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View Full Version : Surface grinder drive belt – which type?



DaveR
05-25-2010, 11:37 AM
I have an old (1946) Delta 6x12 surface grinder that I've been refurbishing. One thing I'm still having some trouble with is reducing vibration in order to improve surface finish.

The grinder came to me with an old Craftsman table saw motor that vibrated a lot. I've installed a three phase motor and a VFD, and that's reduced the vibration considerably, but I'd like to do better.

Most of the remaining vibration is still present when I remove the grinding wheel and its adapter, so I suspect V-belt and pulleys are the main culprit. Since the motor pulley is just a cheap die casting and probably not well balanced, I plan to replace it, and while I'm at it I wonder if this would be a good time to switch to a different type of belt. I've noticed that the later version of the Delta grinder used a flat drive belt.

So here's the question: would it make sense to switch to either a poly-v belt or a flat belt? Which would be best? What width belt would be correct? I've found a lot of manufacturer's information on poly-v belts but very little for flat belts.

Here are some of the details: the motor is 1/2 h.p., 1745 rpm. The spindle should turn about twice that speed. The center distance is 13.5” and the largest motor pulley that would fit is 5” diameter (so the max. spindle pulley size is about 2.5”).

Any advice would be very welcome! It seems that this sort of information is not easy to find.

Dave

gzig5
05-25-2010, 11:57 AM
I've got the same grinder and am in a perpetual rebuild. The motor and pulley need to be balanced as a unit to get the best results. You can try to do it yourself, there are several tutorials for static balancing, but dynamic balancing is best. Of course it costs to have a motor shop do it. The driven pulley should be balanced as well. You may have acceptable results with the new motor you have and a couple decent pullies and good belt so don't pay to do the balance until the belt is decided. You can stay with the V belt and use a high quality belt or one of the multi-link belts to get rid of the belt effect. If I were to change the belt type, I would go with a poly-V 5/8-3/4" wide so I wouldn't have to worry about a flat belt tracking off. That will probably require custome pullies, which aren't that hard to make if you have a lathe. Also, the original pullies had two steps to give two different wheel speeds, probably one for 6" wheels and one for 3" tool grinding wheels. With the VFD you can adjust the speed, but I don't remember what the ratio is.
Greg

RWO
05-25-2010, 02:44 PM
If you stay with a v-belt, the Fenner Powertwist belts have very low vibration and are worth a try. Being multilink belts, they don't trasmit vibration from the drive source to the load very well. Fenner claims up to 50% reduction.

RWO

DaveR
05-26-2010, 12:45 PM
I switched to a multi-link V-belt, but it seems too “heavy-duty” with steel studs holding the links together (it was the only kind I could find locally). It didn't seem to help vibration much compared to a plain V-belt. I've seen the Fenner Powertwist belt (with links that twist together rather than metal studs), which seems like it would be better but I haven't tried it.

As for the original dual speed feature, I now just use a single belt position and use the VFD to change speeds. This is working very well and I plan to continue this way even if I replace the pulleys and belt. It's so much easier than removing the belt guard to change speeds.

Greg, that's a good point about belt tracking problems with a flat belt. I assume both flat belt pulleys would need to be crowned. I'm leaning towards poly-V belt now, but one thing that makes me hesitant to switch from a V-belt is that there is only about 7/8” of adjustment available at the motor, so I would need to get the pulley diameters and belt length just right. With the multi-link V-belts, it's easy to just add or remove a link.

Thanks to all for your input,

Dave