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