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  • PaulG
    replied
    Thanks to all for the help. It's embarrassing but the problem turned out to be a tool that was just a little high and on a 1/4 piece of course that can make a big difference in how it cuts. All my threads work great now.

    Thanks to all.

    Leave a comment:


  • Randy
    replied
    Yes, Derek, you can reverse the lathe to return to the start if, as Jim points out, you back the tool out for the return pass. In fact, that's the normal way when cutting metric threads on an inch based lathe. (Or conversely, cutting inch pitch threads with a metric leadscrew.) In this case you can't readily re-establish the relationship between the carriage and spindle if you open the half nut, so you simply keep it engaged and run in reverse to return.

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  • Jim Hubbell
    replied
    Lots of good tips above. I never heard of a " spit polish eather ". If you reverse spindle direction after the finish of a pass you must back out cross slide. Gearing backlash will crash the tool into the work if the tool is left in.

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  • Derek13
    replied
    Just a thought... i have almost no threading expierienc.e..

    but opposed to engageing/disengaging the half nut... could you simply reverse the lathe keeping everything still engaged? This assuming you have a 'shifting' type action lathe where you can forward/reverse it immediately.. never tried but just a thought.

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  • Randy
    replied
    And I've never heard of "spit polishing" the final passes. I'll have to try that. I think I'll make a tool grinding fixture like the one shown, too.

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  • Guest's Avatar
    Guest replied
    Thanks Kap, I didnt know about the final .001 move with the cross slide.

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  • kap pullen
    replied
    Here's something I did on threading a while ago.

    Maybe it will be of help.

    http://www.bluechipper.net/ThreadCutting.html

    Good luck!

    kap

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  • Guest's Avatar
    Guest replied
    Don't wish to muddy the waters further, but at 1/4" over any significant length, I'd be using the travelling steady.
    Rgds, Lin

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  • Michael Az
    replied
    So that we are clear on what I'm about to say- the compound is what the toolpost is attached to and the cross slide is what the compound is mounted to. You feed in with the cross slide, NOT the compound for removing most of the stock. After feeding(in small increments per pass) in to full depth with the cross slide, check the fit. If the nut won't go on or the ring gage doesn't fit, feed in a thou or so with the COMPOUND and then check fit again. Run a file over the threaded portion with the spindle turning after each pass to remove any burrs, stop the spindle, and check again. Repeat as necessary to obtain the proper thread O.D. and depth.
    ==============================================

    imakechips, yes, like somebody else mentioned, this is wrong. Lets not add more confusion. The cross slide should come back to a zero setting after every pass and then feed in with the compound.
    Michael

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  • jimmstruk
    replied
    Back to material growing larger afer cutting on it. Cold rolled is actually drawn thru a die and is under stress, then when the outer surface is cut on the metal can expand. How about the ,6061 maybe extruded and under tension? Guy Lautard had long discussion on this in one of his books.

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  • Randy
    replied
    <font face="Verdana, Arial" size="2">Originally posted by PaulG:

    My goofus lathe of course has the compound marked with 0 as parallel to the bed so it would need to be turned 60 from that position. But of course it's only marked to 40 degrees. So I had to use a protractor set to 30 and measure that from perpendicular to the bed. I suppose it could be a little off.

    </font>
    My lathe is marked the same way. (Well, it goes to 45*.) I put a secondary mark om the compound 45* away from the primary mark, so for threading I set the secondary mark at 15.5*. It sounds confusing, but it's really not. I just take a bird's eye view of the compound and swing it to where it looks about right and say, "Oh, I remember now. I need to be a bit off 15*." Thinking visually about what I'm trying to accomplish tells me which way to nudge it, and I wind up at 15.5*.



    [This message has been edited by Randy (edited 06-29-2005).]

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  • Shuswap Pat
    replied
    Threading takes practice. The tools must be sharp, and on center. Also the closer you can get to the optimum cutting speed, the better the finish will be. This has a direct correlation with your reaction time for engage/disengage the half nuts. Also 'Rapid Tap' or a 'chlorinated' ( and nn-healthy) cutting oil will give you optimum results.

    Pat

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  • Guest's Avatar
    Guest replied
    Hopefully, I have returned to a more level of discussion.

    The problems with what you call "drill rod" pops up in the UK too. We call it silver steel is anyone's guess. It can machine with difficulty and one suggestion is to use Shell Garia H which is a neat cutting oil. There is little merit in recommending something which cannot be found and the following or something similar would also be ideal for deep drilling
    BP CFS 35
    Castrol Ilocut 173
    Duckhams Sulfcut 300
    Esso Dortan 12
    Fina Vulcit X C 12

    I hope that something from this list will assist

    Norman

    Leave a comment:


  • SGW
    replied
    imakechips, I think you've got the use of the cross slide and compound reversed. My understanding is you want to feed with the compound, set at a 29 1/2 degree angle to the work, so nearly all the chip is taken on one side of the toolbit. If you feed with the cross slide, you're trying to cut a chip with both sides of the toolbit, which leads to chatter.

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  • imakechips
    replied
    So that we are clear on what I'm about to say- the compound is what the toolpost is attached to and the cross slide is what the compound is mounted to. You feed in with the cross slide, NOT the compound for removing most of the stock. After feeding(in small increments per pass) in to full depth with the cross slide, check the fit. If the nut won't go on or the ring gage doesn't fit, feed in a thou or so with the COMPOUND and then check fit again. Run a file over the threaded portion with the spindle turning after each pass to remove any burrs, stop the spindle, and check again. Repeat as necessary to obtain the proper thread O.D. and depth.

    You are turning the stock to .250 before attempting to cut those threads right? How long of a section are you trying to thread? Are you using a center in the tailstock to support the end of the part? If the section is very long, more than a couple of inches, it may just be pushing off, the same thing will happen if the outside end of the part isn't supported by a center.

    Also, even threads(10,12,16 tpi) can usually be cut by engaging the half nut at any line on the threading dial, odd threads(7, 11, 13 tpi) can only be cut on either odd or even numbers-once you start on a number, say 1 or 3, you must use either 1 or 3, not 2 or 4, otherwise the leadscrew will not pick up in the same place and will ruin your threads. There are exceptions to this- I ran a lathe recently(with an inch/metric quick change threading gearbox and inch/metric dials) that wouldn't pick up even threads on any number on the threading dial, only odd or even. I was cutting an even thread and started on 2, finished the pass, went back and engaged on 1, then it tore the first two or three threads off before I could disengage the half nut and back the tool out. I went back to the starting point and restarted on 4, leaving the tool just far enough back to avoid any cutting and engaged the half nut, let it run about half an inch and then turned off the lathe. The tool was back in the proper place as verified by me dialing in the cross slide to just touch the tool to the part. I really don't know why this happened, my only guess is that it was because the lathe was an import(pretty good lathe except for the threading problem), the brand of which I cannot remember.

    Anyway, I hope some of this is helpful. I sure made a few mistakes when I was learning, though nothing quite like you are describing. Good luck!

    Leave a comment:

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