Shopsmith Forums

I'm am largely out of action again, this time because of a spinal stenosis. So I have time on my hands and I started looking into how DC motors from treadmills have been used on various machines, many lathes especially. I saw a Youtube about a guy who put some kind of DC motor in a Shopsmith, and it appeared to completely replace the original motor and mechanical speed controller. There weren't many details though.

Read on if this subject interests you. I'll provide a summary of my thoughts and if anyone is interested I'll flesh it out.

So, replacing the motor in a Shopsmith headstock with a treadmill motor. It would need an adapter/coupler to provide a 5/8" shaft for the fan sheave and spring. The motor would be a little smaller than Shopsmith motors, but probably wouldn't leave enough room for a variable DC power supply in the motor area, and that supply would produce a lot of excess heat. I think the power supply and motor controller should be in an external control panel box connected to the headstock where the power switch is. The control panel would have an on/off switch, forward/reverse switch, spindle RPM display, and a dial control for the motor speed, maybe a motor RPM display.

So what does that create? The DC motor has a top speed in excess of 6000RPM at full power. With the Shopsmith speed controller at the fasted setting the spindle speed could be over 9000RPM. However, when the motor is running at full speed the slowest speed could be higher than 1300RPM. To get slower the motor has to be slowed down, that's what the dial control for the motor speed is for. The motor can slow down a lot, to 60RPM or less. The catch is that the motor is slowed by reducing power to it. There are practical limits to how slow the spindle can get and still produce useful torgue.

These motors are typically rated at 2.5HP. Might as well throw that number out the window. When loaded it might produce half that, or 1.25HP which is still better than the Shopsmith 1 1/8. The motors usually have a large flywheel that improves their performance characteristics, and the Shopsmith speed changer improves torque at lower speeds. Reducing voltage reduces motor speed and power together. At half speed you might only have performance comparable to a 3/4HP motor. Half motor speed is something over 3000 RPM, very similar to the standard AC motors, and the power available in the oldest Shopsmiths. I use a Greenie for years and it's 3/4 HP motor was just fine in most cases. At half motor speed, Slow on the speed dial will be around the same as the standard Shopsmith. You can keep reducing motor speed and spindle speed down to the point where you have no effective power left.

Ok then, why?
1. A treadmill motor and controller is nearly free. Depending on some details, actually free.
B. Installed in a headstock as I suggest it will increase max spindle RPM to over 9000. Within some range of spindle speed and loading it would outperform a 1 1/8 HP motor.
III. It can also slow spindle speed down to less than 100 RPM, albeit with a corresponding loss of power.
𐤃. The direction of rotation can be reversed.

This does interest me, but there are a lot of projects that need doing first. Perhaps next year when i semi-retire.

There is group on Facebook that focuses on this exact subject that you may find of interest.
https://www.facebook.com/groups/shopsmithdigital/about

I've managed to avoid Facebook so far, and much to my disappointment they aren't even close to collapsing the way their predecessors did. I may have to admit defeat, give up a another piece of my soul, and join the crowd.

My recent problem finally gave me the time to look at these DC motor conversions and the many questions I had previously were easy to answer. If I join Facebook and looked there I'd probably find even more useful information. The main problem with the simple DC motor installations is the simple voltage based speed control for the motors. There may be ways to maintain higher torque from the motors at lower speeds. This is most important for the low end of the speed range. Increasing spindle speed over 9000 RPM at full power is competitive with a PowerPro but in fact there isn't that much need for that kind of high speed apart from routing. At the low end the torque can be very important for operations like drilling with Forstner bits, turning pieces with a wide diameter, and in my case I'm interested in working metal which needs low speeds for milling and turning.

Anyway, my interest is nothing but interest now, I'm way behind on so many things and I doubt even a year from now I could find enough time to do anything like this even if I'm back on my feet and doing things soon. But for the time being it is theoretically interesting.

