Thread milling not working out for me

[Anonymous]

I am at the last operation for this part, had quite a bit of help from this forum to get this far.

I have a single point thread mill from Sandvick 

327R06-12 100VM-TH 1025
I set it up as a slot mill in the tool library and have a tool path, file is attached. is the insert number on the Coromill 327 tool. It has a min pitch of 1mm 

So I will admit, thread milling is somewhat confusing to me and I was not sure what to have as a pitch diameter offset for a metric thread of a 1mm pitch. I tried to wing it a little, just to get the tool cutting and put in several values, starting with 0.2 and now all the way up to 1.4mm. It still does not quite touch the part.

In the simulation it does however, so I was expecting to some result, but on the table it does not. My part measures correctly, both on the table and in the attached file.  

The insert is 11.7mm according to Sandvick and I ended up measuring it with vernier callipers and the max diameter I could get was 10.4mm. The tool guy said this was not possible to measure it like that,  and trust Sandvick. I would have expected it to be close to that 11.7 however.

The insert label matches their website and the slot mill insert I used on the same tool also measures less , but has cut the slot as expected. So, must be my values. I tried to get my head around the major/ minor and add the value for the point on this insert, which is 0.12mm and from some charts I saw, the offset would be 0.63mm + 0.12 = 0.75, which of course I tried without success. 

Can anyone see an obvious flaw (other than me not understanding much on the subject) why it might not be working?

[LibertyMachine]

Couple of things:

1) You do not need to define your threadmill as a Slot Mill. You needed to do that quite some time ago, but those days are long gone. (thank heavens)

2) What is the actual thread size you are trying to machine? Diameter Offset is simply the difference between the thread Minor and the Thread Major. For instance, an internal thread of M10 x 1.25 has a minor diameter of 8.78mm

10mm - 8.78 = 1.2205

Now, in order for this to work (threadmilling) you will need to make sure that the part is modeled to the correct minor diameter. If you model it to the full diameter of the thread (10MM in the above example), you would set the offset value to zero.

3) No, you cannot measure a 3 flute tool across two points. There are basically only two methods of easily checking that diameter:

1) 3 Point External Micrometers (yes, they exist)

2) Optical Comparator

In closing, make sure the tool is modeled correctly, as well as the thread minor diameter

Use cutter compensation to get you where you need to be

[Anonymous]

The hole in the model is to the minor diameter. 35.494mm and the thread I wanted to do was a 1mm pitch. 

Later I want to change that to 0.75, but I am happy to work with 1mmm for now, as that is the min of my insert. 

I made the tool over 6 months ago, maybe longer, so that is why I did as a slot mill I think.

Thank you for confirming the measurement of the 3 point tool, I didn't know that. Thought at first I has=d the wrong insert.

So the minor is 35.494 with a pitch of 1mm.

There is a 0.12mm add on for the point of the tool . In the simulation I am seeing  the tool touch the model, but in the machine I am seeing the tool not quite touching. 

I saw the pitch offset listed as .6 something and added the 0.12 was basically 0.75mm, which does not work. I doubled it just to see a cut and it looks the same. 

[sportbikeryder]

If practical, I would start over and try producing a generic external milled thread in a "standard" size for which you may have an existing nut to test the fit. Make a generic external model at the nominal OD of the thread, set the offset to the difference in the pitch diameter, and attempt to make a dummy part. 

Using this approach will allow you to get familiar with the thread milling function and see how your specific tool needs to be "dialed" in to get the result you want. While it may seem odd, I have always had to tweak the manufacturers specified numbers a bit to get the desired thread form / fit. That is the beauty of thread milling as opposed to tapping or using a predetermined die size, the threads can be adjusted to suit. 

John

[Anonymous]

Sounds like a better plan. My table is setup for one part and has very little room as it is a small table, but I can manage something in the vice.