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  1. #1
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    Default Help with 55 degree threads

    Guys and or Gals,
    I need some help. I have a Myford ML7 with a 1.125" x 12 TPI mandrel nose thread. I have in the past made numerous backplates and adapters for the machine using a commercial 55* boring bar or more recently 11 IR AG55 inserts in a SNR0012M11 boring bar. I have also used the same boring bar with 11 IR AG60 inserts for 60* internal threads with no problems.

    However, I recently needed to produce an external thread to replicate the mandrel thread. I have a SER1212H16 holder in which, using 16 ER AG60 inserts I have successfully produced 60* external threads. The problem arose when I tried to produce 55* threads using 16 ER AG55 inserts. I set the tool holder up in the same fashion as I would for 60* i.e. the holder's left face parallel to the chuck face or at 90* to the work and the result is a sawtooth looking thread. My thread setup gauge is too large to accurately accommodate the small cutting tip on the insert so it's a bit of a guess going that route.

    Why?

    Do I need a different holder? I don't seem to be able to get an answer from the insert supplier. The inserts are manufactured by two different companies.

    When held on top of one another for comparison the tips of the cutting edges i.e. the root of the thread seem to be in line, with the "skirts" of the thread forms separated by a similar amount on each side yet the thread produced looks like there was no adjustment made for the 5* difference in the included angle and the right edge is almost vertical while the left edge is way more than 27.5* from vertical. See the attached photo where the thread on the left is from an old mandrel while the thread on the right is my fiasco. imgp6583.jpg

    If anyone can enlighten me as to what I'm doing wrong I'd appreciate their help. If I need a different holder a part number and source would also help. Thanks in advance,
    Twistit

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    did you adjust your infeed angle from the 60* threading?

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    Quote Originally Posted by Twistit View Post
    a Myford ML7
    Huh?

    You are fighting store-bought 60-degree "inserts" into a 55-degree wish-list.. on a 1946 UPGRADE to an even older 1930's lathe design?

    .. and it hasn't crossed your mind that an ML7 is perfectly comfortable with HSS/Cobalt/Stellite tooling that you can JF grind dead-nuts to 55 degree included angle?

    Inserted Carbide tooling doesn't ALWAYS make a small, light, hobby lathe's balls bigger.

    Some days, it just busts them.

    "Why Wuddja?"

    Gots to be a "Model Engineering" venue somewhere as can walk you through grinding HSS for hobby projects? And there ain't MUCH that the Stellites cannot cut.

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    I think the question was why the holder and lathe are fine with 60 degree inserts but can't produce with 55 degree inserts assuming the thread range is correct. i have Whitworth machines so am interested if there are problems interchanging the inserts. Dave

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    Quote Originally Posted by beckerkumm View Post
    I think the question was why the holder and lathe are fine with 60 degree inserts but can't produce with 55 degree inserts assuming the thread range is correct. i have Whitworth machines so am interested if there are problems interchanging the inserts. Dave
    Well. the OP was changing the insert . but asked if he needed a different holder?

    Not a problem a hand-ground and 4-Way mavin would have ever had to be BOTHERED with.

    Even so, this puppy is even smaller than a South Bent, so "nice toy" or even "Grand and very clever toy" a Schaublin nor Hardinge small industrial-class lathe it was never.

    Carbides aren't really a "natural" fit, even to speed and available power AT speed to use their strengths to best effect.

    The final drive motor of a typical ML7? Right about the same HP as a coolant pump on an industrial lathe. That's kinda pushing it - or more accurately NOT "pushing it" for carbides?

    Regardless.. hobby inquiries are better served where they live and prosper in hobby venues.

    Not a "status" thing.

    Simply that those venues are where a larger number of those familiar with Model Engineering and the machines that serve it - ergo have the relevant and USEFUL experience - are to be found.

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    Are you positive that the inserts are the ones you think they are? By this I mean that what you believe is an external bit actually is external, and that right hand actually is right hand.

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    Quote Originally Posted by Twistit View Post
    Guys and or Gals,
    I need some help. I have a Myford ML7 with a 1.125" x 12 TPI mandrel nose thread. I have in the past made numerous backplates and adapters for the machine using a commercial 55* boring bar or more recently 11 IR AG55 inserts in a SNR0012M11 boring bar. I have also used the same boring bar with 11 IR AG60 inserts for 60* internal threads with no problems.

    However, I recently needed to produce an external thread to replicate the mandrel thread. I have a SER1212H16 holder in which, using 16 ER AG60 inserts I have successfully produced 60* external threads. The problem arose when I tried to produce 55* threads using 16 ER AG55 inserts. I set the tool holder up in the same fashion as I would for 60* i.e. the holder's left face parallel to the chuck face or at 90* to the work and the result is a sawtooth looking thread. My thread setup gauge is too large to accurately accommodate the small cutting tip on the insert so it's a bit of a guess going that route.

    Why?

    Do I need a different holder? I don't seem to be able to get an answer from the insert supplier. The inserts are manufactured by two different companies.

