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PostPosted: Wed Aug 26, 2009 7:36 pm 
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RadDavis wrote:
Mike,

It's much easier to cut the tenon to fit the mortise rather than relying on a measurement. Just leave the stem in the lathe chuck and push the stummel onto it. If it won't go, cut a couple more thousandths off and try it again until you get a nice snug fit that you like.

When using this method, there's no measuring involved at all.

Rad


I see what you are saying, and that seems like a good way to do it, normally, but what I've been doing is turning molded stems with a fitting I made in a 3-jaw that is fitted tightly in the rectangular slot to center and drive the tip and I have a live center on the tailpiece in the hole in the tenon end. So it's not as easy to test the fit without disturbing the setup. So, that's why I measure and why I have been trying to developed a knowledge of the exact size tenon which will work in a certain size mortise.

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PostPosted: Wed Aug 26, 2009 9:27 pm 
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Mike Messer wrote:
I see what you are saying, and that seems like a good way to do it, normally, but what I've been doing is turning molded stems with a fitting I made in a 3-jaw that is fitted tightly in the rectangular slot to center and drive the tip and I have a live center on the tailpiece in the hole in the tenon end. So it's not as easy to test the fit without disturbing the setup. So, that's why I measure and why I have been trying to developed a knowledge of the exact size tenon which will work in a certain size mortise.

I use a similar setup for premoldeds. I use calipers to check how close I am to diameter, but IMO it's still easier and quicker to just slide the tailstock, with live centre, back and check the fit.

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PostPosted: Wed Aug 26, 2009 11:19 pm 
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Mike Messer wrote:

I see what you are saying, and that seems like a good way to do it, normally, but what I've been doing is turning molded stems with a fitting I made in a 3-jaw that is fitted tightly in the rectangular slot to center and drive the tip and I have a live center on the tailpiece in the hole in the tenon end. So it's not as easy to test the fit without disturbing the setup. So, that's why I measure and why I have been trying to developed a knowledge of the exact size tenon which will work in a certain size mortise.


I would suggest that you get a 4 jaw scroll chuck. It makes life much easier.

Then you can just chuck up the stem and turn a tenon in about 2 minutes without the need for an elaborate setup.

Rad


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PostPosted: Wed Aug 26, 2009 11:58 pm 
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I mount stems or roughly stem-shaped pieces on the lathe by cutting a slot in a piece of plywood and mounting it on the faceplate of the lathe. Put a piece of tape on one side of the slot, and on one side of the stem (just so you can get an exact repeat of the whole position when you remount), then you can pop the stem on and off the lathe in 2 seconds and remount with no fuss at all. It's really easy to get a solid friction fit in the slot with a bit of masking tape wrapped on the stem, if it is loose at all.

To center the slot on the plywood, I mount the wood and mark the position on the faceplate, then cut concentric rings on the wood to find center. It's dead easy.

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PostPosted: Thu Aug 27, 2009 8:11 am 
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Having performed a lot of Rube Goldberg type stuff when I was beginning, I can assure that there is no simpler and more repeatable method of cutting a tenon than using a 4-jaw chuck on a lathe (not counting a collet chuck). Wether you cut the tenon on a wood lathe or a metal lathe is a matter speed and repeatability, but a using a 4-jaw chuck will save you tons of time and allow you a hell of a lot more flexibility.

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PostPosted: Thu Aug 27, 2009 11:12 am 
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Kurt, I haven't used a lathe but plan to get one in several months' time. Is a 3-jaw thing sufficient for tenon turning on my ABS rods which are manufactured in cylinder form (20mm in diametre) rather than rectangle?

And another question, again, is the wood/metal lathe agony. Since delrin is not available in China, I will have to turn tenons. How do you advance the cutting tool on a wood lathe? Move your tool edge along the length of the tenon like a metal lathe does? Or hold the tool perpendicular to the rod with an edge that is as broad as the tenon is long, so that no longitudinal travel is needed? If it is the former, how do you make sure your tool moves on a straigh track, avoiding a slightly cone shaped tenon?

