Recently I was talking to a fellow tech ed. teacher at school and he was telling me about a stool that he is making. He was saying that he was using some mortise and tenon joionts and that he makes the mortises almost 1/4 of an inch deeper than his tenon length. Now I make a lot of mortise and tenon joints and I have always left a 1/16 to 1/8 of an inch of extra room in their bottoms. After thinking about it, I didn’t see where the extra 1/8 of inch would hurt the joint. So I thought that I would post it here and see what you people thought.
Replies
I'm not sure I understand what wood movement is being anticipated by the extra depth (the tenon is not going to get longer; though I suppose that shrink and swell cycles of the mortise board might loosen things up in a chair or something)? But if extra depth is needed to account for some movement, I can't see how it could hurt at the bottom is an end grain to long meeting that isn't adding any real strength to the joint anyway (the strength comes fromt eh long grain to long grain faces).
In my opinion, the only reason to leave room at the bottom of the mortise is to have a place for the glue being pushed ahead of the tenon to end up so the joint doesn't 'hydraulic' before it seats. Less glue in the first place or a groove along the tenon to let the excess squeeze out is just as effective. Your extra depth works so unless the teacher can provide a compelling reason to change don't bother. Sometimes people do things without being able to say why, but if they are teaching woodworking and can't give a satisfactory reason why, then don't doubt your methods.
Mate, I think that amount of clearance is unnecessary.
I do all my mortises with a hollow square chisel machine and allow 2mm extra depth for excess glue and any unevenness on the mortice bottom, especially at the two ends, as you can get with this method.Anyway , there is nothing more irritating than to find that the tenon is just 1mm too long....
I do not believe issues of shrinkage come into the picture, and having unnecessary voids in narrow sections like stool legs which have lots of work to do is also unnecessary - unless one is trying for inbuilt redundancy for some reason.
Maybe he wanted the stools to weigh less.
When I was young we used to drill holes in the piston rods (and every thing else) in our MG's to make them lighter. As hard as we drove them, the strength didn't seem to matter because we usually ended up pounding the rod bearings flat before we broke the rods! Ah, the good old days. I'm glad I lived through them.
Hal
http://www.rivercitywoodworks.com
Hal, Can you finance me to re-locate in Oregon? I have been looking at your fine work there on your web site- and the situation here is that even the finest of woodworking such as yours is just not called for in this part of the planet....Have a look at my web site http://www.collectablefurniture.co.nz.
I have resorted to banging together the odd dovetailed plane or two in an effort to stave off starvation here-see http://www.marcouplanes.com.
Now, to more serious things: we can't hold a partiality to MG's against you, but if you had concentrated on MK11 Jaguars, E types and Lotus MkI Cortinas as last resort your younger days would have been more fulfilling....And you could have driven those hard-an impossible thing to do with them MG's with mild engines.
Seems like no body is going to insist that there must be extra depth to mortises to allow for dimensinal change due to climate.....Knots is just not like it used to be.(;)Philip Marcou
Edited 10/14/2006 1:31 am by philip
After looking and lurking in this thread for a while philip, I'll state categorically that the mortice needs to be a bit deeper than the tenon is long. There are three main reasons.
1. I rarely see anyone cut a perfectly flat bottomed mortise anyway, except maybe with a router cutter. You may as well go a bit deeper then-- some 2- 4 mm works well. I don't see much point going purposely deeper than that for any mortise, but I can't see how there'd generally be much harm going deeper either.
2. The gap between the end of the tenon and the bottom of the mortice provides a place for excess glue to go.
3. If the tenon end hits the bottom of the mortise during assembly, or at any time after assembly for whatever reason, when the morticed member shrinks, the shoulders of the tenoned members will be forced away from the mating face of the morticed member, i.e., there'll be a gap.
I think all these have been covered in this thread already. I guess I'm simply reiterating what seems PBO to me. (PBO- pretty bloody obvious).
It was your remark about the Lotus Cortina that got me interested in posting. My first car was a Mk 1 Ford Cortina 1500cc. With a bit of tweaking to the suspension, extra welded on bits at the top shock mounts, fiddling with the gearbox, back axle, two engines (I kept blowing the blasted things up) I got that beast a great deal hotter than a Lotus Cortina. My right foot at the time knew only two positions, and both of those were on the floor, which probably explains the need for two engines, ha, ha.
My Cortina looked ultra Plain Jane on the outside with the standard DeLuxe trim or whatever it was, except for the wide wheels, bank of spotlights, and big bore exhaust. The inverted snob in me enjoyed blowing off all sorts of nominally hotter cars at the lights. Slainte.
Richard Jones Furniture
Edited 10/14/2006 10:34 am by SgianDubh
Hey Philip,
Actually I took a look at your web site a couple of nights ago. I was very impressed with your work. I would love to have one of your planes. I'm the kind of guy that would have it on display in my shop, but use it as often as possible.
I did buy a Jag once. A 1968 roadster. But I cancelled the deal just before I paid for it a couple of days later. I had too many cars in the driveway already. I still regret it! We didn't really have a Lotus contingent here. Other than the Europa. And Ford Cortinas were not sold here either.
The first MGA that I had was a 1962 MKII. If you know anything about them, they are a higher compression, sort of a special edition car. Mine had been an SCCA race car, built for that specific purpose at the end of the 1962 race season. It saw two races. The next year they changed the racing rules and mine was so overbuilt for the new rule that the owner bought an MGB to race, put a muffler, a windscreen, and the original interior back in the MGA and sold it to me. I hate to admit it but I drove it as fast as it would go, all the time. It was incredibly fun! It was incredibly fast.
Then I discovered Mini Coopers. The real Mini Coopers.
You would love Oregon, Philip. There are many very good woodworkers here, but we aren't making any money either so you would feel right at home.
Hal
http://www.rivercitywoodworks.com
Can you finance me to re-locate in Oregon?
Hey, Philip. Maybe enough of us here in Oregon can get a "Move Philip" fund together!
Many makers of fine furniture and tools are here. When I was doing commissions, I seemed to keep finding people willing to pay--or they kept finding me. It was getting harder, though. At least in this area. I was beginning to rely on former commissioners having more furniture made and less new clients. But their houses were going to get full at some point.
But the clients are out there.
Take care, Mike
Oh, the topic. When I had and used a chisel mortiser, I adjusted it so the waste at the bottom was at depth for the tenon length. Then I did use a swan neck to clean the bottoms, which typically gave an 1/8" or so. Banging them out by hand they end up somewhere deeper than the tenon is long, but as I don't measure after I get a good fit, I have no true idea how much room is there. I suspect it's about the same, a nominal 1/8". Mike
Yah Mike, can you pass the hat around? All I require is a place where folk actually put FURNITURE in their houses-not stuff imported from VietNam/ Soloman Islands on a sniff....The making of money would then be a relatively minor problem.
Yes, the topic, it is PBO as Richard says, but I had forgotten the use of that useful word -"nominal"- very useful when talking wood matters (;)Philip Marcou
Hah, I'll get the hat a moving...
It's a lot the same here as regards the furniture. I had to bang out some "ordinary" things between the larger commissions. But in a lot of ways, I liked making some of the "lesser" commissions better. Maybe it was I liked a lot of the people for those commissions better.
So I made dressers, night tables, medicine cabinets, beds and the like from common NA woods between the English Bog Oak cabinets, the Bubinga or Cocobolo drinks cabinets. The buffets vs. the credenzas [similar pieces, different prices...].
Now? Saws for others to make the furniture. Sort of ironic in a way. And I still get calls for commissions. For some of the past good customers, I would. I have three projects going. Two for my wife, one for a client. It's a slow go but I am enjoying it.
Well, back to endless paperwork!
Take care, Mike
This forum post is now archived. Commenting has been disabled