Correct Spelling of "Curtate Trochoids"

      Clearing up the confusion about these ubiquitous machining marks called curtate trochoids. That's why we call it the "Knowledge Base," folks. You can't learn this stuff at those other websites. August 15, 2007

Question
A veteran finish carpenter that I work with told me about chirtalk charquoids (imperfections on the surface of milled lumber due to the rotary cut of a planer/joiner). Not your typical planer marks left from vibrations of the machine or lumber, but marks that all finished lumber has unless it has a heliptical (?) cutter. Anybody heard of this? We are both curious about this. He learned of this in an apprenticeship. We have looked online and there seems to be no info of chirtalk charquids (who knows how to spell it, anyway)? I just want to know if this is an actual word or if somebody told my partner a bunch of hogwash years back and now he's unknowingly passing it on to me.

Forum Responses
(Solid Wood Machining Forum)
From contributor C:
I have sold a lot of planers in my life and heard a lot of comments on the work. This is a first for me.

Knife marks, heel marks, chatter marks, roll marks, bites, snipes, shavings marks. I hope someone knows the answer.



From contributor J:
I believe chirtalk charquoids is Klingon for "planer marks"!

I looked in my Webster's unabridged and could not find it under any spelling close to what you had. If it's not in there, it's not an English word, anyway.



From Dave Rankin, forum technical advisor:
I would have thought at first that he is thinking of normal knife marks. The appearance of the knife mark has changed from the use of square heads to the use of round heads. But even with the older design of tools, I would not have thought that there would be enough difference to have a different name.


From contributor D:
I think you are referring to a trochoid. This is perhaps best described as the path followed by a point on a circle as it rolls along a flat surface, or the path of a cutter relative to surface of a piece of timber being planed. Curtate refers to a small part of this shape, i.e. the cuttermark on the timber. Hence curtate trochoid. I now believe the cuttermarks would be more accurately called curtate cycloids, but was also taught at college that trochoids was the correct term.

Anyway, chirtalk charquids sounds much better to me.



From contributor E:
Anybody ever hear of the term "charking"? A finish tech said it's the factures that occur when a hard finish is applied over a softer finish. Sounded neat. It might be Latvian for a made up term to impress dumb Cabinetmaker.

I have to go sand some chirtalk charcoids from some maple pieces.



From the original questioner:
Contributor D, you're the man... Finally somebody knows something about whatever it was I was talking about. I was starting to think somebody was making up words and then telling me all about these mysterious curtate trochoids.

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