Thread: Bandsaw Blade Wobble

Sounds like a bad joint on the blade.

Do you have another, known good quality blade you can swap it out with to check?

(And by good quality, I simply mean that it's known to run true, perhaps a working blade from another BS of the same size. A blade can be brand new and costly and still have this fault slip through QC on a bad day. )

Could be a bad blade, but I've tried a couple and had the same issue with all of them. It's the side to side movement that I find most puzzling. I'm hoping I can fix it otherwise I'll have to replace it.

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If it’s side to side when looking from the front or back of the blade, it could be a bad tyre if your’ve ruled out the blade.

to diagnose the issue

make sure the guides are not in contact with the blade.(ie back them all off)

1. Rotate the upper wheel by hand with a known good blade on the machine.

If the wobble disappears, the problem was a tension related harmonic in the blade under powr. Tension the blade correctly (6mm deflection on the spine side under side pressure from 1 finger, without turning your finger too white.
If the wobble remains, the issue is wheel/tyre related. go to 2.

2. rotate the lower wheel by hand, while running your fingers over the upper surface (where the blade is absent). Note any lumps bumps knicks or cracks in the lower tyre.
Now rotate the UPPER wheel by hand, while running your fingers over the lower surface (where the blade is absent). Note any lumps bumps knicks or cracks in the upper tyre.
If both tyres pass this test go to 3.

3. Rotate the upper wheel by had looking for for and aft movement in the wheel rim on the far side of the wheel, then repeat the process for the lower wheel

4,
Report back here with any supporting photos videos.

I suspect you will find bumps in one of the tyres, most probably the drive wheel, but go through the process anyway.

Thanks T91 I'll give it a go and report back.

Edit - a name.

Originally Posted by T91

to diagnose the issue

make sure the guides are not in contact with the blade.(ie back them all off)

1. Rotate the upper wheel by hand with a known good blade on the machine.

If the wobble disappears, the problem was a tension related harmonic in the blade under powr. Tension the blade correctly (6mm deflection on the spine side under side pressure from 1 finger, without turning your finger too white.
If the wobble remains, the issue is wheel/tyre related. go to 2.

2. rotate the lower wheel by hand, while running your fingers over the upper surface (where the blade is absent). Note any lumps bumps knicks or cracks in the lower tyre.
Now rotate the UPPER wheel by hand, while running your fingers over the lower surface (where the blade is absent). Note any lumps bumps knicks or cracks in the upper tyre.
If both tyres pass this test go to 3.

3. Rotate the upper wheel by had looking for for and aft movement in the wheel rim on the far side of the wheel, then repeat the process for the lower wheel

4,
Report back here with any supporting photos videos.

I suspect you will find bumps in one of the tyres, most probably the drive wheel, but go through the process anyway.

Backed everything off and followed steps 1-4. Blade was moving too slowly to see any wobble at step one so I pushed on. Step 2 showed no bumps but the wheel was coated in gritty dust which I cleaned off with some fine sandpaper. Step 3 showed some lumpy black adhesive substance on part of the top wheel which I removed. Step 4 was to reset the machine re Snodgrass and see if anything changed. Well there was still some side to side flutter but much less than before. I think the bumpy adhesive may have had some effect here.

Step 5 - take a video of the forward backwards wobble which causes the rear guides to rotate as they get knocked by the bump. Sign of a bad weld?
Shared album - Zac Fergie - Google Photos - link to video.

Let me know what you think.

Cheers,
Zac.

thanks for helping out with the photos & video. It makes life much easier

With your video of your guides rotating I am guessing that the gunk has resulted in an increased radius in one spot on your tire, so that you are getting intermittent contact with the side guides, and that the isolated instance of increased radius is also making the effective location of the crown in that spot different from the average crown on other parts of the tyre, which creates the for and aft movement. Rotate the upper wheel by hand and watch the back of the blade to determine if the distance to the edge of the wheel rim is consistent or varying...

having looked at the video and the photos, and read your reasoning, I think you have 2 issues, which we will try to solve in parallel.

