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Thread: Threading issue

  1. #21
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    What's it look like when you clean all that crap off?
    What's the major dia turned to? It looks like you have a sharp crest.
    I have an old 3M gray fiber wheel that I sawed a wedge out of that I like to run over the finished thread by hand. It does a nice job of getting the little furry bits off.

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    Quote Originally Posted by Ratz View Post
    This is my latest trial. Still crappy. Material is sticking out 1.25". Using TPMC carbide 180RPM. This is a second try without chamfered start on this piece of alloy. It was late last night and I forgot.

    Come to think of it this is my first fine thread. Course threads always came up nicely in stainless.

    Attachment 264944
    It appears like you are not engaging the half nut on the same number for every pass.

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    Yea, it looks like possible thread splitting there ^.

    If carbide then 1200RPMish and HSS 350RPMish would be the correct recipe & the thread relief helps.

    HINT! Dry run 6-8 or whatever times you need to prove you can time yourself correctly. At high RPM's with chucked parts I'll have the saddle 2 or more inches back from the thread start.

    You'd be surprised how quickly you get consistent.

    Good luck
    Matt

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    Since you gave some dimensions in mm, is there a chance the thread is metric, and you are cutting with an inch-based leadscrew, and using the thread dial? The tool won't track properly.

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    Or a metric leadscrew, but wrong gear in the thread dial

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    There is something wrong, could be a loose spindle bearing. I often use the same cutting tools, with the machines I normally use. I would find it hard to intentionally make a thread look that bad.

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    Agree with the last several posts. Looking at the picture in post #19 it seems clear the issue is it's double-cutting the thread with the engagement just a little off each pass.

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  9. #28
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    Double starts (double cutting) would not explain all that junk in the photo.

    1. I see no sign of any cutting fluid being used. USE SOMETHING. Don't cut threads dry unless the alloy is leaded. I like TapMagic for threading, but others will also work.

    2. I am not sure about the kind of insert you are using (HSS or TC). But anything but a totally sharp cutting edge will produce problems when threading. I recommend HSS and, even if it is brand new, check it under a 10X or stronger magnifier and if you can see any rounding of the cutting edge. If necessary, touch it up on a fine stone until it is dead sharp. I do not like carbide inserts for threading because most of then have a slightly rounded cutting edge. I think this is a deliberate "feature" to prevent cracks and chips from developing in the hard TC, but you will be fighting it while threading.

    3. Are you feed straight in or at a 29.5 degree angle. Most inserts will have only ONE cutting edge and are therefore intended for use with the 29.5 degree in feed. By feeding them straight in, you will be using two edges to cut and the second one may not be as sharp or have the proper rake angle.

    I do recommend the correct cutting speed, but I do not think it is as important of a factor as the sharpness of the tool and the use of a good cutting fluid are. With sharp tools and a good cutting fluid I have often used a manual crank to cut threads up to a shoulder. These threads were cut at a very slow cutting speed but they were virtually perfect.

    DEAD SHARP tool and good cutting fluid are absolutely necessary.

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    Quote Originally Posted by Joe Gwinn View Post


    Don't try this if your lathe has a threaded spindle. Having a spinning chuck unscrew itself and chase you around the shop is far too exciting for one's health.
    True. But it's highly entertaining if it's chasing somebody else.

    Also, I agree with John though I'm partial to lots of oil. Bacon grease works well and smells like breakfast.

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    Quote Originally Posted by HuFlungDung View Post
    Since you gave some dimensions in mm, is there a chance the thread is metric, and you are cutting with an inch-based leadscrew, and using the thread dial? The tool won't track properly.
    Thanks everybody for your support. Best answer is from “donie” as I am in full agreement.

    Just to touch on some replies, Oil is removed before photo for clearer picture. I am using TPMC and TNMC both in HSS and Carbide inserts. Tried all 4 of them with pretty well same disappointing results.

    I should have give everyone more information. Final thread is to be 14mm x 1.0.
    So to practice, I was threading 1.0mm per thread or 1.0mm per revolution. End just calling it loosely fine thread. After checking all the settings, I looked at the gears and decided to change the gears to 12 TPI NC.
    Result was good and I stopped blaming the metal. See picture.

