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  1. #1
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    Default Wringing cross slide?

    G'day all
    I've got a curious problem on my cross slide that I knew about early in my rebuild, but dismissed as just being dry dovetails...
    Here's the story - I pulled all the lathe apart, cleaned, degreased and stripped the paint off all the parts (in this case, think of the cross slide in particular). I'd put things back as I finished up to check wear, fit and a quick once-over as I was going. When I put the cross slide on the saddle, and aligned the dovetail (the one opposite the gib) there was a huge drag as I tried to push/pull it. No probs, I thought it's just because it was dry, so didn't really think much about it. Bear in mind, the only contact was the one dovetail (closest to the chuck)

    This morning, being half asleep, I put the slide on backwards and suddenly the drag disappeared. I realised the slide was on backwards, so turned it around the right way - and the drag was back...
    It dawned on me then that I might have wringing on those dovetail faces, the same as gauge blocks do.
    It was so pronounced, that I could get it wrung enough to be able to push the saddle the full length of the bed, just by pushing on the cross slide without breaking the bond. That's a 10kg static load!

    Ok, the question is - should I be worried about it? My thoughts are that if it wrings that much, there's probably no room for lube oil when I get all this back together. A possible fix I pondered was to DS tape some 240 W&D on one face and roughen the surface a little. I don't particularly want to machine it if possible.

    Any thoughts?

  2. #2
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    Aug 2019
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    Default

    I know very little about wringing precision flats together, but do know that anything between the surfaces stops the effect. Compressed air, water, thin oil, thick oil, grease, dirt, anything.


    Just try a thin film of oil and re-slide it around?



    P.S. Is the point or the foot of the dovetail on that side maybe digging in and binding?
    That might explain it only binding on one side

  3. #3
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    Default

    Thanks Nigel
    Yeah, I'm like you - I don't know much about wringing apart from that it exists. I don't usually play around with such precision which is probably why I put my problem down to oil impregnated cast iron pores being sticky.
    What I have also seems to be a common problem called 'stick-slip' on lathes. Usually when the bed ways have been honed and can grip a little, slip a little etc, etc. It seems the solution is properly oiled ways (which I do anyway) and with the correct oil (ooops... ). I figure after 80 years, the cast iron is about as honed as it could ever be!

    To answer your questions, yeah, oil does loosen it up but I was more concerned with the oil getting squeezed out again after a few passes. There's no oil ways to keep the oil in, which is why I was thinking of a little roughing with some W&D. The dovetails are OK... there's a tiny space right in the corner that I can get a bit of copper wire in, so I'm pretty sure that's not my problem (The space is smaller than the gib side, but it's still there). I didn't try water, but did try meths (The problems was less pronounce, but still there) and a sliver of paper in the dove tails (Completely gone). The theory holds up for your dust etc breaking the seal.

    An interesting phenomenon that's impossible to get pictures of, and something I wouldn't have dreamed could happen.

    (Edit: A quick video to show what I'm blathering about! )

  4. #4
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    Default

    Thanks for the video. I had never seen that effect on plain old castings!

    1) I note that the cross slide has a small oil hole near the back left top.
    Could easily scratch/grind a squiggly oilway inside the dovetail,
    so that some oil always wipes in along the whole surface?

    2) Roughing up a good surface seems wrong somehow.
    Wind slide all the way back every few months,
    squirt penetrating oil at the front,
    and wind back & fore a few times?

  5. #5
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    Default

    Thanks for the video. I had never seen that effect on plain old castings!
    No worries, and yeah... I was a bit surprised by it too. I think that's why it took so long for me to wake up to the fact of what it was! (you can see why I had trouble explaining it as well)

    1) I note that the cross slide has a small oil hole near the back left top.
    That's what I thought too when I first uncovered them (they were smothered in paint). They're actually 3/16" blind threaded holes for a cover plate over the cross slide bed.

    2) Roughing up a good surface seems wrong somehow.
    Agreed. That's why I was a bit hesitant on doing it. I actually want to try and leave everything as-is as much as possible because the condition overall is pretty good. Even the bed only has .002" wear in it.
    I'll give it some further thought, and maybe I can drill some extra oil holes in the casting (prefer not to, but it's another option I'm thinking about)

  6. #6
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    Default

    Sounds like it would be a good candidate for a light scraping to create some small depressions to retain the oil.

    Steve

  7. #7
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    I agree with Steve, but Just a warning, Do not take material off the fixed side of a cross slide, saddle or compound. If you need surface patterning to improve oil retention make sure you don't reduce the majority of the sliding surface. Taking material off the fixed surface has the effect of moving the drive nut mounting hole out of alignment with the feed screw. I realise this is not your issue but In cases of out of parallel dovetails, always work on the gib side.
    Mal

  8. #8
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    Mar 2017
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    Sydney
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    Default Could this be a scraping candidate

    I'm wondering if this would be solved by hand scrapping.

    See the video below by Stefan rebuilding a Schaublin 102 compound.



    He resorts to some hand scrapping on the dovetails.

    I just saw the suggestion from Steve but the video is instructive nonetheless. Good luck.
    Last edited by Boris Ludwig; 11th Nov 2019 at 11:37 AM. Reason: superfluous

  9. #9
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    Default

    Quote Originally Posted by Malibu View Post
    No worries, and yeah... I was a bit surprised by it too. I think that's why it took so long for me to wake up to the fact of what it was! (you can see why I had trouble explaining it as well)


    That's what I thought too when I first uncovered them (they were smothered in paint). They're actually 3/16" blind threaded holes for a cover plate over the cross slide bed.


    Agreed. That's why I was a bit hesitant on doing it. I actually want to try and leave everything as-is as much as possible because the condition overall is pretty good. Even the bed only has .002" wear in it.
    I'll give it some further thought, and maybe I can drill some extra oil holes in the casting (prefer not to, but it's another option I'm thinking about)
    Just curious, was the cross life difficult or tight to remove in your strip down video, if not would that not indicate that this wringing has been caused since your dismantling.
    I notice that your removal procedure was a little back to front, but the crosslide appeared to move without much effort.

  10. #10
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    Default

    See the video below by Stefan rebuilding a Schaublin 102 compound.
    Thanks Boris (that video seemed familiar to me, so I may have seen it before now)
    Stefan does some pretty good work and he's interesting to watch (along with This Old Tony as well, who is very entertaining). I understand the concept of scraping and I get the why/how it's done - it's my errrrr.... "skill level" that might let me down on the final verdict
    I'd thought about scraping and I've done plenty of wood scraping before now. Scraping cast iron dovetails scares me a bit, but I agree with you, it's really what it needs.

    Just curious, was the cross life difficult or tight to remove in your strip down video,
    Actually, it was a little difficult (that's why I slid the gib out), but because there was probably a little oil in the works, it may have appeared to be effortless. Because all the ways are now dry, it becomes more obvious.
    Just as a trial to satisfy my curiosity, I put a few drops of oil in as a 'bench test', it freed up a whole lot. Wiped the oil out and it was back again. Very weird, but it is what it is

    Mal; Good advice! Thanks!

    Ok, I better get back to it - I just got a 3 phase motor for a conversion

  11. #11
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    Quote Originally Posted by Malibu View Post
    Thanks Boris (that video seemed familiar to me, so I may have seen it before now)
    Stefan does some pretty good work and he's interesting to watch (along with This Old Tony as well, who is very entertaining). I understand the concept of scraping and I get the why/how it's done - it's my errrrr.... "skill level" that might let me down on the final verdict
    I'd thought about scraping and I've done plenty of wood scraping before now. Scraping cast iron dovetails scares me a bit, but I agree with you, it's really what it needs.


    Actually, it was a little difficult (that's why I slid the gib out), but because there was probably a little oil in the works, it may have appeared to be effortless. Because all the ways are now dry, it becomes more obvious.
    Just as a trial to satisfy my curiosity, I put a few drops of oil in as a 'bench test', it freed up a whole lot. Wiped the oil out and it was back again. Very weird, but it is what it is

    Mal; Good advice! Thanks!

    Ok, I better get back to it - I just got a 3 phase motor for a conversion
    So if you reassemble as it was with lube it would be reasonably good without scraping, by your comments it appears that oil was on this particular dovetail, must of been getting in an remaining.

  12. #12
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    Default

    So if you reassemble as it was with lube it would be reasonably good without scraping, by your comments it appears that oil was on this particular dovetail, must of been getting in an remaining.
    Well... yes(ish)
    I see your point and it makes perfect sense. If I reassemble as-is (and that's what I plan to do for now anyway), it won't be any worse off than what it was before.
    The slide in pre-rebuild times had oil in it, because a) I would oil it every time I used it and, b) there was a fairly large gap in the gib (re: a lot of wobble) so there was plenty of room for oil to remain, at least in the short term anyway.
    It's really only once I got it all stripped down and started to analyse things that the 'question mark' moment got into my head It's why I asked the original question... ie: should I be worried about it?

    Once it's all back together, I'll study the situation a bit more and see where it goes from there. I guess in the end, if it slides nicely, it's at least a good starting point.

    A good point though pipeclay, thanks

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