Syncing up Arduinos

Just get an Arduino Due for £30 or so and be done with it. 54 lines of digital IO plus 12 ADC and 2 true DAC, 32 bit ARM Cortex-M3, 84MHz clock - and the same footprint and pinout as the Uno (with some additional pins obviously). No need to synchronise anything, bags of power. No brainer.

There are quite a few versions of the Arduino around, so choosing the right one seems sensible unless you like cutting the grass with scissors or your hair with a lawnmower.

There are several examples where the leadscrew is synchronised with the spindle like this. There's a post above to another such embodiment. This "electronic leadscrew" approach seems like a pretty versatile concept.

Murray

Bob Mc

May I just say thanks for the article

This discussion about Arduino synch issues is interesting, but the big thing for me is that you have produced something that successfully replaces change-wheels.

Good on you, Sir.

MichaelG.

.

P.S. for convenient reference **LINK**

All very interesting, but I can't help thinking that a cheap old PC running Ubuntu and Linuxcnc would do exactly the same job and, if you added stepper drive to the cross slide, full cnc too. Or you could use Windows and Mach3 though threading is reputed to be less reliable (I'll find out this weekend).

I have a series of three articles in similar vein that look at other movements that I received after Bob's article. it takes a a sufficiently different approach to be worth publishing and I'm sure that it will provide more food for thought.

Neil

Thanks to all for your interest, in defence of my design which was started some 7 or 8 years ago there were not many designs aimed at the particular problem of providing an electronic gearbox to replace change wheels on a lathe at that time.

I have to tell you that in no way was I expecting to publish an article on this, and it was something that I required for my own use exclusively. My knowledge of programming Arduino's at the time was zero, I specifically had to learn about it for this project.

I certainly did not want a full CNC system which the Electronic Leadscrew Group were producing, I needed a simple effective and cheap as possible solution to the problem otherwise it would have been much easier to purchase a lathe with everything ready and working.

I can understand why the idea of syncing two boards seems to be like 'cutting the lawn with scissors!' however at the time the main concerns I had about using 2 separate boards were that, yes, they might drift...especially as they had resonators fitted and were of Chinese origin, to be honest I was not over confident about their quality.

I decided to to do a few simple experiments to ascertain how much they did actually drift, however with no proper measuring equipment the only recourse of action was to program each board with the Blink program set to 500ms periods and see if they stayed in sychronisation, it confirmed my suspicions, after perhaps a minute or so I definitely detected a change in the blinking phase.

I was also concerned as to whether variations in supply voltage and temperature variations would affect these things, and I was also aware that there would be a difference in frequency of the two oscillators and that perhaps as one increased in frequency the other might be going down.

After much deliberation and not wanting the onerous task of wiring up for one resonator I had to make a decision, would I take the risk of perhaps ruining a piece of turned work I had spent much time and effort on for the sake of a few minutes of re-wiring? or just get on with it and at least be sure that if there were any more unknown gremlins lurking in the shadows then this would lay them to rest.

One member has suggested using a computer to derive the signals for the drivers, which is ok but then you need a monitor and a keyboard as well next to your lathe, yes you could use a laptop, which nowadays are much cheaper than when I started, in fact many things have changed over the time since I started building it and I would have perhaps designed differently in light of hindsight.

I hope this explains some the reasons for the design, and I hope it shows that an old lathe can be given a new life with a little bit of effort which has become easier since the introduction of new boards and a better understanding of using the Arduino's

All the best for Christmas..... Bob.

Great article Bob, it's certainly got us talking and thinking about what can be done. A lot has changed in the microcontroller / PC world in 8 years, hindsight as they say is always 20:20

Andy...

you are my hero..!! ha ha ha.... lawnmower...!! that's great...

thanks...bob..

I must add my praise for Bob's article, it set me off to design a simple rotary indexer using a PIC chip. Like Bob when he started, I have very little knowledge about programming and don't have the time to become really proficient at it. The result is I make programs that work regardless of how clunky and inelegant they are.

A proper programmer would die laughing at some of my efforts but they work for me and that's all I care about. Please remember that this is not a programming site and while people with good programming skills have a lot to offer please don't make the rest of us feel inferior or discourage us from contributing.

Doug

I second John Haine's comment. Most of the cost of these projects is now in the stepper motors, stepper motor drives, controller board and power supplies. I have two old laptops that were gathering dust running Mach3 to do CNC on a Smart and Brown Model M and a Rong Fu mill. The laptops effectively had zero cost because I already had them. They only have to run XP with no background programs that use up processor power and most of the work is done in an external processor (Smooth Steppers in my setup). Anything that uses something like an Arduino will share most of the cost of a CNC setup because a lot of the hardware required is common to each system. With CNC you do get the option for a lot more functionality than an Arduino setup that is only good for one thing such as threading without change wheel swapping.

I have no problem threading with Mach3 because the limitation is in long threads which I have never had to do. The single pulse per rev of the spindle is also fine for me since I run my lathe using backgear for threading so the chance of the cutting force slowing the spindle down and causing problems is very close to zero (3Ø vfd driven 2hp motor)

I really like the option to set feeds to a per revolution value when using manual data input (MDI) so using the machines in a manual manner without a CNC part program to be seen. Very useful when parting or grooving to get a steady feed rate.

Martin.

And to add to Martin's post, using Mach 3 Wizards I can do almost all regular turning jobs never having to write g-code (though g code is easy to learn and I usually sanity-check the program before running it). Even for one-off jobs it is generally quicker to spend a little time with the Wizards to get the g-code right, then set the machine off to do the job on its own, without having to twiddle handwheels or remember how much you've taken off or worry in case the micrometer dial has slipped, and you don't have to stand over the lathe inhaling cutting fluid fumes.

