Thread: Confusion regarding tap sizes

I'm just getting into metalworking, and tap sizing seems very complicated to me. If I wanted to tap a 1.5 mm hole in hardened steel (58-60 HRC), what size / kind of tap should I use? Does thread size affect the anything along the process other than the screw I would have to use? Thanks!

Welcome to the MetalWork Forums.

In this case the thread diameter 1.5mm is very small, indeed.

I would suggest that drilling a tap size hole- smaller than the thread OD is going to be a very difficult exercise for a beginner.

As drill diameter sizes decrease , the rpm required to run them efficiently,increases.

Without practice and understanding of the procedure, I predict you will snap the drill bit, let alone the tap.

You will need something like a Dremel tool to provide the drill bit RPMs, required. I would be using a Dremel drill press to fix the Dremel tool to enable square to job drilling. Revolutions around around 10,000rpm are required.

Drilling hardened steel is another problem. You do not mention the thickness that is to be drilled.

To my mind,the hole could only be drilled and tapped when the steel is in a soft annealed state and then hardened after the drill and tap operation.

If you have never drilled a hole and run a tap I would try some larger size ,say 6mm before moving ahead and do this on mild steel,first up.

I have 50 years of drill and tap experience behind me and yet when I drilled a 1.5mm in 16 mm mild steel and it took several drill bits and new holes before I was successful.
A light sense of touch and clearing the drill bit often is essential.

As far a tapping a hole that small I have not tried that,so you are on your own there.


welcome to the forums
Grahame

Originally Posted by StevensonCh

If I wanted to tap a 1.5 mm hole in hardened steel (58-60 HRC), what size / kind of tap should I use?

I don't think there's a tap on the planet that's capable of doing that.

I agree with Grahame, I wouldn't even attempt to tap a 1.5mm diameter in anything harder than mild steel .
Would it be possible to anneal the steel and regarded it after drilling and tapping the hole?

More info about the material and task you are trying to achieve might assist us in helping you.

only way to thread steel that hard is to threadmill in a very good cnc mill, or 4 axis EDM. tapping will not work

I'm with the others. Things can turn south really quick with small taps. I generally wouldn't even try at less than 4-5mm and 1.5mm sounds impossible.

Hi Guys,

You could machine a hole in your steel and then use a softer threaded insert ! I've seen Japanese stuff done that way. I agree with the others, there is no way you could thread a hole in a HRC50 hard steel with a tap !

Originally Posted by BaronJ

Hi Guys,

You could machine a hole in your steel and then use a softer threaded insert !

You read my mind.

Yeah, using a special oversize tap and tapping before hardening is possible but still sucks as your tolerance is wholly dependant on repeatability of material and treatment. I think your only hope for tapping 60rc would be EDM, 50 would tap okay with a carbide tap but as stated not happening at 1.5mm

Sent from my SM-G973F using Tapatalk

Is it just me ,or have others noticed that 1.5 mm does not appear in the commonly available drill tap charts online or in books.

ISO Metric Course charts that I saw list 1, 1.1, 1.2,1.4,1.6 and so on. No 1.5mm thread size.

I googled and did find an available 1.5mm taps sold as a single for what is obviously aimed at veterinary surgical implants.


StevensonCh, just curious, is the 1.5mm tap spec a part of something specified in a plan or drawing design, or is it a number you have settled on as being the correct diameter ?

Grahame

TBH, I just saw "tap 1.5mm in HRC 58-60" and didn't bother thinking if 1.5mm was even a thing because it can't be done

It crossed my mind that the 1.5mm is a mix up with reading the threadform and is actually pitch.

The hardest thing I have put threads into was the 10mm thick Bisalloy plate which forms the lower half of the base of my tri-grinder lazy susan

I went through 3 taps cutting the threads for the 12, 3/16" machine screws
One tap broke (luckily enough was poking out to be able to grab it with a multigrips) and two other taps were stuffed by the time I finished.
Mind you they were cheap carbon steel taps - I still don't know why I just didn't use through screws with nuts underneath.

IMG_2911.jpg

Hi Guys,

Metric coarse 1.5 X 0.3 mm and metric fine 1.5 X 0.2 mm are common in HDD assemblies. I've also seen much finer screws used as well, probably around 0.5 mm. All in aluminium components. I think some of the very small ones may be self threading since the screw seems to be tapered, with a coarse thread a bit like a wood screw. I believe that they are stainless steel since you cannot pick them up with a magnet.

Making folding knives common sizes are 2-56, 1-72 or sometimes 0-80 so these are down around the 1-2.5mm size. I regularly tap 2-56 in titanium which can end in tears pretty easily but I would never try hardened steel.