Bolted half-lap for bent frames

[TimothyB]

Hi folks,

I was noodling a question I had and I was wondering what the wisdom of The Forum might be on this topic.

Let's say someone wants to build a bent frame, but they can't find, or maybe afford, stock of the appropriate length to make up the whole frame length. They really don't want to do sawn frames for whatever reasons they have, be they structural or aesthetic.

Now say they CAN find stock that is about 1/3 the right length, and thicker than needed. Let's say it's White Oak or Black Locust for sake of argument.

Would it be horrible to dimension the frames say about 1" thicker, half lap the ends (futtocks, I presume) together with lots of bedding compund and then cinch up the laps two ways with bronze carriage bolts? The diagram is exaggerated for emphasis, and does not show things like washers and other bits that would be needed in this sort of layup:

http://www.ennui.net/~timothy/Boats/HalfLap.gif

This creates a weak/hard spot I know, but couldn't you just do a partial sister at that point, extending ~4 times the width of the frame in either direction with solid, VG timber? For that matter.. would you -need- reinforcement for that spot if you overengineer the frame itself?

Would the layup open up some at the butts? Could you avoid that if you used wedges, forms and copious steam? If not, does it really matter? Could you just plane the slight gaps and fill with compound or would the stresses be too severe?

(Apologies if this has been covered, but I spent quite some time looking through the archives with no luck!)

[nedL]

I'd go with a simple tapered scarf (say at least 6:1 & riveted).

[TimothyB]

Originally posted by nedL:
I'd go with a simple tapered scarf (say at least 6:1 & riveted).Thanks Ned. Thats the same basic idea, except more refined.. the question is not married to the method. The main thing is can you connect several straight grain pieces of wood together with mechanical fasteners and then steam bend her? If so what is the best way? I'm mostly thinking about bigger timbers in the 3"+ range.

[ 10-22-2004, 12:49 PM: Message edited by: TimothyB ]

[Bob Smalser]

Bigger timbers were spliced with keylocked hook scarf with nibs.

http://pic3.picturetrail.com/VOL12/1104763/2595357/70507451.jpg

Attempting the same with short faying surfaces and fasteners wouldn't be near as strong if any stressed surface relies on the skinny bolt shaft or washer for strength....

...not to mention that they always loosen over time with seasonal movement...and even if safety wired the fit will be loose and unstable during the dry season.

I'd much rather cut the tradiitonal scarf than worry about my unwise experiments.

[nedL]

Sorry about that Tim. I can not speak from experience (esp. on 3" frames). I suppose it might work ok if the scarfs can be made to land in areas of minimal bending. I'd be skeptical about its working if the scarfs land on significant bends though (like trying to bend a piece that has a lot of grain run-out). I realize it's much harder bending short lengths but I'd think the way to go about doing it might be to bend the shorter lengths individually & overlapping and then scarf after they take their set. - I'm sure people with much better experience will comment soon.

[PeterSibley]

I can't imagine successfully bending 3" timber with a scarf in it...it just doesn't compute.How about a lamination or the way millions of frames have been built...sawn and bolted.

[Jack Heinlen]

Last I looked, years ago now, white oak in good sizes wasn't exactly scarce in your neck of the woods. A search of this archive, or of WB mag will turn up some good articles on sawing, grain orientation, etc. Spend a little money for your framing and get some good, one piece, stock. I see what you propose as a minor nightmare, or a large headache, or both. I've never seen the bolted joint used anywhere, or a scarf used in new construction. Find some full length, good, stock. When you figure it into the equation it's a small expense.