Biscuits for Breadboard


Is there any reason why I can't use biscuits to glue up breadboard ends to a table top rather than mortise and tennon?
Thanks
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Biscuits can be used but you cannot glue the breadboard all of the way across the table end. You have to allow for expansion or you will split the end of the table or fracture the joint - more likely the table will give.
You can glue and biscuit the center 1/4 or so, depending on the width. Outside edges should be allowed to move and the biscuits can assist with this too, HOWEVER, you should use a more rigid mechanical fastener in slotted holes (bolts, screws, etc.) with the biscuits. That is what the mortise and tenon or spline does.
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A clarification - the outer biscuits are not glued in both pieces, only one if that. The outer edges must slip. You cannot depend on these biscuits for strength - just alignment. The hardware provides strength.
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A good reason you can't. The movement of the main tabletop if glued to a breadboard across it's width will definitely split your breadboard (or the table top itself) over time. The purpose of the mortise and tenon for a breadboard isn't usually to provide a gluing surface. It's to provide a joinery/mating system that can then be pinned or fastened to allow for the constant expansion and contraction of a solid wood table top. That's why you often see breadboards that extend slightly beyond the width of the top they're connected to. That's to allow for expansion.
You could try a single glued biscuit in the center and then try unglued mortise and tenons further out along the edges. You can then pin the tenons with a through or partially through dowel where the dowel hole in the tenon has been elongated across its width to allow for movement. Think the easiest is to make the end of your tops one long tenon and then your breadboard have a matching mortise/slot across it's length. Then dry fit to your table top (allowing extra breadboard length than actual width of your table top), drill holes to pin the tenon into the breadboard, take it apart - widen the holes across the width of the tenon. Then put back together with a little glue in the center and lightly glue the pins into place. Lots of good arts and crafts/craftsman style plans or books demonstrate this.
Rule of thumb I've seen is allow for an 1/8 inch of expansion for each 12 inches of board. Of course, that will vary a lot depending on the woods you're using but it's a starting point.
Just my 2 cents.
Gary in KC

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On Thu, 05 May 2005 20:47:34 GMT, Pharmer

You could use them if you wanted to "glue up" a breadboard, but that's not itself a good idea.
The idea with a breadboard end is that the ends are only fixed in the centre, so that they can allow for moisture movement in the main board. They're not even held with a mortice and tenon - it's more of a tongue and groove and the tenon(s) (if any) are cut with over-width mortices to also allow this movement.
If you biscuit a breadboard end on, something is going to warp or crack somewhere. Of course if the top is actually veneered plywood or MDF (stable against moisture changes), then you could do it.
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Re my earlier post - the tongue and groove or spline is really a very safe choice - and not that hard to execute. The combination biscuit/metal hardware joints I mentioned were in a 8/4 oak coffee table top and I didn't want the exposed spline on the ends. I could have achieved this appearance with a hidden spline but the biscuit/slotted-hardware approach was an experiment. Appears to be successful as the table is about 3 years old; lives in an Arkansas home with partial wood heat and lower than average air conditioning. I have seen the joint edges move as much as 1/16" in or out (21" wide) but everything looks fine.
Some side information - with the wide top and ends I have two layers of biscuits in three places. Two pair surrounding a bolt at the center (about six inches glued in the center area) A similar biscuit/bolt cluster about six inches in from each edge - these biscuits are lightly glued in the table top only - not the ends). The bolt holes and biscuit slots at the end locations are slotted oversize to allow for slide.
By the way, if cutting spline slots on your saw or with a router makes you nervous, consider using your biscuit cutter. If you take your time and apply a little finesse you can machine a nice blind slot with the machine. Most machines do more than one thing.
RonB
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A biscuit jointer is an excellent tool for cutting a stopped groove for just this purpose. Just slide it sideways, maybe make two passes to get a wider groove.
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Biscuits don't allow for differential movement. A proper pinned M&T joint will.
-j

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Yes, but cause the joint will eventually break and will only be held by the biscuits. I can tell you from experience. I built the NYWS bedside table. And used a tenon and slot in the breadboard edge. I have had the table for 5 years now, no problems. I built one for my sister later and decided to take a short cut and just use some biscuits. The edge on this one has broken loose and is only held by the biscuits. It is almost 1/4" off on one end.
Darrell

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