Need Opinions On Belt Drive

[JimDawson]

I am getting ready to convert my mill from a vari-speed to direct drive with a sensorless vector VFD because I have a bearing failing in the drive system and I have been wanting change it over anyway. Makes it easier to get the spindle under computer control.

I thought about a toothed belt and sprockets, or multi-V, but I can't think of a good reason to go either of those routes. Just adds expense with no benefit that I can see.

So it comes down to double groove or single groove V-belt pulleys. The pulleys will be about 6 3/4 inch outside diameter and the same size on both the motor and the spindle shaft. The motor is a Baldor, 3 hp, 1750 RPM and has a max rated speed of 6000 RPM, but I will limit it to 4500 RPM. Back gear will still be available with ~ 8:1 reduction.

I am leaning towards a single groove, B section, and a Kevlar belt.

Any thoughts?
.
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[Bob Korves]

I agree entirely. Here is a reference if you have not seen it. Looks like one B belt will do the job fine and for little money. Easy to make the sheaves, or perhaps even find something off the shelf you can use. Keep a spare belt on hand and you are golden.
http://www.c-rproducts.com/downloads/pdfs/Industrial_vbelt_drives_design _guide.pdf

 

[JimDawson]

Thanks for posting that link Bob. Looks like the only problem in my thinking is the sheave size. I need to use about 5 inch pitch diameter to keep the belt surface speed under 6500 FPM @ 4500 RPM.

I could make the sheaves, but I'm too lazy to do that. I can buy off-the-shelf hardware for about $140 including sheaves, QD bushings, and belt. I'll take the motor and the rest of the new drive system parts down the street to my friends shop and use his balancer to make things nice and smooth.

 

[mattthemuppet2]

not on your list, but personally I like poly V belts - smooth, quiet and a ton of grip. Easy to make the pulleys too.

 

[4GSR]

I agree with Matt on the poly V belts provided you can keep the motor shaft and spindle in perfect alignment. Rather than using the B section belt, go with a 5V section belt. With the larger diameter pulleys, you should be able to go with a 3V section belt. These belt sizes can handle much more HP than conventional A or B section belts.
Ken

 

[JimDawson]

not on your list, but personally I like poly V belts - smooth, quiet and a ton of grip. Easy to make the pulleys too.

I thought about a toothed belt and sprockets, or multi-V

Well I intended to put them on the list, but I used the wrong name. I just can't see the need for the extra expense, and I just don't have time to make them. I'm already working 7 days a week trying to keep up. Pesky customers are keeping me from the projects I would like to be doing. I would just like to get the yard (jungle) mowed!

 

[JimDawson]

With the larger diameter pulleys, you should be able to go with a 3V section belt.

Yup, I agree after looking over the link that Bob provided. 3V it is!

 

[mksj]

I have been looking at the knee mills with digital VFD drives, the ones I am looking at use cogged drive belts in the head and back gear drive. I have also seen poly V- belts used.

I do not know the specifics of why, they are a bit more efficient, have longer life and belt size can be reduced. Given the higher motor speed you plan on using, they may run smoother. With a cogged or poly V belt you could use aluminum pulleys that decrease the rotational mass.

 

[4GSR]

I run a double 3V belt on my 13" Sheldon Sebastian lathe with a 3HP 180RPM motor. Been on the same set of belts for over 35 years! I'm sure they are getting to the end of their life, but I'll keep them running until they break!

 

[John Hasler]

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