Need Exact Tap Size

[jun_celis]

I'm finally working on my acrylic reactor and I need to know the correct size tap for this John Guest shutoff valve thread:

1/4" JG x 1/4" Male NPTF -Straight

I know it's a 1/2" - ?... But I don't know how many threads per inch I should get. Can anyone help? Thanks

 

[rdelong]

THe picture says 1/4" NPT. Regardless of which size you have this has a tapered pipe thread and a 1/4 NPT or 1/2 NPT tap is what you need. You can get NPT taps at most quality hardware or tool stores.

 

[rdelong]

Look at www.mcmaster.com part #2525A115 for 1/2" and 2525A113 for 1/4"

 

[jun_celis]

So, if the description says 1/4, then I should get 1/4"npt even if it looks like 1/2"? I guess what I'm confuse about is the difference between the NPT and the normal bolts tap sizes. Now I know. Thanks so much!

 

[rdelong]

National Pipe Taper (NPT) is different than machine thread sizes. If the fitting is described as 1/4" NPT then get a 1/4" NPT tap. These fitting can also use FPT or MPT standing for Female Pipe Taper or Male Pipe Taper. Both are the National Pipe taper in english unit sizes.

 

[jun_celis]

I actually went to HD and asked around and they don't have the slightest idea of what I was talking about. I even showed them the JG valve and they kept insisting 1/2". That's where I got the 1/2" idea. I will try sears if they have it, otherwise, i'm going to mcmasters.com.

 

[Atomahawk]

If it's 1/4 NPT then thats the tap your looking for, best place to find one is at a plumping supply place. I did find a Vermont American at a box store, but that I got rid of ASAP, in my book VA is junkware, but thats just my opinion.

 

[Douglas LEHMAN]

Ace is the place!

 

[MinibowMatt]

Sears hardware stores have them too. the reason it is called 1/4" and it looks 1/2" is cause in the old days, the pipe wall thicknesses were different. The inside diameter was always the same--in this case 1/4". the thread count was always standard too-- for 1/4" pipe, it is 18 TPI (i think) The pipes have since changed, so now the 1/4"-18, doesn't mean as much as it used too. FYI the JG fitting in your pic is a NPTF thread, so if you can find a NPTF tap, you will get the best results. I just installed one of these in a taper tapped hole, and it gets very very tight. I was worried about cracking the acrylic i was putting it in...

 

[scbasser5]

Also make sure you get the correct drill bit for your tap. It will probably be a 7/16" for 1/4"NPT. Other size taps are not as easy to get they are usually some kind of 64ths of an inch.

But the right size bit is very important to good threads.

 

[KevinM]

Also...don't forget that since this tap is tapered, you can crack your acrylic very easily as the tap tries to make the hole bigger and bigger. Go very slowly, in a tiny, tiny bit, then out again....and repeat.

Kev

 

[MinibowMatt]

7/16" is the correct bit for 1/4" NPT. You can use water as a cutting fluid with acrylic....

 

[AZDesertRat]

1/4" NPT or MIP is the internal diameter of the pipe not the external size like bolts and bolt threads.

 

[jun_celis]

Also, 7/16" drill bit size... would that fit on a regular drill? Seems pretty big, right?

 

[manderx]

i use novus2 as a lube for tapping acrylic. it lubes nice, and polishes at the same time.

 

[BeanAnimal]

Yes the bit should fit in most drill chucks. You can also easily find bits with a 1/4 shank on them if needed. In this case any tap matching the thread pitch and diameter will work. The finished tapered thread is not really needed as long as you cut the threads clean and use teflon tape on the JG fitting. It is very important to only cut a little bit at a time. In and out just a quarter turn or less. As the tap bites in to the hole deeper, you should back it almost the whole way out and make sure the cuttings are being removed.

The process is rather easy in plastic and you should be just fine.

To be honest, most of the time (esp with PVC) I use a drill just slightly smaller than the threads and then use a threaded air compressor fitting (1/4 npt) as a tap. In other words I am to lazy to dig out the NPT taps and tap handle. This is not a good idea for a first time with acrylic though. Also the tap should only be a few bucks

Good luck.

 

[cres]

Also, because the tap is tapered, the further you tap, the bigger the hole (surprise) and the further in your fitting will thread. You can get to the point where your valve (pictured above) will bottom out at the nut/flange and will not seal properly. Stop when 1/2 the tap is in the whole and test fit the valve. You can go further as needed.