Shoptask CNC Lathe and Mach3: Gcode delima

[KaptainKarst]

I'll try to explain this and maybe there is a simple solution....
As you know the 3 in 1 machines like the Shoptask have 3 Axes. The X being left to right along the longest bed. The Y being the table that slides along the X axis and the Z being the overhead R8 spindle that moves up and down.

These are the conventional axes for milling operation and Mach3 works great.

Now to my delima:
If I want to lay out a simple lathe job, I have been using a cad program to draw my object. This is done in the X and Y plane and translates well to the 3 in 1 machine setup and Mach3.
However, conventional CNC (and manual) lathes use Z and X axes. Z being the long, right to left movement and X being toward or away from the center of the object being turned.

What I am trying to do now is to use the CNC lathe of the 3 in 1 machine to cut a radius or ball on the end of a a piece of round stock in the lathe chuck.

I can lay this out in the CAD program with no problem.
and the Gcode is generated via Sheetcam with no problem.

Now, you and I both know that I cannot just plunge my lathe tool in and cut the entire radius in one pass. So now I need to use the multipass function of Mach3, but alas, it only supports multipasses if a Z depth needed.
If I then convert the Gcode for X and Z codes, then the I and J gcode commands are wrong and all is screwed up.

How are you guys using a 3 in 1 machine for CNC lathe operations that involve radius cuts?

I hope that was clearer than mud....

[Ron111]

KaptainKarst,

I have a shopmaster, and being used to using the milling machine conventions I also would generate code and treat the latheing activites like I was milling. Until I converted an harbor freight 9 X 20 to full cnc including automated threading. At that point, I discovered the Mach3Turn Wizards which I think will do what you are wanting to do. They were very handing for threading operations and I think will support your efforts.

I hope it works for you,

Ron

[KaptainKarst]

I too have found the turn wizards.
But are you physically switching the leads of your stepper motors to reflect the axis naming convention of lathe operations (ex. switch the x mill axis to the Z lathe axis and the Y mill axis to the X lathe axis).

Thanks,
Jim

[Ron111]

Jim,

No, I not changing cables and would not recommend doing it. But after a little thought, One way to do this, you could reassign an axis in the config settings of mach 3. There you could redirect your step and direction pins (each motor is controlled by step and dir pulses ). Mach3, the controller, assigns which of the pins of the parellel port, has the step and direction for each of the X, Y & Z axis. Then you could save it to alternate configuration file that you would load when started mach3 when you wanted to use this altered configuration.

Talk it over with Dan Mauch at camtronics and make sure you have it straight in your head and on paper. I know that you can do it this way. But you don't to mess up your original configurtion settings, so save a copy of it.

Ron

Ron

[KaptainKarst]

Ron,
Hey, thats a great idea to try.
I have created seperate profiles already (I have a cnc wood router as well as the cnc 3 in 1 machine). So I will create an alternate profile and will just have to remember what is what.....

thanks, I'll let you know how it works out after the weekend.
Jim

[Ron111]

Jim,
I gave it some more thought, you may also have to adjust your motor tuning in your config file (your back lash and the steps per unit) Let me ask you, was your machine cnc straight from shopmaster? What values are you using for backlash for x, y, & z?

I was monitoring a thread on the conversion of a X3 mill using nook ball screws and he had .011 backlash (and on my x axis I have about .017, which I have isolated to the ball nut, so I courous as to this issue as my shopmaster has nook ballnuts)

Thanks,

Ron

[KaptainKarst]

I did the CNC conversion myself on the shopmaster.
I am using the normal factory installed acme screws.
I will have to check on the backlash values next time I fire up the shop computer.

I suspect that I will have to do a complete motor tuning process with the new profile for the lathe operation.

[Ron111]

Jim,

If I may ask, what size stepper motors did you use and what drivers? And what kind of rapids can you do. The rapids on my machine or set around 30ipm, which I need to use a tapping head.

To be honest I haven't been too happy with the cnc job because of the fairly large backlash and to correct it would take replacing the screws because they welded the ends of the acme screws to them, so you really can't just replace the ball nuts or add a second one to preload the first.

I pocket out a circle (clean out a 1.20 inch circle on a product that I build and I have say a .018 out of roundness issue) . This is one area that the backlash compensation doesn't quite do it.

Thanks,

Ron

[borrisl]

I've got .005" on my x and y axis, and .004" in my Z axis. Using double nut ball screws. Since this is my first time with ball screws I didn't know if this was good or not?

[Ron111]

Borrisl,
Good hearing from you, were those double nuts capable of preloading. With preloading that backlash should get even closer to zero, if not zero. You showed your machine eariler in a previous post, it's really something. I wish my backlash were as low as yours. My screws had the ends of the original acme screws welded on, and I'm wondering if I could take the balls out of a new ballnut and slip it over the weld and load the balls in it and then preload it.

Let's see what the shopmaster guys think,

Thanks,

Ron

[borrisl]

They do have pre-loading capability, however I've been unsuccessful in getting them to zero. Probably just my lack of knowlege in the matter. I did have the welded ones that came with the Shoptask on at first. I didn't have any problems getting the ballnut off. The welded section was smaller in diameter than the opening.

[Ron111]

Borrisl,

Do you think that it is possible to add a second ballnut to the welded ball screw(on my shopmaster). The only way that I see to do it is to dump all the bearing and place the 2nd ballnut on the screw (past the weld) and try to load the bearings. How difficult would that be. Or I guess the question is can it be done.

Thanks,

Ron