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MJ thread

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The MJ thread is the metric equivalent on the UNJ thread used in aerospace.

The UNJ has a controlled root radius on external threads and it requires specific inserts or thread mills to machine

an external UNJ

An  internal UNJ is the same as a UN, but a larger minor diameter is required.

That means you can use UN thread mills to machine internal UNJ threads.

Does anyone know if this is the case of MJ threads.

I have a bunch of internal MJ4-7 holes to threadmill in TI and the LOC required is not available in MJ threadmills

If I can use standard metric 4 x .7 thread mills the problem is solved

 

 

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Yes all should be well. For ref, the effective dia is also a tighter tolerance.

What I would do, is buy the threadmill you want, and as soon as it's in your hand put it on the profile projector. I had some single pointers once (from Horn by memory) and they were 58degrees...

Interestingly enough, for the British standard of threads (Metric), there is no tolerance on the flank angle. Yes, it is 60deg, but as long as the OD/Root/Effective all are within their tolerances, you're good to go. Bit of a slip in attention to detail within the spec if you ask me... :D

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Thanks, this is the last operation on a really expensive part, a cannot fail situation

Tapping is out of the question and the available MJ profile tools are 2mm too short

This is the tool I want to use

a Carmex Hardcut..  It runs M04 G42 from the top down, climb cutting

They work really well in TI and Inconel

 

Carmex MJ-4 X .7.png

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You could surely buy the available MJ's and spin them down to get your extra reach?

I'd still go with a test piece though...

:D

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3 hours ago, Newbeeee™ said:

You could surely buy the available MJ's and spin them down to get your extra reach?

I'd still go with a test piece though...

:D

They are about $100 more expensive and not available in the US with an acceptable lead time

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12 hours ago, Newbeeee™ said:

What I would do, is buy the threadmill you want, and as soon as it's in your hand put it on the profile projector. I had some single pointers once (from Horn by memory) and they were 58degrees...

The helical motion of internal threadmilling increases the effective flank angle; this may be an attempt to compensate.

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4 hours ago, Matthew Hajicek™ - Conventus said:

The helical motion of internal threadmilling increases the effective flank angle; this may be an attempt to compensate.

Saywhat???

How does it do that with a properly form relief ground tool that isn't rubbing???

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18 hours ago, Newbeeee™ said:

Saywhat???

How does it do that with a properly form relief ground tool that isn't rubbing???

Because the vector of motion isn't normal to the cutting face of the tool.  Imagine the extreme case with a really steep pitch, say a four start thread, and think about the tool motion.

Edit:

I think a more clear way to visualize it is the swing of the cutting face.  If motion is straight up or down the profile is way wide, being formed by the swing of the cutting face rather than t's profile.  At a 45 degree lead it's still way wide.  At a normal lead angle it's still just a bit wide, and a 2 degree deviation is probably about right to compensate.

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