Is it possible to reduce a .192 dia. hole to be a proper fit for a .187 dowel pin?
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  1. #1
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    Default Is it possible to reduce a .192 dia. hole to be a proper fit for a .187 dowel pin?

    A long story. .708 diameter steel shaft. The drawing calls out a .188 diameter hole, .430 deep .230 off center. All well and good. I do 25 and get about 6 back, the hole is too small but my size pin fits, wtf? I make a reamer guide block with a thru hole for the shaft and an intersecting hole for a reamer. I reamed the holes to .190, the guy that assembles these things says .190 is perfect. I get 25 more and do them to .190, I get a few back, too tight, now what? I Reamed them and delivered them and got 25 more and a dowel pin and a PO from the assembly guy. I do them to .192 as the assembly guy requested. I delivered a different item on Wed. And was told by the engineer, designer the shaft / pin assy. that the pin was supposed to be hammered in the normal way a dowel pin fits. Now I have about 30 of these shafts to reduce the hole diameter on! Just how am I going to do this? The only thing I can think of is a tool like a engine valve guide knurler but lots smaller. Or how about a 5mm thread forming tap? My fault for working with the assembly guy instead of the engineer, that won't happen again.

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    About a 3/8 diameter ball bearing and a 20oz hammer. Will put a nice chamfer on the corner and displace the material down the hole quite a ways. Do each side and then resize the hole.

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    Quote Originally Posted by gbent View Post
    About a 3/8 diameter ball bearing and a 20oz hammer. Will put a nice chamfer on the corner and displace the material down the hole quite a ways. Do each side and then resize the hole.
    +1 although I would go with a 1/4 inch diameter steel ball.

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    You could give the assembly guy a small bottle of loctite and say there is a carton of beer if you hear no more about it.....Ive reduced holes by pressing with a hydraulic press..... although it would probably cause problems with shaft roundness.

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    Quote Originally Posted by gbent View Post
    About a 3/8 diameter ball bearing and a 20oz hammer. Will put a nice chamfer on the corner and displace the material down the hole quite a ways. Do each side and then resize the hole.
    It is not a thru hole and it is .230 off center on a .708 dia round bar. Not the end, the top of the hole goes around the bar.

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    If the engineer will work with you, I'd take some 5mm dowel pins and turn two diameters - one to be the press in the shaft (fit as needed), one to be the nominal 3/16" to stick out as needed. You press so Assembly Guy doesn't get a chance to mess it up.

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    Quote Originally Posted by moonlight machine View Post
    It is not a thru hole and it is .230 off center on a .708 dia round bar. Not the end, the top of the hole goes around the bar.
    Eat that batch. Double the price so you can eat more, later.

    'been an inconsiderate arsehole as a designer meself.. Now and then.

    Damned seldom.

    Having been a machinist/toolmaker FIRST, I already knew it weren't going to be "free" to be weird, though!

    Got a tough spec? HIS job to make sure it is understood just how tough and the why of it, and what they will call "good" before the work begins.

    Could was this 'ingin-ear" missed that class at school?

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    Quote Originally Posted by Milland View Post
    If the engineer will work with you, I'd take some 5mm dowel pins and turn two diameters - one to be the press in the shaft (fit as needed), one to be the nominal 3/16" to stick out as needed. You press so Assembly Guy doesn't get a chance to mess it up.
    The shaft goes thru a part with a .190 slot that the pin goes thru. the slot limits the rotation as well as setting the location of the shaft. A 2 diameter pin will not work.

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    Quote Originally Posted by moonlight machine View Post
    The shaft goes thru a part with a .190 slot that the pin goes thru. the slot limits the rotation as well as setting the location of the shaft. A 2 diameter pin will not work.
    Well, two slight flats on the larger diameter would give you clearance on the slot during "pass through", but I can see orientation being a pain during the press.

    If they won't accept Loctite then you either have to sleeve the oversize bores or make new parts, it seems...

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    Quote Originally Posted by moonlight machine View Post
    The shaft goes thru a part with a .190 slot that the pin goes thru. the slot limits the rotation as well as setting the location of the shaft. A 2 diameter pin will not work.
    I like his thinking, nonetheless.

    How about a slight bore in the end pointed into the shaft?

    Insert pin, follow with drift or pin punch, "upset" the thinned walls where that bit of a bore is, swelling it to the bore, blind-rivet style.

    It surely doesn't seem a design where that pin is ever MEANT to be removable in any case.

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    Make a "broach" a few thou larger than the hole--use tool steel of some sort--and machine or grind some fairly
    fine serrations around the OD After it's heat-treated press it in the hole and you should find that it (the hole) is
    now a few thou smaller Get it right and you may find that you can press the pin in the hole without resizing.

    I've used this trick on larger holes and it does work but, unfortunately, there's a bit of guess-work involved in
    getting the size right. Also, you're working with a blind hole so you've got to have a way to get the broach out.
    Easy way is to put a thread on the other end so you can use a slide hammer to pop it out of the hole...

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    Quote Originally Posted by LKeithR View Post
    Make a "broach" a few thou larger than the hole--use tool steel of some sort--and machine or grind some fairly
    fine serrations around the OD After it's heat-treated press it in the hole and you should find that it (the hole) is
    now a few thou smaller Get it right and you may find that you can press the pin in the hole without resizing.

    I've used this trick on larger holes and it does work but, unfortunately, there's a bit of guess-work involved in
    getting the size right. Also, you're working with a blind hole so you've got to have a way to get the broach out.
    Easy way is to put a thread on the other end so you can use a slide hammer to pop it out of the hole...
    Good one.

    Seen it work where the PIN was given a whack aligned long-axis with a cold chisel as well. Mind, you can BUY them grooved that way. Just not with the raised welts left in-place.

    Raised double welt is "localized' as to total circumference or a slot - especially if not full-length. Pin may go a tad oval as well. Might not harm the other part it has to pass through. Insures the pin isn't trapping air or oil ahead of it, refusing to bottom and JF STAY there.

    Engineer might even LIKE that last part.

    And then.. there are split and even spiral "roll" or "spring roll" pins. Since the challenge isn't exacty a new one?

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    Don't know if it will work for your application but scoring the sides of the pin with an electro-pencil will raise enough burr to tighten it somewhat. I'm talking about the style electro-pencil that throws sparks, not the vibratory kind although that might work if the pin is soft enough.

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    Quote Originally Posted by thermite View Post
    Eat that batch.

    Got a tough spec? HIS job to make sure it is understood just how tough and the why of it, and what they will call "good" before the work begins.

    Could was this 'ingin-ear" missed that class at school?
    I am modifying an existing part that is expensive so if I can somehow upset ihe ID and then finish the diameter they can be saved.

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    Quote Originally Posted by UncleFrank View Post
    Don't know if it will work for your application but scoring the sides of the pin with an electro-pencil will raise enough burr to tighten it somewhat. I'm talking about the style electro-pencil that throws sparks, not the vibratory kind although that might work if the pin is soft enough.
    It is a hard dowel pin.

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    Quote Originally Posted by thermite View Post
    I like his thinking, nonetheless.

    How about a slight bore in the end pointed into the shaft?

    Insert pin, follow with drift or pin punch, "upset" the thinned walls where that bit of a bore is, swelling it to the bore, blind-rivet style.

    It surely doesn't seem a design where that pin is ever MEANT to be removable in any case.
    The blind hole in the shaft is not totally blind, it is .188 dia to .430 depth then thru at .125 dia. There is a hole through the part the shaft goes through. To remove the pin in the original design you rotate the shaft to line up the hole in the part and the hole in the shaft and drive the pin out with an 1/8" pin punch.

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    This is a goofy thought: Rotate the part until the hole is level side to side in a press (19.812 degrees). And with a hardened bar 1.260" diameter, press until it creates the fit you need. 1.260 should contact evenly all the way around the hole's opening. Use something soft to keep from flat spotting the part's backside.

    Or, plate the inside of the hole.



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    Why are you making random sized holes and hoping the mating pin fits? Does the customer not supply a toleranced drawing? How do you know the diameter of the customer's pins aren't all over the place?

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    I'd try a roll tap

    perhaps deliver the assembled if possible, then never listen to people who are not in charge

    I hate to be 'that guy' too, but you cannot make changes without an ECO

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    not possible other than press in a bushing.
    .
    any knurling or metal deforming not normally acceptable. most would open up hole for bigger dowel pin like a 6mm. or use a roll pin which typically is .010 to .015" bigger and collapses when hammered into hole


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