Cracking in the gullet - and when to change a blade based on hyd pressure?

[acrosteve]

I saw the thread about leaving the blade tension on overnight.  I will admit that sometimes I have forgotten to release it when I finished sawing.

I also have probably used a blade much past where it needed resharpened.  I have thought that that would also stress the blade to the point of cracking.

But recently, I have started watching the pressure gage on my carriage feed more than I have been watching the actual carriage.  It seems that in oak, a new blade starts out at about 600psi, and as the blade dulls, the pressure climbs upwards of 700.  Consistently above 800 and the blade comes off.

My B-20 has a pressure gage on the blade tension also.  I run it around 1,000 psi.


Obviously cracking in the gullet excludes it from being sharpened - therefore I want to avoid having it happen.


My question is, what are the causes of the gullet cracking?

[Larry]

My old mill had electric feed.  As the band dulled I had to increase speed...in other words turned up the rheostat.  On my TK2000 it doesn't have a gauge and it's impossible to tell from the feed dial, but I'm sure I have to turn up the feed as the band dulls on it to.

If your band is coming off I would suspect a problem even though you are feeding with more power.

Cracking in the gullets can come from a variety of reasons.  Band running to far from the roller flange, bad bearings, worn belt (if on steel worn wheel), and probably other reasons I haven't experienced and don't want to.

[redprospector]

In my experience, trying to cut with a dull blade will cause cracking in the gullet.
You're way ahead of the game if you'll change out blades before it really gets dull.

Andy

[dgdrls]

http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2513/NREM-5046web.pdf

This is one place that has info on gullet cracks.

DGD

[ladylake]

My old mill had electric feed.  As the band dulled I had to increase speed...in other words turned up the rheostat.  On my TK2000 it doesn't have a gauge and it's impossible to tell from the feed dial, but I'm sure I have to turn up the feed as the band dulls on it to.

If your band is coming off I would suspect a problem even though you are feeding with more power.

Cracking in the gullets can come from a variety of reasons.  Band running to far from the roller flange, bad bearings, worn belt (if on steel worn wheel), and probably other reasons I haven't experienced and don't want to.

Larry    A band running to far from the flange will crack in the back of the blade, a band running too close to the flange will bend around the guide wheel causing it to crack in the gullet. I set the flange almost 1/4" behind the back of the blade with real good results.  On time the flange got real close to the back of the blade and broke about 6 almost new blades real fast, I pay attention to that now.   Steve

[Tom the Sawyer]

Larry,

"Consistently above 800 and the blade comes off."

I think he meant that once the pressure got up to 800 he would pull the blade to resharpen, not that it came off the rollers.

[Brian_Rhoad]

Not grinding enough in the gullet when sharpening will cause cracks.

[LeeB]

Not grinding enough won't actually cause cracks, it will however allow existing micro cracks to become big cracks.

[acrosteve]

Larry,

"Consistently above 800 and the blade comes off."

I think he meant that once the pressure got up to 800 he would pull the blade to resharpen, not that it came off the rollers.

Correct.