Author Topic: Diagnosing & Eliminating Bandsaw Vibration  (Read 1080 times)

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Offline dlu

  • Posts: 168
Diagnosing & Eliminating Bandsaw Vibration
« on: February 16, 2019, 02:54 PM »
I've been on a mission to get my bandsaw (late '90s Jet 14" with a closed stand) tuned up. The first round involved getting the wheels coplanar and the guidepost vertical and new blades. I also added a Kreg fence. Using Michael Fortune's advice/method () I got the fence aligned to the miter slot and have the blade tracking parallel to the fence. I'm really, really happy with the improvement in saw. Cuts against the fence are dead straight with both a 3/4" Iturra BladeRunner and with a 14 TPI Starrett 1/4" blade.

That said, there is a bit of "washboarding" on cut face (I can clean it up with a 0.5 mm cut on my "jointer" (aka router with an offset fence)) and I notice a slight "throbbing" in the upper blade guide as the saw runs - even when it is not cutting. I'm wondering if this could be the cause of the washboarding and if it could be caused by flat spots on the tires. Or maybe, something in the drive belt and/or pulleys.

I'm thinking my next move is to put a dial indicator on the tires. Any idea how much variation is normal? What do you call that measurement?

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Offline Bob D.

  • Posts: 1253
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #1 on: February 16, 2019, 05:39 PM »
Do you de-tension the blade when not in use? And if you do now did you always?

Check your wheels for runout on the tire surface where the blade rests.

I guess you've gone over the whole saw and checked all fasteners are tight.
Is the table secure on the trunion and the trunion locked down tight?
I drive myself crazy once because I had neglected to fully tighten both bolts
on the table after setting it back to 90. Got distracted and only snugged one bolt
which caused problems when cutting as you might guess. Took me about 20 minutes
to figure I had not tightened both bolts.

What does the drive belt look like when you remove it and it's at rest on the bench.
Is it elliptical or round. Maybe get a link belt. Is the motor mount tight and are the
pulleys coplanar and pulley setscrews tight.
-----
It's a table saw, do you know where your fingers are?

Offline dlu

  • Posts: 168
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #2 on: February 16, 2019, 07:48 PM »
Do you de-tension the blade when not in use? And if you do now did you always?

Check your wheels for runout on the tire surface where the blade rests.

No, Jet's tension knob is (or at least was) awful. I'm sure there were days, if not weeks when the tension was left on. Got a Carter Quick Release so I'd have no excuse.

Any idea how much runout is acceptable? Assuming I don't find zero…

Quote
What does the drive belt look like when you remove it and it's at rest on the bench.
Is it elliptical or round. Maybe get a link belt. Is the motor mount tight and are the
pulleys coplanar and pulley setscrews tight.

I'm not sure that the belt even remembers being round :-)

Sounds like both the tires and the drive (especially the belt) are worth investigating. I hadn't thought about the belt taking a set and the implications of that. Thanks!

Offline Cheese

  • Posts: 6367
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #3 on: February 16, 2019, 09:04 PM »
I’m certainly not a bandsaw guru but I’d think that a run out of .010-.015” on the diameter would be an acceptable value. Possibly more considering the probability of stacked tolerances.

If it’s the side to side wobble of the wheel you’re interested in it’d could certainly be more because the polymer wheel tire is crowned and the crowning will keep the band saw blade tracking in the center of the wheel.

Offline dlu

  • Posts: 168
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #4 on: February 16, 2019, 10:28 PM »
I think it would be radial runout since that's what would (I think) cause the frame to flex and the upper blade guide to move up and down.

I just measured the runout, I get:

  • +0.15 (0.006") / -0.25 (0.010") mm on the upper wheel, and
  • +0.05 (0.002") / -0.15 (0.006") mm on the lower wheel/li]
All together that's about 0.60 mm or 0.024" if the stars line up just wrong. If the old tires are hard and don't flex (enough), then it seems like the runout has to be taken up either in the tension spring or in flexing the frame of the saw - or both. I have no idea if 0.5 mm ish is significant here but I'm thinking it would be worth ordering a new set of tires to see.

Offline Cheese

  • Posts: 6367
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #5 on: February 16, 2019, 10:32 PM »
How do you know the frame is flexing? Did you put a dial indicator on it?

Offline Cheese

  • Posts: 6367
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #6 on: February 16, 2019, 10:43 PM »
FWIW...I have a Delta 14” bandsaw with a cast iron frame WITHOUT a detensioner that’s been tensioned in the same position for the last 25 years and it will still rip stock to within .015 or less of what I dial in.

I also have several Jet cast iron tools and feel that for the most part, they are the equivalent of my Delta tools. So if there’s an issue, it’s probably in the details of the equipment and not in the general equipment itself.

Offline dlu

  • Posts: 168
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #7 on: February 16, 2019, 10:45 PM »
How do you know the frame is flexing? Did you put a dial indicator on it?

No, not sure how to measure that. I guess I could set up the indicator between the table and the bottom of the guide post. Feels a little close to the blade for comfort if it needs to be running…

What I'm seeing is what looks like a slight up-and-down movement of the upper blade guide (and presumably the post), but I haven't measured it. There is also some vibration in the saw and it "feels" about right to be timed with the wheels. But that is all subjective.

