CNC mad

[Bigbadbugga]

I think I may be going a bit crazy here but I've got a few project ideas for 2015.

I'm thinking of getting a 3d printer, looking into CNC converting the chester 20v mill also.

But I've just had an idea for the lathe I'd like to run past you guys. Please tell me if I'm just plain crazy, or if im onto a good idea.

I have a Boxford CSB lathe, circa 1963. It had a 1HP 240v single phase motor and reverse. It is metric and can cut threads and change feeds with changewheels, it will also cut imperial threads with a compound gear which I can get but don't have currently.

Currently I use the lathe as a plain turning lathe, it's set with changewheels to give a fine power feed and I tend not to cut threads on it as its too fiddly.

My idea? Driving the lathe with a large stepper motor and changing the changewheels out for a stepper to drive the leadscrew which I could change out for a suitable ballscrew, adding a stepper for power cross feed and making the lathe a sort of cnc hybrid.
Screw threads and feeds would be programmable but it would also be possible to use the lathe conventionally.

Am I mad or is this possible?

Possibly something like this....

http://plsntcov.8m.com/CNClathe/CNClathe1.html

[vtsteam]

Actually, BBB, you don't need a stepper motor on the spindle. You just need an encoder on the spindle, and a stepper on the leadscrew:

see:

http://www.dakeng.com/threading.html

[Bigbadbugga]

Ah, thank you, that's very useful.
 

[bertie_bassett]

if you have a search for electronic lead screw you might find some useful info.  vI toyed with the idea on my viceroy, but decided I prefer change gears ( not that iv got any)

if done right it seams like a good halfway house between manual and full cnc.

also if you go for a single pulse encoder on the spindle make sure your motor is powerfull enough not to slow down during a cut, otherwise threads could be a bit hit and miss.

[vtsteam]

Bertie, even with a single pulse encoder on the spindle shaft, the gear train ratio will, as a guess, ensure enough pulses per leadscrew revolution for the stepper driver to sense and compensate during a change in motor speed.

[mattinker]

Hi,

The Electronic Lead Screw group on yahoo is a group project which was lead by John Dammeyer, with the goal of producing a low cost alternative self contained threading and taper cutting unit. This replaces the frequently missing change gears. It uses a single pulse encoder and a circuit designed and built by John. It is designed so that if you add a a 100 step encoder and instal the second optional stepper motor, it will plug straight into a PC to run it on EMC2 or Mach.

https://groups.yahoo.com/neo/groups/e-leadscrew/info

I have as yet to finish mine, it's taken me far too long! I've made all the parts, including the electronics, just needs wiring!

Regards, Matthew

[bertie_bassett]

Bertie, even with a single pulse encoder on the spindle shaft, the gear train ratio will, as a guess, ensure enough pulses per leadscrew revolution for the stepper driver to sense and compensate during a change in motor speed.

gear train??  if its an electronic lead screw there isn't a gear train. the encoder is directly on the spindle and the computer does the work of the gear train. unless im misunderstanding??

I know from my lathe that a deep cut at slow speeds can easily bog down the spindle speed and I wouldn't trust a single pulse to be able to give the accuracy needed for screw cutting.

in a worst case scenario if the spindle was to stall at say 60 rpm, youd have at least a second befor the computer realised something was wrong. that's at least a second with the leadscrew dragging the tool through the non spinning work piece.
'
in reality things are probably a lot better then that and it probably works just fine. just my head doesn't trust it


note*  my lathe isn't a very good example of a standard lathe as its not in the best condition and its single phase motor isn't great.

[John Stevenson]

Hard fact, a single pulse encoder isn't good enough for consistent accurate threads.
It's needs a multi line encoder to be consistent and unfortunately  Mach 3 cannot handle this. I can't comment on the ELS but when Tony Jeffree built one and wrote about it in MEW the ELS 'at that time' could not use a multi line encoder.
EMC can

[mattinker]

Hard fact, a single pulse encoder isn't good enough for consistent accurate threads.
It's needs a multi line encoder to be consistent and unfortunately  Mach 3 cannot handle this. I can't comment on the ELS but when Tony Jeffree built one and wrote about it in MEW the ELS 'at that time' could not use a multi line encoder.
EMC can

The multi line encoder was not used on the ELS for economic reasons, the Pic controller used did not have enough capacity to calculate the pulses. This compromise was the subject of much debate, apparently, the single line functions adequately if one doesn't ask two much of it. This is a hobby solution not an industrial one. I stand corrected about Mach, I've never used it and had forgotten that it couldn't run multi lined encoders.

Regards, Matthew

[vtsteam]

What I said earlier though was dumb.   

The spindle doesn't have a gear ratio. It's disconnected -- the stepper drives the leadscrew.

I guess I was sort of also thinking of the the drive from motor to spindle being a ratio. But the encoder is on the spindle, not further up the train to the motor, so one rev of the spindle is one rev of the workpiece, and one rev of the encoder. Not a multiple.

nevermind..........

[woodguy]

Who  sells ELS components or completed assemblies?

