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  1. #1

    Default gluing mdf end to end?

    I am going to be building a triskasub here very soon. I was hoping to build it out of a 2x4 handy panel of 3/4" MDF but I layed out the cuts tonight and it does not look like I can do it. I can get the sides and one top/botttom sheet but not the other. See the cut sheet graphic below.



    My question is if I could cut a 10"x13" piece off the end, then another 3"x13" piece from the upper right region then glue them together on the ends so as to make a 13x13 board. Well I know I can do that but what would I be losing by doing that? I am sure I could even use my dad's biscuit cutter and use biscuits to help attach the two pieces together. I always hear/read that the glue is stronger than the wood, so I shouldn't be losing any strength there, right?

    Yeah I am trying to be cheap.. but mostly I don't really have anywhere to store a piece of MDF properly so it would end up being warped within a few months.. kind of a waste in my opinion.

    Anyway, any input and knowledge are VERY much appreciated. Thanks in advance!

  2. #2

    Default Re: gluing mdf end to end?

    You should have no problems gluing MDF end to end, as long as your edges are straight and clean
    I recommend 2 part epoxy, fills gaps and is dense. Biscuits are a good idea, but with epoxy you probably don't need them. Maybe you can do a test glue up on some small pieces. Try biscuits and water based wood glue and then try some epoxy without the biscuits.
    I've never glued MDF end to end, but I've filled and repaired holes in MDF with 2 part epoxy.

    Quote Originally Posted by kfallscody View Post
    I am going to be building a triskasub here very soon. I was hoping to build it out of a 2x4 handy panel of 3/4" MDF but I layed out the cuts tonight and it does not look like I can do it. I can get the sides and one top/botttom sheet but not the other. See the cut sheet graphic below.



    My question is if I could cut a 10"x13" piece off the end, then another 3"x13" piece from the upper right region then glue them together on the ends so as to make a 13x13 board. Well I know I can do that but what would I be losing by doing that? I am sure I could even use my dad's biscuit cutter and use biscuits to help attach the two pieces together. I always hear/read that the glue is stronger than the wood, so I shouldn't be losing any strength there, right?

    Yeah I am trying to be cheap.. but mostly I don't really have anywhere to store a piece of MDF properly so it would end up being warped within a few months.. kind of a waste in my opinion.

    Anyway, any input and knowledge are VERY much appreciated. Thanks in advance!

  3. #3
    Join Date
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    Default Re: gluing mdf end to end?

    You can glue the MDF end-to-end. Use biscuits and yellow glue. Get a couple of clamps and put enough pressure that the glue starts to squeeze out. Take a damp rag and wipe off the excess glue/ I would glue up a piece so it's a little large than you need then trim it to size after the glue has set. That way you won't have to be so careful trying to line up the pieces you're gluing. Always try to wipe excess glue off MDF because when you try to sand it off, if you're not careful, you'll sand divots in the MDF around the glue before you get the glue completely off.

  4. #4
    Join Date
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    Default Re: gluing mdf end to end?

    Quote Originally Posted by Nowd View Post
    You can glue the MDF end-to-end. Use biscuits and yellow glue. Get a couple of clamps and put enough pressure that the glue starts to squeeze out. Take a damp rag and wipe off the excess glue/ I would glue up a piece so it's a little large than you need then trim it to size after the glue has set. That way you won't have to be so careful trying to line up the pieces you're gluing. Always try to wipe excess glue off MDF because when you try to sand it off, if you're not careful, you'll sand divots in the MDF around the glue before you get the glue completely off.
    +1 on biscuits to join plates. That's what they were made for. Like Nowd said, wipe up squeezeout before it dries because dried glue is harder than the MDF.

    Being a cheapskate sometimes, I've done this with interior braces. I also used edge joining for a set of large 4' long shelves I made for the university to hold student check-out equipment.
    Bill Schneider
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  5. #5
    Join Date
    Oct 2009
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    Chattanooga TN
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    253

    Default Re: gluing mdf end to end?

    Gluing edges is fine. The joint will actually be stronger than the MDF itself unless you use biscuits. Buiscuits bad. They may help with line up but are usually to sloppy (loose fit) to really help. They also add stress risers that actually make the joint weaker (studies have been done.

    Make sure edges straight flat smooth. Apply TiteBond II (only glue I use) to both sides. Dont skimp, glue is cheap, a bad joint costs real money. Clamp starting at one end and line up as you go across. Be quick as TB2 goes fairly quick. Clean glue and your done. Sponge and water ok but I would think that it may allow glue to seep into the MDF and affect the finish. I generally use an cheap wide chisel and scrappers (never your good chisels) to remove the excess.
    Good luck.
    http://www.crewesfurniture.com/

  6. #6

    Default Re: gluing mdf end to end?

    Just a thought

    If the cabinet is being painted won't the seam have a tendancy to show up over time? Maybe someone more experienced could answer for me.

  7. #7
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    Default Re: gluing mdf end to end?

