lathe motor upgrade - or not?

[Lee Alkureishi]

Hi all,

I finally got around to working on the upgrade of my lathe's motor. I built a new stand to accommodate the motor hanging off the back, then butchered a treadmill to acquire the motor and controller. I'm now about 90% done, and thought I'd hook it up to make sure it all runs.

Well, it does run...

Problem is, the issue I'm trying to improve seems to be worse with the new motor. That is, I can stop the motor by applying heavy pressure to the workpiece e.g. with a paper towel or sandpaper.

I get a good range of speeds ranging from pretty slow to scary fast, and the problem seems to be worse at the low end. the whole range will be considerably slower once I receive my new drivebelt in the mail (a poly-v belt to use with the existing, smaller, pulley). Currently, I'm using a standard v belt on a groove filed into the flywheel, which is much larger than the headstock pulley (so my speeds are correspondingly faster).

I have a couple of questions for anyone that might be able to help:

- is this a known issue with using a DC motor, or should I just be looking for a bigger motor? This one is rated at 2.65HP (1.5HP continuous).

- is there anything I can do to improve it?

- if not, what kind of motor should I be on the lookout for? I'm assuming more horsepower would be the key? I thought that doubling what I have (currently 3/4HP Chinese motor) would be more than enough...

-does the controller play a part in this? I also noticed that the motor slows down momentarily as I apply pressure, before speeding back up - kind of like a "rubber band" effect - not ideal.

I haven't cut the connections for the old motor/Reeves drive yet, so I could just hook everything back up the way it was if needed.but, I wanted to see if there was anything else I could do before I go that route...

Thanks in advance, and sorry for the long post!

lee

[Mike Cruz]

Lee, one thing to check is whether you are actually stopping the motor, or if your belt is just slipping. On my PM90, I noticed that I could stop my spinning blank with a 2 hp motor. Scratching my head thinking "That ain't right!", I noticed that the belt was slipping...I wasn't stopping the motor. I got a better quality pulley for my motor and that problem has all but disappeared. My guess is that 1.5 hp is plenty for your lathe. If you get too large of a motor for it, you might do damage to the lathe one way or another because I guarantee you that that lathe wasn't built for a 2+ hp motor!

[Reed Gray]

I can't answer any specifics about the motor stuff, but just looking, the pulley on the motor looks huge! The large pulleys on my Robust (3 hp 3 phase motor) are maybe 4 1/2 inch diameter. That would make a big difference in torque.

robo hippy

[Mike Cruz]

And I agree with Reed, that if you are stopping your motor, it is likely because your motor's pulley is outrageously big. Your motor pulley ought to be a lot smaller than your head stock pulley...

[Dennis Ford]

+1 on using the smaller motor pulley when you get the new belt. The DC motor puts out full power at max speed, it should be capable of good torque at slower speeds but it is not a magic cure. Treadmill motors are rated to about 5000 rpm and your motor pulley is larger than the lathe pulley; so the lathe rpm would be something more than 5000 at max speed. If you are going to have only one pulley position, the motor pulley should be half as big as the lathe pulley. That would give you a max speed of about 2500. Ideally you would have two or more belt positions; one of them perhaps a 4 to 1 reduction for more torque.

[Lee Alkureishi]

Hi all, thanks for the replies.

It's not belt slippage - the motor actually slows and stops then takes a while to get back up to speed. I'm also hopeful that the smaller pulley will make a difference, but have to wait for it to be delivered!

Best,

Lee

[Reed Gray]

I don't know much about DC motors, well any motor for that matter, just tools that I use. I remember an old Nova that had a DC motor in it that was doing that slow start thing. They can be tuned up or programmed for more efficiency, but I have no idea how to do that. Might help to find a book/owners manual for the motor.

robo hippy

[Mike Cruz]

Come to think of it, since it is a motor that came from a tread mill, they kinda always have a soft start and stop... You wouldn't want to be on a treadmill that went from 0-60 immediately. So, if you are bogging down the motor, when it starts back up, it would likely be a soft start.

As we've already discussed and I think you well know, the problem likely lies in your pulley. With your pulley that big and pretty much the same size (or bigger) than your spindle pulley, you get high rpm, low torque. Switch that pulley to something small, and you'll reverse that and get lower rpm, higher torque. Do you know what your motor's rpms are? You probably ought to to figure out what size pulley you want. As someone suggested already, if that motor's rpms are in the 5000 range, you'd want something with a circumferance that is 1/2 of your spindle pulley to give you a top speed of about 2500 rpm. If your motor is a 3450 rpm motor, then to give yourself a top speed around 2500, you'd need a pulley on the motor that is about 3/4 the circumferance of your spindle pulley. IF your motor has 1725 rpms, you are S*$& out of luck because you want your high rpm to be at least if not over 1725 and therefore would need a pulley on your motor the same size as on your spindle. Whew... I can breathe now... pant, pant, pant... :D I think you have it covered with the new pulley. Just do the math and check your motor's rpms.

