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Warped lathe tenons

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Forum topic by doubleDD posted 07-09-2015 08:55 PM 953 views 1 time favorited 19 replies Add to Favorites Watch
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doubleDD

5213 posts in 1503 days


07-09-2015 08:55 PM

I have a question for you experienced turners out there. When roughing in a green bowl blank or whatever I always leave a good 10-15 percent of material on the blank before setting it aside to dry out. The problem that has occurred on occasion is when returning to finish the job, I find the tenon has warped also. Sometimes beyond being able to get it back on the chuck. Is there any solution to this?

Thanks
Dave

-- Dave, Downers Grove, Il. -------- When you run out of ideas, start building your dreams.


19 replies so far

View TheDane's profile

TheDane

4997 posts in 3123 days


#1 posted 07-09-2015 09:24 PM

Is there any solution to this?

Not really … it is a natural part of the process as the wood loses moisture.

Many turners retard this distortion a bit with a radiator hose-clamp tightened around the tenon. You may have to adjust it periodically, but it might help.

Make sure you leave a center mark on the tenon so you can remount the rough-turned bowl with a jam chuck and re-true the tenon.

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View LeeMills's profile

LeeMills

271 posts in 761 days


#2 posted 07-09-2015 09:49 PM

As above, make sure your leave the dimple of the tailstock from the original mount.

On the rough turn if you start between centers this has to be. If you start with a faceplate, woodworm screw, pin chuck or other mounting where you may remove the tailstock support to form the tenon or recess, bring the tailstock back up to make a dimple before flipping to hollow the interior.

Upon remount when dry use you chuck as a friction drive, it may scratch the interior but it doesn’t matter because it is rough anyway. Place the bowl over your chuck and bring back up the tailstock to the dimple you left. On slow speed re-true your tenon/recess. I usually turn about 1.5 inches out from the mount so that I do not have to work so close to the chuck jaws when reversed.

For a very deep bowl where the edge of the bowl hits the headstock, or for a very small bowl which is smaller than the diameter of the chuck you may need to turn a friction drive extension to hold in the chuck jaws in order for the bowl to clear but I have never needed to so this.

The re-trueing is a consideration for your initial recess/tenon size. For a recess I make it as small as possible so the jaws barley fit in; this allows it to be re-trued to the smallest diameter possible for the best hold.
For a tenon I typically go 3/8” larger than needed so that it can be re-trued when dry and still be large enough for a good fit in the jaws on remount. How much larger you go is your guess of how much the wood will warp during drying.

Addition, I always re-true the tenon/recess. Even if the jaws may fit you want the best possible hold for safety.
For re-truing you want the lightest cut possible since it is just held by friction.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

View BobWemm's profile

BobWemm

1803 posts in 1386 days


#3 posted 07-10-2015 02:07 AM

I usually make my tenon well oversize when turning green stock. That way it can be returned to size as described by LeeMills.
Take it steady though.

Bob.

-- Bob, Western Australia, The Sun came up this morning, what a great start to the day. Now it's up to me to make it even better. I've cut this piece of wood 4 times and it's still too damn short.

View Jim Jakosh's profile

Jim Jakosh

17118 posts in 2566 days


#4 posted 07-10-2015 02:39 AM

Dave, what you have to do is mount the bowl on a jam chuck and true up the tenon before proceeding to finish the bowl. You will have to do that to almost every one you let sit to dry. It is better that they warp than crack!!

Cheers, Jim

-- Jim Jakosh.....Practical Wood Products...........Learn something new every day!! Variety is the Spice of Life!!

View doubleDD's profile

doubleDD

5213 posts in 1503 days


#5 posted 07-10-2015 04:08 AM

Thanks Gerry. I will start off with a clamp. Just so happens I have some that will fit. Sounds like a good idea.
Lee Mills, Bob, Jim, Gerry, Thanks for the tips. I will use this on my next ready piece. I always tried to get it back in the chuck without re-truing. This make sense. I guess sometimes when the answer is right in front of you, you don’t see it.

-- Dave, Downers Grove, Il. -------- When you run out of ideas, start building your dreams.

