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Mini-Lathe Improvements, A WIP Thread

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  • Very impressive work on this lathe.

    I agree with RB211 on the need to be able to adjust against flex. Have you given any thought to checking with a local headstone maker? Most of them have reject piles lying out back somewhere, and the size you are looking at could easily be found there for free or very cheap. If you have a strong back or can get some help getting it home, you could locate some epoxied-in expansion anchors matching your lathe mounting holes and using shims and/or double nuts on the anchors, have plenty of adjustment.

    I know, headstones are not 'flat'. But you would not be using it for a surface plate, and it would give you a lot of rigidity.

    Just a suggestion.... again, nice work on this, work that you can be proud of and should last as long as the lathe lasts.

    Dan L
    Salem, Oregon

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    • I think I would just go to the local cabinet maker and get a chunk of granite....1-1/4" is a standard thickness...plenty for a lathe of that size.

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      • Ummmmmm... RB.....

        You might want to compare the massive bed on your picture with the scrawny little bed on most mini-lathes. They can use more rigidity, and a heavy base can provide it.

        Your 3/16" material will also make an improvement, refer to comments about twist above. But it will not be as good as a concrete or heavy steel base.
        1601

        Keep eye on ball.
        Hashim Khan

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        • Originally posted by J Tiers View Post
          Ummmmmm... RB.....

          You might want to compare the massive bed on your picture with the scrawny little bed on most mini-lathes. They can use more rigidity, and a heavy base can provide it.

          Your 3/16" material will also make an improvement, refer to comments about twist above. But it will not be as good as a concrete or heavy steel base.
          One must balance the needs of practicality/convenience and what is best. I agree with you.

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          • Right-o, time to get back on this particular horse. Funds and time led to me shelving my block'o'something plans, so instead i turned my attention to this:


            Like the dramatic lighting? Fitting for a successful decapitation methinks. Anyways, for those unaware thats the cross/compound slide assembly off a mini lathe, and im going to blueprint it, to borrow a gunsmith term. Take it apart, remachine all the mating surface to fit together better than factory, put it all back together and hope it works proper. First step, disassemble everything:


            Got 4 parts, on the left we have the base and slide for the compound, on the right is the carriage and compound slide. As you can see from the pictures already, they... they dont look to great. This is after theyve had all the old oil, grease and chips scrubbed off (small parts are in another castle). The machining in general is pretty chainsaw-y. A quick close up of the sliding surface on the compound base:


            And hopefully that illustrats why im remachining everything. The cross slide isnt quite as bad, but the movement on the compound is bad enough to render it unusable, either i loosen the gibs enough for it to freely move, resulting in an unacceptably sloppy fit and the lack of rigidity that comes with it, or i keep the gibs tight and am left with a compound that still compromises rigidity because of crappy fits and reduced contact on bearing surfaces. No beuno either way, and it affects use. The cross slide isnt as bad, but it aint good:


            The machining on the carriage where it meets the bed isnt too great either:


            You can see the uneven wear pattern that resulted from poor machining from the factory. Clearly this thing wasnt flat to begin with and was only making contact at the 4 extreme points. Again, sacrifice in rigidity. Now, even as it is, this lathe still did good work. I want to be clear on that, this isnt about making a non-working tool work, this is making a working tool work better. That out of the way, im going to start with the carriage and cross slide and work my way up

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            • Carriage first. Before anything, i needed some reference surfaces to cut everything against, as well as give me a way to hold the piece for machining ops. To absolutely no surprise, there werent 2 surfaces on this thing that were actually flat, coplaner or square. Quick couple trips to the surface grinder:


              The faces with the black sharpie marks are my reference faces, ill be cutting all the important bits like the dovetails and bed ways with those freshly ground surfaces as the datum. As well as the 3 surfaces you can see in the photo, the faces opposite to them have also been ground flat and parallel, if that makes sense. Anways, on to re-cutting the dovetails, heres the setup for that:


              Yeah, i know, stupid looking. I was short on options. Anyways, clamped to the table, and ive got one of those freshly ground surfaces dialed in with the X axis. Im not worried about alignment with the bed ways at this point as ill cut those in-line with the dovetails in a later operation. These dovetails are a standard 60 degree dovetail, and im just skimming off enough material to get rid of all the old machining marks, maybe .005" off each surface. The end result:


              Nice and clean. Interior surface of the dovetail looks that way too, but have you ever tried to photograph a dovetail like that? Too much of a PITA for me to care. Now that these dovetails are cut, time to start working on the slide itself:



              As you can tell by the writing that says "grind", ill be grinding those faces first thing to give myself a few reference faces. I also ground the sides to be square to those faces. Now, the bottom face of the dovetails im grinding because thats a sliding face and i want to be making good contact, the top face im grinding parallel so A) i can use it as a reference face as needed and B) my toolpost wont end up at some weird angle because the cross slide isnt parallel to the bed. Anyways, the stup on the mill to do the dovetails:


              Held in the vise this time, couldnt get the cutter around the clamps if i held it on the bed. I tripled checked everything to make sure that the freshly ground face of the dovetails was perfectly trammed with the mill, as well as parallel to the table. Didnt want my dovetails to not be parallel with my reference surfaces on the sides, or end up at a weird angle because the part was crooked. No pictures of the process cause seriously, cutting a dovetail is boring.Heres the end result:


              Nice and clean and shiny, and importantly, smooth. Even without any sort of oil on the ways, the slide still slid like ice, way better than it used to. Now, the next thing i did was all the same stuff but on the compound slide, but thats all the same operations i did on these parts, so lets just skip to the end:


              Hey, wait a second, whered that block come from? Fairy godmother mustve left me a solid tool post . I appreciate it FGM, the extra rigidity of the solid post is nice to have, and i hardly ever use the compound slide anyways. The solid post and the assembled cross slide have even been ground to the exact same height, so i can move between the solid post and the compound slide without changing my tool height. She really did think of everything, huh? The block is mounted to the cross slide with a 10-24 screw in each corner, and matching holes were drilled and tapped in the cross slide, bout 3/16" deep. Plenty of material in the cross slide for those, so nothing to worry about there. The hunk-o-block is just a big old thing of cast iron, about 2.4375" square, and it weighs more than the cross slide assembly does. Probably couldve made it more elegantly, but whats the point really? Needs to hold the tool post, not look pretty

              Now, one thing i didnt show was me re-cutting the bed ways in the carriage. Frankly, i forgot to. Gist of it is i grabbed the carriage upside down in my vise, got the dovetails aligned square to the X axis, the recut the bed faces, taking off a precise .005" from all the contact surfaces. Nothing too it and not much is lost by not having pictures. Here everything is reassembled with the solid tool post in place:


              Had to mess with the shims on the cross slide gibs a bit to get everything moving how it should, but wow what a difference this all made. Everything moves smooth but with 0 play, i didnt have to fight with the grub screws to adjust the cross slide gibs at all, everything just feels nicer. Feel is subjective though, proof is in the pudding. So, i chucked up a piece of 1/2" O1 drill rod, installed a DCMT tool with a dodgy steel cutting insert instead of the aluminium ones i usually run, dialed in a .020" cut and let her rip. I know from past experience that this cut is a no-go for my machine, the inserts took too much cutting force and overwhelmed the rigidity of the machine. Either the choppy cut would piss off the motor electronics, or id have to kill the cut because the chatter was just unbelievable. Now though:


              Pushed a bit of a burr but i sure cant complain about the surface finish. Bogged down the motor pretty noticeably, but no chatter, and i didnt cut on the return pass either, another problem that i previously had. I always attributed that last one to the carriage rotating a tiny bit when the direction of movement changed, pushing the tool into the work. Not a problem now though. I also tried parting off a few pieces, something else ive had trouble with, no problems there either. Havent tried the compound slide yet, but im still calling this one a success

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