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IndustryArena Forum > MetalWorking > MetalWork Discussion > Proper dowel pin pressing..."how to" for this job?
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  1. #1
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    Mar 2011
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    Proper dowel pin pressing..."how to" for this job?

    Hey guys. Wanted to see what some of you think of this and how it can be done possibly better.

    I have (4) holes that are drilled and reamed .0003 undersized for a hardened .125 dowel pin. The pin is .500 long. Tolerance of these pins are really good. Spot on .125 or -.0001.

    The dowels run .385 deep.

    It will not be necessary for this pin to be removed in the future. It just needs to STAY PUT.

    The dowel has a slight chamfer on the end.

    Before, I used the same size of reamer and pounded the crap out of the dowels with a brass hammer. It would sink additionally about .020 (into the drill bit angle apparently) before it would stop.

    Rather hillbilly, but for the most part, it worked but on occasion when removing the mating part, one of the pins would come out. I can't have that. That's REALLY hillbilly.

    So, I went the option of undersizing the reamer and going interference.

    The mating part is already reamed at .125 with a slight chamfer on the hole.

    All drilling, reaming, and chamfering is done on a VMC.

    When complete, and done right, both the mating part and dowelled part should "snap" together. Pretty tight.

    Any correct way to get these little guys in there without them flying off in my face when pressing them in?

    What would be your method of doing this job? It would have to be quick and efficient as this job is repeated quite a bit. Using a press? Using a hammer? Using a jig to press all pins in same time? Anything goes...I'll listen.

    They just have to stick.

    Thanks!

  2. #2
    Join Date
    Apr 2006
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    3206
    On the permant part side ream it to size. Your dowels should be ~.0002 over.

    Grind an ever so small groove (or a small flat) on the side of the dowel that will be in the part, or drill a hole in the bottom of the hole thru ... you're compressing air trying to press this thing in!

    Get some dry ice and put the dowels in it to get cold. You should be able to shrink 'em at least a couple of tenths on the dia.

    Meanwhile, heat the aluminum up to 200deg (a toaster oven should do). It has twice the thermal expansion coefficient of the steel, so you should be able to get the holes to open up a few tenths.

    Using some needle nose pliers, drop the dowel into the hole and QUICKLY press it to the bottom of the hole. When the temp normalizes you should have a very, very hard time getting the pin out.

    .....btw... Good idea to try the method on a sample part first!!!

  3. #3
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    Mar 2011
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    That sounds fine...but I have to use what I have hundreds of already...dowel pins that are .125.

    It also sounds like quite a bit of work (freezing and heating for example) in a production environment. Remember...I have LOTS of these to do....and it's just part of op to achieve the finished part.

    I thought about making a small flat (to relieve the air pressure), but with the size of these suckers, it would be pretty hard to hold onto. They are also hardened. Drilling a hole through the bottom of the part is out of the question since it's about 7" down.

    Any other ideas? I guess with an interference of about .0003 is alright to use. Just putting them in quickly, solidly, and effectively is what I'm hung up on.

  4. #4
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    Quote Originally Posted by FFWD View Post
    That sounds fine...but I have to use what I have hundreds of already...dowel pins that are .125.

    It also sounds like quite a bit of work (freezing and heating for example) in a production environment. Remember...I have LOTS of these to do....and it's just part of op to achieve the finished part.

    I thought about making a small flat (to relieve the air pressure), but with the size of these suckers, it would be pretty hard to hold onto. They are also hardened. Drilling a hole through the bottom of the part is out of the question since it's about 7" down.

    Any other ideas? I guess with an interference of about .0003 is alright to use. Just putting them in quickly, solidly, and effectively is what I'm hung up on.
    Ok. Plan B.
    Use your American Ingenuity.
    If machining was easy, it wouldn't be so challenging.

