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2", 3" & 4" NPT Internal Thread Milling w/ VCarve Pro and CNC Router

Zac Penn

Plastic
Joined
Oct 4, 2019
Location
Jacksonville
I am a complete newbie when it comes to CNC router thread milling, and I am overwhelmed when I am searching for single profile thread mills on MSCDirect.

My immediate need is for a single profile thread mill that will be able to cut internal 2", 3" and 4" NPT threads into 1/2" thick Type I Rigid PVC sheet.

My Spears Technical Information catalog shows all of their NPT threads to be a 60* angle w/ the 2" having 11.5 TPI, and the 3" & 4" having 8 TPI, so maybe something simple like a 60* side cutter would work for this?
Could I use something as cheap as this as my cutter????? https://www.amazon.com/gp/product/B0...OIEGB5VT&psc=1
Obviously not going to be the best quality, but I could have it tomorrow and the price point works hahaha

I mean don't you just need to either Pocket or Profile cut out the center hole and then use a 60* side cutter to make the threads? I don't know why it seems so complicated when looking on MSC for a single profile thread mill???

Some of the products have a specific thread labeled on the product listing, but it says it can cut anywhere from 8-16 threads per inch, so i am confused as to what cutter will work best for me. This one says it has a 3/4" cutting diameter, 60* angle, but then it states a specific thread that it is used for... https://www.mscdirect.com/product/details/81262487
I can always buy a different cutter for any other kinds of threads that I may be interested in down the road, but I need something RIGHT NOW that will work for 2"/3"/4" NPT threads. Finances are tight right now, so i only want to buy a single thread mill for this project IF POSSIBLE.

I have also never used the VCarve Pro thread milling toolpath before, so if you could provide me with some tips and tricks that would make my life easier I sure would appreciate it.

EDIT: I forgot to mention that I DO NOT need my threads to be tapered (which i don't think is an option with VCarve anyways) but if it is possible, I would like to know how to do that as well.

Thanks in advance!
Zac
 
Yes maybe your Amazon thing will work. Thread mills have shallower angle than thread. The leading edge is cutting on the bottom and trailing edge on top. You are cheating a true shape with them- close enough to be correct when you stay in their range.
Being relative small diameter mill to hole size your 60 will not be to outrageous.
Is it close enough without squinting for the job? Well… try one on a piece of scrap.
 
Yes maybe your Amazon thing will work. Thread mills have shallower angle than thread. The leading edge is cutting on the bottom and trailing edge on top. You are cheating a true shape with them- close enough to be correct when you stay in their range.
Being relative small diameter mill to hole size your 60 will not be to outrageous.
Is it close enough without squinting for the job? Well… try one on a piece of scrap.
Thank you. That makes sense about the leading/trailing edges of the cutter forming the thread. Seeing as how my cutter is already 60* and has a diameter of 3/4", it is probably going to cut a ~65* thread if i am thinking about this correctly? That should be fine for my application, but it will get worse with a smaller diameter thread so I probably shouldn't go much smaller than 2" NPT.

I will let you know how it turns out once i receive and test it.
 
You might get more answers in the General or CNC forums.
There are some very knowledgeable router operators here, but most of us don't care about the fine details of threading wood or plastic with quite the same intensity the aerospace milspec billet niobiumstainlesstitanium guys on other forums do.

:)

smt
I have seen other people get called out for posting in the other forums when they were specifically talking about a woodworking CNC, so I posted it here. Maybe next time I will take a chance and see if i get yelled at ;)
 
What is going into your threaded hole? Does it need to be liquid or air tight (the usual reason for pipe threads)?

You'd probably get much more info from the "zone" or a vectric forum
 
What is going into your threaded hole? Does it need to be liquid or air tight (the usual reason for pipe threads)?

You'd probably get much more info from the "zone" or a vectric forum
It is actually going to have a 2"/3"/4" male adapter screw into it, but it doesn't have to be completely water tight. This will be going into a koi pond, so algae and bacteria will grow around the fitting pretty quick and seal up whatever small amount of water goes around the threads.
 
A tapered thread is programmed as a number of arc segments to increase the radius. The centers of those arcs are not on the center of the thread. Giant PITA to do 'by hand', even pulling dim's from CAD.

I think I did some with Surfcam years ago. A bunch of code that had me scratching my head for a bit.
 








 
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