    When held on top of one another for comparison the tips of the cutting edges i.e. the root of the thread seem to be in line, with the "skirts" of the thread forms separated by a similar amount on each side yet the thread produced looks like there was no adjustment made for the 5* difference in the included angle and the right edge is almost vertical while the left edge is way more than 27.5* from vertical. See the attached photo where the thread on the left is from an old mandrel while the thread on the right is my fiasco. imgp6583.jpg

    If anyone can enlighten me as to what I'm doing wrong I'd appreciate their help. If I need a different holder a part number and source would also help. Thanks in advance,
    Twistit
    First thing you NEED to do, is go over your entire set-up and set it correctly for the thread you are cutting.

    That has been the answer to every set if Buttress style threads I have ever seen a new lathe user create, when they were setting up to cut threads. Don't read the derees off the markings using the index mark, start by pointing the compound directly at the work (90 degrees to the axis of rotation) and then move the compound to the correct side from there, by the correct number of degrees.

    If you are not scared spitless of the act of grinding a HSS tool bit, this would be a good time to practice some more. If you are, then get over it. The way to get over it, is to do it. Lots.

    Set the tool up so the point is aiming directly at the work, and the compound is a bit less than half the angle of the tool tip.

    How did you manage to find the only thread gage in existence, that has no external surfaces of the correct angle? Not that it should matter if using a carbide insert boring bar style tool holder, as the only thing you need to align, is the body of the bar, with the ways of the lathe, and all shall align by design! If using an external lathe tool type holder, align the holder body with the face of the chuck. Same result. Almost like the guys that make those things, knew what they were supposed to do!

    Oh yeah. Next go-round, rough out the mandrel, thread it, then worry about the rest. That will save you a lot of making parts pretty or accurate, and then screwing them up by saving the hardest operation till last.

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    Hi BSCustom,
    Thanks for your reply and question. The answer is yes, the compound was set over to 27* and the infeed done from the compound at about 0.005" per run.

    As I had hoped I had indicated in my original post all the things you would usually do for any thread like making sure your tool was presented at 90* to the work face, angle of compound at 1/2 the included angle minus a degree and infeed done with the compound at amounts that the machine and the operator can safely, handle.

    The tool holder in question has a flat face on the left side which, with a 60* insert installed, presents the cutting tip at 90* to the work when that flat side is parallel to the chuck face. In switching to the 55* inserts I did the same setup, except for the compound set over and expected the same results. I didn't get them. So my question was to anyone who uses both types of inserts do you need a different holder for the 55* inserts? If that's the case, and it seems likely to be the case, does anyone know where I can purchase one?
    Twistit

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    The setups for a 16ER60 and a 16ER55 are pretty much identical. I use the same alignment for both including the infeed angle when I'm using the topslide instead of the crossslide for infeed.

    If you happen to have the topslide twisted so you can feed in at an angle, I suspect uou will find that you've fed at approx 60° to radial rather than the approx 30° to radial that you need.

    If your ML7 is the short bed version with the topslide restained by two T bolts in the crossslide slots, then you can't set it over far enough (maximum is about plus/minus 45°. There is a way to get the topslide closer to a radial direction but it is a bit of a lashup.

    I type too slowly!!!

    Yes, you've probably got it set over at 27° from axial, instead of 17° from radial...

    If you really do want to get to the 27° from radial, then either make two long T-bars that are long enough to extend on both sides of the crossslide or two bits of flat bar of similar lenght. Bolt two other bits of flat bar to the protruding ends parallel to the crosslide. Having done that, clamp the topslide to holes drilled and tapped in he centre of these two bars. I'd show photos, but I gave those bits away when I sold my shortbed ML7 when I inherited dad's longbed ML7B.(Which has the Super7 type cross and topslides)

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    Thanks beckerkumm. That's exactly the question Dave. All I'm asking is if anyone else, on whatever machine, has encountered this situation because it doesn't make sense to me.
    Twistit

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    Thanks Mark. My ML7 is the standard machine but I have retrofitted it with the longer and wider SL7 cross slide and compound so I have the infinitely variable compound angle capability and I'm sure it was set correctly to 27* as I had to change it from the previous job doing 60* threads on the other end of the work. A 5C adapter to Myford by the way.

    Even if the compound infeed was at 29* it would only have made the threading more difficult as the tool would cut more on the left side than the normal very light cut on the right. The only conclusion I can come to is that the insert, somehow, was not presented at the correct angle.

    I'll have to set it up again and see if I can fix it by presenting the holder at a compensating angle. Whatever that turns out to be.
    Twistit

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    Not sure exactly yet setting the thread to a gage designed for 60 degrees will misalign. Then too feeding at 29 degrees is fine for a 60 degree thread yet for a 55 degree not so much. Probably does not matter actually. From your picture it looks like your 55 degree tool is off.

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    Twistit

    It is slightly ironic that the Myford ML7 does not make it easy to set up for Whitworth screwcutting, but there you are.

    Despite what previous posters might have said, it is perfectly possible to screwcut on this lathe and vast numbers of British model makers have done so. It just takes a bit more work than you might expect. It is a good few years since I have done this with an ML7 so I had to remind myself of the procedure.

