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Thread: Lathe Parting Tool Spring Type Tool Holder For QCTP

  1. #11
    jjr2001's Avatar
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    Thanks for your comments on the tool Toolmaker51. I never thought about stress at that point
    but now that you mentioned it I can see how it is really moving a lot to absorb the energy
    from the cutting forces and now I see that the roll pin has two functions.

    Cheers JR

  2. #12

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    Hi JJR2001!

    This looks like a nifty solution to parting tool chatter and suddenly digging in. Will your design with the dimensions on your plans work on an AXA100 Size QCTP mounted a Grizzly G0752 10 x 22 lathe? I tried their provided parting tool holder last night, very carefully adjusting the 1/8 wide x 1/2" cutoff blade I got for it, trying dead on center, and both just slightly above or below center. I was using a 3/4" dia. length of 12L14 steel, parting about 3/4" away from the chuck jaws. Running at between 90 and 150 rpm. With cutting oil. I kept having a problem of it suddenly hogging into the piece, even though I was barely feeding in. Chipped the cutter once, so I had to re-grind the end. Also tripped the shutdown on the variable speed drive when it dove in a few times. I've parted things off on my older 7x10 mini lathe successfully, so this is frustrating. I thought maybe your tool might provide a solution. I've got the cross slide gib nice and snug, and even tried tightening the compound gib very snug making it hard to turn the handle, but it is still shocking and a bit scary how much things move when it grabs like that.

    I began to wonder about maybe using a rocker tool post for parting, just to get the load centered better on the compound slide. But I'd rather stick with the AXA if I can.

  3. #13
    jjr2001's Avatar
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    Hi muncher. I think the tool will work fine on most home shop lathes. If your tool post can fit a 1/2" lathe tool bit then it should work fine.
    In addition to the tool which I find invaluable I always lock down my carraige and snug up the cross slide and compound gibs. Works for me when the
    standard parting tool holder just chatters and jumps all over the place.


    There is another way to try to reduce or eliminate chatter when cutting off. I have seen it demonstrated on YouTube. You use a rear mounted tool post
    and invert the cutoff tool so that the cutting edge is down instead of in the normal up position. Lathe is still run in the normal direction. The cutoff tool will
    now be less likely to bite into the work piece. On my list of things to try one of these days.

    Best of luck with your cutoffs, JR

  4. #14

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    I have seen the rear mounted parting tools, and am very interested in them. The more rigid the parting tool, the better it works, in my opinion. I actually found your thread, and this forum, googling for a rear mounted parting tool.

    I was finally able to successfully part off some nylon, then aluminum last night by utilizing the same parting blade I had devised, out of desperation over these same issues, on my 7x10 mini-lathe before. It is a thin 1/2" tall blade, with the typical angled end for relief below the cut, but the top edge is ground with a "bowl" shaped relief cut of maybe 0.040" deep, just behind the cutting edge. Not sure what the radius would be, as I eyeballed it on the grinder. It sort of resembles a cut away cross section of a teaspoon, but much smaller, covering maybe 1/2" or less across the top edge toward the tail of the cutter. Or resembling the profile of one of those nice aluminum ice cream paddle scoops (where I got the idea, actually). I've recently seen a similar profile being shown in some forum threads and articles. But..... it still jammed and failed miserably on that same 12L14 steel round I mentioned before. It starts to cut OK, then suddenly digs deep and in this last attempt, snapped off the lower corner of the blade.

    Have you worked with 12L14 (also called leaded steel)? It is very easy to machine as a rule. I don't know why it won't work with my parting tool.

  5. #15
    C-Bag's Avatar
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    I've had a helluva time with parting off with my 9x20. Somewhere, I think here on HMT, the tip of making a little side relief on both sides of blade was brought up. So I did that on my thicker blade and have been able to part off my steel projects. Something I'd not been able to achieve before that. Sorry, don't know what steel flavor it was.

  6. #16
    mklotz mklotz's Avatar
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    Yes, side relief on the tool is important. Also, rigidity is essential. Lock the lathe carriage down firmly while parting.

    A continuous supply of sulfurated cutting oil while parting can be very helpful with steel. I made a gravity-fed oiler...

    Parting-off oiler

    from plumbing parts that keeps dripping oil directly into the cut while parting. Very effective and not hard to make.

