Replies

1. 
   coolbreeze | Feb 07, 2007 08:30pm | #1

   I have not used biscuits on MDF. I suspect that the problem is that the glue has coused tight biscuit to swell. I personally do not use MDF anywhere a joint of any strength is needed. Just don't do it.  Also, placing screws requires pre-drilling the screw holes at least as wide as the D of the screw or you will have bulging.

   Did not offer help, but the reply is JMHO and is intended for any reader who has not yet used MDF as indicated in your post.

   "Coaches who listen to the fans will soon be sitting with them"  Bobby Knight

1. 
   WingNut | Feb 07, 2007 09:08pm | #2

   Thanks Breeze,

    <!----><!----><!---->

   I think the project my buddy was working on was a fireplace surround.  He was using MDF for the surround’s backing so there was no force pulling the biscuit joints.  All the force was downward.  He needed a way to align the top, horizontal panel to the two side, vertical panels.  He got it assembled on the floor, tipped it up on the wall and then strategically screwed the whole surround the wall.  By strategic I mean he placed the screws in places where he was planning later to cover with various trims and moldings.  It was at the point that he was installing the moldings that he noticed the bulging.  I think he left the whole thing and came to my house to watch the Super Bowl.  He knows he probably has to start over but he’s trying to figure out what happened to avoid it again.  He was considering using pocket screws to join the panels together but he feels that pockets screws won’t give him the bite necessary for MDF. 

2. 
   jeff100 | Feb 07, 2007 09:21pm | #3

   Biscuits do swell, that's how they work, and why it's important to keep them dry.  The swelling helps perform a mechanical lock, aiding the adhesive.  My guess is that the moisture in the glue also caused the MDF to swell.  So there's likely two things going on here, the swelling of the biscuit and the swelling of the MDF.  Hence, it's noticeable in the exterior of the finished product...

   Jeff 

1. 
   WingNut | Feb 07, 2007 09:29pm | #4

   Thanks Jeff,

    <!----><!----><!---->

   For my own education…

    <!----><!---->

   When using biscuits in MDF, should I only use snug fitting biscuits with no glue?  Again, I’m only referring to situations where there are no structural stresses on the joint.  Situations like the one my buddy was in where he was only using the biscuits to align and flush everything up before screwing to the wall. 

    <!----><!---->

   I have a few MDF projects in the pipeline and I want to avoid my buddy’s problem. 

1. 
   Belcoron | Feb 07, 2007 09:56pm | #5

   As moisure seems to be the problem here, is there a glue that could be used that would be wicked up less by the mdf and the buscuit? Polyurethane perhaps? Also I wonder if using a very small amount, a spot in the middle on edge of the buscuit?

2. 
   jeff100 | Feb 07, 2007 11:38pm | #6

   Let me clarify what I said earlier. Biscuits do wick up moisture and swell, that's why it's important to keep them dry 'before you use them'...OK, on to the next question. If the biscuits are being used for alignment only, then I suppose there's no harm in not gluing them. If it were me, I'd consider doweling in MDF instead of biscuits. Don't misunderstand, I use biscuits all the time & have no problem with biscuits. The dowels wouldn't swell is all, and you'd get your alignment and not have to worry where the glue is going. Swelling is always going to be a problem with MDF though and that's why I don't use MDF for any finished product. Baltic Birch is much preferred by me if I need a flat surface and don't want to use hardwood, or when I need a core material. Another person suggested a different glue and I agree that might be a good approach as well. Perhaps even an epoxy? Wouldn't be much wicking with that!! Good luck.Jeff

   Edited 2/7/2007 3:39 pm by jeff100

1. 
   WingNut | Feb 07, 2007 11:51pm | #8

   Thanks Jeff, I like your suggestion on using Birch plywood.  That may be a solution for my bud to look into to.  I also like the dowel suggestion for future projects.  I’m going to look into using polyurethane glue as Belcoron suggested. 

3. 
   nikkiwood | Feb 07, 2007 11:48pm | #7

   Every now and then you hear about someone who has had a problem with this.

   I've used a lot of biscuits over the years, and I've not had a problem.

