[Newbie] Threading Technique Questions (things I Couldn't Find Online!)

[jwest7788]

Learned alot about threading yesterday:


Not looking too sweet. (Sorry about the focus! Threads were forming, but there is alot of tearing that is hard to make out. Fingerprints look great though. Lol.)
I'm thinking I was taking too much material each pass, not certain, but I also wanted to clarify:

(I was using the "never disengage the half nut" technique)
When initially starting a second pass, the proper way of feeding the cross slide is to start the lathe, then feed the cutter into the material to the proper depth, or is it okay to take up the backlash, stop the machine, feed in 0.002 (or w/e) and then start the machine?

I'm also unsure about what speed a threading operation should be done at?
(I was working on the slowest to best reduce the odds of crashing my lathe!)
It seems to me that cutting faster will help improve the finish, but increase odds of a newb mistake.

Any Tips?



Side note, I spent hours getting the above (captive nut) prepared to match a coupling nut I picked up at my local big box, got it to the above state, and realized that I spent all that effort just to thread the bar 1 tpi too many!!
(Must have grabbed the wrong change gear earlier)

And as such, have picked out an empty drawer on my work bench for "failed projects"

 

[T Bredehoft]

One drawer may not be enough. I try to recycle mistakes into something useful to keep from remembering them.

At a guess, you're taking too much material per pass. This is one of many traps thread cutting leads us into. The very few threads I've done on my Clausing/Atlas 6/24, I've taken less than one dial increment (.002 on the diameter) after the first .015 or so. And take two to five 'spring' passes, final passes without increasing the depth of cut. And don't forget to keep it well lubricated. Dark sulfur oil lying on the surface of the screw, or one of the modern (Tap Magic) cutting fluids.

Edit: add thoughts.

 

[aeroHAWK]

jwest,

The important thing to get from this is that YOU CUT A THREAD! It is likely one of the issues it the material you were cutting. Mild steel (1018) is notorious for being gummy and tearing as you cut threads. This is why 12L14 (ledloy) is used by screw machine shops. It cuts much nicer.

When cutting threads for the first time, I suggest using a free machining material such as 12L14, or free machining brass. That way, you can get the process working without having to deal with the machining characteristics of the material (baby steps).

Your photo demonstrates that you do indeed have the process working! Congratulations!

 

[janvanruth]

first feed in then start lathe

check pitch after first cut

speed as high as you dare

 

[blaser.306]

keep at it, and not failed projects! Experience and prototypes!!! You don't mention what the speed is that you are cutting , and also what type of tooling ? HSS, carbide? Are you grinding your own?

 

[higgite]

If you don’t disengage the half nuts, you don’t need to worry about leadscrew backlash. It will take care of itself.

You mentioned feeding the cross slide. You might want to try setting the compound at 29.5 degrees from the cross slide and feeding the tool with the compound. That may help clean up the threads. I use that method (as do many folks) and the threads turn out cleaner than straight in plunge cutting with the cross slide.

Tom

 

[Ebel440]

Are you using the tail stock? You may be out too far if your not. Some material also just does not thread too well either. Sometimes I'll cheat a little and use a wire brush after I thread it to clean it up a little bit. Also the tool height is pretty important when threading. I need my tool just centered or a tiny bit below to get the best threads on my lathe. You can also leave a little bit on the thread when single pointing then use a die to clean it up. It makes my threads look perfect and nice and smooth.

 

[Wobbles]

All very good suggestions.

 

[GarageGuy]

I learned to thread by watching tubalcain (mrpete222) YouTube videos. Here are three of the best when you are starting out:

Watch all of his machine shop videos. Short of having your own personal instructor, Mr Pete's videos are great because he takes the time to explain why he does things the way he does. He is a wealth of knowledge. Good luck!

GG