    As Mark has said, the the way in which the topslide is retained is less than ideal. You will not be able to rotate the topslide to the correct angle with the tee nuts in their standard position and I am guessing that this and the lack of comprehensive angle graduation is what has caused your problems. You need to move the tee-nuts to their alternative positions at the other ends of their slots and then set the topslide angle correctly. I never used to use the graduations for this - a protractor is a better choice.

    You can use your selected insert and toolholder, or a HSS tool, whichever you want; it really doesn't matter.

    Rather than try to explain this in painful detail, I had a look for a video which shows you the setup. I don't claim the methods in this video are the best, or what I would do, but they will get you on the right track.

    Screw Cutting on Myford ML7 Lathe - Part 1 - Setting up - YouTube

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    Twistit

    Just noticed that you have posted that you have a Super7 cross slide and compound, so disregard what I said about the tee-slot nuts.

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    Quote Originally Posted by Trueturning View Post
    Not sure exactly yet setting the I’d thread to a gage designed for 60 degrees will misalign. Then too feeding at 29 degrees is fine for a 60 degree thread yet for a 55 degree not so much. Probably does not matter actually. From your picture it looks like your 55 degree tool is off.
    It could save a ton of guess work to go and do your best idea of a set up - freeze the compound.

    Make a cut with cross advance ONLY (straight in).. into a material as won't crash the little pup when so approached, as-in a PVC pipe coupling, or a DWV cut-off...

    And see WTF you HAVE ....vs what you only suspect you had or WISHED you had.

    Five thou advance at a pass can be kinda teasing to a Carbide as to deciding to cut - or just skate - when on a horse that is more flexible than it is rigid.

    Different tool shape, finely ground then honed HSS at literally "razor sharpness" could make life easier?

    As it generally HAS done for fine work on light lathes, lo since sharp HCS was good enough.

    And may STILL be?

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    Hi Trevj. Thanks for the answer. Already done. I went over the setup, once I'd seen the result, and checked everything.

    The holder, as I indicated elsewhere, has a flat face on the left of the tool which was presented to the side of the chuck in order to set the parallel to the chuck or 90* to the work as I've done many times before doing 60* threads with the same holder and a 60* insert. Only difference was the insert changed to 55* and the compound to 27*. And before you ask, yes the holder was reset to parallel after the compound was changed. I may be old but not senile. Yet!

    My thread gauge has a 55* side to it but the insert tip is so short that the tip will not register in the smallest slot on the gauge so setting the tool to 90* is a guess at best and as far as I can see its ok.

    As to grinding my own tools, I've done it in the past before insert tooling was available to me but I purchased these inserts and insert tooling when I came to Canada as I had to renew my tooling so went with what is readily available.

    As to the sequence of events, the adapter was supposed to be an ER 25 - 5C adapter but I screwed up the thread on the ER25 end. I remade the 5C-ER25 adapter and decided to reuse the already machined 5C end to make a Myford adapter as it just meant turning the end down and threading to suit. It'll work as is but I'd like to know why it went wrong. Guess I'll have to try again and see if I can fix whatever was wrong.
    Twisit

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    Hi JR. Yes I' as sure that the inserts are correct in that that's what they were purchased as. Like the internal ones they are a different colour so as to distinguish them. I have seen ones that are labeled 60* and 55* but these don't appear to be. The internals are much smaller being 11 mm as against 16mm for the externals. As to the "handing" they are basically the same shape as the 60* and if I clamp one above the other with the straight faces parallel to each other, the "tips" appear to fall in the same plane i.e. the tips are above one another. Only the "skirt" angle is different.

    I have seen advertised, "left" and "right" tools for threading to shoulders etc. The right tool is basically what I have. The "left" tool appeared to have an adjusting screw that worked on one of the unused tips presumably to correct the angle or something but I don't know what as I've never used one.
    Twistit

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    Bilmac, I just watched that YouTube bit and as far as I can tell that guy just set his compound to 55* and not 27*. I also checked my old cross slide and contrary to what he said in the video 27* is obtainable with that compound. Yes the tee nuts have to be in the opposite end of the slots but mine usually were anyway. I'll have to see if I can find part 2 of the video where he actually stops waffling and gets on with cutting a thread.

    The gauge I have is not a "fishtail" but a four sided one that will do 60*, 55* 471/2* for BA and Acme setups.
    Twisit

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    Excuse me! This forum is "Practical Machinist" Not professional machinist. I was not aware that its a BIG boys site.

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    Quote Originally Posted by Twistit View Post
    Bilmac, I just watched that YouTube bit and as far as I can tell that guy just set his compound to 55* and not 27*. I also checked my old cross slide and contrary to what he said in the video 27* is obtainable with that compound. Yes the tee nuts have to be in the opposite end of the slots but mine usually were anyway. I'll have to see if I can find part 2 of the video where he actually stops waffling and gets on with cutting a thread.

    The gauge I have is not a "fishtail" but a four sided one that will do 60*, 55* 471/2* for BA and Acme setups.
    Twisit
    If you are actually setting the topslide at 27 degrees right from straight in then your problems must lie somewhere else. Not getting this angle correct is a primary cause of the butress thread shape you are seeing.


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