Repeat that at each spot between:

1. cable at the entrance of the machine (the switch e.g.) in and out (after switch) If you measure a sudden drop when you switch on the machine at the end of the switch, measure over your switch

- if your voltage is over the switch between in and out - take the switch out, sometimes you can take it apart

- clean it and put some more tension on the springs (stretch) - clean the contacts with a fine sandpaper and put it back - or simply replace it. with saws dust likes to creep in the switches too. If you are that far and the fault is not found, we will guide you further.

Good luck In principle, the part you measure the voltage over is suspicious.

It can be: bad connection or contact in plug - a worn out wire (invisible crack) - switch - your end switches if built in - a bad safety stop if built in - Your motor can be it too - but you tried a different one - so go on with the previous first.

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#4

Re: Volts Disappearing

06/08/2010 10:33 PM

I was hoping I had done something obvious and stupid and that someone would point it out. The complete picture is as follows. Original motor failed because the centrifugal switch contacts burned. Replacement centrifugal switch not available. Sears said they still had a complete replacement (NEW not refurbished) motor in stock. Even so it took 6 weeks to be delivered . New motor installed and saw worked about five times Total run time on new motor was maybe an hour then the saw quit . No hum, no motion and apparently no power draw.

Even when I have the breaker OFF I always check a circuit with one of the inductive probes. It says AC is delivered right to motor as the power switch is cycled ON/OFF. Next step is continuity check. From blade on cordset to switch is fine ditto for continuity check from switch to motor terminals. Also checked switch thinking it might have carboned up from arcing. Switch continuity check gave me same resistance as shorting out meter leads. Also checked out the thermal switch and the internal centrifugal start contacts and changed out the starter cap. Reading of leads was 0.01 ohms. Next checked voltage at the point leads enter motor. Reads 7.990 volts. load connected and 120.2V load off. Same reading at power switch . Hmmmm? Some molded cord sets get flexed so much the wires fracture at the flex point. Can't find any signs of flexing or stress. Cord looks clean and new. This is after all a hobby machine. Lots of cycling on off but not much real use. Saw is up against wall and plugged into dedicated wall outlet. If there is cord damage it is hidden well enough to give negligble resistance during meter test including flexing it. But I can't see most of the lenght buried inside machine

The saw has one of those 'key lockable" safety switches. Parts no longer available according to Sears contract service depot. Replacing cordset may or may not be the problem but it's the time needed to tear down and re assemble the arm which contains three angle transducers that is the real PITA. Spending half a day driving into town then a half a day (or more) dismantling saw and reassembling it with new cordset would be a real bummer if that didn't cure it.

Jumpering with loose wires makes motor turn but flying leads external to saw is not a safe mode of operation. Remember its a radial saw so motor moves for every cut and switch is on end of arm. Using a generic swith will not fit into die cast recess in the arm. Leaving switch dangling would foul motor every time you move saw motor to make a cut.

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#6
In reply to #4

Re: Volts Disappearing

06/08/2010 10:54 PM

Looks to me that you have to do some operative job. Your meter that shows 7.999 needs to be set on the right setting too, or needs to be connected well before reading. I still suspect your cord - probably the part in the arm. If you can find a European one, that will probably last longer. The wires inside are more pure.

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#9
In reply to #6

Re: Volts Disappearing

06/10/2010 9:09 AM

"If you can find a European one, that will probably last longer. The wires inside are more pure."

Sorry but on this one I have say the only thing pure here is the BS. Copper wire is copper wire. The European ones will probably be undersized as they are designed to operate at 240V instead of 120V and will therefore carry less current.

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#13
In reply to #4

Re: Volts Disappearing

06/10/2010 10:05 AM

I think you have a break in the neutral side. The key thing here is your inductive probe indication. Such probes only indicate on the "hot" side of the circuit. This is easy to check, use your ohmmeter to read the resistance from the neutral blade of the plug (the one that goes in the largest slot on the receptacle) to the neutral connection on the motor, this value should be close to zero. There should be no switch on this side of the line. If however if it is switched (which is not normal but is done on machines designed to run on 240VAC), then measure with the switch closed.

