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  1. #1
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    Default Need help with threading

    I am new to machining and running a lathe. I have been practicing threading and hope to do my first barrel soon. The issue Iím having is my threads are looking like the tool is tearing not cutting? And itís a new carbide bit that I am using. Could it be that my tool isnít set at the correct hight?

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    I only use a hand ground HSS bit for cutting threads. Its simple to make, cheap and lasts a very long time, and can be easily resharpened over and over again. I'm not saying its the only way to go, but many say HSS at low speeds and cut rates we tend to use is superior.

    Here's a video showing pretty much what my instructor 30 years ago showed us:

    YouTube

    South Bend Bulletin no. 35

    http://www.cutterod.com/cutter_zone/...athe_Tools.pdf


    I am curious to hear other's opinions.

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    What material and what ďbitĒ are you currently using?

    A quick check for center height would be to face a piece of material so there is no tit in the middle and measure the height of the insert off of the carriage and compare this against your threading tool. Some will moan and say to check against the tailstock but indulge me with a pair of calipers.

    Lower is better than higher in this case within reason.

    Are you using any lubrication? How fast are you running? Your best bet is to go as fast as you can stomach. This is one case where a mag back dial is superior to a DRO as one can anticipate the mechanical movement much easier than running digits on a display.

    How about some pictures of your setup and threads and we go from there.

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    Could be many things.

    Do you have the tool height correct? It should be at, or a couple thousandths below the centerline of the work.

    What grade of steel are you cutting? Some of the button-rifled barrels cut like $#!+. I use a piece of cratex to deburr the threads when I'm done. Do you have some 12L14 to play with?

    Sent from my Pixel 2 using Tapatalk

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    When you say carbide bit, is it a brazed carbide bit? Even tho those are 60deg most do not have clearances needed for threads, they are sometimes erroneously called threading bits by crappy vendors.

    Either grind HSS or invest in a lay down style holder that takes ER style inserts.

    another common error is setting the compound to ~29 deg on a lathe that the compound is marked so that at zero the compound is parallel to the bed ways.

    On those you actually need to set to ~61 deg.

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    Iíll take some pictures of what I have today after work. I plan on getting some hss blanks but have to buy a bench grinder yet also. I am still getting used to running threads at 70 rpm, my next gear up is 200, and that scares the hell out of me at this point! I have already crashed my lathe once because I forgot to put it in low gear! I know many will turn their noses up, but I have a grizzly 750g.

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    Some companies do make HSS inserts.

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    In all honesty if you have no experience whatever in cutting threads, you seriously need someone to instruct you,and if that's not possible please go to the internet and look at some of the thousand or so U-Tube Videos on the subject. Tubal Cain comes to mind. Safety is of the utmost importance, and should practiced every time you walk up to the machine. You have stated that you have already crashed the machine and even a small machine can maim or kill you.
    Cutting good threads on a rifle barrel usually offers one chance at getting it right. Cutting threads to a shoulder on a 1 inch shank correctly is not for the faint of heart starting out. Good luck and be safe!

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    Brownell's sells HSS threading tools in both 55 and 60 degree if you don't want to grind your own.

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    A.R.Warner makes HSS inserts. Use a positive rake and run it slow. Carbide needs a faster surface speed to cut properly. Good cutting fluid also, most use dark sulphur pipe cutting oil. Bacon grease or lard works well also. I have been cutting threads for over 40years and find that the old methods still work best. Get a piece to practice on and scribe a mark with the tip of tool to simulate a shoulder to stop at. This way the worst thing that could happen is to run past it instead of crashing.

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    Buy the Warner HSS tool holder and threading inserts. Of course you need a good setup and machining practice. I use Vipers Venom sulphurized oil.
    Unless you are doing a lot of barrels and speed is needed, the HS tools are best. Yes, I do have carbide inserts also, but the HS tooling gives a better finish.

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    Unless you have very quick reflexes you are better off inverting the tool ans running the lathe in reverse when threading to a shoulder. If you have a thread-mounted chuck, do not try this.

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    Quote Originally Posted by Illinoyance View Post
    Unless you have very quick reflexes you are better off inverting the tool ans running the lathe in reverse when threading to a shoulder. If you have a thread-mounted chuck, do not try this.
    I will disagree, I thread to the shoulder and I ain't quick anymore.

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    I started with Warner hss, went to carbide (often full-profile inserts), cut dry and have no issues with typical .004-.005 advances on the compound.

    Confirm your compound is set slightly LESS than 30 degrees (29-1/2 or so).
    Use a dial indicator clamped to the front way .100 from your stop point.

    My 9A has DRO's, but it's much easier to watch a needle on a dial to be able to kick the half-nuts out and spin the cross slide handle at precisely the right time.

    No harm in making a small thread relief cut ahead of the shoulder, either and in some cases it's necessary.

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    Agree fingernail sharp HSS is very good...

    Steel often like a little side rake perhaps 5* off the cutting going lower to the right of edge. Likes 30* compound in-feed
    (actually 29 1/2 degree). less in feed as you get deep. A little hone or fine file to the part OD before the a finish pass.
    Be sure not very much part hanging with no support.
    Perhaps 50 to 70 RPM learning.

    Good to have and use a fish tail gauge.

    Get a slug/rod of steel and practice till it is easy as pie.
    I put a slip of tape on my chuck to look at when getting to last turn so know exactly where to pull every time.

    QT[at the correct hight?} look at the tail center and line bit even with that / on center is OK. You can look at a chuck jaw set horizontal or even the parting line of a held collet when you get lathe handy.

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    Square my qctp to the ways by running it up against the extended tailstock ram.
    The toolholder and insert can't be anything but perfectly at 90 degrees to the work.

    No fishtail needed. Obviously still required if you want to grind hss.

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    Quote Originally Posted by Illinoyance View Post
    Unless you have very quick reflexes you are better off inverting the tool ans running the lathe in reverse when threading to a shoulder. If you have a thread-mounted chuck, do not try this.
    This requires an undercut at the base of the shoulder.

    Quote Originally Posted by tobnpr View Post
    No harm in making a small thread relief cut ahead of the shoulder, either and in some cases it's necessary.
    Not unless you need pick up the threads and set the barrel back at a later time.

    It's not really that hard to learn to kick out the lathe while threading. Get a dial indicator on a magnetic base and remember to back the cutter out of the work before you stop the carriage. This is how I was taught in school and I'd never run a lathe before.

    Sent from my Pixel 2 using Tapatalk

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    I use a Trav A Dial. I thread to the shoulder and then only disengage the half nut. I have plenty time to back out the cross slide. Yes, it leaves a vee groove, but looks better than a thread relief. A thread relief is fine, but I like the "look" without the relief.

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    Once you get confident with the imaginary shoulder line on your practice piece, the next step is to make a sliding collar to act as a shoulder. Line the edge of collar up with your marked line and practice stopping without hitting shoulder. If you do "crash" into the "shoulder" collar, it will slide or rotate and not cause problems. The next step is working to an actual shoulder. Just practice till the motions of disengaging the half-nuts and pulling the cross slide become a natural movement.

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    Look at you chuck with a slip of tape on one jaw at 50 or 70 rpm and note how long it takes the tape to come around. That is a lot of time for you to pull out and drop the half nut / or shut the feed..threading should be easy with practicing.
    (60 seconds divided by a 20 thread)

    I knew a guy who put a sharpie line on his part and watched for it to come to a certain place. Turn of tape around the part with a sharpy line.. agree just looking at the thread can be harder than using a simple help device.

    Wooden broom stick is a good practice stock.. 1/2" wood dowel from the hardware store. 3/8 or 1/2 aluminum dowel..

    Yes soft wood does not lathe cut very will so don't expect the nice clean cut like yo might find on steel or aluminum, so this is mostly just for practice for pull out and ending to a shoulder.

    A very sharp HSS bit would do best , with it having a high amount if side rake angle of perhaps 15-20*
    https://littlemachineshop.com/images...ngToolBits.pdf
    Last edited by michiganbuck; 04-20-2019 at 07:47 AM.

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