Unibit / Step Drill, love or hate?

[tedmich]

I just destroyed my last set of Harbor Freight TiN coated "HSS" step bits on a nice 0.040 SS (304?) welded box I am making into an amp cabinet. Damn stuff seems to heat harden and the bit glowed red and melted. My original Irwin Unibit has needed sharpening for the last ~ decade, since it seems to need a special grinding jig ...the popular diameters are too dull to cut much.

I was happy to see Irwin and Klein Tools ( rebranded?) offer a M35 cobalt HSS Unibit, anyone try these?

They cost about $40 for the 1/4-3/4 step one and money is tight so I was happy to find an Ebayer selling something similar for $11 delivered.
M35 cobalt step drill 3/8" shank 9 hole 1/4" to 3/4" - eBay (item 140339587832 end time Dec-11-09 07:17:12 PST)

I know TNSTAAF but I'll report back if it cuts the mustard!

[black_labb]

i severely dulled one of the steps on a step drill on a SS bowl. SS is not kind to cutting tools.

[rudutch]

NOT cheap, but durable

Greenlee 660 Kwik Change Stainless Steel Hole Cutters, Greenlee - Toolfetch.com

[defaced]

Austenitic stainless steels (like 304 and other austenitic alloys) work harden. Use a very slow RPM and high loads to take deep cuts. I'd take the time to dig up feed and speed tables for drilling stainless.

The other option, if you don't need to weld the stuff, is to switch to 303 stainless which is a free machining grade. Basically 304 with increased sulfur content to make it easier to machine.

[DIY_Guy]

I use Greenlee step bits, and so far so good when drilling through SS(drilled probably over 100 holes so far, probably time to sharpen it).

I found that the key is to work extremely slow. My drill press is retrofitted to spin the chuck at 250 RPM, and I think the conversion also increased the torque. I also take about 3 minutes per hole, only giving the minimum amount of pressure needed.

So either the Greenlee stuff is just plan good, or my slow method takes lees of a toll on the bit. But it works for me!