Jointed Moulders Explained

      Here's the rundown on what makes a jointed moulder different from a regular moulder, how it works, and what it's good for. October 4, 2007

Question
1) What is a jointed moulder and how does it differ from a non-jointed one?
2) What are the benefits of one over the other?
3) Would a jointed or a non-jointed moulder be more appropriate as a first machine?

Forum Responses
(Solid Wood Machining Forum)
From contributor A:
A jointed moulder has a built in apparatus on each spindle that allows you to joint the heads. Running a jointed head allows you to run faster than a regular (single knife finish) moulder. When you "joint" a head, all you are doing is lowering a chalky abrasive stone down onto the knives when they are spinning at full speed. When they contact the knives, it precisely grinds all the knives' diameter virtually exactly the same. You must be running hydro cutter heads as well for this to work. For every knife in the head that is jointed you can run an additional 32 ft per minute. There are usually a minimum of 3, and in some shops (not fun) may be 6-8 knives in the head.

A non-jointed moulder can usually only go about 30 feet per minute and produce a quality finish. A non-jointed moulder head usually has two knives. Although both knives help with chip removal (if they are closely ground), only one of the knives produces the finish. There are exceptions of course, but this is the general idea.

Basically the benefit of a jointed moulder is speed. 30 ft per minute compared to 180+ feet per minute. If you think you'll be doing serious production, 20,000 lineal feet of moulding per day, jointed may be the way to go. Realistically most companies have to build up to levels of that nature. The rest of your shop must be able to handle levels like that too. (Dust collector, storage space, ripsaw, etc.)

Also, running a moulder correctly can take a good bit of practice and skill. The faster you're running means the faster you can make a mistake. For example, 5" cherry crown at 180 feet a minute. A two minute mistake would cost over $750.00 in lumber alone.

Personally I'd only invest in a machine that I had a solid business plan for using in the next two years, max. These are actually some really big questions and I'm sure some other guys will help flesh out the topic properly.



From contributor T:
A jointed moulder has a stone or stones that keeps all the cutting edges (knives) on the jointed cutterhead at equal length so that all the blades are cutting. On a non-jointed machine only one blade is actually cutting regardless of how many are on the head. The advantage is higher feed rates with the same number of toolmarks per inch (same finish quality at higher speeds). Jointed machines usually have more powerful motors as well to support the higher feed rate. If you need to run faster than 30-40fpm with a straight knife head, then a jointed machine is a good choice. Every jointed machine I've seen was in large flooring and S4S mills, so if that's your business and you need the output, go for it. If you are doing flooring at those speeds, you may want to look at a true side-matcher, where the horizontal heads are directly across from each other instead of staggered, and all the heads are jointed, but then you're talking $500k+ for a new machine.


From contributor R:
Contributor A did a good job explaining the differences between the two. In my opinion, if you can't give the operator 5,000 lineal feet of the same product every day of the week, stick to a non-jointed moulder. Maybe look into a non-jointed machine with 12,000 rpm, and you could run 60 lf per minute. Jointed machines are for companies that are milling a lot of the same products, fast.

Remember, if you go with 3 knives (90 feet per minute), you increase your tooling cost by 1/3. Four knives (120 fpm) tooling cost doubles. Six knives (180 fpm) tooling cost triples, not to mention the set up time it takes to grind them all, cost of the tooling, time to make jointer stones for them all, set up time of the machine. You will make up some of that time in production of the product, but do you have big enough volumes to justify the cost? You can use a jointed machine as non-jointed, but why would you spend all that money for an option that you would not use daily?

In all my years as a tech, I rarely set up a high speed machine as the company's first moulder, except in new MDF plants where high volume is the name of the game. In my opinion, my first moulder would be non-jointed, somewhere in the range of 6000-12,000 rpm, and you can get 30lf per minute through 60 lf per minute based on the rpm's.



From contributor R:
One thing I forgot to mention is material handling. If your feed rates are over 90 feet per minute, you will also need to buy a feed table to keep up with your feed speeds. It is very difficult for an operator to keep the lumber fed correctly at speeds over 90 feet per minute. Just one more thing to think about.


From contributor R:
Here's a little information on how to figure your feed speeds and knife marks per inch. Industry standard is 13-16 knife marks per inch. Up to 20 kmpi is premium grade. The more knife marks per inch, the smoother the product.

Rpm x the number of knives finishing
(non jointed = 1 all the time as contributor A explained).
Times that # by 12 (12" in a foot)
Divide that # into the number you got from the rpm.

Example, non-jointed:
6000 rpm x 1 knife finishing = 6000
30 feet per minute x 12" per foot = 360
Divide 6000 rpm by 360" = 16.666 knife marks per inch.

Example, jointed:
6000 rpm x (let's say 4 knives in a cutterhead jointed) = 24,000
120 feet per minute x 12" in a foot = 1440"
Divide 24,000 by 1440" = 16.666 knife marks per inch.

I hope you can better see the same knives marks per inch but at a faster speed, because the knives are in the exact same cutting circle on the jointed machine. The hydro cutterheads are taking out the bore tolerance of the cutterhead when pumped up, and the jointer stones are creating a perfect cutting circle, allowing all 4 knives to cut.



From the original questioner:
Thank you all very much for your valuable input. Wouldn't accurate grinding of the knives of a non-jointed moulder, at least in theory, create a perfect circle where both knives would be cutting the same depth and thereby increasing feed rates? Does a 6 head non-jointed moulder have the same feed rate as a 4 head non-jointed moulder? All grinding being equal, do faster spinning heads such as the new HSK types from Weining produce better finish and/or higher feed rates?


From contributor T:
Unfortunately, no, it would be nearly impossible to get the edges all in the same circle, and even if you did, as soon as you started cutting, one blade would lose its cutting edge slightly less quickly and become the one cutting edge.


From contributor R:
Contributor T is correct in his statement. All cutterheads have a bore tolerance built in. I believe industry standard = .000 -.001" or 25 microns. Conventional or non-jointed cutterheads bore tolerance is +5 to +20 microns, almost .001". Hydro cutterheads even less than that. When you put the cutterhead on the shaft in a non-jointed moulder, the spindle shaft touches the inside bore at the top, leaving the slop at the bottom of the bore, creating 2 different cutting circles.

On a jointed machine, you must use a hydro cutterhead. When you pump up the hydro head with hydro grease gun, the bore tolerance is taken away by the inside of the cutterhead collapsing around the shaft, taking away any slop. Then in theory you still have different cutting circles until you run the jointing stone into the knives until you have a perfect cutting circle. High knives are knocked down to the lowest knife. Your product is not "in joint" until the product shows the right knife marks per inch based on feed speed and number of knives finishing.

The finish product is all relative to rpm's, feed rates, and knives finishing as explained above.



From contributor J:
Contributor R has a good point with the bore tolerance thing. I run non-jointed machines. When I set a head with the straight edge, one knife out of two rubs because of that. However, I'm a picky SOB and will loosen the nut and spin the head 1/4 turn until I feel both knives hitting. But even then, as explained above, only one is doing most of the work.

With proper tooling and good shop configuration you can run a lot of moulding non-jointed. I agree on a proper entry level+ machine.



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