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Delta 46-250 (LA200) midi-lathe powered by variable speed treadmill motor?

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Forum topic by BobBlarney posted 04-12-2016 08:08 PM 3511 views 2 times favorited 53 replies Add to Favorites Watch
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BobBlarney

46 posts in 736 days


04-12-2016 08:08 PM

Topic tags/keywords: delta 46-250 lathe la200 lathe polybelt microgroove pulley treadmill variable speed motor

Hello,

I’ve a chassis from a Weslo treadmill (formerly used as a clothes rack). It has a variable speed (0-5600rpm max.) 2HP permanent magnet DC motor. I had intended to convert the chassis into a widebody sander, with a 3-4” drum turned on my lathe.

When I disassembled the chassis I noticed that it has a micro-groove pulley/belt drive similar to the drive on the lathe. It would be very nice to eliminate belt pulley changes, as well as have variable speed. It so happens that the belt from the lathe fits the treadmill pulleys, but the treadmill pulleys have 9 grooves instead of 3 grooves. (The treadmill belt uses 8 of the 9 grooves, btw.)

So, my questions are:

1. Is the DC motor suitable for driving the lathe? As I recall, DC motors develop maximum torque when stalled, and minimal torque at maximum speed. I don’t anticipate running the lathe > ~3800 RPM (spindle speed).

2. Is a 3-groove belt sufficient to handle the power? When properly aligned and tensioned, I don’t think that the 3-groove belt would jump off the 9-groove pulley, but is that a reasonable assumption?

-- Curator, Museum of Unfinished Projects


53 replies so far

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Rick M

8908 posts in 1981 days


#1 posted 04-12-2016 11:38 PM

Yes, and I don’t know.

I use a treadmill motor but mine uses a v-belt. Many people switch the flat belt pulley to a V, I’m told they just screw on and if you run the motor in reverse it will come right off.

And if you have a separate PWM (MC60) you can ditch most of the electronics.

-- http://thewoodknack.blogspot.com/

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BobBlarney

46 posts in 736 days


#2 posted 01-28-2017 12:27 AM

I’m a bit late getting back to this, but the treadmill DC motor conversion went well.

The Delta lathe pulleys and the treadmill motor pulley are poly-vee “J” series; it’s just that the lathe pulleys only have 3 grooves. So I ordered a new belt from www.Beltsforanything.com and they work together just fine. The flywheel on the motor pulley helps too.

At first I used the treadmill console for speed control, but it took up too much space, and so I did like others do and wired the motor controller board (MC-40 or -60) with a 5k potentiometer. , I found out something that I hadn’t seen on internet about the wiring. I wired in the treadmill safety pull-out microswitch between the pot and the “H” connection on the controller board. This allows me to stop the motor without changing the speed for restarting of the motor, although the time delay is still there. Also, I used an audio taper pot, and wired it so that a large fraction of the knob’s arc sets the low speed adjustment for finishing and sanding, and the smaller fraction of the arc for high speed. At the end of the session I unplug it all.

-- Curator, Museum of Unfinished Projects

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Rick M

8908 posts in 1981 days


#3 posted 01-28-2017 01:32 AM

Interesting, thanks for the update.

-- http://thewoodknack.blogspot.com/

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BobBlarney

46 posts in 736 days


#4 posted 01-31-2017 03:48 PM

Let me elaborate a bit on the wiring:

Line cord (Note 120VAC lethal voltage) :

White > AC2 lug on the controller board
Green > chassis ground

path for Black (Hot) > Switch > Fuse > Blue wire to motor’s thermal breaker(either one) > other Blue wire goes to the AC1 terminal lug on controller board. Some people don’t connect the thermal breaker, but this seems foolish. It’s in the ciricuit to prevent burning out the motor.

Motor (Note: 0 to ~100VDC potentially lethal voltage) :

1. Red wire goes to A+ terminal lug on the controller board.
2. Black wire connects to one of the black wires of the choke (it looks like a transformer) > other black wire of choke goes to A- terminal lug of the controller board.

Some people do not include the choke transformer, but that is not wise. It smooths out the PWM current going to the motor, thus prevent the ‘jerkiness’ (known as ‘cogging’ for DC motors).

