Making Tight Finger Joints
Glue is holding finger joints open, reports a craftsman. Pros offer suggestions for clamping long boards tightly end to end. November 9, 2005
Question
I need to build two 1 x 10 17' stair skirt boards out of red alder. All I could get was 6-8' material. My plan was to buy a finger joint cutter for the shaper and a Titebond HiPurf polyurethane glue that sets in 60-75 seconds. I plan to glue the joints together and move on to the next joint quickly. The joints dry fit just fine, but when I put glue on I can't get them back together. The glue doesn't seem to be letting the joint close before the glue sets. In all the joints I have tried the best I could do was 1/32" gap on the face. I need to get these joints tight. I reduced the amount of glue I used and that helped a bit but I haven't been successful yet. Any suggestions would be greatly appreciated.
Forum Responses
(Architectural Woodworking Forum)
From contributor A:
It seems like you need to put pressure on the joint halves. Since it would take some really long pipe clamps, you could try pinch dogs instead. Pinch dogs are U-shaped steel tools that have bevels ground on their legs and will force two pieces together when they are driven into the parts with a hammer. Pinch dogs leave some serious damage on the surface that they are driven into so they are usually only used on the side of the work that won’t be seen. Other than that, perhaps the adhesive you are trying to use has too much viscosity.
From contributor B:
It is interesting that this question came up. This morning I was looking at the sales flier that came with my HiPUR kit that I purchased last year. I also had some joints that did not close up properly. I was using the 75 second glue. The numbers on the Titebond website are a little different from the brochure on the subject, however they point out the difference in viscosity of the three HiPUR products (WW30, WW60, and WW75). It seems that the WW30 is the thinnest of the three. WW75 is in the middle, and WW60 is the thickest. I plan on trying the 30 second glue to see if that solves my problem (miter joints on crown moulding). With only 30 seconds, I will have to work fast. However, if everything is set up correctly this should not be a problem for my application.
From the original questioner:
I didn't think of pinch dogs. Those are easy to get.
From contributor D:
Try this experiment. Set your dry fit on the two joints. Instead of applying glue to the joints, dip the joint ends in water for about 5 seconds. Now check the fit again. It will be pretty tight. The water in the adhesive is only a vehicle to get the solids from the applicator (brush, dipping, automatic spreader) to the joint. When the water is squeezed out of the solids, it transfers into the wood fiber. A complete cure is when that water dissipates from the wood. You also need to get penetration into the wood fiber, therefore too little adhesive is going to cause a failure down the line. You need to apply enough adhesive to the joint, squeeze out some, then let cure for an hour or two (depending on the ambient temperature) before machining or using. If the dry fit, amount of adhesive, amount of pressure, and squeeze time are adequate, you'll solve your problems here. To get a good glue line, the solids must be sufficient enough to accomplish a consistent glue film in the joint after squeezing.
From contributor E:
Try the trick used to clamp sections of counter top together - hot glue some small blocks of wood to the faces of your workpiece then pull the joint together by putting clamps across the blocks. Then chisel off the hot glue.
