Threading T304 on a lathe

Hey folks! Been a while. I've been very busy, hope the same is true for you (if that's what you want).

A customer wants me to make some small stainless "straws" to retrofit into old Italian espresso machines. I made a batch of them from solid stock (T303) a year ago and swore not to do that again, at the price point anyway. Took too long to drill out; it's a long, small, hole to drill with lots of pecking to clear chips. I can get tubing that eliminates that step, but not in 303, only 304. In my first year doing this I got humbled by 304, primarily it's propensity to work-harden, so I'm a bit put off by the thought of threading it.

The straws are 1/4" on the OD and get a metric OD thread. My concern is that threading is just asking for work hardening issues since DOC will necessarily be small on some passes. The straws thread into brass so the threads must be very smooth. Anyway, before I order a stick of 304 tubing, anyone thread 304 on a lathe? How'd it go? Getting tool height right on such a small OD will be critical, I'd think, and not easy.

Thanks for any info.

I don't understand, are you using a tap for the internal threading?

OD thread ...

Should be fine if you can keep the SFM's up, which if you are doing these on a manual lathe, will be hard. Cutting oil, high-quality insert.

Regards.

Mike

Finegrain said:

OD thread ...

Should be fine if you can keep the SFM's up, which if you are doing these on a manual lathe, will be hard. Cutting oil, high-quality insert.

Regards.

Mike

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Correct, OD thread.
Yes, it's a manual lathe. I have an Iscar threading tool with carbide inserts but I prefer my Warner with HSS inserts.

I think I'll pass on the job.

Farm out the threading to someone with a CNC lathe. Sounds like a piece of cake. What kind of quantity are they looking for?

Ed.

Why not use a die?

Limy Sami said:

Why not use a die?

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Or a Geometric die head. One pass, with cutting fluid, and done.

Larry

L Vanice said:

Or a Geometric die head. One pass, with cutting fluid, and done.

Larry

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And I've got 4 extras for sale so I have to agree with you!

atex57 said:

Farm out the threading to someone with a CNC lathe. Sounds like a piece of cake. What kind of quantity are they looking for?

Ed.

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Quantity is small- 20 or 30. Price is low. Just not worth it. Thanks guys.

I routinely single-point 304 rounds on a manual lathe and don't see the problem. I use coated carbide inserts, start at .010 DOC and step down to .001 or less to finish.