Hi all again....

with reference to John Haine's and Martin Connelly's posts, I had a quick look at the Mach3 cnc system and it is very impressive and to be honest is probably the way to go if you have the equipment..... and therein lies the problem..., from what I can ascertain, and I may be completely wrong, but is it not the case that you need a proper cnc lathe with digital encoders and ballscrew drives for Mach3 to be of any use?

Please don't think I am being discourteous to your posts or finding fault, I have been on the receiving end of this sort of response in other forums and it can be very dis-heartening.

Unfortunately my old lathe which is about to have its 70th birthday soon does not have the benefit of these new fangled devices and it would not be economical to try and fit them at this stage in its life, the idea behind using the Arduino system that I have outlined is that it does not require any encoders and will operate with whatever type of leadscrew is installed.

Please correct me if I am wrong, and again I thank you for the interest shown in my article on using the system I described.

rgds..Bob.

It is less of a problem using old leadscrews on a lathe than on a mill because almost all working motion is in one direction only. Having said that I did replace my cross slide lead screw with a ballscrew. I did this without modifying the lathe so I can always return the machine to the as built parts. I wanted to be able to do curves as needed for ball turning with minimal backlash. I put a ballscrew on the carriage with just one M6 hole drilled and tapped for the connecting bracket. I also put one M6 hole in the end plate of the headstock for a spindle sensor but this is hidden under the cover. All other mounting uses existing features on the lathe. It may not be pretty but it works.

Martin

Edited By Martin Connelly on 17/12/2015 18:59:55

Bob;

I converted an old Unimat lathe to CNC operation, and it has done some good work.

I use the original feed screws. The spindle motor is not great, so am looking for another solution for powering the spindle. (may go with the stepper route)

I use a BeagleBone board, running the development fork of LinuxCNC, and I did discuss it at last June's CNC Workshop over in Michigan.

There should be information on it here: **LINK**

I have 4 pictures of it in my albums, here's one:

John.

Hi Bob, Hi all.

I too have been looking for a solution to produce an electronic gearbox for my old Myford ML7. To buy an old Myford gearbox to fit it is costly and it would give me a limited combination of gear ratios. For me the sheer simplicity of Bob's (working) design was a revelation. I have looked at the Electronic Lead Screw project and it's far too complex for my needs and much more costly. I have racked my brains for some time to come up with an inexpensive system of my own which works and is not too complex to code as I'm not a programmer but can throw a few lines of code together for the Arduino as long as it doesn't get too deep.

Using two synchronised chips makes the whole thing so simple, bravo to Bob for working it out and sharing. If anyone else comes up with an even better solution I'm all ears. Thanks Bob nice job.

regards Quenton

Martin Connelly's comment that "The laptops effectively had zero cost because I already had them." reminded me of an unpleasant encounter I once had with a Finance Manager when he laid into identical logic in one of my carefully crafted Business Cases.

It's a dodgy argument because not everyone has an old laptop and because old laptops become unreliable and have to be replaced. Putting it another way, someone telling us "my Hurco Machine Center is effectively zero cost because I already have one" definitely wouldn't help the debate much.

That said trying to drivie a real CNC machine with Arduinos would also be a false economy.

Douglas Johnston shouldn't be discouraged about his programming skills. Many professionals also "make programs that work regardless of how clunky and inelegant they are".

Cheers,

Dave

Thanks John A Stewart for sharing your cnc groups ideas which seem very comprehensive, I can't help asking if you know if the Atlas/Craftsman lathes were made in Michigan ...?

Also thanks to Martin for clearing up a question I had about Mach3 for a lathe, and Mr Q for his words of encouragement .

I would agree with Mr Q, that it would be better to see what other designs are in the pipeline before committing yourself to any particular design, at least these days there is something to use as a model, I hope our Editor Neil would give us a hint in the magazines or in the forum as to what sort of solutions others are going to be submitting for publication, and using his editorial skills I have no doubt he could do this without spilling all the beans..!

nb...were you employed in the communications/radio industry..? I can't help but have a smile when I greet you with..... Hi Q..! (refers to inductor quality).

Thanks also to Mr S.O. Duffer for taking the trouble to have a look how Arduino clocking varies, and his program for providing two tones... I have to agree with Mr S.O. Duffer that using Arduino based systems for CNC is probably not the best way to go, however others have produced something which is very impressive, unfortunately the one I looked at on Utube was all in Russian and there were no details of how it was achieved.

rgds...Bob..

Hi Bob. High Q is appropriate.

I have been a radio enthusiast since my early teens. I achieved my Radio Amateurs certificate at 14 but didn't take a licence until some years later due to the attraction of the fairer sex, then added motor bikes to girls and was led even farther astray. But I did go on to further study radio and television at the local tech after leaving school and become a radio and TV technician. I eventually took a radio amateur licence in my early 30's and go by the call sign of G0IHE though I am not active at the moment. Electronics has been an enduring interest both as a living and a hobby since my school days and I'm never far from a soldering iron. Now I'm retired I have eventually got round to steam engine building, though I'm still setting up the workshop at the moment.

rgds Quenton

Edited By Q on 19/12/2015 02:03:28

Picking up on this very old thread. Those with an interest in Electronic Lead Screws might like to follow this series of videos starting at 

https://www.youtube.com/watch?v=FTs9GygRQ-U

Edited By Brian Oldford on 03/09/2019 18:35:41