Hardware needed for my lathe setup

I'll preface this by saying I'm not new to CNC, but am new to CNC Lathes, and I've never used LinuxCNC. I am very likely buying either an old Unimat lathe and adding motors, or a small Sherline 4000, to make some very specific parts for work. I already have a manual mini lathe but I want to be able to make some small parts with more repeatability, and without having to stand at the machine for hours on end. Everything will be made of Delrin, possibly HDPE. So these are the machines I'm looking at. 

Motors: I expect to replace the original motor with a used Teknic Clearpath that we already have here, which will allow me better control over the speed. This has an integrated driver. I also expect to have to replace the X and Y motors. For these I have some closed loop stepper motors with drivers.

Sensors: Homing switches could be mechanical or proximity, I have both kicking around, (5V).

Computer: I could either use an old MiniPC that should be plenty fast enough for a lightweight linux distro, or possibly an RPI 5. I don't need a touch screen but will likely have a keypad with common functions mapped (something like a small XKeys module). I think I'd like some kind of MPG control as well.  

This leaves me wondering what kind of interface I need between all these things. Right now I use a Masso G3 on my CNC Router and haven't ever really had to think about this kind of thing, but it's more than I want to spend on this little project, which is why I'm looking at LinuxCNC. 

I'm looking to keep this as inexpensive as possible. What am I going to need to tie it all together?

You could use the Parallel Port but I don’t think that will have the amount of I\O you want.
There are a couple of projects discussed on the forum that use an Arduino.
Scott’s remora project might be an option, but the RPi5 is not an option for SPI communications due some major changes. The RPi4 is still an option for SPI communication.
Obviously any of the Mesa Ethernet cards are a good choice, it really depends how far your budget spans.
If this is your first dip into Linuxcnc just use the supplied ISO running Debian.
Have a browse of the forum see what others have done. It’s kinda hard not knowing budget, how much of your own time you want to put in and such.
Even browse YouTube there’s some good stuff there as well.

Thanks. I bought a Denford Microlathe on ebay and am waiting for it to arrive. This uses what looks like a Sherline 4000 inside.

I'm leaning more towards repurposing a mini PC we used as a server under windows, but hasn't been in use for a while. it's all solid state, and pretty fast (i7 if I recall correctly). It's small enough that it won't take up much room.

That leaves mostly the interface. So I take it a Mesa 7196S would be sufficient? it's 5 axis and I only need 2. Can the Sherline spindle be controlled by the analog spindle speed outputs on the Mesa? I might try using it at first before I dive into upgrading it to the Teknic. If it works, why not? Of course it probably needs an encoder added as well.

The 7196S has 11 ins and 6 outs so I should be covered for homing switches. it looks like an MPG uses the generic I/O ports as well?

friolator wrote:

Thanks. I bought a Denford Microlathe on ebay and am waiting for it to arrive. This uses what looks like a Sherline 4000 inside.

I'm leaning more towards repurposing a mini PC we used as a server under windows, but hasn't been in use for a while. it's all solid state, and pretty fast (i7 if I recall correctly). It's small enough that it won't take up much room.

That leaves mostly the interface. So I take it a Mesa 7196S would be sufficient? it's 5 axis and I only need 2. Can the Sherline spindle be controlled by the analog spindle speed outputs on the Mesa? I might try using it at first before I dive into upgrading it to the Teknic. If it works, why not? Of course it probably needs an encoder added as well.

The 7196S has 11 ins and 6 outs so I should be covered for homing switches. it looks like an MPG uses the generic I/O ports as well?
 

Spindle:  Do you know what kind of motor the spindle uses, and what is driving it now?  Those details will help determine if the 7i96s can drive it properly with the analog pins.

Teknics: Which model do you have on hand?  And do you have an appropriate power supply(~75vdc)?  Again, the model will determine if it's suitable for use as a spindle.

MPG: which MPG are you considering?  Some use Mesa IO, some use USB.

IO: depending on the limits you use, you could be in good shape with just the 7i96s.  One input for estop, one for X, and one for Z.  Once homed to the switches, LCNC's softlimits will keep you out of trouble so you don't need two (or 3) per axis.

