Bandsaw maintenance

[Overs Pianos]

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Hi all,

Yesterday I lost almost the entire day servicing my 
only-just-big-enough resaw bandsaw.

The saw has a 2hp motor with 45 mm (1.75") wide 500 mm (20") diameter 
pressed steel wheels and a cast iron tilt table and adjustable fence. 
I run a 2" wide Simons Red Streak blade, which has a 0.89 mm (35 
thou) thick back with 20 thou of tooth set per side with tooth pitch 
of 1". Theoretically the blade cuts a 75 thou curf, but after all the 
vibration and blade flex is taken in account, the reality curf width 
is around 100 thou (2.5 mm).

When I first bought the saw, being the commercial quality (read cheap 
and nasty) item that it was, performance was less than startling. 
After much fiddling getting everything shimmed up and straight, and 
after building a custom roller bearing guide system for the upper 
guide post and under the table, and speeding the blade up to 5,000 
feet per minute, the saw remained an ordinary performer. After some 
further reading I realised that the wheels, which were rubber tyred, 
probably were not crowned properly and had axial run out. So I set to 
work and ground the wheels with a 1 degree crown angle which peaked 
at 1/3 width back from the font edge of the wheels. Bandsaw wheels 
are usually crowned slightly closer to the front of the wheel to 
allow them to properly track a thinner blade, should this be required.

It's been many years since I first crowned the bandsaw wheels. 
However, over recent months the saw has been acting up and refusing 
to track well. When a blade is cutting well it should never come in 
contact with the back guide. But this started happening regularly and 
over the weekend we lost an expensive piece of wood when a blade 
stepped right forward off the wheels and had a chew at the cast iron 
table.



A view of the saw showing the roller guide system. These are now 
available as an accessory item. The roller guides shown were custom 
made over fifteen years ago.

Should anyone wish to receive a higher resolution close image of the 
guide rollers, email me privately. The images shown are re-sampled 
lo-res to get them onto the pianotech list.

An examination of the wheels revealed that there was little wear of 
the rubber tyres. But, while the original crowning machine marks 
remained just visible, the crown was almost flat in the middle of the 
wheel.

The industry standard for crowing steel band saw wheels is 1 degree 
of crown.  After reading a few articles on crowning wheels I found 
that some recommend a crown angle of up to 7 degrees.

Four useful articles on band saw maintenance can be found at;

http://www.owwm.com/FAQ/Default.asp

I decided to re-crown the wheels to 1.5 degrees. A higher crown would 
probably increase the stress on the blade back, and the original 1 
degree of crown seemed to track reasonably well. I am very pleased to 
report that the saw is now performing better than ever. We did a test 
cut on an 8" (205 mm) deep board after re-assembly. The cut was 
straight and the blade didn't budge from its free-running track 
position during the cut.



A view of the wheel surface, shown against a square, clamped to the 
housing, to show the crown of the freshly crowned tyre

While I often feel cheated of time when I lose a day doing something 
like yesterday's bandsaw maintenance day, it was a different case 
yesterday. Its most pleasing  to have the saw performing better than 
I could have imagined.

Now its back to work to finish the resawing I started over the weekend.

Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:ron@overspianos.com.au
_______________________
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