I know this is pretty hard to express in words, particularly to someone who has never actually used a lathe. But I would really appreciate your advice since that would probably save a life or a limb. Eh...by the way, you needn't reiterate your disclaimer this time, we don't have such a mature legal system in this country. :mrgreen:

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PostPosted: Thu Aug 27, 2009 11:24 am 
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m.c.-

I started turning tenons on a wood lathe as you are talking about doing. It can be tricky, because you have to have a really steady hand in order to make a nice straight and even tenon. Not impossible, but there is definitely a learning curve.

Another option would be to invest in a tenon turning tool. If you don't have the cash to buy a metal lathe and are worried about trying to turn tenons by hand with a wood lathe, a tenon turning tool is a good choice. PIMO sells a cheaper one that is functional, from what I understand, and JH Lowe sells a more precise one with a micro adjustment ring to make slight adjustments to the diameter. I have one from JH Lowe, and I use it with my lathe to cut tenons quickly and precisely.

I would prefer to cut tenons with a metal lathe, as that would be the most precise approach possible; however, until I have the money saved up to acquire a nice metal lathe, I am quite satisfied with my tenon turning tool.

Hope that is helpful info!

:)

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PostPosted: Thu Aug 27, 2009 12:00 pm 
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A 3-jaw is best for holding cylindrical work. The scroll 4-jaw (all jaws move equally together, self-centering) is useful for stem blanks that are not cylindrical, but have at least bilateral symmetry. If you have to hold something really oddball, the independent 4-jaw is used.

Jack


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PostPosted: Thu Aug 27, 2009 12:04 pm 
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m.c. wrote:
... I haven't used a lathe but plan to get one in several months' time. Is a 3-jaw thing sufficient for tenon turning on my ABS rods which are manufactured in cylinder form (20mm in diametre) rather than rectangle?
The short answer is, Yes,

m.c. wrote:
Since delrin is not available in China, I will have to turn tenons. How do you advance the cutting tool on a wood lathe? Move your tool edge along the length of the tenon like a metal lathe does? Or hold the tool perpendicular to the rod with an edge that is as broad as the tenon is long, so that no longitudinal travel is needed? If it is the former, how do you make sure your tool moves on a straigh track, avoiding a slightly cone shaped tenon?
Since, by your own admission, you've never used a lathe before, you will be throwing away a lot of tenons/stems before you get even one with a decent fit, if you try freehand tenon turning, i.e. on a wood lathe. As little as one thou (0.001") can make the difference between a good or a lousy fit. Since Delrin is not available to you, I would suggest getting a small diameter ABS rod for the tenons (approx. 3/8"), with matching sized drill bit for the mortise.

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PostPosted: Thu Aug 27, 2009 12:56 pm 
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m.c. wrote:
Kurt, I haven't used a lathe but plan to get one in several months' time. Is a 3-jaw thing sufficient for tenon turning on my ABS rods which are manufactured in cylinder form (20mm in diametre) rather than rectangle?


Ditto what Jack said. The three-jaw is best for stock that is cylindrical. The 4-jaw is, however, will give you freedom to hold square, oval, diamond, and other shapes of stock that are at least symmetrical. For a lot of premold stem blanks, a 4-jaw is very helpful.

Quote:
And another question, again, is the wood/metal lathe agony. Since delrin is not available in China, I will have to turn tenons. How do you advance the cutting tool on a wood lathe? Move your tool edge along the length of the tenon like a metal lathe does? Or hold the tool perpendicular to the rod with an edge that is as broad as the tenon is long, so that no longitudinal travel is needed? If it is the former, how do you make sure your tool moves on a straigh track, avoiding a slightly cone shaped tenon?


Practice. Practice. Practice.

