Running down cause of vibration on belt sander

T

Taz575

Well-Known Member
I am experiencing a weird issue on my new belt sander. I have an Ameribrade Fastback, running it with a motor (1725rpm) in a cross slide vise and step pulley/pillow block/driveshaft arrangement. I have a 1 3/4" pulley on the motor and a 2, 3, 4, 5 step pulley on the drive shaft itself (KMG 14" precision ground). The belt sander and the cross slide vise are both mounted to 2x10's, so it's got a nice, thick heavy base, the heavy vise, motor and belt sander. Running it this way works great, 4 speeds (~1400-600 roughly), smooth, little vibration, etc. I can use the vise to get good tension on the adjustable v belt and to line up the pulleys. Whole machine runs pretty smooth. Worked great on some rehandles I just did!

When I put a 5" pulley (and another 2, 3, 4 step pulley I tried yesterday to see if it was the 5" pulley) on the motor end, I get a wicked vibration where the whole assembly wants to walk off the bench. I get the same vibration even at the 5" to 5" and 4" to 5" speeds, which is just a bit over what the fastest speed is with the 4 speed setup that has none of the vibration, since both are nearly 1:1 ratios.

When I touch the pillow block when its running with the 4 speed setup, not much vibration. When I use the 2,3,4 or 5" pulley, the pillow block closest to the step pulley has a lot of vibration and when I press down on it, it lessens, but still has a ton of vibration. I am guessing the pillow block may be bad? Is there any way to check this out? Anything else I should check out? Stumped why a few hundred RPM's more would cause massive vibration or if it's a bad bearing, why it wouldn't be effected at the slightly slower speed? I checked and made sure all of the screws are tight, too. Could the bearing in the pillow block be slightly out of alignment or something?

Video of running the 1.75" to 2" pulley:

KVID2488.mp4

drive.google.com drive.google.com

Nice and smooth. But once I go to a different pulley on the motor (5" and 2, 3, 4 step pulley), it starts buzzing and walking all over the bench! Should I try a new pulley in case the 2 I have are bent or really out of balance??
 
Is the belt at the same tension for the 5" pulley as the 1-3/4"? Is there any lateral "slop" in the bearings on your motor or pillowblocks?

Put a sharpie mark at 12 o'clock on your 5" pulley and your step pulley. Remove the v-belt and the grinding belt from the machine. Does either shaft turn on its own from gravity? If not, rotate both 90 degrees and see if the marks stay put. Rotate another 90 and check. If the marks move at all after removing your hand, then something is out of balance. Make sense?

Does the motor vibrate when you're just running the pulley without a v-belt? How about if you're running the v-belt but not a grinding belt (at top speed)?

The other thing you can check is runout, but you'll need a dial indicator. Motor shaft runout should be less than .001". Ideally your jack shaft runout should be similar. For pulleys and wheels, I'd probably look for, or expect less than .002". The more runout, the more vibration.
 
That is a clever use of a X/Y vice! Here are some thoughts:
- All rotating things have vibrational harmonics to varying degrees - that is, there will be a speed at which any rotating shaft will find a point where it will vibrate in relationship to its speed and mass. In fact there is often several harmonic speeds that show peak vibration.
- One way to minimize vibration is to minimize shaft misalignmnet and bearing tolerances. In your set up, you have several places that can either be the source of vibration or places that transmit the vibration to another location. Since the jack shaft is new, I'm guessing that it is not the problem. But keep in mind alignment of the jack shaft must be perpendicular to the motor and grinder.
- Your motor is mounted too far off a solid base, (mounted too high). The vice has some amount of "slop" in the machined parts. That "slop" is amplified by the distance your motor is located above the vice. Any vibration will be magnified because of that distance.
- The motor pulley MUST be aligned exactly to the cone pulley on the jack shaft. To make sure it is, take a straight edge and place it on the motor pulley and make sure it aligns with the cone pulley. That can be tricky on a cone pulley. After initial alignment move your vice slightly to see if helps.
- It appears that you may not have enough tension on the green belt, and that looks like it may be allowing the belt to "flop". That movement in the belt can be the source of the vibration you are seeing. The belt needs to be tightened so that there is only a small amount of deflection. There are tables showing the amount of deflection for a given belt, but it will likely be around a 1/4" with finger pressure. Shortening the length of that belt will also help.
 
I try to keep the belt tension the same and I can adjust it with the cross slide vice; the belt tension didn't make much difference at all in the bad vibration. Motor is new and tight. The shaft is tight in the pillow blocks.

I get what you mean about balancing the wheels, so I will give that a try. They are cheap die cast, so I wonder if they got bent or out of round at some point?

Motor w/o v belt is smooth with both pulley setups. I even got another adjustable V belt and it did the same. I may try a narrower belt and see if that lets it sit lower in the groove?

I have 2 more pillow blocks, so I may swap out the one and may add a third one and see if it's a bad/misaligned pillow block bearing. I used the tool that Ameribrade has to align the drive wheel to the frame and since the drive wheel is on the shaft in the pillow blocks, that should have kept everything straight and square to the frame/drive wheel.

I try to run the belt pretty tight, but I was worried about bending the jack shaft with the step pulley.

I wanted to mount the motor lower, but with the XY vise and the foot of the motor not fitting into the vice jaws, it's up a lot higher than I like.

I will swap out one of the pillow blocks and make sure the pulleys are in line with each other. I wonder if the vise/motor/pulley is slightly out of line with the step pulley on the jack shaft, especially when I tighten the belt?

Thanks for the ideas of what to check out!
 
OK, try this: with your green belt off, grab the top of the motor and tug back and forth parallel to the belt. That will tell you whether you've got a loose connection for your motor mount.
 
Ah, gotcha! I will try some of these things out today and tomorrow! I am looking into getting a 220V outlet to the garage so I can do with a direct drive and VFD :)
 
Motor pulley wasn't square to the jack shaft pulley, so I fixed that. Still vibrates a lot. When running, I saw the step pulley on the jack shaft was wobbly and oscillates a bit.

Then I found this: https://drive.google.com/file/d/15UJKDi5eZ45K0Cl_zYxl5XTDZVXf-bvG/view?usp=drivesdk

Bearings are loose in the pillow blocks and allow the shaft to wobble and get out of alignment with the blocks. Gotta order 2 more pillow blocks now!

The first jack shaft I got wasn't precision ground, so it was a tight fit to the bearings, I had to tap the bearings on and off, so that probably loosened then up. I ordered 4 and I think all of them have the bearings that can shift in the block, which I don't think is good?
 
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The bearings are supposed to be able to pivot axially within the blocks for minor alignment. Once you add the second pillow block, it should eliminate the movement you're seeing.
 
Ah, Ok. Some of the pillow blocks have a lot more play than others and are easier to move axially so I wasn't sure if that was right or not? The one in the video had play in the bearing itself, as well as the entire bearing being able to move in the pillow block.

I am seeing wobble in the 2,3,4,5 step pulley on the jack shaft, so I have something else to check into now, too.

When touching the pillow block housing when the vibration Is bad, the pillow block itself on the step pulley end has a ton of hard and fast vibration felt, the one on the drive wheel end doesn't have much of any vibration. I changed out the pillow blocks and it almost seems worse after aligning the motor pulley and jack shaft pulleys.
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Yeah, there shouldn’t be any noticeable play in the bearings themselves, or in the blocks once your shaft is installed into both. Does it change if you take your drive wheel off the shaft?

The pulleys, shaft, and drive wheel should look almost like they’re not even moving when they’re up to speed.
 
I got one of the causes of the vibration chased down. The motor mount table wasn't level and square to the frame itself. The bolts loosen during shipping and when I tightened it, the table was canted. With a very tight belt, I can get the vibration out to where tools on the 2x10 don't walk off of it, but there is still vibration. The drive wheel has some bounce to it as well, so I need to keep working with the pillow blocks and change one out and re align the pieces.
 
