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Thread: Dumb questions for the day

  1. #1
    Don Taylor is offline Former Member (by the member's request)
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    Dumb questions for the day

    I finally unloaded the big worktable and have begun to replace the top.
    I'm going to line the three sheets up, (Two sheets of MDF and one of Masonite) clamp them so they won't shift and use the Festool guide rail system to trim them to size all at the same time.
    I have never made anything with MDF so I'm a little worried about certain steps.

    Dumb question #1 should I glue the two MDF sheets together? If so, what is the best glue to use? Would Titebond III be good enough?

    Dumb question #2 Do both sheets have to have glue on them? Working alone, it would be quite a trick getting one messy sheet on top of another without getting glued to the table myself.

    Dumb question #3 I am REALLY paranoid about putting screws into MDF. The holes in the table braces are already there from the other top.
    Should I pre-drill the MDF as well or just screw into it? (From the bottom)
    Would the sheet rock screws I used for the other top work ok or do I need a special wood screw?

    Dumb question #4 is there any reason I should not use the DowelMax for the 2X4 trim?






    Thanks in advance

    DT
    Last edited by Don Taylor; 07-03-2007 at 12:52 AM.

  2. #2
    Don, Here are my dumb answers,
    Wes
    Quote Originally Posted by Don Taylor View Post

    Dumb question #1 should I glue the two MDF sheets together? If so, what is the best glue for to use? Would Titebond III be good enough?
    Dumb Answer #1 I wouldn't glue them - my bench isn't glued and has been together for a lot of years without movement - why you ask? Because one day I'll need to remove it!! Titebond III works fine on MDF.
    Dumb question #2 Do both sheets have to have glue on them? Working alone, it would be quite a trick getting one messy sheet on top of another without getting glued to the table myself.
    Dumb Answer #2 I usually glue one side, then drop the other onto it and slide it around.
    Dumb question #3 I am REALLY paranoid about putting screws into MDF. The holes in the table braces are already there from the other top.
    Should I pre-drill the MDF as well or just screw into it? (From the bottom)
    Would the sheet rock screws I used for the other top work ok or do I need a special wood screw?
    Dumb Answer #3 I put drywall screws into mytop from underneath - yes they were predrilled. Conformat screws are better for cabinet work etc, but for this application drywall screws have worked fine for me.
    Dumb question #4 is there any reason I should not use the DowelMax for the 2X4 trim?
    Dumb Answer #4 Don't know why not?

  3. #3
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    Don,

    IMHO, you should sand the mating surfaces of the MDF before applying glue. I really don't like TB III and prefer I or II, but thats a personal thing based on what must have been some bad TBIII. Screws in MDF tend to push out where they join. It is better to drill through one sheet, then relieve the mating side. This gives the displaced MDF some place to go. I used dry wall screws on my work bench top and don't have a problem with them. Don't know anything about the dowel max.

  4. #4
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    Quote Originally Posted by Matt Dunlap View Post
    Also after you pre-drill, if possible, counter-sink both sides of your MDF. When you screw into MDF, it will lift the paper and without a counter-sink, the paper will cause a bulge and your MDF won't be perfectly joined.
    Same thing I have read, counter sink for sure.
    Rise above the rest

  5. #5
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    Dumb question #1 should I glue the two MDF sheets together? If so, what is the best glue for to use? Would Titebond III be good enough?

    - I used TB II. I use a pastry roller to spread the glue. Its kinda like a short paint roller but covered with a silicone rubber sleeve. Spreads fast and even, great for large areas.

    Dumb question #2 Do both sheets have to have glue on them? Working alone, it would be quite a trick getting one messy sheet on top of another without getting glued to the table myself.

    - I just put glue one side.

    Dumb question #3 I am REALLY paranoid about putting screws into MDF. The holes in the table braces are already there from the other top.
    Should I pre-drill the MDF as well or just screw into it? (From the bottom)
    Would the sheet rock screws I used for the other top work ok or do I need a special wood screw?

    - When screwing into MDF you should have a pilot hole that is the correct size and just a bit longer than the screw. Hardcore advise is to pilot drill both pieces at once, separate and slightly countersink the holes where the surface will mate to avoid dimple-factor. I've done with and without.

    Dumb question #4 is there any reason I should not use the DowelMax for the 2X4 trim?

