This may have been discussed before, but how would I clamp up a cube with all the intersecting edges at 45 deg? The front will be open with flush doors. This is a credenza 80″ long by about 24×24. What I need is a giant picture frame clamp and then I would have to pull the back tight somehow. This seems like a daunting task. The material is MDF with birdseye Maple veneer. I don’t want to screw it up. Thanks in advance for any tips.
Chuck,
Replies
First, I haven't done what you need to do. I'm just giving you insight based on similar clampups.
It sounds to me like you'll have the top, bottom, and both sides cut with 45 degree edges for all sides except for the front. Sort of like a giant mitered picture frame. The back sides will also have 45 degree cuts so that the back slides in. You need to clamp all of this up.
Consider using your biscuit jointer to cut slots for biscuits, say every 6 to 8 inches. These are for alignment. The biscuits would be at 90 degreed to the mitered face. Fitting the top, sides, and bottom are easy as they just slip together. The problem is getting the back to go in at the same time. I'm not sure I'd use biscuits for this one as the assembly might be impossible. Let's assume no biscuits for this portion of the glueup.
To get the joints tight and clamped, make a series of jigs. For each joint you'll need to jigs ... or, more precisely, one jig. That one jig will be a piece of hardboard (1/8th of an inch should do) which goes from one corner to the other. The jig for the top will be a piece of hardboard almost as long as the top. Likewise for the bottom and sides. At the end of each jig glue on a strip of hardwood which is cut at a 45 degree angle. The 90 degree and of this strip is opposite the hardboard. When placed on the top the inside edge of this strip provides a clamping surface which is parallel to the 45 degree miter cut. Simply use clamps to hold the four jigs to the four pieces your're gluing up and then use clamps about every 3 inches at the corners to pull them together. The biscuits keep the corner aligned and the clamps keep it tight.
When the box is glued up (make sure it's square), you should be able to simply slide the back piece into place. A similar method can be used to clamp the back into place if required.
Note that during the first glue-up you could use the back piece (unglued) to ensure that the piece is exactly square. Or, if you have enough hands around, you could glue the back into place while the other joints haven't yet set. I'd want to do a dry run or two on this because I suspect it'd be like a Chinese fire drill.
Consider using Titebond III, which has a longer open time than Titebond II.
John
John,
Yes, yes, You know exactly what I am trying to do, and thank you. The instant you started to tell me how to go about it the light bulb went off. I may have read it sometime in the past (old timers disease). It is a Chinese puzzle. Yes, you are right, the back can be used as a stabilizing device while glueing, but can't be biscuited.
Chuck,
My pleasure. Hope it turns out OK. Post pictures when you've got it completed.
John
Chuck,
I agree with Johnhardy, but instead of clamps why not use the nylon rachett strap clamps around the box.
ASK
If you build the clamping jigs as I described, and use clamps, you'll get direct, even pressure directly on the joint ... without having the possibility of having a strap create an indentation in the corner itself.
I use this method to clamp up table legs that are made of 4 pieces (this is another story in and of itself, as I use this to create quartersawn legs where all four surfaces are Q-sawn ...) and the joints are so tight you cannot even see them. The joint itself is exactly in the corner and blends out to the eye. And the biscuits keep everything aligned.
John
Johnhardy,
I would use the straps with a jig at the edges so no indentations would be made.
I think the pressure would be equalized around the box.
ASK
I guess that would work, but my own belief is that the use of actual clamps give you more control over the pressure and a more precise glue-up. The clamp pressure is exactly perpendicular to the joint if you use my jigs. The straps have always seemed to me to give uneven pressure. But that's just my opinion.
What I'd suggest to the original poster would be to figure out a method and do some dry runs. And to time the dry runs so that the glue-up works within the setup time for the glue used.
John
Thanks to both of you. I had thought of the web ratchet clamps as an alternative as well. I will try both with a dry run. I am just getting the materials together now and it is golf season in Minnesota, so it will be a while before I get there, but will let you know how it works out. Since it is Birdseye Maple, I did not want to screw it up. Later.
Chuck,
Chuck,
Being you haven't started to build the piece, I'd suggest that you choose a different method of construction to eliminate the long miter joints.
Trying to cut eight perfect 24 inch long miters, four of them on the ends of 80 inch long panels is simply asking for trouble and clamping them tightly enough to get gap free seams will be very difficult. Using veneered panels also adds considerably to the difficulty, you'll have zero room for errors. I'm not saying it can't be done, but it is going to be a high risk project.
Also worth considering is the fact that these will be weak joints for a large piece of furniture. The finished piece will also have very sharp and easily damaged corners that, because of the veneer, can't be rounded off.
John W.
JohnW,
Good point, I have been fighting this design for some time now and have expressed similar arguments. Thanks,
Chuck,
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