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#7

Re: Volts Disappearing

06/09/2010 4:45 AM

did you check if the switch ( is it a contactor or manual operated) is closing?

check may be any safety device on the saw, may be it is preventing the switch to close

this what I get to mind, hope it will help

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#8
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Re: Volts Disappearing

06/09/2010 12:44 PM

Yes I did check the switch. In fact this was the first thing I looked at after verifying I had correctly connected the motor. I know I'm not infallible and probably have forgotten more than I remember. As I approach my dotage I figgered I must have forgotten something basic.

I have worked as a maintenance electrician including as an engineering tech for a power utility.

I currently work as an electrical designer and am often asked to diagnose problems by email etc. But this one promises to be a bear. I really am not looking forward to spending 8 hours dismantling the saw in order to change the cord set. This is what I heard from someone who had to do a similar repair on an identical model.

The alternative is equally unattractive. Running new wiring on the exterior of the machine and drilling through the castings to get to the switch buried inside.

Since its not a fault to ground or short between conductors even my megger is of no help in locating the exact spot where the wire has failed. So far all tests say the switch is working.. any substitute switch would have to be mounted externally on the moving motor housing or track.

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#12
In reply to #8

Re: Volts Disappearing

06/10/2010 9:59 AM

One more thing:

Some motors have Thermal Fusing devices inserted within the windings. If this device was triggered OFF (fused or Open Circuit) they might not re-close on cooling!

Check the Motor Winding Continuity to make sure the circuit of the motor is not Open somwhere(?) ...

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#17
In reply to #8

Re: Volts Disappearing

06/10/2010 12:49 PM

Checking the switch (properly!) involves switching on and measuring the volt drop over the switch when in the "On" position, with an AC voltmeter set to at least 120 or 240 volts (depending on where you live of course).

A meter check without mains voltage is simply not good enough unless only a few milliamps are required. Here AMPS will/should flow.....a bad connection will show a large volt drop and will usually get hot.....a true break will remain cold.

In such situations I stick one side of an AC voltage meter in the neutral side, (if you don't understand or know why you stick the prod in the neutral and not in the phase line, just ask and I will tell you!), switch on and work from the live side of the socket towards the neutral with the other prod.

You will see full mains at first (assuming socket is OK!!) and suddenly the volts will be gone!! Then you will know what is broken.....

I suspect your cable is the problem if the switch is OK and you have the right motor properly connected........

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#20
In reply to #17

Re: Volts Disappearing

06/10/2010 1:30 PM

Thanks Andy.

Speaking of safety; I managed to survive 4 years of doing maintenance work in a 2 megawatt power station where the switch gear was carrying 26,700 volts. Unfortunately I no longer have access to the sophisticated test gear like I had them. I was the underground fault locating specialist. Sometimes I had to make a judgement call to bring in back hoes and dig up a street intersection if the faulted underground cable failed somewhere under the pavement. Admittedly this is not as serious. But I still would like to pinpint the exact place of the fault before dismantling the machine Trouble is now I only have a megger and a DVM to work with instead of some real test gear. I used to have a TDR that could identify a fault location to within inches.

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#22
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Re: Volts Disappearing

06/10/2010 1:46 PM

The DVM is all you need with my method. Its all I would use for the same problem...

Best of luck.

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#10

Re: Volts Disappearing

06/10/2010 9:29 AM

From reading your posts, I also would think that the cord is giving you the problem. With the blade removed, you could try switching it on, and moving the saw through the full range of motion, and see if there are any movements that cause the saw to start. In my experience, a break in the wire will usually find a connection if moved enough. Good luck.

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#11

Re: Volts Disappearing

06/10/2010 9:49 AM

I understand that jumpering the whole thing eliminates the problem?

Try jumpering the switch only.

