Has something with 2D Thread (threadmilling) changed lately? Or tool library?

[TJS01]

A few weeks ago I programmed a 1/8-27 NPS threadmilling operation.  The selected face was the hole diameter modeled as the drill size, so I input a number into the Pitch Diameter Offset (PDO) field under Passes.  I few test cuts later, tweaking the number, I achieved the fit I was looking for.

Fine.
Today, using the same strategy, I programmed a M14x1.5 threadmilling op. and have found if I enter the PDO, the tool goes way beyond the desired nominal thread major diameter (in this case 14mm).  The selected hole is again, modeled at the drill size, so the PDO should be about 0.059".

In the screencast below I begin with the 1/8-27 op from a few weeks ago when I ran these parts - I highlight the 0.049" PDO entry before Simulating to demonstrate the tool cuts almost to the outer circle (representing the 1/8-27 major diameter of 0.398").

Then, I flip over to a quick model demonstrating the difficulty with the M14 operation -

The first thing I show is a 0 in the PDO field.  This SHOULD walk the tool around the inside of the inner circle since it is modeled to the minor diameter for M14x1.5 (0.492").  Instead, it cuts beyond the major diameter (outer circle modeled at 0.551").

I then enter the delta in the PDO field (0.059") which should put the tool at the inside of the outer circle - It's way beyond that.

Lastly, I change the PDO back to 0" and enter 0.011" in Stock To Leave, which represents the fit I'm looking for based on some hours of _____ around with this.

 All simulations are run with the FLUTE selected to display, so it's not the shank I'm seeing beyond the major diameter.

What could be going on with the PDO behavior in the M14 op?  All the tool parameters are entered correctly, including the diameter of the threadmill cutting area, which is on my tool is clearly labeled 0.360". 

Before posting, trying to figure out if the problem is me, I have subsequently modeled up a quick representation of the 1/8-27 op just to prove to myself that I'm not crazy - it works as expected.  I then modeled up an M6x1.0 threadmill op and it does the same as the M14 going way out of bounds...so thinking it's somehow a "metric thing" I then try out a 1/4-20 and it does the same as the metric threadmills.  Seems that new threadmills I've entered in the tool library exhibit this behavior.  The 1/8-27 has been in my library since ~October 2017, I believe.  All others are new additions.

[LibertyMachine]

I've seen this before, but I'm having a difficulty recalling exactly what the cause was. I think the issue lies in your tool definition, actually. Could you export and share your file?

File > Export > Save to local folder. Return to thread and attach the .f3d file.

[TJS01]

Thanks Seth,

The file where I discovered this is a mess of setups and test cuts, so I just made a quick, fresh one.  Pitch Diameter Offset is set to 0, when simulated (flute display only) you can see the tool going beyond the major diameter (outside circle).  Tool is an M14x1.5 threadmill.

-TJ

[LibertyMachine]

I don't believe there is actually anything wrong. I've added a drill just to provide some clarity.

What you are seeing from the "top down" view is actually the shank of your tool. It's set to .375, but your cutting diameter measures .360. It's this difference you are seeing from the top.

File attached

[TJS01]

When I run the simulation, I select only the flute to be shown.  It's not the shank.  My tool is a multiflute threadmill - x1 360° revolution and I have all the threads in a 3/8" thick 1018 plate.

In my test runs on the machine, I get my preferred thread fit by leaving the PDO at 0" (which should be cutting air in the drilled hole) AND I have to add 0.011" in stock to leave.  I make x4 0.007" stepover passes.  That aspect could probably be more aggressive, but I have one tool to get the job done.

I should add, I didn't discover this in simulation, it was on the machine when the tool made the first pass (supposed to be 0.007") and it sounded and looked like full depth...then I saw what was going on in simulation and started backing the PDO off to figure out what was going on.
 

[LibertyMachine · Accepted solution]

Okay, I see the issue now. And I think I've figured out the "WHY".

The number of teeth (15) x pitch (.05955) is greater then your flute length. Your flute length is .875, whereas your actual flute length (assuming you have 15 full teeth) (and there is a country music joke in there somewhere...) is .8857

Set the flute length to the correct value of roll it back to 14 teeth

This does sound like a bug though. I'll try to tag someone in this thread when that part of the forums decide to start working again....

[TJS01]

Wow...weird.  I changed the flute length to 0.89" and the shoulder to 0.9".  Now all my fine tuning hard work is undone and the tool appears to be doing what I'd expect!  Good catch Seth!

I would think that a red box around the flute length would appear if the number of teeth calculated length exceeds the flute length input.

[angelo.juras]

Thanks for the post @TJS01 and also Seth @LibertyMachine for helping out. I'll be looking into this and provide an update as I gather more info.

[peter.pretsch]

Thanks TJS01 and Seth,

I have created ticket CAM-9374 to track this.

Kind regards,

Peter

[angelo.juras]

Thanks for creating the ticket @peter.pretsch

[TJS01]

Thanks @angelo.juras & @peter.pretsch!

[Anonymous]

Hi guys,

I've read through this thread and am definitely having a similar issue with a 1.00mm pitch threadmill.

The thread I am attempting to cut is an M19x1.0mm Female thread. The hole is modeled to the minor diameter of 17.92mm . 

I thread mill regularly with imperial 24TPI, 28TPI and single point 60Deg threadmills without any issue.

My normal method of developing a thread mill program for the first time (as I have used here in the attached file) is to accurately calculate the Pitch Diameter Offset (Major - Minor dia.) then compensate to get the fit right (Yes I am aware that 60Deg cutters will cut undersize based on these calcs), however when I simulate the cut with the metric threadmill it is definitely far from being a full form thread and the resulting cut is the same.

I can try compensating by increasing the PDO by maybe 0.5mm but is there something that I am missing.

Please find my file attached.

Best regards,

Jeff.

[daniel_lyall]

On a post this old with a solved tick on it, it pays to start a new post of your own most people see that it is solved and skip over it.

[Anonymous]

Thanks for the heads up Daniel.

I'm actually flying out to the UK today and will probably try and post the issue again in another thread when I return and am more able to reply.

JB