G0602 threading issues (not disengaging the half nut)

[GunsOfNavarone]

Hey all,
I have had my G0602z for over a year and finally have been playing with threading. Compound set at 29.5 degrees....threading tool is 60° and used a gauge to make sure it is set with work piece. Not backlash on my slides doing 12tpi on mild hot rolled 1/2" stock. My first scribe line looked good and I I did the reverse direction/ no disengage half nut. It seemed to be slightly scribing in two places right next to each other. My final product looked closed to metric 2.0 threads but we're very thin. Though there is no slop anywhere...there is on the leadscrew...but not how it connects to compound slide, but within the change gears. Lash adjustment is as tight as I can get it....but there is ample back and forth play within the gears. I'll post a picture of threads on a moment. Thoughts?

 

[GunsOfNavarone]

Picture of thread

 

[markba633csi]

Looks like something was moving during the cut- tool, toolpost, compound, leadscrew or even workpiece itself- something was causing those two scribe lines and it isn't right, there should be only one, especially since you kept the half-nuts engaged
You are pulling the tool away from the work when reversing the carriage correct?

 

[GunsOfNavarone]

I'm not gonna discount what your saying....but I've checked everything...it's all rock solid...it's just that leadscrew/change gears. It has a good 7 degrees of play. I feel like if be better to disengage half nut, pull away from work with compound. I know this is the less preferred technique, and I would really like to figure what's up with my lathe. This thing may have 4 or 5 hours of use on it and none threading.

 

[benmychree]

It is not a good idea to pull out with the compound, it should be left at the same setting that the cut was taken on, pull out with the cross slide only. Start out with the cross feed handle at about the 10:00 or 11:00 position and the dial zeroed, and take each successive cut by feeding the compound in, however much you dare, you can take heavy cuts for the first several passes, then ease up for the finishing passes. Some folks do the 29.5 deg thing, I do not, I set on 30 deg. Hot rolled is not a nice thing to thread, it does not cut freely or finish nicely. I would try disengaging the half nuts ands sucessively take trace cuts with not feeding in and see how the tool tracks on each cut, or rather does the tool track in the same location on the successive cuts.

 

[DAT510]

It looks like the angles of the two sides of the tread are not symmetric, which could be because your compound is set to 150.5 degrees vs 29.5,

 

[darkzero]

That thread looks like the compound was not set at 29.5°. This happens a lot with people that have smaller asian import lathes. Commonly the compound scale on asian import lathes will read 0° & not 90°. If your scale reads 0° you have to set the compound to 60.5° to get the correct angle for flank threading. Typically the scale won't even read that far (only on lathes where the degree markings are on the cross slide) & you need to set it with a protractor, etc. My 12x36 is this way also, I made my own marks instead of having to use a protractor every time.

Edit: Well the scale should read 0° instead of 90°, what I should have said is that small import lathes usually don't have the additional scale directly on the cross slide like bigger lathes do.

 

[benmychree]

Hold a 60 deg "fishtail" thread gage against the front side of the compound, it should appear to be 90 deg. to the ways.

 

[fitterman1]

Use your scribe line to verify your tpi.
First passes you can go slightly deeper.
Subsequent passes get shallower as you feed your crosslide in.
If you're leaving your halfnuts engaged, and reversing, then you must back off your crosslide a reasonable amount to clear your thread tops and then reset to depth for the following cut.
Make sure you remember last depth of cut, or write it down to help you.
Backlash in the geartrain can never be eliminated, we all have to wear this one.
Cheers alby

 

[benmychree]

If you reset the cross slide to zero after pulling out at the end of each cut, and do not mess with the compound setting until ready for subsequent cuts, there is no need to remember or write down anything, you just feed the compound in a bit for each successive cut.