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Thread: Lathe Rebuild & Refurb

  1. #1
    High Speed Low Drag aMaff's Avatar
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    1992 Miata / 2003 Pathfinder

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    Lathe Rebuild & Refurb

    Yeah, it's not really a Miata build but it is Miata adjacent, as some of the first parts turned on it will be for my car. Figured some of y'all might be interested.


    I've been shopping for a small lathe for the shop for some time now, but kinda had a deal fall in my lap for a used, neglected, Emco 8x20 lathe. A buddy had bought it at a "used tool" auction at his work many years ago, then had a kid (and inherited his grandfather's lathe that also needs work), so this one was just collecting dust.




    Moderate sketch factor, but I stopped a couple times in the first few miles to cinch the straps down as it settled in place (and secure the rear door that had swung open), and it was fine the rest of the way back home.




    And just for fun, I turned Baby's First Chip just to say I had before the teardown started. Because boy did it need to be gone through.

    Last edited by aMaff; 12-05-2017 at 08:24 AM.
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  2. #2
    High Speed Low Drag aMaff's Avatar
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    With a little help from a couple friends, we got it down to my workshop. If you've ever seen where my shop is, you know how sketchy THAT was. Backed the trailer down the hill, used the winch to slowly slide it off, etc.

    One of the first things I noticed (and was pretty worried by) was the runout on the chuck. Hopefully the entire headstock won't need to be rebuilt, because I found the most likely culprit. A bunch of swarf built up between the back of the chuck and the lathe's face plate. Hopefully tidying this up will improve that situation, or else I'm going to have to figure out what's crooked in the system. The nice thing is that the lathe can be used to true itself up if need be lol




    Next up was the sticky lever in the quick-change gear box for the power feed for the compound. Apparently they've been using grease in this thing instead of machine oil. This...will become a running theme. I let it soak in simple green then oiled it while the machine ran for a few minutes and that freed the lever up to move freely side to side. The lead screw will need to be taken off and THOROUGHLY cleaned, however, as it is caked in fine chips. This too will become a running theme.




    My next biggest problem is both the free play and stiction in the cross slide. The free play can be tuned out by adjusting the gibs and the tension on the nut that the adjustment screw rides in, but a lot of the stiction is from old, crusty grease. So, the entire compound / cross slide / top slide and apron are going to come apart to be thoroughly cleaned up. I'm not going for "car show" levels of cleanliness, but I want it to run well even if it's not the most beautiful belle at the ball
    Once again, a ton of crud under the tool post. I actually couldn't find the witness mark for setting the tool post angle because it was caked in dirt and oil. It should turn much more freely now.



    Got the cross slide wheel & screw out. Again, CAKED on grease everywhere I turn (unintentional lathe joke!). To be clear, this isn't grease as you think of it, just heavily applied. This is stuff that's been on there for 20 years, dried up and left a thick coating of dry crap that has to be scraped off by a fine pick in many instances.




    And finally, the compound comes off the ways. This is the bottom of the compound, where it would slide on the lathe bed. As you can see, some surface rust (not anywhere it actually touches the lathe ways, thankfully), and a lot of old oil & dust and grit that will need to be cleaned off.

    Last edited by aMaff; 12-06-2017 at 09:46 PM.
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  3. #3
    High Speed Low Drag aMaff's Avatar
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    With the compound, apron and lead screw off, she's now pretty stark naked.



    Up next was to work on the apron (ie: the gearset that uses the lead screw to run the power feed for the compound, and rides under the compound).

    This is what greeted me when I took it off:



    With the cover off, it's even worse. Take a moment to click the picture and zoom in on just how bad it is. The amount of crud caked in the threading half-nuts, the caked on grease (more...). After I'd run it for a while, the handle for the power feed was jammed on and couldn't be disengaged because of what ended up being a chunk of dried grease getting caught in its working. It was bad.





    A bath in the parts washer made almost no difference in the grease on the gear train there. I ended up to have to disassemble the power feed engagement lever and gear assembly and then go through the entire gear train and the lead screw, tooth by tooth, thread by thread, with a pick to actually get the hardened gunk out of the system.

    It was a ton of work, but MAN everything turns smoothly now. It's such a huge difference. I put the barest whiff of white lithium grease on it per the factory service recommendations, and then it's maintained afterwards with 140W gear oil.




    I'm waiting on some finer cleaning supplies (0000 Steel Wool, for example, that I was utterly unsuccessful in sourcing locally) to be delivered in the next day or 2 to really tackle the lathe bed and the compound components, and then it can start going back together.
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  4. #4
    Ex FSAE. New MS3. JamesCH's Avatar

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    Looks good!

