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Thread: Gluing Douglas fir to hardwood butcher block top (and general bench design questions)

  1. #1

    Gluing Douglas fir to hardwood butcher block top (and general bench design questions)

    I am new to woodworking, which will probably be readily apparent as you read the below

    I've got an 8' craftsman butcher block workbench top that I've had laying around, and I'd like to use it as the top for a woodworking bench: https://www.kmart.com/craftsman-8'-b...p-00914965000P

    Two issues:
    1. It's 1 3/8" thick - I'd like a thicker top to allow me to use holdfasts
    2. I need to figure out a way to attach the top to a base. The workbench will be in a detached garage in Pennsylvania, so will experience significant fluctuations in temperature and humidity.

    Questions:
    1. How likely am I to run into issues if I face glue a couple of kiln dried Douglas fir 2x12s to the underside to get me the bench top thickness I want? Sears says the top is made of rubberwood/parawood - looks like shrinkage is on the low side: https://www.wood-database.com/rubberwood/
    2. What would be the downsides of the below design (view from end of bench, would also have stretchers lengthwise mortised, all stretchers 2x6)? Legs would be 3 laminated 2x6s, with the vertical dotted line indicating the middle 2x6 extending into a cutout in the 2x12. I'd then put dowels through apron/leg/2x12 underside of bench top. Is there a better and/or easier design I could use?
    workbench.JPG

    Hope this makes sense, please let me know if unclear. Appreciate any thoughts/suggestions!

  2. #2
    Join Date
    Dec 2007
    Location
    Berwick, PA
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    42
    Hi Dave! I don't know anything about that kind of wood, but if it were me, I'd see about using something mechanical rather than glue to allow for differences in wood movement. I'd also consider wider aprons front and back to minimize racking.

    Lots of PA folks on here!

  3. #3
    Join Date
    Mar 2003
    Location
    San Francisco, CA
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    8,739
    Kiln dried construction lumber like that Doug fir is usually dried to 19% EMC. Thatís enough to prevent mold growth, which is what framers care about. However, indoors wood is going to dry down to 9% or so, which means it will shrink, and maybe warp.

  4. #4
    Quote Originally Posted by James Brown View Post
    Hi Dave! I don't know anything about that kind of wood, but if it were me, I'd see about using something mechanical rather than glue to allow for differences in wood movement. I'd also consider wider aprons front and back to minimize racking.

    Lots of PA folks on here!
    Thanks James. My concern if I go with something mechanical to allow movement is that it would potentially lead to the dog holes being misaligned, which would defeat the purpose of what I'm trying to accomplish!
    Regarding the aprons - I could certainly go wider. I was actually more worried about the top 1/3 of the apron where it would meet the edge of the 2x12 and whether that area would have sufficient strength to prevent racking. Was planning on using a couple of 1/2 dowels per leg. Not sure if it'd make sense to add transverse support ribs underneath the top.

    Quote Originally Posted by Jamie Buxton View Post
    Kiln dried construction lumber like that Doug fir is usually dried to 19% EMC. Thatís enough to prevent mold growth, which is what framers care about. However, indoors wood is going to dry down to 9% or so, which means it will shrink, and maybe warp.
    Thanks Jamie, I neglected to mention in my initial post that the 2x12s are currently measuring at 8%. The butcher block is just over 5%. Both have been in my garage for the better part of two weeks. I measure a few of the studs in the garage, and they're just below 12%.
    If I head over to http://www.woodbin.com/calcs/shrinkulator/ and plug in the numbers for a final 21" width with an initial moisture of 8% and final of 12%, I get the following:
    douglas fir shrinkulator.JPG
    Unfortunately, there's no option for rubberwood/parawood on that site. Would any of the above change your thinking?

    I may be better off just gluing a 2x4 underneath where I want to use dog holes. Or scrapping the idea of using this top for a woodworking bench, and instead building a storage/assembly table with it - then taking what I learn and tackling building a top out of lumber. I'm open to options.

  5. #5
    Join Date
    Oct 2008
    Location
    Carterville, Illinois
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    369
    If the only reason is to help hold the dogs, I don't see any reason to glue the 2x12 all the way across the top. Just glue the 2x12 in the middle of the top, or better yet, use screws in oversized holes to attach it to the top. Then the top can expand and contract without the restraint of the 2x12. The other way is to just glue blocks under the dog holes to increase the depth at those spots.
    The hurrier I goes, the behinder I gets.

  6. #6
    Join Date
    Jan 2019
    Location
    Fairbanks AK
    Posts
    164
    I am not crazy about the idea of laminating dissimilar woods. From a stability standpoint I like the "build a base for this thing as an assembly table" to get more experience, and then deal with a bench using all the same species for the top.

    You could certainly attach a vise to it and use it as a work bench while you build your next bench that can use holdfasts. That could be a really handy option.

    M2c

  7. #7
    Quote Originally Posted by Tom Wilson66 View Post
    If the only reason is to help hold the dogs, I don't see any reason to glue the 2x12 all the way across the top. Just glue the 2x12 in the middle of the top, or better yet, use screws in oversized holes to attach it to the top. Then the top can expand and contract without the restraint of the 2x12. The other way is to just glue blocks under the dog holes to increase the depth at those spots.
    Quote Originally Posted by Scott Winners View Post
    I am not crazy about the idea of laminating dissimilar woods. From a stability standpoint I like the "build a base for this thing as an assembly table" to get more experience, and then deal with a bench using all the same species for the top.

    You could certainly attach a vise to it and use it as a work bench while you build your next bench that can use holdfasts. That could be a really handy option.

    M2c
    Thanks guys! I've been convinced to abandon the idea of laminating the fir to the top.

    I'd like to come up with a solution that'll enable me to remove the top (repeatedly if necessary).

    Thinking of gluing some blocks to the underside of the top and bolting those to support ribs in the base. I'd drill oversize holes in the rear only to allow for movement while the front stays flush with the legs.

    If that makes sense, are there any guidelines regarding how big the blocks should be, and how I should orient them?

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