beginner lathe conversion .

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14 Jul 2014 09:59 #48748 by skeeter
Hi, I am a new member to this site . I use and like linux . I want to use linux cnc on a lathe conversion . This will be a combination of mechanical and electrical / software questions . so here goes.
1 I have an old 1945 hardinge collet lathe that I am restoring which is just about done .
2 I have repowered it with a inverter duty motor and ac drive . so my spindel speed will will be controlled by me at the ac drive itself .
3 I am making an add on feature that will support an X and Y axis . that I want to drive with steppers because they are cheaper these I would like to drive with new acme screws and nuts .
4 My goal is to use linux cnc to cut threads, profiles, cams and tapers am I correct in assuming that linux cnc will do all of these functions remember I am new .
5 what size steppers should I use
6 I will be using a desktop pc .

so what do you guys recommend to get me started . I have a complete machine shop here all manual machines. I am also a lost duck in the woods when it comes to cncing something but willing to learn. I will need software for cad and whatever that needed to get it to gcode then to machine part . I am on a small budget very small so these are my parameters . I hope you guys can and are willing to help me .

Kindest Regards
Terry

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14 Jul 2014 12:50 #48750 by Rick G
Replied by Rick G on topic beginner lathe conversion .
Hello,

For ideas on hardware you may want to look here...
www.kelinginc.net/index.html

The size of the stepper motor and driver will depend on many factors including the size of the lathe, the type of work, the gear reduction, etc., as well as budget.
You might want to search on line for kits available for your lathe size for ideas, motor sizes, ball screw sizes and such.
Small lathes may use nema 23 steppers, I used nema 34 on a 13" lathe.

Linuxcnc will certainly do what you want, you can load a simulator version to try it out.

For most of my lathe work I use NGCGUI instead of a CAD CAM package.
linuxcnc.org/docs/html/gui/ngcgui.html

Rick G
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14 Jul 2014 19:10 #48764 by skeeter
Replied by skeeter on topic beginner lathe conversion .
Thanks Rick, looked over this site . I guess # 34 stepper motors will do the job . On your lathe Rick did you use the stock screws or retro fit ball screws ? Do you drive the screws direct or use tooth belts for reduction ?

I am really going to enjoy this and learn a whole bunch in the process . Without the magic smoke i hope LOL. Am I correct in assuming that once I complete the lathe project most of the learning curve is behind me ? Making the mill conversion a bit easier ?

Regards
Terry

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14 Jul 2014 19:46 - 14 Jul 2014 19:46 #48766 by andypugh

2 I have repowered it with a inverter duty motor and ac drive . so my spindel speed will will be controlled by me at the ac drive itself .

It is fairly easy to have LinuxCNC control the inverter. This then allows you to run constant surface speed mode, and to do rigid-tapping with taps held in the toolpost.

I am making an add on feature that will support an X and Y axis . that I want to drive with steppers because they are cheaper these I would like to drive with new acme screws and nuts

Something like the old Anilam "Lathemate"? Not a bad plan, and it means you can use the lathe in manual mode still. (Possibly at the same time...)
I would consider ballscrews, even the cheap ones are likely to work better than acme screws. The cheap ones are quite cheap: www.zappautomation.co.uk/mechanical-prod...-ballscrew-4703.html

My goal is to use linux cnc to cut threads, profiles, cams and tapers am I correct in assuming that linux cnc will do all of these functions

Profiles, tapers and threads are standard and easy. Cams are possible:



but a bit of custom configuration was needed. Both threading and cam profile cutting need some kind of encoder on the spindle. These are often home-made slotted discs.

what size steppers should I use

My 9x30 lathe uses Nema23. They work fine, both axes can stall the spindle. I wouldn't mind a bigger motor on the Z for pushing toolpost-mounted drills. I would suggest looking hard at the new closed-loop stepper systems, an example here: www.ebay.co.uk/itm/CNC-Hybrid-Closed-loo...&hash=item461fd4f7c8
Last edit: 14 Jul 2014 19:46 by andypugh.
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15 Jul 2014 00:35 #48770 by skeeter
Replied by skeeter on topic beginner lathe conversion .
Hi, Andy . What are the advantages of this servo system ? This attachment will come off of the lathe in less than 3 MIN. and be right back to manual mode . It has it's own tail stock and crossslide and compound . My attachment will go on the ways of the original bed and clamp down . this will have it's own saddle cross slide compound and tailstock essentially a lathe with out a headstock. This collet lathe does not have a longitude leadscrew like a conventional lathe . But you probly already new this . Yes I know it will reduce the Diameter of what I can turn a bit I am ok with that . The encoder you mentioned i have one already on the spindel for a tach. Can I take the signal fron this and use for the software requirements or will I need another one These is simply a hall effect transister I think . If not what is the encoder you recommend ?
Do have any cad programs that you would cecommend for me to use either free or very cheap ? Then next a way to convert to gcode ?

Thanks
Terry

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15 Jul 2014 01:07 - 15 Jul 2014 01:07 #48774 by andypugh

Hi, Andy . What are the advantages of this servo system ?

Because the drives know where the motor has actually got to, it can either recover lost steps, or trigger a fault output if it can't recover position. This is rather an improvement, especially on a lathe where you can sometimes lose steps and not notice (running too hard into a shoulder, for example)

this will have it's own saddle cross slide compound and tailstock essentially a lathe with out a headstock.

You don't need a compound slide on a CNC. It's better to have a stronger cross slide. It might be advantageous to use the original tailstock (if there is one)

The encoder you mentioned i have one already on the spindel for a tach. Can I take the signal fron this and use for the software requirements or will I need another one These is simply a hall effect transister I think

Threading need an index pulse once per rev. That is the bare minimum. More pulses + index is better. For rigid-tapping you need index + quadrature to sense the spindle direction as well as the speed.

If not what is the encoder you recommend ?

I ended up using a commercial encoder, geared 1:1 to the spindle, after experimenting with laser-print and home-made. But only because it turned up very cheap.
An opaque disc with a set of radial slots, with one slot longer than the others for the index detector, and then some slot detectors similar to uk.rs-online.com/web/p/products/171-1830...n=PSF_438299|QVTN-LL works well for many people. (That particular sensor has two channels, so does quadrature in one device).
You would need to choose the number of slots to match you intended PC interface. The parallel port can only generally count reliably at 10kHz, so if you have a 3000rpm spindle you only want about 100 slots. This is one reason not to use a standard encoder as they often have many more slots than that. If you are using a PCI card or EPP-interfaced FPGA card then that limit is removed. (I am using a Mesa 7i43 on my lathe which counts at 10Mhz)

Do have any cad programs that you would cecommend for me to use either free or very cheap ? Then next a way to convert to gcode ?

I don't tend to us CAM on the lathe, I typically use a set of macros I have set up ( www.linuxcnc.org/index.php/english/forum...s/26550-lathe-macros ) But CamBam claims to have a lathe mode.
Some people have made the (free) add-in to (free) Inkscape work, but I didn't. www.cnc-club.ru/forum/viewtopic.php?t=35
FreeCAD is nearly there: www.freecadweb.org/wiki/index.php?title=CAM_project and the CAD part is quite well developed.
Lots of other options exist, Autodesk Fusion might be worth a look. I have a full license for Inventor, so quite like that as the interface is vaguely familiar. That's Windows/Mac only though. CamBam, Inkscape and FreeCAD all run on Linux too.
Last edit: 15 Jul 2014 01:07 by andypugh.
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15 Jul 2014 03:22 #48778 by skeeter
Replied by skeeter on topic beginner lathe conversion .
Thanks, Andy . I got alot to chew on for now .

Terry

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15 Jul 2014 21:35 #48808 by Einar
Replied by Einar on topic beginner lathe conversion .
I strongly suggest using ballscrews and forget connecting/disconnecting the steppers (or servos).

Acme screws have much higher losses then a ballscrew (appx 3 times higher). And that is before adding any contraptions to minimize backlash.
So you will need much bigger steppers (or servos) and much bigger drivers for them. Thus the price goes up. And for a big lathe (not small anyway) it will be placed higher that the cheap stuff aimed at hobbyists.

The high efficiency of a ballscrew will however let it be backdriven by the load if there is nothing but a handwheel in free air to stop it. You could rig some kind of brake contraption to connect with manual operation. But it sounds like a lot of fuzz.

The disadvantage of always having the stepper/servo connected is that you need to have them powered and LinuxCNC running to use the lathe.
Then I would (in fact I will) hook up pulse generator handwheels to feed pulses into LinuxCNC and jog the axes. The handwheels can then be placed wherever you like them to have the best view of what's going on at the business end. You will then also get DRO's along as a freebie in manual/jog mode. ;)

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16 Jul 2014 00:17 #48813 by Rick G
Replied by Rick G on topic beginner lathe conversion .

On your lathe Rick did you use the stock screws or retro fit ball screws ? Do you drive the screws direct or use tooth belts for reduction ?


I started with a new lathe so the backlash was pretty consistent from one end of travel to the other.
As I needed a lathe to make the parts for this conversion (and I only had this one) I used the stock screws and kept the hand wheels in place for manual operation. With no power to the steppers the lathe can just be used as a manual lathe.
The idea was to convert to more precise and efficient ball screws later when there was the time and the need.
Currently I am driving the screws with timing belts with a 1 to 2 ratio.

This has worked well for me with the following considerations..
I always cut one direction (such as toward the head) using tools with a rake angle that does not pull the tool into the work. This way the backlash is always in the same direction.

Some NGCGUI subs are posted here...
www.linuxcnc.org/index.php/english/forum...-subroutines-library
John and ArcEye have others posted elsewhere but here are a few.

Rick G
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16 Jul 2014 15:47 #48837 by Einar
Replied by Einar on topic beginner lathe conversion .
If you turn the handwheels with the steppers connected through the belts then disconnect steppers from the drivers before turning!
The motors will be generators when you turn them and could damage the drivers which will not have the same means of protecting themselves when they are not powered up.
Turning slowly ususally does no damage, but noone knows the definition of slowly in this case.

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