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Knock down mitre

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Forum topic by jeth posted 09-20-2011 04:16 AM 3426 views 0 times favorited 7 replies Add to Favorites Watch
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jeth

249 posts in 2305 days


09-20-2011 04:16 AM

Topic tags/keywords: question joining

This has had me scratching my head for a while now. I would like to build a large frame with mitre corner joints, for a platform bed. The frame itself will not have legs at each corner like a traditional bed frame, just think extra large picture frame.
The problem is that I want this to be knock down-able. I have looked at lock mitres, mitres with secret dovetails inside and various others but I am finding it hard to visualise soemthing that is going to pull that mitre tight together so it looks good and still be knockdownable. The only remote inkling I have had is some kind of tenoned mortise with some kind of removable “drawbore” peg using a bolt and threaded insert to pull a tapered pin itno an offset hole on the tenon to pull the joint together. I have thought of doing this with a box joint with just top and bottom mitred, as it may be stronger and could be worked to pull in both directions. I would prefer to hide end grain though..

Worth noting that the joint just needs to pull itself together to look nice and hold the corners square, it will be floating on a pair of “sleeprs” so I don’t expect many racking forces on the corners as in a more typical bed frame, the stress will be along the long rails which attach to the sleepers and they will therefore be suitably hefty :)

Is the idea workable? Does anyone have a better one?


7 replies so far

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WayneC

12642 posts in 3564 days


#1 posted 09-20-2011 04:58 AM

Something like this?

http://www.leevalley.com/US/hardware/page.aspx?p=67659&cat=3,41306,41319&ap=1

-- We must guard our enthusiasm as we would our life - James Krenov

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jeth

249 posts in 2305 days


#2 posted 09-20-2011 05:12 AM

Thanks for replies folks. Wayne, not really, don’t want any visible hardware and I can’t see how to use bed bolts in a mitre, if you’re pulling it just one way then it will tend to slide leaving an imperfect corner. That is why I figured some kind of joinery, tenons, dovetails or other to lock the peices in position, then perhaps some form of mechanical fixing to really pull it and keep it tight.
cr1, good thought but that was my starting point. I was concerned blocks on the inside of the corner would pull the inside together and likely cause an open looking joint on the outside of the corner where it most matters.

I have just been pondering a simple tenoned/ bed bolted type structural frame with a mitred sub frame that slips on top for the look.

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rance

4245 posts in 2627 days


#3 posted 09-20-2011 05:34 AM

What CR1 said. Like this:

To make it pull it tight, drill the holes slightly offset like one of those dowel joints where it pulls it tighter as you drive the dowel in. With lag bolts, you have to screw them in place on the individual pieces, then disassemble and put them in place on both. Only offset by 1/16” should be sufficient. Here’s the axial offset between the position of the bolts in the corner block and the place they screw into the rails:

Here’s how it lines up as you begin putting the bolts in place. Note the gap between both rails and the post. As you tighten up the bolts, the miter will have tension to pull itself together:

If you are still worried about bowing of the rails, you could insert a veritcal hardwood shim about 1/4” wide at the point where you see the arrows in the last picture.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

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gfadvm

14940 posts in 2157 days


#4 posted 09-20-2011 06:36 AM

Rance – Your SU skills are amazing! I may have to fly you to Tulsa!

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View Jorge G.'s profile

Jorge G.

1537 posts in 1942 days


#5 posted 09-20-2011 06:37 AM

How about secret or hidden dovetails, you don’t need to make a lot of the dovetails, maybe 2 or 3. Here is a reference link, look at figure Nº 4

http://chestofbooks.com/crafts/popular-mechanics/Amateur-Work-5/Dovetail-Joints.html

-- To surrender a dream leaves life as it is — and not as it could be.

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TopamaxSurvivor

17676 posts in 3143 days


#6 posted 09-20-2011 07:44 AM

As I understand it, you want the frame to be flat like a picture frame. How about using dowels to maintain the position of the joint; then, use blocks and bolts to draw it up tight below?

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View jeth's profile

jeth

249 posts in 2305 days


#7 posted 09-21-2011 10:14 PM

Thanks for further replies folks, haven’t been on for a day or two so just come back to this.

Thanks for the sketchup, maybe I will give that a test run. Thinking of building a few sample joints to see what works. i still tend to think a block on the inside of the corner will pull the outer edges of the mitre apart, more so considering these rails could be 3 or 4 inches wide.

Topamax, that is another option I have considered, and like the tenoned mitre joint this could be pinned/bolted through the dowel or tenon to pull the joint together.

JGM, hello, thought you had vanished again :) I mentioned I had looked at hidden dovetails, do you think they would hold alone without mechanical assistance or if not how would you bolt it? Last night I sketchedup (new verb, to sketchup) a joint with a large single sliding dovetail key which gives me endgrain but more balanced and clean looking than a box joint or standard pins and tails. The “pin” or key could even be glued into one of the pieces after fitting giving a dovetailed mitre but with a symmetrical appearance.

i think the best approach is to try a few options with scrap, good practise anyway :)

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