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

LaRea

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?

YYZRC

Cobalt step bit. 

TonyG13

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. 

LaRea

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

YYZRC

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. 

LaRea

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.

YYZRC

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. 

captkevin

YYZRC said:

Use lots of oil to keep it lubricated and you will be golden. 

Thats what she said.

LaRea

I ordered the reamer -- on the assumption I'll use it more often than a big-a$$ drill bit.  

raybo3

Greenlee knock out punch

LaRea

@raybo3 - looks great but I don't have access to the back of the plate.

Liberty44140

Looking forward to seeing this hole! (And curious about the bit)

Ian

Liberty44140 said:

Looking forward to seeing this hole! (And curious about the bit)

After he uses the reamer - eek.

LaRea

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.