Replies

1. 
   Sean2112 | Jun 29, 2008 05:37am | #1

   Jeremy-
   If a sliding dovetail is cut right, a minimal amount of glue is needed. As Krenov says, any glue that squeezes out is glue you didn't need. Slide the joint together as if to dry fit, but leave the last 3 inches or so out, then only glue that much. This prevents a disaster like binding before the joint is complete.
   Regards,
   Sean

1. 
   Glaucon | Jun 29, 2008 06:25am | #2

   Sean is right. If properly fitted, a SDT does not need to be glued down its length. Some bookshelves use a stopped DT with a dado along the rest of the shelf- the mechanical strength is fine. If your SDT is not tapered, fit it carefully. If you back out a bit from your dry fit, you can apply glue to the exposed 2" of the tail, and to the corresponding part of the "pin" on the other side. Tap it together- you can put masking tape along the mating surfaces to minimize the clean up of squeeze out. Wait 45 minutes and remove the tape and clean up any remaining glue with a sharp chisel or chisel plane. A properly fitted, SDT glued for 4" along its length should be extremely strong.Glaucon

   If you don't think too good, then don't think too much...

2. 
   Jimurock | Jun 29, 2008 06:30am | #3

   I use polyurethane glue. It has a long open time, and it acts as a lubricant so that the joint doesn't bind -- you shouldn't need more than a tap or two with a mallet to drive the joint home.  Other glues have the opposite effect -- they start to dry quickly and the joint is very difficult to move.  Apply a little glue to one piece and wet the other.  Poly glue tends to foam up if you use too much, though it scrapes off easily enough when dry.  It's probably not as strong a glue as some, but that doesn't matter for sliding dovetails -- if they're accurately cut they form a good mechanical fit that holds together well even without glue.   Poly glue has a limited shelf life, especially when opened.  I'd buy a small amount.

   Jim

3. 
   hammer1 | Jun 29, 2008 05:39pm | #4

   There is a fine line between too tight and too loose on sliding dovetails. Getting it just right takes some practice. It's very important that the work pieces are straight and flat so you can get a consistent cut. If you have to force the joint together with more than hand pressure, it's probably too tight.

   Application of glue can be just as exacting as cutting joints. It can be hard to control with a stick or wimpy brush like an acid brush. I like to use those 99¢ natural bristle brushes in 1/2". I use scissors and cut the bristles down to 3/4" long. This makes a nice stiff brush that can control the application. In many cases, I will apply a spit coat of glue, called sizing. This will prevent the end grain from drinking up the glue you want in the joint and allow a more judicious application when assembling. Too much and the joint may swell. I hate dealing with squeeze out and try to keep it to a minimum. A little care in the beginning saves a ton of work later, that never comes out quite right.

   On a sliding dovetail, you don't need to glue the entire joint. Just doing the first third will be fine in most cases and allow movement when needed. I prefer to place the assembly glue in the dado, sliding or otherwise. This way, if you miss the slot, you won't be stamping wet glue where you don't want it. If you have 'sized' the male part and let it set up you don't need a puddle of wet glue in the joint.

   I use sliding dovetails quite often. I seldom use tapered ones due to the extra work. I've made many that were too tight or too loose. I try to make the fit slide together with just hand pressure. Too often, I've almost got the joint fully together when it jams. Clamps, hammers and sweet talking just don't do any good. Try to avoid this situation. The sliding dovetail doesn't need to be a tight a fit as other joints.

   Beat it to fit / Paint it to match

4. 
   philip_r | Jun 29, 2008 07:23pm | #5

   If I understand you correctly (im still drinking my coffee), you are eventually going to make a 56h by 40w oak bookcase.   

   Do some research on Tapered Sliding Dovetails or cut a dado and DT the last 4 inches, at the front of the case.  Both will provide the same visual effect and go together easily.

1. 
   jeremyillingworth | Jun 30, 2008 07:37am | #6

   The bookcase is going to be an arts and crafts style bookcase with a door on the front.  The sliding dovetails would be totally invisible; I just thought they would add more strength that dadoes and tenons.  After making the practice cabinet, I think I may stick with the traditional joining techniques.

   jeremy

1. 
   Jimurock | Jun 30, 2008 04:39pm | #7

   If you're going to use a book case for books  (some people still do!) the weight can be considerable, and sliding dovetails do add to the strength.  Just for the hell of it try the polyurethane glue on a small mockup.  No need for tapering, fighting the clock, or heavy hammering.  Just reasonably well-fitted joints.

   Jim