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I spent a many hours milling out maple and laying out the joints for a presentation case for a Sharps rifle (51" X 8" X 4") this week. The learning curve for through dovetails using my Incra router set-up on each corner of the box was long and painful, but I finally managed a decent joint. Running the stopped dado's for the top and bottom pannels was frightening but I managed to get that done without trashing anything.

Yesterday I set up the assembly, dry fit the whole thing, buttered up each end and slid in the floating top and bottom panels of the case (like a floating bottom of a drawer slid into dado's). I had carefully checked each surface for square. BUT, when I took off the clamps the box was twisted and IMHO, a POS! as a finished product. The only thing I can think of that may have created the twist in the box would be too much pressure on the pipe clamps. I had applied enough pressure to draw all the dovetails in tight and then left the clamps on till the glue was dry. When I removed the clamps and set the box on my table saw there was a noticable rock on two opposite corners. Even when I sliced off the top I could tell it was crap because the saw kerf's didn't line up. :furious:

So, I guess I'm asking how to clamp the next box up so it won't twist? Should I draw in the joint then remove the clamps to "relax the whole frame? What am I missing? My dovetails are really beautiful so want to continue with this tool.

Questions ? Observations ? Comments?
 

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Where did you put the clamps?They're prob twisting it.
It could be compression stress in the freshly milled wood,prob not.
I would pull them together with the clamps,loosen them a little,check for square,then retighten.Don't clamp too tight.The instinct is to tighten the clamps almost as hard as you can.
You could also use cauls to clamp the box down to a flat table.
 

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Discussion Starter #4
I used blocks under the clamps to spread the pressure across the width of the joint. Clamping the box to a flat surface may be a good idea,

I'm milling out the stock for a new box today. Will let you know how it turnes out.

Thanks
 

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Boondocker:

I'm going through the very steep learning curve on dovetails too. I can't find a picture of your jig so I can't comment intelligently. But, here's some observations that may help.

1. don't rely on positioning of the tool to be correct, hold it in place. My dovetail jig requires that I position the router on top of the comb and follow it to cut the pins and tails. I literally have to push down on the router to be sure the comb is in complete contact with the board.

2. I found that when I tap the joint together, it doesn't always seat perfectly. You need to "adjust" the attitude of the drawer. (in my case)

3. I developed a checklist in my mind before cutting a joint. Is the side board perfectly flush with the front board? Are both boards perfectly square to the jig? Is the comb out of position? (I have to explain here -- on my jig, the comb is on the ends of two arms. At the base of the arms is a screw and some springs. If you don't check, the comb never gets in the same place twice, really screwing up the joint.)

4. Never assume your jig is square and that your workpiece will sit squarely in the jig. Always check first. At the beginning of each project I get out my engineer's square (accurate to some ridiculousnumber too fine for me to see) and check all of my critical machines: mitre saw, table saw, rules (just in case one got dropped and is out a bit)

5. I always use measuring blocks before rules.

Don't scrap the box yet. study it. Are all the joints perfectly smooth with the box ends? Maple is pretty tough stuff and doesn't move easily. I doubt if the problem is just your clamps. It might be some sort of adjustment that you won't easily see until you really look for it. Take a look at pages 17 to 19 in the Woodstock Dovetail Jig manual. I'd be looking at the "uneven fit" part on page 19.

http://www.woodstockint.com/images/manuals/D2796_m.pdf

I don't think your jig is like the Woodstock one but maybe it will give you some ideas.

Good luck and keep us all posted of your progress.
 

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Discussion Starter #6
Thanks again for the observation.

The jig I'm using is the Incra Ultra LITE. I made a number of practice corners befor I cut into the box material. The last practice joint was very clean and tight and the corners of hte box were also snug.

I worked as fast as I could to clamp the corners after I smeared the glue but even then I could feel some parts already setting befor I could close the joints completely - which is why I realy put the pressure to it to get it close.
 

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Just some suggestions:
1 Try using a slower setting glue to give you more time to work.
2 Clamp lightly with the pipe clamps to get the box fit together.
3 Clamp the box to a very flat surface with additional clamps to keep it true. A table saw top surface can work well if it is wide enough.
4 Do a squareness check of the box.
5 Snug up your pipe clamps to your satisfaction.
6 Do a final squareness check to make sure the box hasn't gone out of true with the final clamping.

This should give you a square flat box. keep in mind that all wood will move with humidity/temperature changes, and there might be some changes with time, but they shouldn't be too bad.

You could try clamping the box you have down to a flat surface, with wedges under the low points, and hitting it with a heat gun. It might move enough to come flat.

Gerry
 
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