Thread: grinder build

Hey All,
I am building a 2x72 grinder on a budget with ideas taken from KMG lones and No Weld Grinder plans.
Coming together but hit a snag. I am using my trusty old Abbott & Ashby grinder to power it. It is a solid 15 year old beast about 3/4 hp. Already own it so keeping things cheap.
I put on a four step pulley system. The lowest two speeds work just fine. But when the belt is on the wheels for the top two speeds, it just does not drive the belt.
Any suggestions why this is and what i can do?
Or will I just have to find a more powerful motor?
Any advice shared considered and appreciated.
Regards,

The motor is likely not strong enough.
The torque is a function of the motor torque and the transmission ratio (ratio of the gear wheel diameter). For the lowest gear, the motor side pulley is smaller than the drive wheel pulley and the torque will be multiplied Think of the pulleys as a lever to move a heavy object. For the high gear, the long end of the 'lever' is on the other side, meaning that the torgue will be smaller. If you don't have much torque to begin with, it won't be enough to drive the wheels under load. If you try, you are likely to burn out the motor.

So the possible answers are a) not to use the high gears, or b) use a stronger motor.

Yeah 3/4 hp isn't going to be enough. In my opinion you need 1 hp as an absolute minimum.

I'd suggest at least 2hp, and 3 is even better. I have a 3hp with a variable speed set up and it works great. You may be able to find a good used motor or a rebuild at an electric motor shop, if you have one in your area. Good luck with your build.

I have a 1.5 hp and that never slows down. .75 is too little power.

Guys are dead on here. 1.5 is as low as I would go. Plus an old bench grinder motor just wasn't built for the job; it was turning two spindles with two wheel only inches from the source. Now its turning one large wheel and two guide, one tensioner, and your large step pulley 3 plus feet from the source, rpm comes into play when you are actually grinding, torque is the key for running the parts efficiently under load.

Originally Posted by skipnord

I'd suggest at least 2hp, and 3 is even better. I have a 3hp with a variable speed set up and it works great. You may be able to find a good used motor or a rebuild at an electric motor shop, if you have one in your area. Good luck with your build.

I have seen Skip's setup in action and it is awesome. I have no desire or plans for a grinder but if I did, it would be like Skip's rig.

Dave

Thanks guys. Appreciate your experience.
I just scored a 1.5 hp motor from a swimming pool filtration unti.
it is a tad lighter, quieter, vibrates less and twice as powerful. The spindle is a little narrow so just need to thread a shaft of correct diameter and cut a keyway. Hopefully this weekend coming. Exciting stuff.
Thanks again guys.

That should do you fine. I run a 2 hp myself, I wanted to be able to run all day long if I wanted without burning up a motor if I was running slow rpm's on the vfd

got any pregress pics Adam ??
I love these threads, all mental notes & more learning for when the day comes to start a grinder LOL

these go with 1 of my life mottos,

"Learn from other peoples mistakes, for life is to short to make them all yourself"