Single point threading questions

[jdsantiagojr]

Hello. Last night I spent a few hours attempting to make a captive nut. My main goals were to
1. Practice single point threading on my mini lathe
2. Hit dimensions
3. Make something for my kids.

Everything was going well until I got to a point that I needed to make the threads. My target was 11.96 OD, which was hit (doubled checked). I set the top-slide to 30 degrees and arranged gears for a 1.75mm pitch. After scratch pass, I made few cuts and then it was a lot of repetition. I did begin to notice the diameter of the piece looked smaller . When I measured It was the perfect size for an M10. . . my target was M12.

I parted off the piece and chalked it up to good practice. Still felt really crappy going to bed since I wasted material and I didn't hit all of my goals.

I want to try again but had few questions:

- What did I do wrong ? Did I not zero the cross-slide. ?
- Why does the thread look rough? Is this chatter ?

 

[DavidR8]

Do you have some pics of the result and the tool you used?
As a newbie myself. I have practiced threading starting with 1" stock and just kept going until it was about .25" Just to get the 'dance steps' down...

 

[jdsantiagojr]

Do you have some pics of the result and the tool you used?
As a newbie myself. I have practiced threading starting with 1" stock and just kept goig untill it was about .25" Just to get the 'dance steps' down...

Sorry. Just attached them to the post. I used a pre sharpened but from little machine shop.

Threading Tool Bit and Center Gage 4115

Lathe Threading 4115 5/16" HSS Threading Tool Bit; 60 Degree Center Gage; The threading tool bit is sharpened on both ends to a 60° angle for threadi...

littlemachineshop.com

 

[DavidR8]

I think your compound was set to 60 deg.

Threading issues

Good evening, I'm new to the forum, and new to machining. I have a HF 7x10 lathe and the small HF mill. I've been working on threading on the lathe, and have so far not been successful. I am currently using a sandvik tool holder with a 16er ag60 insert. Compound is set at 29.5 degrees, and I've...

www.hobby-machinist.com

 

[graham-xrf]

You could have a good time checking out Quinn Dunki's video on YouTube.
Then there is also Mr Pete. and This Old Tony and others.
Particularly, check out the ones from Joe Pieczynski.

and..

and , if you happen to have a collet chuck, or at least a chuck that won't come undone if you run the lathe in reverse, then see a great trick.

Just about every issue, including vibration and chatter is in these.

 

[KevinM]

The degree marks on some lathe compounds are referenced by the angle parallel to the X axis (cross-slide direction) and are rotated in the counter clockwise direction for threading. Yours and mine are different, they are referenced by the angle parallel to the Z axis and increase in a clockwise direction for threading. I believe that your compound setting should be 60, this makes the tool plunge more than move laterally. Normally you will see 29.5 degrees are used for threading, if you want to do that then yours should be 60.5 degrees (90 - 29.5).

 

[DAT510]

From the pictures ( I'm not sure if it's an artifact of the angle the picture was take from), but, it almost looks like your treads are not "symmetric"? If that is indeed the case, then your compound could be set to the "other" 30 degrees. Some lathes have the angle scales of the compound in reverse (many mini lathes). So what you think is 30 degrees is in reality 60 degrees (as w/ respect to the threads).

Also, some compounds scales read in "True" feed ie: 0.001" on the scale = 0.001" Feed in (or 0.002" change in Diameter) other compounds read as change in Diameter ie: 0.001" on the scale = 0.001" change in diameter or 0.0005" actual feed. As one can imagine, this can give you fits if you think the compound reads one way when it's in fact the other.

But given the compound is set at an angle, any in-feed with respect to the Diameter will be a product of the SIN or COSIN of the compound angle. I've found mounting a dial indicator on the cross-slide, indicating off of the compound as an easy was to know my exact in-feed.

Here a pict of my setup.

Hopes this helps.

 

[Mitch Alsup]

Yes, the problem is that your lathe needs that "other" 30º !!
The compound slide needs to slide across the trailing edge of the partially cut thread, cutting on the leading edge and burnishing the trailing edge.

 

[Larry$]

I just use the Joe Pie method. Simpler, works great, eliminates the problem you had.

 

[ttabbal]

I just use the Joe Pie method. Simpler, works great, eliminates the problem you had.

I do as well. In fact, I rarely have the compound on the lathe. I only use it for tapers. On a mini lathe, there might be rigidity issues going straight in, only way to know is to try it. I suspect it would work fine though. Just remember that it's a form tool and you need to reduce the feed in per pass compared to normal turning. Heck, try it both ways and see what works best for you. We all learn by making scrap metal, don't feel bad about it.