Wet Spreaders

Countersinking into Stainless

Recommended Posts

I have to machine up a small stainless plate with a countersunk #10 hole in it. I've drilled stainless many times (slow speed, high pressure, oil) and the process works well. I have had zero luck countersinking - generally just seems to fuck up the countersink bit. What product and process do I need to get this done right?

Share this post


Link to post
Share on other sites

I’ve had good luck with a sharp new countersink and with having a machine shop do it. 

Share this post


Link to post
Share on other sites

Are you using a carbide bit? I use Anchor Lube and the slowest speed possible with the piece clamped to the table or held in a vice otherwise it chatters.

Share this post


Link to post
Share on other sites

carbide...  I have used router bits with brazed in carbide inserts marketed for wood working, but chucked in a mill with the appropriate speeds and feeds these will cut stainless like butter

Share this post


Link to post
Share on other sites

The vast majority of countersinks are M2 tool steel. They also sell cobalt M42 and titanium nitride coated.

Share this post


Link to post
Share on other sites
5 hours ago, Bruno said:

Can use a larger drill bit instead of countersink

Quick and easy by our local machinist.

Share this post


Link to post
Share on other sites

Don't use carbide, it's too brittle and too expensive. The best countersink for metal is a single flute counter sink, you can buy them on Amazon, multi flute countersinks like you buy at the hardware store only work well if everything is clamped down, not worth the bother. Get the fancy coated one if you want they are only a couple of bucks more. You are looking for an 80 degree angle, that will match the angle on the flathead fastener. Don't go wild with the rpm, you're not in a hurry. A large drill bit will sort of do it but it's the chamfer angles are wrong and won't match the fastener.  I was a machinist for 35 years probably done a million countersinks and chamfers and more dumb boat projects than I can think of.

  • Like 3

Share this post


Link to post
Share on other sites

CS angle depends: 82 for Imperial, 90 for metric. If you have no rigidity in your setup (e.g. hand drill) then a single flute will chatter less. If you have a rigid setup (e.g. milling machine) then a 6 flute HSS will work better. It is very difficult to get enough cutting pressure on SS by hand - if it isn't cutting on SS then it is work hardening the material making it harder to cut. The single flute ones sold at the big box stores to homeowners for wood are unlikely to last even a single hole. McMaster has a wide selection.

Share this post


Link to post
Share on other sites
22 minutes ago, DDW said:

CS angle depends: 82 for Imperial, 90 for metric. If you have no rigidity in your setup (e.g. hand drill) then a single flute will chatter less. If you have a rigid setup (e.g. milling machine) then a 6 flute HSS will work better. It is very difficult to get enough cutting pressure on SS by hand - if it isn't cutting on SS then it is work hardening the material making it harder to cut. The single flute ones sold at the big box stores to homeowners for wood are unlikely to last even a single hole. McMaster has a wide selection.

Are cobalt countersinks for handheld drills or drill presses a thing? Can we use lathe center countersinks in a drill press? I've noticed a big improvement in cobalt over HSS for cutting 300 series stainless. Would like to try out a countersink in it.:)

(A Drill Doctor sharpens cobalt twists very well, tho it tends to leave a burr on the cutting  edge. Have to sharpen maybe half as often with cobalt.)

Share this post


Link to post
Share on other sites

Wow! Those McMaster carbide countersinks are expensive! ($160). Even hardened steel is not cheap at around $30 for the tool. Very spendy when you consider that I'll likely smash the carbide one and blunt the steel one - so they end up being more or less disposable due to a vicious mix of incompetence and material science.

Share this post


Link to post
Share on other sites

They’ve got different typesTiN coated cobalt single flutes on Amazon for $14.

Share this post


Link to post
Share on other sites

dont use a bigger drill as a countersink if the fastner will see any type of load. As others said the shoulder angles are wrong and it will spot load on the fastener head. If its a couple holes your dont need best quality, but crap will fail on one hole.  

You have to gauge, if you take it to a machine shop, the ones around here sort of have a $50 minimum for anything. Cant blame them, so is it worth $50 or buying a $50-100 cutter and having it forever?

Share this post


Link to post
Share on other sites

Cobalt works well on stainless, hand held or machine held. Carbide is less sharp, more brittle, but more heat resistant if you are going to run it hot. A 1/2" 6 flute cobalt from McMaster is $17. That is mostly what I use unless I am doing it in the CNC mill. Don't use a lathe countersink, they are normally a different angle (60) for a lathe live or dead center. 

Cobalt drills, even cheap ones will drill a lot of stainless if rigidly held and properly fed. I can do several hundred holes through 1/2" 316 before needing to think about sharpening (in the CNC). You won't do that hand held. 

  • Like 1

Share this post


Link to post
Share on other sites

Years ago I did find an extra long #8 3/4" dia 82 deg center drill that I use in the field and in conflicts. Have a 1/2" regular length that gets used all the time. Not really expensive but not all that common.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now