Powermatic 3520b #1: Remote controller modification

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Blog entry by PASs posted 12-07-2013 05:21 AM 4306 reads 2 times favorited 7 comments Add to Favorites Watch
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Powermatic 3520b Motor Controls Rewire

I got my Powermatic a couple years ago.
As I was researching its features I came across an article about removing the entire motor controller panel and putting it into a switchbox.
I like that Idea much better than the factory on/off remote option.

After a year and a half I finally got around to doing the job.
Since a picture is worth a thousand words I decided to photo-archive the job.
Also it’s easier than writing down which wire goes where.
The whole job took about 3 1/2 hours, but I broke a wire connection and that added 45 minutes to the job.

Photo 1 – First I took the controller panel off and photographed the general layout and specifically the wiring layout.

Photo 2 – I found it interesting that the speed control potentiometer (a.k.a. pot) was wire-nutted. There are 5 wires that connect the controller panel to the motor controller:

- A blue wire to the on/off switch

- A black wire to the Fwd/Rev switch

- A white wire to the Fwd/Rev switch

- A green wire to the speed control (pot) terminal 2

- A yellow wire to the speed control (pot) terminal 3

Photo 3 – My intent was to make every connection a spade-type. The blue, black, and white wires were already spade connectors, so there would be no work required to convert them. Because the wires soldered to the pot were both white I decided to make them Male/Female – Female/Male connectors so that they could not be connected backwards.
I removed the wire nuts to the pot and replaced them with the MF-FM connectors. Then I unplugged the remaining wires. That was it for the evening. Next day…hardware store.

Photo 4 – Next morning I went to HD. My goal was to put the controller in a “E” type conduit body (one hole on the end) but I ended up with an “LL” (one hole on the end, one on the side).
The 3/4” was the size that would take the depth of the switches, allow me to screw the controller plate directly to the body without any modifications, and put a threaded compression entrance into the body.
I got a 3/4” slip to 1/2” female threaded adapter and a 1/2” compression entrance for the remote cord. I had to get the cord a the local trailer supply store. It is 6 conductor trailer wire, 14 gauge stranded in a full jacket and 1/2” OD. I got 12 feet, but should have gotten 15 because it’s a long lathe and the routing of the wiring took up a couple of feet.

Photos 5 and 6 – I took the controller to HD with me to make sure it would fit. Due to the off-center location of the on/off switch, and my desire to run the cable out the end of the box the controller would only fit with the on/off switch next to the hole on the end. Here’s a dry fit.

Photo 7 – Threaded adapter glued in place.

Photo 8 – Outer jacket stripped off. Six wires, but I only need 5, so the brown one is the odd man out. Fortunately except for a red wire instead of a white wire, all the colors are exact matches. So the red will hook up to the white.

Photo 9 – Cable run through the compression entrance, screwed into the body and connectors installed for connection to the controller panel.

Photo 10 – DISASTER. The #3 wire broke off at the pot. It’s not a robust setup and the wiggling while working the wire was too much for it. I saw extensive delays getting the lathe running, excessive expense to order a new pot, and general unrest from the chief cook and bottle-washer that I broke my big toy. The day was looking glum. So I figured I’d try to fix it. (I have played with electronics since 1970, spent 20 years playing with electronics in the Navy, have been to soldering school, was an experienced micro welder, so what was to loose.)

Photo 11 – I broke out the dremel. The bearing on the shaft is worn and I didn’t want to bounce the bit on the work so I broke out the flex shaft I’ve never used, had to figure out how to screw it all together, then got out one of the 500 or so dental burrs I got for a dollar about 25 years ago (and have almost never used) and chucked it into the handle. It’s a teeninsy little thing with about 20 teeth on it, reverse conic section. Why the need to dremel….?

Photo 12 – …because the lead broke off right at the body, and the leads are epoxy covered. So the dremel was perfect for grinding down to the lead.

Photo 13 – Out came the tools of the trade…well an old soldering iron and supplies from decades ago except for a new can of flux.

Photo 14 – The broken off piece of the pot lead on the lead wire.

Photo 15 – Off with the old solder and broken lead, ready to attach to the stub.

Photo 16 – First time, pried the stub up and soldered the lead wire back. Quick and easy. Too easy, I forgot the leads are on the same side as the shaft, which passes through the metal plate on the controller panel. So sticking up like that isn’t a good thing. Drat, will have to unsolder the lead, bend the stub back down (bending back and forth is never a good thing to do), and solder from the top.

Photo 17 – Tab bent back down (whew) and soldered back on.

Photo 18 – Next problem, the epoxy, and a lock washer, were the only insulation between the tabs and leads on the pot and the controller panel. Since I had removed the epoxy and soldered a wire into the gap I would have to insulate. Fortunately, the control panel is low voltage and I have several square feet of EPDM (plastic rubber) sheeting so I cut off a small piece and punched a hole for the shaft. I noticed when I took the pot off that there was a locator pin on the pot, but no corresponding hole in the control panel. Since the EPDM was thinner than the lock washer I drilled a locator hole half way through the panel.

Photo 19 – Pot back in position. Locator pin in locator hole. EPDM doing its insulating thing. Ready to resume plugging wires together and stuffing everything into the conduit body.

Photo 20 – Wiring stuffed into conduit body. Control panel screwed on. Ready to plug in to the lathe wiring.

Photo 21 – The remote cable was JUST small enough to push through the controller wiring entrance on the back side of the lathe. The other two cables were quite loose in the hole so I was not concerned about crushing or crimping anything.

Photo 22 – Wire run out the front of the headstock. The wire is run under the motor shaft with plenty of clearance, but none of the pictures of that turned out good enough to post. The other wires from the controller also run under the motor shaft, so I wasn’t worried about abrasion.

Photo 23 – Spade connectors attached and everything plugged together. Note: I mentioned earlier that I did a MFFM for the pot wires. You might wonder why I bothered when there was going to be a 12 foot cable between the original connections. If I decide later to remove the remote feature I can plug everything back together and still maintain an idiot-proof (me-proof) connection.

Photo 24 – Everything stuffed into the headstock. You can see the black cable running down and under the motor shaft and can just make out the shaft itself behind the yellow wire. There is a 1 1/2” to 2” clearance between the wires and the shafts and pulleys.

Photo 25 – Temporary cover in place. (Side note: That’s a piece of MDF flooring. I LOVE that stuff. It’s like formica coated on both sides, tough as all get out. My main workbench is covered in it, my table saw inserts are made out of it. I’ll have to blog about it later.)

Photo 26 – Having the remote is one thing. But being able to slap it anywhere on the lathe is better. So I epoxied 4 rare-earth magnets to the bottom. I did file the bottom a little to rough it up and give the epoxy something to bite into. You can see how much the controller plate hangs over the conduit body. I like that ‘cause there’s enough room to put a little RTV around it to seal out the dust. But the inside of the headstock wasn’t exactly a clean room, so I’m not too worried about it anyway. And the big, gaping hole in the side will get a custom turned plug in some exotic hardwood.

Photo 27 – BAM. It sticks to the ways. I can pull the on/off switch with just one hand. Rare-earth magnets are the bomb.

Photo 28 – BAM. It sticks to the side of the bed. Not quite as strong a grip, but I can still pull the mushroom with just one hand.

Photo 29 – BAM. It sticks to the side of the tailstock. And yes, that’s a long extension and a short extension. I usually run the lath with the headstock just over the middle leg, but I moved them as far apart as I could for this photo.

Photo 30 – BAM. It sticks to the end of the lathe. Somewhere in the distance is the headstock.

Summary. This did exactly what I thought and hoped it would do, allow me to fully control the lathe from anywhere. Now I gotta get back to makin shavins.

-- Pete, "It isn't broken, you just aren't using it right."

7 comments so far

View stefang's profile


15881 posts in 3363 days

#1 posted 12-07-2013 09:30 AM

Looks like a good result and pretty handy too. Your lathe bed looks about a mile long!

-- Mike, an American living in Norway.

View nonickswood's profile


554 posts in 2416 days

#2 posted 12-07-2013 11:54 AM

Nice work Pete, with a Lathe bed that long, this is going to save a lot of running back and forth.
I will admit, I’m Envious!

-- Nick, Virginia,

View darthford's profile


610 posts in 1953 days

#3 posted 12-07-2013 03:44 PM

Dang that’s some lathe! I like modifying machines so good job. FYI sometimes wire nuts are used vs solder on purpose, something shorts out, wire gets hot and melts solder, hot wire pops loose touches the machine and pops you BANG! Just saying. ;-)

View PASs's profile


595 posts in 3127 days

#4 posted 12-08-2013 02:52 AM

Thanks Stefang…the bed is 98” between centers.
Nick, the nicest thing is being able to turn from the back side with full control available.
Darth, I have really enjoyed this lathe. And roger on the wire nuts vs solder, but the pigtails were soldered on to the pot. I like those crimp-on spade connectors.

-- Pete, "It isn't broken, you just aren't using it right."

View Roger's profile


20929 posts in 2833 days

#5 posted 12-10-2013 01:33 AM

Super nice job on the picture tutorial Pete. If that bag o money ever falls in my yard, I’ll buy me a beast of a lathe like you have. Is that last pic of you getting ready to turn a pen???? LOL….........jus kiddin my friend. I’ll thank you again, for your service, sir.

-- Roger from KY. Work/Play/Travel Safe. Keep your dust collector fed.

View oldmntn's profile


1 post in 849 days

#6 posted 02-26-2016 11:17 PM

Came across this post today when I was searching for Powermatic speed controller. I was in the final stages of making this same modification to my lathe when I, too, broke the tang on wire #3 to the pot. I tried your fix but managed to break the tang off again after grinding away the epoxy. My modification just got $85 more expensive!

View PASs's profile


595 posts in 3127 days

#7 posted 02-27-2016 04:27 AM

Ouch oldmntn. I was sweating bullets while I was working on my repair. It isn’t the most robust pot.

-- Pete, "It isn't broken, you just aren't using it right."

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