I have a project detail that I’m sure some of you have encountered and experimented with. I am building a roof structure over a deck. The plans show an exposed 6×12 cedar beam and exposed 6×6 cedar posts. The beam bears on the posts with a concealed “T” shaped steel strap dropped down in a slot cut in the beam and the post to accept the strap. Then a through bolt is installed with the strap sandwiched in the beam/post.
I am trying to figure out the best way to slot the post top and the beam with minimal tolerances so that the metal is fairly snug in the slots.
The metal strap is 1/2″ thick and penetrates 12″ into the post and is 23″ wide in the beam. There are 12 locations where this detail occurs. Any thoughts would be appreciated.
Replies
I hate knifeplates.
If there is a way with the engineering/inspector, a traditional pegged mortise and tenon joint is way faster, plus it looks cool.
Without specialized timberframing tools, you really only have two options that I can see for the deep slot in the posts. You can either drill from the endgrain, which will suck, because your drill bit will deflect a lot, making for a sloppy fit by the time you finish.
Alternatively, how good are you with a chainsaw? I would use a chainsaw plunge mechanism...some people can freehand it. At the timberframe shop, they have Mafell slot mortisers that do exactly this.
Thanks Jesse,
I see a lot of massacred cedar in my future if I attempted the chainsaw method. I had the same thought and then let it go.
Andy
Andy, do you have a decent sized chainsaw? I bet a chainsaw plunge guide would be worth the cost, you could probably sell it when you are done.It clamps on to the end of the timber, and then the chainsaw "plunges" into the endgrain on a set of rails. Pretty slick. Scary at first, but you get used to it and realize that there is nowhere for the saw to kick to.I'll try and find a picture...hold on.
Jesse,
Yes, I do have a substantial chain saw. If I had a chain saw guide that I thought would be somewhat precise and safe, I would gladly invest in it. I haven't heard of one before. What type of tool retailer would carry it?
Andy,I have been looking for the tool, or at least a picture of it. If no one else produces it, I will call the shop on Monday morning to find out where they get them.It will solve all your problems, guaranteed.
Thanks a lot Jesse. I'll check back and see if you had any luck. I appreciate it.
By the way, I had another thought. There is a timber framer in my area. I wonder if he would be less expensive and maybe faster, if he has computer aided mortising machines that might be able to do this.
I' lay the parts down to do the fitting, chainsaw as referenced. I wouldn't be Overly concerned with slack in the mortises on the first one or two. after you have the slots cut, holes drilled and are satisfied with the setup, fill the slack with epoxy. save a whole lot of trying to get a perfect mortise. you'll get better w/ the chainsaw before you're done and most likely stronger joints than w/out the epoxy. Jim
Andy9
Since others aren't really interested in helping you (or don't know) the simplist, easiest way is to do it with a router and guide.. Your guide can be anything say a piece of plywood to a professional guide.. However with a round post you will have to adjust the guide to ensure it remains square IF you can clamp it very tightly.
Now the router bit should referance the guide but project out the required depth.. if the hinge is 1/4 inch thick that's how much you want to let it project.. (do this with power off and unplugged)
You will need a sharp chisel to clean out the corners unless the hinge is rounded..
frenchy,
they aren't talking about mortising hinge leaves, they are talking about slot mortising for steel connection plates on structural timbers
View Image
the plates are buried at the intersection of the timbers.
carpenter in transition
Timkline..
Normal tool is a chain morticer. but it could be a chisel morticer or done by hand..
I use a long ship auger bit in a Hole Hawg and drill a series of holes in the end grain. Usually 1/32 of a gap on each side is allowed so I would use a 9/16 bit for 1/2 inch connectors. I then trim the radius leftover by the ship auger bit flush with a sharp chisel. This is how I learned, at it has always been fast and precise.
Layout the post slots ,bore a hole at the end of the slot. Bore halfway from each side til the holes meet.Now set an 8 1/4" skil saw to full depth and saw til you meet the hole. Two sawcuts, each edge of the slot. Turn over and repeat. Finish last little bit with a sawzall.
Layout mortise on the beam,top and bottom. The top is routed out if the T is not deep.The bottom is done like the posts using a router first,boring the rest out and finish with sawzall.
Have you ever used the Porter Cable mortising machine? They can mortise 4 7/8" deep.I do not know if they make a smaller diameter cutter . If I recall the standard cutter was 13/16". They are expensive, $900.00 if I recall. If you haven't used one ,forget it as they have a fairly steep learning curve. If you have used one see if you can rent one. You can do the posts while they are standing. The beam would be a piece of cake. Ten minutes or so to do each column, probably 20 minutes for each beam.You may be able to rent one.
mike