What size holes to bore for 3/8" bolts?

[guillemot]

I need to drill holes in the bedlogs of my centerboard trunk to fasten it to the dory floor. It'll be held down with 3/8" bronze carraige bolts on 6" centers and bedded in something gooey/sticky. What size holes would you all drill for the bolts - 3/8" even or slightly oversized to allow for swelling of the bedlogs?

Waiting at the drillpress,

Jeff

[Klaus]

I'll throw the spanner in and say 10mm

Klaus ;)

[guillemot]

No being difficult!

[mmd]

I'll go out on a limb here...

Robert Stweart, in his book "Boatbuilding Manual", states that all through-bolt holes in ship's structures should be coated with a sealant to prevent moisture from entering the exposed wood. Assuming that such googe has thickness, I would drill the holes 1/32" larger than the bolt hole.

If you don't anticipate using googe in yer hole, drill same-size in softwood, and 1/32" over for hardwood.

[Venchka]

Or follow the Gougeon Brothers advice...drill a hole oversize with chamfers top and bottom, fill with peanut butter thick epoxy and then drill through the hardened epoxy for the bolts...with sticky gooey stuff in the hole.

Wayne
In the Swamp. :D

[kc8pql]

I drill a hole the same size as the bolt, seal the hole with two coats of thin epoxy and then run the bit back through to clean the hole up. The epoxy soaks into the wood enough to seal it and the snug hole gives full bearing to the bolt.

[ 07-13-2005, 11:10 AM: Message edited by: kc8pql ]

[Ken Hutchins]

If, you are using proper bolts with a solid body ie. not threaded all the way to the head, just drill with a 3/8 drill the bolts should have to be driven into the holes which will be plenty tight enough without any googe. If you have a mic or digital caliper measure to body diameter they should be slightly over 3/8 near the head end which is a result of the heading operation when they are made. Drill a hole in a test block to be sure the drill is not cutting oversize.

[Gary E]

I agree with Ken, and this means clamping all parts together then drilling. You have no room for misalignment here, so as you drill one, install the bolt before moving on to the next.

[Stephen Hutchins]

Or if the bolts are threaded all the way you can run a tap through the wood first, wet hole with epoxy, screw in bolt, wrap bottom with cotton/thinned lead paste or other goo before washer and nut. Ok, I just re-read your post and actually what I wrote above will only work well if the bedlog is already clamped tight to the dory bottom. Otherwise, the holes in bedlog should allow the bolt to draw the log tight to the bottom.

[ 07-13-2005, 04:08 PM: Message edited by: Stephen Hutchins ]

[Ken Hutchins]

Got to disagree, if the bolts are threaded all the way, send them back to the supplier and tell them to send that Asian junk back to Asia, get good proper bolts. If you soak them in epoxy googe you will regret it someday when you have to remove them.

[Stephen Hutchins]

Ken, I've tried it with short bolts (1/4"x1 1/2") and found the bond will break with a wrench. Although it was only about a 1 month period after the initial cure. I didn't know the bolts with threads all the way up are cheap. I'll keep that in mind for next time.

[kc8pql]

You can loosen bolts that have been epoxied in by heating the bolt head. I use a butane pencil torch. The bolt doesn't have to get very hot to soften the epoxy enough to back the bolt out.

[Jay Greer]

The next size oversize for a 3/8"drill is the letter drill
"V". A test block is always a good way to go first.
Carriage bolts will seal better if a thin thread of candle wicking soaked in linseed oil is wound one or two turns under the head before driving the bolt.
JMG