Forstner bit versus cutting tool for facing stems?

[maddis]

I'm in the middle of moving my drilling and stem work from my wood lathe to the metal. Typical M.O. for me has been to face with a forstner, delrin tenon, etc. I'm considering doing the same thing with the metal lathe. So the first question is: If you're going with delrin, any advantage to facing the stem with a lathe cutting tool versus a forstner?

If there is, what kind of HSS cutting tool would you suggest I learn to use for that?

And then there's the bigger follow-up question: If I'd like to turn an integrated tenon, what's your preferred approach to that? So far I've experimented with a right hand quasi-diamond shaped tool and made several passes along the length of the stem. This produces an accurate diameter tenon but the shoulder ends up beveled because of the shape of the tool on it's cutting edge. I've heard of backing the tool out after turning down the tenon, but I'm having a hard time imagining what a tool looks like that can cut vertically (toward the spindle), and then cross cut "back out" to create a face. Anyone got an image of one?

Sorry for the extended verbage. Once I got going, I figured I might as well try to explain the whole conundrum...

[oklahoma red]

That is one of the benefits of the metal lathe, being able to make accurate facing cuts. The reason for counter-sinking the end of the shank at the mortise is to provide clearance for the bevel on an integral-tenon stem.
High speed steel or cobalt is the material of choice for cutters. One can put a much sharper edge on these materials vs. carbide. You want the cutters sharp enough to shave with at all times.
Cutters with slightly rounded noses tend to leave a better finish. Said cutter will be at an angle with the stem axis. Move toward the spindle, stop then back the cutter out with the cross slide. No problemo.
Chas.

[wmolaw]

I'm in the middle of moving my drilling and stem work from my wood lathe to the metal. Typical M.O. for me has been to face with a forstner, delrin tenon, etc. I'm considering doing the same thing with the metal lathe. So the first question is: If you're going with delrin, any advantage to facing the stem with a lathe cutting tool versus a forstner?

If there is, what kind of HSS cutting tool would you suggest I learn to use for that?

And then there's the bigger follow-up question: If I'd like to turn an integrated tenon, what's your preferred approach to that? So far I've experimented with a right hand quasi-diamond shaped tool and made several passes along the length of the stem. This produces an accurate diameter tenon but the shoulder ends up beveled because of the shape of the tool on it's cutting edge. I've heard of backing the tool out after turning down the tenon, but I'm having a hard time imagining what a tool looks like that can cut vertically (toward the spindle), and then cross cut "back out" to create a face. Anyone got an image of one?

Sorry for the extended verbage. Once I got going, I figured I might as well try to explain the whole conundrum...

I too am totally confused in this area, which is part of the reason I've been avoiding my workshop. Well, that and the lack of time. But, seriously, I bought a taig to do stem work with and I haven't even cut my first stem!

I am such a deadbeat, but I just can't seem to get the knack of cutting the tenon!

[maddis]

That is one of the benefits of the metal lathe, being able to make accurate facing cuts. The reason for counter-sinking the end of the shank at the mortise is to provide clearance for the bevel on an integral-tenon stem.
High speed steel or cobalt is the material of choice for cutters. One can put a much sharper edge on these materials vs. carbide. You want the cutters sharp enough to shave with at all times.
Chas.

That makes sense. So it sounds like there's an inevitable bevel (ooh, great band name, huh?) at the junction of the tenon and face.

One other thought - my lathe came with a micro-carriage stop. If that thing works the way it should, wouldn't a series of equivalent passes to cut the tenon result in a perfectly faced stem?

[oklahoma red]

One other thought - my lathe came with a micro-carriage stop. If that thing works the way it should, wouldn't a series of equivalent passes to cut the tenon result in a perfectly faced stem?

In theory I would say yes. However, I would rather trust the squareness of the cross slide to the spindle axis and back the cutter out. Otherwise you are relying on the edge of the cutter to be absolutely perpendicular to the spindle/stem axis. Can you guarantee that to be set accurately every time? And again this all ties back to using a cutter with a rounded nose for the smoothest cut.
Chas.

[maddis]

One other thought - my lathe came with a micro-carriage stop. If that thing works the way it should, wouldn't a series of equivalent passes to cut the tenon result in a perfectly faced stem?

In theory I would say yes. However, I would rather trust the squareness of the cross slide to the spindle axis and back the cutter out. Otherwise you are relying on the edge of the cutter to be absolutely perpendicular to the spindle/stem axis. Can you guarantee that to be set accurately every time? And again this all ties back to using a cutter with a rounded nose for the smoothest cut.
Chas.

So are you saying that you use a rounded nose cutter both to turn down the tenon, and face the stem? I guess I'm not understanding both the type of tool needed, and the way it's used. I've seen Kurt's video, for example, and it's clear what he's doing turning the diameter of the tenon. But it does not show how an accurate facing is achieved.

[oklahoma red]

For integral tenons, and using a cutter that has a slightly rounded nose you can do three operations without changing the orientation of the cutter in the holder: face off the end of the rod stock to make it smooth and square, turn the o.d. of the tenon and by backing the cutter out create a square shoulder, leaving a fillet at the base of the tenon.
This all works as long as the included angle of the cutter is less than 90 degrees. Lock the cutter into its holder and then loosen the tool post and turn the cutter and lock it down at 45 degrees to the spindle axis. You will now have clearance on both faces of the cutter in respect to the spindle axis (for turning the tenon o.d.) and perpendicular to the spindle axis (for creating a square shoulder). Make sense? Let the lathe movements do the work rather than the cutter's geometry.
This works for me. Like all things there are usually more ways to get from point A to point B.
Chas.

