CNC Lathe Conversion - finally some progress!

[raynerd]

Hi

I have been working on this for weeks and finally after a long day sitting at the computer screen   I got the motor up and running for one axis. The aims was just to get one axis going and then finally with that confidence, complete the project.  CNC interested me from the beginning so it has always been on the cards and the redundancy of my little lathe due to the arrival of the boxford had left a perfect opportunity.

The hardware:

4 wire bipolar Nema23 - 270 oz/inch, 2.8A not a huge amount of muscle but big enough I should think for one of the axis on this mini lathe
Routout CNC Bipolar driver board 2.5A
Standard 25 way breakout board
18-20V 3.5A Laptop Charger that I had lying around the house with no use.

Software: Mach 3


So some of you may notice that the driver doesn`t actually power the motor to the maximum but seeking advice from a few people, I was advised that for the extra cost of the 10A driver boards, the 0.3A would be virtually unnoticeable and certainly not worth the extra money for this test. The guys at Routout CNC were excellent and a few phone calls to them have helped me no end. Here is a piccy of the lathe with the computer in the background (perhaps should have tidied up!):



This is the driver, motor and BOB connected:



At this point I could confirm that the driver was engaging the motor as when powered, the motor was locking up. However I spent ages trying to setup and correctly configure the software to actually move the motors. For future reference if this helps anyone, here are some screen shots of the critical settings in Mach3:









My first attempt at a bit of simple G-code which worked and turned the motor "forward" 0.5 inch!




So now I have my motor turning under CNC and next is a case of correctly hooking it upto my lathe. I bought quite a few bits off Lee and so the Y axis should be quite straight forward. The first job however is going to be the tailstock - the motor is mounted but the motor centre spindle is turning in the connector block so here is the thing dismantled and next job is to drill and tap the connector lower down so that the grub screw correctly engages and locks with the motor spindle.



Hopefully I should make some more progress over the next few days.

Chris

[John Stevenson]

One word of advise is as soon as you can afford it get rid of that DB25 connector board and get a proper breakout board.

They are advertised as breakout boards but in fact are not. A proper breakout board either buffers the signals or opto isolates them from the computer.

The type you need depends on the drivers, drivers with full opto isolation only require a buffered board so the logic signals are constant, laptops are notorious for putting weak signals out and the buffered board will give a genuine 5 volts.

Drivers with no opto isolation or a history of noise, require full opto isolation or any stray voltages can take the computer out.

John S.

[raynerd]

Hey John, great advice - I noticed you are from the UK, do you have any suggestions as to where one could be purchased? I`ve found it really tricky to get the parts as most supplies or at least recognised suppliers are USA. The driver has apparently got full opto isolation - so I guess I`ll just need a buffered board.

What do people usually use to mount all the drivers and electronics? I`ve obviously not started cutting metal but at present they are not enclosed and I really don`t have a clue how they should be covered.

Chris

[John Stevenson]

Chris,
I use Roy Harding at http://www.diy-cnc.co.uk for things like spindle boards and breakout boards. Arceurotrade http://www.arceurotrade.co.uk for steppers and drivers for most of my work but this is just personal choice and what I have found to be reliable and have good support.

I have seen all sorts of cases used from surplus wall mounted switch boxes, old computer cases to custom made ones.

One of the nicest, cheapest ones I made was out of one of those old mini computers called Shuttles.





Two plugs fitted at the back for steppers and limits where the video and usb connections used to fit.



Inside showing transformer Roy's Optoport breakout board and the small stepper drives from Arc



Other side showing the cap and fan, I managed to scrounge two dead computers from a local firm, apparently they are not very reliable as a computer and breakdown a lot so keep you eyes open for dead ones.

This powers my small bench top router and with the two large flexy cables, surplus from a Chinese CNC conversion it make a very near job.

John S.

[raynerd]

Great job,  John. I`ll keep my eye out for one of those small shuttle cases. I wa going to use an old computer case but it looked a little too big for what I needed. I actually have a desktop unit that is only fit for the skip - if I rip out all the insides I may be able to cut it down to size.

Thanks again for the pics and links.

Chris