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LMS 8.5 x 20

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MAE

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#1
Anyone know if this machine can somehow be slowed down to lower than 100rpm?
 

higgite

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#2
Hi MAE,

I asked Chris at LMS if it could be done and he said not that he was aware of. I would like to slow mine down some for threading, but the more I practice, the more comfortable I'm getting with it.

"Mcripper" posted a mechanical mod he made to slow down a smaller Hi Torque lathe using an additional belt and some custom made pulleys and mounting brackets. He essentially added a "low" speed range. It's quite a project. Very impressive. http://www.hobby-machinist.com/show...own-mod-for-hitorque-lathe?highlight=hitorque

Let us know if you find an easier way.

Tom
 

JimDawson

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#3
Given that the machine has a BLDC motor, it should be capable of going down to about 1 RPM. This sounds like it is limited in the controller software. I would contact LMS and see if they can offer any advice.
 

MAE

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#4
Thanks guys. I don't know anything about controls but I wonder if you could just put a different speed pot on it.
 

MAE

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Tom

This is off topic but how accurate does yours thread fine pitches like 32 and higher.
 

JimDawson

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#6
Thanks guys. I don't know anything about controls but I wonder if you could just put a different speed pot on it.
I'll give you a qualified MAYBE. Let's say it currently has a 5K ohm pot, going to a 10K won't hurt it. Maybe it's worth a try. The problem may be that the analog signal from the pot is converted to digital in the controller, so once the voltage reaches a certain low point, the digital output the the BLDC controller just won't go below it's programmed low set point. In that case all that putting in a 10K pot would do is limit the range of the pot. I'm not sure if it's possible to do what you want without going into the firmware and reprogramming it.
 

MAE

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#7
I see. Thanks Jim.
 

higgite

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#8
MAE,
Sorry, I haven't tried anything finer than 20 tpi, yet. It did 20 just fine, though. I have no reason to think it won't do finer threads okay, too.

Jim,
I asked Chris, the owner of LMS, about slowing it down and he said he didn't know how to do it and had not heard of it being done.

Both,
Are you guys talking about changing an internal speed pot? The 8.5x20 doesn't have an external pot for controlling speed. It uses membrane buttons to change speed in 10rpm increments. As for 1 rpm, I'm sure you know that could present a motor cooling problem. I have wondered if that's why the minimum from the factory is 100 rpm, for prolonged threading sessions, but haven't found an answer.

Tom
 

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#9
Jim,
I asked Chris, the owner of LMS, about slowing it down and he said he didn't know how to do it and had not heard of it being done.

Both,
Are you guys talking about changing an internal speed pot? The 8.5x20 doesn't have an external pot for controlling speed. It uses membrane buttons to change speed in 10rpm increments. As for 1 rpm, I'm sure you know that could present a motor cooling problem. I have wondered if that's why the minimum from the factory is 100 rpm, for prolonged threading sessions, but haven't found an answer.

Tom
I didn't know it does not have an external pot. In that case, you are changing a counter in the controller with the keypad, thus the entire system is digital. In that case, the only option would be to make firmware changes. I have seen analog control of BLDC motors, but it is always converted to digital in the controller through an A/D converter.

As far as motor cooling, is that motor not cooled by a fixed speed fan driven by it's own small motor? All of ones I have seen are cooled that way, not dependent on motor RPM for cooling.
 

MAE

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#10
Well that stinks. I never noticed the speed control until you mentioned it. It really goes up by increments of ten? That's not mentioned anywhere in the specs. You figure that would be good to know.
 

higgite

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#11
Jim,
It does have a separate small fan which I assumed (I know, I know) was to cool the electronics. Thanks for the education. (I hate it when I find out I'm not as smart as I think I am... again.)

MAE,
I got used to the pushbutton speed control pretty quickly and think nothing of it now. Hold the up or down button down and it will accelerate/decelerate smoothly. Short presses will increment the speed up or down by 10 rpm. I like being able to stop this lathe and then restart at the previous speed, in either direction. Handy for threading. My 7x14 had a speed control pot that had to be returned to zero to restart the machine after stopping it for any reason.

Tom
 

MAE

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#12
Thanks Tom. Does this thing stop on a dime when you hit stop. Just curious if it will thread to a shoulder. How did it come out of the box? Any complaints?
 

