Reaming in drilling

Now a Lathe is whole other animal when it comes to single point threading. There you have a direct synchronization of the RPM and FEED to form the thread and they must be matched. I attached an example tapered thread mill for NPT that has a multi tooth profile. You can get lost is some of the math there. Oh my where has the time gone... Got to scoot!

So as an example I've thread milled extremely large Acme threads with a rough and finish pass only. I typically use cutter compensation for a perfect fit to a thread gage.

Reaming operation

So I'm delveing into thread milling and I'm starting to understand the concepts of Pitch offset diameter and Major and Minor diameter but what I don't understand is how to calculate my stepover when doing multiple passes. I'm doing fairley small threads 8-36 and 4-40 so I want to do work the thread mill out in 3-5(?) passes with an additional spring pass so I don't break the thread mill.

Reaming operation PDF

One of the beautiful things about thread milling is the the RPM of the cutter and the feed rate have zero effect on the path that is machined. So the speeds and feed can be optimal for chip load to cut the material. Additionally the shape is determined by the cut motion being created. So you can speed up or slow down RPM and FEEDs and the shape is still followed.

An additional aspect is the cutter profile a multiple tooth or single tooth. just as an example with a single thread profile cutter for an 8-36 thread pretend you hole is 1/4" deep. you would have to make at least 36 thread divided by 1/4 you would need 9 helical revolutions for that one tooth cutter to get through the part. VS a multi tooth profile cutter might be able to cut it with one single helical motion. The cutter manufacturer should be able to provide this information.

Just passing time and along some thoughts... So that is an interesting question and it certainly could involve some calculations. But inherently it is a machining question by nature.