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  1. #1
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    Is it me or the lathe?

    For some dadgum reason...I can't for the life of me get this parting tool to work. I'm coming in from the side slightly above center. I've tried hi RPM's, low RPM's, dry, cutting oil...I just can't seem to make it work right. I either get chatter or the tool gets grabbed and pulled under the work and I have to start over. I've tried tightening the tool post, the cross slide...everything seems nice and rigid. I've tried going dead center, less angle, more angle, yada yada yada...

    I'm at my wits end...any tips on finning and parting?

  2. #2
    Randomhead
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    parting tools are a problem on a less rigid/powerful lathe. You didn't tell us what kind of parting tool you are using. I use a carbide tipped blade because I'm not smart enough to grind them myself.

  3. #3
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    Probably the lathe size and power as was mentioned

    I can't use them on my wimpy lathe either.

  4. #4
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    Ma lathe:

  5. #5
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    Basically ground a parting tool out of tool steel like the one on the second from far left

  6. #6
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    Those aren't mine...I Googled those.

  7. #7
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    I can part off 45mm diameter bar on my tiny Taig lathe. Use the slowest RPM you have and lots of continuos high feed. A rear mounted blade type tool works better on the larger stuff but a nornall parting tool will be ok up to 30 mm diameter bar

    Doug, what's this you say
    Probably the lathe size and power as was mentioned

    I can't use them on my wimpy lathe either.
    Attached Thumbnails Attached Thumbnails Is it me or the lathe?-parting.jpg  

    Is it me or the lathe?-partimg2.jpg  

    Last edited by yetibetty; 06-08-2010 at 07:14 PM.

  8. #8
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    I don't have much trouble with the parting tool on my lathe. The lathe isn't very large or powerful. Speed and feed is pretty important for parting. This isn't one of those operations where you'll get the best results by guessing. It's really worth looking up the SFM recommendation for the material in a machinist handbook. Use about 1/2 the SFM for parting as you would for normal machining operations. That also means you may need to vary the speed from start to finish of the operation to get the best results due to the dramatic diameter change from start to finish.

    To cut the fins on my lights reliably using CNC and a parting tool, I have to vary the spindle speed during the operations.

  9. #9
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    Quote Originally Posted by yetibetty
    I can part off 45mm diameter bar on my tiny Taig lathe. Use the slowest RPM you have and lots of continuos high feed. A rear mounted blade type tool works better on the larger stuff but a nornall parting tool will be ok up to 30 mm diameter bar
    his lathe may actually be less rigid than the Taig. Is that a single edged parting blade?

    Sounds like the rocker style toolpost is giving the OP problems. I've seen the machinist at work put some rake in his parting tools from side to side so it comes to a point.

    My lathe is really sloppy, but it has a reasonable amount of power. When I'm winging it, I set the parting blade a little high. If it's low there is always the chance that the workpiece will walk up over it towards the end.

  10. #10
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    Is that a single edged parting blade?
    Mine is a T section blade.

  11. #11
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  12. #12
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    For the smaller lathes keep the parting blade thickness 1mm max and make sure the tool is sharp. Best keep the tool dead center to start with and run he spindle speed 1/2 of your normal turning speed. I always ran a little below center. Keep the tool as close to the chuck as possible if possible. Always run from oil to improve the cut. Try to feed by hand an keep it quite fast to stop the chip from breaking off and the tool just rubbing on the surface. You will feel when it is correct.

    Once you start to get to know your lathe everything will fall into place
    Last edited by brad72; 06-09-2010 at 02:45 AM.

  13. #13
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    I have a big lathe and even when parting off aluminium you need to be careful. The biggest problem is that the side of the part will grab or bind into the parting off tool. Always take a few cuts to make sure the parting off tool is not doing its cutting on the sides. You'll waste an extra fraction of a mm of material but you won't run into problems.

    Even on the biggest machine just running a thin parting off tool into the job may cause it to grab, particularly if there is the slightest amount of play in the beds.

    If you're doing aluminium then you can use some methylated spirits (denatured alcohol to you guys?) as a cutting compound.

