I building a frame for a large bathroom mirror—36″ x 29″ x 1/4″—out of QS hard maple. The frame will be 7/8″ thick and 3″ wide. I was going to use splined miters for the joinery, but was looking through Yeung Chan’s Classic Joints with Power Tools last night and saw an array of stronger miter joints. I am now considering using a mitered slip joint for the frame. What is the strongest miter joint, and what would you recommend for this particular application?
Thanks,
Norman
Replies
Just finished one about that size using only pocket screws. All the joints you mentioned will be very strong if machined properly. I've seen lapped miters so poorly machined they may have the strength of a butt joint at best. A spline is very easy to incorporate into a miter and helps reinforce a miter joint. I've made many picture frames in the size you mention with spline miter joints and they haven't failed.
Thanks. Yes, pocket screws should be pretty strong, but I do want the joinery to stand out subtly to add a little interest off the plainness of the QS maple.
Norm,
I've done a couple of LARGE mirrors and was shown by a framer how to hang it on the wall using the standard wire. Attach the wire to the bottom and the sides with one continuous piece.
See the attached.
ASK
Wow, that's quite the clever rigging. And very helpful. I was puzzling over how to hang the mirror, and was going to opt for some keyhole hardware set into the frame to help the mirror hang flush to the wall. Does the mirror hang pretty flush with your wiring? Do you use conventional hanging hardware on the wall?Thanks,
Norman
A couple of big sucker screws in the studs. If I remember, 3/8" or better.
Used something like this on the frame.
http://www.leevalley.com/hardware/page.aspx?c=2&p=46698&cat=3,40914,50630&ap=1
Not perfectly flush. I've done this twice both times in 1/2 bathrooms so it's not big enough to actually tell if it's flush or not.
ASK
Thanks. I half-bathroom is exactly what I'm doing. Very helpful.
--N
A lot of it depends on how much exposed joinery you want. FWW just did a strength test on all the basic joints using Titebond III glue.
(Feb 09)_ The strongest of all the joints proved to be the half lap then the bridle and then the splined miter and they used a spline that the grain direction was parallel instead of perpendicular to the sides. I would not hesitate to use your original design unless you wanted more exposed joinery. The mitered slip joint is a variation of the bridle joint but more complicated to construct. It all comes down to surface area, the more surface area to glue the stronger the joint. If you wanted no exposed joinery you could do a blind splined miter and it would be a very strong joint and invisible. If you don't have the article FYI the bridle failed at 1,560 lb. of racking force and the splined miter failed at 1,498 lb. , not much difference.
Edited 2/12/2009 9:49 am ET by terrylee86
Terry, thanks for that info. Looks like I'm overthinking this, as usual. Seems a well-made splined miter joint should work fine. I forgot about the article you refer to; I'll have to downloaded it.Thanks again,
Norman
This here's how I do em', and I've never had a failure.
Jeff
Lovely. I was thinking of using some mahogany scraps for the splines to get that effect.Thanks,
Norman
I made a jig that holds all my door frames at a 45° angle to the tablesaw top, and I just use an 1/8" kerf blade. I usually make the triangle splines from an accenting wood, also, unless the job calls for something else.
Jeff
Jeff, I've a got a small jig similar to that for cutting slots to accept accent keys in the corners mitered boxes, but I already figured I'll need to make a bigger one for this mirror frame.Thanks,
--N
Cope and stick, reinforced with pocket screws.
And be sure to use the wire-loop method that ASK shows in his response.
I agree with JeffHeath. Splines are the strongest. Make sure the grain of the spline runs perpendicular to the joint.
norm,
two techniques, not yet mentioned, work well for me. one is to cut one or two diagonal dados 1/4" wide on the back of the frame and to glue 1/4" splines into these grooves. one may use different colored woods and all you see when looking at the front of the frame are neat little squares on the edges. another method i've recently tried seems also to work well. on the back of the frame, drill as many flat bottomed holes half way into the thickness of the frame and spanning the 45 joint as needed, depending on the width of the frame parts, and pour epoxy into these"pockets". the round shape of the epoxy "disk" now prevents the joint from pulling apart. i did the epoxy method for the first time, two years ago, and the joint show no compromise.
cool huh?
eef
That epoxy trick is a new one on me . . . Thanks,
--N
My preference is a straight miter joint glued and cross nailed. It's a simple way to do it and very strong... easy to do accurately (which makes it strong). If you buy picture framers brads the heads are quite small and easily filled and camoflaged.
I'm currently making two large frames in ash, one 850mm square, the other 970 x 760 or so. 90mm wide (that's a bit over 3 1/2" I think). I'm using loose tenons, two of them, across the joint. The one nearest the corner is 15mm deep, the one nearest the rebate 25mm deep. It's quick, easy and strong. I have a Domino, so it is a piece of cake, but even with a router and mortice jig it is fast. The best bit is that it is totally invisible (although I agree that maple lends itself well to a contrasting spline).I fully expect these frames to last for ever!Cheers
SteveSpace is more valuable than the junk that occupies it.
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