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#13
MAE,

It stops very quickly, but I wouldn't try to time it to stop tight up against a shoulder. Maybe a thread or 2 short and run it up against the shoulder by hand. I usually cut a relief groove to stop the tool in. Mine came out of the box darn near ready to run. A light clean up with mineral spirits, lubed it up and ran it. I took the top cover off and cleaned off the internal gears and lubed them with some spray on lithium grease, similar to chain lube. I don't know if a "break-in" is recommended or not, but I ran mine at 300, 500, 1000 and 2000 rpm for 10 minutes at each speed before I put any load on it. I figured it couldn't hurt. The more I use it, the more I like it. Hope this helps.

Tom
 

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#14
I haven't worked with the smaller BLDC motors like this, most of my work is in the 10 to 30 KW range. So I'm learning a bit here also. The controller theory is still the same.

One thought did occur to me, if the BLDC controller and the keypad controller are separate entities, then there may be an analog signal going to the BLDC controller, and it MAY be possible to manipulate that signal externally. This would require breaking the connection between the controllers and inserting some electronics between them. This could be as simple as inserting a pot. One would have to sit down with an oscilloscope and take a look at the signal to know how to approach the task. It could be a step pulse stream, a PWM signal, or it could be an analog voltage.
 

higgite

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#15
I thought about that, too, Jim, but I'm afraid of releasing the magic smoke from the electronics and/or the motor. I'm a EE, but on the power side of the equation. They have written text books about what I don't know about electronics. I know that for a fact because I used some of them for door stops in college.

Tom
 

MAE

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#16
That helps a lot thanks guys.

Tom, how accurate is the machine? Do you know the spindle runout? Again sorry for all the questions. There's a few lathes I'm looking at in this price range and I want to make the best decision. Plus it doesn't seem like there's too many owners of this particular lathe.
 

wrmiller

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#17
I thought about that, too, Jim, but I'm afraid of releasing the magic smoke from the electronics and/or the motor. I'm a EE, but on the power side of the equation. They have written text books about what I don't know about electronics. I know that for a fact because I used some of them for door stops in college.

Tom
You could possibly cobble up a 'translation circuit' between the hall-effect's feedback and the controller, but this could likely cause more trouble than it's worth. :)

What about making a back-gear for it? Don't know if it's even feasible, just throwing it out there.
 

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#18
Could you install a hand crank at the back of the spindle?
 

higgite

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#20
Tom, how accurate is the machine? Do you know the spindle runout?
MAE, spindle runout on mine is .0006" in the center bore and .0005" on the register.


What about making a back-gear for it? Don't know if it's even feasible, just throwing it out there.
Bill, not sure about a backgear. But, did you check out the link I posted in message #2 above? That mod was done on a smaller machine than we're talking about, but offhand I don't see why it couldn't be done with a 8.5x20. I was impressed when I saw it.

Tom
 

MAE

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#21
Is this have an imperial or metric lead screws ?
 

wrmiller

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#22
Bill, not sure about a backgear. But, did you check out the link I posted in message #2 above? That mod was done on a smaller machine than we're talking about, but offhand I don't see why it couldn't be done with a 8.5x20. I was impressed when I saw it.

Tom
Yea, remember reading that one. I was considering it, but my lathe will get down to 50 so figured it wouldn't benefit me that much. Nice project though. Maybe you should consider it? As long as you are just slowing the spindle down, you won't affect your spindle to leadscrew ratios for threading. Sounds like a nice project. I'll watch! :D
 

higgite

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#23
MAE,
The main leadscrew is metric, 2mm pitch I think. But, I find it immaterial as the lathe doesn't have a threading dial. You leave the half nuts engaged to cut threads, same as cutting metric threads on a lathe with an inch leadscrew. Cross slide and compound slide leadscrews are 20tpi with "true inch" type dials graduated in .001" increments, one turn equals .050".

Here's a link to the owner's manual if you haven't found it already. It answered a lot of my questions and I called LMS and grilled them about the lathe and its features before I hit the purchase button. They were very helpful. I'm glad to answer any questions that I can.
http://littlemachineshop.com/gallery/ug/3540 Bench Lathe Users Guide.pdf

Bill,
I'll have to mull over that project for awhile. :thinking: I was a little leery of the 100 rpm minimum speed, but so far, so good.


Tom
 

wrmiller

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#24
If you have to leave the half nuts engaged, then just put a handwheel on the tailstock end of the leadscrew. That will give you very good control, especially threading up to a shoulder.
 
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