    Use kerosene, not oil, when parting aluminum and use nothing when parting brass.
    ---
    Regards, Marv


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    Toolmaker51 (07-10-2017)

  8. #17

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    Thanks for the tips! I'm gonna check out that drip oiler. I'm not set up for flood cooling, so I repeatedly add small amounts of coolant as I work. Having an adjustable tool to do that would be a blessing.

    I really don't like smelly coolants, as my shop is in our attached garage, plus there is always the issue of getting it on clothing. Although I have the sulphated one, and access to kerosene, I currently use a very low odor coolant called Reli-On. It works equally well on pretty much all the materials I work with that need coolant. However, I do admit that ferrous materials are not my first choice most of the time. I work with aluminum, brass, nylon, and UHMW Polyethelene (the latter mostly because it is very cheap, machines very well, and is non-absorbent) whenever I can. But I will use steel when it is needed.

    I really don't like cast iron. I just finished the custom back plate for the 8" 3 jaw scroll chuck I added to my 10x22 lathe. It turned out very well, but that was the dirtiest, nastiest stuff I ever machined. I used Re-Lion and a shop vac dust collector to eliminate airborn particles, but it sure is messy cleanup. Like machining graphite, I imagine. I couldn't get a pre-machined backplate, as Grizzly uses a 1 3/4 - 8 thread on its spindle, and all the pre-machined plates I found used a different size. So I uad to machine a threaded blank.

    Sorry if I got a bit off topic here.

    Still looking into what I want to try for a different parting tool. One I could mount optionally on the top surface of the cross slide, forgoing the compound, would take half the flex problem out of the equation. Perhaps this spring model of yours, but made to mount flat onto the cross slide top.

  9. #18
    mklotz mklotz's Avatar
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    Cast iron is normally machined dry because it's self-lubricating - one of the reasons it's so often used for metal-on-metal sliding parts.

    When turning it, lay some oil-soaked shop towels on the ways. They will trap the dust. Discard safely when done.

    A "Gibralter" tool block to replace the compound has been suggested in at least one of the older magazines. It seems counter-productive though to have to remove the compound and tool holder and mount Gibralter to cut-off, then remount everything. I suppose a carriage-mounted Gibralter size base for interchangeable tool blocks is a possibility but you still lose the angular capability of the compound.

    Remember, just because you CAN part off with a lathe doesn't mean you MUST part-off. This is especially true if you have the ubiquitous horizontal bandsaw. Cut a starting groove on the lathe as a blade guide for the saw and let the saw do the work.
    ---
    Regards, Marv


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    Toolmaker51 (07-10-2017)

  11. #19
    [email protected] tonyfoale's Avatar
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    I made something like this a while back, the only essential difference being that instead of the bolted on block to clamp in a standard tool holder I cut dovetails and fit it direct to the QC main block.

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    Toolmaker51 (07-10-2017)

  13. #20
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    Quote Originally Posted by tonyfoale View Post
    I made something like this a while back, the only essential difference being that instead of the bolted on block to clamp in a standard tool holder I cut dovetails and fit it direct to the QC main block.
    I emphasized Tony's comment.
    Cut-off can be iffy on ANY lathe, for a host of reasons. Usually, operators logically point to clearance, cutting fluids, speeds and feeds; and each is correct.
    #1 But in my book, all depend on rigidity first and foremost. None of those conditions reach acceptable percentage without it.
    #2 Stepped blades must remain so, as with tapered blades. The radius tempts alteration too, yet not so easily reproduced. In a proper setup it rolls and narrows the chip in most materials other than cast. That simultaneously relieves pressure on blade, admits coolant to cutting edge, and helps eject the chip. It also helps to listen. Any sound other than cutting, indicates something amiss. Like the squeak of a dull endmill or drill, the feel of a loaded tap, or motor loading up, often precede the distinct dull tone of $$$=Oops.

    Tony eliminates 1, perhaps 2 losses of rigidity by eliminating the adapter and tool holder, by mounting to QC block directly. It worsens if the connections aren't hardened - to accept and transmit deflection and near impossible zero clearance in QC block and holder.

    Marv also points out an imperative. Cover the ways and wipers! Oil soaked towels at a minimum. To me, they are a little coarse oiled or not. I use newsprint, oiled so it sticks in place, or plastic food wrap with water based coolants. Cost of either is practically nothing.
    Last edited by Toolmaker51; 07-10-2017 at 02:19 PM.
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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