cutting of profile for chair leg - Woodworking Talk - Woodworkers Forum
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post #1 of 8 Old 04-24-2019, 09:36 AM Thread Starter
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cutting of profile for chair leg

Hi there

I am new to this forum, hi there !!

I am currently designing and making a dining chair and I am stuck with the following problem.
the back leg and back support of the chair is one piece of wood (image attached, dimensions in mm). I have limited machinery in my workshop to process the profile I need.
Here is a list of my machines : Plunge router, Circular saw, jigsaw, electrical planar, belt sander, drill press.
I am looking to make 6 of these chairs so maybe a jig or cutting template to produce the components.
Any suggestions how to produce this profile will be helpful.
The timber will be either birch plywood or solid oak between 18mm and 22mm thick.
Also attached is the side profile components of the chair, half lap joints will be used.

Thanks in advance
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post #2 of 8 Old 04-24-2019, 10:36 AM
where's my table saw?
 
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Just starting in woodworking?

I will assume by your problem statement and your limited types of tools, that you have limited woodworking experience. This means that any advice you receive should emphasize safety over expediency.


The safest way to cut out that shape from a solid or glued up wood section is with your jigsaw. First, a "master" template can be used to draw the shape on the wood and locate it for maximum use of clear, knot free material.
Second, after the shapes are cutout to within 1/16" of your line. they can be sanded, or hand planed to the exact dimension OR if you are comfortable using the plunge router with a template or pattern bit, that would reduce the sanding time immensely. Bits like these:
https://www.amazon.com/s?k=template+...l_8be4qzu630_b


In this manner:



The pattern must be as smooth as possible since the resultant piece will be an exact duplicate. Use sticky tape sparingly to hold the pieces together while routing. and secure the workpiece to the bench top as well. This is important because you do NOT want anything to shift during the routing process!


The next issue I see is making the lap joints. A Japanese pull saw or a back saw will give you the control and fine cuts you need for accuracy. A sharp hand chisel and a small rabbet plane will be required to level out the bottoms of the laps. A word of Caution here. More folks have been severely cut using sharp hand tools than by power tools. I know this from my own experience! ..... power tools "0", ......hand tools "too many" to count or remember.

I would make the chairs one at a time, to make certain the design and the pieces all work together precisely. A whole batch of parts that are "wrong" won't make you a happy woodworker! Dry fitting each parts is the standard operating method to assure good fitting joints.

Clamping and gluing is the next step in the process. Strap clamps and squeeze clamps are handy when working with taper shapes and by yourself. A helper is recommended if you have one. Glue the pieces together in sub-assemblies rather than working your way around the chair from leg to leg. The sub assemblies would be the back and cross pieces, the front with the cross piece, and finally attach them together with the cross pieces.

Finishing would be the final step. I'll leave that for a later discussion.
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The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 04-24-2019 at 01:19 PM.
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post #3 of 8 Old 04-24-2019, 10:41 AM
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Quote:
Originally Posted by Christiaan View Post
Hi there

I am new to this forum, hi there !!

I am currently designing and making a dining chair and I am stuck with the following problem.
the back leg and back support of the chair is one piece of wood (image attached, dimensions in mm). I have limited machinery in my workshop to process the profile I need.
Here is a list of my machines : Plunge router, Circular saw, jigsaw, electrical planar, belt sander, drill press.
I am looking to make 6 of these chairs so maybe a jig or cutting template to produce the components.
Any suggestions how to produce this profile will be helpful.
The timber will be either birch plywood or solid oak between 18mm and 22mm thick.
Also attached is the side profile components of the chair, half lap joints will be used.

Thanks in advance
The design you show on the illustration won't work. By making a half lap joint you are literally cutting half of the leg away and it needs all the wood it can get. The joint would be better off doweling the rail to the legs. This would require the edges of the legs to be square with the face of it and with the tools you have would be difficult to say the least. The only way I see to do it would be to make a plywood pattern for the leg and rough cut the leg with your jig saw. Then finish it out by attaching the leg to the pattern and use your router in a router table and dress the edges. This would make the edges square with the face as though you had a jointer. Then to dowel the rails to the legs it's very hard to do without a doweling jig. When you drill into the end of a board it tends to follow the soft grain of the wood instead of going where you need it. The two dowels would have to be exactly in position with the holes on the legs or they won't go together right. A doweling jig would position the bit where you need it and prevent it from drifting into the softer grain.

With the tools you have it will be close to impossible to make the legs you are wanting to make. Not only does the legs have angles to deal with the face
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post #4 of 8 Old 04-24-2019, 11:04 AM
where's my table saw?
 
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Strength is important!

I don't know if I agree with Steve entirely, but a half-lap joint is very strong compared to a butt jointed/doweled joint. The half-lap need not be of equal depth on both pieces, one piece can be thinner than the other, in this case the stretcher. The most common chair failure comes from someone rocking back on the rear legs putting all the stress on the joint at the seat intersection. This is what Steve is concerned with ... I think?


If it were me, I'd stick with the lap joint, just change the thicknesses.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #5 of 8 Old 04-24-2019, 12:35 PM Thread Starter
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Thanks guys.

This helps allot.
The limitation of tools I have is purely because they are very expensive in South Africa. I grew up in my dad's workshop and also worked in a fabrication company as
product designer so I know my way around the tools.

I will make use of the jigsaw for rough cuts, that makes sense.
I will then get some master router templates cut and work round the template with the router.
I might invest in a router table top and mount my router.
I agree that the half lap joints is the more stronger joint especially if you take into consideration the forward backward rocking. The seating and backrest
that will be cut and bent sheetmetal will sort out the sideways movement.
And the tip to make one chair at a time also makes sense.

Thanks for the inputs and advise.

I will do a post project post.
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post #6 of 8 Old 04-24-2019, 02:46 PM
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Quote:
Originally Posted by woodnthings View Post
I don't know if I agree with Steve entirely, but a half-lap joint is very strong compared to a butt jointed/doweled joint. The half-lap need not be of equal depth on both pieces, one piece can be thinner than the other, in this case the stretcher. The most common chair failure comes from someone rocking back on the rear legs putting all the stress on the joint at the seat intersection. This is what Steve is concerned with ... I think?


If it were me, I'd stick with the lap joint, just change the thicknesses.
Yes that is what I'm concerned with. When you machine that much out of the leg it tends to weaken the leg where either the leg breaks off at the joint or the back breaks off. Even sometimes when a leg is mortised too big for a mortise and tenon joint it weakens the leg.
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post #7 of 8 Old 04-25-2019, 08:33 AM
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Rather than doweling similarly to the way a mortise/tenon would go, how about doweling through and across the lap?
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post #8 of 8 Old 04-25-2019, 01:12 PM
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To answer your question:

Make a guide for your circular saw:
http://sawdustmaking.com/SkillsawGui...llsawguide.htm

Use a piece of scrap plywood the same length as your guide and make two spacers the thickness of your material to go across ends of plywood base.

Draw cut lines on material, situate material under guide lining up first cut line, remove guide, fasten material to ply with two screws in waste area. Replace guide in position and clamp ends, make cut, then repeat for other cuts. You will have to finish inside cuts with a hand saw.
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