... also meant to mention that many of the "Farmer/Lawn and Garden" variety V belts have a slight overlap in the ends of the fabric sheath that encapsulates the belt. When the joint goes through the pulleys, it changes the effected PD of the pulley as well.

When threading, EVERY dinky detail must not be overlooked.

Russ

Russ,
The multi-V belts as used on a treadmill would likely give you a much more constant speed.  You'll notice that the treadmill motors all have the motor pulley made as part of a very heavy flywheel which I would think really helps stabilize the speed. That type of pulley is easy to make too.

Have you guys tried the multiple link belt that are red. I can't remeber the manufacturerof them. It might be fenner? They work real well and don't require dissassembly of the machine for install. They shouldn't suffer from the ovality issue.
Mike(full of red wine)

Hey Mike, thanks for chiming in !

Yes, I have used those in quite a few apps., mainly with conveyor drives and such. Some with a fairly substantial load but most with light to moderate no-variable loads. Although the ovality issue would be eliminated, there is still the issue of varying widths of the V throughout it's periphery and this type would probably tend to dig deeper in to the pulleys under intermittent loading due to it's thinner cross section ...... as Gary mentioned earlier.

Thanks for the input, appreciated,
wine ? have 1 or 6 for me,
Russ

Russ,
The multi-V belts as used on a treadmill would likely give you a much more constant speed.  You'll notice that the treadmill motors all have the motor pulley made as part of a very heavy flywheel which I would think really helps stabilize the speed. That type of pulley is easy to make too.

I like this idea Gary, have used that type of belt before.

Did some experimenting:
Mounted a slotted disc and sensor to various motor/drive combinations just to see the differences.

Disc on 1/2 hp 110v  ac single ph motor .. rpm pretty stable   +/- 1 rpm at around 1750

       "             230v        3 ph              Fugi  vfd         (rotary phase converter)       +/- 5 rpm at around 1000.

same as above but with a new Automation Direct GS2 vfd (120v single phase in)    rock solid, barely   1 rpm fluctuation.

One thing i didnt try, but will, is the 3 phase directly from the phase converter to the 3 ph motor.

The Fugi is an older unit, maybe newer technology is more steady at the output ?

Seems "jittery"..... is this typical with this type of set-up ? Rotary Phase Converters ?

And the flat belts are the best at transferring the rpm consistency.   All V combinations introduce variations to some degree.                 

Regards,
Russ
 

Note: all tests above were done with "Averaging" OFF.
Russ

Russ,
Right on in saying all the little things add up and need to pay attention to detail.

One of the things that would be interesting to do is see / test out all the details ( and there are a lot of them) to have a flavor of  each influence.
Could probably do a spread sheet to mimic senerios.
Note that if a belt dosen't dosen't slip or is not pefect in grab it would be quite repeatable per each revolution.
You would find that belt adjustment / tension will affect steps per unit and would do likewise the same relative to output RPM.
Tough to test properly.

RICH

Hi Rich, I like the spread sheet idea, just not learned that yet.

Yes, can vouch for the tension too.
BTW, all tests were done with absolutely no machining load on the spindle.

When the heavy utility type v belt was on, I used 3 tensions. Light, med.(normal) and very tight, all of which produced different amounts of variations at the Mach reported rpm.

The looser settings were the best, but still unsatisfactory.
The tightest setting varied the most.
The relative output rpm isn't really an issue at the spindle as it is with an axis, just needs to be steady and consistent .... but, I see what you mean.

Thanks Rich,
Russ

Russ,
The multi-V belts as used on a treadmill would likely give you a much more constant speed.  You'll notice that the treadmill motors all have the motor pulley made as part of a very heavy flywheel which I would think really helps stabilize the speed. That type of pulley is easy to make too.

Hi Gary, when first reading this, I casually overlooked the significance of the flywheel effect.
My machine is very light and just uses 4C collets so the rotating masses are minimal.
I might make up a flywheel to add some mass to the spindle. That is a good (another good) suggestion.

Even running a 4 or 5" chuck would seem substantial.

Thanks again,
Russ
 

Russ,
The load on a treadmill isn't constant, it changes with every step you take.  Every treadmill maker has a flywheel and I would guess it is because a person walking or running would really feel the speed changes when their foot hits the belt and it suddenly is loaded.