Centroid Community CNC Support Forum

Hi Clay,
I found a source for reasonably priced HTD pulleys. From what I have discovered thus far, the GT2 is a little better than the HTD and also more expensive. I just don’t know what kind of performance one needs for a spindle motor for rigid tapping, etc. Does the belt/pulley system need to be as good as what you’d use on an axis drive? I’m assuming it doesn’t have to be that good.

ScotY wrote: ↑Tue Nov 21, 2017 10:58 pm Hi Marty,

That's what I need to do in order to use the DMM servo motor. My mini mill uses a v-belt. I would need to find a way to replace this with some sort of timing belt and pulleys.

I'm looking to purchase a 750 watt servo motor. Any suggestions on size/type of timing belt to use? My current spindle pulley has a 30mm bore with a keyway. The motor has a 14mm shaft. I want to gear it 1.5:1. The motor runs around 4000 rpm max and I want 6000 rpm at the spindle. I'm not sure I'm going to have enough room. I also don't know how I would cut a keyway.

Is there a setting in CNC12 that would allow ratio adjustment for the spindle? Hadn't thought about that until you mentioned gearing 1:1.

Sorry for missing this, I hadn't subscribed to the thread....
Keith answered your question about why the encoder needs to be 1:1 as did Clay
MXL timing belts and pulleys are very popular. You might look for an aluminum pulley with a diameter that allows you to bore it out and clamp it to your spindle. Then use a jackshaft arrangement for the same tooth count pulley and couple it to your encoder.
Marty

ScotY wrote: ↑Sun Nov 26, 2017 1:43 am Hi Clay,
I found a source for reasonably priced HTD pulleys. From what I have discovered thus far, the GT2 is a little better than the HTD and also more expensive. I just don’t know what kind of performance one needs for a spindle motor for rigid tapping, etc. Does the belt/pulley system need to be as good as what you’d use on an axis drive? I’m assuming it doesn’t have to be that good.

If you're not planning on a "C" axis, the HTD should be fine. They are noisier than GT2. The backlash on an HTD is a little higher as well. HTD is designed as a drive belt not a timing belt therefor can handle higher stress. I think for tapping and threading it will be okay.
Did you look at the speed rating? Not sure if they go all they way to 6000rpm.

Clay

i know space is a issue on some of these smaller machines.. but as an alternative i wanted to mention you can get small three phase AC motor and drive packages that run off of 110 VAC wall outlet power.. see this site http://dealerselectric.com/motor-and-dr ... ontrol.asp
alternatively automation direct sells similar setups. combined with a spindle encoder this setup can give you constant surface speed, threading and rigid tapping capabilities.

Thanks, Keith...I appreciate the reply.

FYI, if anyone is looking to buy a keyway broach, I can recommend strongly that you stay away from cncbroachtools.com. I just called them because I was looking for some sort of broach tool so I can make some custom pulleys for the servo motor. I know I can grind one myself but I'm lazy, strapped for time, and don't even have a bench grinder. The guy on the phone was incredibly rude and ended up hanging up on me. He refused to even give me a ballpark idea on tool price without sending him a written request with all kinds of specs like keyway width tolerance, etc. He just couldn't understand that I have no tolerance specs for that. I explained that I was just a guy working in my little shop at home and he was really not cool. Anyway, enough of my ranting, it's just so disappointing to speak to a company that just doesn't care one bit about the little guys. Glad Centroid is not like that at all.

I've been doing some research on pulleys and stuff and it seems the more you read, the more questions you end up with.

My $0.02 here. Don't use keyways. Setscrews loosen and keys develop slop adding to backlash and other problems. Check out Fenner Tran-Torque couplings - http://www.fennerdrives.com/trantorque/

Cheers,


Tom

Hi Tom,
Thanks for the link. Those couplings look nice but a little expensive...$150 for the 2 I would need. Then again, time is money and it would be easier than cutting a keyway. Any idea how long they are? I need one for a 30mm bore and another for 14mm. I'm not sure if I'll have enough space for them if they are very long.

Scot,

Click on the individual coupling links and it will take you to a page with tabs for 3D models and dimensions. FWIW, McMaster sells Fenner couplings - they just don't tell you the brand name. https://www.mcmaster.com/#keyless-bushings/=1agxrbf

They are sold based on shaft sizes. You may have to re-bore your pulleys to fit.

T