[jivetin]

I would like to install Cnc contol on the vertical axis of my sherline mill which I use as a tool grinder. The vertical movement advances the tool blank onto the grinding wheel. I am doing it by hand right now, but would like to automate it. One very important aspect is that I need the feed to be super slow, about 1/2 of a revolution per minute or even slower than that to allow the grinding wheel to remove the material in time. I am totally new to Cnc so i have no idea if any cnc stepper motor is capable of achieving this speed of feed or if I need something special, perhaps a reduction gear? I looked at the conversion kits and controllers that sherline offers for their machines, but their slowest speed is 1" per minute which is 20 rpm instead of 1/2. Would appreciate any advice anyone can offer.

[rpovey]

Steppers as their name implies have steps, you can't really accurately move less than one step. Some controllers have "microsteps" but they are more about smooth motion than actual steps.

So about the minimum you can move is ~1/200th of a turn, there ought to be nothing to stop you doing that very infrequently, but the 1 inch / minute might be a limitation of the controller software.

As far as I can see EMC has no issues trying to move the axis at 0.02 inches a minute, I haven't tried it on my mill.

It's also possible that the steppers don't have enough torque or might stall at that speed, but I have no expertise here.

[jivetin]

Thank you for the reply. I will ask sherline if it is just the limitation of their controller, or the motor. Meanwhile, is there a chance you can try to replicate such a slow motion on your mill, if it is similar to sherline and if you have a chance. And let me know. Would much appreciate your further input. Thank you.

[jivetin]

Sherline acknowledged that it was their controller that limited the feed rate. Apparently it is not the limitation of the stepper motor. I guess I need to look elsewhere for a controller. Any suggestions for a nema 23 motor independent controller? (I don't really need any more than one Cnc axis, so don't want to invest in the whole system)

[rpovey]

Let me check what my gecko drive does this weekend.

[rpovey]

It appears to work fine, you can see the steps as the controller moves the axis, but I put some force against the table and it didn't stall.
As a point of reference I'm using a sherline mill with a geckodrive G540, 270oz steppers, and EMC2 as a controller.
I bought the CNC ready mill and the rest as a package off EBay, I think the sellers name is deepgroove1.

[jivetin]

That is great to hear. Thank you very much for trying it out. I am not necessarily concerned about the smoothness of motion, but just the overall rate of feed. And thank you for giving me the specs of your hardware and coordinates of the seller. I think I will get a cnc conversion kit from Sherline and everything else on e-bay. What about software, I heard it was a touchy subject. Is this also available on e-bay? I am mostly familiar with 3-D modeling, and programs that run cnc routers and engravers, but what do you suggest I need for a seemingly simple operation of one axis like that?

[rpovey]

For something that simple I'd just type in the gcode.

I have a collection of small GCode fragments, that have parameters at the top of the file to do mundane operations like facing, CAD/CAM involves a lot of messing around to generate a tool path.

For control software I use EMC2 it's free. I have a demo copy of MACH3 on a second machine I've been looking at, I like a lot of the convenience features in Mach, but EMC2 will do anything Mach will.

If you decide you want CAD/CAM, it depends what you want to spend, what you want to do and what interfaces you find intuitive, about all you can do is pick a price range and try out the demos. I've yet to find CAM software that I really like.

[rpovey]

Double Post

[cyclestart]

The Gecko G540 uses 4 G250 drives.
G250X 10 Microstep Drive

One of those drives along with a power supply and some type of BOB (breakout board) should be all you need to control a stepper (well that plus a computer and software).
There's probably a really cheap DIY way to hook this all up, I'll leave that explanation to the electronically competent

Are components from Sherline really necessary for one axis of movement ?

[jivetin]

I was gonna get the stepper motor base from Sherline, and they recommend changing the leadscrew to fit the steppers. That's why I though I might get their kit. Is there an alternative?
So what is a breakout board? Where can I find this?

[jivetin]

Found out what the breakout board is. I am not sure I can hook it up, though, since I am not that electronically savvy. Hmmm. Will look to see if I can find geckodrive you suggested with the transition together, so I would just plug it into the computer.

[cyclestart]

I was gonna get the stepper motor base from Sherline, and they recommend changing the leadscrew to fit the steppers. That's why I though I might get their kit. Is there an alternative?
So what is a breakout board? Where can I find this?

I like the DIY approach, it's educational and usually saves money. otoh it can be expensive in terms of time so it's not for everyone.

It's very common to drive a leadscrew via timing belt and in your application the pulley ratios could be used to advantage.
An example in this link:
http://www.cnczone.com/forums/408116-post11.html

I'm not familiar with Sherlines or how their cnc leadscrew differs from the manual version.

It's should be possible to wire a G250 directly to parallel port. The simplest BOB would be a parallel port cable splayed off into individual screw terminals. Commercial BOBs provide opto-isolation to protect the computer.

[rpovey]

The issue with a pulley setup on the Sherline Z Axis, is that the column isn't very stiff to start with and any additional weight hanging off to one side of it isn't going to help you out any.
The Sherline is designed to machine small parts, probably only weighs 40lbs total, so the steppers are significant additional weight.

I thought the only difference with the Sherline Z Axis lead screw for CNC, was the addition of an anti backlash nut, which Sherline sells separately. Although I could be mistaken.

[jivetin]

Is there a reduction gear mechanism sold somewhere that could be used instead of the pulley system? 1/4 ratio would probably be all that is needed.