   I wonder if your friend 1) cut the biscuit slots too close to the "show" surface, and/or 2) applied too much glue to the slot.

   ********************************************************
   "It is what we learn after we think we know it all, that counts."

   John Wooden 1910-

1. 
   WingNut | Feb 08, 2007 12:03am | #9

   Hey nikkiwood, I bet that’s exactly what happened.  He was probably just a bit too liberal with the glue and when that already tight fitting biscuit expanded it created that bump the “show” surface.  Do you use biscuits and glue when you use MDF?  In reading some of the earlier comments I think I may start skipping the glue (or use polyurethane glue) and just go with tight fitting biscuits to align everything and then chase as normal with screws. 

1. 
   nikkiwood | Feb 08, 2007 12:57am | #10

   I use biscuits in MDF of plywood with a fiber core all the time. If the biscuits fit tightly in the slot (without glue), that's a sign they have taken on ambient moisture. In that case, you should either toss them, or sometimes you can bring them back by giving them a dose of heat in the microwave. Many people like the polyurethane glues, but they are too messy for my taste -- and hard to remove the squeeze out. When gluing biscuits, I use a spritz of glue in each slot, then swab it with an acid brush (the small ones just fit the slot), then use a roller applicator to apply a thin layer of glue across the edge.********************************************************
   "It is what we learn after we think we know it all, that counts."

   John Wooden 1910-

1. 
   Rich14 | Feb 08, 2007 01:39am | #11

   "Many people like the polyurethane glues, but they are too messy for my taste -- and hard to remove the squeeze out "

   I really like polyurethane glue because it is so easy to remove the squeeze out. It's almost paradoxical that it's described as messy.

   First, of course, it's best to apply just the right amount so there is not a lot of clean up to do. When the foaming has stopped, and before the squeeze out is firm, wipe it away with an acetone-wet rag. The wood will be absolutely clean of glue with no staining whatever. Very nice.

   Other than hot hide glue, which can be removed as though it were rubber cement, if you get it just at the right time after glue-up, leaving absolutely no residue, polyurethane is very pleasant to use. The open time is long, which is good. The downside is that it requires upwards of 12 hours of clamping time.

   Rich

1. 
   nikkiwood | Feb 08, 2007 02:49am | #12

   I'm glad it works for you. But I hate the stuff, and will use it only when absolutely necessary.********************************************************
   "It is what we learn after we think we know it all, that counts."

   John Wooden 1910-

4. 
   BossCrunk | Feb 08, 2007 03:59am | #13

   The Industrial Strength Woodworking forum (iswonline.com) is a place frequented by guys who build tons of bulk cabinet products with biscuits and sheet goods.

   Might as well go to the source.

   We sip tea and pine after Cuban Mahogany around here.

   And biscuits can telegraph through sheet goods.

   
   

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   Edited 2/7/2007 8:39 pm ET by BossCrunk

5. 
   eddiefromAustralia | Feb 08, 2007 09:47am | #14

   Hi WingNut,

   This is a common situation.

   You're probably aware that wood swells when wet and shrinks when dry, and that compressed (bruised) wood can be made to swell back to original size by leaving it under a damp tissue. Biscuits are sold compressed (about 3mm thick) and swell back to 4mm thick when wet or if left in a humid environment for a few months. The biscuit slot cutter is 4mm wide, so biscuits, ideally, swell to fit the slot. If the glue sets before the biscuit swells fully, remaining moisture in the sheet material swells the biscuit further and causes the surface of the material above the biscuit to stand proud, so the biscuit telegraphs through to the surface.

   As I prefer to finish in satin, it's not been an issue (yet) but it's well warned against by others.

   The biscuits, as other posters have intimated, often telegraph through to the surface. On gloss projects, I dowel in preference to biscuiting where possible, having been forewarned.

   Best regards,

   eddie

   Edited 2/8/2007 1:54 am by eddiefromAustralia

   
   

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   Edited 2/8/2007 2:01 am by eddiefromAustralia

1. 
   Lataxe | Feb 09, 2007 01:53am | #15

   Eddie,

   You mention that, "Biscuits are sold compressed (about 3mm thick) and swell back to 4mm thick when wet".

