I'm going to get off my ass and at least tap my scout box for hydro assist. I did a search and went through about 300 various posts but didn't find what I was looking for.

One of the places I'm going to tap has no problem as far as depth or thickness of what I'm tapping(3/4" or so).

For the other port, I've got about 3-4 different places I can look at but I'm concerned about the depth/thickness of what I'm tapping.

What is the minimum depth I should look at when tapping the box? I'm using a 1/4" NPT tap.

FWIW, I am NOT tapping the end caps. I don't care for the look and in my case, it won't work :p

here is a chart courtesy of Machinery's Handbook 26th Edition

Originally posted by bgreen
here is a chart courtesy of Machinery's Handbook 26th Edition

Cool... now the question is, for those of us mechanical engineer illiterates, which column do I want to check? :p

I'm sure it isn't the diameter(e3) nor the height of thread.

The two I'm guessing at are:
I4, Overall External Thread
I5, Norminal Perfect External Thread length

In one case, I'm good to go, in the other I'm in trouble :p

Thanks for the killer chart :)

good rule of thumb is to tap in far enough to leave 3 threads exposed on the tap.:D

Originally posted by bgreen
good rule of thumb is to tap in far enough to leave 3 threads exposed on the tap.:D

:p If I do that with my tap, I end up needing 2 inches :(

This is 1/4" NPT which if I recall right is tappered.

I've got approximately 5/16" of material I can tap into. I could weld more material onto the PS box... but I'm curious how close this is :p

.3125" is enough, IMHO. But what would I know:p Try it and let us know if it fails!:D I would want at least 3 complete threads engaged in the material, preferably 4 or 5. with a 1/4-18 npt you would have .3125/.0555=5.68 threads. I dont know what the formula is for #of treads required for specific psi, but I think you would be fine.

brook

I watched a machinist tap several holes for a pipe thread (tapered threads) and he measured the fiting then measured the tap for the same size(probly just a little smaller) then he counted the threads on the tap for the right number of turns ( Im guessing from common sence that with the tapered tap if you go to deep then DEPENDING on your fiting the threads might be loose and will not seal properly CORRECT me if I am wrong)




Good luck
Jason

jstarnes: that method works fine, just dont forget you have to account for sealant and wrench makeup. in my experiance SS fittings need to have the holes tapped about one complete pitch deeper. When in doubt use a chart. For most of our applications, the 3 thread method is just right.

brook (machinist by trade)

Originally posted by bgreen
.3125" is enough, IMHO. But what would I know:p Try it and let us know if it fails!:D I would want at least 3 complete threads engaged in the material, preferably 4 or 5. with a 1/4-18 npt you would have .3125/.0555=5.68 threads. I dont know what the formula is for #of treads required for specific psi, but I think you would be fine.

brook

The 3 complete thread engagement rule is for standard threads, not tapered threads. Jstarnes is correct on that account. Besides counting turns tapping a very slightly chamfered hole, a plug gauge is a common tool used to determine the proper depth for NPT tapping. If you tap too shallow, you won't get proper thread contact.

here is another chart

Originally posted by bgreen
here is another chart

a picture says a thousand words!!
although Ive never been keen on NPT(but who am I):flipoff2:

http://www.emuge.com/taps/un8tapered.html

.689" Minimum drilling depth, according to this chart..........

JSSN: sorry, but I beleive you are wrong, rule of thumb for standard threads is to have at least one full diameter of theads. (1/2" bolt, needs 1/2" of thread engagement.)Just imagine only having 3 threads engaged on a fine threaded fastener. Thing would rip out asap. Besides I wasnt talking about only tapping in three threads :rolleyes:

the three thread rule that I was refering to is to leave three threads at the top of the tap. that will determine when you need to stop, has nothing to do with how many threads are engaged in the material. Its just a way for the common guy to tell if he is getting close.

I personally would not feel comfortable with 3 threads engaged in the material, but the formula in machinery's handbook only calls for 4 at hand tight engagement. 7 fully tight.

Brook
most arent going to have a thread gage laying around the shop. most machine shops dont even have them :D

Originally posted by JSSN
http://www.emuge.com/taps/un8tapered.html

.689" Minimum drilling depth, according to this chart..........

right on!

Cool:smokin: Just what I was looking for.

Thanks again.:D