View TheDane's profile

TheDane

4997 posts in 3123 days


#6 posted 07-10-2015 01:38 PM

doubleDD—As the wood dries, the tenon will shrink, so keep tightening the clamp until the piece is dry enough to re-turn.

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View doubleDD's profile

doubleDD

5213 posts in 1503 days


#7 posted 07-10-2015 01:40 PM

Thanks Dane, I will. Do you think it would help to seal the tenon portion to reduce shrinkage?

-- Dave, Downers Grove, Il. -------- When you run out of ideas, start building your dreams.

View TheDane's profile

TheDane

4997 posts in 3123 days


#8 posted 07-10-2015 01:43 PM

Do you think it would help to seal the tenon portion to reduce shrinkage?

It might, but I haven’t tried it, and you might not gain much of an advantage.

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View doubleDD's profile

doubleDD

5213 posts in 1503 days


#9 posted 07-10-2015 01:52 PM

Well, I roughed out two bowls yesterday, I’ll seal one and watch for the results.

-- Dave, Downers Grove, Il. -------- When you run out of ideas, start building your dreams.

View Nubsnstubs's profile

Nubsnstubs

826 posts in 1190 days


#10 posted 07-10-2015 02:52 PM

DD, I always turn my tenons to fit the largest size that my chuck will allow. When the piece dries, I usually remount it with the tenon in the chuck and true up the rim of the form unless it’s a natural edge* (see the dot below my signature. don’t ask). After the tenon is trued, I then use a jam, friction, plug, or rim chuck to mount the face onto, then true up the tenon and outside. I have a tool that allows me to do this without needing a live center to hold the form in place. After truing the outside, it’s remounted into the chuck to finish the inside.

When I’m ready to remove the tenon, I use the same jam, friction, plug, or rim chuck and my tool to hold the form centered.

About 95% of the wood I use is Mesquite. It doesn’t move very much, so sometimes I just remount it and do my turning to completion.

If you had Cole Jaws or Longworth Chuck, you could do the same as above without the tool that I use…....... Jerry (in Tucson)

  • (a natural requires the use of a plug chuck)

-- Jerry (in Tucson)

View LeeMills's profile

LeeMills

271 posts in 761 days


#11 posted 07-10-2015 06:03 PM



Well, I roughed out two bowls yesterday, I ll seal one and watch for the results.
- doubleDD

That may work for you. I seal the exterior of the tenons on mine as you still have end grain in the side of the tenon. I have had just the tenon split/crack. I don’t think sealing will prevent shrinkage, just cracking.

The hose clamp is a novel idea that may work. It probably depends on the wood because strong movement may also cause the flexible clamp to go oval just like the tenon.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

View Sasha's profile

Sasha

615 posts in 673 days


#12 posted 07-10-2015 06:53 PM

Dave, Good Evening. My opinion – the Nature gives surprises and idea. Leave all roughnesses and keep as is. I don’t see a photo. Perhaps, I didn’t understand something????

-- Ganchik Sasha

View DrDirt's profile

DrDirt

4167 posts in 3202 days


#13 posted 07-10-2015 06:55 PM

skip the tenon, and turn with a screwed on faceplate glued to the bowl with Hide Glue.

-- 'Political correctness is fascism pretending to be manners' ~George Carlin

View doubleDD's profile

doubleDD

5213 posts in 1503 days


#14 posted 07-10-2015 07:17 PM

Nubstubs, I’ll keep that in mind. Keeping the tenon as large as I can when possible will help.

Sasha, I’m just trying to remount the tenon to the chuck as easy as possible.

Dr Dirt,(cool name) I tried gluing a tenon on the wet wood but it failed once and never tried again.

Lee Mills. That makes a lot of sense. Same thing as I was thinking. We shall see.

-- Dave, Downers Grove, Il. -------- When you run out of ideas, start building your dreams.

View Grumpy's profile

Grumpy

21556 posts in 3311 days


#15 posted 07-11-2015 01:15 AM

Dave, there is a way that might work without a delay at all.
I did a blog some time ago on using a microwave oven to cure small bits of wood.
If you can’t find it let me know if you are interested.

-- Grumpy - "Always look on the bright side of life"- Monty Python

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