Offline dlu

  • Posts: 168
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #8 on: February 16, 2019, 10:50 PM »
FWIW...I have a Delta 14” bandsaw with a cast iron frame WITHOUT a detensioner that’s been tensioned in the same position for the last 25 years and it will still rip stock to within .015 or less of what I dial in.

Thanks, I feel like a better person now  :)

With a fresh blade and all nicely tuned up, the saw is cutting very well - but there is some vibration and the cut isn't perfect. I'm hoping that if I dealt with the vibration the cut would improve and the saw would be more pleasant to use. Rips are pretty much dead on and a pass over my "jointer" taking about 0.5 mm leaves a very nice surface. Just being greedy (and wanting to do less sanding on curved parts).

Offline Cheese

  • Posts: 6367
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #9 on: February 16, 2019, 11:06 PM »
The vibration could be bad bearings or the v-belts. V-belts are known to delaminate from time to time.

I’ve substituted link belts for the v-belts on my drill press and also on my lathe. They seem to transfer less vibration.

Offline Cheese

  • Posts: 6367
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #10 on: February 16, 2019, 11:26 PM »
I just took a look at my Delta and I’m positive the Jet is constructed in the same manner. The blade guides are suspended from the cast iron frame and for them to move vertically would take an act of God. The blade could be dancing around but the guides themselves should be immune from that action as they are isolated from the wheels.

Offline dlu

  • Posts: 168
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #11 on: February 17, 2019, 01:21 AM »
I just took a look at my Delta and I’m positive the Jet is constructed in the same manner. The blade guides are suspended from the cast iron frame and for them to move vertically would take an act of God. The blade could be dancing around but the guides themselves should be immune from that action as they are isolated from the wheels.

Yes, with the exception of some details, I think the basic construction is the same. I took heart in your belief that it would take super natural power to move the frame - I figure even Loki has higher priorities than messing with my head through my bandsaw…

So, I tried hanging from the guide post mount and sure enough it moved. No higher power required. When I let go it moved back, with a slight "thunk." Repeat. Same.

The saw has a riser block installed and I shimmed blade side of the block to make the blade and guide post parallel (effectively moving the top wheel a bit to the left. The shim wasn't quite thick enough so I moved it away from the blade (towards the bolt joining the halves of the saw), so it forms a fulcrum around which the top half of the saw can rotate. Looks like my first move is to get some thicker shim stock.

Offline kevinculle

  • Posts: 297
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #12 on: February 17, 2019, 08:25 AM »
You have identified the problem, with the lever arm from the column to the guide acting on the joint at the riser block anything that introduces slop at the riser block interfaces will allow movement.  If you need a shim here the shim needs to run all the way across the riser block joint surface, you can avoid disassembling the column by making a matching shim half and installing from the other side with the riser block joint loosened a bit.

Offline Cheese

  • Posts: 6367
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #13 on: February 17, 2019, 09:57 AM »
You found the problem, that's a good thing.  [smile]

FWIW...I read an article several years ago about tensioning band saw blades on a standard cast iron 14" Delta style bandsaw. When they tensioned a 1/2" wide, carbon steel blade to the typical 15,000 psi standard, there was about 300# of load on the wheels. When they tensioned a 3/4" wide, bimetal blade to the typical 25,000 psi standard, there was about 800# of load on the wheels.

So obviously, hanging on the saw shouldn't cause the arm to move.  [eek]

Also, don't get me wrong, I think adding a Carter Quick Release to a band saw is a smart idea. I just haven't gotten around to it yet.

I did add the Carter ball bearing blade guides and consider that to be a MAJOR improvement. Don't even think about "Cool Blocks", that was a waste of $40.

Offline dlu

  • Posts: 168
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #14 on: February 17, 2019, 06:51 PM »
I did add the Carter ball bearing blade guides and consider that to be a MAJOR improvement. Don't even think about "Cool Blocks", that was a waste of $40.

What do you notice? I've been on the fence about the Carter guides - my saw came with Cool Blocks or something like them and they seem to work "well enough." Then again, I have nothing to compare them to.

Offline Cheese

  • Posts: 6367
Re: Diagnosing & Eliminating Bandsaw Vibration
« Reply #15 on: February 17, 2019, 10:00 PM »
What do you notice? I've been on the fence about the Carter guides - my saw came with Cool Blocks or something like them and they seem to work "well enough." Then again, I have nothing to compare them to.

Well this somehow seems unlawful to tax an old guy’s memory. I just can’t waste it all tonight as I’ll probably need a bit more for tomorrow.  [smile]

Thinking back 25+ years ago when I purchased the Delta, the first thing I did was to change out the guide system to Kool Blocks. I was new to a band saw and Kool Blocks were new on the market. As I remember, they were a little better than the standard guides but not much. I think the standard guides lasted for 6 months and the Kool Blocks lasted maybe another 9 months before all were thrown out and I purchased the Carter guides.

After switching over to the Carter guides, I noticed that the cuts were smoother, had less ripple and the blade ran cooler. Also the thickness of the material that was removed was more uniform. They are easier to set for proper clearance. There’s also a rear bearing that supports the rear edge of the blade and prevents the blade from flexing and moving backwards as you engage the item to be sawn with the band saw blade. It’s a pretty slick setup.

I’ve read that they were designed to replicate the band saw guides that are used on expensive European band saws.
« Last Edit: February 18, 2019, 08:31 AM by Cheese »