Controller Board (0 to 12VDC—safe, but never push your luck):

Obtain a 5k ohm potentiometer (~$5). I used an audio taper for the reason mentioned above, but a linear is ok too.

1. With the potentiometer turned fully counterclockwise, connect one lead of an ohmmeter to the middle (‘wiper’) lug, and then determine which one of the other lugs reads ~5kohm resistance. This lug is wired to the H terminal lug of the controller board, and can be passed through a safety switch to stop the motor. I used the safety switch that came on the treadmill, and it should be placed in an easily accessible place on the lathe.

2. The middle lug of the potentiometer is connected to the W terminal lug on the controller board.

3. The third lug of the potentiometer is connected to the L terminal lug on the controller board.

I installed the potentiometer in a separate box in a convenient spot, and the safety switch can be put in the same box if there is enough room. I plugged the AC line cord into a separate receptacle that is controlled by a 120VAC switch for cutting off all power at the end of the day.

-- Curator, Museum of Unfinished Projects

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Rick M

8908 posts in 1981 days


#5 posted 01-31-2017 06:22 PM

Note that wiring a switch into the wiper may not work on other types of controllers (non-mc series). I had a different brand of controller on my last lathe and attaching switches to any of the pot wires caused unexpected behaviors but did not work to stop or start the lathe.

I might try an audio taper on my next lathe.

Had a discussion on another forum about the effect of different pot resistances but I didn’t fully understand. Apparently it changes the usable speed range. Some day I might do some experiments.

-- http://thewoodknack.blogspot.com/

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MrUnix

5066 posts in 1800 days


#6 posted 01-31-2017 07:04 PM

I did these a while back… here is a stock MC60 controller wiring diagram:

And here are two mods to add the run/stop/reset and forward/reverse features:

Locations on the board:

Everything needed can be found in the treadmill, except perhaps for the 10K pot… but many older treadmills with the dial speed control have that as well:

Cheers,
Brad

PS: Not all motors can run in reverse. Verify before attempting mod #2

-- Brad in FL - To be old and wise, you must first be young and stupid

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BobBlarney

46 posts in 736 days


#7 posted 01-31-2017 07:39 PM

yes, I should have repeated the model of controller – an MC-40 series.

About adjusting the speed range, I think there are two considerations. The first is safety and the second is convenience.

1. The motor that I have has a max rpm of ~5600 rpm, and so depending upon the pulley ratios it would be possible to turn a piece way too fast for safety. Some controller boards have adjustable pots on them that can be set to limit the maximum rpm. Another way to limit the max speed to would be to put a fixed resistor in series between the H terminal and the pot for this MC-40 .

2. So far as the convenience of making finer speed adjustments, I think the best way to do that would be to use a multi-turn 5k pot instead of a cheap single- or partial- turn pot. There are 3,5, and 10 turn pots available, and I think a 3-turn pot with a counter knob would be the most convenient. One could also play around with parallel resistance combinations of a pot with a fixed resistor, but i think a 3-turn pot with a counter knob would be simpler and thus better.

About placement of the safety switch, I did try installing it between the L and W terminals, but that had an unexpected result. With the switch closed and the pot at full resistance between H and W terminals, the motor started and ran, but when the switch was opened the motor did not stop, and in fact accelerated as I recall. This suggests to me that the control circuit is something like an R-C circuit and the pot acts as a voltage divider to charge a capacitor, and that without the L-W portion of the pot (i.e. opened switch) the voltage of the capacitor gradually rose to the full voltage (12VDC). Alternatively, by placing the switch in the H-W side, the voltage could not rise, and the capacitor discharged through the W-L side thus cutting off the motor.

-- Curator, Museum of Unfinished Projects

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BobBlarney

46 posts in 736 days


#8 posted 01-31-2017 07:52 PM

Oh, I’ve just seen your excellent diagrams, thanks! The MC-60 is functionally identical to my MC-40, and your modifications are too ( but substituting a 10k for 5k pot), and

In my scheme the safety switch does double duty, acting as your Run/Stop switch does. My setup does not reset the speed to 0rpm – the motor will return to the speed set before the shutdown. Also, although my modification looks the same as yours, this did not eliminate the starting delay. But, this does not bother me in any way – I’m not in a race or speed demo! In fact I like it because it gives me a moment to think before applying the tool to the wood.

