Getting tenon round for second turning

[Ron Warman]

I have cored out several blanks ( 24 ) with the McNaughton tool with a laser light attachment starting with a screw chuck on what will be the top, made a tenon on the bottom that the jaws will clamp into, removed the screw, mounted the wood in the chuck, cored out a blank, mounted the core back on the screw, made another tenon etc. This method works better if you go for the big blank always because of where the laser shows up on the wood. If it matters the wood is Boxelder, a type of maple.

My questions are. Now that the wood is dry and oval how do I true up the tenon to twice turn it? Will I have enough hold to just put the oval tenon in the chuck? It is a dovetail about 1/8" deep. I have tried my vacuum and longworth chuck and neither one works to keep the blank very true. This is my first go at using a "clamp into" tenon for this. I usually use a "clamp on" tenon which is easy to true up between centers.

Ron

 

[hockenbery]

Hi Ron,

I plan the greenwood turning to make remounting easier by making my green tenons a ½ inch larger in diameter so I’ll be able to true the tenon in the dried piece and get it to fit. I leave the mark from tailstock in the tenon and just re-use it for the center of the tenon.

for your bowls
If the grain is fairly balanced and the opening is toward the center of the tree.
Mark the two High spots on rim (endgrain) and the two low spots (sidegrain) on the rim.
Find the center of the tenon (endgrain to endgrain and Side grain to side grain.
Put a small hole here with a scratch awl.

Open the chuck jaws a bit and put the opening over the jaws and bring the tail stock center into the hole. I used to put a block of wood in the chuck but Al Stirt convinced me is was better not to. if the bowl seem to rock a bit open or close the jaws a bit until it seats better.
Line up the two high points so that they are equal distant from the head stock. I loosen the tail stock an pivot the bowl on the tail stock center. Then line up the low spots on the rim in the same fashion.

Tighten the tailstock. The bowl is now in the best possible alignment.

I then turn the rim flat. This is the area that will be most out of balance.
and the bowl vibrates much less after the rim is even.
Then I true the tenon and turn the face of the bottom that will eventual rest on the table top. Then I turn from bottom to rim to true the curve. The idea is that there will be one line on the bowl that has no wood removed. These all need to be finish type cuts as the surface left may be the finished surface. I shear scrape and Sand the outside.

Mount in the chuck, turn the rim, turn out and sand the inside

Happy turning,
Al

 

[Joe Greiner]

"Clamp into" tenon seems contradictory. Do you actually mean a "socket" or "mortise?" That would seem compatible with use of the bowl saver to maximize yield from the large blank. Even with tailstock assist for centering, the Longworth would be iffy. Probably better to use the vacuum with an oval pad if internal, and tailstock assist for centering in the hole from the screw. Then remove the tailstock and proceed to cut the socket. I can't claim experience with this, though; I use clamp-on tenons myself.

Joe

 

[john lucas]

I don't have a bowl coring outfit but I start my bowls between centers, rough out the outside and the tenon, turn them around and hollow. then when it's dry I put a rubber pad over the chuck and place the bowl over this. I bring the tailstock up to the original hole that is still in the tenon. this centers it so I can true up the tenon and turn the outside of the bowl.
If you don't have a center mark in the tenon it would be pretty simple to measure from the long side of the oval tenon and then the short side of the oval tenon and mark these to find the center. Then put the tailstock center in this point and true up your tenon.

 

[n7bsn]

I don't have a bowl coring outfit but I start my bowls between centers, rough out the outside and the tenon, turn them around and hollow. then when it's dry I put a rubber pad over the chuck and place the bowl over this. I bring the tailstock up to the original hole that is still in the tenon. this centers it so I can true up the tenon and turn the outside of the bowl.
.....

I've done something similar to this, only I have a rounded chunk of wood that goes in the jaw, and for a pad I use a fine-sanding sponge pad (aka friction chuck)

 

[Ed_McDonnell]

I don't think he has a tenon. I think he is expansion chucking into a recess. What I got from the post is that heknows how to true up a tenon between centers, but is having some sort of problem with not being able to true up the recess.

The same techniques for truing up a tenon between centers should be applicable to truing up a recess between centers, so I'm a little puzzled. The only thing I can figure is that there isn't enough meat to allow it to be trued up without going through the side of the recess. If that's the case then I think expansion chucking was going to be an iffy proposition anyway without risking cracking the wood.

A picture of what he's got to work with would really help.

Ed

 

[MichaelMouse]

Conventional thinking has checked in. Let me suggest some unconventional thinking.

1) Leave a good center mark in the bottom of the bowl. Prop the bowl level on the drillpress table and re-true the sides of the tenon with a holesaw. Be sure to plan ahead and make that tenon oversize initially, because, as indicated it will lose diameter. One reason I don't use one.

2) Leave a good center mark on the bottom and on the inside. Gives you your centers to do anything you want to do. Extend your drive area with a mandrel to center on the inside, mount between centers, re-true the outside and press on. http://www.robin-wood.co.uk/turnframe.htm should key you to what I'm saying. You'll grab the mandrel with your chuck.

If you're using a recess and coring, #2 and a home ground dovetail scraper will do.

