Single Point Threading on a PM-1030V?

[erikmannie]

So I made a male 1/4-20 thread as seen below. The fit seems to be perfect because it started out tight and the Grade 8 nut served as a die.

I am having an issue with the lathe turning a taper. I have suspected this since the first day I got it. It has nothing to do with the tailstock. I might need to adjust the position of the spindle.

If I chuck up even the most rigid round stock and turn it as carefully as possible, I will get a taper of about .0007" per inch.

For this bolt, I attempted to turn a major diameter of .2500", I turned .2500" at the far end, and the workpiece was .2514" at the chuck end. Same story for the .2175" pitch diameter. This was the first time that I used my Shars screw pitch micrometer, so I was happy to be anywhere the ballpark there. I have a bad time with Shars mikes. I bought Starrett outside mikes, but not one for threads.

So I will cut a 9/16-20 male thread tomorrow with an eye on this taper situation. I will start by turning some large round stock to get some exact measurements for the extent of the taper.

 

[mikey]

Erik, there are three key reasons for the lathe cutting a taper. First, the headstock may not be aligned with the ways. Second, the lathe may not be level. Third, the tailstock may not be aligned with the spindle. Lots of info on the net about each of these issues. Also do not overlook the possibility of tool deflection causing inaccuracies

I wanted to point out that your threading tool has a very positive rake. That typically produces gnarly cuts in brass and will often produce torn or jagged edges on your threads. It also tends to dig in on many other materials when trying to thread on the lathe. It is better to use a threading tool with zero rake, especially for brass. If you grind it with 15 degree relief angles on each side you will cut much cleaner threads.

It also appears that the carbide tool you're using is not cutting well. Not sure if this is due to too low a turning speed or a bad/junk insert of what but brass should cut with a near mirror finish. Something is very off with your tool.

 

[ttabbal]

One thing with the gear change. Don't hammer them. I did that initially and broke one of the bushings. PM sent me a couple of spares. I used files to get things fitting better. It doesn't take much, and make sure not to go too far. You don't want slop. Glad you got the charts figured out. They are weird at first, but you get the hang of it.

 

[erikmannie]

Erik, there are three key reasons for the lathe cutting a taper. First, the headstock may not be aligned with the ways. Second, the lathe may not be level. Third, the tailstock may not be aligned with the spindle. Lots of info on the net about each of these issues. Also do not overlook the possibility of tool deflection causing inaccuracies

I wanted to point out that your threading tool has a very positive rake. That typically produces gnarly cuts in brass and will often produce torn or jagged edges on your threads. It also tends to dig in on many other materials when trying to thread on the lathe. It is better to use a threading tool with zero rake, especially for brass. If you grind it with 15 degree relief angles on each side you will cut much cleaner threads.

It also appears that the carbide tool you're using is not cutting well. Not sure if this is due to too low a turning speed or a bad/junk insert of what but brass should cut with a near mirror finish. Something is very off with your tool.

My lathe is not yet level. It is tilted a little down on the “front side, tailstock end” corner. I can tell because this is where the excess way oil pools in the clean chip tray after a clean and lube. Thanks for the troubleshooting help; I will also read about aligning the headstock with the ways.

I didn’t use any carbide in this thread. I did use Made in China HSS inserts.

The threading tool is a preground “combination chamfer & threading tool bit”. I will only use it for chamfering from now on.

Tomorrow when I cut the 9/16-20 I will use some carbide or HSS inserts made just for threading. The stock will be mild steel.

 

[erikmannie]

One thing with the gear change. Don't hammer them. I did that initially and broke one of the bushings. PM sent me a couple of spares. I used files to get things fitting better. It doesn't take much, and make sure not to go too far. You don't want slop. Glad you got the charts figured out. They are weird at first, but you get the hang of it.

I wanted to file them, and do so patiently and incrementally. It was my Dad’s idea to forego filing and hammer them. I’m surprised that I didn’t break a bushing because it required a lot of force.

 

[Aukai]

I have no idea if this is pertinent or not, but does running the machine in high range, vs low range make a difference? you seem to be in high range I think.

 

[erikmannie]

I have no idea if this is pertinent or not, but does running the machine in high range, vs low range make a difference? you seem to be in high range I think.

I do have it in high range because I like carbide inserts for turning, facing and boring.

As you know, the range (high or low) or spindle speed (RPM) has no effect on the thread pitch that is cut. For my reaction time, I can’t do threading with an RPM much higher than 270. I usually choose about 170 RPM which allows me to properly engage the threading dial.

 

[mikey]

My lathe is not yet level. It is tilted a little down on the “front side, tailstock end” corner. I can tell because this is where the excess way oil pools in the clean chip tray after a clean and lube. Thanks for the troubleshooting help; I will also read about aligning the headstock with the ways.

I didn’t use any carbide in this thread. I did use Made in China HSS inserts.

The threading tool is a preground “combination chamfer & threading tool bit”. I will only use it for chamfering from now on.

Tomorrow when I cut the 9/16-20 I will use some carbide or HSS inserts made just for threading. The stock will be mild steel.

Those Chinese inserts seem to suck! You would be far better off grinding and using HSS tools, Erik. This goes for both turning and threading tools.

 

[Aukai]

LOL I'm not sure what I know, that's why I mentioned it to see.

 

[erikmannie]

Those Chinese inserts seem to suck! You would be far better off grinding and using HSS tools, Erik. This goes for both turning and threading tools.

I have had good luck with the inserts that I received from PM. The carbide inserts used for boring on mild steel remove a lot of material quickly, and you can use a faster RPM so the work goes faster. I have never tried premium inserts.

I just started grinding HSS tool bits. I bought ten preground ones so that I could get a look at the angles. Many have already required sharpening. The ones that I bought were very handsome: