This seems too simple - differential screw adjustment, am I missing something?

Larry$ said:
I always thread @ 90 degrees, easier. So is threading away from the chuck. Thanks Joe Pie.
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I've seen his video, but haven't tried it yet. I've threaded at 29.5 and @ 90 degrees. Since I had so many things going on at once (see all the mistakes I made already!) I used 90 degrees. Have to say the feed rate was on the slow side, but that's what us beginners have to do...

With multiple threads on the same rod 1mm and 0.75mm, there's little advantage to feeding away from the chuck as one has to stop before messing up the other thread! I really need to rig up a micro switch stop to this lathe. It would make things so much easier.
 
@homebrewed thanks for the suggestions. I will try that to see if I can get things a little closer. If I trust my vision, the TS is high as well as offset horizontally. Seems I won the lottery on this one. Thought I'd reduce the error on one axis before attempting the other. Suspect I have to do both axes before things get much better.
 
WobblyHand said:
I really need to rig up a micro switch stop to this lathe. It would make things so much easier.
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Would your micro switch apply a brake or just cut power to the motor? If just the motor, will the spindle continue to turn
from momentum? My lathe has a foot brake that also cuts power to the motor
 
WobblyHand said:
I do have a mill. It's unclear to me where the reference surfaces are, and how to deal with the 90 degree prism cut. I don't trust my abilities to do that without tossing the piece. There's other places to try surface removal, but I'm just too new at this game to try it. If I had local guidance, maybe I'd try it.
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I used this as a guide for milling my tailstock. I also published my TS mod on my blog here. It is the March 24 entry, about halfway through that particular page. Instead of using a reamer blank to help align the base, I used linear bearing rod. Drill rod would work OK, too. It has to be long enough to stick out past the base enough to use a DI, basically like tramming your vise (except you're tramming the base's alignment).
 
Larry$ said:
Would your micro switch apply a brake or just cut power to the motor? If just the motor, will the spindle continue to turn
from momentum? My lathe has a foot brake that also cuts power to the motor
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The micro switch would initially just cut power. The spindle I expect would turn some. The spindle diameter is relatively small in a mini-lathe so the moment of inertia is a lot smaller than for a full size lathe. 1/2 m r^2. It would be much better to apply a resistive load to the motor, but I don't know how to implement that yet. I haven't looked at the schematics yet, so I can't venture a guess.

When metric threading, I would go until I hit the thread relief groove and hit the E-stop. It would be nice to set up a switch to keep my reflexes out of the loop. Of course I need to use two switches in series as some sort of safety.
 
homebrewed said:
I used this as a guide for milling my tailstock. I also published my TS mod on my blog here. It is the March 24 entry, about halfway through that particular page. Instead of using a reamer blank to help align the base, I used linear bearing rod. Drill rod would work OK, too. It has to be long enough to stick out past the base enough to use a DI, basically like tramming your vise (except you're tramming the base's alignment).
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Thanks a lot! I will read this.

It's been a bit frustrating, since the lathe is out of alignment, it's hard to make precise parts (screws) (to bring the lathe into alignment). Because the TS is out of alignment, using the TS dead center introduces errors into the screw I am trying to make (taper error).

A while back, I tried aligning the headstock. I managed to reduce the error by a factor of 4. However, I haven't revisited the HS error since installing my ER32 chuck. The chuck has about 0.0002 runout, but I haven't checked the HS error since. I have some 20mm linear bearing rod, (for this purpose) but no 20mm collet. Right now I only have imperial ER32 collets. None of the sizes fit. I have some 5/8" tight tolerance O-1 rod I could use initially, if it doesn't sag too much.

Edit: Both very helpful links! Seems like this is a rite of passage, for mini-lathe users. Either junk it and move on, or modify it to better standards. Beginners are the usual buyers of these lathes, and are usually not that well equipped to make these modifications.

I made a 6mm rod with two different threads on it. The 6mmx1 / 6mmx0.75 has so much taper in it that the 6x0.75 end won't fit in a 6x0.75 tapped hole, (nor will a 6x0.75 die start) where as the 6x1 end a nut will spin on 10mm (10 threads) before the rod is too large. The spindle end was the 6x1 end. The 6x0.75 end was in the tailstock. Total stick out (with dead center) was about 50.00 mm, 16mm of 0.75 pitch, 1.5mm thread relief, 25mm of 1 pitch, 7mm at end. I have removed the dead center and turned sections at a time to try to reduce the taper. Mostly successful. You know, I forgot I had bought thread wires. Digging out the thread wires and will try again.
 
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When we get down to small diameter threading the cutting tool introduces more lateral displacement, causing tapers. Even very minor off center will have a larger affect at these small sizes. A very sharp HSS tool, repeated final passes and turning away from the spindle and @ 90 degrees, reduce the Chinese fire drill so you don't have to be so tense. No limit switch, instant braking needed.
 
WobblyHand said:
Beginners are the usual buyers of these lathes, and are usually not that well equipped to make these modifications.
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Yes, I hear you there! It took me awhile to get to the point where I thought I could do it without turning the TS into (even more obvious) junk.
 
homebrewed said:
Yes, I hear you there! It took me awhile to get to the point where I thought I could do it without turning the TS into (even more obvious) junk.
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That is why I am proceeding with caution. The links you provided showed me how things were done.

Where I am admittedly weak is at the mensuration part. Machining is easy, it's the mensuration (exactly what to measure and how to measure it) and setup that is hard for me. Not confident enough that I will account for all the errors on all the surfaces correctly. This is due to my lack of experience in this area. At this point, I can't make a truly square part, all the time, so correcting TS vertical, pitch and roll errors feels like a huge stretch. Hopefully with time and lots more practice, both my abilities and confidence will increase. I fully realize a new TS casting is only $51, but mensuration errors, and failing to comprehend what really should be measured and why, can easily trash two TS's in a heartbeat.

The differential screw should fix the cross axis error. I will work on that some more. My first use of thread wires was, umm, amusing. If I had a video of that, I could use it to make me laugh. Holding the wires is non-intuitive, even though I know what I need to do, my hands and fingers were fighting me. I can barely measure the thread pitch with the mic in a stand. Somewhat struggling with how I can do this with the workpiece still in the lathe chuck. I'll figure it out eventually.

Despite all my fumbling, I have found this exercise to be really fascinating. If would be better if there were no errors to correct, but I am slowly learning how to systematically identify and decompose the errors and to correct them. These are good skills to learn.
 
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