 

[Ron Warman]

As someone said I am using a recess not a tenon. My problem is I do not want to bring up the tailstock because there is no room for a tool then on the small bowls. I use the Batty long jaws and the large one does give me enough room to use the rebate tool Sorby sells to cut the rebate when threading the female threads. I would have to regrind it to make a dovetail and I am not sure I want to do this either.

I hoped someone else who uses the McNaughton system with a recess could give me an answer.

Ron

 

[Ed_McDonnell]

Ron - I've used a Sorby Multi-tip tool (with the small flat sided cutter that is included) to fix up dovetail recesses in tight quarters around the tailstock. I think they call it the RS2000KT now. If you have any other type of tool that will hold a small HSS bar cutter at an angle, you can grind a profile on the cutter that should allow you to do what you need. You will probably end up cutting at an angle that is highly unrecommended for hollowing (cutter close to 90 degrees to the handle), but with a light touch it works to round out a warped recess.

I use the Kelton (McNaughton) coring system and I've never found a reason to use a recess rather than a tenon. Maybe I'm missing out on something here, but I find that if there is room for a recess there is usually room for a slightly smaller tenon. I've had a few bad experience with expansion chucking into a recess where I cracked things when I got carried away tightening things up.

Good luck.

Ed

 

[MichaelMouse]

As Ed says, a narrow scraping tool will reach around and do the job well. Triangular will do both bottom and side of mortise when introduced carefully.

You could also do what I did once to see if it worked, and found it solved the problem, though I don't core, so it was curiosity only. Circular template on a tripod of adjustable legs made with jam-nutted bolts and a Colt trim router with collar. I made my template small, which made it difficult to hold and rout simultaneously. Were I to do it again, I'd have a longer piece of ply, reinforced with 1x2 "rails" which could be clamped in position outside the footprint of the bowl.

It would be nicer if you had a small plunge router, but the only ones of that type I have are 12 and 15 amp models. You'll want the 14 degree slope on the bit for the Nova chucks.

 

[Brian Hahn]

Truing up a recess

My questions are. Now that the wood is dry and oval how do I true up the tenon to twice turn it?

I usually rough turn bowls using a recess. I use a two-step process to reshape the recess for final turning.

1. True up the top face of the bowl. Usually I can grip the oval recess with a chuck. Often I need to use the next size smaller jaws at maximum open. Rotate the jaws until all four jaws are holding the wood, then tighten. This isn't a real secure grip so light cuts will be needed to flatten the front face of the bowl. Other methods that I've used include flattening the base with a sander, jointer, or power hand planer; gluing it to a waste block; holding that with a face plate or chuck; and then truing up the face. I've even resorted to truing up the face of the bowl on the jointer.

2. Attach the bowl rim to a face plate and form the recess. I use a large scrap of plywood or particle board mounted on a face plate and glue the rim of the bowl to it with hot-melt glue. Scribing circles on the face plate board helps in centering the bowl. It's also a good idea to cut a shallow groove across the piece of wood so you can get a screw driver under the lip of the bowl to pry it off when you are done. The hot-melt glue is usually adequate to hold the bowl for both reforming the recess and final turning the outside of the bowl almost all the way to the rim. For large pieces, I will improve the grip by running a bead of hot-melt around the joint and/or use strapping tape for extra support.

 

[Bill Pottorf]

Kel McNaughton Coring System

Ron, Ed McDonnell is very correct here. It is wise to only use dovetailed tenons on the back of the outside bowl with a diameter about 1/3 that of the largest diameter of the blank. Using a recessed area with expanding dovetails can crack the wood on expansion, making the operation extremely hazardous. Several people including some from the McNaughton web site have written good articles which you should get and read. There have also been some threads in this forum as well. I have been using the McNaughton system for a long time and this is just word for the wise.

Go ahead with the one at hand but then switch away from recessed dovetail areas for expansion jaws. Not a good idea at all. Happy turning and be careful.

Bill

 

[rsser]

I don't bother to true a tenon or recess inside a roughed bowl. Though if its soft wood I'll check how the jaws line up with the grain and if they compress it significantly then I'll check to see if repositioning them reduces run-out.

As noted, recesses need care. I used to use them all the time but would ensure the dovetail angles matched and go in deeper than an eighth on large bowls.

 

[Jim Silva]

I may be missing something here so all apologies if I'm overlooking something, but...

If the issue is how to turn the oval recess round again why not use a donut chuck? They're fairly easy to make, cheap and simple to align if you have some scribed circles in place to use as a guide.

Jim

 

[Joe Greiner]

I may be missing something here so all apologies if I'm overlooking something, but...

If the issue is how to turn the oval recess round again why not use a donut chuck? They're fairly easy to make, cheap and simple to align if you have some scribed circles in place to use as a guide.

Jim

The outer element of a donut chuck would normally have a circular opening. The rough-turned blank may have varying amounts of eccentricity, may be offset from the original center at the horizon of the outer donut, and the rim is probably not planar. The outer donut will have only two purchase points on the long axis of the oval in any case. I still vote for tailstock assist. A hook tool (made from a surplus Allen key) can reach into the region for the new socket past the live center, and a long-enough stub spindle can press the bottom center against the tailstock (called a jam chuck by some folks). It may need a few trial mountings to reduce or equalize wobble of the rim. After the new socket has been prepared, regular turning can proceed. Unless the bowl explodes from too much expansion pressure.

Joe