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Motor RPM for Jointer

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Forum topic by greatgates2340 posted 688 days ago 1878 views 0 times favorited 12 replies Add to Favorites Watch
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greatgates2340

1 post in 834 days


688 days ago

I have a four inch jointer from the fifties. it came without a motor. The specifications call for a 1/3 HP, 1725RPM motor. I have a 3450RPM motor. How can I cut the RPMs down to the 1725? Friends have suggested putting a pulley on the motor that is twice the size of the one on the jointer…will this work?


12 replies so far

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Mainiac Matt

3834 posts in 927 days


#1 posted 688 days ago

To slow the motor down, put the small pully on the motor and the large pully on the jointer shaft…. then it will take two revolutions of the motor shaft to turn the jointer shaft once.

That said… the physical layout may preclude getting a large enough pully mounted on the jointer.

-- Pine is fine, but Oak's no joke!

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mtenterprises

815 posts in 1292 days


#2 posted 688 days ago

Is this an AMT jointer? If so I have the correct size pulleys and motor on mine and can give you the proper cutter head rpm. (after I go check it)
MIKE

-- See pictures on Flickr - http://www.flickr.com/photos/44216106@N07/ And visit my Facebook page - facebook.com/MTEnterprises

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MNgary

235 posts in 1016 days


#3 posted 688 days ago

When you find the correct pulley sizes called for in the original design, reduce circumference of the motor pulley to one-half the original spec. Note that it’s circumference, NOT DIAMETER.

-- I dream of the world where a duck can cross the road and no one asks why.

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mtenterprises

815 posts in 1292 days


#4 posted 687 days ago

Ok, on my AMT jointer with orignal pulleys and a 1/3 hp 1725 rpm motor, the motor pulley is 4” and the cutter head pulley is 2” which will make the cutter head run at half motor speed which is 862.5 rpm. I could use a 3450 rpm motor for another project. Want to trade?
MIKE

-- See pictures on Flickr - http://www.flickr.com/photos/44216106@N07/ And visit my Facebook page - facebook.com/MTEnterprises

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shampeon

1288 posts in 782 days


#5 posted 687 days ago

What you want to do is figure out the cuts per minute (CPM) for your cutter head, and get pulleys to match your motor. For example, my old King-Seeley Craftsman jointer specified 11,000 CPM, so I used a 4” pulley on my 1725 RPM motor, and a 2” pulley on the 3 blade cutter head.

Use the OWWM calculator here:
http://vintagemachinery.org/math/cpm.aspx

There’s no reason why you couldn’t use a motor with more horsepower (to a point), so if you wanted to find a 1725 RPM 1/2 or 3/4 HP motor you’d probably have less trouble face jointing.

-- ian | "You can't stop what's coming. It ain't all waiting on you. That's vanity."

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Loren

7235 posts in 2247 days


#6 posted 687 days ago

12-15000 cuts per minute is a good speed for jointing,
so if your cutterhead has 3 knives, you want about 5000 rpms
on the cutterhead.

Those specs are BS. You’ll get better jointer performance
running a 3450rpm motor. If the cutterhead pulley is 2”
then a 4” pulley on a 3450 motor gets the cutterhead
moving fast enough for clean jointing.

Just my opinion, understand. I’ve set up a lot of jointers
with motors over the years.

With a 1725 rpm motor you need a 7” or 8” pulley. I know
because I have such a big old motor in my yard I pulled off
a jointer and I cannot get the big pulley off the shaft. I
was going to throw the motor away (big old repulsion
motor) but desire to possess the pulley stayed my hand.

-- http://lawoodworking.com

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shampeon

1288 posts in 782 days


#7 posted 687 days ago

A 4” pulley on a 3450 RPM motor with a 2” pulley on a 3 blade cutterhead makes 20,700 CPM. That may be above the spec of the bearings.

A 2.5” pulley on the motor works out to a little over 12,000 CPM.

-- ian | "You can't stop what's coming. It ain't all waiting on you. That's vanity."

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JimmyJam

31 posts in 1078 days


#8 posted 686 days ago

MNGary – If you reduce the diameter by half you automatically reduce the circumference by half as the circumference = Pi * Diameter.

View mtenterprises's profile

mtenterprises

815 posts in 1292 days


#9 posted 686 days ago

If this is as I asked “is this an AMT Jointer?” No the bearings will not take that rpm because they are bronze bushings. Guys remember greatgates2340 has a four inch jointer from the fifties, this is a CHEAPY, I know I have one and 850 +/- rpm is about all it will take. Yes the more Cuts Per Inch you can make the better but not at the expense of the machine. This is like an under $50 machine it’s not a Dewalt from the same time period. In this case it is easier to go to the flea market and pick up the correct motor 1/3 hp 1725 rpm off from a furnace blower for $15 than to futs around trying to slow down a 3450 rpm motor. Man in my neighborhood you can find a blower out for the trash and the motor is usually good.
MIKE

-- See pictures on Flickr - http://www.flickr.com/photos/44216106@N07/ And visit my Facebook page - facebook.com/MTEnterprises

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MNgary

235 posts in 1016 days


#10 posted 685 days ago

Good point, JimmyJam.

-- I dream of the world where a duck can cross the road and no one asks why.

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shampeon

1288 posts in 782 days


#11 posted 685 days ago

If it has bronze bearings, you definitely don’t want to go over spec on the CPM. But I don’t think the OP has stated what model his/her jointer is, and I think by the ‘50s most jointers were using ball bearings.

-- ian | "You can't stop what's coming. It ain't all waiting on you. That's vanity."

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mtenterprises

815 posts in 1292 days


#12 posted 685 days ago

Personally guys I think we’re just debating amonst ourselves greatgates2340 hasn’t chimed in since this was written.
MIKE

-- See pictures on Flickr - http://www.flickr.com/photos/44216106@N07/ And visit my Facebook page - facebook.com/MTEnterprises

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