stool making and assembly - part 3

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stool making and assembly - part 3

Postby gavin » Tue Jan 08, 2013 6:23 pm

continued from part 2
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Hold the leg firm in a sash clamp and drill your mortices. I count 20 turns or use a depth stop.
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My guide to drill vertically is ply fixed to a piece of softwood. A carpenter's square is ok provided it is heavy enough.
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components ready for assembly
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I have not illustrated here the fine tuning of the tenon size to the mortice. In summary, I whittle the vertical sides of the tenon to between 14 mm and 14.5 mm. I prefer to have the growth rings horizontal. Going with the Grain from Mike Abbott covers this more fully than I have done here. I turn the tenon green and let it shrink oval..
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driving the first rung - I prefer the lump hammer for stools, others like sash cramps
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Drill next mortice 10 mm lower than the first tenon. This creates interlocking tenons. Here I use 2 carpenter's squares as sighting guides.
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and now go to part 4
Last edited by gavin on Tue Jan 08, 2013 7:52 pm, edited 2 times in total.
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Re: stool making and assembly - part 3

Postby mstibs » Tue Jan 08, 2013 6:31 pm

Whoa! Great series! Thanx for all the work!
Saxons. Were good wood-turners, they had to be because they were poor potters...from "A Short History of Woodturning with the Pole-lathe" by Brian G. Howarth; My bilingual (de/en) Blog: http://mstibs.wordpress.com
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Re: stool making and assembly - part 3

Postby Donald Todd » Fri Jan 11, 2013 1:39 pm

gavin wrote:I have not illustrated here the fine tuning of the tenon size to the mortice. In summary, I whittle the vertical sides of the tenon to between 14 mm and 14.5 mm. I prefer to have the growth rings horizontal.…… I turn the tenon green and let it shrink oval..

It makes more sense to shave/whittle the tenon green, then use a tenon cutter for the final sizing.
What are the sizes of the final tenon and mortise? I have used a (turned dry) tenon which is an "exact" fit in the green mortise. As the tenon goes in it absorbs moisture from the mortise, so this needs to be done quickly and is a one way trip. Also, you have not mentioned barbing the tenons.
I can't believe you are belting the posts with a lump hammer without any cushioning!
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Re: stool making and assembly - part 3

Postby gavin » Fri Jan 11, 2013 2:34 pm

Donald Todd wrote:It makes more sense to shave/whittle the tenon green, then use a tenon cutter for the final sizing.

Welll, the tenon cutter works a little easier in green wood than dry. The tenon will shrink oval if you cut it when green. IMO the greatest benefit of cutting when green is the oval shrinkage after drying indicates where to whittle flats on the tenon - I whittle them on the long sides. I understand you don't have Mike Abbott's Going with the Grain but the technique I use is laid out there. Occasionally I have forgotten to cut the tenon when green, and have had to cut a dry tenon. It makes for a slightly harder job and gives you a little extra wood to whittle off.
Donald Todd wrote:
What are the sizes of the final tenon and mortise? [/u]!

14 mm mortice, tenon is between 14.5 and 14 mm across the growth rings i.e. horizontal or tangential to the growth of the wood. I don't measure the radial i.e. vertical dimension of the tenon; it comes out of the tenon cutter green at 5/8 inch i.e. 15.8 mm. It will shrink a little after that.

Donald Todd wrote: Also, you have not mentioned barbing the tenons.

No, I have not found that necessary.
Donald Todd wrote:I can't believe you are belting the posts with a lump hammer without any cushioning!

It is surprising, isn't it! But it works gloriously well.
It carries my body weight!
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Re: stool making and assembly - part 3

Postby Donald Todd » Sat Jan 12, 2013 12:06 pm

I haven't read "Going with the Grain" so I don't have Mike's latest techniques and philosophy. I found that in "Living Wood" he seemed to be departing from some of his earlier philosophy. This departure seemed to be driven by the needs of the courses he runs, rather than the aim of making a good product. In particular I am concerned with the crushing of the wood when driving an oversized tenon into a green mortise. Obviously, Mike has more experience than I, but it is the long term strength that is the issue. You are taking the damage to the wood fibres further and it must mar the outer surface of the posts. Do you not have problems with the tenon you are striking mushrooming when you put the first rails in?

Another point is the the posts can split if the tenon is too fat. This is even more likely if you do not drill a small (3mm) pilot hole with a twist drill, as the auger lead screw acts as a wedge. Remember, the wood splits more easily when green. I wrote an article on this for the gazette in 2008, but I don't think it was published.
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Re: stool making and assembly - part 3

Postby gavin » Sat Jan 12, 2013 12:20 pm

Donald Todd wrote:Do you not have problems with the tenon you are striking mushrooming when you put the first rails in?

No. It has not happened at all. I have made possibly 10 stools by this method - approx 48 tenons driven in.

I do understand you have reservations about the lump-hammer method. Why don't you try it yourself? I may well have missed some vital thing you could put me straight on.

If you chamfer the tenons at each end of the rung, the chances of mushrooming are reduced.

