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If smoke, then there is Fire

Uglydog

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#1
Burnt up my bandsaw today.

I've got a 1945 Wells 8M vertical bandsaw which I resurrected from a barn a few years ago.
These past several weeks I've been rebuilding a 5ton Atlas arbor press.
The press was rusted tight with multiple parts missing. The ram had been cut off with a torch.
Milled a new ram... etc. (I'll post when the press is complete)

Picked up a #400 pound piece of 11inch diameter hot rolled to make a platen and a turn a hand wheel.
The 11inch fits on the horizontal band saw just fine.

Got a third of the way through when the motor started smokin!
6hours and $25 dollars later I've a new/used 3phase motor installed.
I lost nearly a day to the repair, but could have lost my shop.

First thought was must of been a bad or tired 1hp 3ph motor, what ever that means.
However, I believe it is more likely that I was working her to hard despite the slow speed and sharp blade.
I remember the many threads here about shop safety and proper thermal protection etc.
Fortunately I was able to extinguish her by simply turning the saw off.
Had I walked away from the running saw (this will take hours to cut with a slow speed and a sharp blade) my shop might have been filled with flames instead of smoke.

I'm gonna have to step up my understanding of wiring, and thermal protection on all my machines.
I hope you electrical gurus don't mind when I start asking pesky questions.


Daryl
MN

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David

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#2
Re: Where there smoke there is Fire

Glad it was only labor and a few dollars you lost. That cut would work most saws to death, especially mine!

David
 

terrywerm

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#3
Ouch!! Glad to hear that resolution was easily achieved with a minimum of time and expense.
 

jpfabricator

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#4
Mabe you could do a knowledge swap. Like how many fire extinguishers, and where to put them to be code compliant, in exchange for the electrical knowledge.
Glad you didnt have to call your fellow firemen to come douse the shop. (You probably would never live that down!)
Jake Parker
 

DMS

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#5
Not the first time I have heard of bandsaw motors catching fire; whenever I have a long cut, I am always conscious of it and stay within earshot, never leaving the immediate viscinity for more than a few minutes. I am guessing it was a combination of the heavy, long load, and the age of the motor. I think the failure mode is the insulation on the motor windings fail, then you get an arc, which starts the fire. Some newer motors have embedded temp sensors so you can de-rate, or shut down. You would need some sort of controller for that. Another option would be to just have a thermal switch clamped to the motor case. Only problem there is that the motor would start up again automatically after it cooled, which is probably not what you want...

The one saving grace about this situation is that there is not a lot of combustible material in the motor itself, so as long as you don't have the saw up against a wall, or draped with a cloth it should burn itself out. My saw is setup in an open area, several feet from the walls of the shop with nothing overhead.

If you find a solution to the overheat/shutdown issue, I would be interested in hearing about it. I do my best to play safe in the shop, but I know I could be safer.
 

jpfabricator

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#6
Would the thermal switch work if it was run through a magnetic switch? Once the switch lost power the mag switch opens leaving the circut open.
Just my. 2¢

Jake Parker
 

ray hampton

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#7
Would the thermal switch work if it was run through a magnetic switch? Once the switch lost power the mag switch opens leaving the circut open.
Just my. 2¢

Jake Parker
usual when a tool with a thermal switch open you will had to restart the tool don't you ?
 

JimDawson

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#8
In any 3 phase motor circuit (except in a VFD circuit), you should have the properly sized thermal overloads in the motor starter. This will sense excess current and trip out the contactor in some period of time, depending on the load condition. The higher the overload, the faster they will trip. Not many standard 3 phase motors have a built in thermal sensor. Those that do would have to be wired in series with the motor start circuit.

Just for those who are not familiar with 3 phase motors, and starter circuits. A 3 phase motor starter consists of two separate parts, the contactor (relay), and the overload relay. In newer IEC motor starters, both parts may be in one housing, unlike the older NEMA rated units. The overload relay has heaters in it that are sized for the specific motor it is connected to, some of the newer units have a small dial to set the proper motor current. When these heaters get too hot due to excessive current draw, they melt the low melting point (eutectic) alloy in the relay, and which allows the circuit to mechanically open. The relay has to cool off for a few minutes before the eutectic alloy becomes a solid again, thus allowing you to reset the overload relay. It is necessary to properly size the motor starter to the load for overload protection.

