Protecting the tenon

[Dave Fritz]

Sometimes I want to use the tenon in the final product yet I need to hold it in a chuck to finish the top. I've found a rubber band that works ok, but it's too narrow to completely cover the tenon. If you too protect the tenon what do you use to keep everything protected and free from jaw marks yet running true?

 

[hockenbery]

I use the perfect circle grip with dovetail jaws - it does not mark the wood.
This requires a tenon diameter size that atcmatcheshes your Chuck jaws perfect circle so may not work for your application

My vicmarc #2 dovetail jaws have a perfect circle grip at 48 mm
I turn down to 50 mm and turn a groove 1mm deep.

this is a design for a Christmas ornament using glass that I’m workin on.
Two 48 mm grooves let me grip ti to work each face



I have also used this to hold spheres with a 48mm groove turned in them.

 

[Owen Lowe]

Rubber bands are too soft for my liking. I use a trick that machinists often use and that's placing a soft metal between the jaws and the workpiece. Aluminum works well for this, is readily available, inexpensive, and cuts easily with utility scissors. I have a roll of roof flashing that I trim off strips just a tad narrower than the width of the tenon. The strip is almost full circumference, but not quite, and is positioned with the strip's gap placed in any of the gaps between the chuck's jaws. This creates really smooth and perfect jaws. The key to using this effectively is that your tenon is in the sweet spot of the grip range of the jaws. Since the strip isn't destroyed in any way, save it for a future tenon that's roughly the same size.

 

[Dave Landers]

As Al said, if your design can be adapted to the perfect-circle size of a chuck, you're good to go.

The other choice is to get your chuck to match the design. That is, either make a jam chuck (probably unique for each piece). Or build a collet chuck (there've been a couple designs in the forum recently). Or create your own jaws - I think you can buy "blank" plastic jaws for some chucks (I believe I saw these for Vic chucks at Woodworkers Emporium).

In other circumstances, I've tried rubber bands, but usually I can't find a decent one. For one-off projects I might use electrical tape or rubber tubing (on pin jaws) or hot-glue the piece to a waste block.

 

[robo hippy]

There is a 2 part bowl turning video with Richard Raffen, and done for Fine Woodworking on You Tube. He uses a 'perfect fit' tenon for reverse turning. If the fit is close enough, it will leave almost no marks, or barely visible marks. Other than that, I used to use a nitrile glove when I was turning green wood, and that would prevent metal stains from the chuck jaws. I solved that problem with concentrated lemon juice which removes metal stains instantly if you get them fresh off the lathe. If you wait over night, it takes a bit longer.

robo hippy

 

[Tom Gall]

Sometimes I want to use the tenon in the final product yet I need to hold it in a chuck to finish the top. I've found a rubber band that works ok, but it's too narrow to completely cover the tenon. If you too protect the tenon what do you use to keep everything protected and free from jaw marks yet running true?

Not sure I understand. ".....hold it in a chuck to finish the top." I hope you don't mean for hollowing. Why can't you use a jam chuck, friction chuck, or vacuum chuck to clean up or redesign the tenon - after doing what you want to do to the top?

 

[Dave Fritz]

Thanks for the replies. Tom, I'm making lids for Oui yogurt containers. I got the idea from Sally Ault who posted some on another site. On this one I've used the dying technique I saw on Tim Yoder's site. The wood is soft maple. I stopped at Bennett's hardwood to get some curly hard maple but they didn't have any. The owner said to try soft maple as curl is more frequently found in it.

I turn it round and put a small tenon on one end, the reverse it in my chuck and make the final tenon which is the part that goes inside the jar. I then reverse that and hold that tenon to finsh the top. I don't want marks on the piece that goes inside the jar. (Note, Sally put an o ring around the tenon for a tight fit) Beyound my pay grade right now.

 

[Vicki Hayden]

How about cole jaws?

 

[hockenbery]

Thanks for the replies. Tom, I'm making lids for Oui yogurt containers. I got the idea from Sally Ault who posted some on another site. On this one I've used the dying technique I saw on Tim Yoder's site. The wood is soft maple. I stopped at Bennett's hardwood to get some curly hard maple but they didn't have any. The owner said to try soft maple as curl is more frequently found in it.

I turn it round and put a small tenon on one end, the reverse it in my chuck and make the final tenon which is the part that goes inside the jar. I then reverse that and hold that tenon to finsh the top. I don't want marks on the piece that goes inside the jar. (Note, Sally put an o ring around the tenon for a tight fit) Beyound my pay grade right now.

When I have a project where I want to hold a finished side my mind goes to double sided tape.
You might consider using double sided tape to hold the finished top while turning the tenon to fit in the jar.

here is what I would try
1. Turn a tenon larger than the finished tenon leave the mark from the tailstock center (cup center no point)
2. hold the lid in in Chuck finish turn the top
3. Put a turned block in your Chuck apply double sided tape
4. Put the tenon side over the tail center using the marks to center it and use the hand wheel to press the lid against the tape
5. Turn the tenon to fit the jar opening. Hollow the center of the tenon to remove the center Mark
Add a decorative bead or some texturing marks to the center.
6. Remove the lid from the tape. Residue from the tape comes off with naphtha ( use nitrile gloves).

if you are making several lids at a time you can problem turn 3 or 4 on the same tape before it looses its holding power

I use the double sided tape from woodcraft.
If you have not used double sided tape I used double sided tape in this demo to hold a disc.

View: https://www.youtube.com/watch?v=Ha9yiBEZvTQ

 

[Tom Gall]

Thanks for the replies. Tom, I'm making lids for Oui yogurt containers. I got the idea from Sally Ault who posted some on another site. On this one I've used the dying technique I saw on Tim Yoder's site. The wood is soft maple. I stopped at Bennett's hardwood to get some curly hard maple but they didn't have any. The owner said to try soft maple as curl is more frequently found in it.
View attachment 37417View attachment 37418
I turn it round and put a small tenon on one end, the reverse it in my chuck and make the final tenon which is the part that goes inside the jar. I then reverse that and hold that tenon to finsh the top. I don't want marks on the piece that goes inside the jar. (Note, Sally put an o ring around the tenon for a tight fit) Beyound my pay grade right now.

Got it. Can't tell the size but I assume it's about 2-3" Ø. A small vacuum chuck would be perfect for this application but I'll assume you don't have one. There are several options to try - depending on size and chucks or chuck jaws you have available - and, how many you plan on making.
1 - Use your method and make the tenon (for jar) and drill a shallow hole to expand your jaws into (depending on size) and finish turn the top surface. If you have smaller spigot type jaws(1"ø) drill a slightly deeper hole to expand into and finish turn the top. If desired you can turn a button to cover the hole.
If you plan to make a lot of these:
2 - Buy some flat jaws (if available for your chuck) and make custom wood plates sized to fit your piece. Grooves can be turned to fit many other projects as well.
3 - Make a custom wooden collet type chuck (expansion or contracting) with a drawbar. This is not worth the effort unless you plan to make several hundred or thousands of these things.

 

[Ron Solfest]

Just to add another option. If you have dovetail jaws instead of Oneway serated ones you could start with bottom towards tailstock friction driving to turn round and turn final bottom tenon on at same time. Use point of skew to create groove at the 90deg point where tenon meets flat of lid. This groove will be hidden by rubber o-ring you put there when completed (you could also create a second o-ring groove a little further down the tenon if you want a double o-ring seal). Then reverse and hold tenon in dovetail jaws which really just bite that groove holding flat against top of jaws; turn outside and top to desire. Lots of ways to skin a cat, that's what I think I'd do.