Thread milling multi lead

[KTMDAVE]

Could someone let me know if I'm on the right track? Thread mill with version 9 5/16-18 double lead thread with a multi tooth cutter. Would it

be the pitch /2 and a start of 0° and 180°

 

Thanks

[Guest]

I do alot of thread milling but have never done a multi start thread. I think you are correct on everything except the pitch.

 

pitch * 2

[John Summers]

The 'pitch' would be 9 threads/inch. You still need to go around the whole 360 degrees.

[Guest CNC Apps Guy 1]

2x 9, ahhhhh. I've never threadmilled multi lead before. So John, if we have say 4 leads, would that then be 4.5 TPI on the pitch(in this 18 TPI instance)?

[Guest]

What I meant by pitch * 2 was the pitch of an 18TPI is .0555

 

You would enter .1111 in your pitch dialog on the threadmill page.

[Guest SAIPEM]

You should start both at 0° ( or the same orientation for both).

Accomodate the number of starts by shifting the start point in Z just like on multi-start threading on a lathe.

 

Pitch doesn't change.

The shift in Z is (thread lead / # of starts).

For 18 TPI the shift is (0.05555/2) = 0.02777

[chip]

I think everyone's right about the pitch angle. That doesn't change. In V9, (something like a mold core) I think you just want to change the start angle?

 

Might be a bit difficult with a multi-tooth cutter. Trying to accomplish a double thread. We use single tooth cutters. (similar to lathe boring bars).

 

We have been experimenting blunt starts on the lathe. I have yet to get that perfect.

[Greg Williams]

You need to check that the tool has anough clearance for a multi start thread

[crazy^millman]

Chip need to use a single point tool in my opinion. 9 pitch is correct and angle of 180 is correct as well. Can do 4 and 5 leads the same way just need to break your pitch down and start angles down respectfully.

 

Here is link: Linky

[Guest SAIPEM]

Oops....

Mazatrol spoils you after a while for Multi-start threads.

 

I should have said:

 

You CAN start both at 0° ( or the same orientation for both).

Accomodate the number of starts by shifting the start point in Z similar to multi-start threading on a lathe.

 

The shift in Z is (thread LEAD/ # of starts).

For 18 TPI w/2 Starts the shift is (0.11111/2) = 0.05555 .

You enter (2*PITCH)=0.11111 as the helical cut pitch.

 

The shift in Z by this method eliminates having to rotate the engagement point 180°.

 

[ 02-21-2006, 09:34 PM: Message edited by: SAIPEM ]

[Guest SAIPEM]

This should work but my head is spinning

 

 

code:

---

(5/16-18 - 2 START THREAD 1" DEPTH)

(EXTERNAL THREAD MILLING)

(0.375 DIA - SINGLE PT TOOL)

(FIRST START)

G00 X0.4757 Y0.0

Z0.2222

G01 G91 Z-0.0556 F15.0

G01 G41 Y0.1875 F1.5

G03 X-0.1875 Y-0.1875 Z-0.0278 I0.0 J-0.1875

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G03 X0.1875 Y-0.1875 Z-0.0278 I0.1875 J0.0

G01 G90 G40 Y0.0

G00 Z0.2222

(SECOND START)

G00 X0.4757 Y0.0

Z0.2778

G01 G91 Z-0.0556 F15.0

G01 G41 Y0.1875 F1.5

G03 X-0.1875 Y-0.1875 Z-0.0278 I0.0 J-0.1875

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G02 Z-0.1111 I-0.2882 J0.0

G03 X0.1875 Y-0.1875 Z-0.0278 I0.1875 J0.0

G01 G90 G40 Y0.0

G00 Z0.2778

---

[Guest SAIPEM]

quote:

---

Chip need to use a single point tool in my opinion. 9 pitch is correct and angle of 180 is correct as well. Can do 4 and 5 leads the same way just need to break your pitch down and start angles down respectfully.

 

Here is link: Linky

---

You have to use a single point tool because you'll violate the thread form if you use a multi-tooth thread hob for multi-start threads.

 

The angle of 180° is only correct if you do NOT shift in Z for each start.

Rotating 180° will cause you to cut a single thread along the same helix if you shift in Z.

 

BTW, Mike Lynch's example has a big mistake in it.

A 4-16 4-Start Thread has a lead of 0.25" not 0.5" .

He probably meant to call it a 4-8 4-Start Thread.

You still have 8 TPI after all four starts are cut.

 

In the case of 5/16-18 in the above code, you'll have 18 TPI after both starts are cut.

[KTMDAVE]

Thank you all for the help!

 

Dave