4th axis as a "poor man's lathe"

**A_Camera** · 17-05-2021

I bought a rotational axis ( 4th axis or A axis call it whatever you like) for my CNC with a 4 jaws chuck. I intend to use this as both a 4th axis on my CNC, or as an independent "poor man's lathe". I know, it will be a very primitive lathe with a lot of limitations, but I intend to try it out anyway to toy with and to learn. Maybe later on I'll buy a real lathe as well, but for now this will do. I am sure I can use it for some sort of work, but I will see that later.

To get the lathe function I had to design a control box. This is based on an Arduino Uno module with a 2x16 lines LCD. It is a very simple design, using only three buttons, one for clockwise rotation start, one for counter clockwise rotation start and of course, one for stop. Stepper acceleration and deceleration is also implemented, with a possibility to select acceleration in 7 steps. The chuck rotation can be adjusted between zero and 380 RPM, which is the maximum. This corresponds to 2280 RPM on the stepper, due to the 1/6 reduction pulley the stepper drives the chuck with. So it is a respectable rotation speed for being a stepper. The rotation speed is set using a rotary encoder and that speed is saved in the EEPROM, so after a power off, the last used rotation speed is restored. The rotary encoder push button is connected to the Arduino reset and acts as an emergency stop, in case there is a need for stopping as fast as possible. Of course, this means no deceleration, just an abrupt instant stop.

For powering and control I also built a separate PSU, which provides 48V 7A DC through four individual 12V power supplies connected in series. Three of these are 9A supplies, the fourth is though only 7A, which is why the maximum is limited to 7A, but considering that the stepper is only 3A, I figure that the PSU will be good enough for the purpose.

The PSU box also contains a DM542 stepper driver, which is configured to the maximum current and 2x micro stepping, which results in 400 steps per rev.

There is also a relay inside the box. This relay decides if the 4th axis is to be driven as A axis by my CNC using UCCNC software, or independently run as a "lathe", controlled from my control box and rotated non-stop until i press the stop button. The relay can be switched from the control box and the default setting (with the relay off) is that the rotational axis is controlled by UCCNC.

Yesterday I made a short video about testing the control box functions and showing the rotations. I have not used it yet as a lathe, still waiting for some necessary tools before I can do any real tests, but I thought this can be interesting to show as well. Maybe it will give other people some ideas as well.

I intend to share the Arduino code here as well. It is well commented, so based on the code, the simple box can easily be built by anyone understanding the basics of Arduino. I will need to add some file header information before I post it here, but it will be posted soon.

I hope you will enjoy watching this video. I will make a new one once I start using it as well.

Edit:

If anyone is interested to use the Arduino code, here is a link which you can use to download it:

https://drive.google.com/file/d/1CJN...ew?usp=sharing

**Kitwn** · 18-05-2021

Nice project. I'm looking forward to seeing what you make with it.

Kit

**Pilsbury** · 18-05-2021

Brilliant work there!

**A_Camera** · 18-05-2021

Thank you to you both. If it works for something (I expect it will work for plastics and soft metal) I will toy with it and see if I like it enough to upgrade the motor, or to buy a real lathe. My problem is space. I already have too many machines and right now I don't have any space for a real lathe. Anyway, it will be fun to build something similar to a lathe, which I can use for simple things and for learning. ...and if it turns out to be useless... then so be it. We only live once, and the road ahead is more fun than the goal. Failing is part of the fun, but of course, success is even more fun.

**magicniner** · 21-05-2021

I find speeds of 1000rpm and over to be ideal for small parts, Aluminium and plastics on the lathe.

**A_Camera** · 21-05-2021

Yes, I know it would be optimal and much better, but that would require 6000 RPM for the stepper...

**A_Camera** · 22-05-2021

My experimental project continues. I couldn't wait, I just HAD to do some tests, which I documented yesterday in a short video.

While one could wish for higher possible speeds, I think considering it is driven by a stepper motor, the results are very good so far, so I will definitely continue. I am still waiting for cutters to be delivered, but for drilling it seems to work. I am now pretty sure that it will work also for turning, but of course, that still remains to be seen. Anyway, I'll be happy I made this, also because I often end up wanting to drill centre hole into something, and that's not that easy without a lathe, so if for nothing else, I will definitely be able to use it for that.

