Pulley Help, ignorant about the process

[Scott Brandstetter]

I am interested in building a homemade 12 inch jointer and from my research, it appears that most jointers this size run at a speed of approximately 4400 RPM's with a 3-5 HP electric motor. I have found a 3HP harbor freight motor with an rpm of ~3700. I am wondering if there is a mathematical calculation to increase the speed to 4400 rpm's. I also wonder what I really lose if I keep it true at 3700 rpms......maybe it means i push the lumber through a bit slower. Anyone with knowledge on this subject and the time to respond, I thank in advance. And don't hesitate to tell me issues to look out for.

[Mark Kornell]

The math for converting RPMs via different pulley sizes is pretty straightforward. Google "pulley calculator". I picked one page (http://www.culvermotor.com/Engineering-Formulas/Pulley-and-RPM-Calculator.html), and it shows that a 3" pulley on the motor, paired with a 2 1/2" pulley on the cutterhead will get you pretty close.

You didn't mention the cutterhead, though. If it is of average size and 3 or 4 knives, that calculation is probably good. If the cutterhead is quite a bit larger or smaller than normal, or has more (or less) knives, you'll want to look at the speed at the tips of the knives and number of cuts per minute.

And if you are looking at a segmented head, talk to the manufacturer to get recommendations on speed and torque requirements. They will generally want more torque than a similar size straight knife head.

But yes, you can adjust your feed speed to control cut quality and/or torque deficiency.

[Andrew Hughes]

Last year I was facing some hickory on my jointer.A piece of the cathedral grain pop out from the middle of a 6/4 board.The empty spot n the board was about two inches long 1 1/2 wide 1/4 inch deep.It somehow made its way between the head and the table lips.My jointer weighs 1900# s.And it rang like a bell.
Save your time and money and buy a old jointer that you can tinker with.Theres a reason jointer are made of cast iron.

[David Kumm]

Many old jointers ran at 3600 rpm but usually had a 5" diameter head. 4500 would be more normal for a smaller head depending on how supported. i don't know how you are making the machine but be careful. Small heads have less mass but still need a good solid point of attachment to minimize vibration and to be safe. Chips can come off the stock and get between the head and table lips. Tables also need to stay true within a few thousands. Good luck and stay safe. I've owned about a dozen jointers from 6" to 24" and a home made one would be something I'd prefer my enemy to use first. Dave

[Gerry Grzadzinski]

If you're using a ~2" diameter cutterhead from a portable planer, they usually run at about 10,000 rpm.
Om my homemade jointer, I used a 3450 rpm motor, with a 5-1/2" power steering pulley, and on the cutterhead I used a 55mm (2-1/8") alternator pulley. This gives me somewhere around 8700 rpm. It works very well.
http://www.thecncwoodworker.com/jointer.html

[John TenEyck]

That's an impressive build, Gerry. Nearly every time I think about building a machine I realize I can buy a used one cheaper.

John

[Gerry Grzadzinski]

Good luck finding a 12" jointer with a Shelix head for less than the $750 I spent to build one. Not counting all the time I spent, of course.

[John TenEyck]

I'd have more than $750 in it after I first built the CNC router you used to make some of the parts with. Otherwise, I would have to pay a machine shop to mill them, and they don't work for free.

You built what looks like a great machine. It's an anomaly compared to most home built machines I see; it looks good and appears to work w/o problem.

Just curious: How many hours did it take to build it?

John

[Gerry Grzadzinski]

I really have no idea. About 3 months of weekends, maybe 5-10 hours per weekend. Plus quite a few 1 hour week nights for paint. Probably more than half the time was spent on paint and prep. For most of these machines, paint is just slapped on at the end. I put a lot more effort into the paint and prep.

Plus a lot of CAD design work before I started building, maybe 20-40 hours??

The two bearing blocks are the only parts that I couldn't do without the cnc. Everything else is pretty basic.

[Matt Day]

Gerry, that's a heck of a homemade jointer! I tend to agree with John though, your cnc changes things up a bit vs a normal hobby shop. And how'd you get all that material (plywood, pulleys, bearings, switch, paint), a spiral head, and a motor for $750? All that little stuff really adds up.

To the OP, I'd take Andrews advice and find an old jointer. I have a 12" Northfield I got for $600 that I'm going to restore. I don't see the point in a spiral head in a jointer unless you have a money tree. Everything goes though my planer, so that's where a spiral head will go first.

[Bob Vaughan]

Sometimes Harbor Freight (and many other sellers of import motors) will offer a motor with high horsepower ratings for what seems cheap. The 'gotcha' detail is "duty cycle" rating. Cheap motors intended for air compressors have a short duty cycle, that is, they run for a short amount of time then rest for three times that. The windings aren't made to take continuous duty. You'll need to get a motor rated for continuous duty.

[Gerry Grzadzinski]

Used Shelix head from Sawmill Creek member - $200
2HP motor from Ebay - $200
Bearings - $20
Aluminum blocks for bearing mounts - $20
2 - LVL's and 1 sheet 1/2" baltic birch - $150
stainless steel sheets - Ebay - $95


All the other wood used were scraps in my garage. I was fortunate to grab a lot of small baltic birch cutoffs from a big job at work a few years ago.

I may have actually spent closer to $800 when you add up all the misc. little things.

Here in the Detroit area, I see used 8" jointers (DJ20 or similar) selling in the $800+ range. I've never seen a 12" jointer for under $1500-$2000.

[John TenEyck]

They are around: http://nmi.craigslist.org/tls/5640429340.html


(http://nmi.craigslist.org/tls/5640429340.html)

[Matt Day]

They are around: http://nmi.craigslist.org/tls/5640429340.html


(http://nmi.craigslist.org/tls/5640429340.html)

But they go quick!

[John TenEyck]

Seems so. It was a Fay 12" cast iron monster and I think they wanted less than $1K. I see those old iron jointers for sale pretty regularly. There is almost always some rehab required with them, but you still get a great deal if you have the means to move it. All that mass gives a feel when using the machine that no modern machine can match.

John

[Alan Schaffter]

The one problem I see is that with a small diam. head the bearing blocks stick up above the level of the table. That is not a big deal but is does have an effect on some operations, like no rabbeting.

A general comment- if built accurately, I really don't see a need for adjustable tables for a surface planer, especially parallelogram style. It adds too much complexity which can also result in too much slop. I would have made it with a fixed outfeed table permanently set to TDC and an infeed set just a tad lower to take off just a smidge per pass. At the very most I would have had leveling screws just for alignment.

It is a good solution for face jointing wide panels. You really don't need cast iron tables either, as long as your tables are durable, relatively flat (and will stay that way), smooth, and have surfaces parallel to each other and the cutter. You'll only be using it to prep one face anyway and a planer for the other face.

I was looking for a 16" 3-toed Oliver, Northfield, Crescent, Moak, Yates, etc. years ago, but don't think my shop floor would hold it.

[Gerry Grzadzinski]

A general comment- if built accurately, I really don't see a need for adjustable tables for a surface planer, especially parallelogram style. It adds too much complexity which can also result in too much slop. I would have made it with a fixed outfeed table permanently set to TDC and an infeed set just a tad lower to take off just a smidge per pass. At the very most I would have had leveling screws just for alignment.

After having built this, I agree with you 100%.
The infeed table lifting mechanism adds a lot of complexity, and reduces the rigidity of the infeed table.
If I were building this again, it would definitely have both tables fixed. Fixed tables are also much easier to align and setup flat than the parallelogram, which needs to be shimmed to align it and flatten it if it's not perfectly flat.