Going further with this requires looking into more complicated means of controlling motor speed. I'm looking at PWM (Pulse Width Modification) controllers intended to do this but I have a new question to resolve there, why are the available units so limited in power? These motors are likely to consume the 1800 watts available from a common 120V AC outlet converted to something around 120V DC, it is rectified AC passed through a choke, so averaging something under 120 volts. The common controllers operate at lower voltages, or when they can tolerate higher voltages then less than the potential 15 amps of current consumptions. Basic circuit designs for PWM controllers are common, relying on a MOSFET for switching, and I know as current and voltage requirements increase it is more difficult to implement the simple designs. My electronics background is insufficient to customize such a circuit, I'm just a digital logic guy, this kind of stuff is beyond my experience.

I would never think of trying to convert a shopsmith to a metal lathe. if you have spent any time on a metal lathe you will soon find out the shopsmith is not near strong enough for the forces put into the tool holder and that is just a start as to why i would not do it.

A 120v full wave rectifier will create voltage close to 170v.

Pulse Width Modulation requires rapid switching response at high currents and typically higher voltages.

Components to do that are $$$$$.

I do wonder if these DC motor conversions are practical. I read the FB Shopsmith DC motor conversion group with great interest a year or two ago and there was some great information there. However, I am not sure if these are one-off demonstrations meant to grab online attention, or if the owners are using them to do actual work on a regular basis, e.g. how well do they work in tablesaw mode, lathe operation, drilling or powering SPT's? I don't think I have seen one yet that fits nicely inside the headstock, with the cover on. Also as has been pointed out, perhaps the motor controllers don't work adequately across the entire speed range. IF you have to build your own motor controllers, by the time you buy all the components and print your own PCB you'll be out at least a couple hundred bucks easy (likely even more). Even if you get a treadmill motor for free, is it worth it to spend this much on a science project? Guess it depends on your motivations and what you are looking to get out of it. I contemplated giving it a go before, i.e. to make my own PowerPro on the cheap, but in the end decided it wasn't worth my time especially when you can buy the DVR motor and controller off Amazon for around $500.

The conversion uses the PWM controller board out of the donor treadmill. This is a YouTube video by Norman Harrison who an admin on the FB group,
He has a newer version that has a smaller control panel, but that video isn't on YouTube.

https://www.youtube.com/watch?v=QbrjPOZqHPI

rpd wrote: ↑Wed Aug 25, 2021 12:36 pm The conversion uses the PWM controller board out of the donor treadmill. This is a YouTube video by Norman Harrison who an admin on the FB group,
He has a newer version that has a smaller control panel, but that video isn't on YouTube.

https://www.youtube.com/watch?v=QbrjPOZqHPI

I agree, often these conversions reuse the existing PWM controller that came with the treadmill. Ed was asking about making his own PWM controller which is what I was responding to before. I have seen this guy from the YouTube video on the FB group before, but my question is whether he is using it to actually make sawdust with it? Or is he only using it to demonstrate his ability to put a treadmill motor in the existing headstock. Has anyone confirmed that using one of these is better than the stock headstock? Is it comparable to a PowerPro? I would be curious to find out if anyone has done one of these treadmill DC motor conversions and showed it ripping through some 8/4 hardwood. It still seems like kind of a science project for science project sake to me so far...

So you guys have looked at this. I'm tempted to join Facebook and see what is over there.

It's an interesting concept but there are just more questions around every corner. The link from Ron up above is something I've seen before. There isn't much detail there on how he did it. How did he mount the motor and mate it to the shaft for the lower sheave? And while he has an impressive looking control display, it's driven by software, and a complication that's not really necessary for me. I believe I've seen a video where he has the reduced the size of the controller but even less detail was shown there.

So far I'm not getting a good idea of how effective these motors are in a Shopsmith headstock. I've seen videos of several metal lathe conversions that seemed to satisfy their creators, but I I think they were replacing smaller motors. How do these motors perform under full load? Are there overheating problems? There may be a lot of specific applications that could do fine with a highly affordable DC motor, but the Shopsmith is not a simple application, it has to perform in numerous modes with varying conditions.