Trying To Determine Potentiometer Needed For Grizzly G8691 Lathe

[jhill84]

Okay. Just got off the phone with Grizzly (the manufacturer) about this lathe. Here's what I know so far.

The lathe was given to my shop (a band instrument repair shop). I do not know anything about the history other than there was sticker on the top of the lathe suggesting that the only thing wrong with it was that it needed a new switch. (Not the case.)

My suspicions are that the original owner probably had a near death experience using the tool and managed to damage the internals somehow, but that is purely speculation.

SO...

My problem at this point is that I need replace a potentiometer that I have no information for. Quite literally, what would be the housing of the back part of the potentiometer is gone, so I have no idea what the specs are for the part. I spent an hour on the phone with the manufacturer while their technical people looked for information on the unit, but they were unable to come up with enough information to offer a solution they felt good about. I was told that the original manufacturer of the pot went bankrupt.

At any rate, the wires and electronics had been dismantled and left in shambles when it came to me. Here are some photos of my reconstruction of what needs to be where. Grizzly did send me a very poor quality wiring diagram, but again it has no actual specs on it.

Close up of the motor:


Bird's eye view of everything. To the left is what's left of the pot. The pot was mounted in the faceplate next to on/off switch, and the fuse holder you see was mounted in the faceplate also. This is just laid out so I could figure out where it all was supposed to go.

Close up of circuit board:


Close up of damaged fuse holder which had the wrong fuse installed - Fuse required is a 10A 250V.


Wires from circuit board to pot:


Remains of pot:


Under side:


And here's a spec sheet and wiring diagram (a poor one) from the manufacturer.


That's all I have on this. Can this be determined? I am not an experienced electronics person, but I'm not totally ignorant either. If someone has sites or suggestions on where to get parts, etc. I'm wide open to any advice. Thanks to everyone who takes a look at this.

Jeremy

 

[Bluejets]

Appears there may be enough left of the damaged pot to get some sort of reading of the value.
It will be a linear or curve B pot, and perhaps you can get a resistance reading off the 2 outer pins of what is remaining. If not there then carefully move the probes onto the exposed carbon track until you get some type of reading.
I'd suggest you start with the ohm meter set fairly high, maybe 20K range and if a reading is obtained, scale the reading down until you get someting definite.
I suspect it should be somewhere in the range of 5K ohm.
The rest of the unit looks intact so maybe you'll get lucky.
Just don't do testing with mains supply with all that stuff laid out, could be a dangerous practice.

Edit:- the outer metal casing of the pot would have had the value stamped on it, no chance it is still being around I suppose??

 

[Arouse1973]

Found this site. I know they are in the UK but it might be worth sending them an email.

http://www.amadeal.co.uk/acatalog/Potentiometer-AMA_SP_CJ18_157.html#SID=189

Cheers
Adam

 

[tedstruk]

It looks to me like there is a High speed and Low speed and thats all. No adjustment for RPM, just high and low.... a standard switch is involved with no rheostat or potentiometer... the POT may have been added later in an attempt to fix a broken switch???.

Moderator note: tedstruck should not be considered an expert. In many cases you would be best advised to take almost any route other than what he suggests.

 

[Bluejets]

Broken part shown is a pot.
Diagram shows variable speed switch.
Front panel shows variable control.
3 out of 3 I'd say it's a pot.

 

[Minder]

10K Linear Pot.
M.

 

[Alec_t]

At the centre of that 'pot' there seems to be an operating tag for what could be a rotary switch. Can you post a pic of the other side of the 'pot' to verify ?

 

[Bluejets]

Other side already shown above. Old pots had this tag as centre pickup.

 

[Alec_t]

Other side already shown above.

So tiz. The image had scrolled off my screen

 

[jhill84]

Thanks so much gentlemen. I got everything wired back up with the exception of the pot and gave her a whirl after confirming I had continuity in the motor and replacing the damaged fuse holder. She fired right up, so now I'm down to finding a replacement pot.

My next question is: What are the possible consequences of not having the correct pot in here?

@Bluejets unfortunately the carbon ring you were referring to is also busted. I just laid it on there in the pictures, but it's actually detached completely.

General thoughts seem to say 5k-10k, but I have literally no experience here on what linear means vs anything else. Is there any reason why getting a few and trying process of elimination would be harmful? Just a thought.

Thanks again humbly, this woodworker is not an electrician! Can't tell you all how much I appreciate the help.

 

[Alec_t]

unfortunately the carbon ring you were referring to is also busted.

You can still measure the resistance. Measure from end to end of the track (or from end to end of each arcuate chunk, if it's broken; then add the resistances).

 

[Minder]

They are not critical, 5k to 10k should work and are fairly common, linear as opposed to logarithmic type used for audio etc.
Roughly means that the linear type, the centre slider type increases in resistance in a linear fashion from one end to the other, e.g. a 10k pot would be 5k at centre position.
M.