Replies

1. 
   DennisS | Jun 01, 2005 03:37am | #1

   I've been on jobs where biscuits were used successfully for MDF joinery, the only thing you have to be cognizant of is - when the biscuits swell, as they're designed to do, they can often cause a perceptible irregularity on the surface of the MDF. You probably wouldn't notice it until you start laying down your finish, if indeed the MDF will be finished and exposed.

   Unreinforced butt joints would be pretty inefective I would think. If looks aren't a concern, consider pilot holes and countersunk drywall screws for butt joints. Dado joints would provide more resistance to shear depending on the loading of the joint. But little resistance to moment or racking force. Dowels, in MDF, would perhaps be as effective as biscuits but biscuits are, in my opinion, easier and faster.

   What's the nature of your project?

   ...........
   From Beautiful Skagit Co. Wa.
   Dennis
2. 
   KeithNewton | Jun 01, 2005 05:33am | #2

   Butt joints glued and stapled, spackled and sanded.
   There are also some KD fittings that work pretty well if you have the templates or drilling set-up to get the holes right.

3. 
   Routerman | Jun 01, 2005 05:41am | #3

   Jig in pix link has shallow t&g, followed x four 1/4-20 x 1-3/4 capscrews captured in threaded steel x-dowels. No glue, made to dissassemble.

4. 
   jackplane | Jun 01, 2005 04:06pm | #4

   It depends! All the methods you describe work well. How would you join if it were plywood? What matters is the load and force on the joint.

    

5. 
   Jellyrug | Jun 02, 2005 04:15am | #5

   I have never experienced problems gluing MDF, using yellow PVA glue, in any joint. No end grain to bother about.

   If you research the technical stuff published by the manufacturers, they claim a stronger than glue joint for butt joints. Biscuits will help align, but not necessarily add strength.

1. 
   WillGeorge | Jun 02, 2005 08:28pm | #6

   Biscuits will help align, but not necessarily add strength.

    Not true.. Take some scrap MDF...  GLue with and without with Biscuits and try to bang them apart!  I have,, 

1. 
   Jellyrug | Jun 02, 2005 08:33pm | #7

   I guess with MDF this is possible, as the tensile strength properties of the biscuit may be higher than the MDF itself.

   How long did you cure the joints and what failure did you get, MDF, or glue failure?

1. 
   WillGeorge | Jun 04, 2005 01:48am | #10

   I did a 'test' once... SEVERAL heavy hammer blows later.. The MDF  AND  The Biscuits BOTH broke..!

   EDIT::: MDF is OK if ya can stand the dust!

   MDF sort of shears off in sort of random layers??? Biscuits sort of follow the layers...

   Edited 6/3/2005 6:50 pm ET by Will George

   Edited 6/3/2005 6:51 pm ET by Will George

2. 
   WillGeorge | Jun 05, 2005 04:10am | #12

   Both failed.. But I was hitting it to make it break just to see what would happen..

   MDF broke in chunks and it took much harder blows to break the joint when biscuits were used..

2. 
   XNDSN | Jun 03, 2005 02:35am | #9

   Mr George is absolutely correct regarding the added strength achieved using biscuits in MFD construction.

   In fact, a test performed and reported in Fine Woodworking more than 5 years ago indicated that biscuits create a joing stronger than the MFD itself.

   The test comparred the load handling ability of various joining methods such as screws, glue and biscuits holding  a stack of magazines laying on a cantilevered ( unsupported horizontal ) shelf. The biscuits won hands down. The impressive point was the photo depicting the mode of failure: The vertical piece of MFD tore diagonally indicating that the joint was stronger than the base MFD.

6. 
   Andrew | Jun 03, 2005 01:32am | #8

   I tried using PL premium glue (polyurethane construction adhesive) for glueing MDF and it is amazing. Way stronger than PVA glued joints, just try not to get any on your hands.

   Andrew

7. 
   AlbionWood | Jun 04, 2005 05:57am | #11

   Biscuits and poly glue - it won't make the biscuits swell, and won't get lost into the edge-grain of the MDF the way PVA can. PL Premium is probably the best for this.

   "Everything should be made as simple as possible, but no simpler."  A. Einstein

   http://www.albionworks.net

1. 
   WillGeorge | Jun 05, 2005 11:53pm | #13

   Biscuits and poly glue - it won't make the biscuits swell

    I thought ya sprawed water on joints with POLY GLUE!

1. 
   AlbionWood | Jun 06, 2005 12:32am | #14

   Not in my climate (70% humidity)!You only spray water if the wood is so dry that there isn't enough moisture to react with the glue. For me, not a problem. For the guys in Moses Lake, Washington - big problem!PU glue has other problems, but it's pretty good for MDF, in my experience."Everything should be made as simple as possible, but no simpler."  A. Einstein

   http://www.albionworks.net