Delta Midi Lathe - Tenon Procedure

custom300 · Post by **custom300** » Sun Mar 30, 2008 12:23 am

For the last two years I have used my Delta Midi Lathe to execute the "Kurt Tenon Procedure". Usually, when I take my time it has been tremendously successful... 5/16" mortise on the shank and the 5/16" delrin tenon fits great. Recently however, something has changed. The mortise is ending up a hair bigger than 5/16 creating an unworkably sloppy fit. I finally figured out that for some reason the tailstock and the headstock on the Delta are somewhat out of line. You can see the 5/16" forstner actually rise as it goes into the shank. In other words the point on the forstner finds the spinning center of the shank which does not align with the center on the tailstock. So the resulting mortise is slightly out-of-round. I don't know if the bearings are worn or if something has just gotten out of whack. Like I said it used to work fine.

First, has anyone else had this issue with the Delta? If so, any suggestions on how to correct.

Second, if the answer is to replace the Delta, how is the Jet equivilant, or is there a similarly priced lathe that is better than others.

Third option, maybe its time to invest in a small metal lathe and start cutting my tenons.

Just interested in your opinions and insights. Thanks in advance.

JHowell · Post by **JHowell** » Sun Mar 30, 2008 1:01 am

Try a twist drill instead of a Forstner. You can knock the edges of the point down and it'll drill a slightly smaller hole. Start with a center drill, of course.

Tailstock alignment is always tricky with wood lathes. They rarely have any consistent alignment side to side, and when I used a Delta midi I always used a pencil to put a center mark on the spinning work and then aimed the drill right at that dot before locking it down. If the drill hits low, the ways or tailstock have worn. Not uncommon, especially if you use lots of sandpaper on the lathe, the grit gets in between the bed and the tailstock and wears away metal as you slide it back and forth. Look at the bed -- are there grooves where the tail stock has slid? take off the tailstock and look at the bottom -- are there grooves there?

If so, you might be able to build the tailstock bearing surfaces back up with Moglice, or epoxy on thin strips of Turcite, both proprietary preparations used to rebuild worn sliding surfaces on machines.

If not, and the misalignment isn't due to wear, check the barrel in the tailstock. It may have worn in its housing so that it droops a little. Which isn't the end of the world, if there's slop it will just pop up into the center hole. Changing to a center drill/twist drill should yield improvement, the Forstner isn't quite so accommodating in finding center. While a twist drill will seek center, the Forstner will try to drill where it started, whether that's actually the center or not. Also, check the drill chuck. The shank may have gotten bent -- if a drill hits low, try rotating the chuck 180 degrees, see if that changes things.

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Frank · Post by **Frank** » Sun Mar 30, 2008 2:14 pm

Jack,
Your post got me reading about Moglice, which lead me to a thread on Practical Machinist where a guy mentioned ball bearing gibs, which in turn got me looking at this site: http://www.turnomat.com/bearing.html
Are these frequently used? They seem like a great idea, but I'm guessing they're pretty expensive.

JHowell · Post by **JHowell** » Sun Mar 30, 2008 6:13 pm

Frank wrote:Jack,
Your post got me reading about Moglice, which lead me to a thread on Practical Machinist where a guy mentioned ball bearing gibs, which in turn got me looking at this site: http://www.turnomat.com/bearing.html
Are these frequently used? They seem like a great idea, but I'm guessing they're pretty expensive.

Sure, for linear motion assemblies. I guess, anyway, I've seen them in catalogs and whatnot, but I don't know of a regular lathe that uses them. I don't know if that was your question. They would need a really flat, smooth, hardened surface to roll on, and wouldn't last long with the chips and grit we produce. Moglice isn't cheap, either, and I don't know that a Delta Midi is really a good candidate for a tailstock rebuild. I'd hope for a wonky drill chuck. Hitting low doesn't mean it's unusable -- my 11" Logan is so clapped out that a drill in the tailstock hits visibly low, but the drill always pops up into center. I could shim it up between the base that slides on the ways and the top casting that adjusts east and west, but it doesn't seem to be hurting anything.

custom300 · Post by **custom300** » Sun Mar 30, 2008 6:33 pm

Try a twist drill instead of a Forstner. You can knock the edges of the point down and it'll drill a slightly smaller hole. Start with a center drill, of course.

That is a great suggestion. I'll give it a try. Not sure why I didn't think of that. I can shape the tenon to fit nice and tightly to the angle of the mortise made by the twist drill. If that works that will be a big relief...I have a deadline on 5 pipes and I don't want to have to learn a new process or break in a new lathe. Thanks again.

Jamie

kkendall · Post by **kkendall** » Sun Mar 30, 2008 10:39 pm

The point of a forsner bit should find center on a rotating rod. Then the point of a twist drill should center up on the dimple left by the forsner.

JHowell · Post by **JHowell** » Mon Mar 31, 2008 2:28 pm

I hope this doesn't sound argumentative, but Forstners really aren't meant to be use as center drills. The point is at the end of a long, relatively whippy shank, and even if the chisel point is perfectly concentric to the shank (not a great bet since the Forstner primarily uses the spurs at its circumference to maintain direction) it's not as good as a center drill. Center drills are pretty cheap, and the small point at the end of a short, stiff shank is very effective. At least when it comes to alignment and precision drilling, we pipemakers are better off copying machinists than woodworkers.

kkendall · Post by **kkendall** » Mon Mar 31, 2008 3:16 pm

Sorry - I wasn't clear I guess. I don't use small forsners. In my mind, I was using my 1.5" forsner to face off and square the rod, then a twist drill for the mortise which drops right into the dimple made by the forsner. But you're right, a centerdrill is short and ridgid and will find the center.

Tano · Post by **Tano** » Wed Apr 02, 2008 9:29 pm

I finally got rid of my Delta lathe, primarily because of centering problems. I replaced it with the recently introduced general wood lathe. It is awesome, centers beautifully and has a variable speed dial. You don't need to fiddle with the belt as often, to change the RPM'. For those of you that can handle the cost; I recommend it highly.
http://www.general.ca/pagemach/machines/25200a.html

custom300 · Post by **custom300** » Wed Apr 02, 2008 9:58 pm

I found this in case anybody is interested...its an article on lathe alignment.

http://jlrodgers.com/pdf/lathe_alignment.pdf