It is not a good idea to use that old 10HP motor starter you have on the shelf to run your 1/2 HP motor, unless you can find the correct heaters for it.
 

rdhem2

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#9
Remember Guys;
There are two types of thermal overload protection. The type that is embedded in the motor windings and actually senses the temperature of the motor and the electrical type that monitors current flow and shut down when too much current for too long of a period of time. Both need to be connected to a mechanical relay type device to operate effectivly.

OK, now for a little electrical control wisdom. Most thermals embedded in the motor its self are of the KLIXON type that once tripped must be reset manually via a push button on the motor its self. The ones that do AUTO reset are wired in series to the operating coil in a magnetic starter via a three wire control scheme (pushbutton). This three wire input is called a momentary circuit. An OFF/ON switch is called a two wire maintained circuit.

In a two wire control when the switch is closed the energy is transmitted to the coil of the control device is a steady/uninteruped way. Any device placed in series between the switch and coil will shut the circuit down. However if allowed to close again automaticly will restart the motor.

In a three wire control when the start pushbutton is pushed (momentary), the coil of the starter is energized and pulls in. The power to the coil is maintained via a maintaining circuit on the starter its self. Any device placed in series between the start pushbutton/maintaining circuit path and the coil will shut the starter down. The starter will not start again until the start button is operated.

Remember three key rules to motor control. There is only two ways to connect a device in a circuit, either series or in parallel. The switching device is either normally open or normally closed, and the switch is either open or closed in reality. Quite simple if you take it one step at a time.

Please also remember that these control devices are there not only for convience of operation but for personal safety and fire prevention.

Why aren't these devices on the equipment when I purchase it? MONEY!!!!!! If you are in compitition with the guy next door putting a product on the market. Would you include things that some law does not require you to supply? You will either cut your profits to nothing or be way over priced in comparison. Let them buy the equipment then find out they must spend more to safely operate it. Look at all the new mini lathes and mills these days, they all have starters and relays. Look at a 1970's vintage ATLAS lathe, no starters there because they were not required to provide this protection as they are today. Average guy says it does not come on the machine I don't need it to run, WRONG. Taper attachments and follower rests do not come with all lathes but that does not mean you don't need them.

I am getting way windy as usual but remember motor control, no matter how simple or complicated must be utilized for personal safety and fire prevention. Besides all the convience it provides. :thinking:
 

Uglydog

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#10
Yes, I've been losing sleep over this problem.
Perhaps I've seen to many fires with an electrical cause.

I decided that I had to do something.
After making some phone calls, purchasing new was not an affordable option.
Ended up at Tried and True in Fridley, MN. The owner didn't pretend to be an electrician.
However, based on his used electrical inventory which he had on hand, for 1/4 the price of new, set up with a 1.5hp Baldor 1phase with a Furnas magnetic switch and an amperage matched thermal.
He didn't have any used on/off switches.
Additionally, he cautioned me to carefully examine my wire gauge and existing switches.

When I disassembled and examined the existing switches I was surprised to find that the auto-off switches that were on the saw when I got her, were rated for 120volt 1/3hp. Arrgh.

I've taken those switches out of the mix and picked up a $6 220volt on/off toggle rated for a 1.5hp from the local True Value.
Does anybody know if this will work and be "safe"?
Perhaps you will need more data in order to advise me.

While it will take a while I'm planning to make all of my machines thermally protected.


Daryl
MN
 

JimDawson

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#11
Yes, it will be safe, The mag switch is doing the heavy lifting, the toggle switches are switching the coil in the mag switch. The coil draws maybe 1/10 amp or so, almost nothing relative to the rating of the switch.

If you were using a 240 Volt, 1.5 HP switch, and trying to run a 120V, 1.5 HP motor directly with it, then that would not be safe, because the current draw of the motor would be twice the current at 240V.
 

Ebel440

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#12
I may be a little off topic but I have seem one of the 4x6 saws get the blade jammed and kept running with the motor rubbing the belt until it's smoking and melting. It happened because the motor tensioner vibrated loose. I'm unsure if it would start a fire but it may be able to. It's another reason not to leave it cutting unattended.
 

ray hampton

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#13
I may be a little off topic but I have seem one of the 4x6 saws get the blade jammed and kept running with the motor rubbing the belt until it's smoking and melting. It happened because the motor tensioner vibrated loose. I'm unsure if it would start a fire but it may be able to. It's another reason not to leave it cutting unattended.
I saw this loose belt belt too and the belt or pulley will get hot enough to start a fire IF YOU touch one or the other with your skin as the fuel
 
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