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Thread: A dumb lathe threading question

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    tmoore4748's Avatar
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    A dumb lathe threading question

    Spent almost three hours searching and found nothing, so, here goes: is there a boring bar, preferably 3/4" diameter, with the right geometry to hold both threading and turning inserts? The closest I've seen is one that holds a triangular turning insert (can't remember the name), but might also accommodate standard 3-sided 60 degree internal threading inserts. I'm still learning terminology of insert names, so it's all pretty confusing.

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    LMMasterMariner's Avatar
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    LMMasterMariner's Tools
    Hi,

    I also spent too much time searching for threading tools, bars and inserts, but I have good excuse.
    Can't speak Chinese. And I found them all at www.taobao.
    So, these bars for threading inserts are called SNR Indexable Internal Threading Tool.
    But I think that these can't be used with 60 deg boring inserts. Will check if possible once I
    am home again. I already collected all information and placed order for 3 different sizes
    of above and also for threading inserts. Here below is what I will get soon in China.

    Best regards
    LMMasterMariner
    Attached Thumbnails Attached Thumbnails A dumb lathe threading question-snr-tool-holder.jpg   A dumb lathe threading question-16-ir-tr.jpg   A dumb lathe threading question-16-ir-ag60.jpg   A dumb lathe threading question-11-ir-a60.jpg  

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    You may want to check this China website. A large selection of carbide inserts and holders. And it's in English.
    https://www.banggood.com/search/carbide-insert.html

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    LMMasterMariner (08-06-2017)

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    tmoore4748's Avatar
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    It's not so much the inserts in thinking about, but whether or not the bar has the right geometry to hold both a turning or threading insert. I'm not entirely sure such a thing exists, because I know the geometry might be different

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    tmoore4748's Avatar
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    So totally didn't expect this in the daily email! Basically, I'm looking for a boring bar with the same geometry that would work with a basic finishing insert, as well as a bar that also has the right geometry for a threading insert, but, I don't think it exists, as they seem to have angle setups just barely different from one another. I'm okay with getting two different bars, but want to get something that works if that's possible. Either that or make it myself

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    Toolmaker51's Avatar
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    My solution would center on variety of threading inserts termed ''on-edge''...The issue between internal threading and boring hinge on deflection of the bar mass, where boring depends on the leading edge un-congested by chip interference and can be quite substantial depth of cut. Threading is more of a form tool operation involving far less metal per pass, to maintain smooth thread flanks, and generally slim proportion bars. Consequently, ID threading tools accommodate a greater range of bore diameters as there are varied combinations considering standard thread pitches and diameters, and more for proprietary combinations.

    After decades of ID/OD threading, most have been accomplished with self-ground bits and bars, even ACME, Dardelet, and other buttress varieties. Access to tool & cutter or at least surface grinders helps, but definitely not essential. Even square threads, very uncommon to me past blackpowder gunsmithing, that took careful work all round.

    I haven't seen full-form threading occur on conventional lathes. It wouldn't be my choice unless I could setup directly in front of the holder and centered over carriage to greatly minimize deflection.
    Last edited by Toolmaker51; 08-23-2017 at 01:01 PM.
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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    I purchased some of these for threading, and really like the result. I made my own holder from a piece of square steel bar stock, a bit tedious though. As I recall, the inserts require some tilt to achieve the proper clearance angles, maybe 5 degrees? Note that there are many basic types of insert. One type for internal and another for external threads. Assuming you are talking single point threading inserts that look like the photo, they are available in two different profiles. The Vee thread profile insert can be used for a range of threads per inch, for example 4-7 TPI, 8-16 TPI, or 12-24 TPI. These are most economical for the hobby user.

    A full forming profile is also available which cuts the thread to exact dimensions. Each insert is designed for only one thread per inch but it will cut the thread with the ideal root width, and when the correct depth is reached will cut the major diameter smaller as it cuts the thread deeper. These are made for production but a full set will be quite expensive. Sandvik Coromant has a lot of details on their website (http://www.sandvik.coromant.com/site...ing/turn_c.pdf). They have tool holders listed as well.

    Bob

    Quote Originally Posted by tmoore4748 View Post
    Spent almost three hours searching and found nothing, so, here goes: is there a boring bar, preferably 3/4" diameter, with the right geometry to hold both threading and turning inserts? The closest I've seen is one that holds a triangular turning insert (can't remember the name), but might also accommodate standard 3-sided 60 degree internal threading inserts. I'm still learning terminology of insert names, so it's all pretty confusing.


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