Issue 1 is the tire issue... the black gooey stuff. I would remove the blade and try to clean it off the wheel/rubber by hand using a scotch-brite type of green abrasive pad and metho. If that doesn't work, scotch-brite and Coles white double strength vinegar (wear rubber gloves).
If that does not work, try sand paper glued to a flat stick (watch this video around the 20min mark Installing and Crowning Bandsaw Tires - YouTube )
If that doesn't work think about getting some carter-blue or blue max urethane tyres for your machine. This will entail cleaning your wheels of all the old rubber and glue,and then correctly fitting the correct size of tyre...so try fixing what you have first

Issue 2 is the blade.
with the blade installed, rotate the wheel by hand with your finger tips on the back of the blade trying to detect the back of the weld. If you can detect any lumps or bumps, run it under power using any cheap old carbide stone to contact very lightly on the back edge of the blade at a slight angle, from one side, then the other. What you are trying to do is to wear off the inconsistency, if it exists, without creating a knife edge on the back ( You want a rounded back. )

Do not use pressure on the back of the blade under power as you do not want to run the blade off the tire under power. Use a feather touch. You are only trying to correct a bad weld. If it turns out that the blade was misaligned in the weld rather than just a poorly executed mechanical joint, scrap the blade & get a good quality one.

If the above doesn't work, or if you still detect a bad weld, use another blade for your diagnostics




Let us know how you go

Change the band. 99% of problems are from a buckled body on the blade.

I think he has tried to eliminate that as an issue,

"Could be a bad blade, but I've tried a couple and had the same issue with all of them"

but its possible he got a crook batch. It would not be a first.

Get a paddle pop stick or similar and balance it on your finger and on top of the wheel and rotate the wheel by hand, if the stick moves up and down, the wheels and the tyres (not the correct term) need truing up. It’s usually easier to source new ones and fit them or have them done at a machine shop. Seen plenty of flat spotted wheels on machines that have been left for ages with the blade tension still on, especially urethane lined ones.

And if all the above establishes that the wheels are true and round and that the blade is correctly joined and has no kinks then it could be worthwhile to establish the correct tension is being applied to the blade.Bandsaw "tension indicators" are often only close to being somewhere near right. The right way to do it is to measure the stretch of the blade when it is under tension. It's not really all that complicated, there is some mathematics involved and I wish I had paid more attention when the teacher was dealing with formula transpositions but I got there in the end. You can find all the info via Professor Google and Dr. YouTube and it's worth taking the time to experiment.
We were having problems with our big bandsaw, the blade was wandering all over the place and in desperation I set out with a simple digital vernier caliber and a couple of clamps on the blade, then tensioned things up until we got the required stretch in the 32mm wide blade. I used a torque wrench to measure the torque on the tension bolt and we just tighten things up to 40ft/lbs before we start sawing. Problem solved.

Hello
Side to side issues could be a few things.
It could be as simple as not enough tension on the band.

First by replacing the blade for a stout one, not really thin gauge, and making sure it's clean .
I would look for a different company, it made a difference with my machine.
It may well not need anything more than this, and was the first thing I should have done.
Get the widest blade that your saw will comfortably handle.


Is the jacking bolts tight or could they have loosened and changed the angle of the lower wheel shaft.
If you decide to change this, then both a narrow curve cutting blade and wide blade might be necessary in order to not be chasing your tail.
Take pictures beforehand so you can remember the position of the shaft, the bolts and locking nuts!

If both tires are the same profile and the wider blade is staying put, then I am guessing low spots.
Either way that could mean dressing if the jacking adjustment is of no use, and new blades properly tensioned won't sort it out.

It looks like your tires are flat?
If they are not flat then disregard my advise.
I see a sawdust pattern at the rear of the tire, not the other side of the centre of the tire.
That's where your blade is either being tracked intensionally by yourself or someone else beforehand, a huge wide blade could have done the same.
if this is a flat tire then you overhang the teeth off of the edge of the tire.
If you are trying to track it like so, but the saw is not running well, then you could dress it with a plane iron clamped up on its side.

This is best adjusted by backing off the large f clamp and rotating the block to adjust depth, NOT by adjustment of the blade in the lock, as it will cause a slice in the rubber.
Turning by HAND, and not under power I might add.
The arrangement of the iron is like a scraper plane, so is leaning away from the centerline of the wheel, although it doesn't look like it.
Place plywood on the base of the machine and where ever else to not chip paint from a dropping clamp.
Nice to have a good f clamp for the job, (I have done this a few times, on this machine as these tires were badly damaged)

Tom