Band Saw Misbehaving

[dusty]

Playing a hunch here: can someone tell me what the factory specified lower back up bearing is?

Here's my hunch: The lower back up bearing is not adjustable front to rear. But if the wrong sized bearing was used there, one with too large a diameter, I believe it would cause the very issue I am seeing.

I've never changed the bearings but who knows if the PO did or if someone at the factory grabbed the wrong bearing....

That bearing on my machines are 627ZZ (7mm x 22mm x 7mm). They were originally 827Z (7mm x 22mm x 10mm).

[STB]

My Shopsmith band saw is acting weird.

I don't know if this will help but this is my recent band saw experience.

Inspired by Fredsheldon I decided to make a band saw box. I am not sure if I should thank Fred or blame him.

My band saw has the factory guide blocks and my SS brand 1/4in blade normally lives on the band saw. To make the resaw cut I installed a SS brand 1/2in blade. The first cut ( thin side) turned out just fine. The second cut (thick side) was bowed. Next I replaced the 1/4in blade and readjusted the guide blocks made some cuts. After the cuts were made I replaced the 1/2in blade. I was having a hard time adjusting the guide blocks. After removing the guide blocks, finding my glasses, and examining the blocks I found that I had created a wear step on the backside of the guide blocks. I think I pushed the blade past the wear steps and skewed the blade on cut 2. The next challenge was to sand the correct angles in the guide blocks. I clamped the blocks in the miter Gage and used the disk sander (not spinning) to restore the angles.
The second picture shows the results after truing the guide blocks. Because of the shape of he piece I cut it from both sides the nick in the thin piece is where the cuts come together. It is less than the width of the curf.

[ATTACH]26942[/ATTACH]

[ATTACH]26943[/ATTACH]

[JPG]

I don't know if this will help but this is my recent band saw experience.

Inspired by Fredsheldon I decided to make a band saw box. I am not sure if I should thank Fred or blame him.

My band saw has the factory guide blocks and my SS brand 1/4in blade normally lives on the band saw. To make the resaw cut I installed a SS brand 1/2in blade. The first cut ( thin side) turned out just fine. The second cut (thick side) was bowed. Next I replaced the 1/4in blade and readjusted the guide blocks made some cuts. After the cuts were made I replaced the 1/2in blade. I was having a hard time adjusting the guide blocks. After removing the guide blocks, finding my glasses, and examining the blocks I found that I had created a wear step on the backside of the guide blocks. I think I pushed the blade past the wear steps and skewed the blade on cut 2. The next challenge was to sand the correct angles in the guide blocks. I clamped the blocks in the miter Gage and used the disk sander (not spinning) to restore the angles.


The second picture shows the results after truing the guide blocks. Because of the shape of he piece I cut it from both sides the nick in the thin piece is where the cuts come together. It is less than the width of the curf.

[ATTACH]26942[/ATTACH]

[ATTACH]26943[/ATTACH]

Why not??????;)

P.S. I am curious why the fence is outside the blade? I would think the workpiece would be more accessible if the fence were in the throat.

[STB]

[quote="JPG"]Why not??????]

After recent events I am confused as to the meaning of thread hijacking. If this is hijacking I apologize to algale.

After clamping the block I used one hand to move the miter Gage back & forth the other to bring the disk to the block. I felt that spinning the sanding disk might remove stock to fast or catch the block & send it flying. I figured better safe than sorry.

Are you familiar with the term screwup? The particle board fence extension is finished on one side only. I marked and drilled the screw holes from the wrong side. So thats the reason the fence is on the outside.

[charlese]

Algale,
5" wide walnut board. The blade bowed in the cut really bad, as if it were not tightened enough. I use a pointed fence 1/16th or so ahead of the blade. I tightened it a bit more and got the same result. Gave up.

Try your pointed fence with the point right on the teeth. now ahead or behind them.

