Linuxcnc servo spindle encoder with pulleys

I have read a lot of posts about threading and rigid tapping with Linuxcnc. Most seem to discuss making sure you have at least an index pulse(for threading) and quadrature for rigid tapping.

I have retrofitted my hardinge DV-59 with a 1 1/2 hp servo motor and controller. I have it up and running. The servo has 4096 quadrature encoder with index(From what I have read I will need some sort of MESA board to interface that encoder resolution). My eventual configuration will have the spindle also able to perform as a C axis(the servo controller has a slave step/direction mode).

My question comes on the fact that currently the servo and the spindle do not have the same pulley size and finding one that matched has come up empty. I know eventually I will have to have timing pulleys for the C-axis functionality. Of course finding a matched set of timing pulleys where one has a center bore approaching 2 inches and another about 1/2 inch is difficult. So my immediate need is just to be able to thread and possibly rigid tap with current pulleys.

If I use the index pulse off the servo it will not be in the same point per revolution(ratio is about 1.125:1).

Anyone know a way to get an index pulse without putting another index pulse encoder on the actual spindle?

Any thoughts would be appreciated.

Thanks,
Chris

Can you just find 2 identical pulleys and bore them out to fit?
To give you 1:1 that is.

I guess I need to figure this out also. I want a C axis on a lathe I am building. I will be using 2:1 gearing
In my head it seems 2:1 would work, as it would just waste 1 revolution waiting for the index before syncing.
However with 1.125:1 or 9:8 (easier for me to think about it) maybe it would just waste 8 revolutions while waiting for the index?

Not sure if my math is right, but maybe you get the idea.

Im curious for a more confident answer.

Actually I tried that. But finding 2 pulleys over 2.5 inches OD with ID of .5 and 1.8 inches any ones with hubs would end up with no way to attach to spindle. That was my original plan but couldn't find 2 pulleys with .5 inch ID and over 2.5 inch OD with hub larger than 2 inches that I could bore out.

I figured when I went to timing belts I would probably have to buy pulley stock (at over $100) to make my own. Was hoping to find a quicker solution initially.


Any thoughts would be appreciated.

go to this website: sdp-si.com and search part # A 6A55-044NF1516

they have a huge selection of pulleys, I'm sure you can find something.. Cheap too.

Yeah I looked there. Close but I don't think it will work. The hub diameter is less than the spindle diameter, so when machined the hub will be completely removed along with method to lock set screw on the key.

I'll keep looking around. Actually that was the site I was looking to buy the pulley stock to machine my own from, but it is a little pricey @ over $120, but it would do both pulleys for sure and probably have some left over.

Thanks for the ideas though.

set screw holes could be drilled on the belt surface of the pulley.
Also they have a shaft-lock thing which doesn't use set screws, I'm not sure if they have a size to fit what you need though.

What I was planning on my spindle was sandwiching the timing pulley between a bearing cover and a locknut for setting bearing preload.
This, along with a keyway, is how the original v-belt pulley was secured.

Oh that is a good idea. Also I wasn't sure how the original pulley was mounted for sure, hadn't taken apart the back-end of spindle yet. The old bearings are a little noisy, but still running true. I have a new set I picked up old stock to replace them. Was just waiting until the old bearings started to get bad before taking that job on.

Do you have DV-59 also? In case your interested in the servo I used, I picked up a Parker apex drive and motor. Actually works pretty good. But I currently to set speed via a serial port, which should be an easy M code later when I get the CNC part running. Also will have to use serial port to put in C axis mode. The motor I bought also has a brake built in, uses 24 volts to release or set the brake, which is really needed for most C axis stuff.


Thanks for the ideas.

No, I wish I had a real lathe, I am building one from ebay and scrap parts.

Well I know the feeling. I bought basically a DV-59 bed and spindle only off ebay seller(didn't really want the other 800lbs of stuff on it since I was eventually going CNC with it so most would get replaced). I have added most of the other pieces off ebay also.

Another way is to use a separate encoder run by small gears or timing belt geared 1:1 off the spindle.