on the same rebuild of the 6" craftsman jointer - needed a pulley for the
motor. original was 5", all Northern Tool had was a 4-1/2". obviously this
will increase the rotational speed of the jointer head by something close to
some 5% the radius and some factor of pi - i dont care about the exact math
- i just know it will be a bit faster. should this be an issue or should i
look further for a 5" pulley?
With the smaller pulley you will have marginally less power and the belt
will probably have to be shorter.
With that in mind, my boat anchor 6" Craftsman jointer only has a 2.5"
pulley on the motor and a 2" pulley on the cutter.
IMHO if you maintain that ratio approx. 4 to 5 you should be ok. If you
pullies are much different than that I would say that your cutter rpm's will
be way off.
If it's on the _motor_, going from 5 inch to 4-1/2 inch will *decrease* the
rotational speed--from a safety viewpoint there should be no problem with it
at all unless the smaller diameter results in the belt coming into contact
with something that it shouldn't. The decrease will be about 11 percent.
That said, try Grizzly and McMaster--both list 5 inch pulleys for a
reasonable price. If you absolutely positively gotta have it today Grainger
has them too (4.95" anyway, which is close enough) but they want twice what
Read the fine print at McMaster though, about belt types and effective
radius--two pulleys with the same outside diameter can run the belt at
different depths in the groove and give very different RPMs.
The factor(s) of pi cancel out so it's simply the ratio of radii.
Others have noted the difference is somewhat slower on the driven side
instead of faster.
I'd only comment that whatever you decide on the size, get a good
quality turned pulley, not one of the cheap-ass pot-metal things on the
On While I cannot comment on the Jointer question directly / from
experience, I can offer an accounting of an experience helping an
electrician pal years ago with a restraint exhaust fan problem he was
It seems they called him when the fan stopped working and he came,
found a broken driven pully and replaced it - problem solved, fan
working. He got paid and left.
He wound up calling me to take a look because the fan stopped working
the next day - blowing the breaker (and the breaker he replaced) and
he could not figure out why.
I climbed up on the roof to find that, fortunately, he was a less than
diligent repairman and hadn't cleaned up the work space after leaving
the first day. I found a bit of the original pulley laying about near
the fan motor and asked if it was a piece of the old, broken pulley.
When he confirmed that suspicion, I held it up against the replacement
he'd installed and determined that it was larger (or smaller) by a
half-inch or so than the original.
Off to ACE Hardware and back to install the correct size pulley on the
fan and the problem was finally solved.
For what it is worth, tools are designed by engineers who have done
all the calculations and assembled a device with all the appropriate
parts. Absent some Engineering knowledge and an intent to "tweak" your
tool a bit, safe bet to to replace parts with the exact same thing
they were designed with.
The story would indicate more than simply a pulley diameter change
problem--the additional torque of a minor speed increase causing failure
to start would only be an issue if the starting load were already very
near limit of motor and circuit or the change was a very significant
For a jointer a 5-10% speed change is minimal altho slower rpm will
require a slightly slower feed rate to continue to get the same degree
of smoothness in the jointed edge...
It is not that important to keep everything running at a speed determined by
the engineers. That speed changes when you start running stock through
anyway. It really slows down when you start surfacing a 6" wide board.
Granted a drastic pully diameter deviation would not be a good thing but a
small jump such as the one proposed would probably help to maintain speeds.
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