[kablerj]

Are you familiar with the term screwup? The particle board fence extension is finished on one side only. I marked and drilled the screw holes from the wrong side. So thats the reason the fence is on the outside.

Not a screwup, a "problem solving challenge and opportunity for design modification".

[algale]

My hunch was wrong. It is the correct diameter bearing (using Dusty's measurements).

But I discovered there is a lot of pressure between the blade and the lower back up bearing. I don't know what is considered normal, but, as a test, if I use my finger to spin the lower back up bearing, it spins the blade and both wheels with no slippage. (Obviously the headstock is not connected to the band saw during this test ).

I checked the cant of the upper wheel and it is correct. I even tried taking a little of the cant off and saw no difference. Maybe I need to take a lot of cant off?

Here's a another symptom (perhaps). If you spin the wheel backwards, the blade switches the direction of its twist (teeth move from facing left to facing right). I recall someone else observed this very problem (can't find the thread) and I don't think it was ever solved. EDIT: Found it. Here it is. http://www.shopsmith.net/forums/showpos ... stcount=58

I was not having this problem when I first bought this blade. I have a hypothesis why not. I normally adjust the guide blocks so they are just behind the gullets. I've just discovered that on the 5/8 blade, the blade is too wide to make this possible. The back of the blade will bottom out on the guide block bracket casting before the guide blocks are all the way to the gullets. On my band saw there is a tell-tale groove groove in the casting of the upper and lower guide block brackets. I suspect I adjusted the guide blocks as far forward as possible and inadvertently cut those grooves, which held the blade in position.

[dusty]

My Shopsmith band saw is acting weird.

I needed to resaw some 3 x 5 inch sappele. I mounted my 5/8 blade, tensioned it up to the recommended 1/2, set my Kreg fence (which i had previously adjusted to this blade) and started up. The work pulled away from the fence and the cut was bowed. Stock ruined.

I stripped everything down, checked and recalibrated the tension gauge, checked and adjusted the autorack bearing, checked readjusted the upper back up bearing, checked and adjusted cool blocks. Checked wheel cant. All good.

Remounted the blade. It is riding properly in the autotrack bearing groove. It is riding against the lower back up bearing. There is the recommended 1/64 space between the back of the blade and the upper back up bearing. All good. All is as it should be.

Except one thing: the blade is at an angle where it goes through the table insert. The front of the blade (teeth) point left and the rear of the blade points to the right! The angle is such that there's not enough play in the trunnion brackets to allow the table to be set up with the miter slot parallel to the blade.

I remember another user had this problem with this blade and I don't think we ever got him straightened out (literally or figuratively).

Called Shopsmith and described my problem. Checked the blade weld and back of blade. All good. They suggested first increasing upper wheel cant (no effect) and then reducing upper wheel cant. Reducing the upper wheel cant has reduced the angle of the blade to where I can adjust the table so the miter slot is parallel to the table.

Readjusted the Kreg fence for drift and tried to resaw some scrap. Same problems. Work is pulled away from fence after the cut and the blade is bowing. And cuts using the miter gauge are drifting too.

I will try mounting the blade in my recently acquired older vintage Shopsmith band saw and see if it is a problem on that band saw too. I will also try mounting some smaller blade in both saws and see what gives.

At the moment I am at a loss and very frustrated.

Is this a powered condition or an idle condition?

Is the 5/8" blade from Shopsmith or a 3rd party? This most likely makes no difference but if I am going to mount a blade for testing I might as well do one that simulates your setup if I can.

Is the problem unique to this particular blade?

Have you tried running without the lower backup bearing?

[algale]

Is this a powered condition or an idle condition?

Definitely idle and I think under power.

[JPG]

Let us see if I understand what I have just read.

The back of the 5/8" blade bears against parts that are not intended to be tolerating the blade.

Does not this provide an explanation for unexpected results?

The back of the blade should always ride against the rear guide bearing and the lower guide bearing, and against the upper backup bearing ONLY when under cutting load. It should not be contacting anything else.(period)