Results 1 to 28 of 28

Thread: How to countersink for a carriage bolt?

  1. #1
    Join Date
    Nov 2000
    Location
    Tallahassee, FL USA
    Posts
    755

    Default How to countersink for a carriage bolt?

    I will need to install some carriage bolts to attach the bedlogs through the apron (inner keel), planking and keel. I want to recess the carriage bolt heads in the bottom of the keel. However, I need to through drill from the top end (the bedlogs) which will have the washer and nuts. This way, I will be able to remove the bedlogs in the future if they need replacement or repair.

    So I will have a 1/4 inch hole in the bottom of the keel, how do I get a drill the diameter of the carriage bolt heads centered in the 1/4 hole without it drifting all over the place?

    I have had this situation arise before in several cases and never found a good way to drill the counterbore when there was already an existing hole.

    I sure there is a good way to do this, but how?

  2. #2
    Join Date
    Jul 2002
    Location
    Seattle, WA
    Posts
    8,061

    Default Re: How to countersink for a carriage bolt?

    I would drill the counterbore for the carriage bolt first. 5/8s spade bit...you may have to grind the carriage head down a bit.

    Am I understanding you?

  3. #3
    Join Date
    Nov 2000
    Location
    Tallahassee, FL USA
    Posts
    755

    Default Re: How to countersink for a carriage bolt?

    The problem is that I need to drill the other end first because the bedlogs are fairly narrow and the exact position is important. So I plan to drill the holes in the bedlogs first in my drill press, then place the bedlogs in position in the boat and then drill the rest of the way through the keel. That way, I will be sure the holes are exactly in the right position. The only problem is then I have to drill the counterbores last.

  4. #4
    Join Date
    Mar 2001
    Location
    Grosse Pointe, Michigan, USA
    Posts
    10,962

    Default Re: How to countersink for a carriage bolt?

    I would think a Forstener bit would center itself in a 1/4 ins. existing hole If not, you could start with a hole saw to cut a guiding groove, but that sounds like too much effort.

  5. #5
    Join Date
    Oct 2000
    Location
    Wellesley, MA USA
    Posts
    8,836

    Default Re: How to countersink for a carriage bolt?

    and if you're really picky, clean up the hole-saw crater with a forstner bit.

  6. #6
    Join Date
    Nov 2000
    Location
    Tallahassee, FL USA
    Posts
    755

    Default Re: How to countersink for a carriage bolt?

    Jim: If I can find the right size hole saw with a 1/4 inch pilot, that sounds like it would work pretty well. I can probably then use a forstner bit to clean up the hole.

  7. #7
    Join Date
    Nov 2000
    Location
    Tallahassee, FL USA
    Posts
    755

    Default Re: How to countersink for a carriage bolt?

    Jim: sorry if my responses seem a little out of order. You responded while I was typing!

  8. #8
    Join Date
    Mar 2007
    Location
    SPID
    Posts
    4,721

    Default Re: How to countersink for a carriage bolt?

    Alan,

    The right tool for this is a type-X counterbore bit. This is a bit that slides on a 1/4-inch drill bit and tightens with set screws. It will cut a 3/4-inch flat-bottomed counterbore for the carriage bolt head. There will be no wobble, since it is guided by the 1/4-inch bit in the hole drilled initially from the bedlog side. They are available from Fuller. Here's the link:

    http://www.wlfuller.com/html/type__x_.html

  9. #9
    Join Date
    Apr 2005
    Location
    Petoskey, Michigan
    Posts
    1,183

    Default Re: How to countersink for a carriage bolt?

    Someone offered a good solution to a similar problem I had last week - and it works well: after you have your bolt hole- drill a larger hole in a piece of scrap plywood, center it over the bolt hole and temporarily fasten with short screws or clamps- use the plywood hole as a guide template. I used a hole saw but a forstner bit would give you a nice flat bottom to seat the carriage bolt head on.
    When the last tree is cut
    When the last river is dry
    When the last fish is caught
    Only then will Man realize that he cannot eat money.

  10. #10
    Join Date
    Feb 2002
    Location
    Hoffman Estates IL
    Posts
    2,347

    Default Re: How to countersink for a carriage bolt?

    Tap in a dowel, center up and drill away. Tap out what's left of the dowel.

  11. #11
    Join Date
    Dec 2002
    Location
    New Zealand
    Posts
    129

    Default Re: How to countersink for a carriage bolt?


  12. #12
    Join Date
    Jan 2008
    Location
    Padanaram, MA
    Posts
    146

    Default Re: How to countersink for a carriage bolt?

    Cheers...

    Dave

    "Bíonn caora dhubh ar an tréad is gile."