Might want to make a list of all desired IO (current and future - power collet closer?)

Never used a Sherline so I don't really know what the spindle motor is. It is, from what I can see in the photos, the same motor the sherline 4000 lathes use. There's a pot on the front control panel for spindle speed, so I'm assuming that a simple voltage change handles that. I can always put a PWM to voltage board in there if need be. I guess once I have it and can look up the motor for sure I'll know.

The Teknics we have are these: teknic.com/model-info/CPM-MCPV-2311S-ELN/. -- would need to pick up a power supply for it. it's about .4NM torque (constant) so might need to be geared to get a bit more. That said, I'm inclined to leave the default motor in there if we can hack an encoder onto it and control the speed. I don't need absolute precision here, just good enough.

I *think* the lathe already has limit switches on it - how many I don't know, but should have answers next week when it's in front of me.

I think really all I need for the controller is the limit switches, the encoder for the spindle motor, and I might want to add a tool setter though to calculate offsets automatically. Other than that it's just the spindle and axis motor controls, which are separate from the I/O ports on the 7I96s.

Haven't looked closely at MPGs, but most likely one of the cheap ones you can get on aliexpress or amazon that have bare wire connections.

The sheline 4000 looks like the spindle motor is a brushed DC thing, with a DC speed control on top of the headstock.  The speed control likely has a potentiometer inside, so it may be possible to hack something in there.  It's not going to be a plug-n-play affair unless there are external speed control inputs somewhere I cant see in the parts diagram.  If the speed control uses a standardish pot and 0-10v (or close), desoldering it and replacing it with wires to the 7i96s might do it.

The Teknics MCPV has a 'manual velocity control' mode, but that uses a quadrature a/b input signal to set rpm.  So the 7i96s analog out won't be helpful.  I think it would be possible to use a couple of the 7i96s outputs to mimic a (low speed) quadrature output to set RPM.

There's nothing 'off-the-shelf' inside LCNC, but the stepgen.comp component can output a quadrature signal.  Just guessing here, but the configuration would probably be something like a look-up table (lut.comp) that takes commanded RPM in and outputs the correct 'position' number of steps to a position-mode stepgen component.  i.e. M3 S1000 = N steps 'clockwise'.

MPG - the discrete wire MPG's usually take a fair amount of IO to work. Just an estimate, but for a 2-axis lathe:

• Encoder
  • A-pin
  • B-pin
• Increments
  • increment #1 pin
  • increment #2 pin
  • increment #3 (both #1 & #2 off, no 3rd pin needed)
• Axis select
  • X - 1 pin
  • Z - (X pin off)

So that's 5 input pins for a useable but bare-bones MPG.

A physical feed and/or spindle override would be nice.  The 7i96s doesn't take analog in, but a single knob encoder can do it with 2 pins.  If you use one of the encoders with a built-in push button, a 3rd pin would let you toggle between FRO & SRO.  Or even multi-click through FRO/SRO/RRO, and jog speed functions - all with one encoder.

By my count, with 11 inputs you can have an external estop in, X/Z home, MPG as above, and a multi-function override encoder.  Not a bad setup.

Next step is to wait for the lathe to show up and see if you can work out the DC speed control.

Oh yea.. the tool setter...

I wouldn't bother.  Unless you are changing tools constantly in the holders, it's easy to take a skim cut, measure, and input your offset.  Buy a few more holders and leave your 'go-to' tools set up all the time so the offsets don't change.  Insert tools are so cheap these days, and sharp inserts for aluminum work great for under-powered lathes (even in steel)... I wouldn't bother with HSS tools unless you need a specific form tool.

A CCMT, a VCMT (left and right), threading tool, and a narrow parting tool are about all you'll need for most simple-ish jobs.  Four insert shapes to keep on hand.

There's a thread about connecting a parallel port type MPG to a  7I96S's P1:

forum.linuxcnc.org/39-pncconf/51733-7i96...configurator?start=0