I know that's not a very descriptive answer, but once you start trying to do it, you'll find a method that works for you. What I do when cutting a tenon on the wood lathe (actually rare these days):
- Using a 'scary sharp' 1/8" thick parting tool, establish the diameter of the end of the tenon
- test fit this and tweak as necessary
- cut the rest of the tenon, in 1/16" 'bites' back to the shoulder, taking care to maintain a diameter slightly larger than the established end of the tenon
- using a sharp (scary or beyond) 1/2" skew, fine tune the entire length of the tenon, using the established end as the guide
- test fit and tweak as needed
- you may find it helpful to take the tenon the last tiny bit needed with some fine sandpaper - not less than 400 or 600 grit (or 180 or 360 of silicon carbide abralon or equiv micromesh)

If your tools are 'scary sharp', the finish will be smooth and ready for some fine polishing with a rag and some compound. Something like EEE Ultra Shine is very helpful - it's essentially brown tripoli in a paste binder ideal for lathe polishing round parts (mostly marketed to pen turners).

Quote:
I know this is pretty hard to express in words, particularly to someone who has never actually used a lathe. But I would really appreciate your advice since that would probably save a life or a limb. Eh...by the way, you needn't reiterate your disclaimer this time, we don't have such a mature legal system in this country. :mrgreen:


Hopefully this helps. Just don't cut yourself on those scary sharp lathe tools! :D

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PostPosted: Fri Aug 28, 2009 12:01 am 
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Thank you all buddies, for such quick and detailed replies.

Simeon hit on the flexibility and trickiness of a wood lathe. That attracts me, your know, the best price-FUN ratio! Just that a tenon turning tool is not practicably available to me due to the prohibitive postage. The self drilled delrin suggested by Frank is an easy way to go. I suppose I will do that for my lathe honeymoon exercise. And, I got you Kurt, bit by bit cutting to be crowned by a final sanding. Nice that it SEEMS simpleI :wink: I had no idea what a skew is and did some pic-googling. Honestly, the edge turns me on! :twisted:

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PostPosted: Mon Aug 28, 2017 4:46 pm 
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RadDavis wrote:
Mike Messer wrote:
No problem, Kettletrigger. I did not measure the #U bit .3680 in. I measured the mortise with a simple caliper marked in 32nds of an inch, but magnified. I can estimate maybe to about 1/8 of 1/32, .0039, but usually only about 1/4 of 1/32, .0078.
I like to have a somewhat accurate target dimension when turning the tenon on a my metal lathe, which is marked in large 1000ths of an inch, so I can estimate easily to .00025 in., then I don't have to keep taking the tip off of the lathe to see if it fits the mortise, But that's just my method, for now. I do stop and measure it with calipers frequently.
I can't say for sure how accurate this is, but it seems to work okay, except when I forget I need to take another .025 in. off the diameter of the tenon and I crank .025 more on the lathe which is the radius measurement, and then I cut .050 in off the diameter, and the tenon is too small. Have to make a new one.


Mike,

It's much easier to cut the tenon to fit the mortise rather than relying on a measurement. Just leave the stem in the lathe chuck and push the stummel onto it. If it won't go, cut a couple more thousandths off and try it again until you get a nice snug fit that you like.

When using this method, there's no measuring involved at all.

Rad


“It's much easier to cut the tenon to fit the mortise rather than relying on a measurement.
Leave the stem in the lathe chuck and push the stummel onto it. If it won't go, cut a couple more thousandths off and try it again until you get a nice snug fit that you like.”

This seems to assume the stem is chucked rather than the stummel. Although I’ve just bought a JET 9x20 and am still figuring out my best procedure, I’m used to chucking the stummel [I guess from my wood late past?]. I’d push the tenon into the mortise while turning it on a Taig.

For Rad, I guess, the stem is still round [or square for that matter]? To do that I’d have to remove my official Lamb stummel Alignment Chuck, & use a 3-jaw [or 4-jaw] chuck to shape the tenon, right?

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PostPosted: Mon Aug 28, 2017 8:42 pm 
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Yes, I mean, all Rad was saying there is that you drill and shape, then fit the stem. Naturally the stummel is "free" at this point, and the stem material is in a lathe chuck, so you can just test fit as you go.

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