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#14

Re: Volts Disappearing

06/10/2010 10:05 AM

Look at the motor terminals and how they are connected to the winding leads. it is possible that you have a bad solder joint on the motor winding lead terminals. Everybody is using lead free solder these days and the stuff is crap. It doesn't wet worth a *&^%* and it is prone to cracking and cold solder joints (because the soldering temp is so high.) combine that with lacquered wire that may not have had the lacquer stripped properly and you may just have a bad "new" motor. You could try taking the centrifugal switch off the new one and putting it on the old motor and see if the problem resolves itself.

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#15

Re: Volts Disappearing

06/10/2010 10:54 AM

These motors have a centrifugal switch to get the motor up to speed and then the centrifugal force pulls it out of the circuit and the motor runs as an induction motor.

If this switch is not operating properly, stuck in position or jammed with a bit of sucked in wood the motor will not run. The cure is to remove the motor and inspect the centrifugal switch to see what is up with it.

However, I would first unplug it and then blow it out and hand spin the motor, you may free it to turn? then plug in and try?

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#16
In reply to #15

Re: Volts Disappearing

06/10/2010 12:41 PM

It has to be the wire.

Switch was bypassed completely and the internal harness substituted with an external cable. Then motor worked but the internal wire still had the problem. My Hitachi megger also has a low ohms test and indicates a very low but consistent reading of around 0.05 ohms which is consistent with my digital meter reading 0.1 ohms and less resolution than my megger which is specifically designed to test wires. WE even tried to wiggle th ecable hoping to find a weak spot that would make the reading vary but no luch. Tested both hot and neutral wires.Unfortunately the manner in which the radial arm is constructed means a lot of work to remove and replace the wiring. A visual inspection of what wires portions can be seen shows not the least sign of any physical bending crimping or chafe to suggest where the wire has sustained damage.

Looks like this one defeated me. I showed my buddy ( saw owner) the results of my tests and told him we would have to dismantle the saw. Given the warning about not disasembling due to need for factory jigs to realign it he decided we should leave it for time being unless a better idea comes along. Wiring in an completely external harness and switch not only looks crudde but forces relocation of a switch to a les desirable thus not so safe a location. It would mean locating the switch further away from the hand grips or possibly an awkward reach if something jammed.

Thanks for the trouble shooting tips.

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#18
In reply to #16

Re: Volts Disappearing

06/10/2010 12:50 PM

Yes, I see. There must be a break in the wire. Is there a fusible link in there somewhere that might have over heated and opened the circuit?

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#23
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Re: Volts Disappearing

06/10/2010 1:54 PM

No fusible link. Motor is thermally protected. And that was the first thing I pressed to reset it. Then I did a continuity check; still good. Ditto for centrifugal switch and I even replaced start cap on the new replacement motor. Just in case.

Breaks in wire are usually caused by physical mechanical stress. In the absence of such stress marks I'm stumped as to where to look.

I was hoping someone on this forum had experience with dismantling this particular model of Craftsman radial arm saw. Reassembling it looks to be difficult in view if the warning labels saying factory alignment fixtures are required. And the factory no longer makes them.

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#24
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Re: Volts Disappearing

06/10/2010 2:14 PM
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#26
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Re: Volts Disappearing

06/10/2010 2:33 PM

Aurizon many thanks for the Craftsman links. The discussion threads did confirm it may be difficult to reassemble and ALIGN the saw to factory condition. Which would explain why I was told it would take 8 hours or so to reassemble it. Like most mechanical things you can generally tear it apart in a hurry. Having a saw that does not track or cut straight can be as frustrating as having one that does not run at all. At least if it doesn't run it wll not spoil expensive materials.

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#25
In reply to #23

Re: Volts Disappearing

06/10/2010 2:23 PM

Elnav, before you take everything apart, there is one last thing I'd try before you grabbed the wrenches. try cutting off the plug end and replacing the plug, a lot of times the failure is right where the wire enters the molded plug due to poor strain relief design. Cut the wire say an inch or so short of the plug and put a new plug on it and see if that fixes it. It is cheap and easy and you really can't lose much in trying it.

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#27
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Re: Volts Disappearing

06/10/2010 2:49 PM

Tried that yesterday.

