Router roundover bit size for rounding over stringers

Discussion in 'Boat Design' started by mariobrothers88, Nov 15, 2020.

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What router roundover bit size would you guys think would be optimal for the inner edges of stringer

  1. 1/4"

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  2. 3/8"

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  3. 1/2"

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  4. other, please specify in comments

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  1. mariobrothers88
    Joined: Sep 2020
    Posts: 51
    Likes: 1, Points: 8
    Location: San Diego, CA

    mariobrothers88 Junior Member

    Hi guys, my plans call for 3/4" x 1.5" stringers and rounding over the inner edges but doesn't specify the router bit size. What router roundover bit size would you guys think would be optimal for the inner edges of the stringer? 1/4", 3/8", or 1/2" ?

    Thanks for all the help and input, this forum is an amazing resource!!!
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    About 1/8"
     
    hoytedow likes this.
  3. mariobrothers88
    Joined: Sep 2020
    Posts: 51
    Likes: 1, Points: 8
    Location: San Diego, CA

    mariobrothers88 Junior Member

    Thanks for the reply gonzo! Would it be difficult to lay fiberglass cloth and epoxy over such a small round over like 1/8"? I'm thinking of going with the bigger size like 3/8" to make it easier to lay the glass and epoxy. Are there any disadvantages of going with a bigger round over bit?
     
  4. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    The larger roundover bit will reduce the remote fiber area of the stringer. The stringer will suffer some minor loss of stiffness in that case. Router bit sizes are stated as the radius of the curve. A 3/8 bit would create a perfect half round top on the 3/4 width stringer. Sure enough a larger radius is easier to drape glass cloth over. That is not the problem, it is at the intersection of the stringer and whatever skin or other surface it contacts. The parts of that area forms a right angle that is difficult for glass to fit into. Of course you could use some fairing compound and create a radius there.

    All of which brings up the question: Why do you intend to cover those little stringers with glass? If the stringers are presumed to need more strength then why not simply make them larger without the complication of glass and resin.

    Tell us the part of the boat where stringers are located, (bottom probably) what skin material and skin thickness is under the stringers, How fast do you expect to go, and what size is the boat to be.
     
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  5. Russell Brown
    Joined: Jul 2012
    Posts: 115
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    Location: washington state

    Russell Brown Senior Member

    3/16 is the size I would use, but 1/4 would work fine too. 3/8 is huge and wouldn't really work as the bearing on the bit would let the bit cut deeper on the second side of the stringer. Try a sample to see.
     

  6. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    I typically use 3/8" short of full cut for all glass radius prep. 1/4" is fine as RB says; less is more difficult to avoid air entraining on the layup.

    As for the landing getting too narrow. Often, a cleat can be epoxy glued to each side and filler added back to increase the glue surface for the sole. I have watched this done many times on Merten's boats. They typically land on 3x3/4".. Mertens fell yesterday and got hurt; not sure how bad.

    In my own build, no stringers, but for a no glass seam for a sole or splashwell; I generally, not always, widened the contact area from 9/16" to 1 9/16". It largely depends on anticipated foot traffic for me.
     
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