Getting a 240v outlet in the garage soon! Vfd wired up, 240v outlet is wired, needs to be mounted and tied into the panel by an electrical, and motor is getting ordered next week!!KIMG2542.JPG
 
It's exciting to step up into the variable speed world!

I know some folks will disagree with me, but I absolutely hate those type of VFDs. I have spend endless hours, both on the phone, and in person, trying to help people solve issues/problems. Everything from them simply stopping working, to surging, to turning on/off by themselves, and everything in between.
I can't say it enough. Buy a KBAC 2X series VFD, they are simple, easy, and reliable...... and you will never have to buy another.
 
Yup! I had variable speed (KBAC) on my KMG several years ago; it was sweet! I moved and have a panel in the garage, so it's easy to have a 250V outlet put in so I can get a 2HP motor. I just ordered the IronHorse this morning, so I may have it Weds!

I've spent a lot of time trying to square everything up on the grinder, its frusturating. I can use it currently for handles, but anything above say 1500 rpm, it vibrates a ton. Something in there is not right; I keep trying to square everything up and it still gives issues, plus the motor being on the cross slide vise doesn't help!

Hoping the VFD gets me through the next year or two; I don't do it full time, on my days off and here and there after work. I got the remote cords, so I will have the VFD mounted away from the grinder and use the removeable panel to control it at the grinder. Fingers crossed it works!
 
EdCaffreyMS said:
It's exciting to step up into the variable speed world!

I know some folks will disagree with me, but I absolutely hate those type of VFDs. I have spend endless hours, both on the phone, and in person, trying to help people solve issues/problems. Everything from them simply stopping working, to surging, to turning on/off by themselves, and everything in between.
I can't say it enough. Buy a KBAC 2X series VFD, they are simple, easy, and reliable...... and you will never have to buy another.
Click to expand...
X10 what Ed said!
 
Taz575 said:
Yup! I had variable speed (KBAC) on my KMG several years ago; it was sweet! I moved and have a panel in the garage, so it's easy to have a 250V outlet put in so I can get a 2HP motor. I just ordered the IronHorse this morning, so I may have it Weds!

I've spent a lot of time trying to square everything up on the grinder, its frusturating. I can use it currently for handles, but anything above say 1500 rpm, it vibrates a ton. Something in there is not right; I keep trying to square everything up and it still gives issues, plus the motor being on the cross slide vise doesn't help!

Hoping the VFD gets me through the next year or two; I don't do it full time, on my days off and here and there after work. I got the remote cords, so I will have the VFD mounted away from the grinder and use the removeable panel to control it at the grinder. Fingers crossed it works!
Click to expand...
I think the cross slide vise might be part of your vibration problem. Before I upgraded to a VFD I tried using a cross slide vise on the motor to make changing belt positions easier, and had vibration problems and other issues as well. After upgrading to the VFD I haven't had any vibration problems at all.
 
It vibrates so much the cross slide vise starts to thread/unthread at high speeds! IronHorse 2HP should be here this week, so just waiting on the electrician to tie in the outlet to the panel!! Super excited!
 
Got the vibration solved!! Iron Horse 2 HP, 3 Phase, 3600 RPM motor direct drive with 4" wheel, Lapond SVD-ES VFD. VFD was set at 60hz for some things, but I was able to follow the manual and program all of the motor parameters and stuff. Working well so far! I got 2 of the 2M remote cords, so I can just hold the tiny panel near the grinder and the VFD unit is actually away from the grinder/dust and on the other side of a thick plastic curtain.

https://drive.google.com/file/d/1Esyt_bRo8B4OI-pqk4V63hMhsezQuDVY/view?usp=drivesdk
 
Nicely done, my compliments to you. You identified the problem, figured out a solution and implemented it - way to go!
 
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