Band mill question

[KGNC]

Couldn't fine anything in a search. Hope it's not a old topic.
Has anyone every made a band saw, (large or small) with a number of small blade wheels instead of two large ones? I'm not sure that it would be a good idea but I just like to consider different ways of doing things.

[Ianab]

I think the problem with doing that is that the smaller wheels forces the blade to bend tighter as it travels around them. Would limit the thickness of the band you could use and reduce it's life. Bands would break earlier due to metal fatigue  :(

Cheers

Ian

[amberwood]

In the interests of blade standardisation and trying to reduce the physical size of the mill my original design had a 3rd (smaller) wheel. It was situated above the blade on the upper return length. It required the blade to flex on both directions and thus destroyed a blade in about 5 minutes. In fact destroyed a coupe of blades.
If you are using a very thin blade this might work. Otherwise as prev suggested it fatigues the weld.

DTR

[mike_van]

I've read that even the small woodshop bandsaws with 3 wheels go through blades faster, it's that small radius.

[jkj]

KGNC,

From the "Bandsaw Handbook" by Mark Duginske:

"Thick blades will break more easily from the bending action, especially when run on small wheels.  Each revolution flexes the blade near the elastic limit of the steel, which causes the metal to fatigue and break quickly."  He includes a chart of wheel diameters vs blade thickness recommended by (unnamed) manufacturers:

4-6" -- .014" blade thickness
6-8" -- .018"
8-11" -- .020"
11-18" -- .025"
18-24" -- .032"
24-30" -- .035"
30"+  -- .042"

Now if you used a larger number of small wheels positioned in a arc the bending could be minimized, but seems that would add an undesirable complexity to the design.

JKJ

[KGNC]

So is metal fatique still a cause of blade breakage on most mills?

[slowzuki]

Yes the bending of the blade on each trip around is what causes most blade breakage.  Even with many small radius pulleys the blade just get bent and unbent more times each trip around.

[iain]

I had a design for that sort of thing worked out, to make a hand porta band mill, the logistics of the tracking was a pain, real cool design but way expensive to make



iain