Manual and CNC Control?

[Dave Berryhill]

Is it possible to build a machine that has both handwheels and steppers/servos so it can be used as a manual mill and as a cnc mill? It would seem to be the best of both worlds for a small shop or hobby machinist who doesn't have the space for both.

[sti2011]

They have existed for a long time.........Look at Southwest Industries for a quick example or two......

[halfstep]

Originally Posted by sti2011 They have existed for a long time.........Look at Southwest Industries for a quick example or two......

Do you mean southwestern industries?

[Dave Berryhill]

Interesting but a little pricey. Is there anything available, either as a complete machine or a conversion kit, for a bench mill the size of an Industrial Hobbies or Novakon NM-135/NM-200 machine?

I posted the question in this forum because the IH is available as a manual or a cnc mill so it would seem to be a likely candidate for such a conversion.

[mvcalypso]

Dave,
here are some things to consider when thinking about a dual manual/cnc mill approach....

manual mills typically use acme screws for the axes. acme threads have the nice property that they are hard to back drive - thus when you stop turning the screw the table stays where it is. Alas, acme screws also typically have backlash. we deal with the back lash buy cutting in/from one direction on a manual mill.

CNC mills use balls screws to eliminate backlash. Since CNC motion is very unlikely to be from a single direction re cutter forces, backlash is bad in the cnc world. hand driving a ball screw feels real smooth - but ball screws are also easily back driven - thus things like cutter forces tend to make the table move out of position - during cnc operation those forces are countered by the stepper or servo motors.

If you use ball screws to remove backlash, and turn off the motors to get a "manual mill", it becomes very hard to keep position.

I believe the CNC machines that have manual modes use an electronic interface to the operator (mpg dial for example) and then use the cnc control to drive the screw to match mpg inputs. This of course does not give the "feel" of a manual mill.

It's another of life's trade offs...

Dave

[Runner4404spd]

actually ball screws are not used to remove backlash. i have built anti backlash acme assemblies, the drawback is that the acme screw is not very precise, or at least the stock ones aren't. and also the anti backlash feature adds alot of friction. so what you end up with is a mill that needs to use acme screws to be able to be manually operated and therefor you need really large motors or a really large pulley reduction so the mill ends up slow under cnc control. can it be done? Yes. i operated a bridgeport that had a conversion on it once upon a time and it was equiped just like described above. also it had handles that would fold into themselves when under cnc control so you wouldn't have a swinging lever that would wack your fingers.

[TOTALLYRC]

Originally Posted by Runner4404spd actually ball screws are not used to remove backlash. i have built anti backlash acme assemblies, the drawback is that the acme screw is not very precise, or at least the stock ones aren't. and also the anti backlash feature adds alot of friction. so what you end up with is a mill that needs to use acme screws to be able to be manually operated and therefor you need really large motors or a really large pulley reduction so the mill ends up slow under cnc control. can it be done? Yes. i operated a bridgeport that had a conversion on it once upon a time and it was equiped just like described above. also it had handles that would fold into themselves when under cnc control so you wouldn't have a swinging lever that would wack your fingers.

The Y axis handle can whack something a lot more sensitive than your fingers. That is why the folding handles are needed.

I find on my machine which was made from the start as a CNC machine and has no handles or provisions for handles either. I will either use MDI for the quick cuts or I will use the the gamepad/pendant. An mpg would also work well in this situation but I haven't made one yet.

Mike

[Dave Berryhill]

Originally Posted by TOTALLYRC ...I find on my machine which was made from the start as a CNC machine and has no handles or provisions for handles either. I will either use MDI for the quick cuts or I will use the the gamepad/pendant. An mpg would also work well in this situation but I haven't made one yet.... Mike

It sounds like that is a workable solution but I don't know how practical it would be for someone who learned machining on a manual mill and is just starting to learn about cnc. I didn't realize that the dual control mills that I've seen actually use an electronic control for the "hand cranks" but it makes sense to do it that way.

Thanks to everyone for your input!

[TOTALLYRC]

Originally Posted by Dave Berryhill It sounds like that is a workable solution but I don't know how practical it would be for someone who learned machining on a manual mill and is just starting to learn about cnc. I didn't realize that the dual control mills that I've seen actually use an electronic control for the "hand cranks" but it makes sense to do it that way. Thanks to everyone for your input!

Hi Dave.
For those quick cuts you can use the tab flyout, set the jog percentage speed to what feels right, and then jog using the keyboard arrow keys.

I don't remember how long it took me to realize what MDI actually was or what it did. It is manual data entry and allows you to do g code one line at a time.
Most of my MDI is straight line moves or rapid moves. I do most of my work with the cam program, but it is a great feeling to know that you can go to the MDI and make the machine do what you want.

Keep learning.

Mike