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Replace change gears with a stepper?

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savarin

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#31
Some time ago there was an extensive series called Building the stepper head lathe in Model engineers workshop magazine.
The instructions seemed to be very thorough although I didnt read all of them as the project was well out of my comfort zone.
It may be of some help.
 

gzoerner

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#32
My project to drive the leadscrew of my G4000 with a stepper motor is complete. It's been a work in progress for several months.

The features are:
- measures the spindle RPM then computes the proper stepper speed for the selected feed rate
- feed rates from 1 thou/Turn up to 10 thou/Turn
- forward and reverse
- tachometer
- micro-adjustable electronic stop (after stopping, the leadscrew reverses 1/2 turn to relieve pressure on feed lever)
- generic 1602 LCD display (2 lines of 16 characters) with I2C 2-wire interface

This version is not intended for threading. That's the next challenge.

The microprocessor is an Arduino Nano. This little gem doesn't even break into a sweat when calculating the acceleration profiles in real time (in floating point). I'm only using about 1/3 of the Flash so there's plenty of room for more features. Best of all the Nano cost about $3.50. I can't say enough good things about the Arduino platform. The code is written in C++ and their development environment is pretty good.

It was an interesting exercise to research the stepper acceleration. I found a paper from 2005 by David Austin that worked like a charm in this application. With Mr. Austin's equations, the stepper can achieve about 1600 RPM even though it only needs 1100 RPM at the max feed rate and max spindle speed.

Attached are a few photos of the setup.

I'll be happy to share the schematics and the software if there is any interest.

102_4617.JPG
Overall picture of the system. The cover is off of the power supply.

102_4616.JPG
Close up of the stepper and coupler.

102_4615.JPG
Closeup of the tachometer sensor. Note that the gear train is disconnected.

102_4614.JPG
Front panel of the controller

102_4611.JPG
Arduino Nano with all the wiring.

102_4605.JPG
Micro-adjustable stop sensor

Glen Zoerner
Spicewood, TX
 
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#33
Neatly done,
 

ttabbal

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#34
Very nice! Am I correct that it is for feed, not threading? I think that would work for me, just use the gears for threading and the stepper for feed. I love the idea of doing it all electronically, but I have a few problems to solve before I feel like attempting it.
 

jwmelvin

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#35
This looks great. I’ll likely do something similar with my G0602. I’d like to look at your code if you can put it somewhere accessible.
 

gzoerner

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#37
Very nice! Am I correct that it is for feed, not threading? I think that would work for me, just use the gears for threading and the stepper for feed. I love the idea of doing it all electronically, but I have a few problems to solve before I feel like attempting it.
ttabbal, yes, it's just for feeding. I've started working on a threading version. There's a lot to do to make that work.
 

Boswell

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#38
Very nice project.
 

Cadillac STS

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#39

Cadillac STS

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#40
And here it is ELS II:


Does anyone know what bottle that is to spray the oil? Looks like a slick way to do it, oil in the can, pressurize the can, long tip to oil on the spot.
 

RJSakowski

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#42
And a video of the ELS -II in action.
 

gzoerner

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#43
This looks great. I’ll likely do something similar with my G0602. I’d like to look at your code if you can put it somewhere accessible.
jwmelvin,

Attached are the schematics some other documentation and the source code in a ZIP file. Please feel free to contact me if you have any questions about what I've done. I know that taking other people's software can be a challenge.
 

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rwm

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#44
How about some follow up to this? How is it working out? Do you have any examples you can post.

Robert
 
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gzoerner

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#45
How about some follow up to this? How is it working out? Do you have any examples you can post.

Robert
Robert,

I've been using the stepper system for a couple of months now. It's nice to be able to switch to very slow feed speeds without having to stop and change the gears. The lathe is quieter and gear train wear is eliminated (since they are disconnected). With a 3 N-m stepper there is no shortage of torque on the lead screw. I'm in the process of modifying the whole software system to do threading. It will thread US or Metric threads equally easily.

Modifications to the current system include: changing the 24-slot spindle sensor to 64-slots with a Top Dead Center (TDC) indicator, new tachometer software, new stepper speed calculation software, a new user interface and new cabling from the spindle sensors to the controller. The software will measure the spindle speed 64 times per revolution, averaging over 4 slots each time. The stepper speed will be adjusted 64 times per spindle rotation. The stepper will start a threading pass after the third TDC signal. This ensures the spindle is up to speed. For each threading pass the carriage must start from the "Home" position which is monitored by software. The first 1/4 to 1/2 turn of the lead screw (less than 0.030 travel) will be dedicated to acceleration of the stepper so the Home position must be off the end of the thread.

I started the threading software by researching Phase Locked Loop (PLL) techniques and implementing a second-order Sigma Delta PLL. The complexity rapidly got out of control. I believe that as long as the stepper has enough torque and doesn't miss any steps, a simple synchronized, open-loop system will be sufficient. Of course experiments in the shop will verify that it actually works.

I hope to have the prototype up and running within several weeks. It's pretty hot in Texas so shop time is limited to mornings.

Glen
 

whitmore

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#46
I've been using the stepper system for a couple of months now. It's nice to be able to switch to very slow feed speeds ... It will thread US or Metric threads equally easily.
There's other threads (like on glass jars, and that nice soap dispenser that got its pump broken) that I'd like to be able to cut,
which aren't notably US or metric, that would likewise be better done with such a system. Eventually, there'll be
a thermos cap or other oddball that you'll want to match, and sticking to standard threads (and threadforms) won't
be advantageous.
 

gzoerner

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#47
There's other threads (like on glass jars, and that nice soap dispenser that got its pump broken) that I'd like to be able to cut,
which aren't notably US or metric, that would likewise be better done with such a system. Eventually, there'll be
a thermos cap or other oddball that you'll want to match, and sticking to standard threads (and threadforms) won't
be advantageous.
While I'm going to stick with standard threads (US and Metric), it's a simple matter to change the User Interface to accept any thread pitch. It's just a (non-integer) ratio that drives the stepper control routines.

Glen
 

P. Waller

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#49
While I'm going to stick with standard threads (US and Metric), it's a simple matter to change the User Interface to accept any thread pitch. It's just a (non-integer) ratio that drives the stepper control routines.

Glen
I am guilty of making odd thread combinations just to confuse someone in the future, a CNC lathe will turn any thread lead within it's accuracy.
One may single point a 1"-7 63/64 TPI thread if desired, I would never do such a thing (-:
 

Tim9

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#50
This guy did it. Andy Pugh shows his mini-mill synced to his lathe. Its quite impressive. He built the encoder which fits his mill and synced it to the spindle/stepper he mounted on the lathe.
I wish he went into more specifics. But it shows that with a bit of ingenuity it can be done.

 

markba633csi

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#51
Verry interesting
 
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