Utilizing press fit for cutting tool extension
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  1. #1
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    Default Utilizing press fit for cutting tool extension

    I am working on creating an extension for a 9/16 counterbore cutter. This thing has a 1/4" shank on the end that is 7/8" long. This application calls for the addition of a drill rod extension to this cutter, about 9" long it happens to be a 1/2" drill rod. I need a way to hold the cutter inside a bore in the drill rod extension. I am thinking a press fit would be best. Maybe I am wrong? Now the question is if a .0015" interference fit will do the job? Nothing is worse than to see that extension slip around the cutter shank when it really should be driving it. I was thinking, just a simple MAPP torch on the female end of the extension and worse case scenario, have the cutters 1/4" male end sit in some dry ice. Just use some gloves to slip the two parts together and wait till they cool and warm to room temp. Will this work?

    Thanks guys

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    I would just loctite it. BTDT. It will hold if you clean and assemble correctly. 0.0015 interference on 1/4” is too much. That’s .006 interference on a 1” shaft.


    Sent from my iPhone using Tapatalk

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    OK, so now we are getting closer to the right direction. Thanks for the reply. A.)How much you think will be enough interference? .0005"? I am thinking that that much shrinkage on a shaft can be easily achieved just with dry ice. B.)Will this suffice for a good press fit between a cutter and its extension?
    Thanks again.
    C. Wizman

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    Another for just Loctite it.

    IME press fits in that type of application are at best a moveable feast.

    Just make your extension the closest sliding hand fit you can and leave the rest to technology.

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    Or slip fit and silver braze.

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    Are you driving this with something with a power feed? If you are driving this by hand in a drill press or with a cordless drill I would be less concerned about something slipping and breaking stuff. If you are putting this in a CNC machine I might put flats on the shank and use a few set screws to make sure it won't spin.

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    I'd shrink fit it.

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    I've done the exact same thing and just put a few small set screws in the side of the extension that go thru to the bore. A small flat on the c-bore shank to help drive it and you're done. Just an idea to consider.

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    doesn't soft silver solder offer more psi Of hold than thread lock bearing retainer?

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    Quote Originally Posted by madmachinst View Post
    doesn't soft silver solder offer more psi Of hold than thread lock bearing retainer?
    First off you won't be using thread lock or bearing retainer but the ''full fat '' retaining compound like 638 LOCTITE 638 - Henkel Adhesives

    Yes silver solder does, but what has the cutter got to do and how many times (materials & machinery etc etc please)

    Bear in mind you've already a 9/16 cutter with a 1/4'' shank so you ain't gonna too wind much torque and cut on that - are ya

    FWIW I know (cos I've BTDT) you will wring a Loctited 1/4 shank off (Just like a noodle) long before the Loctite gives way.


    Another danger with any heating method is distortion causing the tool to run off true.

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    BTW, what this cutter is cutting is between HRC25-30. Most people will be using a hand drill some a drill press. Thanks for the link to the retaining compound.

    I guess I will have to try out the 2 methods and see what works best. Probably with a beater end mill and my lathe.


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