Anyway, while I will finish this with the stepper I have on the chuck now, I am already planning for an upgrade with a more powerful servo or a closed loop stepper. I have already started to look for solutions even for that step. Unfortunately it is not just about changing the motor, because it means I have to change the plate it is fixed to as well, and also get a new timing belt as well as maybe a new pulley. So it may take some time before that step is done.

Right now I am considering this motor:

https://www.aliexpress.com/item/3285...4b6e2e0eyN2Gxo

I have no experience with any closed loop stepper, so I would like to ask the experts. Do you think it is worth the money? My steppers are 1.8Nm type, and this is 3Nm. Would that 1.2Nm make a big difference? Would it run faster? Remember that my current stepper is running at 2280rpm in the video, which due to the 1:6 reduction means 380 chuck rpm, so anything below that is not good. Currently I run the stepper at 2 microsteps, so 400 steps is one rev. and I intend to continue with that. The test condition in that link says 1600 microsteps but I think they mean 8 microsteps per step, which will give 1600 steps per rev. The motor is weaker at that high microstep, and is easier to get higher RPM at lower microsteps.

**A_Camera** · 27-07-2021

The fun continues. I continued with my "poor man's lathe" project, which has become quite an expensive activity. I made the first major upgrade, changed the stepper to a 180W servo, which required changes in gearing, the pulleys are now 60-20 teeth, so the ratio is 3:1. I also replaced the aluminium extrusion with heavy duty type, added 1605 ball screws and 20mm linear rails on all axes. Of course, the control box also needed to be updated since I can now get 1000 rpm chuck speed.

The change in gearing forced me to replace the belt to a longer one, and I also had to make a new fixture for the motor. I wish I could replace the old fixture with a new one, but I could not find any way of removing the old one, so I added a sort of piggy back plate. Anyone ever removed the motor holder plate, please tell me how to do it without destroying the whole thing. I can not for my life figure it out, and removing the chuck and the large pulley is not enough. Looks like the spindle needs to be dismantled, and I don't want to do it without knowing how.

One thing I am disappointed is the noise. I find the servo is quite noisy. I don't know why, but it is not what I expected. Also, the holding torque seems to be a joke compared with the stepper I had, so maybe this servo is far too weak as a rotational axis, where high holding torque is necessary. Anyway, I will finish the project first, before I buy a more expensive and larger servo.

**JAZZCNC** · 27-07-2021

Originally Posted by A_Camera

One thing I am disappointed is the noise. I find the servo is quite noisy. I don't know why, but it is not what I expected. Also, the holding torque seems to be a joke compared with the stepper I had, so maybe this servo is far too weak as a rotational axis, where high holding torque is necessary. Anyway, I will finish the project first, before I buy a more expensive and larger servo.

That doesn't sound right to me, that doesn't sound like a true servo but more like a very resonant stepper motor.
Both DC or AC brushless Servo's are very quiet even at 3000rpm. This video I did about electronic gearing shows just how quiet, jump to the 4min and 16min marks and you will see the motor spinning and hear just how quiet. The motor is a 600W AC brushless servo but DC brushless servos are just as quiet.

**A_Camera** · 28-07-2021

Originally Posted by JAZZCNC

That doesn't sound right to me, that doesn't sound like a true servo but more like a very resonant stepper motor.
Both DC or AC brushless Servo's are very quiet even at 3000rpm. This video I did about electronic gearing shows just how quiet, jump to the 4min and 16min marks and you will see the motor spinning and hear just how quiet. The motor is a 600W AC brushless servo but DC brushless servos are just as quiet.

Actually, the sound is normal. The noise comes from the timing belt, not the motor. It is not fair to compare your servo on a test bench with one attached to this spindle through a timing belt. Anyway, my servo is also quiet when there is nothing attached to it. I also made a test bench video, but hadn't had the time to edit and publish it yet.

BTW, what's an AC or DC servo? There is only one servo, but I think you call AC servo a servo which has a drive connected to AC current and DC servo one which has a driver connected to DC current. The only actual difference is that in one case you have the rectifier built into the driver and in the other case you have it built into the PSU. Mine is called AC servo with integrated driver, which requires 20-50VDC, but it is still an AC servo and not a stepper.