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Thread: Mini-Lathe Improvements, A WIP Thread

  1. #141
    Join Date
    Jul 2017
    Location
    Springfield Mo
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    484

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    So, to check the alignment of the centerline, im going to do what i find to be the best method, and thats to fit a test indicator on a bar held in the headstock and sweep the taper of the tailstock. If im perfectly aligned, i should get the same reading on all points of the taper. First, the horizontal direction, front to back if you were using the lathe. Zerod at the front:


    And rotated 180 degrees to the rear:


    So, the tailstock is .005" too close to the front. Thats easy enough to fix, back-to-front alignment is built into the tailstock after all. Next we need to check the vertical alignment, and this is already known to be off. Same process, zeroed at the bottom:


    And rotated 180 degrees to check the top:


    Indicator is reading that the taper is sitting .005" higher than the centerline of the lathe, which i found odd. Last time i checked it was .010" higher, but that was before i changed the headstock casting. New one sits higher than the old one i guess. Anyways, now ive confirmed what i need to fix, the question is how. Theres 2 methods i can use for this, i can either make the headstock taller or i can make the tailstock shorter. Making the headstock taller would require me to dismount it and shim the entire thing up to match the height of the tailstock. Im not a fan of that idea, removing the headstock is quite the chore to do, and im not fond of the idea of the headstock resting on a stack of shims. That just leaves option 2, making the tailstock shorter, and thats the move im going to make. It doesnt seem like its a very common move, most people seem to opt for the headstock route with the theory being that as the tailstock base wears they can remove shims from the headstock to keep things in line, but id prefer adding shims to the tailstock for that. Plus, i get to play on the surface grinder this way.

    Before anything hits a tool though, still need to do more measurement. Onto the next post!

  2. #142
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    Jul 2017
    Location
    Springfield Mo
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    484

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    First things first, i want to establish exactly how much higher the tailstock is so i know how much needs to come off. I know i already checked this with the test indicator, but personally i see test indicators as a way to get a relative dimension for comparison, whereas i want an absolute dimension for this. In my mind the question is using a DTI to tell if part A is higher than part B, versus using a micrometer to measure the exact thickness of part A.

    Now that thats out of the way, im going to start by finding out the height of the center of the axis of rotation. The way im choosing to do this is to chuck up a piece of scrap, but it to run true, pick up the height of said piece from the ways with a height gauge, then subtract half the diameter of the part from that measurement. Should give me the exact height with the minimal amount of work. Picking up the height of the piece:


    Followed by some math. Yes, i wrote this all down on top of the compound slide. Couldnt find a post-it


    Up top is the diameter of the piece i turned, .4848". Clearly, i was not shooting for a precise dimension, just getting the piece to run true. Under that is the height from to the bed to the top of the piece, 3.804", minus half the pieces thickness, .2424, giving me the precise height of the centerline, 3.5616". Weird number, but matches up with the advertised 7 inch swing of the lathe.

    Next, i need to repeat this process with the tailstock. Problem is, i cant just turn a piece to be concentric with the tailstock axis the same way, because the tailstock doesnt spin. I could hold a gauge pin in the drill chuck and use that to measure, but then id be bringing in possible runout of the chuck. A collet would work better, but i dont have anything of the sort that would fit the tailstock. In the end, i chose to indicate off the outside of the quill. I did measure the diameter, its consistent through its length and is as straight as i can measure, and im choosing to operate under the assumption that the taper is concentric with the OD. Same process, pick up the height from the bed to the top of the quill:


    Then math:


    Again, could find a post-it. If you cant make that out, the tailstock quill measured .8648", bed to top was 3.9985", which left the centerline at 3.5661". So, if the tailstock centerline is 3.5661" and the headstock is 3.5616", that leaves the tailstock needing to come down by .0045" to be in line. Time to plan that one out!

  3. #143
    Join Date
    Jul 2017
    Location
    Springfield Mo
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    484

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    Luckily for my plans, the tailstock on these lathes is actually 2 pieces, there the main part that hold the quill, and a base that actually contacts the bed that the main bit is bolted to. My plan at this point was to take the quill apart, take the metal i needed to off the base, then sit back with a drink after a quick and easy job. First things first, some disassembly which im not going to bore you with the details of. Millions of people have already gone over how to disassemble the tailstock on a mini-lathe already. All that off camera, so heres the workpiece:


    Yikes. This just got a lot more involved of a project. My initial plan was to just stick the part on the surface grinder and take off .0045" from the 2 bearing surfaces That plan went right out the window as soon as this touched the surface plate and turned itself into a see-saw. I dont think that "flat" translates very well into whatever language the guy making this part spoke. Quick flip the check out the underside:


    Didnt know you could use a chainsaw to machine parts. This is honestly the first time ive been flat out disappointed with one of the parts of this lathe. For the price i dont expect much, but still, the v ways arent square, somehow the flat faces of the v arent straight, the entire base is out of flat, the surface finish on all machine parts doesnt deserve to be called a finish or even machined, its just a mess. Really, after measuring this im not even going to try to fix is, for the 4 thou i have to take off the height theres not even enough material to take off to fix some of the issues. Ive got a hunk of durabar in the basement, im just going to take off a slab of that and make a new base, ill need to pick up a 90 degree chamfer mill but i cant possibly do any worse than this.