    Then it dawn on me as I looked at “HuFlungDung” and “Blackrainstorm” post, that in all the years I never used this lathe to thread metric.
    So I think we are on something here. All I assumed was, since the decal indicated metric
    thread pitch, I installed correct gears as per diagram and set the knobs/levers to C, 3, and MII.
    When I started the first scratch (about 0.005 deep I checked it with metric 1.0 thread gauge. It all appeared good, right on the money. Rest is what you seeing from the start of this conversation.

    So I am afraid something is not right with this Lathe for this metric threading.

    dscn1381.jpg

    dscn1382.jpg

  13. #31
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    Test it. Never mind the pitch gage, see if the carriage moves .03937" (that is one mm) per one exact full turn of chuck by hand with half nuts engaged

    Easy with mag base indicator on bed and tip of indicator on carriage and all back lash taken out

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    Quote Originally Posted by johnoder View Post
    Test it. Never mind the pitch gage, see if the carriage moves .03937" (that is one mm) per one exact full turn of chuck by hand with half nuts engaged

    Easy with mag base indicator on bed and tip of indicator on carriage and all back lash taken out
    Thanks johnoder. I am going to change the gears back for 14mm x 1.0 and let you know the result.

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    Quote Originally Posted by Ratz View Post
    Thanks johnoder. I am going to change the gears back for 14mm x 1.0 and let you know the result.
    Wow. I got 0.0192". That is like 2x less. How could it look good on a thread gauge? Now what, this is really screwed up.

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    Quote Originally Posted by Ratz View Post
    Wow. I got 0.0192". That is like 2x less. How could it look good on a thread gauge? Now what, this is really screwed up.
    Hold it, discard my last comment. It is 0.0397" I forgot to flip 3rd setting from MI to MII so I am OK 1mm per turn.

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    Quote Originally Posted by Ratz View Post
    Hold it, discard my last comment. It is 0.0397" I forgot to flip 3rd setting from MI to MII so I am OK 1mm per turn.
    Now you know where you are at

    And you also know where .5 mm resides

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    Quote Originally Posted by Ratz View Post
    Wow. I got 0.0192". That is like 2x less. How could it look good on a thread gauge? Now what, this is really screwed up.
    First, you can NOT release the half nut when cutting metric threads with an imperial leadscrew. This was causing a tracking problem which led to the torn up threads you were getting before. Easy fix, leave half nut engaged and reverse spindle at end of each pass.
    Your second problem, the incorrect lead, should be easy to solve as well. Start by rechecking the positions of all the end gears. They must be set up exactly like the diagram. Count the teeth, assume nothing. Also check that you have all the levers in the correct position. Unless someone has done something really funky to your lathe, like changed gears in the QCGB or sheared a pin causing the leadscrew to slip, you should be good.

    On edit: Glad you sorted it out, I was typing during the last couple of posts!

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    Quote Originally Posted by johnoder View Post
    Now you know where you are at
    Nice, never thought of it. Now I still have to solve my original problem. Why is the thread not cutting?

    from my last photo the 12TPI is quite decent (Except chatter on the relief, my fault).

    So the tool is 90 degrees to the shaft, angle is at 29.5 degrees. Thread height is 0.613mm (0.024") end it turns itself to shreds. I tried it on 316 stainless same diameter. It looked somewhat better, but unsatisfactory.

    Maybe I will try the upside down tool, threading outwards tomorrow. I kept increasing RPMs and when I was turning it at 330 I broke the insert as I am not quick enough. No big deal as this is worth the experience.

  21. #38
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    The diff between 12TPI and metric is......

    You can open half nuts on 12 tpi

    You cannot open half nuts on metric using your Imperial lead screw

    See post # 36

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    Quote Originally Posted by Gordon B. Clarke View Post
    That sounds like the voice of experience You don't just happen to have a video?
    Experience, yes. But vicarious. There must be a video, but I've never seen one. Probably lots of photos of walls with a chuck-shaped hole in them.

    Having heard all those stories, one hard requirement I had was a lathe that could run backwards without drama. L00 spindle nose.

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    Quote Originally Posted by Ratz View Post
    OK, good to know I am not dreaming. I never threaded this way, so I will do some practicing.
    Here is some recent background, complete with a crash story, fortunately minor.

    American Optical Stereo Zoom; Accessory Thread


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