Milling M3x0.5 internal thread - need help

[MGPL]

I ordered this tool and it's my first time using it,
so any help appreciated
I work metric and with mm/min g-code

Goal:
To thread a 1.3mm deep M3x0.5 hole in extruded aluminum (probably 6061) using this tool without breaking it.



Tool:
Single form thread milling cutter for M3x0.5
*listed specs are in inches

• Thread size: 3
• D1: .0717
• Neck diameter: .040
• L3: 5/32
• Flutes: 2
• D2: 1/8
• L1: 1-1/2

Information from tool manufacturer:
"start with 15,000 RPM and a chip load of .0004 per flute. Using these parameters, there is a calculated linear feed of 12 IPM. To get a circular feed rate, you will need to scale back the linear feed. Circular Feed = linear feed * (major diameter of hole – cutter diameter)/ major diameter of hole"

So...
major diameter of hole: 3mm or maybe 2.5mm..
cuter diameter: 1.82mm
( 2.72x25.4 =69.088mm/Min -- feed: ~F70.0 )

I tried using an online feed/speed milling calculator with .0004 (0.0106mm) chip load per flute but the feed rate was crazy fast, so I just didn't use this info.

G-code:
i found this...
from carmex.com
"
Thread Milling CNC Program for Internal Threading
Program is based on tool center.
This method of programming needs no tool radius
compensation value other than an offset for wear.
Right hand thread (climb milling) from bottom up.

I filled in the fields accordingly.

G90 G00 G54 G43 H1X0 Y0 Z1.0 S15000
G00 Z-1.3
G01 G91 G41X0.295 Y-0.295 Z0 F70.0 D1
G03 X0.295 Y0.295 R0.295 Z0.0625
G03 X0 Y0 I-0.59 J0 Z0.5
G03 X-0.295 Y0.295 R0.295 Z0.0625
G01 G40 X-0.295 Y-0.295 Z0
G90 G0 X0 Y0 Z0


What is this code doing, and what am I missing in order to complete my goal?
Thanks,

[neilw20]

You need extra lines for each 360 degree turn
Note the G91, making it relative, so each line has Z0.5, then G90 (absolute) on last line.

G90 G00 G54 G43 H1X0 Y0 Z1.0 S15000
G00 Z-1.3
G01 G91 G41X0.295 Y-0.295 Z0 F70.0 D1 (MOVE TO START POINT)
G03 X0.295 Y0.295 R0.295 Z0.0625 (90 DEGREE ARC APPROACH)
G03 X0 Y0 I-0.59 J0 Z0.5 (ONE **ONLY** TURN OF THREAD)
G03 X0 Y0 I-0.59 J0 Z0.5 (ONE **ONLY** TURN OF THREAD)
G03 X0 Y0 I-0.59 J0 Z0.5 (ONE **ONLY** TURN OF THREAD)
G03 X-0.295 Y0.295 R0.295 Z0.0625 (90 DEGREE ARC EXIT)
G01 G40 X-0.295 Y-0.295 Z0 (BACK TO X-Y START POINT)
G90 G0 X0 Y0 Z0

[PixMan]

Why would anyone design a part needing a threaded hole that's less than 1/2 as deep as it is in diameter? You get 2.6 threads. For any semblance of strength, you need 1.5 x D (length of thread to diameter) which would give you 9 threads. Only 2.6 threads is boneheaded.

Anyhow...

Why not use a multi-lead thread mill and git 'r dun in one rotation?

[MGPL]

Pixman,
I'm new to milling, and "boneheaded".. common.. useless.
The 1.5 X D equation isn't a golden rule. The odd hole depth you mentioned is irrelevant for it's the result of tests I've done that worked sturdily for its application. The cutter is just a first cheap alternative to test thread milling. I will think about upgrading once I got a handle on this.

I've read that several passes are usually necessary for a clean thread, what do you think based on this tool and etc?

[juergenwt]

Am I seeing this the right way. M3 in a 1.5mm thick material thru or is it thinner aluminum 1.5mm deep x 2.5 extruded? Why not just drill 2.5 and tap it or just tap it if extruded? Am I missing something?

[neilw20]

As MPGL says the hole is 1.3mm deep, and most likely a blind hole.
More than strong enough, if not much screw tension required.
Like most jobs, if done to a specification, it will be fine.
We answered the question.
Now as for the number of passes, it is sometimes best to try a few different ways an find which is better.
This is a great way to do tapped holes if the machine won't do rigid tapping.