Thread milling

[Anonymous]

I having problems with thread milling and not sure what the issue is. I made a hole with mill with a radius of .359.for a 1/2-14 NPT fitting Then setup thread routine using a .372 single flute mill from Maritool

https://www.maritool.com/p16219/Single-Form-Thread-Mill-.372-Diameter-X-1.125-Max-Depth/product_info...

Within THREAD window (Passes)

Right hand

Pitch 0.0714286 in

Pitch diameter offset .08in (Started at 0 and worked up to .08

Visually the threads look fine but the male part will not thread. I am not sure if its the thread or the hole size. 

Any thoughts ?

[LibertyMachine · Accepted solution]

An NPT thread is tapered. You will either need to interpolate the hole with a tapered endmill or use a full form NPT threadmill for this to work.

NPT thread dimensions

[Anonymous]

Need to learn about tapered mills. Can you suggest one that will work or direct me to a mill ?

[LibertyMachine]

Do you have one hole to do? Model it as tapered and surface mill it (Ramp)

Many holes to do? Get a tapered endmill. Unsure of the supplier for that, as I've always used full-form NPT threadmills, which form the taper as they cut. That will likely be more cost effective.

[Anonymous]

One hole, I searched for tapered end mills but all I got was tapered mills.  You pointed out the problem and got me on the right track I will have to hit google and you tube.

[Anonymous]

I found a thread mill for NPT.  IT says the mill has a tapered ground into the mill. Can this also be used for outside cuts ?  Since the taper is only one way I dont understand how it can be used for both inside and outside cuts.

Here is the lakeshore mill

http://www.lakeshorecarbide.com/12-14carbidethreadmillnpt-1.aspx

• These thread mills are able to produce internal or external threads

[Steinwerks]

I couldn't think of a great way to explain this without multiple photos, so I found a video: