Belt pulley diameter - grinding machine

[Thoomy]

Hello to all,

I had a discussion with my coworkers about a brake disc grinding machine that is pretty old, regarding the optimum diameter of driver pulley. We will put a new EM on it together with new driver pulley. We have the info from the grinding disc manufacturer about maximum allowed tangential speed (= 30 m/s). The whole transmission system is similar to the one in the added picture, except that in our case diameter d2=d3 and the diameter of the grinding disc with diamond powder is lets say d5. The question is what is the right diameter of the driver pulley (d1) directly from EM in order to get tangential speed of 30m/s on the d5 (grind disc) diameter? I calculated it to be around 200mm, but my coworkers think it should be smaller (currently it is around 90mm).

We know that:
n1= 2900 RPM
d2=d3=76mm --> (machine grinds both sides of brake disc at the same time, pulley #2 is in the middle of the shaft with same diameter that has two belts connected for each side)
d4=55mm
d5 (grinding disc)=200mm
v_tangential=30m/s.

Any ideas what the right diameter d1 should be?
Thank you!

 

[electricpete]

If the motor is a 2-pole induction motor powered directly by 50hz, then 2900rpm is the full load speed, but the motor can spin up to 3000rpm at no load.

Is the grinding disk on shaft 2? (you danced around it, but not 100% clear to me)

=====================================
(2B)+(2B)' ?

 

[Tmoose]

Not diameter related, but what type of belts are you using?

For many machine tools and skate sharpening machines flat belts are the required for smooth running and good finishes.

 

[Thoomy]

@electricpete

Yes it is and induction motor, running at around 2900-3000rpm. The grinding disc (d5) is on the same shaft as d4 pulley on the picture (so equal RPM for both).

@Tmoose

You guessed it correctly, it has some old flat belts without grooves. Only the belt from EM to the first pulley will be a triple V-belt. But we don't grind the discs with belts, we use special grinding discs with powder on them.

 

[Tmoose]

Did the machine originally have any v-belts in the drive?

V belts (not poly V) are lumpy and have thick and thin spots, and v belt sheaves have runout. The end result is the intermediate spindle d2/d3 etc usually gets pushed and pulled and tugged by the v-belts this way and that. The pushing and pulling will then get transmitted as uneven belt tension thru the good natured smooth running flat belts to spindle d4 that supports the actual grinding disc, or grinding wheel. And the ground finish will have some chatter at frequencies related to the V-belts' bad manners. Poly V belts with high quality sheaves are nearly as smooth running as flat belts.

If the face of grinding disk is perpendicular to various shafts, perhaps the small motions inline with the belts won't turn into chatter, but I'd still be giving those v-belts the stinky snake eye.

 

[Thoomy]

Yes, the machine had the V-belts before, but we will install a bit bigger EM which wwon't fit on the existing mounting plate. Therefore the axial distance changes so longer belts are required. That chatter is not so important since the discs we are machining mostly are old-used ones bent for this or that reason. We are grinding some AlMMC discs on this machine where the surface texture could be better though.

 

[DAVIDSTECKER]

The 200mm disc has a circumference of 628.3mm or 0.6283M per revolution
30M/s divided by 0.6283M/Rev = 47.74 Rev/s
60 times 47.74 Rev/s = 2,864.8 RPM
Almost 1:1 to the motor.
D1 = 55mm.
Best regards, David

 

[Thoomy]

Thanks for the answer. You calculated the 55mm diameter from the gear ratio from EM to d5? Or from the rpms on grinding disc and the EM?