    Before i dive into all that though, i want to check the main part of the tailstock to make sure all of its important machined surfaces are in-line with each other. The only really important ones i see are the pads where the main casting meets the base piece, and i need to make sure those are in-line with the quill. To do this im just going to set that main casting on the surface plate, then sweep the quill top with the DTI on a surface gauge. Zeroed at the far end:


    And then checked at the close end:


    So, the contact points on the main casting are out of line with the quill by about .002" over the length. Not horrible, but it still like to take that out. The leading idea for this is to throw the piece in the mill vise, align it so that the quill is perfectly inline with the mills X axis, then remachine the contact surfaces. That way, when i make the new base plate i know that as long as the contact points on the baseplate are parallel to the ways, the tailstock axis will be too.

    Thats all for now, ill get to work making the new base piece at some point. Need to source a chamfer mill first, although i am considering just grabbing a v grooving router bit instead and using that since theyre more commonly available. Ive had decent results using router bits for milling purposes in the past, no reason it wouldnt work for this. As an added bonus, id be able to make the base immediately, rather than waiting for something to show up in the mail. I think ive got a router bit on hand, and if not i can run to Grizzly and grab one of those today.

  4. #144
    Join Date
    Jan 2010
    Location
    Jonesborough, TN
    Posts
    418

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    I've been quietly following your progress, and WOW! I have owned a MicroMark 7x14 for 18 years and have enjoyed using and learning with it. I would love to have the skills to do what you are doing.
    BTW, the last 2 pictures in your last post don't show for me...
    Ignore the naysayers! Keep on truckin'.

  5. #145
    Join Date
    Jul 2017
    Location
    Springfield Mo
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    484

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    Quote Originally Posted by chucketn View Post
    I've been quietly following your progress, and WOW! I have owned a MicroMark 7x14 for 18 years and have enjoyed using and learning with it. I would love to have the skills to do what you are doing.
    BTW, the last 2 pictures in your last post don't show for me...
    Ignore the naysayers! Keep on truckin'.
    If any of this took skill i wouldnt be doing it...

    In all seriousness, none of the mods ive shown so far have required anything beyond the basics of machining, its mostly been a lot of measuring. Even making the new baseplate for the tailstock is going to be simple, though theres going to be a lot of milling involved

  6. #146
    Join Date
    Mar 2013
    Posts
    1,499

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    Knowing what to measure and how to measure is more than half the knowledge of being a machinist in my book.

  7. #147
    Join Date
    Oct 2012
    Location
    San Antonio TX, USA
    Posts
    2,353

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    quick tip for the long run - mill/ grind some oil grooves in the bottom of the carriage and put in a couple of GITs cups for way oil, then make some way wipers. Being able to get way oil to the sliding surfaces will let you run the gibs tighter and still have smooth movement = less chatter and wear. Made a noticeable difference on my Atlas.

  8. #148

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    I dont think that "flat" translates very well into whatever language the guy making this part spoke.
    This looks rather familiar The problem with these types of machines seems to be that the visible parts on first glimpse are rather well machined and seem to possess at least some degree of functionality (like the main bed and ways), but all of the hidden parts like underside of tailstock, the cross slide and compound are just in a horrible state regarding flatness. I've had blind luck with my unit: despite the hacksaw machining job on the hidden parts, the machine has actually performed rather well over long years. So I've not really done much to rectify the uneven surfaces, just the occasional tightening and some adjustments. I can not justify the amount of work involved in a full scale improvement job. On a bigger more rigid machine it would make sense to me, but on these little ones I'm not up to it really.
    I do not mean to say in any way that one should not go through with all of this....it is a great project that I follow with interest and there is much to be learned from these activities. So keep up the progress and let us know !

  9. #149
    Join Date
    Mar 2015
    Posts
    2,597

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    Million dollar question. After putting all of this work into the lathe, would you do it all over again? Or buy a slightly larger lathe that was ready to go, like the 8xXX series?

  10. #150

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    I guess this more of a learning curve enhancement and recreational topic than actual intention to improve the performance of this little machine to such an extent as to be worth the effort

    For example I rebuilt an old rotten BMW once for similar purposes and had a lot of fun doing it (ended up driving the thing for over 120000km too). In retrospective it was a fun and educational project, but hardly worth the work and effort I put into it. In retrospective I would not find it in me to do it again.

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