plastic intermediate gears or metal for mini-lathe?

[vtsteam]

Okay, no problem.  I was saying I could believe "Every pass is bang on the previous one."

I have metal gears on my Craftsman 12", and they're somewhat worn, I'm sure, because they're old. But wear probably evens gears out -- if a single tooth were displaced in poorly made gears it would wear faster on the tight side. Because you make up different trains for different threads, the gears and ratios would spread out the wear that the displaced tooth applied to any other gears, so would not cause a problem to other gears.

When you set up a train of gears, you set them into each other with a small clearance -- in my case, the thickness of a piece of paper. Since I do that anew each time I set up a train, I am unconsciously compensating for whatever wear the gears have.

It seems to me that gears are remarkably resistant to defects and wear as far as overlapping threads goes. Not saying they can't introduce other problems, but it is kind of interesting how well they work.

[unc1esteve]

I do not understand the 'tone' of this thread.  There seems to be some dark, hidden undercurrent?  Some taking offense where I do not see offense.  Am I wrong?

[Brass_Machine]

I do not understand the 'tone' of this thread.  There seems to be some dark, hidden undercurrent?  Some taking offense where I do not see offense.  Am I wrong?

Well with communication the way it is, sometimes it is hard to read something in the tone it was meant. I do believe that whatever misunderstandings there were are pretty much done.

I would hope no-one is offended.

Eric

[Joules]

First of all, let me apologise to anyone who may have been offended, especially Woodsman22.  It was never my intention, and I suspect I maybe suffering from Grumpy Old Git Syndrome.   I think perhaps my way with words is not what it once was, so please let me communicate in a manner I am more familiar with.

This is my mini lathe, mostly standard but it does haver taper roller bearings fitted.  I for now just use the plastic gear set as they have proved more than adequate for my uses.



I have it set for the smallest thread pitch the mini lathe can cut (0.4mm)



The cross slide is set over at 29 degrees, just under half the 60 degrees of the finished thread.  You can see that I swapped over the standard hand wheels for brass knurled, this was because I got fed up with the clashing wheels and also the time I caught the cross slide wheel, didn't realise and added to my cut so much it ruined the part I was making.



This is the thread I cut and you can see the lathe tool I made.  It was a small parting tool I had made and broke the tip off, so reworked it into a thread cutting tool.



I don't have a tool and cutter grinder, so all my tools are hand ground on a bench grinder for larger tools or to remove bulk and then finished with diamond stones to get a good finish.  The lathe tool was very roughly made and doesn't have all the angles they say you need, but I find generally I get good thread engagement and its good enough for me.



Finally a check of my finished thread against my thread gauge.  The overall thread I made was 0.2mm undersized as on my second pass I engaged the thread dial on the wrong number, as others have mentioned doing  ...  But it doesn't matter as this was just a practice part, and proved I still need more practice cutting threads and that its better to back out the tool, reverse the lathe then re apply the cut without disengaging the leadscrew nuts in my case.

The point I was trying to make from the very beginning is that the lathe is capable of accurate work as is, and it is a good tool to learn on due to its low cost.  The mini lathes do seem to come in for flak from people far more skilled than I.  However the best way to get to grips with it is just to do it, in some cases over, and over again till you get it right.  I will now decide what I am going to do with this item and make something else to go with it.

 Hope this is of interest to you Woodsman22.

               Regards

                             Joules       

[vtsteam]

Wider interest, too, Joules. A fine set of photos! Thank you. 

[Joules]

Right I figured out what I should do with that part I made, make a thread forming tap.  Since the mini lathe was setup for threading I found some silver steel on the bench that was close to the diameter I needed, about 4mm.  A quick bit of turning to size, round the end off with a needle file and polish with the fine diamond stone.  This time I took half the cut depth I used on the brass and used paraffin (kerosene) as cutting fluid, wondering if my tool tip would hold up.  It did and I got the tool below, it has 0.05mm larger diameter thread than the brass part .



This was put into the drill press and pulled firmly down onto the bit of brass I had drilled a 3.6mm hole in.  The brass nut being in the drill vice, I turned the drill chuck manually whilst keeping the pressure on to force the form tap through the brass.  Don't let the pressure off or back the tap out before you have completed the threading as you will never get it realigned.



Test fit the part.  I had taken my measurement of the brass threaded part from the lathe dials and forgot about the brass deforming so my brass part wasn't out at all.  A very fine curl of brass came off the part as it was screwed into the half hard brass sheet.  It's a snug fit but I could fit them together with finger pressure.  A couple of times screwing it together produced a silky smooth fit.  I forgot to mention I de burred the nut with a drill bit as the form tool raised quite an edge as it exited the brass sheet.



Final shot of both parts together.  It serves no purpose other than to test I could make a tool to form the thread and that the fit was good.  I am very pleased as my thread cutting tool is still as sharp as when I made it.  The thread forming tool is only really practical for sheet metal, as a small billet would impart too much force on the tool and most likely snap it at the neck, could be OK on soft alloy though.  Another tool made another technique learnt, it's good to play.