Results 1 to 12 of 12
  1. #1
    Join Date
    Aug 2019
    Location
    Revesby - Sydney Australia
    Age
    54
    Posts
    523

    Default Compound slide improvements?

    I have never been happy with the surface finish from my Hercus 9C.
    It is OK on parallel turning Aluminium, but steel varies a lot.
    As does facing off. Parting off is a crap shoot.



    Ignoring the obvious, and hard to fix things for now
    (badly worn bed Vs, cross slide dovetails and feed screw/nut),
    I thought I would try to stabilise the tool post.


    My compound slide casting is sad.
    Missing a lot of casting, from years of school student abuse.
    Which means there is a lot less surface for tool post to sit on/clamp onto.

    In a perfect world, I would machine up a new one from a nice block of 4140 steel,
    but who has the material, time, or motivation for that?

    Time for some surface grinding. The frst thou removed showed a lot of wear in the middle, and on the mangled chuck side:
    IMG_2216.jpg

    Roughly another 5 thou off:
    IMG_2223.jpg
    and it's starting to get there.

    That is all I dared to remove, because the T slot is modest, maybe 1/4" or 7/32" at the thin step?




    So, I'll mount it back, and try some test cuts in steel, to see if there is any improvement.


    Probably not, which means the next step would be to replace the compound with a solid block.

  2. #2
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    56
    Posts
    5,977

    Default

    You would be better off replacing it with a cast cross slide if replacement is the way you are going. Steel will 'ring' whereas cast will not so much. Unless you are using known steel that turns well, judging your lathe rigidity by surface finish is a bit dicey. The first thing I look at when I have poor surface finish is my tool grind/ tip.

    My 2c worth

    Michael

  3. #3
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    2,932

    Default

    Quote Originally Posted by Michael G View Post
    You would be better off replacing it with a cast cross slide if replacement is the way you are going.
    I think Nigel is better off replacing the compound with a solid block of steel as he suggested. The increase in rigidity is significant. Of course, the compound is still needed when angled cuts are required, so improvements there are still worth persuing.

    If you don't have a slotted cross slide omit the cap crews.
    Attached Images Attached Images
    Chris

  4. #4
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    56
    Posts
    5,977

    Default

    Quote Originally Posted by nigelpearson View Post
    My compound slide casting is sad.
    Missing a lot of casting, from years of school student abuse.
    Which means there is a lot less surface for tool post to sit on/clamp onto.

    In a perfect world, I would machine up a new one from a nice block of 4140 steel
    I was responding to this bit.

    Michael

  5. #5
    Join Date
    Aug 2019
    Location
    Revesby - Sydney Australia
    Age
    54
    Posts
    523

    Default

    Quote Originally Posted by Michael G View Post
    You would be better off replacing it with a cast cross slide if replacement is the way you are going

    It doesn't look like Mal has Hercus 9 compound parts, only Hercus 260,
    and that would be many hundred dollars.


    • Steel does ring. The experts say that either machining complex shapes (think webs, asymmetrical cavities), or attaching dampening (lead shot? granite epoxy mix), makes it similar to cast iron.
    For shapes like the simple compound cross slide castings, not really an option. The thing has to be functional


    • Steel theoretically dampens less than cast iron. If I'm reading this correctly:
    Mechanical Properties of Gray Iron - Damping Capacity
    Steel is between 20% and 400% worse than ductile iron.
    (and Aluminium between 1000% and 4900% worse!)
    Not sure what Hercus castings from the 1960s would be


    • The larger the chunk of metal, the lower the resonant frequency (er, frequencies).
    So, a steel compound that was 6" wide, instead of the 3" wide original, might be much better?




    Anyway, jack620's suggestion might be my next step. I only have the standard cross slide, so its contact area is about 4" diameter. This was my design from a few months ago:
    Hercus compound removal.jpg

    However, I have some large cast iron slugs, that someone scrounged from the railways. Maybe 5" diameter, and 4" tall. That would be more solid - just machine a groove in the bottom, to clamp in with the two Hercus set screws, and a large thread in the top for a large cap head/socket screw.


