1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Hidden pin idea

Discussion in 'Design' started by dancom, Oct 28, 2014.

  1. dancom

    dancom Dust Maker

    Likes Received:
    1,207
    Trophy Points:
    113
    I am experimenting with rear bolster that has hidden pins. I've read of some different approaches from a variety of makers on the net, but so far all seem to rely on the epoxy to do the bulk of the holding. You know threaded rod that fits into the hole in the bolster piece, gooped with epoxy and so on. The the pin doesn't do much holding and seems only for shear resistance.

    I reckon that hogging out the bottom of the hole in the bolster piece, having an over-length pin and using a press would create a sort of rivet when it expands or mushrooms to fill the space inside the bolster piece. I've made some graphics to explain and go along with my tests.

    Here's the idea.

    [​IMG]

    [​IMG]


    [​IMG]
    Anyone tried this before? This may be a common way of doing it, but nothing I have found so far explains a true mechanical fastening, in other words, things would fall off without the epoxy.

    Any tips?

    I'll post the results here.

    Thanks,

    Dan
     
  2. Roman

    Roman Active Member

    Likes Received:
    105
    Trophy Points:
    43
    Interesting idea. I don't see why it should not work. You have to get the length of your pins right though...
     
  3. Grouch

    Grouch Active Member

    Likes Received:
    32
    Trophy Points:
    28
    Dan
    Could you not tin the threaded pin after its through the whole. Tin the bolsters. You have to tin the area where the bolsters are going to sit on the knife as well. Put it together and clamp and heat them to solder them.
    Kind of old school but it might work for you.
     
  4. Mythtaken

    Mythtaken Staff Member CKM Staff

    Likes Received:
    273
    Trophy Points:
    83
    The idea might work, but you'd have to ensure the bottom of the pin hole was shaped so the expanded pin would lock in. Cutting that out at the bottom of the hole might prove tricky. And you'd have to ensure the pin material expanded enough to fill the space.

    There are a lot of "ifs" to it, but with some experimentation, perhaps you could develop a reliable system.
     
  5. dancom

    dancom Dust Maker

    Likes Received:
    1,207
    Trophy Points:
    113
    I'm going to try tapering the hole with a diamond ball and Dremel so pin expansion should lock in. I have some 8-32 brass which should squish pretty well with the press. The only thing I don't have is time!

    Ha ha ha...Trick-or-treat the weekend is coming. I'll take some photos and notes and see how it comes apart.
     
  6. dancom

    dancom Dust Maker

    Likes Received:
    1,207
    Trophy Points:
    113
    OK, just back from the shop. Early Friday morning. Happy Halloween everyone.

    This is my experiment with the Hidden Pin idea.
    I didn't waste a bunch of expensive materials for this, only things I had handy in the shop.
    I tried to keep this a simple as possible, so no CNC machine required.

    [​IMG]
    1/8" x 1" plain steel bar
    3/8" x 1/2" alloy bar, 2 pieces
    Machine screw, 8-32 x 1"
    * Later found this machine screw was steel with a brass coating. Caveat emptor!!
    9/64" HSS bit - for tapping to #8
    Cutting fluid
    5/32" HSS bit

    [​IMG]

    I marked off the depth of 3/16". The masking tape is a good visual depth gauge.
    We don't want to drill any deeper than 3/16".

    [​IMG]

    Drilling the bolster pieces to 5/32" on drill press.
    Stop at 3/16" deep. This is important.
    If you have a drill press, you can set the depth stop for 3/16". (Mine is broken so I used tap or makers.)

    [​IMG]

    Two pieces drilled to the same depth.

    [​IMG]
    With the diamond ball moto-tool bit make the bottoms of the holes larger in diameter than the hole openings. This will create a taper.
    You don't need to take a whole bunch of material out, just make a taper. My diamond ball moto-tool is kind of a weird shape. I'd prefer to have a real Dremel accessory such as 7103.


    [​IMG]

    Drill tang with 9/64" bit, add a drop of cutting fluid and tap to 8-32.

    [​IMG]

    Cut the machine screw. This is the critical part.
    You need to calculate the correct length for your application.
    Different tang and bolster thicknesses alter this length.

    For 1/8" tang and 3/16" deep holes + /8" squish = 5/8".
    I'll make a table for suggested lengths. Basically you want to
    "squish an 8th" for an 8-32. So deeper holes or thicker tangs need to have longer pins.

    Hole1 depth + Hole 2 depth + tang thickness + 1/8" = screw length.
    If you really hog the holes in the bolster pieces, use 5/32" as your squish factor.


    [​IMG]

    Thread the machine screw in 1/2 way so that the same amount of screw is on each side of the tang.
    If you want to add a spot of Loc-tite or super glue that's okay, I didn't see the need to.

    [​IMG]

    Slip the two bolster pieces on hold them in place while you get over to the vise or press.

    [​IMG]
    Squeeze! I used a 4" vise and that's lots of PSI.
    Compress until the surfaces meet.

    [​IMG]

    Ta da!

    [​IMG]

    Note: I could not rotate the bolster pieces by hand, even though this has only one pin in the centre.

    [​IMG]

    To reveal , I cut the bolster piece with a hacksaw. Nothing came loose, I gripped the underside bolster in the vise and hack sawed away.

    [​IMG]

    This is the inside. Perhaps this can show us how the mechanical connection was made.

    [​IMG]

    The threads appear to assimilate into the bolster. Nice!

    Two pins and this bolster isn't going nowhere.

    Conclusion
    I think this is a great way to do hidden pins. My notes will be posted at my blog. Look for Hidden Pins in the top menu.

    Happy knifemaking!

    Dan
     
    Last edited: Oct 31, 2014
    Roman likes this.
  7. Mythtaken

    Mythtaken Staff Member CKM Staff

    Likes Received:
    273
    Trophy Points:
    83
    Nice one, Dan.

    That definitely looks like it will hold. I like the idea of threading the pin through the knife to keep the same amount on either side.
     
  8. Roman

    Roman Active Member

    Likes Received:
    105
    Trophy Points:
    43
    This is definitely a great experiment. Well planned and well executed. I like the result and it's good to know that it works with the steel pin/bolt as well.
     
  9. dancom

    dancom Dust Maker

    Likes Received:
    1,207
    Trophy Points:
    113
    Thanks guys. Excuse some of my early morning typos. "tap or makers" should read "tape or markers". /8" should be 1/8". Left index finger not firing properly at 6:30 A.M. LOL

    The threads make this technique quite forgiving. Two pins on a typical bolster and add some epoxy as a sealant and it should be good for life.

    Ya, I thought for sure the screw was brass until I cut it. Cheap hardware!

    My current build will have a stainless rear bolster with hidden pins, so I get to try it for real this time.

    I'll keep y'all posted.

    Dan
     
  10. Icho-

    Icho- Staff Member

    Likes Received:
    154
    Trophy Points:
    63
    I like it. I will have to try it. The only other test I would like to try is a torsion test. Put one side of the blade in a vise about 1" from the bolsters and an adjustable wrench about 1" on the other side of the bolsters and give it a bit of a twist. Even though a knife isn't supposed to be a pry bar you can count on at least a few people doing it sooner or later. I'm sure the bolsters won't separate from the blade but still something I will try just for a piece of mind. By twist I'm talking light and realistic pressure.
     
  11. dancom

    dancom Dust Maker

    Likes Received:
    1,207
    Trophy Points:
    113
    Icho, I understand. I'll experiment some more and blog it. This was more to test the internal rivet idea and I know it's kind of hard to test much of anything with a single pin. I'll be using two pins and some Acraglas on the next edition.

    Dan
     
  12. Icho-

    Icho- Staff Member

    Likes Received:
    154
    Trophy Points:
    63
    Cool. I'm actually knife of anxious to try it myself. I don't think there will be an issue. I did something similar but without the pressing on my first knife which was actually the Scandi kith here a while back. I used 2 hidden pins in a 3 piece dymondwood handle sandwiched together. it seemed to work out pretty good but it was different than pressing on the bolsters.
     
  13. Brad

    Brad Active Member

    Likes Received:
    87
    Trophy Points:
    28
    Cool experiment looks like it would work well for scales and bolsters
     
  14. dancom

    dancom Dust Maker

    Likes Received:
    1,207
    Trophy Points:
    113
    I was thinking about this again today and pondered the use of a 1070 carbon steel spring pins. This wouldn't technically make a rivet, and the bolsters would still have to be pressed on. But, the the the pin length and hole depth would be less critical. Another technique may be to heat the bolster pieces in the oven and press them on a chamfered solid pin with say 0.005" interference. I am thinking 1/8" pin into a #31 hole or 0.125" into 0.120".

    Something else to try.

    Dan
     
  15. dancom

    dancom Dust Maker

    Likes Received:
    1,207
    Trophy Points:
    113
    OK, did some playing in the shop this morning. I drilled a 7/64" hole in some 3/8" 304 stainless and deburred the hole. Placed it in the oven at 150°C (about 300°F).

    For a pin I cut a short piece of 1/8" 304 rod, chamfered and cleaned it up a little with some 320 grit.

    I took the heated piece from the oven and I was able to press the pin in fairly easily, I am guessing about 1 ton of force.
    Once cooled, that pin was stuck in there good. There will be no way to remove it easily. I am thinking it would have to be drilled out.

    :)

    I am going to try this on my next build.

    Dan
     

Share This Page