The Lost Art of Running Screw Pipe

jburd964 · 08-01-2012, 09:57 PM

Could so one help me out with measurments for running screw pipe? I can make it work if there's enough pipe on hand, but I would like to be better. Is there a formula to allow for measurements that account for the pieces once there screwed together? Say I want a overall 1/2" x 10" finished length nipple screwed into a 90. How much should I thread nipple so when it's put together it makes a completed piece 10". Wording this isn't as easy as the question. Is the a table for different common household pipe sizes, maybe even one including allowances for different fittings overall lengths ? Question is also for other pipe sizes as well 3/4", 1"..

**oh'mike** · 08-01-2012, 10:12 PM

One of the old timers might have a chart somewhere---I used to know the approximate take up for 1/2" and 4" --But those numbers haven't been needed for years in my word---

Alan · 08-01-2012, 11:18 PM

Typically (given good thread pattern and cut) threads on a pipe will disappear approximately 3/8" into the fitting. Give or take just a little depending on what position said fitting needs to be in when you're done.

Alan · 08-01-2012, 11:21 PM

I'd like to also add, that the example in your question is slightly vauge, given that you haven't mentioned where you want your 10" measurement to end up in reference to the 90. End of 90 to end of pipe? In that instance, i'd measure the 90 at the 10" mark on my tape where I want it to end up, whether it be end of pipe, center of fitting, end of fitting... etc etc...

Then i would note the measurement on the end of the fitting where i want my pipe to screw into, and add 3/8" to it. That should be the length of nipple you need to make up your overall dimension, wherever you're hoping it ends up at.

jburd964 · 08-01-2012, 11:42 PM

Is the 3/8" standard for all household pipe sizes? I pretty much do as your saying, but I guess my problem may not be the know-how but the frequency of doing or the lack there of.

**TheEplumber** · 08-01-2012, 11:47 PM

Here's one chart. I have better one in my fitter's book but I never use them. I simply measure the fittings.
http://www.engineeringtoolbox.com/np...ads-d_750.html
The cut threads should hand tighten 2 or 3 turns If more it will affect your make up and possibly its seal and like Allen said, total make up is about 3/8 for 1/2" pipe.
I always to measure from center to center of any kind of pipe I'm working with- plastic, cast iron, steel, etc. It's about the only consistent point. For instance, Center of a 3/4 90 to the center of a 1/2 branch of a 3/4 tee. Then you simply subtract the take off of each fitting to arrive at the cut length.
Hope this helps.

Javiles · 08-02-2012, 04:10 PM

WHY?

paintdrying · 08-02-2012, 10:24 PM

eplumber x2