2x72 Questions

Colby L.

Colby L.

Joined
Feb 3, 2020
Messages
91
Hi All -

I recently received my 2x72 grinder and set it up over the weekend and have a couple questions regarding mainly vibrations and belt wobble.

Regarding belt wobble. After about 6 motor remounts I have a few belts that run dead on. However 7 out 8 of my Norton belts wobble. Is that a normal hit rate? Some are pretty small while some are what I would consider wobbly. Should I be expecting a majority of belts to have at least a bit of play in them? Or should the majority be dead on?

The second question is around vibrations which bother me a bit more. I am getting some fairly significant vibrations. I set a silicone shot glass of water on the work rest in the lower tool slot with either the platen or the contact wheel in the upper slot. The glass will start vibrating and then start walking around. Is that normal? I am about to drive myself nuts trying to diagnose the problem, and I wanted to make sure I am not chasing my tail here.

The third thing I noticed is that the idler wheels on the platen assembly seem to heat up pretty quick. Is that normal just due to them being small (2"). They don't seem to free spin super great which I am thinking is causing some extra heat. I have loosened the bolts holding them in place nearly as much as I can while still keeping them "tight".

Thanks in advance.

Colby
 
There will be people along shortly with waaay more experience than me, but the tracking and vibration issues you’re discussing are not normal or “within tolerance” for a 2x72.
 
Yeah I agree tht doesn't sound normal. I'm not sure on what the fix would be but there are people here that will
 
Pictures of your setup would be helpful. How far off the frame does your drive wheel sit?

also, seemingly silly question, but which direction is your belt moving? Some VFDs come default in “reverse” and tracking is tougher.
 
The belt is running forward (down on the platen). Here is a picture of the side as well as a video of the vibration with one of the belts that doesn't wobble. The tracking seems fine as its stable. The tracking wheel is a bit more tilted than the drive wheel however the belt seems to be fairly centered in the drive wheel and tracking wheel.

3jbdmkQ.jpg


Video - https://imgur.com/E2loY3h


E2loY3h.mp4
 
I have a similar issue. I've mounted and remounted, aligned and realigned. Some belts are dead on and stable and some suck. I would think if it was an alignment issue all belts would do it but maybe the stiffer the belt the more it stays aligned?
 
Nice looking grinder. Wish I had bought a different one than the turd I did.
Bilj said:
The belt is running forward (down on the platen). Here is a picture of the side as well as a video of the vibration with one of the belts that doesn't wobble. The tracking seems fine as its stable. The tracking wheel is a bit more tilted than the drive wheel however the belt seems to be fairly centered in the drive wheel and tracking wheel.

3jbdmkQ.jpg


Video - https://imgur.com/E2loY3h


E2loY3h.mp4
Click to expand...
 
I have no personal experience with this grinder, but it looks like you might be able to adjust the tension somewhat depending on how far you pull the tool arm out. In my experience, more tension helps with belt wobble. Some belts are worse than others.

The amount of vibration depends a bit on what the grinder is mounted to. I think a wooden base can work well for vibration damping. It is hard to tell from your picture what surface the grinder is mounted to, and how the surface is supported. If it is a thin sheet of plywood covering a big OSB box without internal supports, it might be a contributing factor to the vibration. I had a grinder on a torsion box worktable made from 1/2" plywood with very little vibration and then moved it to a stand with a 3/4" plywood top and I noticed an increase in vibration. It is subtle and only really noticeable at some speeds, but definitely there.

I have a set of wheels from Ameribrade, and they are not getting hot at high speeds. I would contact them and ask for help, they were very responsive when I asked them questions.
 
I haven't seen that one before, have you more photos, especially straight on from each side.


What's under the tape ?
 
Bilj said:
Thanks! Ya I am pretty excited overall. It is a well made machine. Just need to get these couple issues dialed in.
Click to expand...
Did you run grinder without belt ? If no vibration that will eliminate motor and drive wheel .Remains tracking wheel as source for vibration , small wheel are to small in Dia. to make vibration if they are unbalanced.............
What size bolt is used on wheels ? I really can t understand WHY they make wheels like that ???? They must be made in a way so you can tight bolts without pressure on bearings !
About wobbling belts , try more tension ..............
 
