Can I just use 2 v belts on my 16" instead of 4

leod · Nov 27, 2015

I am switching to a larger motor and shaft and the new pulley will be a problem due to the much larger shaft dia. Do I really need four belts, or will two do.

kitno455 · Nov 27, 2015

You want to put a larger HP motor in it, and reduce the number of belts at the same time. Think about it.

allan

moonlight machine · Nov 27, 2015

You have all those belts because the pulley is so small in diameter, there is not enough belt contact area, you need all 4 for sure if you are putting a bigger motor on it. You can turn the motor shaft down to work with your old pulley. I have had to do it a few times to put a new motor on an old machine. Once I shortened the whole motor. I have never had a problem with any shaft I turned down. It's on an old sb, not like its loaded to the max 24 / 7

dkmc · Nov 27, 2015

First, without knowing some of the facts and data, assuming he needs 4 belts is silly.
What size are the belts?
What was the HP
What is the HP of the new motor?
What are the pulley sizes?

Most always in a multi belt setup there is a large overload factor.
Most lathes hardly ever get taxed to full motor HP.

With this above data, a fair and reasonable determination can be assessed as to
the power transmission capability of the 2 belts you propose, and the potential for sucess determined.

metalmaster10 · Nov 27, 2015

Really depends on how heavy you cut...
When I replaced the belts on my 17" turnado's I put 2 on instead of 4 on purpose... The thought was, If someone gets too crazy the 2 belts should slip far easier than 4.
I'm not sure where the limit is, I turned some 10" pipe the other day, fairly heavy cuts, no slips. In 3 years I've never seen a slip. Turn, thread, knurl, drill 1-1/2" diameter... Nothing.
If you are going to cut super heavy, yeah, you need the extra belts. But my use doesn't push the limits so 2 have been fine.

YMMV

wheels17 · Nov 27, 2015

This document goes into great detail about v belt power transmission.

http://www.c-rproducts.com/downloads/pdfs/Industrial_vbelt_drives_design _guide.pdf

moonlight machine · Nov 27, 2015

wheels17 said:
This document goes into great detail about v belt power transmission.

http://www.c-rproducts.com/downloads/pdfs/Industrial_vbelt_drives_design _guide.pdf

I have the same machine, I had belt slippage problems with 3 belts and 1.5 HP He is putting a 3hp motor on it. The motor pulley is 2.0 dia., driving about a 10" dia. pulley. With about 8" or 10" shaft centers. The belts probably only contact the pulley for about 90 - 100 degrees at most. He needs all 4, They should be a matched length set available from any good industrial supplier. This is first hand experience talking, not guessing.

leod · Nov 28, 2015

That's about what I thought, I am putting in a 3hp and will be working it hard. I hate having to put in a larger pulley, but I really don't want to turn down my motor shaft.Going from 3/4 to 1 1/8 is a big jump, There would only be .110" left after boring my pulley to 1 1/8" and it does not have a set screw on a boss beside the grooves. It is steel ,so I could weld one on there, but I don't know about three hp and a 1/4" set screw. After two hours of looking I have not been able to find anything close on ebay. Three groove are rare and four, nope. I am sure I could get a 2 1/2 from a pulley company, for a price. It looks like I will start figuring out my angles and widths to make one. Since it is my first pulley, that will probably add two days to my motor swap.

leod · Nov 28, 2015

Any reason that two 2 groove pulleys side by side with the set screw bosses on both ends wouldn't work? I suppose I could even braze them together, but I don't really see the need for that. Sure would save me a lot of time, and it $16.00 apiece and expedited shipping it would be worth it to me. I am not embarrassed to admit that I sometimes buy things that other people have made.

IronReb · Nov 28, 2015

The original 4 belt pulley cant be bored out for larger shaft, or bored out and sleeved with a hub for larger shaft?
Would be easier than dicking with turning the motor shaft and risk messing up something in the motor.

Seems if engineers of machinery thought for a second that two was better than four that's how they would have done it
and saved the cost of using 4 belts versus 2.

moonlight machine · Nov 28, 2015

Remember, bigger pulley = higher spindle speed, is this what you want? No reason 2 pulleys would not work as long as the belt center lines are ok with it.

moonlight machine · Nov 28, 2015

IronReb said:
The original 4 belt pulley cant be bored out for larger shaft, or bored out and sleeved with a hub for larger shaft?
Would be easier than dicking with turning the motor shaft and risk messing up something in the motor.

Seems if engineers of machinery thought for a second that two was better than four that's how they would have done it
and saved the cost of using 4 belts versus 2.

If you bored his standard pulley you would have a stack of rings, the side of each shiv.

PeteM · Nov 28, 2015

You might consider using larger pulleys on the new 3HP motor (more contact area, as Moonlight notes) and adding a VFD. You'd want to check, but a pair of v-belts with sufficient pulley contact might handle that power. There's also likely no reason you couldn't go back to 4 sheaves with the somewhat larger pulleys.

The VFD on a 3 phase motor would be a pricey addition, but it adds a great deal of convenience, ease of working around some chatter issues, and maybe a lower low (though low torque, given the larger pulleys) and mostly likely a higher high end up to whatever your bearings can handle.

leod · Nov 28, 2015

I just bought two 2.5" double groove pulleys that already have 1 1/8 bore. They had the size selection on the ebay add for dia. and bore. I already figured I was going to use the larger pulley situation to justify a VFD. Gotta finish paying off the other two first. It is $260 for a teco. You can get a huanyang for about a $100 but I don't think I will waste the time and money. Glad I did not pull the motor out of the lathe before I tested my motor I got on ebay, looks all shiny new and the bearings howl like a coyote. They even took the placard off and taped off the zirks before giving it the ebay special spray paint rebuild. Gonna cost him big for two way shipping. I guess now I start a thread, or look up one on replacing bearings on a baldor 182T

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