automatic lathe video

I have started discussions in the past about some production turning and while I haven't done any yet, this came across my youtube feed so I thought I'd share it. The lathe here at 1:55 or so looks like the finish knives have the profile cut into the face of the knife so it looks like an extrusion, if that is right, I wonder how they do that..

Amazing Modern Wood Lathe Machinery in action - Fastest CNC Technology Woodworking Machine - YouTube

Some other cool machines as well, I never got to tool up to cut a handrail (6:30) on the 5 axis at my old job but would have liked to.

Those finish knifes are doing a classic skiving cut. A form tool, presented tangentially. By angling the flat rake face (which we can't see from the camera angle), you can reduce the effective width of the cutter using a kind of shear cut action. Part of the profiles (usually the deepest points) cut first. By the time the rest of the knife comes in contact, the first parts are already done cutting and have moved past the point of tangency with the work. Cutters of the length shown should last forever (well, 50 to 100 years of production use, anyway) by light regrinding on the flat rake face which we can't see from the camera angle.

As to how they grind the profiles on the knives, it's probably a CNC process these days, but back in the days of yore you would dress (partial) profiles on your grinding wheels with a Diaform or similar template-following form dressing tool, then grind a section of the knife.

sfriedberg said:

As to how they grind the profiles on the knives, it's probably a CNC process these days, but back in the days of yore you would dress (partial) profiles on your grinding wheels with a Diaform or similar template-following form dressing tool, then grind a section of the knife.

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There was a custom molding place near me a while back and I knew one of the kids who worked there. He did the knives by hand. Yes, the blades were not radial in the cutter heads so there was a lot of hand-eye judgement and some trial and error. They guys who were good at it got that job, the rest could lift and carry boards all day

I can easily believe eyeballing a shaper/molder knife for wooden molding. The profile is only as deep as the business edge of the cutter blank is thick, call it 1/4", and usually only 1-2" wide (although some are certainly much longer). The profiles on the finishing knives in the linked video are clearly at least 6-8" deep and 4-6" wide. Nobody is doing those knives completely by hand, although I could imagine someone eyeballing the cross- and down-feeds on a surface grinder and working to a template. But hand-holding them on a bench grinder? Not plausible.

sfriedberg said:

I can easily believe eyeballing a shaper/molder knife for wooden molding. The profile is only as deep as the business edge of the cutter blank is thick, call it 1/4", and usually only 1-2" wide ...

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These were hi-dolla duplicates for really old moldings, from back when people would chop down a forest to decorate the bedroom. Way wider and deeper than you describe but you are probably right, not as big as the skiving tools for turning.

Kinda peripheral but years later I was told that real connoizeeyurs can spot the difference between the real thing and these phonies instantly. The real things were done with planes, so there's none of the chop-chop-chop marks that a molder makes ? Somebody had to be damn good with a plane to do that !

That's pretty cool - like an old backknife lathe, but with segmented, sequential back knife, and not cutting on a skew. Bet the knives are way cheaper than a full length back knife, too!

There was a custom molding place near me a while back and I knew one of the kids who worked there. He did the knives by hand.

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I make all my own cutterheads and have ground almost all my large moulding knives by hand on a pedestal grinder. (hundreds, at this point) I grind some multiwing moulding cutters by machine for long runs. and have made lugback MTP knives in bars cut into segments, for long runs that are sharpened face only.

I would never try to grind a back knife lathe knife by hand. I doubt it is in any way practical. (I've studied them, never made one.) As has been stated, diaform job; and that is one tedious process. Some real back knives can get into 5 figures.

smt

i've seen the video. Very cool! i thought they did woodworking manually. No wonder the result is very awesome. They cut the wood in high precision, very quick and look so easy.

Lots of interesting machines! Back in 1984, I attended the IWF in Louisville and they had a "automated" lathe set up making 20" chair spindles, using the back knife method, no pre cutting. They didn't have a perfect finish, but they sure could punch out a lot of them.