Parting with internal thread

[Blackwatch42nd]

Hi,
New here and to machining. Hoping for some help with a small project.
I'm trying to part a brass rod that has been bored and internally threaded. Unfortunately, when the part separates, it does so leaving some of the thread attached from the parting tool width. I know why it's happening, just trying to find a work around. Any thoughts greatly appreciated.
John

KnurledNut.jpg (45.17 KiB) Viewed 4432 times

OD: 1"
ID 3/4"

[John Hasler]

Screw a sacrificial mandrel into it and part right into that.

[johnfreese]

Bore an internal groove at the cut location before parting off.

[Harold_V]

It is generally desirable that the thread receive a chamfer after parting. If the task was mine, I'd use soft jaws, bored to hold the piece not only on center, but perpendicular, then I'd take a miniscule facing cut, followed by the chamfer, inside and outside, all of which would be done with the same tool. Done! And no damage to the knurl. Using soft jaws as I suggested provides the perfect stop, so you can control length to a high degree of precision, all without effort.

Harold

[Blackwatch42nd]

Thanx to all for the quick reply.

JohnH: My latest thoughts were along yours. But I'm thinking a sacrificial all thread rod. I could thread it in to the piece, center drill it and use a live center to support the whole business.

JohnF: I would have to get the grove at the exact spot of the leading edge of the parting grove, which is possible. I'll have to think on that one.

HaroldH: Still real new at this and not sure of the setup for your idea. What are "soft jaws"? Are they made or acquired?

Here's what the part looks like before parting

Thanx again
John

[SteveM]

Here's what Harold is referring to.



The jaws are soft steel (they can also be aluminum) and you bore for the needed diameter down to a depth that holds the part flat.

If you don't have jaws that bolt on, you can always make these:


If you do have bolt on jaws, I have several sets of soft jaws for sale:
http://www.chaski.org/homemachinist/vie ... =soft+jaws

Steve

[John Hasler]

Thanx to all for the quick reply.

JohnH: My latest thoughts were along yours. But I'm thinking a sacrificial all thread rod. I could thread it in to the piece, center drill it and use a live center to support the whole business.
John

That's what I meant.

[GlennW]

When the parting tool breaks through the brass part it may grab it and tighten it on the threaded rod pinching the parting tool.

That wouldn't have a happy ending.

[Harold_V]

What Glenn said. I can think of no faster and better way to break a thin parting tool (keeping in mind, I hand grind parting tools from square stock, I do not use commercial parting tools).

While using a sacrificial mandrel (threaded) can be a solution, it's not a good one, nor does it allow for the critical operation of chamfering the thread. Soft jaws, or a step collet, are the answer. Either permits "fine tuning" to resulting part, while other methods do not.

Harold

Edit:
Want to learn more about soft jaws, the "magic bullet" of lathe work? Follow this link: http://www.chaski.org/homemachinist/vie ... =44&t=4266

[Russ Hanscom]

A parting tool with a angled end, instead of square might reduce amount of tear out. Since you are going to have to face and chamfer anyway...

[John Hasler]

When the parting tool breaks through the brass part it may grab it and tighten it on the threaded rod pinching the parting tool.

That wouldn't have a happy ending.

I see no reason to expect that with a short, fat, stiff parting tool, which he can use here since the cut is wide and shallow.

Perhaps use aluminum of maybe even plastic for the threaded rod..

[johnfreese]

If you use a properly shaped boring tool to groove the ID before parting it can do the chamfers and eliminate the need for a second op.