    You did just the right thing by cleaning stuff out and refreshing the fluids. Seems like a solid grab.

    Take care adjusting the carriage and other slidey-dovetail bits back into aliment and you'll be off to the races.

    Also, don't use motor oil as a cutting fluid! It can do bad things to your way oil and the smoke it makes is cancer-rific. There are lots of water-based fluids that won't rust your lathe and kill you.


    Maturity is knowing that you were an idiot in the past. Common sense is trying to not be an idiot right now. Wisdom is knowing that you will still be an idiot in the future.

    2009 MS3
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  5. #5
    High Speed Low Drag aMaff's Avatar
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    Quote Originally Posted by JamesCH View Post
    Looks good!

    You did just the right thing by cleaning stuff out and refreshing the fluids. Seems like a solid grab.

    Take care adjusting the carriage and other slidey-dovetail bits back into aliment and you'll be off to the races.

    Also, don't use motor oil as a cutting fluid! It can do bad things to your way oil and the smoke it makes is cancer-rific. There are lots of water-based fluids that won't rust your lathe and kill you.
    Cutting and Way Oil! I knew there was something else I needed to buy. Definitely won't use motor oil. Manufacturer recommends using regular ol' 140 weight gear oil for quick change gear box, lead screw and apron gear box.
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  6. #6
    Ex FSAE. New MS3. JamesCH's Avatar

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    My side business uses KoolMist for everything rather than a traditional cutting oil. Our experience is that it cools more effectively and lubricates well compared to traditional oils. We use it on heavy aluminum, steel, stainless, and titanium with a mister or spray bottle.

    I have a hard time believing that oil coated on top of a part is lubricating the cutting interface at all, despite that being how I was taught to 'oil a cut' in a mill or lathe. Oil is flammable, water-based coolant is not, and a lathe spinning really fast makes a nice fan... and that is why I needed to use a fire extinguisher once.
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  7. #7
    High Speed Low Drag aMaff's Avatar
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    Got the first pass with mineral spirits and soft brushes done to knock the big dirt and clumps of crud & crust off. Next I'll be cleaning all of the mating surfaces with 0000 steel wool soaked in WD40 to get the ways and gibs properly cleaned up, then apply oil where necessary and reassemble.

    The compound angle was really tough to set earlier. This is what I found between the angle dial that's pressed onto that arbor, and the tool post.




    Still needs work, but it's getting close

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  8. #8
    High Speed Low Drag aMaff's Avatar
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    It still needs several things (solid footing, the power switch needs to be replaced, lead-screw shear pin, I need some tooling) and wants a few more (might need to replace a feed screw on the cross slide, I want to add an E-Stop), but it cleaned up real nice, and everything runs and turns SO much more smoothly now.

    Before and After (in the same shot) on the ways. 0000 Steel Wool and WD40 (and some elbow grease) did the business on that crud




    The spindle face got similar treatment:




    All back together. It may not LOOK too much different in pictures, but man it feels like a completely different machine.

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  9. #9
    Ex FSAE. New MS3. JamesCH's Avatar

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    Looking better all the time!
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  10. #10
    High Speed Low Drag aMaff's Avatar
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    I turned up my first useful part today (*cough* after several tries *cough*)

    The tapered shear-pin that connects the lead-screw to the quick-change gearbox was in pretty bad shape. I had to pound it out when I disassembled the lathe, and I'm pretty sure it was a replacement and not really sized correctly.

    So I made one



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  11. #11
    High Speed Low Drag aMaff's Avatar
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    Fixed another couple of little niggles on the machine.

    The cross-slide feed was really sticky. I thought maybe the feed screw was bent (because it's super weedy). I took it all apart and everything measured relatively straight, so I dove a little deeper and found that the graduated ring was binding up against the screw's housing at the same spot on every rotation. If I took the ring off, the handle turned perfectly smooth.



    I could make it loose enough to work but then it wouldn't hold its position, or I could make it tight enough to hold its position and it would be impossible to turn through that rough spot. You can sort of see where it's interfering here, on that dark ring:



    Broke out the emery cloth and a fresh can of elbow grease and spent a few minutes knocking it back just enough that it turns nice and freely now.

    Next, I wanted to line up the tail-stock so it's properly centered with the bore of the chuck. Usually you'd use a couple of tapered centers for that, but, well, I ain't got those yet. So I turned a center from a piece of steel...




    And then used a centering bit in the tail-stock (which also comes to a point) and got it trammed in. It's probably not *perfect*, but it's well within good-enough range.

    Before:




    After:

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