I suspect there is a cable clamp buried inside where I can't see it, that keeps the wires from tangling in the moving arm lock mechanism. The arm swings 45 degrees or more each side of center position. Something is needed to keep the wires from being pinched by the moving parts. The constant vibration from saw teeth striking wood could conceivably create a fracture even in fine stranded wire over a 25 year period. Sadly the discussion threads said models from about 1980 onwards were not as rigid as older models. this one dates from 1982.

Unfortunately getting in there means removing the arm from the column and in the process unbolting the critical parts that align column and arm not to mention the digital angle position stuff. One bracket has lettering cast into it saying align arrow with mark but I can't even find the mark being referred to. and also dismantling the track on which the saw motor rolls on. Track is in two pieces.

I will go back to the Craftsman threads to see if anyone has come up with a guide on how to align this beast. Somewher ther must be a sequence of assembly that facilitates making parst fit correctly and align to each other.

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#28
In reply to #27

Re: Volts Disappearing

06/10/2010 2:59 PM

buy yourself some spray machining bluing and scribe very fine match marks across every adjustable assembly that you take apart, you should be able to get it back together again within a fairly decent tolerance by aligning the marks again when you put it back together.

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#29
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Re: Volts Disappearing

06/10/2010 4:10 PM

THANKS!! Now why didn't I think of that? Admittedly I haven't used that stuff in over a decade. But this is why I went to the collective wisdom of the forum. being semi retired I must be entering my dotage.

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#35
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Re: Volts Disappearing

06/10/2010 5:21 PM
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#39
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Re: Volts Disappearing

06/10/2010 5:52 PM

Perfect! I found a manual for the exact model. Its a 1985 electronic 10" saw. Unfortunately it only shows the metal parts not the wire routing. From the diagrams I see why the user forum said the saw was not solid and the track was just sheet metal, in two pieces. As soon as I remove the bolts I can see; it looks like the whole thing falls apart.

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#19

Re: Volts Disappearing

06/10/2010 1:12 PM

Use a voltage logger to check your incoming voltage

Your incoming voltage changes throughout the day because the demand changes during peak hours

If your voltage is too low your motor will not fuction properly

If your voltage is too high it can damage your motor

This can be caused by bad weather or a surge in demand

This is your starting point.....Good Luck!!

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#21
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Re: Volts Disappearing

06/10/2010 1:41 PM

Thanks green brand. this is not a situation which justifies acquiring a data logger.

Besides utility voltage does not fluctuate from 120V to around 5 volts over a couple of seconds. And if it did I would notice flickering of the lights fed from the same electrical panel.

I could buy a replacement saw at a garage sale for less than a data logger cost. One of the tasks I had while working for the power utility was installing such dataloggers when a customer complained of not getting quality power.

This is clearly a case of a wire harness failing. I just wanted to see if I could avoid an 8 hour headache dismantling a piece of equipment needlessly.

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#30

Re: Volts Disappearing

06/10/2010 4:17 PM

Elnav, don't know if it would help you as you may have them but I have a similar saw purchased new ~1982. Being somewhat of a pack rat, I believe I still have the manuals that came with the saw. This included a relatively thick set-up alignment manual. If you like I will look for the manuals and forward the information to you.

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#31
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Re: Volts Disappearing

06/10/2010 4:30 PM

Gee thanks! There is a user's guide but it really doesn't have much in the way of information except constant reminders to keep fingers away from cut line and a 1-800 number for service. Trouble is our local Sears Canada no longer services the saws.

Alignment guides for disassembling and reassembling the column and swing arm would be informative. The locking mechanism has a cable arrangement leading to the lock lever on front of radial arm. No doubt there is a preferred sequence that should be followed.

If you can scan in the relevant page(s) you can email them in a PM.

Many thanks!

Elnav

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#32
In reply to #31

Re: Volts Disappearing

06/10/2010 4:41 PM

I will look for them tonight. Haven't needed them for many years but I "never" throw anything away per my wife...she's mostly right.

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#33
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Re: Volts Disappearing

06/10/2010 5:06 PM

....they always are!!

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#34
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Re: Volts Disappearing

06/10/2010 5:13 PM

I find that being a packrat is part and parcel of being a tinkerer.

