Thread: So, where should the blade REALLY run on the top wheel?

Guy's

just at thought from left field , when we were setting the blades , with the center of the blade on the crown of the wheel, are we creating a PIVOT POINT?????

With the blade on the crown of the wheel , neither the front or the back edges are supported, hence a PIVOT POINT.

With the blade supported at the back of the tooth Gullet, the support is at the front of the blade , and the guides in a similar position the teeth of the blade are supported in such a way that they will be more resistant to wondering.

Just a thought.

Jeff
vk4

Originally Posted by vk4

Guy's

just at thought from left field , when we were setting the blades , with the center of the blade on the crown of the wheel, are we creating a PIVOT POINT?????

With the blade on the crown of the wheel , neither the front or the back edges are supported, hence a PIVOT POINT.

With the blade supported at the back of the tooth Gullet, the support is at the front of the blade , and the guides in a similar position the teeth of the blade are supported in such a way that they will be more resistant to wondering.

Just a thought.

Jeff
vk4

That was Snodgrass' point, and the reason he says to set the tracking this way - support of the teeth.

Originally Posted by pmcgee

Hi Steve - very worthwhile discussing.

For one thing, given a tight metal band round rubber-coated wheels, I assume that under the contact area of the blade on the wheel will be a flattened area - not a single point on a curve - so there's no doubt some leeway to move the blade left and right from the 'centre on centre' arrangement.

Also Snodgrass says (I think) that only the top wheel will run how he suggests and it will be different on the bottom wheel. I am assuming without going out to check it that with the 'centre on centre' arrangement it would be that way for both wheels.

So they may be - I'm sure are - two possible ways to achieve what we want which is a stable dynamical arrangment of two wheels and a metal band that is resistant to being moved away from that arrangment ... like a punching clown that you can push around but comes back to the upright position.

To properly compare the two would need some proposals of experiments that could be duplicated with 'identical' materials under the two different setups.

Eg. Setup a fence each time using the cut halfway by hand method, then cut 20mm, 10mm, 5mm thick slices off of xxx type of wood that is 1", 2", 4" thick by 18" long. Several times.
Then repeat with different woods.
Then report back here.


Paul.

Originally Posted by Hermit

It is interesting, isn't it?

Snodgrass says that centring the blade on the rear of the gullets on the top wheel won't affect tracking on the bottom wheel.

While this can of worms is open, another potentially controversial point raised in the video is his claim that the wheels are supposed to have co-planar misalignment and are designed intentionally that way to keep the blade controllable when adjusting tracking.
He goes on to say that if you align the wheels perfectly, you will lose tracking control.

This talk of tracking has recently dug up some long forgotten memories of farm life many moons ago. Living on a dairy farm, we had a number of stationary engines that powered the milking machines and well pumps, all driven by big flat belts. It was remarkable to me that the stayed put on flangless pulleys and I was told it was because one pulley was crowned. I had forgotten about this but now with the power of Dr Google here are some links that may help to clarify or muddy the water about this BS tracking.
My experience that moving the the tracking position of the top BS wheel does affect the position on the bottom wheel as you can see if you run it up at different positions and then has a look at the position of the blade on the bottom wheel - I don't see this as being particularly important, nor do I believe in the necessity of having a small coplanar misalignment to aid tracking. What is important is to have the shafts parallel within a small window otherwise the blade will drop off the front or back of one of the pulleys. If you're within that window the blade will stay on and sit between the full forward and full rearward extremes on the top wheel and so long as the flat bottom wheel is aligned well enough, the blade will just move to the 'best' position guided by where it is on the top wheel (of course the thrust bearing may have other things to say about that if it is in the way). All this is not to say anything about how/why/wherefore you should optimise your BS blade, it is just to give an idea of the fundamentals of flat belt tracking...
Flat belt tracking on pulleys.
How crowned pulleys keep a flat belt tracking
There is an interesting video in the second link and some pertinent comments relating to BS (band saws, not the other contraction). OK enough BS from me

Hi All,

I tried setting up my small bandsaw as per the ALEX SNODGRASS, video,

Well the results are in after a few tests, I set the tooth gullet on the wheel crown, and the guides as suggested, just behind the gullet of the teeth, I then found the top wheel osolating slightly, this was traced back to the 3 small grub screws behind the top wheel.
When tightened the osolation stopped, .

Well to the point the cuts are now verticale, drift has nearly all disappeared, all this with a blade that is not really new , and has been resharpened twice.( by me).

A convert , I don't know as yet but it appears to do what he demonstrated and said. I also tried the test , cutting into a piece of timber , then moving it to the back of the blade and letting the blade run in the cut, my saw would never do this before ( due to all the misalingments), it will now .

You never stop learning , and I have learnt a lot from ths forum.

Jeff
vk4

Jeff is that stack of wood in the last photo after you tuned the band saw? If so that is still quite far from optimal. You should be able to make a stack of cut wood that are visually identical in thickness and straight.

Originally Posted by mic-d

Jeff is that stack of wood in the last photo after you tuned the band saw? If so that is still quite far from optimal. You should be able to make a stack of cut wood that are visually identical in thickness and straight.

The label on the photo says old set up

MIC-D,

that was from before I reset the whole saw .

I ran the block in the other PIC's,. through several times to remove all the chainsaw marks, and the results , were straight cuts with only 1 slight bow in a cut, and that was before locking the grub screws on the plate behind the top wheel.

Jeff
vk4

Originally Posted by vk4

MIC-D,

that was from before I reset the whole saw .

I ran the block in the other PIC's,. through several times to remove all the chainsaw marks, and the results , were straight cuts with only 1 slight bow in a cut, and that was before locking the grub screws on the plate behind the top wheel.

Jeff
vk4

Another happy customer.
Its just got to be a whole lot nicer when it works as you expect an not a hit and miss affair.

Jeff: I'll bet you quite happy with the result your getting now.
Peter

Originally Posted by vk4

MIC-D,

that was from before I reset the whole saw .

I ran the block in the other PIC's,. through several times to remove all the chainsaw marks, and the results , were straight cuts with only 1 slight bow in a cut, and that was before locking the grub screws on the plate behind the top wheel.

Jeff
vk4

Sorry, just checking. Good-o

Hi All,


Yes I am pleased with the results , i will be interested to see what it will do with a new SHARP Blade, and I will treat myself to a 1/8" blade as well, for the tighter radius cuts I always seem to need.

Jeff
vk4

I was side-tracked for much of the day and didn't get a chance to do much with the bs, but I'll try this tomorrow too.
Who knows, it might cure my gouging problem.

Hi All,

when I reset the bs , i started from scratch, .

1 moved all the guides away from the blade
2 reset the blade track.
3 cleaned and set the top guide
4 cleaned & set the bottom guide
5 replaced guards, & ran machine.
6 test cuts.

The blade runs on the center of the bottom wheel and all looks good.

Jeff

Originally Posted by vk4

Hi All,

when I reset the bs , i started from scratch, .

1 moved all the guides away from the blade
2 reset the blade track.
3 cleaned and set the top guide
4 cleaned & set the bottom guide
5 replaced guards, & ran machine.
6 test cuts.

The blade runs on the center of the bottom wheel and all looks good.

Jeff

Good one. Thanks for putting it to the test Jeff.

My original question when starting the thread was "So, where should the blade REALLY run on the top wheel?"

The answer, in my case, is with the bottoms of the gullets in the centre of the wheel, exactly as Snodgrass recommends.
There is absolutely no doubt.

For anyone following my bs bs troubles over the last few weeks, this was the cure.
No more gouging whatsoever and I'm getting lovely clean cuts compared to previously.

The change did introduce a couple of degrees of constant, predictable drift, although I can loosen the bolts and swing the table that far. In fact, it probably is very slightly crooked now, so in effect I have no drift. When I adjust the table, the cut will be parallel to the slot.

I'm definitely another convert. Made an almost useless bandsaw for me into a useful one.

Before: -
Attachment 212396

After: -
Attachment 212397

(Any roughness in the 'after' shot is because I was stopping and starting, steering down a line to check tracking.)

Edit: Like Jeff, moving the blade on the top wheel did not move the blade on the bottom one. It stayed centred.

This makes me feel like screaming out "Eureka" and running down the road, after my hassles.