    I've never been a fan of edge gluing MDF, but it should work so long as you aren't trying to make a 4' shelf out of 2 - 2' pieces, I don't think that would work very well. Personally I'd back up the joint on the inside with a 2" - 3" wide scrap of MDF or even a scrap of 1/4" ply or hardboard. I don't recall where the driver is located on the Triska sub, but if possible, put the splice on the bottom where it won't show.

    Brian Walter

  8. #8
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    Default Re: gluing mdf end to end?

    Quote Originally Posted by jeffa View Post
    Just a thought

    If the cabinet is being painted won't the seam have a tendancy to show up over time? Maybe someone more experienced could answer for me.
    It will, if you don't prep the MDF surface first. A coat of bondo, or even wood glue/water mix completely covering the surface. Then sand sand sand.

  9. #9

    Default Re: gluing mdf end to end?

    Quote Originally Posted by Pete Schumacher View Post
    It will, if you don't prep the MDF surface first. A coat of bondo, or even wood glue/water mix completely covering the surface. Then sand sand sand.
    I'm of the opinion that the seams will eventually emerge regardless.

    MDF already has moisture in it when you buy it, and surface treatment only seals the top fraction of a millimeter... the other 99% of the volume of the MDF still expands and contracts

    I question whether ANY surface treatment can ever completely eliminate emerging seams. (of course sealing the surfaces helps a lot, and is critical).
    Form does not follow function
    Form is simultaneous to function

  10. #10
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    Default Re: gluing mdf end to end?

    Quote Originally Posted by lunchmoney View Post
    I'm of the opinion that the seams will eventually emerge regardless.
    Does it matter on the bottom?

    And doesn't anyone scarf anymore?

  11. #11
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    Default Re: gluing mdf end to end?

    Quote Originally Posted by lunchmoney View Post
    I'm of the opinion that the seams will eventually emerge regardless.
    I agree if you're talking about ordinary but* joints. However I've had success IF the material orientation is the same for glued joints. The expansion of MDF must be anisotropic - in other words, different across the "grain" than through through it.

    Here's some evidence that if the grain aligns, there won't be a tendency to show joint lines. I made a coupler for a Linkwitz Pluto out of rings of MDF glued together...



    Here's the finished coupler, painted with Krylon semi-flat black from a spray can...



    It's been three years since I've built them, and there's absolutely NO trace of joint lines. (But who knows what will happen many years later).

    By contrast, my recently completed Overnight Sensations are already showing joint lines at the but* joints even though they were completely invisible in the days after painting. I even let the assembled cabinets "cure" a couple weeks before painting to see if that would minimize movement later, but lines still appeared.

    This makes me think that miter joints for cabinets might have a better chance of resisting line formation. I'd also bet that edge joined MDF will also be somewhat more resistant to joint lines because the expansion direction will be the same.
    Bill Schneider
    -+-+-+-+-
    One word = one milli-picture

  12. #12

    Default Re: gluing mdf end to end?

    Oh wow, I was not expecting this many replies.. thanks!

    As far as glue goes, I always use titebond. I tried the gorilla glue on my DIII's several years ago and gave up on it after just a few joints.. that stuff is WAY more trouble than it's worth in my opinion.

    I had planned on using biscuits but not if the will actually weaken the joint. This joint will be on the bottom so it won't have the stress of my feet sitting right on it, so not sure how big of a deal that would be.

    I am also building a set of overnight sensations and according to my cut layout, I should have a enough extra to cut a 13"x13" piece from the 1/2" MDF. I could just glue that to the bottom of my triska, giving a 1 1/4" thick base but then would have no worries of joint weakness. I think I might do that.. assuming the real world cutting matches up intended cut layout

    Again, thanks for all the input! Is very much appreciated. At least I know I am not planning on doing something really stupid

  13. #13
    Join Date
    Oct 2009
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    Chattanooga TN
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    253

    Default Re: gluing mdf end to end?

    Has any one tried several coats of shellac befor finishing. I'd try a 1 to 1 1/2 lb. cut. (a can of Zinzer is 3 lb. cut, dilute by 1/2 to 2/3 denatured alchohal) Apply 3 to 4 successive coats (20 - 30 min between) and let dry over night. I think the shellac will penetrate quite deep and will allow a very fine sanding. It will also be compatable with most any finish you wish to continue on with. Just a thought.

  14. #14
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    Default Re: gluing mdf end to end?

    I'm a big shellac fan, but straight Seal Coat doesn't prevent joint lines on but* joints.

    I didn't cut it with alcohol though, but used at least three coats - especially on end "grain" where MDF is thirsty. It was sanded dead flat after coating. Lines developed later under painted but* joints, and even showed under veneer on two builds. That really honked me off!

    I'm going with two layers of veneer on a Zaph ZDT3.5 to see if that helps. I've also waited 6 months (so far) without veneering to see if a long glue cure will help.