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#36
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Re: Volts Disappearing

06/10/2010 5:30 PM

Quote"being a packrat is part and parcel of being a tinkerer" end quote.

bUT WHAT CAME FIRST?

Did the person become a pack rat because of all the neat things he thought he could do with left over stuff or did he start to tinker and realized he needed stuff to tinker with.

Case in point. I found a curved cutter from a farm implement. Its big and weigh s a kilo. When I saw it I figured; "wouldn't it make a dandy curved knife for carving canoes or Totem poles?" I have regular curved knives for wood carving but not one six inches long suitable for carving whole tree trunks.

So now after I sharpen it and affix a handle ( maybe an ax handle) I will go looking for a big cedar tree so I can carve a totem pole for my front yard.

Hmmmm wife will just love that! Not to mention the landlord.

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#37
In reply to #36

Re: Volts Disappearing

06/10/2010 5:39 PM

Which came first? the chicken or the egg?

I suspect that both urges come from the same primal need. Tinkerers look at an object, not as what it was designed for originally, but what else it can be used for or made into. To us, a piece of pipe or barstock or an electric motor or some other thing takes on a completely new life in our mind's eye and like a sculptor, we feel the need to bring that life out into the light of day. It is our cedar tree and we feel the need to make our totem pole from it.

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#38

Re: Volts Disappearing

06/10/2010 5:48 PM

Check the motor do you have the voltage jumpered for the wrong voltage. 120 vs 240. Also check the voltage across the cord. How many feet of cord? The longer the cord the greater the voltage drop. A power cord (twist wires) act like a transformer when powered. Its possible to have a break in the cord, when you checked continuity the cord was good when you plugged it in the break is opened.

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#40

Re: Volts Disappearing

06/10/2010 9:42 PM

I had one of those saws, I got rid of it because of this;

"The Craftsman Radial Arm saw was originally made by the Emerson Tool Co., for Sears. Early Craftsman Radial Arm saws, dating back from 1958 through 1992 are now subject to a safety recall because of a problem with the protection (guarding) of the blade. The current product is "not" subject to this recall notice. However, purchasers of a "used" Craftsman radial arm saw may want to check out the U.S. Consumer Product Safety Commission notice of November 14, 2000 (http://www.cpsc.gov/cpscpub/prerel/prhtml01/01031.html). Some of these saws can be modified; however, earlier models cannot and must be scrapped. As such, you may be better served in considering the current product in light of this situation. In addition to having better safety features, a new Craftsman Radial Arm saw comes with a warranty, no wear (an important consideration with this tool), and thus improved accuracy."

That said, I don't know if you ever indicated what voltage you are running at. If you were running 220V, and you bought a new motor, it would have come set up for 110V because you always had to modify it to work on 220V; you could not order it that way. If you put 220V on a motor strapped for 110V, it would probably run 4 or 5 times before a winding opened...

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#41
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Re: Volts Disappearing

06/10/2010 10:34 PM

Thanks J Raef,

the motor is powered by 120V and yes I confirmed the replacement was also for 120V

The proof was in jumpering out the internal wiring with a direct power cord which did make the saw motor start up normally.

There was a notice written in the owner's manual about This sawblade safety notice thing having been dealt with.

To be perfectly frank us northerners tend to view all these 'consumer safety' warnings in a slightly different light. Try running an Alaska Sawmill and you will see what I mean. This saw had been run for 20 years without a mishap before the safety recall notice. Then all of a sudden we need some effen bureaucrat in Washington telling us how to run saws? ya gotta be kidding!!

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#42
In reply to #41

Re: Volts Disappearing

06/10/2010 11:21 PM

To be perfectly frank us northerners tend to view all these 'consumer safety' warnings in a slightly different light.

Good for you EL, I've got the saw that's one notch down, no digital, bought it in '92.... "Guards, we don't need no stinking guards".... LOL,, Find me a decent cabinet maker that still has the guards on his table saw.... You wouldn't be a federal EL by chance?

