00-90 tap and Metal car floors

[freedj]

I am having a really tough time getting tapped 00-90 holes in metal car floors (concor, roundhouse).  I am able to drill the hole using a 1mm carbide PCB drill but when I go to tap the hole the tap always gets stuck.  My drill size is slightly larger than the recommended tap size of #65 (.89mm).  I've tried light machine oil as a tapping fluid but don't have any dedicated tapping fluid.  My tap always slips in the pin vise and gets stuck.  I can't tap further and I cant back it out.  I've had to resort to using some fairly beefy pliers to hold the tap and the spin the car floor to release the tap and do the final turn to get all the way through the floor.  It always seems to stick at the end.  I Tried countersinking both sides on my last attempt and i don't think it made a difference in getting stuck.

So far i've been able to get two holes tapped without breaking the tap, but i know that i'll break that tap soon.  I have both a 3 jaw pin vise and a collet pin vise and neither one seems to be able to hold the tap firmly enough.

What is everyone using for lube, and how on earth are you holding the taps firmly enough?  I am using a MTL 00-90 tap.

[Lemosteam]

Is this an MT tap?  If so that is a thread forming tap, not a thread cutting tap.  I also assume you are backing off the tap every 1/8-1/4 turn as you go- especially if you go out and buy a thread cutting tap.

[freedj]

Yes, it is a microtrains tap that I got as part of the kaydee #1059 set.  It really looks like a cutting tap to me.  It has 3 flats ground on to it rather than lobes like a rollform tap but its so small its hard to tell for sure.

I am backing off, but not every 1/8 turn, probably closer to every 1/2 turn.

[Lemosteam]

Its not. the flats are an obtuse angle to the tangent at the OD of the major diameter of the thread and do not form a cutter, just a pusher, shown below is ground on 5 sides instead of three'



A thread cutting tap will have acute reverse grinding under the tips of the threads.  The drawback is the core diameter is much weaker, especially on a 00-90 tap.

[freedj]

OK, i agree, it's a forming tap!

[nickelplate759]

I've successfully used the Microtrains tap on these floors many times.   I used the drill that came with the set (not sure of the number).   Process was

Drill(hole);
Mount tap in pin vise;
Lubricate(tap); // I use an old tube of Life-Like model train motor oil
Try {
Do {
1/4 turn;
backup 1 turn;
} until done
} except ( STUCK) {curse; remove pin vise; grab pliers and turn}


// Yes, I know my syntax is sloppy

[Lemosteam]

Keep in mind that forming taps also wear over time as well, so I keep several new ones about.

[Maletrain]

Sources for 00-90 cutting taps?

[Lemosteam]

Google is your friend, but here's one:  https://gyrostools.com/91-10090-high-speed-steel-tap-00-90-plug.html

[randgust]

I think micro-mark has them, for a price, of course.

[Rasputen]

I have my 00-90 tap permanently held in a dedicated pin vise, that I have tightened the collet on with two pairs of locking pliers.

[Lemosteam]

Harbor freight has tap wrenches that tighten onto the square shank above and provide for much better control than a pin vice:  They will not work on a round shank.  Smallest one is 1/16"  Most miniature cutting and forming taps will have a 1/8" shank.

https://www.harborfreight.com/3-piece-t-handle-tap-wrenches-38560.html

[thomasjmdavis]

Can anyone tell me whether what Micro-Mark calls a "threading tap" is a thread forming tap or a thread cutting tap? They seem to sell "taps" and "threading taps", likewise "dies" and "threading dies".

[randgust]

I don't know but they worked just find on cutting threaded holes through rather hard cast brass on my Jamco 4-6-2; same material that kept eating drill bits.

The thing that still will get me isn't hard metal, it's soft - like pewter - where the flakes jam it.   You really, really, have to follow the lubricate / quarter turn / remove / clean   (lather, rinse, repeat) or you'll get the tap stuck for sure.

[Lemosteam]

Can anyone tell me whether what Micro-Mark calls a "threading tap" is a thread forming tap or a thread cutting tap? They seem to sell "taps" and "threading taps", likewise "dies" and "threading dies".

These are thread cutting taps and actually might be worth that price.  I use all of these sizes pretty regularly.  You can tell by the axial grooves.
https://www.micromark.com/Four-Piece-Micro-Size-Tap-Set?gclid=CjwKCAiAhJTyBRAvEiwAln2qBwe5nHupxiXteSVT4hdTUoSKLZgVAg3fQxAFW3o3THGBKyRBGZjbKxoCywsQAvD_BwE