Why does my lathe bore tapers? - Page 4
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    I know Buck. Took me a few minutes.

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    Quote Originally Posted by crossthread View Post
    I know Buck. Took me a few minutes.
    What cutting off chicken heads, or what way do they first run?

    If boring on the opposite inside with bit/insert fracing up proves straight, good. If so then it should be good going in or out, and there may be a few tenths advantage going one direction over the other direction. This is an older lathe thing and I don't know why. Sometimes the boring bar length can get you into a different worn/ways area and so be another source of a few tenths adjustment of straight.

    I like traveling out (away from headstock) because if you get side-tracked you don't run into something.

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    When you butcher chickens you never allow them to run after you cut off their head. It often bruises the meat. You hold them by the legs until they bleed out.

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    Just some feedback on my issue. I think now it is something in the compound (jibs etc.). What I did is axially align the compound to the ways with a DTI using a piece of ground stock in a collet unsupported by the tail stock. I moved the boring bar to the back of the stock and turned the OD in reverse using the compound to feed the bar instead of the entire carriage. I just wanted to use the boring bar to turn the OD to check for spring. No taper (well a half thousandths over four inches which is about all my compound will do). I drilled and bored the stock and basically did the same thing on the ID. No taper. I then turned the bar another 180 and bored from the front side (the conventional direction) and got .0015" of taper and yes as always smaller at the headstock end. I am going to pull the compound apart this weekend and check the jibs. They do seem to be a little loose. I adjust them by feel but I can see a little oil squish out just above the dovetails when I yank on the compound.

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    If you get near straight with back-side boring it may be good to just get in the habit of doing so.
    Due to wear you may not be able to tighten the gibs enough because of wear in the gibs dovetail. Wear can cause being able to only get so tight and then a lock-up with still .002 or so along the travel. Still, it won't hurt to tighten them as much as is possible.

    Back-siding gives the same twist to anything that can give.

    RE: What way does the chicken/roster run..? what is your answer?
    I remember when my sister and I would chase the headless chicken around the yard.
    Last edited by michiganbuck; 09-17-2021 at 09:32 AM.

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    I hear you Buck. I got a lot of useful information from you folks as usual and one suggestion that keeps popping up is "bore from the back side you idiot" (or something to that effect). Sometimes when you do something for fifty years or so, you just assume that's the way it's done. As things wear (machine and operator for that matter) you just might have to change your technique.

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    Quote Originally Posted by crossthread View Post
    I hear you Buck. I got a lot of useful information from you folks as usual and one suggestion that keeps popping up is "bore from the back side you idiot" (or something to that effect). Sometimes when you do something for fifty years or so, you just assume that's the way it's done. As things wear (machine and operator for that matter) you just might have to change your technique.
    OK, you are not going to answer the chicken question so I'm not going to buy you a coffee and doughnut/or a beer.

    What way does it run ......The headless chicken runs away.

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    Man you got me on that one. I thought the answer was if you cut off the head of a chicken with your left hand you would be holding it with your right and it would be pointing to the left and therefore run to the left. The one you cut off with your right hand would be pointing to the right and therefore run to the right. I've got to ask my doctor if Prozac is right for me.

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    Quote Originally Posted by crossthread View Post
    Man you got me on that one. I thought the answer was if you cut off the head of a chicken with your left hand you would be holding it with your right and it would be pointing to the left and therefore run to the left. The one you cut off with your right hand would be pointing to the right and therefore run to the right. I've got to ask my doctor if Prozac is right for me.
    It has nothing to do with cutting forces but only has to do with running away.

    For non-chicken choppers, a chicken will run about 50 feet with its head chopped off. Yes, with blood squatting about the yard.

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    RE: thanks for that like Richard. You are the man on this so a like is appreciated.

    For a time I thought nobody was seeing what I was trying to say.
    Buck

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    Quote Originally Posted by crossthread View Post
    Just some feedback on my issue. I think now it is something in the compound (jibs etc.). What I did is axially align the compound to the ways with a DTI using a piece of ground stock in a collet unsupported by the tail stock. I moved the boring bar to the back of the stock and turned the OD in reverse using the compound to feed the bar instead of the entire carriage. I just wanted to use the boring bar to turn the OD to check for spring. No taper (well a half thousandths over four inches which is about all my compound will do). I drilled and bored the stock and basically did the same thing on the ID. No taper. I then turned the bar another 180 and bored from the front side (the conventional direction) and got .0015" of taper and yes as always smaller at the headstock end. I am going to pull the compound apart this weekend and check the jibs. They do seem to be a little loose. I adjust them by feel but I can see a little oil squish out just above the dovetails when I yank on the compound.
    Close...

    The intent of my suggestion was to be able to repeat all motions in a different place.

    By cutting on the back side with carriage movement it is same extension of tooling and similar forces.

    Easier to make good measurements and make repeated test cuts and evaluate the results.

    It could be simple as worn ways closer to chuck that combined with the extension of the boring bar gives it leverage enough to cause the carriage to tilt some.

    Using the compound allows one to correct for any errors as well but it is a bit of work to cut.

    If lathe has taper attachment it could be used to correct but that is a last resort.

    You also could place a dial indicator on the carriage and check for deflection of your boring bar.

    Sent from my SM-G781V using Tapatalk

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    Yeah this is a complicated subject without just one simple answer. To find out the true cause you'd need to check a lot of the geometry of the machine. Generally if you have a bed wear problem you can either work around it or fix it. Sometimes to work around it you can change the stickout of the boring bar and find a sweet spot that will cut straight for the length of your bore. You could also bump the tool. You could also try cutting in reverse on the far side of the bore. There are plenty of workarounds.