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#43
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Re: Volts Disappearing

06/11/2010 1:21 AM

Baxterm@kos.net asked: You wouldn't be a federal EL by chance?

REPLY

Heck No!! I aint even an American. Born in Denmark and Canadian by courtesy when I joined their Navy as a young man. Eventually married a northerner who comes from a third Generation logging family. Safety on a family run saw mill is a whole 'nutter topic. By age ten you damn well know saw blades can throw planks a considerable distance so you make damn sure you are not down range of the artillery.

I learned to drive tractors at age seven on my uncles farm and was driving cars by age twelve. These days they don't think you can drive before age 18 or mebby 21.

Todays 'consumers' gets coddled and pampered and protected from themselves and the real world till they reach old age. ( sheesh!)

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#51
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Re: Volts Disappearing

06/11/2010 10:48 AM

I follow your view and hope that saw never gives you a problem. It is only when an accident occurs, that your personnel insurance company might be difficult on the liability issue. In Europe e.g. stationary saws need to be switched on with a relay (contactor) and after a power faillure MAY NOT start automatically, but need to be restarted by the operator. Push on - push off. I know a specific case where due to negligence the employer had to pay back all the medical costs to the insurance company. On the other hand, a machine can be so secured that it is too restricted to operate well. Just some info.

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#53
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Re: Volts Disappearing

06/11/2010 11:26 AM

Agreed, the problem with guards is that they are only designed to work in situations the designer can envision. In real life, you find yourself needing to make cuts on equipment or parts that the guards often get in the way of.

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#44

Re: Volts Disappearing

06/11/2010 7:18 AM

I am a Little late joining the forum thread but thought some advise for futer problems might help. It seems you identified the power cord as the fault so this will not give you much more help now. Anyway to safely check cord and switch fit a heavy wattage 12v lamp across switch where motor supply connections were and apply 12v across plug pins, engage switch if lamp lights brightly you have good continuity then you can manipulate the cable to see if there are any damaged sections usually where it flexes in normal use.

Hope it will help in futer.

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#45
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Re: Volts Disappearing

06/11/2010 8:41 AM

And if the switch is faulty or off, the lamp will blow instantly (110 VAC on a 12 VDC lamp?)

What does that do for us please? I must be misunderstanding something my friend....

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#46
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Re: Volts Disappearing

06/11/2010 9:08 AM

What he's saying is to energize the system with 12VDC and a high wattage dummy load (the headlamp or similar) in place of the motor instead of 120VAC as a means of putting a decent load on the wiring to find hot spots/bad connections while keeping the applied voltage low and safe. One thing I would point out is that you need to make sure that the motor and it's start capacitor is completely disconnected from the circuit when doing this or you'll blow the cap if you aren't careful.

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#47
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Re: Volts Disappearing

06/11/2010 9:45 AM

AH!

Many thanks.

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#48
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Re: Volts Disappearing

06/11/2010 9:52 AM

De Nada my friend.

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#49
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Re: Volts Disappearing

06/11/2010 10:29 AM

I did say were the motor connections were, indicating removal of motor connetions.

Cheers Garth

Sorry in reply to 46.

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#50
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Re: Volts Disappearing

06/11/2010 10:38 AM

The cap will be at the live wire and connect the start coil through the centrifugal switch. Normally when the motor is disconnected, the capacitor (condenser) is too. The 12 Volts DC won't do any harm either, while the capacitor is probably designed for 200 Volts AC plus. It will just get a 12 volts load (if connected?) and lose this load slowly or faster if it has a discharge resistor built in. What Garth proposed is a safe way to test the whole circuit under low voltage and a "reasonable" current. The capacitor is IMO no obstacle.

The 12 Volts test can also be done with the motor connected. The coils, fed with DC will also use more current. (R ><Z)

Polarity is not important.

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#52

Re: Volts Disappearing

06/11/2010 11:19 AM

If I were in your situation, I would dig out the old Christmas light testers. Power up the saw and carefully follow the wiring from one end to the other.

