Thread: Chair arm help

Steam bending or bend lamination are IMO your best options

I'm looking at the top of a cheap bookcase. It has a but joint between the side piece and top piece and then the top piece is rounded over at it's end to make it look like a curved corner. You could cut a mitre on the lower arm piece so it's a 60 d corner rather than a 90. Have the top arm piece sitting on top and round over. Or maybe a 30 d miter on each piece. Start with one piece of wood and the grain should look decent too. Would need splines internally for strength I imagine but someone with more experience might know.

Cutting some sort of mitre should mean you only need one block if you go that way.

Jarrah doesnt steam well and even if it did, you would have difficulty producing the same thing twice, let alone four times, which is what is required here. As you are intending to remake the arms, a block glue on the underside at the arm end would give sufficient thickness to shape in any manner you wish. The brace can be brought into the shaped end, or set behind the block.

Yep,steam bending is definitely out as 20mm thick and 55mm wide so no go on that one. And last time I looked I only had 2 arms, well unless I'm entangled with the minister of war and finance. Hahaha. Yep it's just a single chair thankfully. And in pic.2 at the top it shows the brown as the resulting shape but the black lines are the original wood pieces I will cut with 2 pieces added behind for strength. Then I will use a forstner bit to get the internal round and a compass to get the correct outside 20mm shape

i did a quick mock up of this with some 42x19 pine I had knocking around and it was successful, photo to follow. I have tried to break and it seems sufficiently solid enough to hold. So watch this space.

cheers all.

In the photo you can see the 3 pieces as described and I outlined the 3 pieces in pencil. I'd say a success.

IMG_4421.jpg

Edited out - better explanation and demonstration of my thought is above

Originally Posted by Fumbler

Yep,steam bending is definitely out as 20mm thick and 55mm wide so no go on that one. And last time I looked I only had 2 arms, well unless I'm entangled with the minister of war and finance. Hahaha. Yep it's just a single chair thankfully. And in pic.2 at the top it shows the brown as the resulting shape but the black lines are the original wood pieces I will cut with 2 pieces added behind for strength. Then I will use a forstner bit to get the internal round and a compass to get the correct outside 20mm shape

i did a quick mock up of this with some 42x19 pine I had knocking around and it was successful, photo to follow. I have tried to break and it seems sufficiently solid enough to hold. So watch this space.

cheers all.

Sorry about the four arms. Im just so used to doing chairs in pairs or more.

The picture looks like you cut mitres and added one block behind/inside the joint. Is there a second?

Originally Posted by Mnb

The picture looks like you cut mitres and added one block behind/inside the joint. Is there a second?

No, just the 1 block and yes each piece had 30deg cut, but unlike my test piece which is unbreakable, my Jarrah finished product 1 did break so I will need to put splines in.

Looking at the photos of the test pieces;
Where the brace meets the rest there is a short glueing surface which is all end grain glueing
&
Where the block meets the brace it’s pretty close to end grain as well.

With end-grain gluing I’d expect it to break, perhaps not now but at some point down the track.

Difficult one.

Maybe use a bandsaw to cut it so it’s a bridle joint. At least then you have very strong glueing surfaces, oriented correctly.

Splines will work too, but they will have to dominate the joint.

Cheers
Arron

Originally Posted by Arron

Looking at the photos of the test pieces;
Where the brace meets the rest there is a short glueing surface which is all end grain glueing
&
Where the block meets the brace it’s pretty close to end grain as well.

With end-grain gluing I’d expect it to break, perhaps not now but at some point down the track.

Difficult one.

Maybe use a bandsaw to cut it so it’s a bridle joint. At least then you have very strong glueing surfaces, oriented correctly.

Splines will work too, but they will have to dominate the joint.

Cheers
Arron

agreed, so I have come up with a few ideas, in the attached pic, the yellow lies show face contact, the green end/face contact, so I can either put a dovetail through the joint in contrasting pale timber, or with the same timber from the offcuts, I can put a centre spline and 2 outside splines both pictured on the right. arrows showing direction of grain. and the red shaded area the straight splines and the area covered. Something I should've thought about earlier. But recovery is part of creation I like best. Its a challenge, but one I'm prepared to take on.

Failing all the above, I can run a jarrah stained piece of Tassie oak Dowel through the drop, up into the top rest as a bracing piece, or something similar but may look ugly and detract from the clean lines. The blue lines denotes the general shape of the chair frame.

anyway I will post pre/during/post photos to sho progress, or heaven forbid, the receptacle that may receive the piece if it goes pear shaped, which doubt.

If you go with the spline idea, I think you only need one. One thick one. That will look neater then having three (I think) and will provide more then enough glueing surfaces, and the surfaces will be properly aligned for maximum hold.

I always tend to overengineer chair joints as well, but if you look at the average chair then it’s usually held together at critical points just by dowel or m&t joints, despite the enormous forces exerted by humans getting in and out, and those joints provide no more gluing surface or mechanical hold then your single spline would.

So the technique I would use (which I expect you have already thought of, but here goes). Cut the rest and brace and the triangular joining block. Leave them oversize and glue together. Cut a spline from same material - nice solid one, maybe from 15mm stock. Make a cradle for passing the arm assembly over the tablesaw blade, pointed end down. Pass it over several times till youve cut a slot of the same width as the spline. Glue the spline in with copious amounts of pva glue. When glue dry, machine away the oversize till you have the desired shape.

I’d use pva for the glueing. Reason being it will provide a tiny amount of flexibility and hence shock absorption. A glue like epoxy will glue rigid so when exposed to shock it will tend to either hold or crack - nothing in between. If the joint fails down the track, you can usually get a pva joint separated and cleaned up with a bit of heat and soaking, not nearly as easy as hide glue but doable. I have read that old time chair makers, because they knew they didn’t have a glue that would last forever, made their chairs to be slightly loose, so that every decade or so they could be pulled apart in a nondestructive way and reglued. Hide glue was ideal for that. Some of those chairs were made 500 years ago and are still with us. I sat in one once - it had a groove worn by the sitters swords. It was loose but had survived all that time in continual use. I suspect it had been reglued many times. Fascinating.

And yep, you’re right, the additional brace would uglify it. No MCM designer would ever have done that.

Cheers
Arron

Arron, I have done just that. But used tas oak splines as a bit of a feature. Unfortunately in my haste as I had made a jig for the arms to sit in I forgot to change the blade to a flat top rip blade and as such ended up with a slight ridge. But I fashioned a thin sanding board out of the spline I was going to use but I cut too deep, so not right. Anyway see pics.

IMG_4464.jpg IMG_4465.jpg IMG_4467.jpg IMG_4468.jpg

Looks like you are doing well. What did you cut deep?