Howdy folks, I have quite a few pieces I haven't finished yet simply because I need to remove the tenon and/or get rid of chuck jaw marks. I've heard of people wetting the marks and using a heat gun to remove them, but wondering what your favorite methods might be to simply and quickly finish the bottom. Thank you!
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What is your favorite (and easiest) method for removing chuck jaw marks from a tenon?
- Thread starter Maggie Shapiro
- Start date
If the tenon is almost exactly the same size as the closed jaws, it is not an issue. Tomislav just did a video about that if you are familiar with him. Most of the time I use a recess anyway, except on spindles.
robo hippy
robo hippy
Most often I would turn the tenon off. If it is to be part of the foot, then it gets shaped and the marks would be turned away.
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I plan the finished bottom before I put the tenon on. I most often turn the tenon away
I use a bowl gouge
then a spindle gouge.
I rotate the bowl by hand to cut the last away leaving a ting nub to sand off
In the seed jars i have a tenon on both halves.
I use the wood in the top tenon for the finished opening which I turned in the top before hollowing. So I cut away the tenon to blend the opening to the form
I use the wood in the bottom tenon for the foot. I have already turned the bottom of the foot so I turn the edge of the foot into the form
This might give you ideas on using the wood indside actenno
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I support with the live center in the tailstock and turn away the tenon. What tiny bit I can't remove cleanly because of the support, I remove off the lathe with a chisel if needed, then smooth with a hand scraper. If unsure of the method there are probably plenty of turners near you who could show how.
But to answer your question about how to "simply and quickly" finish the bottom, I use another method you might try for a future piece. I've simply quit using tenons on bowls and bowl-like things made from dry wood. Since there is no tenon I never have to turn it away. Instead I use a recess in the bottom. The following is my basic procedure:
- Mount the blank by a flattened top, face off the bottom as needed. I hold the piece on the lathe with a screw chuck.
- Mark the foot diameter and make the wood inside the foot slightly concave so the piece will sit flat.
- Turn the entire outside of the piece from the foot to the rim.
- Form a recess in the bottom. For the recess I actually turn a narrow ring, the outer diameter a tiny bit bigger than the closed chuck jaws (say 2-1/16" for 50mm jaws), the inner diameter small enough the clear the inside of the closed jaws. For good wood the recess can be shallow, an 1/8" or less, and should have straight or nearly straight sides. Don't try to match the dovetail on the chuck jaws. (If the recess is a narrow ring wide enough for the closed jaw to fit, it leaves nub of wood inside the ring recess that can be shaped, decorated, or mostly removed - lots of options.)
- The bottom of the recess ring should be made perfectly flat or slanted down slightly towards the center to allow clean contact with the jaws when the piece is reversed later. I use a sharp parting tool as a gentle scraper and small negative rake scrapers for this.
- Smooth and sand everything, the outside form and inside the foot. (Hint: small negative rake scrapers are perfect for smoothing anything inside the foot. Large curved NRS are great to remove tool marks from the outside of the form.) Note: I remove the screw chuck from the lathe and mount it in a carving/finishing stand for smoothing/sanding by hand.
- Make sure the outer circumference and flat of the recess ring (the "outside corner") is clean with no debris.
- Apply finish to the entire bottom of the piece, inside and outside the foot. Let the finish dry/cure. (Note: the finish can be applied later, when the top is done but I prefer doing it this way. If finishing with a spray I might do things a bit differently.)
- When the bottom is done, remove the screw chuck from the wood, turn the piece around, and expand the chuck into the recess. (Apply pressure firmly by hand to the center to seat it nicely while expanding the chuck jaws.)
- Turn the inside and rim, smooth and apply finish.
The recess remains in the bottom and with a bit of detail I think it looks great. I watch people's expressions when they turn the piece over and see the bottom. They seem pleased. If they don't like it I'll give it to someone else. So far that hasn't happened.