I'll shortly assemble a test tenon and mortice, then cross-cut it in section to examine for damage.
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Re: stool making and assembly - part 3

Postby gavin » Sat Jan 12, 2013 12:25 pm

Donald Todd wrote:... the posts can split if the tenon is too fat. This is even more likely if you do not drill a small (3mm) pilot hole with a twist drill, as the auger lead screw acts as a wedge.


I have not had this problem. I use an auger twist bit with a lead screw because it is easily located at the start and does not wander off and is easily used by human energy. Mike Abbott's Going with the Grain makes it clear he has no definitive answer on the best drill type to use. You can use an engineer's bit. This solves any lead screw problem. But even when the leg is too thin and if the drill goes too far and the auger twist bit's lead screw pops out the far side, the leg still holds up fine in use. You can use a hybrid of starting with auger and then switching to the engineer's bit but I find that distracting. The engineers bit works better in a powered drill than any of the hand drills I have.
Subsequent edit:
I only drill the mortice when the leg is part-dried e.g. 24 hours from wet-green and ideally near a source of gentle heat. It should be wetter than the tenon.
Last edited by gavin on Sat Jan 12, 2013 9:15 pm, edited 1 time in total.
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Re: stool making and assembly - part 3

Postby Donald Todd » Sat Jan 12, 2013 2:12 pm

Mike makes the comment of posts occasionally splitting in "Living Wood". In subsequent correspondence he said he had adopted my practice of drilling a shallow pilot hole. I am using old two spur bits which have a wider (lead screw) angle than the newer, metric bits, so the problem is worse for me. I did a series of test drills an found that over 50% had split the "post" before the spurs started to cut!

My stools and chairs made this way are of mostly turned parts and there is no way I am going to start whacking them with a lump hammer!

The damage I am referring to will not be visible after assembly, but may be more apparent after the joint has fully dried, which takes months.
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Re: stool making and assembly - part 3

Postby Donald Todd » Sun Jan 13, 2013 9:19 am

gavin wrote:I only drill the mortice when the leg is part-dried e.g. 24 hours from wet-green and ideally near a source of gentle heat. It should be wetter than the tenon.

I have a (turned Cherry) stool frame beside me which I made 3-1/ years ago using my methods, putting dry (1/2") tenons into fully green posts. It was a battle getting some tenons in (using sash cramp): two rungs stated to bend! The posts shrank 9-1/2% in the first 3 weeks and have now shrunk by 12%. It's rock solid, no splits, no damage.
Also this subject has been discussed previously here.
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Re: stool making and assembly - part 3

Postby TonyH » Mon May 27, 2013 7:59 pm

I am currently trying to make a stool from ash with a woven seagrass top. The lower rails are no problem, but the tenons of the top rails are quite close to the top of the leg, making splitting of the leg when driving the tenon home a problem. Do I need to leave the top of the leg a bit longer above the joint, and tolerate the discomfort of the top of the legs digging into the back of one's legs when sitting on it, or make the joint less tight, possibly resorting to titebond 3, or should I have selected a wood which does not spilt so easily ...?
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Re: stool making and assembly - part 3

Postby gavin » Tue May 28, 2013 9:12 am

TonyH wrote:I am currently trying to make a stool from ash with a woven seagrass top. The lower rails are no problem, but the tenons of the top rails are quite close to the top of the leg, making splitting of the leg when driving the tenon home a problem. Do I need to leave the top of the leg a bit longer above the joint, and tolerate the discomfort of the top of the legs digging into the back of one's legs when sitting on it, or make the joint less tight, possibly resorting to titebond 3, or should I have selected a wood which does not spilt so easily ...?

You should read Mike Abbott's Going with the Grain. He suggests leaving the top a bit longer when assembling and later cross-cutting the top once the stool is assembled.
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Re: stool making and assembly - part 3

Postby TonyH » Tue May 28, 2013 9:46 am

Ah yes, I had thought of that option too. It does mean I can't turn a nice rounded top to the leg though.

I have a fair amount of experience of sitting on the traditional Greek cafe chair, which has a woven seat. The top of the front legs of these is left rather prominent, and do indeed dig uncomfortably into the back of your legs, such that I often end up sitting skewed round on it for comfort, which is what I was trying to avoid.

Thanks Gavin, I probably should do some book work.
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Re: stool making and assembly - part 3

Postby gavin » Tue May 28, 2013 10:46 pm

TonyH wrote:Ah yes, I had thought of that option too. It does mean I can't turn a nice rounded top to the leg though.

I have a fair amount of experience of sitting on the traditional Greek cafe chair, which has a woven seat. The top of the front legs of these is left rather prominent, and do indeed dig uncomfortably into the back of your legs, such that I often end up sitting skewed round on it for comfort, which is what I was trying to avoid.

Thanks Gavin, I probably should do some book work.

I think you could turn all the way , but leave some sacrificial part you know you'll cut off later from the top.
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Re: stool making and assembly - part 3

Postby emjay » Wed May 29, 2013 8:32 pm

Turn your rounded top then put a jubilee clip around it to stop splitting. Once the joints have settled down you can remove the clip.
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Re: stool making and assembly - part 3

Postby TonyH » Thu May 30, 2013 11:10 am

Jubilee clip. What a great idea. Wish I'd thought of it.

Here's the stool finished, with one replacement leg :oops:

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