ELS Electronic Lead Screw Concept

[jcdammeyer]

Looking great!. I would still put a piece of aluminum on the ELS regulator. Cooler is always better than warmer. Even if the ELS drew only say 0.2A the 12V down to 5V is a 7V drop x 0.2A is 1.4W. A power resistor that is dissipating 1.4W is not finger touchable.

Looks like you have a decent size motor on the lead screw. If you can score and use a 36V power supply you will get higher RPM on the stepper before the torque drops off. Won't matter at low speeds.

 

[whydontu]

Step number 478.

Bought a 36v power supply. Reality doesn’t match the online product drawing, and it’s 1/4” too wide to fit in my case. Sigh. Fiddled with the existing 24v power supply and cranked it up to 30v. Seems to be stable, a couple of mV ripple so it’s likely not at its limit.

Motor is a NEMA 23 425 oz-in, seems to have lots of grunt. Geared 5:2 and running maybe 200 shaft rpm at a typical feed rate.

Spent a bunch of time scratching my head trying to develop a method to glue the Mylar overlay to my metal cabinet, and hold it in place while the glue dries. Cabinet is kind of thin and bulgy, so the overlay wouldn’t lay flat. A zillion magnets to the rescue! Fingers crossed that this works.

 

[jcdammeyer]

Love the magnet approach. Clever!

 

[jcdammeyer]

Oh and are you actually moving the carriage with it?

 

[whydontu]

Oh and are you actually moving the carriage with it?

Yes, works just fine. First test was doing a straight turning demo, 1” 1018 round bar, 0.050” feed rate, 0.050” depth of cut, 350 rpm, HSS cutter, no coolant. Nice dark blue spiral chip, no chatter. Second test was same setup, same feed rate, 0.125” depth of cut, using HSS Eccentric Engineering tangential cutter. Test failed, lead screw worked fine but the cutter got pushed down in the holder. So the ELS arrangement puts out more force than my cutter can handle.

 

[jcdammeyer]

I usually use light cuts with my tangential cutter. One of these days I must really sharpen it again. The holder was an initial prototype donated by an ELS user. I've never been able to actually stop my lead screw. I've got a 280 oz-in motor on 42V and 2:1. The only reason I'd upgrade to 1:1 is to get faster return rates. But it's also an old lathe, with bronze half nuts and never designed to run those kinds of speeds. I could see doing more damage just by being impatient and wanting modern CNC ball screw speeds.

 

[slow-poke]

I started with the C42 hardware, but wanted to make some improvements, so I made a custom board with touchscreen and then rewrote the C42 code. This solution does not require the launchpad or any other boards.

The intent is to provide more of a low cost plug and play solution for those who don't want to have to wire boards together and use CCS to load the code etc.

I want to add a few more features before creating the website and actually selling some. The fun stuff is in the wizards.

 

[Susquatch]

I want to add a few more features before creating the website and actually selling some.

That's WAAAAY too cool!

I love the display colour segmenting by function.

Where did you get the project box?

Are you "Lathe-Pro.com"?

 

[slow-poke]

Thanks, I find color simplifies the interface. For example when you toggle to metric, the color changes from Blue to Cyan, so you instantly know what mode your in without even looking at the button or label. Similar for Feed/Thread etc.

Tweaking the feedrate on the fly is so handy I would not even consider not having ELS on a lathe after adding it. I use it pretty much every time I use the lathe, and smile every time I push the button.

Project box Digi-Key

I am lathe-pro.com, No website yet but yes I own the domain.

 

[Susquatch]

Thanks, I find color simplifies the interface. For example when you toggle to metric, the color changes from Blue to Cyan, so you instantly know what mode your in without even looking at the button or label. Similar for Feed/Thread etc.

You did well. I'd have to use it to fully appreciate it though.

Tweaking the feedrate on the fly is so handy I would not even consider not having ELS on a lathe after adding it. I use it pretty much every time I use the lathe, and smile every time I push the button.

I dunno. I'm not there yet. Too old fashioned as an individual. Doesn't mean I can't appreciate it though. My career got me deep into all that kind of stuff. Maybe that's why I still prefer manual transmissions, and changing gears to cut threads.

But that DOES NOT MEAN I can't or don't appreciate ELS or CNC.

Project box Digi-Key

Thank you!

I am lathe-pro.com, No website yet but yes I own the domain.

Ya, kinda what I figured. It doesn't resolve on the DNS network yet so not yet assigned. Most hosting systems will let you setup a simple one-page "Under Construction" page. Doing so prevents scammers from hijacking your page. In addition to the obvious, putting up an under construction page will also stop the rest of the world from adding your domain to their blacklists - which you will fight for the rest of your life. Ask me how I know!

 

[DPittman]

I hope it was not pointed out in previous posts that I missed but I'm wondering how the servo/stepper motor for the the leadscrew is adapted to lathes that have the separate feed rod and separate leadscrew? Are two motors required ?

 

[Susquatch]

I hope it was not pointed out in previous posts that I missed but I'm wondering how the servo/stepper motor for the the leadscrew is adapted to lathes that have the separate feed rod and separate leadscrew? Are two motors required ?

What a great question.......

I'd guess that electronically controlled feed rate isn't nearly as useful as electronic threading.

 

[DPittman]

What a great question.......

I'd guess that electronically controlled feed rate isn't nearly as useful as electronic threading.

No it wouldn't be as important but eliminating the gear box/gear changes with the dual purpose leadscrew/feed rod is an advantage I see with els.

 

[jcdammeyer]

Most of the Electronic Gearing pretending to be an Electronic Lead Screw takes high rate encoder pulses from the spindle and Multiplie/Divide by a ratio and use the result to step the motor connected to the lead screw. The half nut remains engaged.

For example say you get 800 pulses per rev of the spindle. Your stepper motor is 200 steps per rev with 4x micro-stepping so also 800 steps per rev of the lead screw. To turn lead screw pitch of 10 TPI ( 0.1") the spindle turns once for each turn of the lead screw so for each spindle encoder pulse the gearing is 1:1 and the lead screw motor is stepped once.

Now say you want 20 TPI. The lead screw turns at half the speed of the spindle or for every 2 encoder pulses there is one pulse out to the lead screw stepper motor. The electronic gear ratio is 1/2.

For turning of say 0.010" per spindle rev where the lead screw is 0.1" per rev the ratio is 1/10. It's 1/20 for 0.005" etc.

For odd numbers like 11.5 TPI the ratio may be an infinite repeating number but as long as the numerator/denominator accumulate the error and add that extra step now and then the electronic gearing remains synchronized. Eazy Peazy.

If you are just turning to get a dimension then it's like using your gearing. You engage the half nut, turn at entered pitch and disconnect at the end of the pass and wind the carriage back with the hand wheel after moving tool clear of the work. Move tool back in for next depth of cut pass and engage half nut. The spindle and lead screw are essentially physically linked.

This is the way it was done way back with this system and no micro-processor. I started doing it this way with programmable logic devices back in 2002 or so. But then went the micro-processor direction.

With an Electronic Lead Screw as defined back in 2005/2006 the system works more like CNC. The distance for the thread is a parameter, as is the pitch of the thread or turning per rev. The velocity is calculated from that based on the spindle speed. Since stepper motors cannot accelerate instantly the acceleration of the motor relative to the spindle index pulse is repeatable and results in the tool tracking the thread correctly. That allows threading with a Sherline or Unimat at 6000 RPM. Something the Electronic Gearing systems cannot do. Something CNC systems can do.

 

[DPittman]

If the half nut is always engaged on the leadscrew for any carriage movement then dramatically increased half nut wear would be my concern. However a keyed leadscrew would eliminate that possibility.

 

[Susquatch]

Most of the Electronic Gearing pretending to be an Electronic Lead Screw takes high rate encoder pulses from the spindle and Multiplie/Divide by a ratio and use the result to step the motor connected to the lead screw. The half nut remains engaged.

For example say you get 800 pulses per rev of the spindle. Your stepper motor is 200 steps per rev with 4x micro-stepping so also 800 steps per rev of the lead screw. To turn lead screw pitch of 10 TPI ( 0.1") the spindle turns once for each turn of the lead screw so for each spindle encoder pulse the gearing is 1:1 and the lead screw motor is stepped once.