The recess ring is also a a good place to write a signature (someone else's if you don't like the piece), species, date, etc. Since the diameter of the recess is almost identical to the jaws there will be no marks. If worried about the steel jaws making marks on the recess or flat of the ring, cover the jaws with scotch tape before mounting the piece in the chuck.
What the bottoms of some of my pieces look like:
This is the method I teach in my shop. I've done a number of demos on this method and I know a bunch of people have used it.
(I should write a document specifically on this someday with photos and everything. I did write a doc that includes this but it's not the focus.)
Sorry, I've posted some of these pictures before but couldn't find the thread.
JKJ
Wonderful description and some beautiful bottoms! One question—why make the recess walls straight and not dovetail since the jaws are dovetailed? Won’t there be less contact?
Thanks. That's my implementation of a Frank Penta idea.
Thank you for the kind comment.
The danger is making the dovetail angled too much so the sides of the jaws contact the top first, at the surface of the wood, where the wood is weakest. No such problem if the recess angle ls angled less, a bit straighter than the dovetail on the jaws. But it turns out vertical sides on the recess hold just as well since the angle of the dovetail concentrates all the forces right at the bottom, compressing the wood slightly there. Since the rim of the dovetail is tight against the bottom, the wood is very strong there and there is no chance the piece will come out off the lathe (unless the turner is REALLY good at violent catches!)
Here's a little sketch. The jaws are represented by the red lines.
(In addition to the angle, remember for the most holding power the diameter of the recess should be as close as possible to the outer diameter of the closed jaws in order to have the maximum contact all the way around. Most know that as the recess diameter increases from the minimum, the jaw contact length and holding power decreases. A vertical side on the recess can help a bit since the jaws don't have to be expanded as much!)
BTW, the piece pictured with the multi-axis base in my post was a nearly 20" diameter heavy sapele platter. The recess was less than 1/8" deep (and comprised only the inside of the three little curved triangular pieces - note the insides of the three make a circle). It held great for turning the top of the platter.
JKJ
Fascinating. I’ve never seen this recommendation or explanation. Would you recommend and say the same—straight sides—on a tenon?
Many of the Nova jaws I have don't have a dovetail on the inside but what some call a small "beak", the jaws are otherwise straight inside. I put straight sides on the tenon and rely on the beak to indent and bite into the wood of most species, wet or dry. If the wood is very hard like dry dogwood or persimmon, I think it's sometimes good to put a very slight groove at the base of the tenon to let the jaws bite in a bit. I don't think this is needed on green wood since it can be more compressible. But as mentioned, I rarely turn green wood.
If the inside of the jaws are dovetailed instead of "beaked" I might cut a "mild" dovetail on the tenon, again being careful not to make the angle too much or the same problem of crushing the wood at the end can happen.
The best holding is as with the recess with the diameter close to but a bit bigger than the closed jaws. However, if the tenon diameter is too big one advantage over the recess is the four jaws will the grab the wood with 8 sharp corners instead of with 4 too-small curves.
Another thing, which I think everyone knows, is to make the tenon short enough so the ends of the jaws bear on a flat turned at the base of the tenon and not long enough to bottom out inside the jaws.
But as mentioned, I rarely use tenons (except on spindles and end grain work). One big exception is roughed out (twice-turned) bowls. Since the wood warps and goes out of round as the rough bowl dries, so will the recess or the tenon. However a tenon is easier to make round on the lathe! Harder to make a dried, warped recess round when held between centers. I made a custom tool to make recesses when there is limited space, for example, with the tail stock in the way. This has helped a lot, lets me sneak past the bulky live center to clean up a recess or cut one on a new blank, with either straight or slightly dovetailed sides.
The caveat with all this is my experience in turning bowls, especially from green wood, is limited compared to many, some with very different opinions. But I've never had a bowl or platter come off the lathe. I was at a class once when a guy pried a bowl off his lathe multiple times. Fortunately, it was a small bowl and no one got hurt. (he had a problem with tool control)
JKJ