Replies

1. 
   Woodspirit | Apr 08, 2005 04:35am | #1

   I too have only recently heard about the telegraphing problem but like you haven't found any concerns with the projects that I have used them on. I nearly always use the full size machine on 3/4" material but occasionally use a small face frame jointer on light materials, picture frames, solid wood edging on plywood etc, most of the projects are still in the family and no dips or depressions where the biscuits are.

   Cheers.

2. 
   dondownunder | Apr 08, 2005 06:58am | #2

   fred

   I've heard that some of the plastic laminate tops have had an issue with a raised semi-circle when the biscuits have either been too tight to begin with or of dubiuos quality & expanded beyond normal limits. When used in solid timber construction it is likely that in most cases any telegraphing of a biscuit would be removed by further finishing. Again I havn't seen any problems in my workshop & we use about 1000 a month in both solid & man-made products.

    Don

3. 
   Rich14 | Apr 08, 2005 08:19am | #3

   Fred,

   I don't know how the term "telegraphing" came to be applied to this problem. Telegraphing, as when the grain pattern or defects of a layer under a finish veneer is apparent on the surface, is caused by the top layer (whatever it is) closely bonding to and following the subtle contours of the substrate.

   The biscuit problem is related, but is somewhat different. It's the result of swelling of the biscuit by absorption of water in the glue. It can be grossly visible or very subtle. The swollen biscuit raises the wood between it and the surface. It's not the swelling that's the problem. The problem is surface planing or sanding the glued up piece before the swelling subsides.

   The swelling will completely resolve if given enough time. But that's generally longer than most people appreciate - sometimes a week or more. When the surface is sanded or planed before the swelling has completely returned to it's pre-moistened state, the raised wood is shaved off so that the area is level with the surrounding wood. It looks fine at that point. Then the biscuit's shrinking continues and the area that was raised and removed, sinks lower than the surrounding surface.

   It's quite noticeable, but completely avoidable, if you wait until the moisture has completely equilibrated with the surrounding wood tissue before planing or sanding the glued-up piece.

   Rich

   Edited 4/8/2005 1:22 am ET by Rich14

   
   

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   Edited 4/8/2005 1:23 am ET by Rich14

1. 
   oldfred | Apr 08, 2005 03:27pm | #4

   Thanks,  Rich, Dale, and Dondowunder for the replies.  That's the information I need. 

   A friend asked my advice on  biscuit jointers, and since I had read about the problem, I was reluctant to give an answer.

4. 
   Dave45 | Apr 08, 2005 04:45pm | #5

   I've used biscuits for several years and have never seen this "telegraphing" problem - even in 1/2" material.  I understand the concept but I've never seen it happen.

   I've always put the biscuits in the approximate center of 3/4" and 1/2" stock, so maybe I've just been lucky. (Better lucky than good, right? - lol).  Next time I'm making biscuit glueups, I think I'll experiment with some scraps and see if I can make it happen.

1. 
   oldfred | Apr 08, 2005 06:00pm | #6

   I've never seen it either and, like you, Ive always centered the biscuits, but Rich's explanation makes perfect sense to me.  Think I'll experiment a bit too.

1. 
   hairball | Apr 08, 2005 07:28pm | #7

       The closer to the finished surface the biscuits are placed, the greater the chance of this problem arising. Try gluing up some 1/2" ply with the biscuits above center, closer to the face. Sand, finish and look across the surface under low angle lighting. This would represent the most likely scenario for this to happen.

1. 
   MarkRD | Apr 08, 2005 08:56pm | #8

   I could see it happening in plywood without any difficulty. I'd be surprised with hardwood when there is 1/8" of material above the biscuit...Mark

   Measure it with a micrometer, mark it with chalk, cut it with an ax.

2. 
   oldfred | Apr 08, 2005 09:22pm | #9

   That would make sense.  I would think the glue between the laminations might inhibit moisture from spreading out in the plywood, hence more moisture and swelling in the biscuit.