what size drill for tapping an M1.6 thread ?

I need to tap some M1.6 threads for my C12 project.  What size should I drill the hole ?  I'm thinking 1mm is going to be tough work for the tap, & 1.5mm will mean that the threads aren't deep enough.

typically you can find multiple listings of this kind of information by googling your thread title.

I found 1.25mm in less than a minute, but just to be safe you may want to click on a few links for confirmation.

JR

Good call, Thanks John

My understanding is that you need to take the thread pitch from the diameter.

So, for M5 x 1, the hole diameter would be would be 4mm

For M1.6 x 0.35, the hole would be 1.25mm

If you end up with a hole size for a drill that is not available, round up (although use common sense, you can not round up so far that there is no meat to cut the thread in)

For example, for M8 x 1.25, the drill would be 6.75mm, which might be bit hard to come by, so a 7mm should be ok.

Cheers,

T

Timothytitus88 said:

My understanding is that you need to take the thread pitch from the diameter.

Click to expand...

to be really anal about it, the pitch is the distance between the threads and not the depth, if threads were 45 degree angle each way, then your method would work, but they are not.  dont ya love smart arse ex mechanical engineers!
Cheers from the east coast of Oz 

dont ya love smart arse ex mechanical engineers!

Click to expand...

Heck yesssssss, cos I am one myself.

Of course theoretically, you have me there.

I should have mentioned that the pitch subtracted from the diameter is more of a shop floor rule of thumb. No point in telling the boys on the shop floor to look in the ISO standard to find a drill size that no body has. So this rule of thumb has always worked nicely for me, but of course would not be appropriate is you were building the Sydney Harbor Bridge or where calculated bolted connection strengths are important.

Cheers from the west!

Assuming you already have the tap for this thread, I would mike up the end of the tap and drill a hole just large enough to allow it to enter straight.  I cannot see that the tap would be destroyed in cutting the small amount of metal from any size hole that you can get the tap into!

David

Is this a machinist thing? Why are we still guessing and speculating when it is so easy to look up the precise answer?  When in doubt do it right.

JR

Rob Flinn said:

I need to tap some M1.6 threads for my C12 project.  What size should I drill the hole ?  I'm thinking 1mm is going to be tough work for the tap, & 1.5mm will mean that the threads aren't deep enough.

Click to expand...

See here: http://www.icrank.com/cgi-bin/pageman/pageout.cgi?path=/tapsizechart.htm&t=2

Junction said:

to be really anal about it, the pitch is the distance between the threads and not the depth, if threads were 45 degree angle each way, then your method would work, but they are not.  dont ya love smart arse ex mechanical engineers!
Cheers from the east coast of Oz 

Click to expand...

It happens that threads are at 60°, and thus the pitch is the same as the depth. At 45°, the depth would be 0.707 times the pitch.
But in fact, "to be really anal about it", the depth is somewhat smaller than the pitch, because the cut is slightly rounded (depends if the thread is rolled or cut).
This is the ISO norm, american threads may vary.

Excellent thanks for the in depth explanations.  All I need to do now is get a 1.25mm drill & try to make the holes & tap them without breaking the tap or drill .....yikes  !

Good luck, brittle little suckers.

I'll bet I've broken more taps than everybody reading this post combined.  8)  When I was a kid, I had a summer job working in a machine shop and one task was to drill and tap holes at the ends of 50' long steel pipes so they could be screwed together with couplings (for taking cores of ocean floor).

Even though I was working with a much healthier sized screw thread than you (1/4-20 IIRC), with a hard fixtured guide to keep everything true... I was a kid who wasn't paying for the taps I broke, so I broke a bunch... probably hoping I could do something else. As i recall every job I did that summer was as boring as that or worse. 

JR

Yeah, one of my first holiday dobs was drilling and tapping M20 holes in 20mm 316SS flanges. There were dozens of flanges so hundreds of holes too. Start with a 5mm pilot, then out to 10mm then out to 18mm then tap it. Everyone should have to do that once in their lives. Made me feel like a real man.

Rob, its been like 20 years since I have been tapping holes for a living, but trying to visualise in my head, but turn that sucker in 1 turn clockwise and then back it off anti-clockwise half a turn to break off the swarf and then continue like that all the way through, 1 turn forward, 1/2 a turn back. If you just try to plough through without the forward/ back approach, thats when you will either break the tap or tear up the thread.

