Hey you machinists: best way to enlarge a 1/2" hole to 1" in stainless steel?

LaReaLaRea Member, Moderator Posts: 8,064 mod
in General Boating Discussions
The top plate on my light mast is 3/32" stainless, with a 1/2" cable hole.  I need to enlarge the cable hole to 1 inch for some new stuff I'm adding.  Any suggestions?
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  • YYZRCYYZRC Member Posts: 5,416 ✭✭✭✭✭
    Cobalt step bit. 
    2006 390 EC
    2008 350 EC
    Georgian Bay
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  • TonyG13TonyG13 Member Posts: 1,438 ✭✭✭✭
    edited February 2024
    If you don't have enough depth for a step bit, get a 1/4" thick piece of wood (solid works better than ply) and drill the size hole you need in it. Then use it as a template/guide over your smaller hole. I center it over the existing hole using double-sided tape and then painters tape around the perimeter to hold it in place. This will keep a regular hole saw bit from wandering when you're trying to get the bit started. Just did this to enlarge a hole in my cockpit. 
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  • LaReaLaRea Member, Moderator Posts: 8,064 mod
    Like this
    https://www.amazon.com/COMOWARE-Shank-Cobalt-Spiral-Flutes/dp/B0BVTCJBWP

    or this?
    https://www.amazon.com/Cobalt-Step-Drill-Spiral-Flute/dp/B0BWYC1SV4

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  • YYZRCYYZRC Member Posts: 5,416 ✭✭✭✭✭
    edited February 2024
    Yes but if it’s less than $40 it probably doesn’t have enough cobalt in it. Might still be fine for one hole though. Decent amount of cobalt would be 5%. 

    The second one looks futuristic. Wow. 
    2006 390 EC
    2008 350 EC
    Georgian Bay
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  • LaReaLaRea Member, Moderator Posts: 8,064 mod
    It does look like CGI marketing artwork!  I don't mind spending $75 for a tool that will last.  The alternative is spending hundreds for a new light mast.

    I drilled out the hole from 3/8" to 1/2" without too much of a fight using a regular drill bet at low speed, so maybe a reamer will work.
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  • YYZRCYYZRC Member Posts: 5,416 ✭✭✭✭✭
    edited February 2024
    Thinking about this more. Since you are doubling the diameter, you could probably just use a 1” cobalt drill bit and treat the 1/2” hole as a pilot hole. Going slow with minimal pressure of course. 

    Use lots of oil to keep it lubricated and you will be golden. 
    Post edited by YYZRC on
    2006 390 EC
    2008 350 EC
    Georgian Bay
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  • captkevincaptkevin Member Posts: 553 ✭✭✭
    YYZRC said:
    Use lots of oil to keep it lubricated and you will be golden. 
    Thats what she said.

    2004 232
    2021 Yamaha Fx svho
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  • LaReaLaRea Member, Moderator Posts: 8,064 mod
    I ordered the reamer -- on the assumption I'll use it more often than a big-a$$ drill bit.  
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  • raybo3raybo3 Administrator Posts: 5,614 admin
    Greenlee knock out punch
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
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  • LaReaLaRea Member, Moderator Posts: 8,064 mod
    @raybo3 - looks great but I don't have access to the back of the plate.
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  • Liberty44140Liberty44140 Member Posts: 4,414 ✭✭✭✭✭
    Looking forward to seeing this hole! (And curious about the bit)
    07' Cruisers 390 (Previous Rinker's: 06' 342EC & 01' 310FV)

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  • IanIan Member Posts: 3,062 ✭✭✭✭✭
    Liberty44140 said:
    Looking forward to seeing this hole! (And curious about the bit)
    After he uses the reamer - eek.

    Regards,

    Ian

    The Third “B”

    Ravena Coeymans Yacht Club

    https://www.rcyachtclub.com/

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  • LaReaLaRea Member, Moderator Posts: 8,064 mod
    I should have bought one of these tools a long time ago.  Not only did it work perfectly on the stainless steel light tower, but I also used it in a couple places on my new dash panels.  

    I started by enlarging the hole to 3/4" to see if that will work.






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