    - If you mean to connect the trim to the MDF core around the edge, sure. I just generously glued and clamped mine, no problems in 2 years and I clamp stuff to the top using the edge for part of the support.
    Last edited by glenn bradley; 07-03-2007 at 05:50 AM.
    Any sufficiently advanced technology is indistinguishable from magic.
    - Arthur C. Clarke

  6. #6
    Don Taylor is offline Former Member (by the member's request)
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    Ok, no glue, (Thank goodness!) I'll pre-drill and countersink screws the length and width of the top.

    As for the Masonite. My plan was to raise the border the width of the sheet and not attach it at all. That way I can replace it easily.

    I thought of another thing. I don't think screws into MDF would support a vise and it's different uses. How about a nice flat bottom Forstner bit hole and bolt the suckers on?

    Thank everyone

  7. #7
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    Hey Don,
    Well, here's my two cents (highly inflated) worth...

    Personally, I really don't like to use metal fasteners on tabletops. If you must, screw from underneath and be sure the screws end well before the top surface.

    The weight of the mdf is going to keep it down, so all you have to control is horizontal movement. If you like dowels, I don't see why you couldn't dowel into the mdf....

    If you do glue, the mdf really sucks up glue, so plan to use a lot. Glenn's idea of applying with a roller is good advice.

    MDF would basically be useless for holding down your vise. Bolting is a good idea. You might screw the vise onto a piece of plywood and then bolt the ply to the table, with another piece of ply on the bottom.

    Looks like a real handy table!
    Don't believe everything you think!

  8. #8
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    Don,

    What everyone else said. Except: It's true the weight of one sheet will hold it down, but it won't keep it from sliding around. So I'd be tempted to not screw or glue, but shoot it in several places with inch and a quarter 18g brads. Enough to hold it in place, but not so many that I could never pry it apart. Which brings up the next point: I can't see underneath to see what the support structure looks like. Believe it or not, two sheets of MDF will sag under their own weight across a surprisingly short span... not today, not tomorrow, but the next day... Learned that one the hard way...

    Thanks,

    Bill

  9. #9
    Don Taylor is offline Former Member (by the member's request)
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    Quote Originally Posted by Bill Lantry View Post
    Don,

    What everyone else said. Except: It's true the weight of one sheet will hold it down, but it won't keep it from sliding around. So I'd be tempted to not screw or glue, but shoot it in several places with inch and a quarter 18g brads. Enough to hold it in place, but not so many that I could never pry it apart. Which brings up the next point: I can't see underneath to see what the support structure looks like. Believe it or not, two sheets of MDF will sag under their own weight across a surprisingly short span... not today, not tomorrow, but the next day... Learned that one the hard way...

    Thanks,

    Bill
    Hi Bill,

    I also wondered about the 18g brads, good idea. But then I don't like the idea of metal in the table as Jesse mentioned.

    The table has 1X6 braces every 2'. I didn't want to worry at all about sag. I am really not concerned about re-using the MDF, just being able to replace the Masonite. There will be a border doweled and glued all the way around it.



    How about using 16g brads to tack the first sheet of MDF to the table, drill that piece for the dowels to the trim and then lay the second sheet of MDF and the Masonite as floaters? They won't be able to move for the trim....

    DT

  10. #10
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    If you lay two sheets of MDF together without glue, it is twice as strong and stiff as one sheet. If you glue the two sheets of MDF (or anything) together, so they become one sheet that is twice as thick, it is eight times as strong and stiff as one sheet.

    When I do a project like that, I glue using Carpenter's glue (same as Titebond I, but without the advertising budget). If it is small, I clamp it in a vacuum bag, but realistically, I drive enough drywall screws from the bottom to effectively be a clamp over the whole surface. Predrill is nice, but you should be able to tell if it is being spread apart or pulled together by the screws - do what you have to. When the glue is dry, I remove the screws so they don't sneak into play later when it is least expected. If you glop a lot of glue on, one side should be fine, as long as you screw or clamp it together enough to squish the glue around.

    I would use trim thinner than 2x4... I often clamp work to the bench, and wouldn't want to just clamp it to the trim.

    I didn't see any dumb questions... sorry I couldn't help. The dumb questions are the ones you are afraid to ask.
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at www.solowoodworker.com

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