help tapping 17-4 SS

As I have mentioned in other posts I don't do production. Retired and sold my large shop but still have a small shop at least by my standards. Simply put I have one of nothing except one too many!
I do quite a bit of work for local Poultry plant so all I cut is Stainless Steel, some steel in the non food areas. Usually I'm trying to make parts last longer and in this case I'm using 17-4. I purchased precision 17-4 from McMaster Carr 25mm. I turned the end 20mm X 45mm long. Drilled 10.2mm x30mm deep to the point of the drill like the original. Counter sunk the opening. Bottoming 4 flute M12 X 1.75 hand tap will go 10 turns into the original. Started with taper hand tap in the chuck then with a center to hold the tap straight used a wrench to turn the tap, when torque required was enough to turn the spindle in neutral set to the lowest speed I stopped and changed to a Regal Beloit spiral point 3 flute TIN coated plug tap. Didn't do much with Tap Magic Pro fluid. I redrilled the hole 27/64". By using the spiral point tap until it turned the spindle, then the bottoming tap, back to the plug until the bottoming tap screwed in 12 turns. I have 19 more to do! Is there a tap that will do a better job? I'd like to run a tap full depth, possibly finish with a bottom tap.

Ya, get an OSG VA-3 bottom tap.

Get rid of the spiral point tap and get a spiral flute. The spiral point is shoving the chips in front of the tap into your blind hole. The spiral flute will pull the chips out, instead.

This is one area where McM falls down a bit, as their descriptions of hardened material sometimes mention that they're "annealed", but will then give a hardness value that means they're clearly not.

Presuming the material you ordered was this: McMaster-Carr and that it really is Rc35, then that's a fairly hard alloy for tapping, but well in the range of good HSS or HSSCo taps. I'd look into a performance tap for Ni or Ti, they're usually ground for freer cutting to avoid binding.

Call OSG or a similar premium vendor on Monday and get their recommendations.

I buy quite a bit of SS from McM, like the next day delivery and my customer does not mind the higher cost. I do have an Account with MSC, they list the better taps in their catalog but their Tech help don't seem to be the best when I talked to them! However I can get their products quickly too, no shipping charge for 2 day and sometimes they will wave one day charge. I have used spiral flute taps but they seem to be easy to break. I have a few supposedly bottoming spiral point taps but they don't seem to bottom well as the chips get packed on the bottom. Though I doubt I have them in 12mm. This wasn't a rush job but I'm behind on everything due to the crazy weather so I want to get this done before they start calling! Is there any particular tap you would recommend out of the MSC catalog? Possibly McMaster Carr?

is there something you don't get?

M12x1.75 Metric Coarse, 3 Flute, Oxide 04622361 - MSC

Best I can suggest from McM is this guy: McMaster-Carr but you might call first and get the manufacturer and part number, then contact them and confirm suitability.

And get some Moly Dee tapping oil. Variocut C Moly Dee, 16 oz Bottle Cutting & 45730595 - MSC

I'll call Monday morning! What about tap drill size?
Can I hand tap? I have the torque releasing tap drivers for inch but no metric. I can check to see if metric is available.

You can hand tap, but a more linear machine tapping might be better if chip control is OK. Not sure, but I think tap shanks are standardizes between inch and metric, so you may already have the right size adapter.

Tap drill is whatever you can get away with - larger is easier, as long as the strength or drawing callout is met. If you're using generic 18-8 bolts there's likely a limit where you're rounding over the thread peaks if you torque them too high.

If you use the Molly Dee, it's good stuff but is more difficult to clean fully if that matters.

I'll check to see if taps fit a 7/16" holder, 3/8" will be too big. No print just part to copy. I think it's 316SS, powerful Neo, magnet will not attract even the slightest amount. Not sure what it does, I could find out but might ask if they are done yet! Don't think they will be bolted to anything. Might fit inside a 20mm ID bearings. I'll check, I probably have Molly Dee.

The 25mm 17-4 you bought from McM is annealed, so it will be 'gummy' and difficult to tap.

Assume it doesn't put you over budget I'd get it ht'd to H1150. It will be much easier to work with, and you'll get a better finish as well.

Looking at the specs it states 25mm is C35 and looking at Inch hardened (metric not available) it states C28 and H1150. Otherwise the write up is the same. Turning the bar it seemed hard. If it's not I don't have time to get it hardened plus the chips from tapping didn't look as if it was a gummy material. Am I wrong to assume it was annealed to C35? My customer said to make it from 304 so hardness is not an issue. I cut a lot of SS, very little steel, probably more UHMW and Delrin than steel but 90% of all I cut is SS so cutting this bar it seem quite hard compared to other 17-4 I've cut.

It's probably Rc35, I don't think you'd mistake it for annealed material. But dang, I wish McM would clean up that aspect of their data. I is easily confuseled, don't need any help in that area...

Tap and Molly Dee came today. I opted for OSG powered metal tap, few buck more but I wanted it to work! I used 10.2mm tap drill, tap almost made it full dept. Used 13/32" tap drill, worked! Tapped the hole 1 shot! Thanks guys!!