What drill size to drill and tap M3?

[Buggyjam 141]

Im planning on using RC4WD steel rod ends that come listed as M3 stud. No further info on the pitch etc. Is M3 a fixed pitch? If I sound like I know what I'm talking about I don't! I did some machining training years ago but it's long forgotten and I'm picking it up off google. A few questions -

 

1/ I read that M3 has a pitch of 0.5 and that the hole you need to drill would be 3-pitch = 2.5 mm. Is this correct? What size hole would I need to drill for me to tap M3? Would it be 2.5mm?

 

2/ If M3 is fixed do I just by a decent hand tap or are there different types of M3?

 

Thanks

 

[Granddad Stinky 974]

2.5mm drill size is correct.

There are hand taps and machine taps. Make sure you ask for a hand tap, you'll never start a machine one in the hole.

There are different pitches of M3 but they are very specialised. 0.5 mm is the one you want.

Presuming you're tapping plastic, lubricant with WD40 or Mr Sheene works well. With aluminium, use a drop of paraffin or WD40. You'll need a small tap wrench as well.

[Buggyjam 141]

20 minutes ago, Granddad Stinky said:

2.5mm drill size is correct.

There are hand taps and machine taps. Make sure you ask for a hand tap, you'll never start a machine one in the hole.

There are different pitches of M3 but they are very specialised. 0.5 mm is the one you want.

Presuming you're tapping plastic, lubricant with WD40 or Mr Sheene works well. With aluminium, use a drop of paraffin or WD40. You'll need a small tap wrench as well.

Thanks that really does help. It's aluminium rod I'm tapping. Is it always M number - pitch? So would the hole to use on M4 be 3.5?

[MadInventor 3742]

21 minutes ago, Buggyjam said:

Thanks that really does help. It's aluminium rod I'm tapping. Is it always M number - pitch? So would the hole to use on M4 be 3.5?

Nope, M4 is 3.3mm hole. I think M is for 'metric' and the 3,4,5 size is mm size of the metric bolt to fit the tapped hole.

For ISO Metric coarse threads:

Outer Diameter (mm), Tapping drill (mm)

2.0, 1.6

3.0, 2.5

4.0, 3.3

5.0, 4.2

6.0, 5.0

7.0, 6.0

8.0, 6.8

 

For aluminium you do need WD40, and every couple of turns I back off the tap to break the swarf if you're tapping into a blind or deep hole, otherwise the tap can jam. If it does jam, blast the hole with WD40 and then gently wiggle the tap back and forth until it frees off. I broke several M3 taps before I learnt that trick.

Hope this is of some help.

[Wooders28 4262]

Aluminium is one of the more difficult metals to tap, as its a soft metal, it kind of pushes out of the way instead of being cut. As madinventor said , slow and steady.

[Granddad Stinky 974]

14 minutes ago, MadInventor said:

Nope, M4 is 3.3mm hole. I think M is for 'metric' and the 3,4,5 size is mm size of the metric bolt to fit the tapped hole.

For ISO Metric coarse threads:

Outer Diameter (mm), Tapping drill (mm)

2.0, 1.6

3.0, 2.5

4.0, 3.3

5.0, 4.2

6.0, 5.0

7.0, 6.0

8.0, 6.8

 

For aluminium you do need WD40, and every couple of turns I back off the tap to break the swarf if you're tapping into a blind or deep hole, otherwise the tap can jam. If it does jam, blast the hole with WD40 and then gently wiggle the tap back and forth until it frees off. I broke several M3 taps before I learnt that trick.

Hope this is of some help.

what he said!

[Granddad Stinky 974]

https://www.google.co.uk/search?q=Tapping+drill+sizes&ie=UTF-8&oe=UTF-8&hl=en-gb&client=safari#imgrc=dONNZMak8ZQPtM:

[Buggyjam 141]

Thanks chaps. This has been a goldmine of knowledge. Thanks

 

[SNAKEBITE 40]

Something that is always handy to have around in your workbox/shed/nan cave is a "Zeus Book"

http://www.ebay.co.uk/itm/Zeus-Precision-Engineers-Metric-Data-Book-Chart-Charts-Reference-Sizes-Tables-/310893777034

Worth it's weight in gold.

 

[BigAl69002 7]

Or download a copy from here......http://www.green-oval.com/data/zeus.pdf

 

[GregM 1107]

Speaking of books and charts, this is what I'm using:

http://www.europa-lehrmittel.de/t-1/tabellenbuch_fuer_metallbautechnik-2718/

[BigAl69002 7]

On 5/30/2017 at 8:14 AM, GregM said:

Speaking of books and charts, this is what I'm using:

http://www.europa-lehrmittel.de/t-1/tabellenbuch_fuer_metallbautechnik-2718/

I didn't understand a word of that book.:-)

 

[Ann3x 220]

When you tap, be sure to back out every turn or so. In Alu I do:

• 1 turn cut
• 0.5 turn reverse
• 1 turn cut

It helps clear the tap's cutting edge. As many have said, go slow, use cutting fluid and a 2.5mm hole and itll be fine.

Don't expect a hand cut hole to be as strong as a factory part tho - itll work for sure but the accuracy & profile of the cut is much less consistent than a machine tap.

[Buggyjam 141]

2 hours ago, Ann3x said:

When you tap, be sure to back out every turn or so. In Alu I do:

• 1 turn cut
• 0.5 turn reverse
• 1 turn cut

It helps clear the tap's cutting edge. As many have said, go slow, use cutting fluid and a 2.5mm hole and itll be fine.

Don't expect a hand cut hole to be as strong as a factory part tho - itll work for sure but the accuracy & profile of the cut is much less consistent than a machine tap.

Thanks Ann3x for the tips. I tried drilling out the rod on my bench press and hand tapping. I found as you said, the thread wasn't all that good on my early attempt. This thought process has had me looking back into investing in some machine tools. Not just to tap the rods, but for other ideas. Something I've been mulling for a long time. It's just the outlay and working with my limited space.