Maybe one of you other "ginger beers" would like to comment, but this forward/back process is the way to go.

Michael

That's cool.. I never knew there was a name for the metal chip, but I was tapping holes 50 years ago.

When I was doing my heavy tapping I was just given a gun tap and power driver so in principle I didn't have to stop periodically and back up to break the chip (swarf?).  While +1 to stopping and backing out with small hand taps .

If we are ASSuming Rob needs advice, I'll add another hint. You always benefit from using generous lubrication when forcing shafts into "tight" holes. 

JR

John, yep swarf it is, I have a swarf story ..... imagine a small sheet of aluminium in left hand, right hand armed with an electric drill with 1/8" drill bit, the drill was quite blunt so I was pushing like hell. Suddently the drill broke thru the other side of the aluminium sheet and straight into the end of my finger until it hit the bone. I quickly pulled the drill out and lo and behold, there is was, a nice curly bit of raw meat swarf.

Great thinking, yes lubrication is always good, some light oil would work, have even used WD40 or similar in the absence of anything else.

And if you were not reversing up regularly when u were tapping holes, then it is not wonder you have broken a lot of taps in your time ... they can get bound up with all the swarf when tapping.

Junction said:

....And if you were not reversing up regularly when u were tapping holes, then it is not wonder you have broken a lot of taps in your time ... they can get bound up with all the swarf when tapping.

Click to expand...

I am not sure of John but I have a story. Back in '78 I was doing my industrial placement in an electronics manufacturer. The reason they took me on because they built the (valve) power amps for a public address system that  my dad won the contract for. Of course in those days the import was extremely tight in Turkey and you just could not afford to waste even a swarf. So, these special aluminium heatsink were imported from Germany and there was only one set because they were so expensive. My foreman asked me to be  extremely careful when tapping and not to rush. Of course when you are 17 you do the opposite don't you? All I was thinking of to make it to 5:00PM and dash out to a gig. I tapped the lot and on the last one I rushed and  "crack!!!!". Oh dear. You have no idea the amount of b*llocking I got for it. We spent the next day and removed the broken tap and re-drilled/tapped it to half a size larger.

Junction said:

And if you were not reversing up regularly when u were tapping holes, then it is not wonder you have broken a lot of taps in your time ... they can get bound up with all the swarf when tapping.

Click to expand...

:cringe:

The gun taps have only two wider flutes so there is more room for the chip to curl up and escape before binding up.  The typical hand taps with 4 flutes have less room for the chip to escape so need to be reversed periodically to break and clear the chip. I suspect the gun taps could bind up in a deeper blind hole, but for tapping relatively thin wall pipe, I don't recall having to stop and reverse, until finished.

I broke a lot of taps because I was a kid and didn't handle them carefully. Taps are easy to break even when treating them properly. The hardness required to hold a sharp cutting edge also makes the metal brittle. I would expect smaller taps to be even more brittle, since there is less mild steel inside proportionately. 

JR

Junction said:

Rob, its been like 20 years since I have been tapping holes for a living, but trying to visualise in my head, but turn that sucker in 1 turn clockwise and then back it off anti-clockwise half a turn to break off the swarf and then continue like that all the way through, 1 turn forward, 1/2 a turn back. If you just try to plough through without the forward/ back approach, thats when you will either break the tap or tear up the thread.

Maybe one of you other "ginger beers" would like to comment, but this forward/back process is the way to go.

Michael

Click to expand...

In one of my first jobs, we bought a tapping contraption that was installed in the dril press. There was an automatic reverse; whenever you stopped pressing, the tap would reverse at low speed. Apparently, this doesn't exist anymore; it seems it's much cheaper buying an automatic tap machine...

abbey road d enfer said:

In one of my first jobs, we bought a tapping contraption that was installed in the dril press. There was an automatic reverse; whenever you stopped pressing, the tap would reverse at low speed. Apparently, this doesn't exist anymore; it seems it's much cheaper buying an automatic tap machine...

Click to expand...

Like this? http://www.mcmaster.com/#tapping-heads/=hrxcyy