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Thread: Hub Extension Threaded Inserts

  1. #1
    Junior Member Bart's Avatar
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    Dec 2015
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    Hub Extension Threaded Inserts

    Ever since I turned out my hub extensions, I was not happy with the standard nuts and bolts holding the prop to the hub. I originally attempted to thread the aluminum holes, but not having a accurate method to index the holes. Being a 1/16" off really didn't let the bolts line up to well. so I over sized the holes, and put a nut on the end.
    but looking on the web. https://www.aircraftspruce.com/catal...ages/saber.php there are a few hub makers that offered SS 17-4, 3/8-24 threaded inserts, that can be pressed into the hub. For about 70 bucks...sounds kind of expensive or 6 custom nuts.... the only problem I have the smaller 75mm hub, and am needing 5/16-24 inserts..

    but over the last year. I have updated some of my lathe tooling.. mainly an indexer dividing head set up. so I can locate the 75mm circumference holes on my hub.
    so back to the drawing board.
    took some time to fill in the holes that I had on the hub. Refaced and drilled them out. Using my indexer, what a difference that made....
    Finished the holes out with a .500 reamer.
    then started on the inserts. I never have had to good of luck threading SS, and after looking at the higher quality taps. They probable would have worked. but I really didn't like the thought of busting a tap, with how the SS likes to do that at times. So I opted to purchase a internal threading set up that would allow me to single point turn the 5/16-24 threads..
    the outside of the inserts I turned to .5002" OD for a press fit into the hub. and bored out an internal relief for the threading tool. "I had only 1/2 inch of the tool shank, the threads would be 3/8" in length, which doesn't leave much room for error.
    but things turned out great, and only broke one 15.00 dollar carbide insert.
    I do like how it looks, and like I was saying about how spendy it was just to purchase the prefabbed inserts.
    my cost was
    17-4 SS round 3/4" x 12" 30.00
    tool for threading 39.00
    2 carbide threading inserts 12.95 ea. "shars 06 IR A60"
    time. 4 to 5 hours priceless....

    It really was not cost effective. BUT these were a custom size, and now I have the tooling to do it again when needed just need to get a few more
    I ended up turning the 3/4" lip down to .600 dia. Not much clearance between the 75mm holes and the 2" outside dia. of the center of the prop hub.
    but I am happy with how it looks.
    down the road I may pick up some SS socket head cap screws. 5/18-24 x 3.5" but man they are proud of them..
    later down the road, I may disassemble it and anodize it. but that will be another story....
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    Last edited by Bart; 04-18-2021 at 01:17 PM.

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