Should a frame survive a fall to the floor?

[Leuf]

I recently had an 11x14 mirror with a 2.5" wide pine frame that got damaged while on display in a store. They had it hanging on a door and it got knocked off, I'm guessing about a 4 foot drop. The weird thing is the glass didn't break, except a small chip in one corner. All 4 joints on the frame came apart though, which is sort of the opposite of what I would have expected. They were splined miters with the spline about 1 inch deep at the joint. It appears the splines were either slightly too thin or I didn't use enough glue, as the splines came loose with no damage at all to the frame or splines. I test fitted one and it seemed like a proper fit to me. I'm a little confused.

So here are my questions,

With the proper joinery should a frame survive a fall like this or should it be expected to fail?

Should I be making the spline deeper or adding a key for additional strength?

-Leuf

[George]

The frame was made to hold something, not to protect it from a fall. Especially when what's in it is very heavy. If you want protection in a fall, you'll want something besides miters, keyed, splined or otherwise. A sharp blow is going to break small glue surfaces apart.

[Dave W]

It is a little surprising, I agree. I guess the energy of the moving mirror was absorbed by destruction of the wood structure thus protecting the glass! Just out of curiosity, what kind of glue did you use? I think a deeper spline would have better protected the frame from opening up with humidity changes over the years. Dave

[Swingman]

Judging from your description I would say that there was most likely a combination of factors that caused the behavior.

That said, good glue, properly applied in the right temperature range, would not have normally allowed the parts, particularly the splines in a miter joint, to come apart as cleanly as you describe.

In addition, 1" splines probably didn't give you enough extra glue surface area in a miter joint joining sides of that size.

[Edwin Pawlowski]

The frame protected the glass by absorbing the shock. Take a look at things like the bumpers on your car, crumple zones, the foam packaging appliances/electronics come in and what do they have in common? They all absorb shock.

If you want the frame to absorb the shock of a 4' fall, it must be designed into it. Strong materials do not always do the job as they transmit, not absorb the energy. Frames, with purpose in mind, are made to look pretty, hold pictures or mirrors, and provide support for hanging. Never has falling come into the engineering.

[Toller]

I am not surprised it broke; that is a lot of weight. I am surprised the glue broke; when I have broken joints on purpose, it is always the wood that fails. They must have used way too little glue like you surmised. If you can reglue them properly you should be fine.

[somewildmonkey]

I'd keep making frames exactly like the one you built - apparently it dispersed just enough energy, at an acceptable rate through its destruction to save the mirror :-)

[Scorp]

Maybe no joint would have held, how your joint failed however is a problem and I would think should have been much stronger, 1" is pretty deep for such a small frame.

Was the spline also pine? Maybe a burnished or contaminated surface?

-------------------- Steve Jensen Abbotsford B.C. [e-mail] chopping out the mortise. BBS'ing since 1982 at 300 bps. Surfing along at 19200 bps since 95. WW'ing since 1985 LV Cust #4114

Nothing catchy to say, well maybe..... WAKE UP - There are no GODs you fools!

[Leuf]

Thanks for all the responses..

The splines were pine. Closer inspection shows some of the splines were slightly thinner than the one I tested, and that one barely has any glue on it. Not sure how that happened.

I used elmer's yellow glue. The bottle doesn't list a minimum temperature, the shop has been between 50-55 F which I know is borderline for a lot glues. However there were also applied intarsia pieces on the frame that spanned two of the miters and those both stayed attached to the frame and stayed together, breaking in the wood. Those were glued under the same conditions.

I had been applying glue only on the inside of the spline and not to the spline itself, when I put it on the spline it just gets scraped off when inserted and the frame has a rough edge that I can't sand so squeeze out is a problem.

I'm thinking making the spline a little deeper, applying glue lightly on the spline itself in addition to in the joint, and putting a clamp to make sure there's good contact should be enough. I don't think I'll do a drop test on it though...

-Leuf

[CW]

[Swingman]

My experience is just the opposite ... with frame sides 2.5" wide, it is hardly worth using "miter with spline" frame joinery with just a 1" spline.

At that width, the mitered surfaces being joined are over 3.5" long.

So, and just an off-the-cuff rough estimate, a triangular shaped spline with

2" height would offer over 4 times more glue area to reinforce the mitered frame joint, more glue area being the whole point of this joinery method.

I would probably use a spline height of 2.5", which is about right, IME, for frame joinery with sides of this width ... and it's easy to cut the spline slot in the frame corners to this depth on the table saw.

[Scorp]

Now wouldn't a 1" spline be 1/2" deep?

From the OP:

I assumed the splines WERE 2" wide to achieve this. Other translations may vary :)

-------------------- Steve Jensen Abbotsford B.C. [e-mail] chopping out the mortise. BBS'ing since 1982 at 300 bps. Surfing along at 19200 bps since 95. WW'ing since 1985 LV Cust #4114

Nothing catchy to say, well maybe..... WAKE UP - There are no GODs you fools!