Manufacturing an ACME leadscrew using a following steady?

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    Member Hightower1's Avatar
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    Default Manufacturing an ACME leadscrew using a following steady?

    I would like to manufacture a 6 foot long 2" dia ACME leadscrew with a 2TPI pitch using a following steady?

    I have attenpted a test set-up on some stock material and have found that when I make a pass I run a burr up on the outside diameter edges which then impacts on the steady making me cut deeper than I want to.

    What technique can I use to stop this or do I have to make a modification to the steady so that I can run the wheels on the crest?

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    Default Re: Manufacturing an ACME leadscrew using a following steady?

    hy using a follow steady, with bearings, or rolls, be sure that they won't mess up your thread : tool is harder than material, and a bearing is harder than the tool, as a general, lets say, so even if you cut it correct, on the other side, where the steady makes contact, it will deform your thread more and more, as your cut goes deeper such effect sometimes may pass unoticable, so .... as a consequence, for fine work, like smooth od, or fine pitch threads, etc, use bronze inserts on your steady, thus soft materials, that won't damage your parts; off course, with bearings, damage is at a low level, but consistent, thus it may be there always, progressing, at low scale, thus without noticing it...

    if this effect is discovered too late, and you still wish to keep that part, then you need to deviate from standards; this allows to save costly a part

    to your issue now

    so that I can run the wheels on the crest
    make contact with at least 3-4 crests, and if you use, for example :
    ... 3 bearings, then consider contact length as 3*ul, where ul < crest length
    ... 3 bronze flats, then consider contact length as 3*ub where, as before, ub < crest length
    * how a bearing is tougher than bronze, ul must be >ub, considering also your thread dimensions, and actual case; but, with bronze, also a continous loooong pad may be just fine

    please remember :
    ... making contact only on crest is not a guarantee that deformation wont occur
    ... use contact on as many crestst as possbile; you can conside 3 consecutive, or 12, skip3, then 45 ( your tool should cut at 3 ); thus, many consecutive crests actually may lead to worse than only contact on far ends; actually, many consecutive, may reach a situation where contact is only on 1 crest, and only 1 is not stable .... so a multi contact pad, if not done ok, is as worse as a simple pad, that makes contact on 1 crest;

    the issues with only 1 crest, is that, as cut goes deeper, also cutting force increases, thus more pressure on the steady ... simply material may bend only in that area, not much, but enough to give you inconsistency if you wanna see it, simply use a dial, magnetic base on steady, and tip on part; even so, is possbile to deliver a part with the dial going crazy : rough it in crazy mode ( dial moves a lot ), than change to sharp insert and prefinish&finish in smooth mode ( dial moves minimal )

    you may use standad tolerances to your favor, so to deliver the part with minimal machining time, like smallest tooth height, aka largest crest, and other triccks as well; they deliver time save, especially on long threads, with big pitch; 6 foot is almost 2 meters, so yes, is ok to look for any allowance, so to say

    explanations where a bit rushed, but if you have questions, pls feel free to ask anything

    i just remembered : sometimes the steady itself may buckle : check it (with a dial/etc), and reinforce it needed

    i am more of a metric guy, but if you wish, i will look over those acme dimensions, and be back with dimensions for the contact of your steady / kindly

    Last edited by deadlykitten; 10-13-2022 at 04:09 AM.
    we are merely at the start of " Internet of Things / Industrial Revolution 4.0 " era : a mix of AI, plastics, human estrangement, powerful non-state actors ...


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    Member Hightower1's Avatar
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    Default Re: Manufacturing an ACME leadscrew using a following steady?

    Quote Originally Posted by deadlykitten View Post
    hy using a follow steady, with bearings, or rolls, be sure that they won't mess up your thread : tool is harder than material, and a bearing is harder than the tool, as a general, lets say, so even if you cut it correct, on the other side, where the steady makes contact, it will deform your thread more and more, as your cut goes deeper such effect sometimes may pass unoticable, so .... as a consequence, for fine work, like smooth od, or fine pitch threads, etc, use bronze inserts on your steady, thus soft materials, that won't damage your parts; off course, with bearings, damage is at a low level, but consistent, thus it may be there always, progressing, at low scale, thus without noticing it...

    if this effect is discovered too late, and you still wish to keep that part, then you need to deviate from standards; this allows to save costly a part

    to your issue now



    make contact with at least 3-4 crests, and if you use, for example :
    ... 3 bearings, then consider contact length as 3*ul, where ul < crest length
    ... 3 bronze flats, then consider contact length as 3*ub where, as before, ub < crest length
    * how a bearing is tougher than bronze, ul must be >ub, considering also your thread dimensions, and actual case; but, with bronze, also a continous loooong pad may be just fine

    please remember :
    ... making contact only on crest is not a guarantee that deformation wont occur
    ... use contact on as many crestst as possbile; you can conside 3 consecutive, or 12, skip3, then 45 ( your tool should cut at 3 ); thus, many consecutive crests actually may lead to worse than only contact on far ends; actually, many consecutive, may reach a situation where contact is only on 1 crest, and only 1 is not stable .... so a multi contact pad, if not done ok, is as worse as a simple pad, that makes contact on 1 crest;

    the issues with only 1 crest, is that, as cut goes deeper, also cutting force increases, thus more pressure on the steady ... simply material may bend only in that area, not much, but enough to give you inconsistency if you wanna see it, simply use a dial, magnetic base on steady, and tip on part; even so, is possbile to deliver a part with the dial going crazy : rough it in crazy mode ( dial moves a lot ), than change to sharp insert and prefinish&finish in smooth mode ( dial moves minimal )

    you may use standad tolerances to your favor, so to deliver the part with minimal machining time, like smallest tooth height, aka largest crest, and other triccks as well; they deliver time save, especially on long threads, with big pitch; 6 foot is almost 2 meters, so yes, is ok to look for any allowance, so to say

    explanations where a bit rushed, but if you have questions, pls feel free to ask anything

    i just remembered : sometimes the steady itself may buckle : check it (with a dial/etc), and reinforce it needed

    i am more of a metric guy, but if you wish, i will look over those acme dimensions, and be back with dimensions for the contact of your steady / kindly
    I have had a go with bronze tips and they wore away in no time. I was consantly adjusting the pads as the wore down.

    I agree with the cutting forces being high. I am planning on moving the compound slide to 14.5 degrees so that I cut on 2 sides for the tool and not 3 sides like when using the cross slide. This way I reduce the cutting force to a minimum.

    Like I said before my main problem is a bur forming on the outside diameter using a hand ground HSS tool I am using. Perhaps using a single screwcutting indexable tip would be a better bet?



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    Default Re: Manufacturing an ACME leadscrew using a following steady?

    hello again there is better then simple bronze qualtiy, like with graphite, and something like replacement for brass/bronze, but with better wear quality; check with local material suplier, i don't know english terms

    if such alternatice not possible, then you may need a pad with bearings; is a simple shaft with equal distant bearings on it; takes some time, but definetly worth it

    Like I said before my main problem is a bur forming on the outside diameter using a hand ground HSS tool I am using. Perhaps using a single screwcutting indexable tip would be a better bet?
    you may consider hss-co or vidia inserts

    carbide should be better, and if they don't work from 1st time, then try to check grades that are wear more resistant; not all thread inserts are actually up to the task, even if they have good geometry

    a full profile insert may work fine, but if not, and you find the price/time too expensive, simply take whatever carbide insert that is big enough to be grinded down to the shape you like; thus craft your own from biger types, like 'knux' for example

    14.5 degrees so that I cut on 2 sides for the tool and not 3 sides like when using the cross slide.
    if acme is that trapezoidal at 29degrees, you can cut also 1 single side : bottom, then alternate between flancs

    once achieved stable cuts. carbide cutting force is < hss, so it may handle more sides, or more reliable even on a single side ... trials required / kindly

    Last edited by deadlykitten; 10-14-2022 at 02:08 AM.
    we are merely at the start of " Internet of Things / Industrial Revolution 4.0 " era : a mix of AI, plastics, human estrangement, powerful non-state actors ...


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Manufacturing an ACME leadscrew using a following steady?

Manufacturing an ACME leadscrew using a following steady?