Nice to know
you¡¯re making progress. Sorry my answers are a little long, but if you don¡¯t have
enough info to understand why things work, you can¡¯t evaluate any how
information meaningfully. To respond to your questions.
?
Tension
So far you¡¯ve
only been interested in blade tracking, but once it tracks you¡¯ll need to make
it cut straight and we get to another can of worms. ?If you read the doc in the files section
called ¡®Bandsaw Chip Characteristics v3.pdf¡¯ you¡¯ll get the gist of what¡¯s
happening as the blade cuts. The bits about ¡®weight on the tooth¡¯ and ¡®blade
tension, stress and buckling¡¯ are important (the concepts, not the numbers
which are different for your blade).
?
Your blade
is a ?¡± deep, 0.035¡± wide beam spanning 10 to 14¡± between the two back support rollers,
(depending on how far apart your guides are), with the work pushing up roughly
in the middle. In engineering terms it¡¯s a very slender beam; the only
thing keeping it straight is its tension.
The most important
thing is that the blade cuts in the direction its pointing. When it buckles
it no longer points straight down and it doesn¡¯t cut square down through the
work. ?You need high enough tension and a
low enough bow weight to stop it buckling, but not so high that the blade
cracks and fails. ?Beyond that the actual
tension doesn¡¯t matter very much.?
?
You say you¡¯re
still in the 'thunk' area, but be careful.? Your blade is longer and thicker than a
4x6 blade, both of which will make the tone lower. The tone it makes depends only
on the span, the weight per unit length of the blade and the tension ¨C if you
pluck the back run of the blade between the guide wheels and use a std blade
then tension is the only?thing that changes the tone.?
?
You¡¯d expect
the bandsaw manufacturers to have given you a tensioning mechanism that you can
use, without resorting to anything special, to tension it properly. ?Since you have to choose a repeatable tension
to set the tracking, wind the tension knob as hard as you can with one hand and
leave it at that. Use the scratch and sticky-tape marker method for this blade
and record the tone on your cellphone¡¯s audio app to make it repeatable for
other blades.
?
I¡¯ve looked
into all the methods of measuring tension I can think of, and there are no
simple, cheap, ones where you know what the actual tension is. ?
?
Wheel crown?
Yes, your
wheels are crowned.? That normally means
the tilt is not so important as the blade will ¡®climb up¡¯ the crown when it
runs.? Since it will climb up no matter
which side of the wheel it¡¯s on, it should settle in the middle. You adjust the
tilt to make the crown on both wheels the same, but the wheels need to
vertically in the same plane, like 2 dishes lying on a flat table.? That makes the drive wheel position that much
more important. If the rims are both the same thickness, you should be able to
get it close with a long straight edge that lies across both wheels, touching at
2 points on both wheels.? A piece of extruded
aluminium 1¡±x ? ¡° unequal length angle section, 1/16th¡± thick,
cut to length to fit inside the saw frame casting is the best I¡¯ve found. Find
it at most hardware stores. Extrusions are normally very straight in short lengths and the
angle section stiffens it. ?
?
Drive wheel
Once you¡¯ve
found the optimum position for the drive wheel it should not need to be moved
again, so pinning it again is not a bad option, since you can do it with the minimum
of tools.? 3 setscrews at 120deg is NOT a
good option, as the whole load is concentrated at 3 points with the maximum
amount of wiggle as it wears.? Wheel
bosses are normally fixed to shafts with 2 set-screws at 90deg, though I¡¯ve
seen an engineering paper where they said you get more friction between shaft
and boss if they¡¯re spaced at 45deg! ?Flats
for the setscrews to bear on are a must, though I¡¯ve no idea whether just 2
set-screws will be enough.? The boss on
that drive wheel looks long enough to put in a double row of setscrews and I¡¯d
be pretty confident that would be enough.?
Broaching/cutting a keyway with a setscrew on top of the key is the
preferred solution, if you can get it done cheaply enough.
?
Blade guides
Yes, feeler gauges
are the right way. The blade is 0.035¡± so a set at 0.036¡± or 0.042¡± will do.
The debate over clearance or no clearance is mainly about whether you cut steel
or aluminium and/or use coolant.? Coolant
and cutting aluminium both cause swarf to stick to the blade and get rolled
through between the blade and the side guide rollers, so clearance is
desirable. Steel swarf and in dry cutting the swarf falls away so only minimal clearance required which gives maximum blade direction control.? The best solution is to use minimum clearance and a blade scraper like in doc 'Liquid Coolant Lube on a 4x6 Bandsaw.pdf' in the Files section.
?
Yeah, I
think bow weight and side roller guide separation are your immediate problem
too.? Happy hunting - jv
