Hard time tapping brass

[JeepsAndGuns]

So I made my first actual part from scratch on my lathe. Everything before was simply maching down or facing stuff. I am really happy and excited that I actually made something I needed and it worked! Not to mention I couldnt even find the part.

I got a free air hose reel for my shop, no hose, but I had a good one for it. When I go to put a fitting on the inlet, I found it was cracked. Its made from brass. I take it off and apart. It looks pretty simple. I figure I could make a new one.
I got a peice of 1 inch brass round stock from ebay, and long story short, made a new one.
My problem was when it came time to tap the ends. One end was just regular threads to go on a mounting stud, the other was pipe threads for the inlet. When I went to tap the holes, it was extreemly difficult to tap. I mean so tight that I thought the tap was going to break! It also squeeked when doing this. I have tapped many things before, lots of steel and never had this much trouble tapping a hole. I tried 3 different types of lube, two made for cutting/tapping, and one that wasnt, all with the same result.
Why were these holes in soft brass SO hard to tap? Is this normal for brass? This is the first time I have really worked with brass. Machining was super easy, but tapping almost impossiable.

The part itself is the inlet, it has 2 grooves for o-rings. Another peice rotates around this, which is what the hose attaches to. It also has a snap ring to hold it on. I simply used a parting blade to cut the o-ring grooves, and actually to cut the larger center groove also. I then ground it down real thin to cut the snap ring groove. Drilled it for the air and milled two flats for a wrench, since it was made from round stock, instead of hex like the original. I made it a little longer on the end with the snap ring because I dont have a bottoming tap, and I wanted it to thread all the way on the mounting stud. I left the inlet end bigger, cause I wanted it thicker, thats where it cracked on the old one. Once I put it together, it works like new!

 

[kd4gij]

Do you know what type of brass it is. There is a lot of differnt brass alloys out there some harder than outhers. Also what shape are the taps in.

 

[springer]

i don't know about the brass part of it, but i do know pipe threads are more difficult to tap because they are tapered. i've only needed to do it twice, but they were much more difficult than regular tapping. i don't know how to do it properly i guess, but the hole size i found to start with was smaller than i ended up needing to get the thread big enough to get my fitting screwed on enough, if that makes sense.

 

[JimDawson]

Congratulations on making you first part.

Brass can be a little strange to tap sometimes, especially pipe threads. It tends to squeal at you, and is tough.

 

[12bolts]

Brass will squeak and squeal when tapping. Taps easy enough dry, (no lube)
Pipe threads come in 2 basic styles. Tapered and straight, (parallel) A 1/2" NPS straight tap will want a 23/32" (18mm) tapping drill hole. A 1/2" NPT tapered tap will want a smaller 11/16 (17.5mm) tapping drill hole.

Cheers Phil

 

[JeepsAndGuns]

I had to pull up the auction in my ebay to see what it was. The seller called it 360 brass. I do not know much about brass, so I dont know what that means in terms or hardness. I didnt even know there were different grades.
The taps I were using were new and sharp. The threads for the mounting stud were just regular 3/8-18. Tap was a carbon steel tap. I have only used it a couple times to clean up some threads in steel. This was the first time I have used it to cut new threads. The pipe threads for the inlet was 1/4 npt. As far as I know it is also a carbon steel tap. I have only used it to tap a few holes in a cast aluminum intake manifold for my jeep. I know pipe threads will be harder to tap, expecially the deeper you go, but It cut threads in the intake easy. Didnt think brass would have been that much harder, but I guess it is.
But its good to hear that the squeeking and being hard to tap is normal. I was worried I was doing something wrong.

 

[Lucky 13]

I use skip tooth pipe taps whenever possible. It has every other tooth ground off and requires significantly less torque. 360 brass is free cutting and is typically easy to work with.

 

[Round in circles]

My Tip

When putting gas threads in brittle materials like brass use your lathe if you can as it's safer and more accurate , to get it all centred and solid .
Put the tap in the tailstock chuck , set the tailstock lock to a slight free slide and advance the taper tap into the hole with the tailstock feed screw then gently rock the lathe chuck back and forth about 1. 6 of a turn and advance the tailstock feed in as you do it . Progress like this till you have two & a half full revolutions of the lathe chuck , it won't be long before you get the first few threads made and from then on it's a case of turning the lathe chuck back and forth about 1/4 of a turn at a time several times in each place then advance the tap a bit more to form the perfect thread.

If you have a carriage stop place it in front of the tailstock to give you an indication of when to stop so you don't go & break the tap by bottoming it out or start pushing it too far down in to a thin wall weakening the item . .


In a previous post someone said that brass does not need lubrication , for some strange reason I seem think that 50 years ago I was taught to give such things a squirt of paraffin to flush out the swarf , this stops it squealing and the tap binding up on the swarf which may cause the fitting to split .


Don't use compressed air as you're like as not liable to stick some metal in yourself especially in your eyes.

 

[stupoty]

Congratulations on making you first part.

Brass can be a little strange to tap sometimes, especially pipe threads. It tends to squeal at you, and is tough.

The squeeking always puts me on edge, like a tap could shatter at any moment if i turn it tooo fast

stuart

 

[JeepsAndGuns]

My Tip

When putting gas threads in brittle materials like brass use your lathe if you can as it's safer and more accurate , to get it all centred and solid .
Put the tap in the tailstock chuck , set the tailstock lock to a slight free slide and advance the taper tap into the hole with the tailstock feed screw then gently rock the lathe chuck back and forth about 1. 6 of a turn and advance the tailstock feed in as you do it . Progress like this till you have two & a half full revolutions of the lathe chuck , it won't be long before you get the first few threads made and from then on it's a case of turning the lathe chuck back and forth about 1/4 of a turn at a time several times in each place then advance the tap a bit more to form the perfect thread.

Actually this is exactly how I did it. I dont have a actual tap guide, like what I read that your supposed to use. So I just put a drill chuck in my tailstock and used that. I figured it wasnt "right" but I didnt hanve any other way (other than free hand, which I know would go crooked) and I figured this is not a high precision part anyways, so it doesnt really matter. I turned the chuck by hand a few turns to get it started, but it started getting hard and the tap started slipping in the chuck. So I switched to a tap handle but was only able to get a little futher till the brass started slipping in the lathe chuck. I ended up having to finish it out then mill the flats on it so I could use a vise to hold it and finish tapping it.