  5. #5
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    Quote Originally Posted by fizzissist View Post
    Ok. Plan B.
    Use your American Ingenuity.
    If machining was easy, it wouldn't be so challenging.
    lol I never did say it was supposed to be easy...but there are many ways to skin the same cat.

    Oh yes...who subscribes to the method of reaming a hole...stopping the spindle at the bottom...rapiding out...repeat.

  6. #6
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    Quote Originally Posted by FFWD View Post
    lol I never did say it was supposed to be easy...but there are many ways to skin the same cat.

    Oh yes...who subscribes to the method of reaming a hole...stopping the spindle at the bottom...rapiding out...repeat.
    That method is excellent if you like grooves in the hole.

  7. #7
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    Quote Originally Posted by fizzissist View Post
    That method is excellent if you like grooves in the hole.
    That's what I thought it would do...but another machinist told me in order to maintain proper diameter of the reamer, is to do it that way.

  8. #8
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    Quote Originally Posted by FFWD View Post

    That's what I thought it would do...but another machinist told me in order to maintain proper diameter of the reamer, is to do it that way.
    In this case, it might be indicated.... it could give you the air relief needed.
    It's a perfectly good method. I wouldn't do it in anything that work-hardens though, or is abrasive.

  9. #9
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    Quote Originally Posted by FFWD View Post
    ...I have LOTS of these to do.....
    If you have lots make a jig that the part slides into aligning the dowel pin hole with a hole in a hardened guide bushing that is a clearance fit on the dowel and is just a bit shorter than the length of the dowel that protrudes once it is pushed home. Drop the dowel in the in the guide bushing and then push it home in a small arbor press.

    The most likely reason you are getting dowels pulling out is because hammering them in can swage the hole slightly over size. If you could hammer perfectly in line with the dowel and if you can hold the dowel perfectly in line with the hole hammering might be okay. It is not possible to do either and hammering off line puts a sideways force on the dowel enlarging the hole.
    An open mind is a virtue...so long as all the common sense has not leaked out.

  10. #10
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    Mar 2011
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    Quote Originally Posted by Geof View Post
    If you have lots make a jig that the part slides into aligning the dowel pin hole with a hole in a hardened guide bushing that is a clearance fit on the dowel and is just a bit shorter than the length of the dowel that protrudes once it is pushed home. Drop the dowel in the in the guide bushing and then push it home in a small arbor press.

    The most likely reason you are getting dowels pulling out is because hammering them in can swage the hole slightly over size. If you could hammer perfectly in line with the dowel and if you can hold the dowel perfectly in line with the hole hammering might be okay. It is not possible to do either and hammering off line puts a sideways force on the dowel enlarging the hole.
    That could very well be. I never did like the idea of wacking away to get this job done.

    Great idea buddy. I'll see what kind of American ingenuity can be dreamt up on this. All you guys gave me the food.

    Appreciate you all and have a very Merry Xmas!

  11. #11
    Join Date
    Mar 2008
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    FFWD - first: what material?
    second: What are the dim's?
    third: Re-check your dowel pins. Standard pins are +.ooo2. There are oversize pins available, but I have never seen undersize pins.Unless....they are a special.
    Now: You must get rid of the air. Either groove the hole or put a small slot or flat on the pin. Should not be a problem.
    Guide the pin for pressing it in.
    Your reamer for a press fit should be .1248 (pins .1252)
    Much depends on how far you dowel pins are apart and what tolerance you are holding.
    That will decide how much bigger your holes should be. That is for you to find out.
    Usually what we would do in the Tool and Die Industry is drill and ream two parts together .1248 and than open one part to .1254 - .1255.
    In your case I would start by reaming the mating part .1254 (if the pins turn out to be .1252).
    Ps.: you may hammer the pins (not in Alu) but you must give them a good start by guiding. A drill press should do it.
    Plan "B": Ream the pins for a slip fit and "Loctite".
    That would solve all your problems at once. Make sure you have clean holes and pins and use a primer.

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