  13. #13
    Join Date
    Aug 2005
    Location
    Hartland, Vt
    Posts
    294

    Default Re: How to countersink for a carriage bolt?

    I would drill the bedlogs with a small bit, 3/64 or so, for the pilot hole in your drill press. Then install the bedlogs in the boat and drill through the pre-drilled holes with the same small bit. Then use that for a pilot hole to drill your necessary larger holes, drill the holes for the bolt head from one end of the keel or bedlog, and the other from the other side as necessary. A very small pilot hole will allow you to center either size bit with no problem, IMHO. You might have to buy a long pilot bit for this, but they are available.

  14. #14
    Join Date
    Sep 2007
    Location
    Bass Harbor, ME
    Posts
    1,631

    Default Re: How to countersink for a carriage bolt?

    I just did this for my engine beds. I first drilled a small pilot hole for each bolt. I used a 5/32" bit silver soldered onto the end of a 5/32" stainless rod to make the normal jobber length bit long enough. Once I had the pilot hole in, I used a forstner bit to make the countersinks for the bolt heads. When that was done I drilled the pilot holes out to their final size (1/2"). Not exactly a tough job.

  15. #15
    Join Date
    Jun 2003
    Location
    Central Coast, Ca
    Posts
    8,829

    Default Re: How to countersink for a carriage bolt?

    I have reground the end of a spade bit to pilot in a drilled hole.
    Grind the cutting edges back a bit leaving a 1/4 " wide pilot - about five minutes.

  16. #16
    Join Date
    Feb 2006
    Location
    Pennsylvania
    Posts
    6,017

    Default Re: How to countersink for a carriage bolt?

    I've got Boylesboats winning this one. Quick and realiable.

  17. #17
    Join Date
    Mar 2005
    Location
    FL. USA
    Posts
    6,461

    Default Re: How to countersink for a carriage bolt?

    Quote Originally Posted by Paul Scheuer View Post
    Tap in a dowel, center up and drill away. Tap out what's left of the dowel.
    I have done it this way and just run the first bit back through the hole again to clear the dowel.

  18. #18

    Default Re: How to countersink for a carriage bolt?

    Quote Originally Posted by TerryLL View Post
    Alan,

    The right tool for this is a type-X counterbore bit. This is a bit that slides on a 1/4-inch drill bit and tightens with set screws. It will cut a 3/4-inch flat-bottomed counterbore for the carriage bolt head. There will be no wobble, since it is guided by the 1/4-inch bit in the hole drilled initially from the bedlog side. They are available from Fuller. Here's the link:

    http://www.wlfuller.com/html/type__x_.html
    Terry. Thanx for that link. Just one day too late. I counter bored my skeg to accept 5/16" carriage bolts (after I ground down the majority of the head). Applied epoxy with filler to the bolts. Popped'm through, tighten up and doweled the counter bore.

  19. #19
    Join Date
    Nov 2004
    Location
    Guerneville,CA
    Posts
    4,884

    Default Re: How to countersink for a carriage bolt?

    Just tighten it untill it is flush.
    I love the smell of fresh cut plywood in the morning.

  20. #20
    Join Date
    Feb 2002
    Location
    Hoffman Estates IL
    Posts
    2,347

    Default Re: How to countersink for a carriage bolt?

    I see that the discussion has followed the idea of a round counterbore. I could be wrong here, but I always thought that a carriage bolt had a square section under the head to prevent rotation. The exception being a "rib-necked carriage bolt". Am I wrong ?

  21. #21
    Join Date
    May 2004
    Location
    Cuyahoga Falls, Ohio
    Posts
    2,734

    Default Re: How to countersink for a carriage bolt?

    Fountain pen turners use a flat bottom (sort of end mill) with a pilot that looks like it'd do the job - as would several of the above methods.

  22. #22
    Join Date
    Nov 2004
    Location
    Port Townsend WA
    Posts
    7,305

    Default Re: How to countersink for a carriage bolt?

    I greatly favor fin headed bolts over carraige bolts as they are much easier to set and require only a counter sunk hole to bring the head flush with the surface. Hence they have greater holding power and have much less tendancy to turn in the hole. Bear in mind that the bolt hole should almost be a drive fit. Select your drill diameters accoringly.
    Jay

  23. #23
    Join Date
    Mar 2005
    Location
    Toronto, Canada
    Posts
    2,369

    Default Re: How to countersink for a carriage bolt?

    The easiest, cheapest and lowest-tech way to do what you want is to drill your through-hole, than hammer in a square-ish piece of pine or cedar to fill the hole for an inch or two at the bottom. Saw it off flush, centre your counterbore bit and drill away. Takes about a minute and a half and you don't need a special tool.

    And Jay is dead right about the bolts. I've never liked coach bolts where the head is exposed to water. It doesn't take much corrosion before the head is basically gone. I'd use a rod threaded for a nut on each end if I couldn't get a fin-head to suit.

    On the other hand - are you sure this is a good idea? 1/4 inch sounds real light for the job. How long will they be? Keep in mind that because they go through everything, these 1/4 inch bolts will be under exactly the same load as your keel bolts. If there is ANY movement of the keel, including hydraulic expansion, the new bolts may not hold up. They might stretch, They might break. Isn't there any way to attach the beds without going through all? Are there any floors you could lag or cross-dowel to?

    - Norm

  24. #24
    Join Date
    Nov 2000
    Location
    Tallahassee, FL USA
    Posts
    755

    Default Re: How to countersink for a carriage bolt?

    OutoftheNorm: The bedlogs sit right on top of the apron, then the planking and then the keel. The apron is less than 5/8" thick and the planking is only 1/2" thick. So both are pretty light. The keel is the only member with any size to attach the bedlogs to.

    I like the idea of the rib-necked carriage bolts, but since I want to use Silicon Bronze Bolts, the selection is pretty limited. I agree about the heads being exposed to the water being a bad idea, that is why I want to recess them and then I will cover the heads with epoxy glue to waterproof them.

    The keel in the way of the centerboard slot is actually two members one on each side and they are 1 1/4 wide by 2" deep. I guess 1/4 inch bolts sound a little slim, but there will be ten of them and its only a 12 1/2 ft. boat.

  25. #25
    Join Date
    Mar 2007
    Location
    SPID
    Posts
    4,721

    Default Re: How to countersink for a carriage bolt?

    Lots of ingenious posts above on how to countersink carriage bolt heads, but I have to repeat that the X-type counterbore is the tool for this job.



    I bought this set of six from Fuller about 30 years ago and it has handled every counterboring task that has come my way.





    These counterbores can be attached to any twist drill, including brad points, or to solid rod of the appropriate size. Two stout set screws hold them in place. To my mind, a set of these is an essential shop tool, just as important as a set of Forstner bits, good chisels, and a sharp hand saw.

  26. #26
    Join Date
    Mar 2005
    Location
    Toronto, Canada
    Posts
    2,369

    Default Re: How to countersink for a carriage bolt?

    Quote Originally Posted by Alan Peck View Post
    I guess 1/4 inch bolts sound a little slim, but there will be ten of them and its only a 12 1/2 ft. boat.
    I was assuming that the boat was bigger. 1/4 inch is likely fine , so I take that back. However, if the planking in 1/2 inch and the apron is 5/8, that doesn't leave much meat after you cut a counterbore of at least 3/8 inch. Maybe you should consider the suggestion made earlier to just set them flush. If you're using SB bolts, they should be fine that way.

    - Norm

  27. #27
    Join Date
    Nov 2000
    Location
    Tallahassee, FL USA
    Posts
    755

    Default Re: How to countersink for a carriage bolt?

    outofthenorm: The bolts will go right through the keel, so that is a 2" thick piece, so thickness should be no problem. However, the countersunk portion will be quite close to one side edge of the keel, so if I countersink there will only be about 5/32 between the edge of the countersink hole and the edge of the keel.

    Leaving the bolt heads flush might be a good idea. If I do that, how do I keep water from leaking around the bolt head and into the keel?

  28. #28
    Join Date
    Mar 2005
    Location
    Toronto, Canada
    Posts
    2,369

    Default Re: How to countersink for a carriage bolt?

    Keep em tight with a perfectly sized hole, a coat of thick red lead as they are driven and a wrap of cotton under the head before it goes home.

Similar Threads

  1. Metric Countersink and Bung Set?
    By Songololo in forum Tools / Materials / Techniques / Products
    Replies: 4
    Last Post: 05-10-2008, 06:04 AM
  2. Shop made carriage bolts
    By few3 in forum The Bilge
    Replies: 4
    Last Post: 09-11-2007, 10:43 AM
  3. Monel carriage bolt supply source
    By Clyderigged in forum Tools / Materials / Techniques / Products
    Replies: 23
    Last Post: 03-16-2005, 05:40 PM
  4. Countersink set from Jamestown??
    By dmede in forum Tools / Materials / Techniques / Products
    Replies: 11
    Last Post: 12-06-2003, 07:11 AM
  5. Fire demolishes Fuller countersink factory
    By sawcutmill in forum Tools / Materials / Techniques / Products
    Replies: 5
    Last Post: 03-18-2003, 07:17 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •