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Thread: Mini-Lathe Improvements, A WIP Thread

  1. #131
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    Another day, another project done on the lathe. The new bearings are doing quite well, and the lathe is noticeably stiffer and better running than it was before, but there was still a noticeable amount of deflection at the tool. Not enough to cause massive issues, but enough that operations requiring higher feed pressures, parting, using carbide inserts, tool post drilling, would still cause the carriage to shift enough to mess with things. Next stop on the list of improvements was to do something about the carriage gibs.

    Now, on these lathes, the carriage gibs are screwed in place with 3 cap screws, and in between the cap screws are grub screws and the theory is that to adjust the tightness of the gibs, you adjust the grub screws to give the gibs the right distance from the bed ways, then lock the gibs down with the cap screws. Like many others, i figured that a solid shim would be a better option than those screws. First things first, disassemble carriage:


    Off came the cross-slide and its joining bits, the leadscrew, and the thingy attached to the carriage thats used to move it whos name i cant recall. Apron maybe? Anyways, all this left me was the carriage base.



    Gibs and hardware disassembled and ready for work. First things first, plotting a plan of attack. Some people just use feeler gauges and keep building different stacks until they find the best fit. I wanted something a touch less hit-or-miss, so i broke out the micrometer to take some measurement. Heres what the carriage looks like where the gibs attach:


    To get the value of the shim ill need, im going to measure the distance from the top of the carriage to the bottom where the gibs mount, then take a second measurement from the top of the carriage to the bottom of the bed ways, where the gibs going to be riding. The difference between the 2 measurements gives me the value of the shim i need to bring the gibs where they need to to leave the perfect amount of free play. Take the measurements at the front and rear, right and left. My numbers ended up looking like this:


    Continued next post

  2. #132
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    A quick test with some feeler gauge shims and the gibs clamped on to make sure the measurements track:[
    img]https://i.imgur.com/T37WEOh.jpg[/img]

    And from here there was a small detour. The shim thickness was bang on, but the carriage was still showing some excessive movement. I suspected that a chip, ding or whatever was interfering with the mating of the bed ways to the slot in the carriage, so to take care of everything at once i decided to lightly lap the carriage to the bed ways. Some 400 grit sandpaper spray-adhesived to the ways and a few quick strokes took care of the problem:


    Minimal metal removed, and whatever was causing the tipping issue was no longer a problem. Reconfirmed with the feeler gauges and the clamps to make sure that movement was good, and then off to milling out the material for the permanent shims. The donor material was some steel recovered from the handrail of an old treadmill, brought to rough size on the mill then finish ground to dimension on the surface grinder:



    Continued next...

  3. #133
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    Once i had the 2 shims to thickness, i needed to get the bolt through the shim somehow so i could actually get the gibs installed on the carriage. The way that i saw it, i could spend a lot of time precisely locating the holes, or i could spend a minute and a half cutting a slot with an angle grinder to let the bolts pass though. I went with the second option:


    Doesnt look pretty, doesnt need to, it works and thats what matters. For funsies, i also slapped the gibs themselves on the surface grinder, just to get a flat face for them to run on. From here, it was just reassembly, relatively painless. I did manage to overshoot the target dimensions on the front shim by about .002", im still learning how to operate the grinder. A few bits of shim stock fixed that right up and let the carriage run plenty free, while still keeping everything tight. Here she is all reassembled and ready to work:


    Such a simple mod, such a world of difference. Everything combined lead to a much, much better fit between carriage and bed, and now rigidity is something i have rather than something i use as a curse. Not 'real' lathe rigidity of course, but rigid for its size. Total free play in the carriage movement up, down and rotational is pretty undetectable, which led to the tool staying where it needed to be rather than twisting off course. The most noticable difference was in parting; the lathe could technically part of things before, but the cut was hardly clean and the chips and chatter were pretty nasty. Now though, the blade stays where it needs to, doesnt wiggle around, and i can get nice, curly chips parting stainless without having to baby the cut.

    Other areas were improved as well, my carbide insert tools actually cut well with steel inserts, and i can put some actual feed pressure on the tool post drill chuck without forcing the carriage to rotate and bend the drill. I cant attribute all the difference to the improvement to the gibs, but between the better bearings, improving the gib fit and lapping the carriage to the ways this lathes functionality has been massively improved.

    Next up im tackling the tailstock alignment, ive always managed to get front-to-back aligned perfect, but the quill centerline sits .010" higher than the spindle center line. One of these days ill toss the tailstock base on the mill/grinder and take off the material to get everything perfectly aligned

  4. #134
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    Some of that is really a job to be done by "scraping", but you got it done.

    Good ingenious use of what you have.
    1601

    Keep eye on ball.
    Hashim Khan

  5. #135
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    Question is this... With the amount of work you did, have you noticed an improvement? Also, ThisOldTony replaced the ball bearings in the headstock with tapered roller bearings. No point in doing any of this if you don't get any gains. He seemed to think there was a difference. Don't ask why a "lathe" even ships with non angular contact ball bearings or better?

  6. #136
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    It would be worthwhile to verify that bed thickness is constant from headstock to tailstock, this is a fairly common issue with these machines. Cheap and reasonably easy to deal with, see:
    http://warhammer.mcc.virginia.edu/ty...s/Bedways.html

    John

  7. #137
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    Quote Originally Posted by epicfail48 View Post
    ...

    Such a simple mod, such a world of difference. Everything combined lead to a much, much better fit between carriage and bed, and now rigidity is something i have rather than something i use as a curse. Not 'real' lathe rigidity of course, but rigid for its size. Total free play in the carriage movement up, down and rotational is pretty undetectable, which led to the tool staying where it needed to be rather than twisting off course. The most noticable difference was in parting; the lathe could technically part of things before, but the cut was hardly clean and the chips and chatter were pretty nasty. Now though, the blade stays where it needs to, doesnt wiggle around, and i can get nice, curly chips parting stainless without having to baby the cut.

    Other areas were improved as well, my carbide insert tools actually cut well with steel inserts, and i can put some actual feed pressure on the tool post drill chuck without forcing the carriage to rotate and bend the drill. I cant attribute all the difference to the improvement to the gibs, but between the better bearings, improving the gib fit and lapping the carriage to the ways this lathes functionality has been massively improved.

    ...
    Looks like yes he does notice it......
    1601

    Keep eye on ball.
    Hashim Khan

  8. #138
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    Jul 2017
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    Springfield Mo
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    Quote Originally Posted by J Tiers View Post
    Some of that is really a job to be done by "scraping", but you got it done.

    Good ingenious use of what you have.
    Its still on the project list to go through and scrape the ways of the cross and compound slides, but I keep getting busy with other projects. The bed I don't think I'll be touching, though I do agree that scraping the bed and ways in the carriage in would be a good idea. Outside my skill level at the moment though

    Quote Originally Posted by RB211 View Post
    Question is this... With the amount of work you did, have you noticed an improvement? Also, ThisOldTony replaced the ball bearings in the headstock with tapered roller bearings. No point in doing any of this if you don't get any gains. He seemed to think there was a difference. Don't ask why a "lathe" even ships with non angular contact ball bearings or better?
    Very, very noticeable. No one mod by itself made a huge difference, the bearing replacement, for example, gave a slight improvement, but stack them on top of each other and its night and day. As mentioned, I can actually part things off without a chattering nightmare, and my carbide insert tools aren't shifting around to the point they break tips anymore. More rigorous testing is needed, but even the brief time I've spent playing with everything after the mods really proves the worth

    Quote Originally Posted by GadgetBuilder View Post
    It would be worthwhile to verify that bed thickness is constant from headstock to tailstock, this is a fairly common issue with these machines. Cheap and reasonably easy to deal with, see:
    http://warhammer.mcc.virginia.edu/ty...s/Bedways.html

    John
    I actually had measured the thickness, though I can't for the life of me remember how that went. I want to say it was withing a few thou across the length, though I could be talking out of a different part of my anatomy on that one. I did lightly run a file along the underside, just to take out any high spots. There's still a few ever so slightly tight spots in the travel, so the ways aren't perfect, but its enough for me to live with

  9. #139
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    Another day, another improvement to make on the mini-lathe. This time, Im focusing on this:


    Yup, the tailstock. Ive known for a while that ive got issues with this, mainly that the centerline of the tailstock sits higher than the centerline of the headstock. Tends to make drilling a problem, and creates some interesting problems with a center. So, for this next part im going to get that fixed to get the tailstock quill perfectly in-line. First up is a lot of measurement, i want to get this exactly right and plan everything out bit by bit, so i need to know exactly what im working with. Lot of pictures, so im going to split this up into several posts to explain my process

  10. #140
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    First off, i want to check the alignment of the tailstock as-is. Cant fix something if you dont know what the problem is after all. First up, i want to check parallelism with the ways, to make sure that my drills are actually fed straight into the piece. To do this, im going to extend the quill (ram?) of the tailstock as far as it goes, lock the quill, lock the tailstock to the bed, then use a test indicator on the carriage to sweep the quill. Indicator is zeroed on the top of the far end of the quill:


    And then cranked to the rear of the quill:


    The rear of the quil dropped by .003" when compared to the front, so that axis is out a bit. Repeat with the side of the quill, to determine misalignment in the horizontal direction:



    Slightly better at .001" read misalignment. So, alignment with the ways is just a touch off, but not horrible. Next up is to check the alignment of the centerline

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