Recommended RPM for 5/16” solid carbide drill in 304 SS?

erikmannie

erikmannie

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I have well over 100 holes yet to drill in .125” 304 stainless. I am using 5/16” solid carbide drills. Machine is a 3HP, 3 phase knee mill. I am liberally using dark thread cutting oil on both the work & drill. I peck and I do not get aggressive.

What worked best for me was 1000 RPM with a hand feed, using the quill. The only problem is that the drills aren’t lasting as long as I would like.

I give the drill *a lot* of time to cool. One has to do this in this case; I was really surprised how hot the drill was getting.

I know that stainless work hardens.

These are brackets to connect hardwood fence slats to hardwood 4” X 4” posts in the ground.

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I don’t need the bores to look good as all of these holes will be hidden by a bolt head.

As it is, after about 43 holes I need to retire the drill! This can’t be right.

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Also the material came with some protective coating from the mill. The end user, my brother, wants the SS to be shiny.

I am thinking that I will use these paint removal disks, and then use an orbital sander to take it to 600 grit (by way of 60, 120, 220 grit, etc). I don’t know anything about making stainless shiny.

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While I am asking questions, I would also like to ask what you guys would recommend for a clear coat protective coating after I, say, sand it to 600 grit.

My brother lives about 2 miles from the SF Bay (and about 8 miles from the Pacific Ocean), so there may be some salt in the air.

Rattle can? Auto body shop clear coat?

The powder coater that I use has about a three month turnaround, & I don’t think he wants to wait that long to build his fence.
 
FWIW, my CNC speed feed calculator gives 2000 RPM 10 IPM.

Take this with a grain of salt. don't think you can push it that fast by hand.


Myself, I'd try a split point cobalt made in USA at about 250 RPM, pull on the quill HARD. Use oil liberaly. No peck, let up right as it busts through.
 

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It should respond well to a good machine applied metal polish after the 600 grit. I have started using ShineSeal for the shiny aluminum bats. One component of the set makes a very thin hard coating, and it does not change the shine quality.

:: ShineSeal ::

www.shineseal.com
 
Aukai said:
It should respond well to a good machine applied metal polish after the 600 grit. I have started using ShineSeal for the shiny aluminum bats. One component of the set makes a very thin hard coating, and it does not change the shine quality.

:: ShineSeal ::

www.shineseal.com
Click to expand...

When you say “machine applied”, are we talking a 4-1/2” angle grinder with a buffing wheel? I have never used a buffing wheel, but I imagine something like a synthetic lambswool or a soft cloth.

My brother wants this to be really nice; the job is paid time & materials. I would be willing to buy a cheap (e.g. Harbor Freight) buffing setup.

I won’t apply paint for a customer (not a service that I provide), but I am willing to sand, polish and/or buff.
 
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my rule of thumb with stainless is turn slow, feed hard and DON'T peck. You have to be making a chip at all times as the heat has to go into the chip. I'd probably start around 250rpm for a drill that size and see how it goes. I'd also second the recommendation of using a cobalt split point drill.
 
I think I'd use a water based coolant to keep the hear down, or perhaps TapMagic, I second or third the motion about using a split point cobalt drill and no pecking, which would invite work hardening.
 
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