Now say you want 20 TPI. The lead screw turns at half the speed of the spindle or for every 2 encoder pulses there is one pulse out to the lead screw stepper motor. The electronic gear ratio is 1/2.

For turning of say 0.010" per spindle rev where the lead screw is 0.1" per rev the ratio is 1/10. It's 1/20 for 0.005" etc.

For odd numbers like 11.5 TPI the ratio may be an infinite repeating number but as long as the numerator/denominator accumulate the error and add that extra step now and then the electronic gearing remains synchronized. Eazy Peazy.

If you are just turning to get a dimension then it's like using your gearing. You engage the half nut, turn at entered pitch and disconnect at the end of the pass and wind the carriage back with the hand wheel after moving tool clear of the work. Move tool back in for next depth of cut pass and engage half nut. The spindle and lead screw are essentially physically linked.

This is the way it was done way back with this system and no micro-processor. I started doing it this way with programmable logic devices back in 2002 or so. But then went the micro-processor direction.

With an Electronic Lead Screw as defined back in 2005/2006 the system works more like CNC. The distance for the thread is a parameter, as is the pitch of the thread or turning per rev. The velocity is calculated from that based on the spindle speed. Since stepper motors cannot accelerate instantly the acceleration of the motor relative to the spindle index pulse is repeatable and results in the tool tracking the thread correctly. That allows threading with a Sherline or Unimat at 6000 RPM. Something the Electronic Gearing systems cannot do. Something CNC systems can do.

John, either you misunderstood the question or we didn't ask it correctly.

My lathe has a leade screw and half nut used for threading but not for feeding. For feeding, I have a gear system in my saddle that does not use the leade screw - it is powered by a separate feed shaft.

I would never want to use my half nut to drive regular feed operations - it would wear out too fast.

So, are you saying that an ELS, would force me to use my leade screw and half nut for regular feed operations as well as threading, or are you saying I don't use the ELS for feed operations?

 

[jcdammeyer]

My older south bend uses the key slot in the lead screw to turn the gears in the apron. A clutch wheel engages thise gears and the lever for powered lead screw or cross slide remains in neutral.

The newer lathes went to two shafts.
Normally electronic gearing or electonic lead screws are not connected in front of that gearing.

So boring a hole to a predictable depth is difficult.
And yes a half nut only system creates more wear on the lead screw.
I think most of the 7x14 to 7x20 are like that.

 

[Susquatch]

So boring a hole to a predictable depth is difficult.
And yes a half nut only system creates more wear on the lead screw.
I think most of the 7x14 to 7x20 are like that.

OK, so I take that to mean that ELS is only for threading on lathes with two shafts.

A big thank you to you for answering and also to @DPittman for asking.

I had been studying my lead screw to see how easy it would be to use. I shall abandon that idea for now and focus on using a VFD to get variable feed rate with diameter instead.

 

[jcdammeyer]

OK, so I take that to mean that ELS is only for threading on lathes with two shafts.

A big thank you to you for answering and also to @DPittman for asking.

I had been studying my lead screw to see how easy it would be to use. I shall abandon that idea for now and focus on using a VFD to get variable feed rate with diameter instead.

No my ELS uses the lead screw for both threading and turning. If you want to bore or do an internal thread to a precise depth without panic near the end of the hole on each pass an ELS or CNC is wonderful because you have that precise position control that you don't have with a clutch drive.

Pretty well everyone who adds an electronic drive to their lathe will do it only to the lead screw regardless of Electronic Gearing, ELS or CNC.

In fact if you buy a DC servo you often will find that it comes with an electronic gearing feature. You connect the encoder to the DC Servo drive and set up the numerator and denominator for the ratio of encoder to servo and bingo electronic gearing. That's been around since the 80's at least. But the cost of the servos have now dropped enough that this is possible on smaller systems.

 

[DPittman]

I shall abandon that idea for now and focus on using a VFD to get variable feed rate with diameter instead.

Do you mean variable speed control that would allow speed control of the spindle independent of the carriage feed? That can't be done with just a vfd?