[JohnHaine]

If you are going to do this why not just fit full cnc?  To do tapers and threads with the ELS you need steppers on the leadscrew and crossfeed anyway.  In my experience I don't do much lathe threading but loads of other stuff which involves turning handwheel  and getting bored, why not have a machine do it?  But as JS says, Mach 3 isn't wonderful at threading with a single pulse per rev sensor, better to use Linux CNC so I'm told, I'm going to give it a whirl.

[mattinker]

Who  sells ELS components or completed assemblies?

More information at :-

http://autoartisans.com/ELS/

Regards, Matthew

[mattinker]

If you are going to do this why not just fit full cnc?  To do tapers and threads with the ELS you need steppers on the leadscrew and crossfeed anyway.  In my experience I don't do much lathe threading but loads of other stuff which involves turning handwheel  and getting bored, why not have a machine do it?  But as JS says, Mach 3 isn't wonderful at threading with a single pulse per rev sensor, better to use Linux CNC so I'm told, I'm going to give it a whirl.

The ELS's place is in between manual and CNC, you can use it for turning straight or tapered sections without G code. Turning down a piece of stock is just the same as turning a very fine thread. You don't need to start up a computer to run it, it's all built in!

Regards, Matthew

[bertie_bassett]

just had a random thought regarding the single line encoder issue with both MACH and ELS.

seems that both systems are unable to work with anything more then one pulse per revolution of the headstock.

but why cant you simply use a 4 slot encoder and multiply your screw pitch by 4?  e.g. 1 tpi required, would be inputted as a 4 tpi. thus for each 1/4 of work piece rotation the tool would advance by 1/4 of an inch and a whole rotation would equal 1 inch ?

seem too simple an answer to me, must have been tried already?

I imagine there must be a limit to how fast the control can receive signals and computate the required movement, but surely at thread cutting speeds that's not much of an issue?

[mattinker]

I suggest that you put the question to John Dammeyer on the

https://groups.yahoo.com/neo/groups/e-leadscrew/info 

Yahoo ELS group, you'd get a far better answer from him!

Regards, Matthew.

[RotarySMP]

Threading with a single count encoder works pretty well, as you can cnc thread at much higher spindle speeds, an multi pass with lighter cuts. Bogging down the spindle to a dead stop is not going to give you a usable thread on a manual machine. That is an extreme, unrealistic conpasison.

I use turbocnc for years. It also only supports 1/rev indexing.

Using a four count encoder an tell the software that your leadscrew pitch is a quarter would only work for single pass threading. You would have a 75% chance that a second pass wont line up.

EMC is set up for both an index pulsr plus an encoder. It is no big deal setting that up. It is jusr 2x what you need anyway.

Mark

[hanermo]

First time ever I disagree with J. Stevenson.

A single pulse will thread very well on a converted lathe.
Mach3 will also thread very well. IF you have done the refit properly.

BUT...
We confirmed this when I worked with Kslilabs/Centipede, to develop and debug the threading stuff.
Normal index pulses were crap ! and this is a big part of the problems people encouter.

We used a 633 Mhz bus, and logged the signals into memory, and Sergey then plotted these.
It showed clearly, that the problem was the index pulse being fuzzy and wandering.
After that Sergey developed his index pulse board, that triggers clean pulses.

I could then re-thread on a cold lathe, at 320 rev, vs a warm lathe at 340 rpm, and the tracking would be within 0.01 mm through a 30 mm long 1 mm thread.
On a copper pipe, where the new groove was very visible vs the old groove, and it tracked perfectly.

This just proves that;
1. 1 index pulse is enough
2. most index pulses are no good

Btw.. Apparently the ELS also threads well.

[hanermo]

I am now installing new brushless ac servo drives on x,z,c axis.
I expect to make great threads, soon.

Last mount is done, need to broahc some pulleys and make some supports and stuff.

I also am very much looking forward to the new *servo spindle* as c-axis.
2.5 kW AC brushless, 10 Nm continuous (30 Nm peak).

[awemawson]

First time ever I disagree with J. Stevenson.

  Whoohay ... fighting talk ......     

[Bigbadbugga]

Can someone run their expert eyes over this one?

http://muck-solutions.com/?page_id=186

May need translating.

I've taken a shine to it as it looks more intuitive than the ELS one, I've messaged them to see if a kit or schematics are available for the latest version as I think I'd like to build it. It also uses a multi pulse encoder.

[RotarySMP]

The development of the Zyklen controller is on the german CNCecke.de forum, which is currently down for a servo upgrade. Seems a pretty nice controller. It wont run G code, but if you use your lathe for oe off parts and normally work thorugh the MDI, it would probably do 99% of what you'll need.

I used a schmidt trigger to clean up the optical gate for mine spindle indexer, and never had a problem with the signal.

Mark

[Bigbadbugga]

Thanks.

I'm really only looking for an electronic leadscrew type setup for the lathe, and adding a cross feed also,

The ELS and zyklen both seem to fit the bill, but the zyklen looks a little neater and more user friendly.