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  1. #1
    Join Date
    Apr 2019
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    Default Advice Needed: Lathe Machining Order for Large Gear

    I am about to start making the new backgear set for my Erikson lathe. The largest is around 225mm in diameter and 17mm thick and I will be taking it out of a piece of ductile iron that is 250mm x 100mm.

    Having a hard time deciding how to do this. My initial thought was to chuck up the whole blank, drill a centre and support with the tailstock, drill/bore the required centre hole, machine the OD then part off. I could then continue to make 2 other smaller gears before removing the stock.

    Parting and me are not friends at the moment - I have broken multiple carbide parting tips. Not sure that parting through 250mm is a great idea? I doubt my parting blade will even reach in enough.

    The other option would be to use the power hacksaw to cut off a 20mm slice of stock then mount the slice in the lathe. Not much meat to hold onto. I could drill/bore the centre hole then mount on an arbour to cut the OD and face to the required depth.

    How would you handle this project??

  2. #2
    Join Date
    Aug 2011
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    Melbourne
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    Default

    Hi there,

    Parting off a piece that big would not be a fun exercise. Im sure it can be done by people with better skills than me though. If you have a bandsaw with the cutting capacity I would look into that.

    I have never worked with ductile iron, can you easily weld it? If so then weld some kind of support to it to allow better work holding in the band saw clamp. Go from there.

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  3. #3
    Join Date
    Jul 2016
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    Melbourne
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    35
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    Default

    I would probably do as you said at first, hold onto the whole chunk but instead of parting off id then put it in the bandsaw, slice it off and face the last side.

    Sent from my SM-G973F using Tapatalk

  4. #4
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    1,536

    Default

    ^
    #metoo

  5. #5
    Join Date
    Apr 2012
    Location
    Healesville
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    2,129

    Default

    If this is your lathe Eriksen "Emato" 180-NE, 200-NE & 50/200Rv Lathes with a bit of patience and care it should be able to part to
    a decent depth, depends on the parting blade but 100mm should be achievable, then finish in the saw.
    What size L x H x w blade do you have?
    Maybe first you need to fix the parting problem, the tool holder needs to sit dead flat on the topslide and the topslide also needs to sit dead flat on the cross slide, check them with brg blue, they might have the odd high spot.
    Lack of rigidity is nearly always the cause of parting problems.
    If/when they are ok lock your top slide and make sure your cross slide gib is just very slightly firm, with that diameter start at 30 rpm or so and see how it goes, increase speed gradually as you get in deeper.

    You would start with your parting tool only hanging out maybe an inch and then move it out progressively as you get deeper in....
    Last edited by shedhappens; 13th Nov 2020 at 05:49 PM. Reason: more

  6. #6
    Join Date
    Oct 2011
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    Norwood-ish, Adelaide
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    Default

    Quote Originally Posted by Mk1_Oz View Post
    ...The other option would be to use the power hacksaw to cut off a 20mm slice of stock then mount the slice in the lathe... drill/bore the centre hole then mount on an arbour to cut the OD and face to the required depth.
    Yes
    Michael

  7. #7
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    6,444

    Default

    Hi Guys,



    I personally would not attempt to part off something 250 mm diameter, whilst it can be done, I've seen similar work, people try to part off at too high a speed.

    I would go for the bandsaw and clean up the faces afterwards.
    Best Regards:
    Baron J.

  8. #8
    Join Date
    Aug 2008
    Location
    Melbourne
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    34
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    1,075

    Default

    Bandsaw, face, bore, flip, other face, OD off an arbor. The other option is to do half the OD with each facing operation but that only gives you about 7mm to hold onto.

  9. #9
    Join Date
    Jun 2007
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    sydney ( st marys )
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    Default

    Cut it into biscuits.

    If the saw cuts reasonably square give your self a few mm on the length.

    Make a mandrel first that you can use for all the gears, bore does not need to be to finished ID, secure gear blank by either bolt or nut on the mandrel.

    Wouldn't matter if you use a 3 or 4 jaw chuck for holding.

    Hold only enough of your blank so that you can face and turn OD up to the chuck jaws, for what your doing around 6 to 8 mm clamping will be fine, ( do not finish the OD at this stage ).

    Turn blank around grab the machined OD, place the faced side against the jaw or packers to hold the job square, Doesn't matter if the OD of the blank is not running totally true as the OD will be finished when mounted on the mandrel, face to width and bore/ ream to suit mandrel.( put a 1.5 x 45 degree chamfer on the OD of the blanks ).

    Repeat for your other gear blanks.

    If the mandrel is solid enough you probably won't need to support the end when cutting the teeth, if it needs support then you will need to make sure you have a centre in the mandrel.

    When cutting the teeth cut in one pass at full depth.

  10. #10
    Join Date
    Feb 2013
    Location
    Laidley, SE Qld
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    Default

    I'm with the 'bandsaw a slice and mount it on a mandrel' crowd.

  11. #11
    Join Date
    Apr 2019
    Location
    Adelaide
    Posts
    589

    Default

    Thanks all. A couple of different thoughts to consider.

    I am modifying the power hacksaw with new seals so hopefully it will start to cut square. Have not even thought about how to hold a250mm round whilst sawing!

  12. #12
    Join Date
    Oct 2011
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    Norwood-ish, Adelaide
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    You want something like this -
    P1020375 (Medium).JPG
    Basically an angle plate that you can clamp the blank to. Once the cut is halfway down then you need to wedge something in the cut so that the blade is not pinched towards the end of the cut.

    Michael

  13. #13
    Join Date
    Apr 2019
    Location
    Adelaide
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    Default

    Well, went to mount the 260mm slug in the power hacksaw and nooooo chance. The blade does not lift enough and the vise does not open enough. Grrrrr

    The large gear will have a 39mm centre hole and 226mm OD so I would be parting off through 94mm. My parting off blade will not be long enough to do that.

    I see 2 options, delay the project and find somebody to slice off a few bits in a bandsaw or part off as far as I can then use a hacksaw while the lathe turns. Sounds iffy though?

  14. #14
    Join Date
    Aug 2011
    Location
    Melbourne
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    If you're very careful, a thin cut off blade on a 230mm angle grinder could cut the required piece off. If you scribe a line all the way around, you should be able to get it done with less than 5mm of material loss after facing true.

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  15. #15
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    Quote Originally Posted by Mk1_Oz View Post
    ... find somebody to slice off a few bits in a bandsaw...
    You would need a pretty large bandsaw. Simon's Heska might be able to do it but the majority of us here run 4x6 saws and that won't fit.

    Perhaps buy some slices of stuff from Surman metals. It will cost, but you can then get on with the job. They might be able to cut what you have but there is not a lot to hang onto there.

    Michael

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