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    Quote Originally Posted by eKretz View Post
    Yeah this is a complicated subject without just one simple answer. To find out the true cause you'd need to check a lot of the geometry of the machine. Generally if you have a bed wear problem you can either work around it or fix it. Sometimes to work around it you can change the stickout of the boring bar and find a sweet spot that will cut straight for the length of your bore. You could also bump the tool. You could also try cutting in reverse on the far side of the bore. There are plenty of workarounds.
    ^^^^ This is true. A boring bar flexes the same as long as the load is the same, it’s a beam supported at one end, loaded at the other…

    IME issues like this could be saddle travel direction (ways need work), CHUCKING and/or the spindle & ways are no longer coaxial (vertical and horizontal). Bad workholding (chucking) can make for shitty bores that measure goofy.

    Good luck,
    Matt

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    Quote Originally Posted by crossthread View Post
    I am going to pull the compound apart this weekend and check the gibs. They do seem to be a little loose. I adjust them by feel but I can see a little oil squish out just above the dovetails when I yank on the compound.
    As you suspect, you should not see any oil squishing out, so the gibs are either loose and/or worn into boat-hull shape.

    The first time I replaced some gibs on a Clausing 5914, I put the new gibs in hand tight. (The old gibs had achieved boat-hull shape.) Turned out to be too loose. What I needed to do was to seat them firmly by tapping them into place with a small brass hammer, and then backing off slightly.

    Now, with worn ways, it may be impossible to fully tighten the gibs and still be able to move the carriage over the full length of the bed.

    The same story applies to the cross-slide dovetail ways.

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    I recall watching my grandfather slaughter chickens for Sunday dinner, but I guess he held on to them because they never ran anywhere.

    I had no interest in learning that skill from him.



    Quote Originally Posted by michiganbuck View Post
    It has nothing to do with cutting forces but only has to do with running away.

    For non-chicken choppers, a chicken will run about 50 feet with its head chopped off. Yes, with blood squatting about the yard.

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    Considering this thread it might be a good idea to give a tool post of an older lathe a radial push-pull of perhaps 15 to 50 pounds (depending on lathe size) to see what free movement there is and then calculate how that movement might affect size and taper.
    Has anyone calculated the cutting forces in taking a .002 .030 .100 .250 cut in mild steel and tough steel?
    REF:
    Calculated forces when turning | Cutting Tool Engineering

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    Quote Originally Posted by michiganbuck View Post
    Considering this thread it might be a good idea to give a tool post of an older lathe a radial push-pull of perhaps 15 to 50 pounds (depending on lathe size) to see what free movement there is and then calculate how that movement might affect size and taper.
    Has anyone calculated the cutting forces in taking a .002 .030 .100 .250 cut in mild steel and tough steel?
    REF:
    Calculated forces when turning | Cutting Tool Engineering
    Great link!

    Tables 1, 2 and 3 show how force changes with different doc. Common sense tells you that multiple deep cuts will compound the flex in the system and the taper in the bore. As the taper builds it keeps getting worse with each cut. Once the machine and set up is checked out, its all about cutting the bore without overstepping the limits of the machine and setup. Its also about creating a cutting condition with minimal force. Sharp tools used at the designed doc will help with this.

    A few hogging passes in a less than great setup will more likely lead to a tapered bore. You will have to clean this up on purpose because it won’t self correct or go away by magic.

    The finishing cuts may need a different insert that is designed specifically for very light doc and lowest cutting forces. An insert designed to take off .050 at pass will not work well to remove .002 at a pass. It will just rub and when you try to force it the forces multiply.

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    FWIW, I keep the compound's gib very tight, since I might only tweak it a small amount sometimes. I'd open up its clearance a little if I was going to do a lot of cranking on that handle. Or better, I have a reasonably large slip on handwheel that fits over the crank handles on the compound so I can turn it easily without getting hand cramps.

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    Quote Originally Posted by crossthread View Post
    Man you got me on that one. I thought the answer was if you cut off the head of a chicken with your left hand you would be holding it with your right and it would be pointing to the left and therefore run to the left. The one you cut off with your right hand would be pointing to the right and therefore run to the right. I've got to ask my doctor if Prozac is right for me.
    Fooks sake! Those among us who've actually had to DO this, OFTEN, and pluck and salvage the feathers for bedding, deal with mites and mess.. are FIRSTEST and HAPPIEST to grab a rotisserie roasted chicken at the supermart .....and never have to deal with that mess, ever again!

    Machinashitist ranks in this nation were originally FILLED by "farm boys" who simply wanted a more profitable dark-sulfur-oil stink to their overhauls than cow manure and chikn' s**t!



    Easy as it cudda been to rotate the bar one-eighty, Cee-clamp the cross, see watcha get...

    ..that brute-dumb-simple... and it ain't yet been tried?

    That's kinda headless running about chik'n s**t, too, ain't it?


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    Quote Originally Posted by HuFlungDung View Post
    FWIW, I keep the compound's gib very tight, since I might only tweak it a small amount sometimes. I'd open up its clearance a little if I was going to do a lot of cranking on that handle. Or better, I have a reasonably large slip on handwheel that fits over the crank handles on the compound so I can turn it easily without getting hand cramps.
    Same here. And in addition I take a small block of aluminum or steel and "clamp" it between the top compound slide and the bottom of the compound at the rear so that it's positively locked in place. It's in there at all times if the compound slide isn't in use. This prevents "lost" motion when using readouts.

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