Bandsaw guides - why is the rear one side mounted?

[RobinBHM]

I have a 20" Wadkin BZB and like many old bandsaws it has a rear guide that is mounted sideways.

But when used for resawing it sparks - not surprising really. It does rotate a bit, but it still sparks, or just makes a racket

Why not use an inline wheel so it rotates....I've seen retrofit guides that so just that.


Does anybody know if there's a design principal.

 

[RichardG]

I always thought that the rear guide was there to protect the blade by stopping the teeth coming into contact with the side guides if you occasionally press too hard and shouldn’t be touching in normal use? So it could be you need more blade tension or to back off and cut more slowly or a slightly bigger gap? Not an expert though.

 

[Ttrees]

I find the Axi GT blades to be quite stout, I use a 3/4" one tensioned well, and it will run on flat tires without giving in and rubbing against the thrust guide.
Not sure if your saw has crowned tires on it, and how much of a difference it might make regarding the band working its way across the wheels, but I have seen some folk like John Teneyck use a Woodmaster CT on that wee 17" super stout 300kg Grizzly machine.
So crowned must work well in this regard also, at a whopping 25000PSI blade tension
might help matters also.
This creeker article is rather interesting, (you can see John's posts whilst not being subscribed) if you google
"the incredible woodmaster CT"
He has a web page with cool blade sharpening machines and the likes also.

Might be pushing the boundaries on many a stout machine at this tension, so that needs to be taken into account.
I find a 3/4" is enough to tension for my 24" machine.

Not saying this is the solution but might be worth looking into "beam strength" of stout blades when tensioned to a decent amount.

Tom

 

[Doug71]

I had a BZB for years but never pushed it to it's limits at all. I presumed all bearings were mounted as in the Wadkin but then discovered it's the Wadkin that is different, afraid I don't know why.

I found a groove down the front of the bearing on mine caused by the thrust bearing not spinning and the back of the blade cutting in to it.

 

[--Tom--]

Flat face on rear thrust bearing gives more contact area.

Worth taking them ut and making sure they’re running smoothly and no grooves in them that would catch.

25000 psi is ok for m42 blades, but plain carbon steel typically recommended to run at 12000.

 

[dickm]

Flat face on rear thrust bearing gives more contact area.

Not convinced by that argument. As others have said, the rear bearing should only contact the blade rarely, so why is extra contact area needed? And unless the blade only contacts the rear bearing near to its edge, the variation in surface velocity across the bearing must add to wear?
This topic has come up so many times in the forum over the years, and still noone seems to have a convincing answer. Surely there must be one??