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Thread: What did you machine today?

  1. #1501
    Join Date
    Mar 2005
    Location
    Toronto
    Posts
    11,074

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    Quote Originally Posted by Cenedd View Post
    Why would it not work to turn that between centres?
    haven't turned anything that large, but chatter would be an issue. Proportionally that's like 1" dia x 18".
    .

  2. #1502

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    Quote Originally Posted by Cenedd View Post
    Very nice looking work. Wasn't aware of a cat's head steady before...but have now looked it up. Why would it not work to turn that between centres? Would it sag in the middle enough to throw out your required tolerances or is it more of an issue once you get the eccentric cams throwing off the balance? I'm not likely to need (or be able!) to turn something that large, I'm just interested for the theory.
    You could turn the major diameter between centers but it would be slow going in order to avoid chatter or the use of a follow rest is required. A majority of the offset portion simply holds the ends together and has a fractional tolerance so does not actually require turning however after the lathe work is complete they have key ways milled on the ends that are indexed to the cam, this is what the bolt on saddles are for. Turning most of the large diameter makes an accurate surface for the saddles to clamp on to, the mill finish on HR bars is very inconsistent as you can imagine. The stock weighs 500 Lbs.

    The cats head and steady allow much higher spindle speeds therefore improved surface finishes and lower spindle times. 500 Lb part in a 15,000 Lb machine, they do not shake this lathe at 250 RPM's.
    5" Dia at 250 Rpm's is a respectable 327 FPM cutting speed.

    As for the cat heads we simply make them as needed.

    Copper electrical conductor faced and bored on each end, I use strips of steel banding or aluminum drops under the set screws so that they do not mar the part surface.

  3. #1503

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    Quote Originally Posted by Mcgyver View Post
    haven't turned anything that large, but chatter would be an issue. Proportionally that's like 1" dia x 18".
    Correct, chatter is the major concern.
    I often turn large diameter yet very thin parts, facing can become a chatter festival if they are not held securely like so.

    Aluminum face plate drilled to bolt to a face plate mounted on the spindle, it swings through the gap.


    Bolted to lathe face plate and faced flat.


    Bolt part to plate and turn part.


    It helps if a threaded hole is drilled and tapped on the OD for a lifting eye making it much easier to handle.

  4. #1504
    Join Date
    Dec 2008
    Location
    Kendal, On
    Posts
    1,720

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    This is about as large as I get....

    It goes with these

    To make this

    Which goes on this


    Which goes with a bunch more stuff I'm still working on, and designing as I go with what I have. Boss didn't want to order any material for this job, so it's scrapbin engineering at it's finest......

  5. #1505
    Join Date
    Nov 2017
    Location
    Watford, UK
    Posts
    612

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    Very interesting. Thanks for the info guys. Definitely a different ballgame when it gets to stuff that size - interesting how it makes some issues less of a problem and some more. For example, the issues I've had with chatter have usually been lack of rigidity in the rest of the machine rather than in the part and a brief foray into eccentric turning (of 2" Delrin as it happens) showed that it was very easy to start rocking the machine if I dialed the speed up to anywhere near what it 'should' have been.

  6. #1506
    Join Date
    Jan 2014
    Location
    Edmonton Alberta
    Posts
    1,561

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    Quote Originally Posted by Bented View Post
    Correct, chatter is the major concern.
    I often turn large diameter yet very thin parts, facing can become a chatter festival if they are not held securely like so.

    Aluminum face plate drilled to bolt to a face plate mounted on the spindle, it swings through the gap.


    Bolted to lathe face plate and faced flat.


    Bolt part to plate and turn part.


    It helps if a threaded hole is drilled and tapped on the OD for a lifting eye making it much easier to handle.
    Is that Aluminium For a Disc Grinder/Sander,nice work!

  7. #1507
    Join Date
    Oct 2012
    Location
    San Antonio TX, USA
    Posts
    2,713

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    Quote Originally Posted by Bob Engelhardt View Post
    I like it - it's a KISS
    a big thanks for the tip Bob, worked like a charm! No motor bounce and next to no vibration from the motor now. I'm pleased as punch

    In the low speed setting, forgot to take a picture in the higher speed sheave


    this shows how the other bolt is clear of the motor plate in the other position


    checked the speed ranges in the middle range of the spindle pulley:
    250-1500rpm low
    450-2600rpm high

    both in direct drive. Nice to have options, even nicer to get rid of the flywheel and not have any motor vibrations!

  8. #1508
    Join Date
    Jan 2017
    Posts
    388

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    Quote Originally Posted by mattthemuppet View Post
    ...
    this shows how the other bolt is clear of the motor plate in the other position

    ...
    Nice work. Simple & effective - can't ask for more than that. I'm glad that I could give some useful advice.

    How well does the poly-V belt work? You satisfied with it?

  9. #1509
    Join Date
    Oct 2012
    Location
    San Antonio TX, USA
    Posts
    2,713

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    Thanks Bob, I appreciate the help! I like poly v belts a great deal - they never slip, don't vibrate and don't seem as susceptible to oil as normal v belts. Next big project is replacing the spindle pulley with a poly v one

  10. #1510

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    Quote Originally Posted by Tundra Twin Track View Post
    Is that Aluminium For a Disc Grinder/Sander,nice work!
    Lathe face plate for a large part, the third picture is turning the part which is 304 SS.
    Set up and machining on such a part is easily 16 hours or more, a 30" diameter part is running nearly 400 FPM at 50 Rpms. If facing to zero from 30" at say ,006" per revolution at 50 Rpm's that is .006" X 50 Rpm's or .300" per minute, 15" of facing is 15" \.300" per minute is 50 minutes per pass.
    This machine does not support CSS which every lathe should have.
    This part finishes at .500" and is waterjet cut from 5/8 sheet, it takes 6-8 facing passes to get it to size without chatter, that is 6-8 hours right there.


    Also one of the problems with a gap bed lathe with the gap removed is getting the tools close to the part without the carriage falling off of the ways into the gap, do not do this.
    This lathe has an 18" wide gap, I have to face these parts with a 2 1/2" diameter boring bar hanging 8" out of the holder held upside down and the spindle in reverse just to span the gap, this is unpleasant at best as you may imagine.

    Also rotate the tool post 180 degrees and place the holder on the outside when the part is well larger then the ways.
    Last edited by Bented; 07-15-2019 at 10:51 PM.

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