    Given my experences with but* joints I'm pessimistic, but someone could easily try experiments with cut shellac to see if joint lines are inhibited.
    Bill Schneider
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  15. #15
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    Default Re: gluing mdf end to end?

    If it were me, I would just go to Lowe's and have them cut the sheet in slightly larger sizes. Have them cut one full sheet down to 28" and whatever pieces you desire. The edge gluing is more work than it is worth.

    There is no substitute for raw glue on the end grain. Try for 2 coats. DO NOT CUT WITH WATER, this will exacerbate seem creep.

  16. #16

    Default Re: gluing mdf end to end?

    Biscuits really help with alignment. I successfully used biscuits and Gorilla Glue on some veneered MDF enclosures that I built. I chose Gorilla Glue, because it can be cleaned off the veneer with acetone.
    I often mention epoxy because it has not only superior strength, but fill properties too. Wood glue has little or no strength in a wide gap, not so with epoxy. Epoxy is way stronger than Titebond or Gorilla Glue. And if you let the epoxy overflow the glue joint, it will fill your glue joint. You will have no joint line problems other than some extra sanding to do.
    Think of industrial, aerospace and military applications. Would they use wood glue or epoxy?

    Quote Originally Posted by kfallscody View Post
    Oh wow, I was not expecting this many replies.. thanks!

    As far as glue goes, I always use titebond. I tried the gorilla glue on my DIII's several years ago and gave up on it after just a few joints.. that stuff is WAY more trouble than it's worth in my opinion.

    I had planned on using biscuits but not if the will actually weaken the joint. This joint will be on the bottom so it won't have the stress of my feet sitting right on it, so not sure how big of a deal that would be.

    I am also building a set of overnight sensations and according to my cut layout, I should have a enough extra to cut a 13"x13" piece from the 1/2" MDF. I could just glue that to the bottom of my triska, giving a 1 1/4" thick base but then would have no worries of joint weakness. I think I might do that.. assuming the real world cutting matches up intended cut layout

    Again, thanks for all the input! Is very much appreciated. At least I know I am not planning on doing something really stupid
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  17. #17
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    Default Re: gluing mdf end to end?

    Quote Originally Posted by View Post
    Biscuits really help with alignment. I successfully used biscuits and Gorilla Glue on some veneered MDF enclosures that I built. I chose Gorilla Glue, because it can be cleaned off the veneer with acetone.
    I often mention epoxy because it has not only superior strength, but fill properties too. Wood glue has little or no strength in a wide gap, not so with epoxy. Epoxy is way stronger than Titebond or Gorilla Glue. And if you let the epoxy overflow the glue joint, it will fill your glue joint. You will have no joint line problems other than some extra sanding to do.
    Think of industrial, aerospace and military applications. Would they use wood glue or epoxy?

    are those ceiling tiles i see in that attachment?
    THOMAS BROWN aka "STINKY"

    I've got an idea - an idea so smart that my head would explode if I even began to know what I'm talking about. - Peter Griffin

    I DON'T CARE WHAT KIND OF MUSIC YOU LISTEN TO, OR LIKE.
    SHUT UP, PUT DOWN THE WALLS OF PRETENSION FOR 1 SECOND AND JUST LISTEN TO THE SONGS
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  18. #18

    Default Re: gluing mdf end to end?

    Quote Originally Posted by Thomas Brown View Post
    are those ceiling tiles i see in that attachment?
    Yes, acoustical ceiling tiles.
    A trick I learned from my mentor Henry Wolcott.

  19. #19

    Default Re: gluing mdf end to end?

    So what kind/brand of epoxy would you suggest? I'm willing to give it a shot, especially if it will give a stronger bond and mean less finishing work. I have never been able to avoid the dreaded seams eventually showing up on my speakers

    Quote Originally Posted by View Post
    Biscuits really help with alignment. I successfully used biscuits and Gorilla Glue on some veneered MDF enclosures that I built. I chose Gorilla Glue, because it can be cleaned off the veneer with acetone.
    I often mention epoxy because it has not only superior strength, but fill properties too. Wood glue has little or no strength in a wide gap, not so with epoxy. Epoxy is way stronger than Titebond or Gorilla Glue. And if you let the epoxy overflow the glue joint, it will fill your glue joint. You will have no joint line problems other than some extra sanding to do.
    Think of industrial, aerospace and military applications. Would they use wood glue or epoxy?

  20. #20

    Default Re: gluing mdf end to end?

    Quote Originally Posted by kfallscody View Post
    So what kind/brand of epoxy would you suggest? I'm willing to give it a shot, especially if it will give a stronger bond and mean less finishing work. I have never been able to avoid the dreaded seams eventually showing up on my speakers
    The epoxy I use, I buy at Tap Plastics. It's kind of expensive, they sell it by the pint, quart and gallon. But I'm sure you could get a smaller quantity of just about any liquid epoxy at your local hardware store. Slow to medium set. Equal parts resin and hardener, amber color.
    http://www.tapplastics.com/shop/product.php?pid=28&

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