Biscuits with MDF??

[George Bokros]

Anyone use biscuits with MDF for alignment of a joint gluing two pieces of MDF together?

I do have a doweling jig so I could use that as an alternative.

[glenn bradley]

For alignment, I would use what you prefer. For glue strength, the MDF will fail before the biscuit or dowel. For mechanical strength the dowel would probably win due to depth but, joint type, material thickness and so much more could make that a long discussion if one were so inclined ;-)

[Yonak Hawkins]

I wonder, when exposed to glue, if MDF biscuits would swell, for good or bad.

[Sam Murdoch]

For alignment - no issues whatsoever and they will help to secure the joint. I have used them frequently to attach solid wood edging to MDF panels too - though these day I prefer the Domino.

[Malcolm McLeod]

I wonder, when exposed to glue, if MDF biscuits would swell, for good or bad.

Biscuits that are too close to the surface can 'telegraph' thru to the show surface because they do swell. I know this is true for hardwood (DAMHIKT), and suspect that MDF might be even more susceptible - because the MDF may swell some too. So, be careful where you locate biscuits, or any glued fastener I guess, in an MDF joint. Try to keep them away from the show sides, or at least centered.

[Wayne Lomman]

Gets used all the time commercially to make concealed joint cabinets out of veneered mdf. It's plenty strong enough. Try knocking it all apart after you find out the job site measurements were wrong. Its far superior to dowels for this task. Cheers

[Frank Pratt]

Biscuits don't seem to get much respect these days, but they excel joining sheet goods. I you're careful with layout & cutting the slots, and use lots of glue, they produce a very strong joint.

[Mike Henderson]

I find that MDF glues fairly well without anything (biscuits, dowels, dominos) but whatever you use, it does add a bit of strength. With regular wood, when you try to break a joint, it usually breaks somewhere other than the joint. With unreinforced MDF, it often breaks on the joint.

Mike

[Doug Garson]

Biscuits that are too close to the surface can 'telegraph' thru to the show surface because they do swell. I know this is true for hardwood (DAMHIKT), and suspect that MDF might be even more susceptible - because the MDF may swell some too. So, be careful where you locate biscuits, or any glued fastener I guess, in an MDF joint. Try to keep them away from the show sides, or at least centered.
I think the question was whether biscuits made out of MDF would swell like normal biscuits and whether that would be good or bad. Can the problem with swelling biscuits be corrected by sanding the surface after the glue up dries?

[Mike Henderson]

I think the question was whether biscuits made out of MDF would swell like normal biscuits and whether that would be good or bad. Can the problem with swelling biscuits be corrected by sanding the surface after the glue up dries?

The problem you get into is that the biscuits swell and then you sand. Then the biscuits lose some of the moisture and shrink. Then you have a divot in your panel where the biscuits are - especially noticeable after you apply finish. To avoid that, you have to wait quite a while to make sure the moisture has equalized before sanding.

Mike

[Malcolm McLeod]

...whether biscuits made out of MDF...
I didn't pick up on that subtlety from Yonak. (I guess I inserted a 'with' in there - - MDF with biscuits.) In which case you're on your own! I have no clue.

[George Bokros]

I am not using biscuits made out of MDF. I am using regular biscuits joining MDF pieces.

[Peter Kuhlman]

As Mike said, watch out for swelling at the biscuit location. I did that once sanding shortly after joining and ending up with divots. I prefer dowels for this as less swelling and can get sanding if needed sooner. Both methods work fine. Actually MDF just glued together is stronger than you might think. Depends upon the usage. I have built many speaker cabinets and never used any type additional fastener without problems. Lock miter joints are preferred.

[Yonak Hawkins]

Sorry, George, I missed the "with". Please disregard my comment.

[Martin Wasner]

I don't see the point in biscuits. My use for them is limited to putting stools on windows and putting mitres on handrail together.

Just adjust the joint as you work down the individual clamps.

Another option is to spline it, but once again, I think it's a waste of time.

[Tim Bueler]

A couple of years ago, 20 or so, I installed some MDF baseboard in a kitchen. Start at a wall, around a peninsula, across a bank of cabinets, another inside miter to the end of the cabinet, then mitered back to the wall. All in all 5 - 90 degree turns over 20 odd feet. Glued and pinned all joints as I went. Homeowner changed her mind on the flooring so the base had to come out. I'll be danged if it didn't come out in one piece (no lie!). Three of us very carefully carried the base into an adjacent room and when the replacement flooring was installed we carried it back and re-installed it. Fit perfectly. Glue with a couple of pins is all that held the joints. The glueability (is that a word?) of MDF is amazing.
Tim

[Chris Fournier]

I've used thousands of biscuits in this sort of application, they are quick and effective.

[Curt Harms]

The problem you get into is that the biscuits swell and then you sand. Then the biscuits lose some of the moisture and shrink. Then you have a divot in your panel where the biscuits are - especially noticeable after you apply finish. To avoid that, you have to wait quite a while to make sure the moisture has equalized before sanding.

Mike


That's my understanding as well. I wonder if limiting water based glue in the biscuit slots or using a non-water based glue for the biscuit slots (polyurethane or something?) would help with the MDF swelling? I found it instructive to cut some biscuit slots, put some glue in them, insert a biscuit then remove it - I usually need pliers. it doesn't take much glue to coat the slot and biscuit. I've used biscuits a fair bit with plywood but not that much with solid wood. I didn't notice any issues with biscuit divots where I've used them.

[Chris Padilla]

http://www.sawmillcreek.org/showthread.php?42603-Mirror-Frame

George,

Have a gander at the thread above where I built a mirror frame. That was over 10 years ago. I used biscuits to reinforce the MDF to poplar connection (fancy top) and I'm still waiting for it to fail! :)

[William Fretwell]

I've used thousands of biscuits in this sort of application, they are quick and effective.

Quite right! Just get the right amount of glue in the slot with minimal squeeze out. Biscuits are wonderful! Friend of mine built a cherry end table with biscuits! Imagine! A TV featured wood turner at that!

[Myk Rian]

I did a demo for our wood group last month. Butt joined MDF with TB3. Had to stomp on the joint to break it. No biscuits, dowels, pins, etc.

[Howard Rosenberg]

I have a question for you - how big is the object you're gluing up that you can't just cut it out of a single sheet?

Otherwise, I'd say the MDF will glue up very nicely with just butt joints alone. I have made many, many frame and panel components with just butt joints. But if you must use a joint-creating device, my gut feel tells me biscuits would be a better choice for just alignment.

Howard

[George Bokros]

I am using some pieces I have laying around from a project that got canceled but had already been cut.

[Mel Fulks]

MDF is made of pretty small pieces ! A few more pieces won't make any difference or a bad grain match! Yeah, it's fine to glue the pieces and use it up.

[mike wacker]

MDF is magical stuff. Straight from the pile it's perfect. Can stay perfect for next to forever. Too much glue in a biscut joint it expands and your done. If your jigs made from it are not kept in "decent" climate control they can explode. My assembly table (3x7) flooded 4 times on the top, 2 times underneath with water based finish remains DEAD flat. Router table covered in formica, based some what on "Norm's" design is a twisted sister. Your mileage may vary.