Tap size question

[fishmasterdan]

Today I was removing a stump and it caught on my hydraulic ram and snapped a hydraulic fitting flush with the case.

It was a fitting that went from 1/2" to 1/4" and then attached to my hydraulic line. I belive it is called a reducing bushing.

Any way I took the ram off and drilled as much out as I could (without touching the threads) and want to run a tap thru the threads to clear them out.

Does anyone know what size and thread type of Tap I need? I will assume its 1/2" but I am not sure what pipe threads and regular thread mean?

Thanks for any input.
Dan

 

[Tom_Veatch]

...
I will assume its 1/2" but I am not sure what pipe threads and regular thread mean?
...

Pipe threads (NPT) are cut on a shallow tapered cylinder so that as they are tightened, the male and female threads jam together in an interference fit creating a metal to metal seal.

"Regular" threads, e.g. NC, NF, etc., are cut on a straight cylindrical surface so that the thread diameters are constant along the length. There is a form of "regular" thread (NPS???) that has the same nominal diameter and pitch characteristics of the NPT threads but are formed on a straight cylinder rather than on a taper.

You should determine the thread form and pitch with certainty before you proceed further.

 

[MadReferee]

NPT size nomenclature sometimes doesn't make much sense to the non-machinist. For example, a 1/4 NPT male fitting really has an outside thread diameter of .55" with 18 threads per inch, and a 3/8 NPT male fitting has an outside thread diameter of .67" with 18 threads per inch and a 1/2 NPT has an outside diameter of .87" with 14 threads per inch.

Furthermore, the tap dirll size for a 1/4 NPT female hole is 7/16", for 3/8 NPT it is 37/64" and for 1/2 NPT it is 21/32".

If in fact you have a hole that is about 1/2" in diameter then you probably have 1/4 or 3/8 NPT fittings on the cylinder. However, in my experience I have found that most cylinders would probably be 3/8 NPT. Alot of cylinders have SAE 8 (3/4-16) threads too but you stated your hole is only about 1/2" so 3/8 NPT would be my guess.

NPT taps are very common and almost any hardware store will have them.

 

[RedRocker]

NPT size nomenclature sometimes doesn't make much sense to the non-machinist.

Are you sure about that? I've been cranking handles for 40 years and NPT still doesn't make sense to me!

 

[SPYDERLK]

Today I was removing a stump and it caught on my hydraulic ram and snapped a hydraulic fitting flush with the case.

It was a fitting that went from 1/2" to 1/4" and then attached to my hydraulic line. I belive it is called a reducing bushing.

Any way I took the ram off and drilled as much out as I could (without touching the threads) and want to run a tap thru the threads to clear them out.

Does anyone know what size and thread type of Tap I need? I will assume its 1/2" but I am not sure what pipe threads and regular thread mean?

Thanks for any input.
Dan

There are easy outs for pipe, but it may be too late to use one because youve drilled. An alternative - -If you have any metal left in the bushing at the top you may be able to use a pin punch to form a divot while applying taps in the ccw direction and get it to turn out. Its surprising how effective this is. Make sure the pin punch has a good tip so the edge will bite in.
Larry

 

[RobJ]

Also since you've drilled out some of it, take a punch and fold the fitting into itself. Folding it in pulls the threads in and losens things up so you can get it out by hand or a pair of needle nose pliers.

Good Luck

 

[turnkey4099]

Today I was removing a stump and it caught on my hydraulic ram and snapped a hydraulic fitting flush with the case.

It was a fitting that went from 1/2" to 1/4" and then attached to my hydraulic line. I belive it is called a reducing bushing.

Any way I took the ram off and drilled as much out as I could (without touching the threads) and want to run a tap thru the threads to clear them out.

Does anyone know what size and thread type of Tap I need? I will assume its 1/2" but I am not sure what pipe threads and regular thread mean?

Thanks for any input.
Dan

Others have answered the tap question.

I would not feel comfortable about putting that ram back in service until it was disassembled and cleaned of all drill chips. The filter may catch them but they could scratch up the cylinder bore while working out.

Harry K

 

[3RRL]

On what Mad said Furthermore, the tap dirll size for a 1/4 NPT female hole is 7/16", for 3/8 NPT it is 37/64" and for 1/2 NPT it is 21/32".

If installing new NPT threads, those drilled holes then need a pipe tap reamer (tapered) before tapping and lots of Moly Dee cutting fluid. We also count the number of revolutions for the tap to go in depending whether we wanted a recessed plug to go below flush or if an external fitting went there. (power tapping) You will not need to do that since you are chasing existing threads.

There is also NPS (the "S" stands for straight and the "T" stands for taper) which has the same OD size and number of threads but it is straight, not tapered.

I think Mad is right guessing it's a 3/8 NPT. Be sure to clean out the chips with a magnet and don't tap too deep. Measure the length of your male fitting and then run the tap in there stopping about 3/32" to 1/8" shy of that length to give you enough room to snug up the thread interference.

 

[scott_vt]

NPT size nomenclature sometimes doesn't make much sense to the non-machinist.

Hey MadRef,
They dont necessarily make sense to the toolmaker/machinist either

 

[Soundguy]

Wow.. i think i'd had driven an easy out into the ID of the broke fitting and turned it out.. now that it is drilled.. this may not work, and may be much harder to extract.. even with a thread chase.. Also.. the cyl is now contaminated with metal chips and dust... gonna need to flush it a few times to get all that out.

This is one o f the very few times I will reccomend an easy out, as a fitting / bushing is already thin walled.. compaired to a bolt with a hole drilled down the center.. etc..

The advice about trying to 'tap out' with a punch or chissle sometimes works, as well as crushing the thin shell of the fititng in on itself with a punch.. etc.

Soundguy

 

[fishmasterdan]

Well heres an update for anyone that snaps off a fitting.

First of all dont drill the fitting out. That was a bad move. They sell reverse dill bits that I may have been able use or an easy out (I have never had any luck with easy outs).

I discovered that the threads are 3/8 Pipe threads so that is NPT I believe.

I ended up dremeling the the stuck fitting down until it was paper thin and then running a tap down thru the existing threads. They people at my local Napa store are very helpful with this kind of stuff.

As for cleaning out the ram it is all taken apart and it is easy to clean it up.


A tip I will try on the next one a person showed me. They took a nut that was slight larger than the broken fitting but smaller than the actual threaded hole, then they welded the inside of the nut to the broken fitting.

 

[Soundguy]

That can work on broke studs too.. weld a nut to the stud. etc.

In your case of a hollow fitting.. just be carefull about the penetration and you should be good to go. The weld will probably shrink the fitting too...

Soundguy

 

[RobJ]

That can work on broke studs too.. weld a nut to the stud. etc.

These are also handy...

 

[Soundguy]

Those stud pulers offer lots of mech advantage.

soundguy

 

[BTDT]

If you have the cylinder off, you can also apply heat to help loosen things up. I love my torch.