[Lee Alkureishi]

Mike, that's exactly what I was thinking. I don't know if there's an easy way to reprogram the controller - will look into it, but most likely I'll end up going for a cheap new controller from ebay - I think there were a few threads on here about good options for that. First, though, I need to make sure the torque is there before going to any more time or expense! Come on USPS, bring me my poly-V belt!

On a related note, there's been a slight development.... A new lathe fell into my lap today, courtesy of craigslist and another $50. I'm still working out the logistics, but I might end up putting the DC motor on this new lathe and keeping the central machinery 34706 as is... hmmm....

I'll post the details in a separate post!

Thanks again,

Lee

[Mike Cruz]

Lee, I have to admit that it is fun to pimp up lathes. But I want to warn you about pimping up a machine that might not really be worth pimping up. The HF lathe, while it can certainly do what it is meant for, may not be able to handle the upgrades. Likewise, you might be wasting your money in the sense that when (notice I didn't say IF, because someday you WILL want to upgrade your lathe) you go to sell it, people won't see/care about the upgrades....they'll see Harbor Frieght...and they really don't hold their value. I could tell you that the easy solution is to get a used 2 hp 3 phase motor from your local motor shop or Ebay for about $100, and get an FM-50 VFD (three phase converter) for $150, and your problems will be solved. But that would mean that you would be dumping $250 into that lathe and I think your money would be better spent elsewhere.

What kind of "other" lathe did you...aquire?

[Lee Alkureishi]

Hi Mike,

I totally agree with you. But, before I bought the 34706 I did some extensive reading about it and the universal feeling is it's one of the few worthwhile lathes from harbor freight. It's a clone of the Jet 1236, likely made from the same castings in the same factory - even down to the useless banjo extension. The only major difference is the underpowered motor.

Now, I realize the Jet is not exactly a heavyweight lathe either, but that's precisely why I'm going the cheap/experimental route with a treadmill motor and controller. I don't want to dump several hundred dollars into it, only to find that the headstock is going to rattle itself loose every few minutes! On the other hand, I don't mind spending the time doing it the way I am - I find the process of repurposing (both the lathe and the treadmill) both fun and rewarding.

My other lathe? It's an old Seneca Falls metal lathe, converted for woodturning. It's about 400 times sturdier that the HF lathe, which has me a little bit excited... I just got done with the other post (complete with a thousand questions)!

Lee

[Mike Cruz]

Yeah, even at being a clone of the 1236, not sure it is worth too much invested money... HOWEVER, the fun of it is priceless. Believe me, I'm right there with ya! In my case, the two machines that I chose to pimp out were: First...a Powermatic 90 lathe (weighs 700 lbs) with risers, a 2 hp motor, VFD, tachometer, etc, etc. My first lathe was an old Delta/Rockwell 12" lathe that I cleaned up and boosted to a whopping 1 hp. I trashed the two pine boards that made up the spanners between the cast iron legs. I thought for an old girl, she looked mighty nice. Bought her for $200, sold her for $225. I knew this lathe couldn't stand any real upgrades, and the ones I did, didn't get me any return. The PM90, though...IF I ever sold it, would fetch more than I have in her; The second machine was a Delta/Rockwell 28-350 20" band saw that I not only restored paint wise, but I added a 3 hp motor, Carter guides, etc, etc. If I were to sell her, I would get what I have in her...maybe a little more. But at least she wouldn't be a loss.

Oh yeah, I did pimp out a Ridgid Band Saw, and had well over $550 if not $600 in her... Got maybe $400 for her.

The point, the old iron heavy beasts with a reputable name are worth it. The smaller hobbyist type stuff simply isn't...from a money standpoint. The FUN is priceless and if nothing else is good practice for when you do it to a "real" machine.

Hey, Lee, have fun with it. Enjoy the ride. Tinker away. Just know that it is for your pleasure. Don't expect anyone that might buy it to appreciate what you've done.

Now, I've gotta go. I need to go check out your other thread....!

[neil mackay]

I had a similar lathe several years ago and did a motor upgrade to 3 phase 1hp. What I found was I should have gone for 2hp+ as I used an inverter and in doing so you will lose power or torque with the use of an inverter.I looked at DC but could not find a motor with enough power and in my price range, hence 3phase AC.

It looks like your motor lacks power and your driving pulley is too big, ideally your driver should be smaller than the driven this willgive you a good mechanical advantage on a small motor. Other wise you need a lot more power to a two step pulley set up for high and low. Most of the commercially made a lathes have a large hp capacity 2-3hp in general.

sorry about the pics but I moved the lathe on a few year ago and have no further access

[Jerry Marcantel]

I started with a treadmill motor and controller a couple years ago. It was 2 hp, with a 2" pulley. I made my own 2/ 4" pulley for the spindle and while the controller worked, I had plenty of power from 20 up to 1605 rpm at all times. I eventually burned out the control keyboad and tried other ways of making things work with the DC motor. I finally broke down and got a 2 hp 3 phase motor and vfd.
What I saw in your pictures was your drive pulley should be a lot smaller, and your motor is pulling over 21 amps. That would be my concern as you would be paying more in electricity bills instead of buying new tools........... Jerry