Mounting boxes in boards

Forums Chop Shop and DIY gear Mounting boxes in boards

  • Post
    surfcowboy
    Participant

    Hey all, wanted to start a thread on how to mount boxes in a blank.

    I used a high density insert from Grey Paddleboards in the UK to convert my first SUP to learn on. (Charlie’s a great dude and shaper.) I’ve got another one to do my next board, but I’m about to also make a prone board so I’m looking to experiment maybe. ericfoil brought up mounting boxes to stringers on the Progression Project and then I saw how KT mounts his into divinycell stringers and it got me thinking that there may be ways other than a block of heavier foam.

    Eric can you elaborate on what you’re doing? Do you cut out the stringer or run it alongside the box?

Viewing 15 replies - 1 through 15 (of 35 total)
  • Replies
    ericfoil
    Moderator

    Thanks for listening to the podcast. I’d be glad to elaborate.

    The first thing I do is use a little foaming polyurethane glue (whisked with a half a tablespoon of water) to bond my stringers (1-3/4″x24″x1/4″) to the fin boxes. Use masking tape to cover the slots. Use clamps to hold alignment for the expansion and cure.

    I carefully sand the excess cured foaming glue off of the stringer boxes then use fiberglass fin rope (pulled from woven roving) to bond the bottom of the boxes to the side of the stringer. I add three or so layers of chopped fiberglass mat after the fin rope.

    Using hand, skin, eye, and respiratory protection, I sand excess material off of the stringer boxes after the appropriate cure time.

    I set up the stringers to be on the outside of the boxes.
    I get a foil base plate and screw in the t nuts to hold the boxes in proper alignment. Then i mark the board where I need to cut and remove material for the boxes and stringers.

    With eye and respiratory protection i use my trim router and plunge cut saw to chop and remove fiberglass and foam.

    I keep test fitting until i can drop the stringer boxes down into the slots and they are flush with the bottom of the board.

    I use sheet plastic to go between the stringer boxes and the foil base plate before i foam the stringer boxes into the board. This keeps the foaming glue off of the plate.

    I then mix up a bunch of foaming glue with a little water and use a 1″ chip brush to slather the sides and bottoms of the stringer boxes and insides of the slots on the board.

    Install the boxes in the slots and put some sheet plastic down, something flat like a small rectangle of plywood above the stringers and use weight to hold down the plate and the plywood.

    surfcowboy
    Participant

    Thx man. I’m trying this on my next board.

    Couple of ideas, if I may.

    A foil plate jig is something I wanna make for sure, to hold the boxes.

    I also think I’m going to try a stringer from top to bottom and “I” beam them in with carbon strips/tape, ala KT. The side mount is actually better than what I was thinking but I may play with a cut out too to see how that works. Sort of a hybrid of you and KT (KTX? Heh)

    I have a buddy ripping me some redwood stringers out of 2×4’s with a table saw. We will see how that goes lol.

    I’ll try to repay the info here with some pics if I can. Thanks a ton.

    mattllew
    Participant

    extending the hd foam or stringers as far as where your front foot will be definitely makes sense to stifen up the board (and have no flex when pumping). On the two boards I’ve made I just use charlie’s hd inserts because they’re cheap and simple to install. For the next one I will wrap fibreglass under the insert to meet with a carbon patch on top. Also things like concaves on the bottom and ridges at the edge of a slightly sunken deck all add stiffness through corrugation of the fibreglass…. but it’s no substitute for Eric’s suggestion which sounds rock solid.

    Clamsmasha
    Participant

    Matt,

    I have been using pour foam for my boards. 100kg/m polyurethane. I try a different footprint for every board trying to reduce weight in my builds. So far they have not failed, and my prone boards get absolutely degraded. I chamber the box area with scrap EPS to minimise weight.

    After the “loaf” hardens I use a handsaw laid sideways to cut the foam flush with the blank then shape. I use Future one shot boxes with 2 layers of 6oz carbon twill, then after sanding the boxes flush I cap them with another layer of carbon at 45degree bias.

    This last one (pictured) is a bit over engineered, but it was my first sup/wing board and my first build with 1lb foam.

    The advantage with the pour foam is that it expands in all directions and wedges into the blank. The layer of slightly compressed EPS helps translate any movement of the plate/box into the blank without breaking anything. The stiffness and tensile strength of the carbon does the rest.

    Clamsmasha
    Participant

    Eric’s way is way more elegant though!

    MightyMike
    Participant

    I was considering adding Vulcan style “lightdrive” grooves around the boxes to add strength. What do you guys think?

    BTW I would ask Vulcan first!

    surfcowboy
    Participant

    Thx man. I was considering this too as a test.

    What’s the density of that foam again? 220 lbs per sq. meter seems off. Typo?

    I like your holes. Maybe link them all the way through to tie to deck for extra hold?

    Kane DW
    Moderator

    Lots of great ideas!! Double on Eric’s method, Flying Dutchman attaches the boxes in almost the same way. Works very well and is super light! One warning though, if you’re planning on doing any airs go with full length stringers. I’ve had boards buckle where the stringer ends from hard landings.

    Clamsmasha
    Participant

    100kg m/3 is just over 6lb ft/3 so it’s only 3-4 times more dense than the standard blank material. Very hard though, and super stickY while it’s in motion. Some exotherm though, so 2-3 pours or chambering recommended.

    I have deck anchored the boxes in the past. The one pictured had 4 pillars through with EPS centres to reduce weight.

    surfcowboy
    Participant

    Thx guys. Clamsmasha, I have to try the 6 lb foam for sure.

    Got a buddy to rip some 1×4 redwood to make me some 1/4” x 3 1/2” stringers. Will work great for 3” thick prone boards.

    For standup which will be 4” thick I’m using 2” trim pieces glued on top of each other. Should be fine sandwiched in the blank.

    Here in SoCal I’ve sourced 1.5 lb eps at $47 per 4’x8’x4”. Should get 2 to 3 boards out of that. Another reason to get down to smaller prone boards, $12 blanks lol.

    For now hoping to get behind the boat this weekend on my 7’4” SUP to practice. Wish me luck.

    surfcowboy
    Participant

    Question for the group. What boxes are you using?

    Eric, I’ve always mounted Bahne boxes after glassing. Are you using Futures or grinding the standard boxes down and taping over them to install them pre-glass?

    Just thought of this while going over my build plan.

    Clamsmasha
    Participant

    Futures for me, have used others but that’s the best fit for me atm.

    ericfoil
    Moderator

    I glass the boxes in (without taping over). I included a photo of my “map” that I use to find where to drill to get the router started

    mckeem
    Participant

    I started making my own boxes with chinook fin boxes and 12lb 2part foam.
    I basically made the mould and lined it with the tuck tape or 3M peel and stick membrane, and poured in 3 parts as to fully encapsulate the fin boxes. A mono pour proved to fail just by looking at it once done.

    I poured around the fin boxes about 1/2 depth and let it cure (20min) I then followed up with two more pours and nailed it. I just installed it into my probe blank yesterday.

    dylbert_
    Participant

    mckeem,
    How well does the foam adhere to the boxes? I was thinking about something similar, however rather than pouring the foam into a mould,pouring directly into the cavity in the blank. The boxes could be mounted (upside down) to a plate with mould release on it, flush with the bottom of the blank. When the foam cured, the boxes are perfectly set in the block, and the block fits perfectly in the blank.

    I will report back when I have a chance to try it.

Viewing 15 replies - 1 through 15 (of 35 total)
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