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Update - I think the vibrations are coming from the motor. I took the drive wheel off and ran it with just the shaft. I am still getting vibrations. Not enough that it is shaking the water glass but I can feel the flat of the platen vibrating. My guess is that when everything is installed the vibrations of the motor shaft are being exaggerated/transmitted through the belt and shaking the attachments. The motor body itself is not vibrating much which is a bit strange to me. I can set the glass of water on the top of the body and it does not move - I even tried this with the drive wheel/belt installed and the machine running at full speed.

It is mounted to a wooden box. The box has a 2 x 4 frame with 1/2" sheathing around the exterior. I installed a flat 2 x 8 underneath of the plywood top where I ran the thru bolts of the grinder base. There could not be enough mass to dampen the vibrations which one my theories. I do want to chase down the motor shaft issue to see if what I am getting is within spec.

I am thinking I will order a dial indicator to check run out on the shaft to see if its within spec.
 
That would be my first suspect is a bent shaft or bad bearings. Contact Ameribrade. They can most likely provide help if you got the motor from them.
 
Looking at the water glass sitting on the tool rest it doesn't really look all that bad for where it's at. I have balanced a nickel on edge on the grinder running 4,060 SFPM.

edit: Oops, I see you've already found a bent shaft.
Grinder-Nickel.jpg
 
If the motor shaft if bent, you should be able to see some noticeable wobble when the drive wheel is attached. How are the vibrations with the drive wheel attached, but no belt?
 
Bilj said:
Hi All -

I recently received my 2x72 grinder and set it up over the weekend and have a couple questions regarding mainly vibrations and belt wobble.

Regarding belt wobble. After about 6 motor remounts I have a few belts that run dead on. However 7 out 8 of my Norton belts wobble. Is that a normal hit rate? Some are pretty small while some are what I would consider wobbly. Should I be expecting a majority of belts to have at least a bit of play in them? Or should the majority be dead on?

The second question is around vibrations which bother me a bit more. I am getting some fairly significant vibrations. I set a silicone shot glass of water on the work rest in the lower tool slot with either the platen or the contact wheel in the upper slot. The glass will start vibrating and then start walking around. Is that normal? I am about to drive myself nuts trying to diagnose the problem, and I wanted to make sure I am not chasing my tail here.

The third thing I noticed is that the idler wheels on the platen assembly seem to heat up pretty quick. Is that normal just due to them being small (2"). They don't seem to free spin super great which I am thinking is causing some extra heat. I have loosened the bolts holding them in place nearly as much as I can while still keeping them "tight".

Thanks in advance.

Colby
Click to expand...
Hey Colby,

Ameribrade just posted up an informational video for tips and tricks of set-up of the Fastback on their YouTube page. Good info there. The link is also located in their IG page in the sign line. :thumbsup:
 
Bilj said:
It is mounted to a wooden box. The box has a 2 x 4 frame with 1/2" sheathing around the exterior. I installed a flat 2 x 8 underneath of the plywood top where I ran the thru bolts of the grinder base. There could not be enough mass to dampen the vibrations which one my theories. I do want to chase down the motor shaft issue to see if what I am getting is within spec.
Click to expand...
You don t dampen vibration ....because you can t do that .You must found source and eliminate them :) If everything is perfect , grinder will run even on 1/8 plywood.
 
Drew Riley said:
If the motor shaft if bent, you should be able to see some noticeable wobble when the drive wheel is attached. How are the vibrations with the drive wheel attached, but no belt?
Click to expand...

Without the belt or drive wheel I can feel some very faint vibrations in the tool rest however it barely, if at all, even registers in my little shot glass of water. When I add the drive wheel into the equation there isn't any change in the perceived vibrations. Its not until I add in the belt with an attachment (of which I have tried both the flat platen and the contact wheel) that I get the bad vibrations. I can't see any sort of wobble in the shaft or drive wheel while the machine is running.

Thank you all for the replies, and I did see their new video which was super helpful for understanding proper setup. I spoke with Keven at Ameribrade and he was super helpful. He is actually thinking it might be the idler wheel and is sending me a new one of those. He is thinking that if it really was a motor issue it would be more present without the belt on. Once I get it installed I will update the thread on the findings.
 
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.
 
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.
 
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