Drill/Tap SS All Thread Rod

Kroll

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Guys I have some 3/8 316 all thread rod that in the end of rod I need to drill and tap 10/32 screw.I foresee problems knowing me,but wanting to collect some “how to’s” to increase my luck.I do have some anchorlube and drill bit that is for machining SS so that may help.Thanks guys
 
The biggest trick with stainless is to never let the drill spin without cutting. If you let off the pressure it only takes a moment for the bottom of the hole to work harden and then it is difficult to get the drill to cut thru the hard surface to continue drilling. If you need to peck to clear chips go from cutting pressue to out of the hole as fast as you can, same with coming back in, do not feel for the bottom just come back in fast to start drilling again.
 
Just did some drilling and tapping of 316 Stainless barstock. Tap size was M3.5x0.6 (close to an #6 or #8). I purchased an inexpensive carbide drill from Shars which really handled the SS like butter. I also tried a cheap HSS twist drill which really made a mess of the hole and eventually snapped. I bought a spiral flute tap to cut the thread and found the SS really didn't want to extract chips through the flutes (at least at this size of tap) so I ended up chip breaking every 1/8 turn. I would have preferred a straight flute tap for this since it would have been stronger. Use good tapping oil, not coolant.
 
Macardoso could you provide link to drill bit that you use.I went to Shars they have lot drill bits so next I type carbide several more pop up.One look at was 36.00
 
For Stainless, I prefer to use a 50% thread engagement for better tap life and nearly full thread strength. You would want to use a No. 18 drill (.1695) tap drill in this case. I chose a stub length, uncoated, slow helix drill. When manually drilling on the lathe, it did not break chips much, but long strings ejected from the drill without clogging at all. https://www.shars.com/18-solid-carbide-stub-drill. A coated drill will last a little longer, but I'm more likely to break tools than wear them dull, so I tend to stick to uncoated.

I'm assuming you're tapping a blind hole into the rod. I would stick with a straight flute (NOT a spiral point) tap and maybe buy both a taper and a bottoming tap to make getting a straight hole easier. Uncoated HSS is fine but there are more expensive options (of course :) )
 
I just use a Cobalt drill and it works fine. It needs to be sharp, though. Unless it has to take a big load I usually go one size larger than the table calls for.

I agree with taper taps.

When drilling stainless, the trick is to not dwell. Reduce your cutting speed to about 80sfm. Start drilling and keep up your feed. You can go about 1-1/2 the drill diameter before clearing the chips. When you resume drilling maintain your feed. If the bottom work hardens, increase your feed pressure to punch through and then try to keep up with the feed. You are doing this to avoid work hardening the hole so you can come back and tap it.
 
Ditto - I drilled and tapped a 10-32 hole in 3/4" stainless in the lathe using a cobalt drill and a standard tap set. Had no problems.
 
Carbide is not necessary for this operation, I just had a lot of holes to make and money to spend on the job.
 
Thanks guys for all suggestions this information will help me so much.I think I am going to order few bits from shars cause my plan is to try make more parts etc out of stainless more than just this time.So planning for future projects out of SS
 
Thanks guys for all suggestions this information will help me so much.I think I am going to order few bits from shars cause my plan is to try make more parts etc out of stainless more than just this time.So planning for future projects out of SS

FWIW different grades of stainless have very different machining properties. Sometimes it’s a case of ‘what you can get’, but for ease of machining, 416 grade is hard to beat. Not super corrosion resistant or weldable but cuts nicely and can be heat treated to the equivalent strength of medium carbon steel.
 
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