[QuinnSjoblom]

I have a large gates pulley that i am using for the transmission of my servo driven bt30. It is an 80t 5mgt mounted on the shaft of my 1kw servo. It works but this pulley has a huge amount of inertia to it and greatly limits how fast i can accelerate my spindle without faulting the servo, almost an inch thick and 5 inch diameter solid steel. Since i am only pushing a few hp peak at the most, this pulley does not need to be that beefy and i could about cut the inertia of my whole system in half by hogging out the center of this pulley and replacing it with a spoked aluminum hub. Question is, how much material can i remove before the pulley starts distorting and going out of round? Im not sure what exactly the process is for making these pulleys or what the material is. I would think the rough shape is probably cast and then post machined so probably somewhat stable as i remove material but i just dont know. Do i need to worry much about distortion as i machine it?

[mactec54]

I have a large gates pulley that i am using for the transmission of my servo driven bt30. It is an 80t 5mgt mounted on the shaft of my 1kw servo. It works but this pulley has a huge amount of inertia to it and greatly limits how fast i can accelerate my spindle without faulting the servo, almost an inch thick and 5 inch diameter solid steel. Since i am only pushing a few hp peak at the most, this pulley does not need to be that beefy and i could about cut the inertia of my whole system in half by hogging out the center of this pulley and replacing it with a spoked aluminum hub. Question is, how much material can i remove before the pulley starts distorting and going out of round? Im not sure what exactly the process is for making these pulleys or what the material is. I would think the rough shape is probably cast and then post machined so probably somewhat stable as i remove material but i just dont know. Do i need to worry much about distortion as i machine it?

If it is cast iron then it is not going to distort any that would affect it as a pulley even if it is steel because it is round it is not going to move enough to affect it, Wow that is a big pulley for a small motor like that, I hope you have a Braking Resistor to protect the Drive

Think of it like a auto starter ring gear and shrink fit it onto the aluminum hub, this will take care of any distortion it may have

[QuinnSjoblom]

yep, the reason for being so massive is my rpm needs. its a 5k rpm servo and i wanted 12,500 at the spindle. 1;2.5 ratio, 80t on servo, 32t on spindle. here it is with front plate removed, second pic flipped. and yes, braking resistor installed

[mactec54]

yep, the reason for being so massive is my rpm needs. its a 5k rpm servo and i wanted 12,500 at the spindle. 1;2.5 ratio, 80t on servo, 32t on spindle. here it is with front plate removed, second pic flipped. and yes, braking resistor installed

You could also make the timing pulley in plastic, which would be even lighter and could be used with a small aluminum hub

[QuinnSjoblom]

You could also make the timing pulley in plastic, which would be even lighter and could be used with a small aluminum hub

I would if i had a 5mgt hob, otherwise not sure how i would do that. Ive tried to source gt2 hobs before, seems it isnt something you can just buy.

[mactec54]

I would if i had a 5mgt hob, otherwise not sure how i would do that. Ive tried to source gt2 hobs before, seems it isnt something you can just buy.

No you have to be licensed manufacture with / for Gates to be able to get there hobs, and hob profiles, you can machine the profile of the timing pulley with "Gearotic Motion Gear design Software" software

You may have to do it with thin blanks as deep as you cutter can go and dowel them together

[QuinnSjoblom]

After doing some math, there was only a slight advantage of replacing the center of the pulley with an aluminum hub. About 90% of the inertia is carried in the outer inch or so of radius, so i just hogged out pockets to reduce weight there leaving enough in the center for the taperlock bushing. Inertia is now 40% of what it was. Going with the spoked aluminum center and only keeping the rim of the gear would have only made a few percent different. This was much easier and if i decide i need it better, it will require a new gear from scratch as discussed, probably delrin and aluminum. I think this will be ok though.
It was definitely cast iron, what a mess. First time machining it. Immediately after washing it, there was already a thin layer of rust on the machined areas. Any suggestions on best way to protect it? For now it has some oil on it but it will need thoroughly cleaned before installed and a belt ran on it. Maybe just paint the machined areas?
Here's a pic, pocketed out the same on both front and back. Also took down the overall thickness. Not sure why it was so thick to begin with. Pulley is for 15mm belt and the toothed area was 23mm thick. I took it down to 18mm leaving just the center at original thickness for the bushing.