Much Needed Lathe Mods - A Better Z Axis

Trying to use the Z axis hand crank for anything besides straight, light cut OD turning with no shoulders to deal with or Z axis dimensions that are even kinda close, like +-.03", will end in failure if you use that shitty rack and pinion setup that these mini lathes ship with. In a nutshell, any attempt to machine something along the Z axis quickly turns to shit. Turning tools grab and pull the carriage into the work, or when using the milling attachment, end mills do the same thing--grab and pull and dig in and fuck up whatever it is youre doing. Youre lucky if you dont break the end mill. Plunging an end mill slowly with high rpm, or any combination of  still doesnt help in the least. Up until now Ive had to avoid parts that had medium to high tolerance work along Z axis; counterbores with +-.005" on the depth or  something similar. Plus or minus .005" is not what I would call high precision, and I couldnt even do this the way things were. The good news is, there's an easy fix that works great. Basically we are going to steal an idea from the cnc conversion and also from our common sense that already knows good and damn well that a lead screw of any kind is preferable to a rack and pinion.

Im a bit slow sometimes and Im ashamed to say that this idea wasnt immediate, the way I feel it should have been, looking at it now. The rack and pinion has a good .02-.04 drift in whatever direction pressure is being applied and since the rack and pinion design was designed to transfer loads in a particular way that offers absolutely no resistance if pushed or pulled in either direction along its axis, even facing can be a white knuckle operation when youre taking the last few thou off and your finish size is plus or minus .0005". I have several parts that have tight OAL(over all length) dimensions in the drawings for my 4 cylinder stirling. The only way I was even able to pull it off is because I could get the tool well away from taking any cut, then using an indicator to move the carriage a few thou, then clamp the carriage down in position and slowly go over the face a few times until it doesnt even take dust. Between the shitty rigidity of the compound to begin with and then only a rack and pinion setup to hold the axis still, results were truly disappointing. Thats when it dawned on me.

I could engage the half nut to lock down the carriage when facing. That would better than trying to clamp the carriage down. I also considered a carriage locking method to be a top priority mod since I was basically unable to cut a truly flat face without considerable pains in my ass. What I discovered once I started experimenting with using the half nut to lock the Z position of the carriage is that turning the lead screw by hand with the half nut engaged was pretty easy and that moving it this way had almost zero backlash, with an indicator I could easily dial off a couple thou or even tenths, if I trusted my indicator like that, and I didnt really need to change anything else and Id have not just a decent Z axis feed, but a damn good one. The plan was to machine a handle with knurled edges and possibly a smaller handle for faster spinning, but the handle was absolutely needed and I already had a piece of material that not only was the perfect size, the machine work was almost done already. I still havent finished, or even started on the handle yet since all this other shit seriously side tracked me, but it was worth the distraction.

My earlier method of using a clamp to
attempt to lock the carriage in position
for milling or facing.

The next thing I did was remove all the change gears, and set the feed direction lever to neutral position. Now I have no gears on the back of the machine being powered. This makes it much safer for me to be groping around back there blind, spindle running a couple thousand rpm. The thought of accidentally sticking my finger in those meshing gears pretty much scared me to the point that I didnt want to leave a single gear attached except the one I intended to use as my temporary handle.

Thats pretty much the whole story of how the Z axis found itself being scrutinized by me and subsequently modified to work more like a white man's machine. Ill just show the porn and that should clear up any remaining confusion.

Here all the change gears have been removed and the largest one I have has been put on the lead screw to use as a temporary handle. Larger diameter is easier to turn by hand and this is the biggest gear I have. The cluster of  two white gears directly underneath the spindle gear are not engaged, neither is the gear under that. That big ass gear did make for pretty easy turning of the lead screw with the half nut engaged, but I pretty quickly realized I could make a way better temporary axis jog handle.

This piece of material is damn exactly what I need already. Its too perfect to not do it. I havent even started on finishing this part. It will be knurled on the OD and have a spin handle the way my temporary one does (you havent seen that yet). Ill also need to mill a keyway in it. A broach would be badass.

Here is the temporary in all its glory with spin handle installed. I dont know what else to call the bolt with a piece of aluminum tubing over it besides a speed handle. Because it does make it possible to spin it up pretty fast and get Z moved around quickly. I should also note that Im even getting less chatter using the new method of Z axis feeding/cutting.

                                                                                                                        

Here Im finally setup to make a permanent handle. The indicator is setup somewhere that is not affected by Feeding X and using my temporary handle I have very fine control over Z. Soon as I get the handle finished Ill post it in all its glory.                                                                                










This was definitely something I should have done a long time ago, but it never occurred to me. I can do a slower feedrate by hand and get a better finish. It pushes though heavy cuts way easier, almost too easy and you bog it down. And the virtual absence of backlash is also fucking killer. I need to make a brass half nut and I need to change the spindle bearings. It seems so stupid to me that a mini lathe manufacturer would skimp $20 on construction of a machine for such a vital role. But they all do it except maybe the high end smaller stuff. They all put fucking skateboard bearings on the spindle rather than real spindle bearings, tapered pins that can take any load you can hand the spindle. At first this shit didnt chatter real bad, but as those suck ass bearings start to wear in, I get constant chatter it seems like.  Im still pretty spoiled on industrial grade shit. I have no experience playing with a hobby lathe. I do have perhaps higher expectations when it comes to depth of cut and rigidity.

I think its obvious what has to come next, the dro from digital calipers. I already butchered the calipers, just need to mount it. 6 inches beats 1 inch on a shitty indicator. Ive never had such shitty tools. Its really all junk. Even the mics, which ill usually trust cheap mics, are dodgy as fuck. Either way, the caliper readout beats a shitty indicator.

                                 



I took that hand wheel off the carriage so Ill quit grabbing for it. Ive had a chance to cut on the aluminum piece a little and and extremely pleased at how much better actually using the machine is. I need to fuck with mounting my steppers too. Thats coming soon I get the feel. At least the Z axis. Im so happen with this little shit, Id prolly shit if I had some faintsee pire feed. But, if I do one I know the others will get done too. I would prolly know all kinds of cool shit to do if I really dug around online. I dont know why I dont do that type shit anymore, voraciously seek shit out online, I mean.

Interpolated by hand for the most part. It was polished with some 220 emery, but other than that it was all interpolated thanks to using the Z axis leadscrew for handfeed. Chatter also definitely reduced.