2x72 Questions

[Colby L.]

I say this because it’s a new grinder and it looks like you take it outside to use, and probably don’t leave it plugged in.

If the vfd has not been used or has been on storage for a year, the manual for the kbac27d says to recondition the bus capacitors by leaving it plugged in, powered up, but not running for at least an hour. Failing to do that will cause the bus capacitors to fail.

I had some bad surging and vibrations and that fixed it, at least for a while until I ended up replacing it.

Check the manual under bus capacitors.

Oh interesting I just looked that up in the manual and now have the machine plugged in. I don't know when the VFD unit was manufactured but its better safe than sorry. You would think something like that would be on a sticker on the unit itself...

 

[Colby L.]

I had the solid chassis Ameribrade grinder, but essentially the same setup as you have. Fantastic machine. On mine, any vibration was almost always caused from the belt bump at the splice joint. Belts with a good splice (that also didn't wobble) were the least noticeable. 36-60 grit belts, with a poor splice, made the whole thing shake even worse than you show. The splice will make the belt bump over every point of contact on the grinder, especially the platen and small platen wheels. It will also make the idler wheel jump ever so slightly, creating a tiny bit of movement.

Also, keep in mind you have a 7 inch drive wheel which can run a belt at 6,600 feet per minute. That means those 2'' platen wheels are spinning at 12,600 RPM. They may be precision machined, but they are not high speed balanced and they are not mounted on a precision ground shaft to keep perfect concentricity. You'd need to add another zero to the price to get that kind of precision.

Running a contact wheel, rather than the platen, almost completely eliminated the belt bump on my grinder. Did you get a contact wheel with it to try?

I had mine mounted to a cheap harbor freight stand. I know mounting it on a more substantial surface would have helped eliminate vibration, but it never bothered me enough.

I was thinking the belt splices could be the culprit originally as well. I tried about 10 belts and they all seem to have roughly the same vibration characteristics so I have ruled that out for now.

 

[Natlek]

I had the solid chassis Ameribrade grinder, but essentially the same setup as you have. Fantastic machine. On mine, any vibration was almost always caused from the belt bump at the splice joint. Belts with a good splice (that also didn't wobble) were the least noticeable. 36-60 grit belts, with a poor splice, made the whole thing shake even worse than you show. The splice will make the belt bump over every point of contact on the grinder, especially the platen and small platen wheels. It will also make the idler wheel jump ever so slightly, creating a tiny bit of movement.

Also, keep in mind you have a 7 inch drive wheel which can run a belt at 6,600 feet per minute. That means those 2'' platen wheels are spinning at 12,600 RPM. They may be precision machined, but they are not high speed balanced and they are not mounted on a precision ground shaft to keep perfect concentricity. You'd need to add another zero to the price to get that kind of precision.

Running a contact wheel, rather than the platen, almost completely eliminated the belt bump on my grinder. Did you get a contact wheel with it to try?

I had mine mounted to a cheap harbor freight stand. I know mounting it on a more substantial surface would have helped eliminate vibration, but it never bothered me enough.

My first belt grinder which i make was two wheel grinder , 32m/s .....fast one .When i start it for first time ...........I will never forget it That MF start to walk/jump in shop like kangaroo, dengerous moment .Then I use four big wooden clamps ......and when i switch power on ...the table began to imitate a kangaroo, holding it with hand don t help ....I struggled for a few days to find out what was going on.Then the light bulb came on I forget that i drill SINGLE ONE hole /8mm dia./ in tracking wheel which was about 4 or 4,5 inch dia. Hole was close to rim of wheel.....
Then I drill six hole in equally distance , balanced that MF wheel and start grinder...........like are dream
So yes , speed matters