Enlarging holes in 316 stainless plate

Have a local tool grind shop make you up a coupla step drills....binga badda youre lined up, next thing ya know, your enlarging the holes on location....

Drill press, drop it in and clamp... and away ya go...........dont run the rpms very high, else the stainless will work-harden and you'll burn up the tool....thats why I suggest having two of em made up.....

I'd consider a core drill. I don't know how they would perform in SS and I can work-harden SS just by looking at it. But I'm certain it would start easier and work quickly. I have a small selection that I use consistently, particularly on brass.

DeepDiver said the following on 3/28/2005 8:29 PM:

I second the core drill recommendation. This is basically a three or four flute drill bit made for reaming holes out larger. I've used on lots of stainless with great success.

I've been following both threads and I've not seen what I consider the main piece of advice you need. So here it is.

If you're reaming stainless with a drill that size you need to run sloooow. Much slower than nearly any import drill press that I know about. I'd say that for decent bit life you'd need run around 80 rpm or slower. I think that you'd end up dulling the bit before getting through that many holes if you was running 100 rpm or faster.

As advised already you need to keep a heavy chip load and never ever let the drill slip on the work.

Wayne Cook Shamrock, TX

Thanks to all who've replied so far.

I like the core drill idea. But according to J&L, a single 13/16" core drill costs $100!

Custom grinding some bits so that they have a pilot is a nice idea; I'll look into prices (although, I suspect I'm in the $100 range again).

Irwin Unibits can't handle 1/4" plate, so they're out.

So I may just go with a high-quality drill bit. At least I can re-grind it as it wears. Would you recommend cobalt, or TiN, or ...?

As far as centering the hole, that won't be a problem. Whether I'm using a mill-drill or a drill press, I will make a simple locating jig to position each hole before clamping and drilling.

Regards, Michael

I'm aware of the work-hardening properties of SS. As for the speed, the bottom speed range I'll have available is either 120 or 150 RPM (depending on which machine I use). I guess that will have to be slow enough because the machines won't go any slower!

Any recommendations on cutting coolant or lubricant? I'd prefer something that's readily available as opposed to an exotic. I do have Tap Magic EP-XTRA cutting fluid on hand.

Thanks again, Michael

Polar tool, here in Minneapolis, sells core drills, resharps, for pennies on the pound. I don't think I've ever spent more than $5 for a single one.

Call them, Doug is either the dad or the kid. I know one other RCM user has been successful outstate with them. He's a good egg.

DeepDiver said the following on 3/29/2005 3:38 PM:

Good luck then. Since you're only removing part of the hole you may get by but that's a lot faster than I'd like to see. I just calculated

120rpm to be about 25fpm. That sounds slow enough but it depends on a lot of factors especially the type of stainless. If I remember correctly you mentioned these has been welded. If that's the case they're not likely a free machining variety of stainless.

The best you can get. I've always just used a good sulfurized cutting oil but there are better things out there.

Wayne Cook Shamrock, TX

It's Type 316 stainless steel.

According to my reference, Type 316 has a 45% machinability rating compared to Type 1212 carbon steel (which makes it comparable to oil-hardening tool steel, discounting the work-hardening properties of stainless).

Regards, Michael

It also doesn't take into effect the low heat capacity of stainless. Since stainless is such a poor heat conductor the cutting tool tends to heat up more than with regular steel. Combine that with the "stickiness" which makes it want to gall to nearly anything and it's work hardening properties makes for a different material to cut. This applies especially to 316 when compared to the more machinable 300 series alloys.

With carbide it's not as much of a problem since it can take the heat but my experience with HSS and stainless tells me that you need to go slow if you don't want to burn the bit up. I've not got any reference materials in here to look up the recommended speed but I often find those speeds to be a little fast for good tool life in the real world anyway. Actually I rarely go by the numbers anyway rather I go by what my experience has shown me that I can get away with. I can generally look at a drill bit, etc. while running and tell if it's about the right speed.

Wayne Cook Shamrock, TX