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Elementary question regarding glued on tenons?

B

Barry Larson

Joined
Jan 23, 2023
Messages
190
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307
Location
Calgary, AB
Hi.
I have an elementary question regarding glued on tenons. I've been doing some skill building after a long absence from turning anything; to that end I'm making some small bowls out of some 8/4 KD stock (Cherry). I start out with a faceplate screwed to the face of the bowl and turn the base. Then for the first couple I turned a recess and chucked the base up in a chuck to turn the inside. The first problem I encountered was a bark inclusion that was not visible which split out the recess - catastrophic bowl failure! I then went to a glued on tenon as there isn't really enough material to turn one. I rough cut the tenon out of some 3/8 ash stock - around 2 to 2-1/2 inch diameter. I glued the tenon on the blank by centering with the tail stock center and then using the tail stock to clamp it in place. I figured 3/8 thick should be fine for work this size. Once the glue wad dry I trued up the tenon and then chucked it up and turned the front. I then reversed the bowl again (in a set of jumbo jaws), turned the tenon off and finished off the base. This seems to be working well and I believe I prefer it to a recess - seems to be easier and gets good results.
My question is with regard to my tenon material. What do you use for tenon material for glued on tenons? I believe I read that Odie uses construction lumber that is free from defects, so there is one possibility. Mostly I'm interested in the size/thickness of material used.
Any and all advice is appreciated. Thank you.
Be safe and stay well.
Barry W. Larson
Calgary, Alberta, Canada eh!
 
Most any hardwood that is fairly straight grained. I had some out of sycamore that split straight across at the top of the tenon so I dont use soft hardwood like it or poplar. Straight grain Construction lumber can work, make sure it is dry so the tenon doesnt warp on you - most stuff in inventory wont be completely dry.

Dont turn the tenon off - break the glue joint with a large chisel and hammer, retrue the top as needed and use again.

Turn your tenon glue surface slightly concave (1/16” OD to center), and I make the ID of it a recess, leaving a 1/4-3/8” shoulder width for gluing. Make the bowl bottom slightly concave the same amount - ensures the OD has full contact.

A couple of gluing methods: kraft paper with wood glue on both sides, or thick CA one side, accelerator the other side.

Lyle Jamieson has a good utube video on glue joints/blocks.
 
Eh! .... that is my usual modus operandi. As I was about to comment I see Doug posted a response. I agree with him about the hardwood tenons and gluing advice. However, I usually use a thick waste block (1"- 3") and turn the tenon on that. I make the surface flat in case I have to make any adjustments to the curve of the bowl's bottom by turning into the waste block, and the chuck jaws aren't anywhere near the bowl form. The waste block can be used many times over.
 
Thanks Doug, Tom and Hughie. Doug, the only reason I turned the first few tenons off was they were only 3/8 inch thick so it was easier to turn them off than to find my supply of paper bags - now found, so the next batch of slightly thicker hard maple tenons are going to get the paper glue joint treatment. Tom, I see the value of a thicker tenon for some bowl shapes and will keep that in mind for future projects. Sounds like I'm basically on the right track. I spent some time today on lathe service had to quite down , now on to practice and experimentation!
Be safe and stay well.

Barry
 
Barry Larson said:
Thanks Doug, Tom and Hughie. Doug, the only reason I turned the first few tenons off was they were only 3/8 inch thick so it was easier to turn them off than to find my supply of paper bags - now found, so the next batch of slightly thicker hard maple tenons are going to get the paper glue joint treatment. Tom, I see the value of a thicker tenon for some bowl shapes and will keep that in mind for future projects. Sounds like I'm basically on the right track. I spent some time today on lathe service had to quite down , now on to practice and experimentation!
Be safe and stay well.

Barry
Click to expand...
Barry, I don't believe I've ever used a paper joint ... usually just CA glue. On reversing to turn the foot just use a parting tool to remove the waste block and then finish turn the foot as desired. In certain cases (depending on the size of the piece and the waste block) I use double-sided sided cloth tape.
 
Thanks Tom. The thin tenons I'm currently experimenting with are pretty easy to turn off. For my next experiment I'm trying some small plates. The material is thin (about 7/8 inch) so I used a paper joint since I needed material to screw the faceplate to and didn't want to risk excessive tearout when I remove the faceplate block - well I guess that's not really a tenon though. As an aside, I'm just using yellow PVA glue for this. I never thought to use CA glue even though I'm old enough to remember the construction worker hanging from his hard hat in the old Crazy Glue commercials!
Be safe and stay well.
Barry
 
I've found that paper joints sometimes lead to unintentional flying objects, so I don't usually do that-- it's a very good method when you're making half or quartered spindles for applied decorations. My shop seems to have an inexhaustible supply of hardwood scraps despite feeding them to the pizza oven on a regular basis, so I glue on a piece of maple, walnut, or cherry with titebond matching the grain direction then just turn it off when I reverse the piece to finish the bottom. Simple, cheap, and effective. I'm seldom in so much of a hurry that I'd need to use CA, the titebond is good after 20 minutes or so and I've never had a failure with it, unlike with CA.

I just use any size or shape piece of wood for the waste block then mount the blank between centers to turn a tenon to size and square it relative to the blank. No need for elaborate preparation of a glue block. As long as it's big enough you don't need to worry about centering it other than by eye.
 
My preference for glue blocks is to use hot melt glue. It holds quite strong (even the cheapo $9.99 dollar store glue gun , but then I can't turn much bigger than 10 or 11 inch diameter, so YMMV) and easy to remove without stains (just a dab of DNA on the hardened glue where it meets turning, of course DNA can stain some woods, I suppose....) so nothing to turn away or part off...

as for choice of glue block, pretty much any wood that is stable and not green or cracked will do the trick, just gotta turn a flat and as perfect a tenon as possible for your chuck jaws - though as you may find browsing the forums, there's many ways to mount glue bocks that don't rely on being flat...
 
