Hi folks - this looks like the ideal forum to post this:
I'm a retired engineer who is also an experienced cnc user - specifically a shopbot 3-axis router. I've never built a cnc or automated tool from scratch but I'm ready to go for it now.
I recently designed and built a simple, manually operated, purpose-built, "router lathe" to machine a specific wood product we manufacture. It consists of a slow turning platter (driven by a variable speed DC motor) to which the piece is attached, and two hand-held wood routers mounted on sleds which are moved by hand cranks into the slowly turning piece.
I now want to build a more automated version of this tool to enable higher volume production. Minimally, I need to automate the movement of the two router sleds with configurable incremental motion steps that are synchronized to the rotation of the platter (i.e. they will move a configurable distance with each revolution). I envision using Firgelli Linear Actuators (or similar) with Arduino Uno microcontroller(s) for this. I envision a proximity switch that closes a contact with every revolution of the platter, as the trigger to move the sleds.
It might be nice (but not required) to also automate turning the platter and router motors on/off, as well as controlling the platter speed (currently controlled manually via a potentiometer).
My questions:
Any input or advice on the concept above ?
Is all the logic for the control of both sleds appropriately encoded in a single Arduino controller ?
How about adding the control of the 3 motors and possibly the speed control ?
A little outside this forum perhaps, but:
What is the recommended control "console" ? Is Mach3 appropriate ? ...overkill ? ...any thoughts on if its extendable to control this hybrid device ?
Since the only thing I really need to "parameterize" is the number and size of the incremental movements of the router sleds, perhaps a much simpler "console" is more appropriate ?
Thanks in advance for any guidance,
Tom from Eagle Point Oregon
or if you have a really old PC, turboCNC
shareware
to do it right, you need a post processor. this takes your CAD files, turns them into g-code, adds any tooling cutter offset, and also creates a tool path. most cad files draw lines in the order they were made. that means if you moved a line, it went to the most recent. this results in the tool jumping around and not smoothly flowing.
if you are just doing a simple thing, you can create your own g-code by hand ( I used to use a spreadsheet)
if you are doing production, then you can skip some of the special software.
however, if you do frequent changes, the above packages will offer a lot of speed for you.
also, most the stepper drivers we discuss are hobby versions and are limited to about 24 volts and 2 amps.
you can get a much better driver on e-bay for decent money. look for stepper motors of less then 5v rating, 3v is better.
not sure if you can find 8 wire steppers easily, but driving them with serial coils, you cut the voltage in half and they have the power, but not the heat.
when we discuss CNC we often think X and Y as two linear movements on a stage that moved perpendicularly. with Z being the drilling down axis.
on a lathe, the long axis is Z
the cross slide is x and the rotation of the spindle is Y.
if you are running at over 500 RPM, then you can use a single point on the spindle as your RPM reference.
if you want to move slow, you need to put an encoder on the spindle.
if you want to crawl, then it may make more sense to put a stepper on the spindle and use that to rotate the part.
I am not familiar with the linear actuators you listed. I use steppers and timing belts. and drive lead screws.
with a lead screw, you can driver it direct with a stepper.
do the linear actuators you reference offer step resolution ?
I advise that to cut to any accuracy, that your positioning needs to have 4 times the resolution. if you want to be more precise, then the axis under control should be able to position 10 times more accurately.
First to answer your question about the linear actuators: They are motor driven linear motion devices - often employing ball screws to extend/retract a "piston". I would use either stepper or servo driven units. Stepper would be adequate resolution & accuracy given my application.
To your other comments: I am somewhat familiar with Mach3 functionality. It seems way overkill for what I need and yet misses the mark in other ways, since I'm not trying to build a general purpose cnc machine, but rather a very specific purpose-built machine to do one thing - in a fully automated fashion.
Again, 2 router sleds need to be moved incrementally in a straight line in a specified variable distance, triggered by each revolution of the turntable/platter. Thats it.
I understand g-code and post processors, but again both seem like too general a solution. Some form of simple programmable controller with little or no Mach3-like console seems more than adequate.
if you have an encoder on the spindle, then you know the position.
if you use that as input, you can create the output to be in the relationship of movement based on rotation.
I used to make a product that had a simple operation, rotation, drilling on angles and such.
once I got the machine working I was able to code one while one was in the machine.
ultimately, there were only about 500 variations so it was finite coding.
there is also a board ELS for Electronic LEad Screw.