   I have been reading a bit about various biscuits and their provenance just lately.  There are quite a few types, in terms of the material used and the degree of initial compression applied by the manufacturer.

   However, I know of no biscuit that is compressed to 3mm but will swell to 4!

   I like Lamello, Tanseli and Trend biscuits.  These are beech, although Lamello do some of "fibre" too.  The beech ones are compressed and sold at around 8-10% moisture content.  The Lamello fibre biscuits are a laminate, or ply, of 3 layers, as are the Tanseli beech ones.  The single-layer biscuits have the grain oriented at an angle to the long axis of the biscuit.

   They all start at 3.9mm (at 10-12% mositure content) and expand to no more than 4.4mm when wetted and left to exapnd freely.  (I have measured this more than once).  They should fit into the 4mm jointer kerf snugly (no wobble) but not very tightly - unless they got wet or have been in high humidity.

   Inside a joint, they expand to fill the 4mm of the biscuit-joiner kerf tightly but do not cause a "bump" unless the material in which they are located is soft (eg MDF, white pine, cheap plywood, etc.) and/or the biscuit is too close to the surface (less than 4mm).  I imagine you can keep the pressure down by reducing the moisture/glue, as has been mentioned above.

   American-made biscuits are mostly birch and generally uncompressed.  Wetting makes them expand but not quite as much as the European beech ones, or so I read (never used any myself).  Some reports state that the birch biscuits are manufactured to lesser tolerances than the European ones; whilst others say that birch is inherently less stable than beech and this causes the "lesser tolerance".

   There are also some cheap biscuits from various places in Europe and the Far East that are very poorly made.  They generally have no brand or are re-branded as some ultra-cheapie line.  They break, are too thin or fat, made of various material and best avoided.

   Lataxe

1. 
   eddiefromAustralia | Feb 09, 2007 10:46am | #16

   Hi Lataxe,This was the manufacturer's rep talking.I use Lamello.Next time I open a box (sold hermetically sealed,) I'll measure a few if I remember and post the result.I'd say the original thickness is far less than 3.9mm, as you can really slop a biscuit around in the slot when it's new and dry.For the americans, 1mm = 40 thou or thereabouts.Bear in mind that the compressed thickness is the most compressed part of the biscuit.Even a biscuit that's old can be forced in a slot, albeit far easier if you re-compress it in an engineer's vice. Must make them about 4mm, but I'll defer to your measurements here, as supposition comes second.Cheers,eddie

1. 
   Lataxe | Feb 09, 2007 04:10pm | #17

   Eddie,

   Aha!  You have inspired me and now we are into the interesting minutiae of biscuity thangs.  What could be more fascinating?  :-)  I have been at all my biscuits with the micrometer, one of those with a pressure-limiting ratchet to make sure there is no undue squish from the micrometer jaws.

   Here is what I found with my dry biscuits:

   Trend (from a sealed bag): 3.75mm thick +/- .02mm (3.73 - 3.77mm) variation over a sample of ten.

   Trend from a box that has been open in the house for months: 3.85mm thick +/- 0.04mm (3.81 - 3.89mm) variation over a sample of 10.

   Lamello (sealed): 3.80mm with no detectable variation over a sample of 24 (8 each of 0, 10 & 20).  Amazing QC!

   Lamello opened in the house for some months: 3.9mm with +/-0.02mm variation (3.88 - 3.92mm) over a sample of 10.

   The house is usually between 55 - 60% humidity and furniture registers at circa 10% moisture content with a Wagner moisture meter.

   I can tell you that in over 3000 biscuits, I have never had a sloppy one in a slot.  I have had tight ones, presumably because they got more humid than usual for some reason.  If you have sloppy biscuits, is this because your climate is very dry?  Or is there some other underlying cause, I wonder?

   Lataxe, performing experiments on innocent little biscuits.

2. 
   jackplane | Feb 09, 2007 04:14pm | #18

   eddie,

   where have you been?

   surfing off the coast of Queensland? welcome back.Expert since 10 am.