  14. #14
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    I have a Taig mini lathe and was running into the same problems until i got the parting tool that mounted on the backside - like the one in the picture above of the taig lathe. I also went from a ground parting tool that is like the pictures that the OP posted to one that was T shaped and about a mm thick. It really made a difference and I have no issues anymore.

    Seems that everything that has been posted is awesome advice so far and I have run into each on every item parting pieces (grabbing the sides, too fast, piece breaking off, work becomin gunchucked... squeeling, smoking, etc...)

  15. #15
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    Parting sucks. Can be hit or miss, and I always try to avoid it.



    Use slow rpm speeds, like it was steel you were cutting; increase rpm as you get closer to the middle.

    Hand feed the cross feed very gently and backoff with any chatter at all. Try to get a thin but continuous clip as well.

    Use no lube at all, or alum tapping fluid such as tap-magic.

    Use the correct tool angle for aluminum (if not flat) ...as steel relief angle is different and can gull up.

    Make sure the tool is VERY rigid, so no chatter is possible. Don't hang the tool way out either.

    Align the tool very slightly BELOW the rotational centerline.

    If all goes well, success....

  16. #16
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    If you are having trouble right at the end (the last few mm) you can finish the part using a hacksaw. You're going to need to machine the face anyway. Be careful though if you do this with the machine turning - keep your foot on the brake if you've got one.

  17. #17
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    I've made a couple of lights with the aluminum hex stock, I found parting it to be easier if you go slow, and use a lot of lube, tap-magic is good. I drip it in as I go. Even then, I have broken parting tools.

    I have also found that the thinner parting tools tend to work well, and they tended to work better when I ground them down so the cutting tip was the widest part of the tool.

    --Carl

  18. #18
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    I'm using a parting tool that I ground to 2.5mm thickness for finning. I could make the fins narrower, but I wanted them to be wide enough to let some decent airflow through. I could use a 1mm thick one and just go over it a couple times...dunno how well that would work.

    I found that the 1920's tool holder is just a tad flexy. I also found that the chuck allows my stock to flex just a tad. I'm thinking that the jaws are getting worn out.

    It cuts straight as a freakin' arrow, I can bore really easily with it. Parting has proven to be a dadgum chore though.

    I'm thinking that I should just cut it down with a hacksaw and use the parting tool to fin it with as short a piece as possible so it's as rigid as possible. I'm not ready to buy a new chuck or tool holder for it, so I'll just have to make do.


    Edit: I'm also not using a live center, so that allows the end to move around more than I'd like. Yeti's parting picture above looks like the "hot setup".

  19. #19
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    my life got a lot better when I moved to a BXA toolholder. I got a Phase II, which comes with a parting tool holder. Parting puts a lot of torque on the toolpost, the quick change toolposts are significantly better at resisting.

  20. #20
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    chelboed, have you checked for play in the headstock bearings. If it's possible with your lathe try pre-loading them a bit more.

  21. #21
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    I have...they seem very rigid.

    Can I even get a modern tool holder to fit this?

  22. #22
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    For a start your cutting tip should be bang on centre height and speeds should not change from regular cutting speeds.Use a high feed rate as well. If you can buy a cheap ebay carbide parting tool holder, tool steel parting tools tend to be arse especially hand ground ones if your not up to speed on grinding them up yourself. I've been machining for way too long and have never had a drama with parting alloy.

    Also after re-reading your post it sounds like there is a tool rigidity problem, at no time should a tool be able to be "pulled" under the work. Sounds like the tool post is a little too flexible or the tool is too flexible

  23. #23
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    Go the 1mm parting blade thickness and go over the groove a few times get the desired thickness. Then when you reach the desired depth on all the cuts run back and forth at the base of the groove to smooth her up.

    Also make sure that the parting blade is a bit narrower towards the base to stop the tool binding on the workpiece.

    For a bit of extra help on the correct tool angle etc check out this site http://www.mini-lathe.com/Mini_lathe...ng/parting.htm

    Like i said in an earlier post, once you have got your angles and height correct everything will fall into place.

  24. #24
    Randomhead
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    Quote Originally Posted by chelboed
    Can I even get a modern tool holder to fit this?
    of course, probably an AXA. They are held on by a t-nut just like your current toolholder

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