DC conversion on lathe.

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Torch
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Re: DC conversion on lathe.

Post by Torch »

Adjust it so there is no IR comp.
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LX Kid
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Re: DC conversion on lathe.

Post by LX Kid »

I ordered a 5/8" x 1.75 sheave pulley and will enlarge the bore to 18mm when it arrives. I'm "thinking" the set screw will be strong enough without having to cut a keyway into the shaft. I will make a flat spot with a slight dimple to screw the set screw down into. I removed the flywheel very easily spinning it off it's left handed threads. I've looked all over the web for a left handed nut without any luck at finding one. It's a 1/2"x13TPI thread.

I know the flywheel serves also as a fan and inertia energy for the treadmill but do I really need it? Could just add a 3" little plastic fan on the brush end to do the cooling.
daGrouch
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Re: DC conversion on lathe.

Post by daGrouch »

Yes you can if there's enough shaft to mount it. Since you now have a brush motor you really want to keep grit out so tape or glue a single layer of shop rag over the inlet side of the motor to act as a filter.

The motor you have is often called a "beer can" motor as they are narrow and are usually over rated in both HP and current draw (but should work fine) so don't be too afraid of overloading a controller. Mine never came close to the rated draw under heavy loads.

The benefits of a better controller like KB are more options like instant start and speed stability. My first controller, from a treadmill, was an MC 30/40 and I had to start from 0 and work the knob up to speed. The MC-60 is better and I think the resistor to pull out was to get rid of either the 'soft start' ramp or enable it to start at knob positions other than zero.

I use KB-212G somethingorother controllers and they are pretty sweet for an SCR type. Built in braking, E-stop, reversible, instant or ramped start and stop, 110v or 220v, etc about $50 on ebay. I have a 3-in1 machine and the instant stop and reverse is great for power threading using taps in the mill head. I also ran that size motor (90vdc) on 220v in (180vdc) mode with no ill effects or overheating.

Keeping the flywheel can smooth out the controller pulses mechanically and give a better finish, just turn the ribbed belt portion down smooth to a size you can slip a v-belt sheave over. Also, if you run SCR (no experience with PWM) keep the big motor choke inline to further reduce the choppiness of the controller pulses at the expense of a little laggyness changing speeds.

Really fine speed control isn't really helpful as you'll find a few speeds you like where the harmonics of the motor, frame, belt etc. are the lowest. If you want to try fine control on the cheap just put a smaller pot in series with the 5k. The 5k will be the coarse adjustment and a 1K can be the fine.

Two issues with grounding out the controller that I can think of was that high voltage was carried on the heat sinks of the SCRs so as long as those don't touch ground you're fine and the other is the speed control pot should be mounted in a plastic panel or insert to keep the metal body and stem from grounding. Some pots have the wiper isolated and won't have that problem. Check it with an ohm meter.

Either way you'll really like the ability to change speed on the fly to reduce chatter or get your tool bit in the sweet spot.
Ed
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LX Kid
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Re: DC conversion on lathe.

Post by LX Kid »

daGrouch wrote:
Keeping the flywheel can smooth out the controller pulses mechanically and give a better finish, just turn the ribbed belt portion down smooth to a size you can slip a v-belt sheave over. Also, if you run SCR (no experience with PWM) keep the big motor choke inline to further reduce the choppiness of the controller pulses at the expense of a little laggyness changing speeds.

Either way you'll really like the ability to change speed on the fly to reduce chatter or get your tool bit in the sweet spot.
That's a good idea with the sheave pulley. I'd have to shave it down to 43/64 or about 17mm. I could even take it down a little more to fit my pulled instead of drilling the pulley bore, which was my original plan. I had planned on cutting off the ribbed portion all the way off but your suggestion makes more sense. Thanks

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LX Kid
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Re: DC conversion on lathe.

Post by LX Kid »

SteveHGraham wrote:I don't know the purpose of the resistor. I don't remember. I do know that before I clipped it, the motor was either on or off, with no adjustment possible. I didn't really need 5000 RPM.
I bought a couple 5k and 10k pots to bench test the components before I do any mods. Do know the physical location of the resistor RPS-1 your suggesting that I cut? I know the R stands for resistor but what does the PS mean? Thanks
redneckalbertan
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Re: DC conversion on lathe.

Post by redneckalbertan »

PS-1 will probably be the location/name of the resistor on the board.
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SteveHGraham
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Re: DC conversion on lathe.

Post by SteveHGraham »

It actually says "RPS-1" on the board, and my resistor had a big glob of solder on it. Apparently they set it up so it was easy to disconnect. It was already clipped, and all I had to do was suck the solder off of it.
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LX Kid
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Re: DC conversion on lathe.

Post by LX Kid »

"IF" I were to cut a pulley groove in the flywheel, newbie alert, should I cut the groove twice at 16 degrees on right and left? I guess a single cut would be difficult because it is steel rather than aluminum. I saw where a guy in Australia cut one with a parting tool "but" was cut into aluminum.
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Harold_V
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Re: DC conversion on lathe.

Post by Harold_V »

"ANY" plunge cut, where the chip is forced towards the center of the tool from each side, will be difficult, and the chip tends to stack up at the tip, ofter resulting in tip failure. That's one of the reasons why one uses the recommended 29½° compound setting when single point generating threads.

That being said, if you plunge slowly, keeping the cut well oiled, you can achieve the goal successfully. Use a dial indicator to establish the proper spacing. Just don't get in a hurry to move metal, especially when started each groove. That's generally when you'll damage the tip, all due to chip flow interference. And, if you'd like to guild the lily, rough all of the grooves, leaving a few thou for cleanup---sharpen the tool and go back, recutting each groove to size.

Harold
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