    But, before I jump in, some strategic dial indicators, and levering of the tool post is probably in order, because I'm not 100% sure the issue is in the compound slide. It might be the cross slide, or the carriage Vs, or the carriage gib up the back.

  6. #6
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    2,932

    Default

    Quote Originally Posted by nigelpearson View Post
    because I'm not 100% sure the issue is in the compound slide. It might be the cross slide, or the carriage Vs, or the carriage gib up the back.
    On a light lathe like a 9/260, I reckon it’s all of the above. But the compound will be the weakest link.

    I have no data to back this up, but I reckon the improvement in rigidity gained from removing the compound from the equation dwarfs any difference likely to be found between cast iron and steel. But since you have cast iron slugs I reckon you should make your solid toolpost block from that.
    Chris

  7. #7
    Join Date
    Aug 2019
    Location
    Revesby - Sydney Australia
    Age
    54
    Posts
    523

    Default Materials science, ringing, resonance, vibration damping

    ...In a perfect world, I would machine up a new one from a nice block of 4140 steel...

    Quote Originally Posted by Michael G View Post
    Steel will 'ring' whereas cast will not so much

    Diagnostic question: Do we think a tensile steel (like 4140) would "ring" more than mild steel?


    My gut feeling is yes, but that is from playing with tensile shapes (like bolts).

    I'm also wondering about the stress in a material - either machined or cast.
    If it was normalised, or shot with little ball bearings,
    would that cause less ringing?


    I'm not a materials guy, and can't think how to search for that aspect

  8. #8
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    5,036

    Default

    Hi Nigel, Guys,

    I don't think that the ringing phenomena is worth worrying about for what you are doing !
    Now in a boring bar that would be quite a different issue.
    Best Regards:
    Baron J.

  9. #9
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    56
    Posts
    5,977

    Default

    Quote Originally Posted by nigelpearson View Post
    ...In a perfect world, I would machine up a new one from a nice block of 4140 steel...

    Diagnostic question: Do we think a tensile steel (like 4140) would "ring" more than mild steel?
    Probably not. I can make a gear out of steel (any kind) that will ring like a bell. Out of CI and all I get is dull thunk when I hit it. All steel has the same Young's modulus, so has the same springiness. I think where CI really gets it's advantage from is the carbon in it's matrix which dampens the vibrations shuttling around inside the material. Shot peening etc will only affect the surface and the compressive stresses it generates are unlikely to increase dampening greatly.

    As per John's thoughts, ringing is unlikely to have a great effect on things, especially when lined up against rigidity and tool geometry/ grind but even expensive machine tools are still made of CI so there must be some benefit.

    Michael

  10. #10
    Join Date
    Sep 2009
    Location
    Newcastle
    Posts
    260

    Default

    Ringing (resonance / vibration) does affect surface finish.

    Static stiffness and dynamic stiffness are both important.

  11. #11
    Join Date
    Nov 2007
    Location
    melbourne australia
    Posts
    2,932

    Default

    Quote Originally Posted by BaronJ View Post
    I don't think that the ringing phenomena is worth worrying about for what you are doing !
    Amen to that!
    Chris

  12. #12
    Join Date
    Jun 2007
    Location
    sydney ( st marys )
    Age
    62
    Posts
    4,725

    Default

    The 260 casting is around $130, knock the top off a bit if desired, you can still use it as is if wanted on your 9".
    Another alternative would be to get a piece of suitable size cast round and make your own.

Similar Threads

  1. Sheraton cross slide and compound slide spindle threads
    By ajbvicau in forum SHERATON AREA
    Replies: 5
    Last Post: 20th Jul 2021, 10:43 PM
  2. Setting the compound slide.
    By th62 in forum METALWORK GENERAL
    Replies: 9
    Last Post: 2nd Sep 2014, 09:52 PM
  3. Compound Slide
    By bwal74 in forum THE HERCUS AREA
    Replies: 7
    Last Post: 10th Apr 2014, 12:20 PM
  4. How does the small compound slide come apart?
    By Com_VC in forum THE HERCUS AREA
    Replies: 5
    Last Post: 1st May 2011, 01:21 AM
  5. Compound slide problems.
    By wm460 in forum METALWORK GENERAL
    Replies: 3
    Last Post: 27th Jan 2010, 08:34 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •