# Amping up my toolpost grinder



## Suzuki4evr (Sep 12, 2018)

Hi guys.

I have a toolpost grinder I've built a while back and it works great, but I wasn't completely satisfied with the finish when doing internal grinding on hardened bushing. So I decided to amp up the rpm's from 7600rpm to 13500rpm at the spindle.
To do that I had to make a bigger drive double pulley. I'm using one pulley for the external & internal grinding. 
I made the pulley from aluminium and fitted a taperlock to it.

I don't have a 3/8-16unc tap needed to make the threads for the taperlock, so I made one out of EN8 (drillrod would be better, but it's not easily available around here).I know buying one would have been a lot quicker, but I wanted to see if I could make one.
I made the blank, machined the thread and relief grooves and hardened it.












 Worked well enough for a selfmade tap.
I made the pulley blank and drilled and tapped the needed holes for the taperlock first and then machined the taper for the taperlock.






I then fitted the pulleyblank on an arbor I made earlier and machined the v-belt grooves.






Now I have a toolpost grinder that runs like a sun of a @#$&*. I had to add a belt tensioner because of the large pulley running to a small pulley for more grip. There is a bit of vibration I can feel and hear,but I think I can solve it by setting the preload on the bearings inside the spindle, by compressing the spring washers a bit. 
I am sorry I don't have a picture of the finnish it gives now,because there was no job for it yet,but I wil post as soon as ot happens and post pics of the whole setup as well 
Thanks for viewing. 

Michael


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## benmychree (Sep 12, 2018)

Most tool post grinders use crowned flat pulleys and a high speed rubber and fabric belt and have the motor on a spring loaded pivoted mount, and the pulleys are held on the motor shaft and spindle by threaded nuts on a straight bore and shaft, against shoulders on the shafts, this results in less vibration and since the belts are quite thin there is much less tendency for the belt to bow out due to centrifugal force, as with vee belts, thus being able to transmit power more efficiently.


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## petertha (Sep 12, 2018)

That's what I was going to mention. Themac for example.
https://themacgrinders.com/collections/belts
At high rpm's I would imagine the G-force on belt mass starts to get significant & you probably don't want to have it let go.


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## stupoty (Sep 12, 2018)

round rubber belting might be a good substitute if theirs issues with the Vee belts.

Be interesting to see if theirs any issues.


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## markba633csi (Sep 12, 2018)

Very nice job on those pulleys Michael, and the tap looks like a factory piece
mark


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## pontiac428 (Sep 12, 2018)

Thanks, I enjoyed your story about scratch-building a tap as a side note to the topic.  Good stuff!


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## rgray (Sep 13, 2018)

Maybe it needs balancing. Not sure if a grinding wheel balancer would work but might give an idea as to whether balancing would help.
Found some youtubes of a guy using a vibration app on an Iphone....looked interesting. I think he was using a static balancer and using the phone to judge the changes made. 
Nice project and nice tap you made there.


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## Suzuki4evr (Sep 13, 2018)

Thank you for your comments everyone. Nice to get some good feedback. I forgot to mention that the rpm from the motor is 2810rpm and rpm for the 150mm runs at about 3900rpm at the spindle and the small internal stone runs at 13 500rpm at the spindle. That is how I pulleyd it. But I will sort out the vibration, it is not very bad,but still.


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