[caskwith]

From a machinist point of view the method that Chas mentions (turn towards spindle then back out with the cross slide) is correct.

It's not often I make absolute statements as usually there are many ways to do something, but in this case there is really only one "right" way.

[the rev]

do either of you have a video of facing both the stem and the shank?

rev

[maddis]

This forum is an incredible resource. Hands down. Thank you.

I got thinking about my ignorance, and decided to focus on what I know how to do on a wood lathe. So I ground the other end of one of the tools that came with my metal lathe into a sort of skew with a roughly 45 degree bevel on the bottom and a much steeper one on the top. I also shaped it into a bit of a profile from right to left, and tried to create some downward rake from the top left cutting edge to the top right. Then I tried it with the idea of multiple passes and backing it out. The darn thing worked.

Now, my question is how to do it better. Here's a picture of the tool and the finish it produced. I'm guessing this can be improved greatly. Next steps??

http://s191.beta.photobucket.com/user/s ... 9.jpg.html

[oklahoma red]

I looked at the pic of the cutter you made and you're starting to get the idea. However, you'll note when the tool is backed out to create the shoulder the sharp point of the cutter is doing the cutting rather than a rounded edge. I cannot tell for sure due to the angle of the picture but it appears you got a better finish on the tenon than what you got on the shoulder. Take that cutter and round off that sharp point and you should have better results.

This is a top view of the cutter I've described to you earlier. It's sort of like a thread cutter with the tip rounded:



It would seem you are trying to avoid that fillet at the base of the tenon like the plague. Don't sweat it. It adds a bit of strength. If it REALLY bothers you then switch to Delrin tenons.

I went thru the rest of the photos on the link you posted. Nice lathe, nice pipes and very nice guitars! It appears that at some point you've replaced the Armstrong "lantern" tool post with a quick change as I can just see the corner of it in the first pic showing the tool you made. That's the only way to fly.
Chas.

[oklahoma red]

do either of you have a video of facing both the stem and the shank?

Sorry rev, I don't but perhaps Chris has one (or will make one). He's on a video high these days.
Chas.

[caskwith]

Yes it features on my stem drilling video, I face off a couple of stems before inserting delrin tenons. The same procedure is used on shanks as well. If you can't see it well enough then let me know and I'll shoot a close up.

[maddis]

I looked at the pic of the cutter you made and you're starting to get the idea. However, you'll note when the tool is backed out to create the shoulder the sharp point of the cutter is doing the cutting rather than a rounded edge. I cannot tell for sure due to the angle of the picture but it appears you got a better finish on the tenon than what you got on the shoulder. Take that cutter and round off that sharp point and you should have better results.

This is a top view of the cutter I've described to you earlier. It's sort of like a thread cutter with the tip rounded:



It would seem you are trying to avoid that fillet at the base of the tenon like the plague. Don't sweat it. It adds a bit of strength. If it REALLY bothers you then switch to Delrin tenons.

I went thru the rest of the photos on the link you posted. Nice lathe, nice pipes and very nice guitars! It appears that at some point you've replaced the Armstrong "lantern" tool post with a quick change as I can just see the corner of it in the first pic showing the tool you made. That's the only way to fly.
Chas.

Thanks Chas. You discovered my weakness for stringed instruments.... They've been disappearing as the briar and tools have been appearing. But I suspect there's a balance in sight.

Also, you made a comment in another posting about the angle of the carriage in relation to the spindle determining the line of the cut, not the profile of the cutting tool. That was a very timely piece of information - thank you. I sort of discovered it empirically right after reading what you wrote, and it was nice combination head-knocking/light-bulb shining moment. Within an hour of that I was on the phone with a local blacksmith/machinist and she generously gave me some basics on what qualities a cutting tool has to have if it's going to be held rigidly in place, as opposed to being manipulated by your hands.

[oklahoma red]

High speed steel or cobalt cutter blanks are readily available from many industrial supply houses such as MSC. 3/8 square is a good size to work with. You apparently have a grinder already and know how to use it. Get a half dozen or so blanks and you can make any tool you need.
Chas.

[mrsmitty]

I looked at the pic of the cutter you made and you're starting to get the idea. However, you'll note when the tool is backed out to create the shoulder the sharp point of the cutter is doing the cutting rather than a rounded edge. I cannot tell for sure due to the angle of the picture but it appears you got a better finish on the tenon than what you got on the shoulder. Take that cutter and round off that sharp point and you should have better results.

This is a top view of the cutter I've described to you earlier. It's sort of like a thread cutter with the tip rounded:



It would seem you are trying to avoid that fillet at the base of the tenon like the plague. Don't sweat it. It adds a bit of strength. If it REALLY bothers you then switch to Delrin tenons.

I went thru the rest of the photos on the link you posted. Nice lathe, nice pipes and very nice guitars! It appears that at some point you've replaced the Armstrong "lantern" tool post with a quick change as I can just see the corner of it in the first pic showing the tool you made. That's the only way to fly.
Chas.

Thank god for this forum! Thanks for posting this. I've been having issues with getting a smooth surface when facing stem stock. I ground a blank bit down to look like the picture above and had great results.

-Josh