Drilling 410 Stainless

Yes, 410 stainless is heat treatable, and would likely machine better when it is than when it isn't, depending on the hardness. It can be heat treated as hard as 45Rc. In the annealed condition it should be machined at approximately 90 SFPM. You'll find it has a tendency to tear in the annealed condition, resembling mild steel, but somewhat better. My experience tells me it's a rather soft metal, although somewhat tough.

I am not able to provide any recommendations regards coated tools, but be certain to use a grade in keeping with Carboloy 883 (C2) when machining. While it is a ferrous material, it machines best with that grade.

Sorry I'm not more help.

Harold

The type of bit required is very dependant on the process which will use the bit.

I would recommend using split point HSS drills (of high quality). HSS drills are easy to resharpen, are quite rugged and reasonably priced. Cobalt drills are more prone to breakage and cost roughly twice that of HSS tools. That's a lot of cash if you cannot sharpen them.

Stainless typically requires a high feedrate to prevent work-hardening. High feeds cause stress which can be detrimental to brittle tool materials (cobalt and to a much greater extent, carbide).

The split point is good because it virtually eliminates the need for a predrill. I do a lot of hand drilling through cast tool steels at work so drill geometry is very important (to my arms). Also, if you have several hundred holes to make, you don't want to have to perform two or three operations when one is sufficient.

I'm not sure what the jobber and screw-machine lengths are for the size of bit you're using but if you can use the screw-machine length drills, you'll be better off (better rigidity, less chance of snapping a drill and less opportunity for the drill to wander).

So what is the tool being used? Hand drill, drill press (quality?), milling machine? Does the tool have auto-feed or is it hand-fed?

Lastly, if you cannot make the hole in one shot because the surface of the housing is funky, I wouldn't bother with a center drill. The last thing you want to do is break off a point and have to dick around trying to extract it. A CNC spotting drill works well and should be able to start a hole on a cast/curved surface. They're very rugged because of their (very) short length.

HTH.

Regards,

Robin

get some GOOD Cobalt alloy bits. Not cheap ones.

snip----

How embarrassing! I didn't take note of the dot before the 4, so assumed you were speaking of a 4" hole. Sorry. If your parts are not heat treated, there is no reason to use a cobalt or carbide drill bit. The material will act soft and somewhat tough, but will drill fine with HSS. My comments regards carbide were assuming that you were going to have to bore. If the parts are, indeed, heat treated, and near the top end, cobalt drills will be essential to good success. I would not recommend the use of carbide if the holes are to be drilled by hand.

Harold

Robin,

I think the only tool available is a hand feed drill press.

Thanks to all who took the time to reply. Armed with your advice and comments I think we have enough info to get the job done. We'll be drilling the housings in about a week and I'll post a follow up to let you know how it went.

Bob