Roger Wiegand said:
seldom in so much of a hurry that I'd need to use CA, the titebond is good after 20 minutes or so and I've never had a failure with it, unlike with CA.
Click to expand...
CA for glue blocks has 2 big advantages
1. It will bond to wet wood
2. A flat chisel breaks the glue so the glue block is reusable after turning off the glue ( tite bond is stronger than wood the wood will splinter withba flat chisel on the joint)

when Using CA it is important
to have two concave surfaces, puta thick bead of thick CA on one surface, accelerator on the other surface, give a twist when the meet. The twist spreads the bead out into a wide glue joint makining a good bond. Give the bowl a slight tap to be sure it’s glued on well.

a student once did not do the twist. The accelerator set up the glue in the round bead and just a tiny bit of the bead crown was in contact with the glue block. The bowl fell off before it was screwed onto the lathe well before the tap test.
 
Barry, If you're going to turn away the glue block and not reuse it, you can save yourself a little aggravation. Lining up a pre-made tenon is a hassle and hard to get just right, at least when you're just starting out. Instead, glue on a square block larger than the tenon you're going to make, then turn the tenon on the glue block as if it was always part of the piece.
 
Dean Center said:
Barry, If you're going to turn away the glue block and not reuse it, you can save yourself a little aggravation. Lining up a pre-made tenon is a hassle and hard to get just right, at least when you're just starting out. Instead, glue on a square block larger than the tenon you're going to make, then turn the tenon on the glue block as if it was always part of the piece.
Click to expand...
Thanks Dean. This is basically what I do. Fix a faceplate to what will be the top of the bowl, glue my tenon blank (sawn roughly round) to the base and then true up the tenon when I turn the base. I then put the trued tenon in a chuck (after sanding the outside) and turn and sand the inside. It seems to be working so I'll keep practicing.
Be safe and stay well.
Barry
 
hockenbery said:
CA for glue blocks has 2 big advantages
1. It will bond to wet wood
2. A flat chisel breaks the glue so the glue block is reusable after turning off the glue ( tite bond is stronger than wood the wood will splinter withba flat chisel on the joint)

when Using CA it is important
to have two concave surfaces, puta thick bead of thick CA on one surface, accelerator on the other surface, give a twist when the meet. The twist spreads the bead out into a wide glue joint makining a good bond. Give the bowl a slight tap to be sure it’s glued on well.

a student once did not do the twist. The accelerator set up the glue in the round bead and just a tiny bit of the bead crown was in contact with the glue block. The bowl fell off before it was screwed onto the lathe well before the tap test.
Click to expand...
Good points. I haven't had occasion to use a glue block on wet wood, but that would be a strong advantage. Having a seemingly infinite supply of glue blocks I've never even thought about re-using them-- it's either glue blocks or fodder for the pizza oven.
 
Barry Larson said:
I believe I read that Odie uses construction lumber that is free from defects, so there is one possibility.
Click to expand...

Yes, this is what I use......mostly 2x4 and 2x6 clear studs. They are cheap enough to use one time, and toss them out when the bowl is done. They do have occasional knots and defects, but are mostly usable. Any major defects are removed. Over the years, I've done this over 2,000 times and any failures have been the result of my own carelessness that caused severe catches....which I can count on only a few fingers of one hand!

Center screw faceplates are exclusively used for mounting waste block attached bowls to my lathe.

Bowls are parted away when the second turning is completely done, minus the foot. The bowl is then gripped by Oneway Jumbo Jaws when turning the foot.

I do not use waste blocks on wet wood. For wood that needs further seasoning, I always use a tenon, gripped by a chuck for the rough-out stage of this process.....The glue block is then attached after the seasoning process is completed, and the bowl is dry, and ready for the second turning session. Titebond works well for me.

One of the great advantages of using this old fashioned method of attaching turning wood, is the total lack of dangerous chuck jaws this close to your tools and hands. This doesn't mean you can get lax with safety, but it does mean your concentration level can be more focused on what you're doing.....rather than the obvious danger that exists while second turning with a chuck.

-----odie-----

IMG_1453.JPGIMG_1543.JPGIMG_1546.JPG
 
Last edited:
Thanks Odie, great advise on chucks. I am very mindful of the protruding jaws, but it would be very easy to have a lapse in attention - they will remove skin and knuckle parts very easily!
Be safe and stay well.
 Barry
 
Do not use plywood, even the cabinet grade stuff. The block will shear off! Did that one a couple of times. If I was to use the CA glue, I would not use the accelerator. Mostly because of positioning my waste block. This means that it would have to sit at least over night. The part that is in the middle of the waste block would still not be cured if you went at it straight away. Same with using Titebond. While it is 'supposed' to be secure after an hour or so, the way I turn, I would not trust it till it had sat over night. Poplar is relatively cheap, and strong enough for waste blocks, as is pine.

robo hippy
 
I use waste/glue blocks when creating basket illusion pieces. I glue the block to the turning blank using Titebond wood glue and a paper joint from a heavy-duty brown paper sack (or similar paper). The paper joint and wood glue only work on dry wood. I prefer it over CA or hot melt glue and I can get a clean separation using a chisel. Here is a picture of a glue block currently on my lathe. The glue block is 6" in diameter.

6E25C04F-67FC-4785-8A5C-A81ED3AB7EF8.jpeg
 
Bill, I notice that your glue block is end grain, while the lumber based blocks discussed above would be face grain.
Does anyone think there is a substantial security advantage for one over the other? How about the glue joint integrity?
 
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