Some of the testers will only detect power in the hot side wiring. If that is the type that you have, or find, and your wiring break in in the neutral, you can make up an extension cord and flip the power and neutral. USE THIS ONLY AS A TESTER. It might help to find the exact spot the break is at. Then you could just cut and splice that point. Good luck.

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#54

Re: Volts Disappearing

06/11/2010 3:51 PM

Do not quite understand losing volts but I think you mean you have a volt drop which means you have a resistor somewhere in the circuit.

The resistor could be a bad connection of which there is a lot in a normal system.

I normally can count between 10 and 50 in a lot of situations.

They normally give out heat so is any thing getting hot / warm ?

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#55
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Re: Volts Disappearing

06/11/2010 4:51 PM

Yes I was referring to voltage drop. Pardon me for reverting to vernacular instead of sounding like someone who already knew it all. I don't; which is why I figured on asking the list. And you are right such a fault is usually a resistive fault that creates heat. Unfortunately this fault is so peculiar it does not produce any visible hot spot. At least none my IR thermometer can see from the outside. All the suggested tests have yielded negative results. this leads me to the conclusion the fault must be hidden inside the machine frame. And that is the real problem.

How to dismantle the machine and reasemble it so it is aligned and working properly. People who have done it says the process is a day long task.

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#56
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Re: Volts Disappearing

06/11/2010 10:50 PM

elnav,

Start disassembly on a good day and maybe you will have a working radial arm saw again. If at the end of the day you have not triumphed, you can go buy a good heavy duty table saw. It is a better saw with better supported blade. I can't imagine why a radial arm saw made in 1982 would still make clean cuts considering all the joint and slide wear. A sliding mitre saw and a heavy duty table saw are better in my view.

Luther M

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#57
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Re: Volts Disappearing

06/11/2010 11:34 PM

The saw is not mine. It is owned by a retired minister on a fixed income. The radial arm saw is in lieu of a table saw for rippimg long planks to width,, how do you do that with a mitre saw? He's got one of those mitre saws for cross cutting but the Alaska saw mill does not do a nice enough job of finish cuts for completion of the interior of the log cabin he built. Nor is it good for furniture building.

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#58

Re: Volts Disappearing

06/14/2010 6:37 PM

I don't read anywhere that you checked continuity across the motor terminals. The motor may have an open winding in which case the motor is NG. Being a crapsman, I wouldn't be surprised.

When I troubleshoot, I check voltage only at the plug. The rest of the measurements are continuity tests only with power disconnected. Are the wires that connect to the motor accessible? A continuity reading here will tell you if the windings are open or not. If you get a reading, jury-rig a power cord to the motor, bypassing everything else and see if the motor runs. If it does, then the problem is in the wiring, switch, etc. which will require taking the saw apart anyway.

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#59
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Re: Volts Disappearing

06/14/2010 7:49 PM

Ron I may have omitted mentioning it. However the motor did work for about one hour run time after being installed as a replacement for the original motor that had a defective centrifugal switch. Being still under warranty it was returned and we were told the motor tested out fine. Next came a series of tests including continuity checks. I did say continuity was an ohms reading so low as to be the same as the test leads reading.

I finally located the problem. As someone had guessed, it was a poor connection in the neutral. The neutrals were joined by a crimp pigtail connector but hidden inside the radial arm of the saw. Access to the splice required removal of the arm from the vertical column and dissassembly of the track from the shell forming the arm top. The motor works, but now I have to reassemble the whole durn thing.

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#60
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Re: Volts Disappearing

06/14/2010 8:41 PM

I told you it was the neutral!!

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#61
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Re: Volts Disappearing

06/14/2010 9:52 PM

Yes you did. It just took a bit of effort to reach the faulty connection

Thanks!

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#62
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Re: Volts Disappearing

06/15/2010 2:39 AM

I understand you but continuity readings taken with say a DVM at a few Micro amps, do not always tell the full story.

I agree with you completely in that I would do that first.

BUT if I did not find the fault, the probable/possible reason being that there is a connection/break that allows a few micro amps through, but not normal running/starting current through!!

Thatws when I coonect to the mains and go looking for a voltage drop somewhere it should not be!!

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