However I did not mention the reversing DPDT switch on my setup for a particular reason. If the lathe is run in reverse, there is a distinct possibility of spinning the chuck & workpiece right off the lath, especially when decelerating! Most (all?) woodturning chucks do not have a setscrew to secure them on the spindle, and the spindles do not have flats for seating a setscrew. So, the only way that I can think of to secure the chuck (& workpiece) would be to snug up the tailstock with a live center to prevent a spinoff.

-- Curator, Museum of Unfinished Projects

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BobBlarney

46 posts in 736 days


#9 posted 01-31-2017 07:56 PM

Disregard this! I haven’t discovered how to delete this post.

-- Curator, Museum of Unfinished Projects

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MrUnix

5066 posts in 1800 days


#10 posted 01-31-2017 08:12 PM

By the way, although my modification looks the same as yours, this did not eliminate the starting delay.

The only thing that switch does is allow you to start/stop the motor without having to crank the speed down all the way first (‘reset’ position). I have not noticed any startup delay on mine either way. Also, if you upgrade to an MC-80, you can get speed control feedback to maintain a constant speed, even under load. It incorporates a speed sense circuit based on a hall effect sensor that provides feedback to the PWM circuit. Newer MC controllers (like the MC-2100) require you to provide the PWM circuit yourself as they don’t incorporate one on-board like the older ones do, so you can build it however you like.

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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BobBlarney

46 posts in 736 days


#11 posted 01-31-2017 08:22 PM

Thanks for the info!

Here’s a pic of the safety switch that attaches to my clothes (a good thing because I would probably lose it otherwise!)

-- Curator, Museum of Unfinished Projects

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Rick M

8908 posts in 1981 days


#12 posted 01-31-2017 09:28 PM

I have to admit Brad, your diagram is prettier than mine. Why did you use a 10k pot and what is the effect?

On my previous set up, power on was 0 rpm. A guy told me that changing the pot would change the startup rpm to something >0, so basically it would spin on startup. As I understand, it basically takes some slack out of the pot. But I can’t remember if he told me go up or down in resistance. He said something about using a resistor to accomplish the same thing.

I have another diagram with a switch on the pot but haven’t published it because I haven’t tested it. I sold my GE motor + controller but still have a 2hp DC + mc60 that I might use on a grinder.

-- http://thewoodknack.blogspot.com/

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BobBlarney

46 posts in 736 days


#13 posted 01-31-2017 09:41 PM

I really don’t understand any need for ‘instant’ start at a set rpm. What does it accomplish? I don’t think I’ve ever suffered from the delay and gradual power ramp up, but I imagine that I sure could suffer from a full throttle start by some unforeseen action or inaction.

And I don’t think the ‘slack’ is in the pot. It’s in the design of the circuit itself.

-- Curator, Museum of Unfinished Projects

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MrUnix

5066 posts in 1800 days


#14 posted 01-31-2017 09:52 PM

I have to admit Brad, your diagram is prettier than mine. Why did you use a 10k pot and what is the effect?

That was what I was finding in the treadmills, so I just ran with it. Works just as well as a 5K one. Changing the pot won’t increase power up speed… H is +12v and L is ground, with the wiper (W) providing a voltage between those two. All the way one way and you provide a full 12v, the other way drops it to zero. If you increase the value of the pot much higher than 10K, all you reduce is the usable speed range on the pot… so that instead of going from zero to full blast through the entire turning radius, you would be limited to just a portion of that turning radius (ie: the speed change will occur faster through a diminished turning radius).

As for the ‘instant’ start – it doesn’t just jump up to speed instantly… there is a ramp up time.

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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Rick M

8908 posts in 1981 days


#15 posted 02-01-2017 12:12 AM



I really don t understand any need for instant start at a set rpm. What does it accomplish? I don t think I ve ever suffered from the delay and gradual power ramp up, but I imagine that I sure could suffer from a full throttle start by some unforeseen action or inaction.

And I don t think the slack is in the pot. It s in the design of the circuit itself.

- BobBlarney

I want to know the effect of different resistances because I’m a curious person that likes to learn and understand things. The value is in the knowledge whether it’s practical comes later. If you aren’t interested then don’t participate. But I’ve learned many things in my life where the advantage came later or at times not at all but I don’t regret learning any of it.

-- http://thewoodknack.blogspot.com/

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