Centroid Community CNC Support Forum

dmbgo wrote: ↑Sun Jun 25, 2023 8:22 am Not as easy as you might think, any suggestions would be welcome.

Based on the information given, I suggest using screws.

The information given about the spindle was a little on the light side, wasn't it Tom? Even though I have arrived at a similar conclusion, and think, like you suggest, that I will use screws to mount it and, that I will incorporate a belt as well. Anyway, joking aside, the spindle on the mill uses a set of conical pulleys to vary the spindle speed manually, by closing one pulley, whilst the other opens, and vice versa. This opening and closing action causes the spindle to rotate faster, or slower, depending on which pulley is manually set to have a larger gap, via the manual speed selection. I plan to use a VFD to vary the spindle speed, via 0 to 10v from the Acorn controller, with the manual adjustment only used for a coarse, or approximate speed range of the spindle.
The issue that I am faced with is that there is very little space left within the speed regulating head of the mill for anything else, other than the mechanism it was designed to incorporate. I have a set of 16mm wide toothed pulleys and a belt to drive an encoder that might fit inside the head of the mill, with the encoder mounted on the top of the milling head (with SCREWS!), but even that system will cause me to lose approximately 8mm of vertical travel of the front conical pulley, with a corresponding reduction in minimum speed.
I think that given the incorporation of a VFD, that this loss of minimum speed wont be an insurmountable issue.

I'm still willing to scrap this system and start again, if there are any better suggestions. My proposal is difficult to implement, and has drawbacks.

That's essentially a Bridgeport 2J head. Here's how I did it:
https://centroidcncforum.com/viewtopic. ... le+encoder

Thanks for that Tom. I have to start my day now, but tonight, I'll have a good read. (it's hard being at opposite ends of the earth)

3 weeks later and I have finally gotten the spindle encoder installed. It is a bit of a compromise, given that now the front pair of conical pulleys have their upwards movement restricted by about 8mm, which is the height of my encoder pulleys. I think that by using a VFD for spindle control means that any loss of minimum speed will be offset by the ability to slow the motor electronically, so it shouldn't be an issue.
Here are some photos of my final setup, I made a little bracket, to prevent the belt from running off the pulleys.

BTW, thanks for sharing your post on the encoder setup Tom, I decided to proceed with my planned setup, since I had already started down that path. If I find a reason why mine is a problem, I will consider your setup as an alternative.

Your setup looks great, and will work fine for 99% of your use. The only time it will give an incorrect reading is when the back gear is engaged.

You are correct about the back gear Tom, I knew it would read incorrectly, but for the very few times I use it, I'll just fudge the spindle speed. Thanks for the compliment as well, I was a bit concerned that it wouldn't work, but it seems fine.

There is no need to "fudge" the spindle speed in back gear.

For outgoing commands to the VFD, you need to provide a way to tell the PLC you are in low range; then set Parameter 65 to the ratio.

For encoder feedback with your type of installation, set bit 4 of Parameter 36 (add 16). That tells CNC12 to multiply encoder counts by the ratio in Parameter 65. You still can't do peck tapping, because the index pulse is not synchronized, but speeds and even thread leads should be correct.

Thanks for that info CNCSNW, I'll get the controller box mounted to the mill now (it's currently still on the bench), then revisit the encoder software setup. There's a lot of software tuning and adjustments to do, for the servos, which are operating on the bench, but not tuned for the axis, as well as the encoder. Then there are things like the coolant etc to sort out.
I've got an existing switch box on the mill, with a plethora of contactors etc that I haven't even started on yet (I'm not looking forward to that btw).
I don't really know what I am doing there, but I'm hoping, with everyone's help that it will all be resolved in the near future. I'll post some photos of the switch box and the controller mounting when the controller is on the mill.