Tool dig in. Part, slide and moral totally shattered.

Discussion in 'Mistakes, Blunders and Boo Boos' started by Hauk, Sep 11, 2011.

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  1. Jan 22, 2012 #61

    tattoomike68

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    lazylathe you make some good points. I agree with what you say.


    I found when working and high speed production shops that parting tool with was dependent on the stock , for 6" you want a 1/4" parting tool. too small a tool is as bad as too big.

    Parting 4 inch you might want 3/16"

    2 inch 1/8" wide tool works good.

    For 1 inch or under you can do fine with a 1/16" parting tool.

    When I started working fixing screw machines I saw the guys making parting tools on the surface grinder. I thought their tool geometry was way wrong but I was the one who was wrong, so I shut my mouth and watched the tools in action and got an education from some non college guys.

    The tools they made left little to no burrs. some guys set up tools that would go way down a bore and put a champher then pull out before the part was parted off. No burr and the internal champher was done.

    I learned alot there the boss had 3 nitro funny cars so that ate up half my time, when the car has a parachute you know its not a toy for little boys. It was cool to have a boss make me work on the cars.

    I'm rambling but anyway parting can suck, do it as close the the chuck as you can and get it done. its not magic and you dont need a live center.
     
  2. Jan 22, 2012 #62

    chuck foster

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    well guys as promised i went to work today and tried parting with the use of a live center.

    first item to be parted was brass, i set the parting tool on center and used hand feed. all went well until i got right to the center of the
    work piece, then the pressure of the live center pushed the piece that i was parting off. now it pushed it into the side of the parting tool which in turn pushed the parting tool into the piece held in the chuck. i then lessened the live center pressure and the results were the same. the brass shaft was 1 1/2" in diameter and spindle speed was 800 rpm with a constant flood of coolant.

    the next item to be parted was 1 1/2" diameter steel turning about 400 rpm with coolant...................same results.
    i then tried both set ups over several times using cutting oil and power feed, i varied the rpm,s and the feed rate...............no good.

    i then tried using a parting tool fed in from the back of the work (tool in a rear mount tool holder) and i got the same results no matter what i tried.

    all in all i tried brass,steel,aluminum and bronze. i used no coolant, coolant and 2 kinds of cutting oil, manual feed and power feed (all at various rates) i tried several different ways of sharpening the parting tool i even varied the rpm of the lathe. nothing worked very well. i then went back to the old way of parting and all was well.

    so with all that said i learned one of two things.
    1. i don't know how to part using a live center (greenie please post a video showing how you do it)
    2. it just isn't a very good way of parting

    please note i am not bashing any one i just wanted to know if I could do this and if not i would like some one to show me how.

    chuck
     
  3. Jan 22, 2012 #63

    radish

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    Hi Rick, I thought I would just cut in here, I normally just lurk in the shadows and soak up any ideas I can.

    You are correct, that parting of between centres is dangerous

    Now what this other person is advocating, is not that at all.



    From what I can read of all this, is that one end of the work-piece is to be held with the jaws of the chuck, he's just using the live centre, as you would on a very long traverse of the carriage to reduce the thickness of a job.

    What's with this "fixation" about parting of between centres ?

    He has already said, that is a dangerous practice, and yet you seem to be continuing on, with this wild assumption.

    WHY ARE YOU ADDING FUEL TO THIS FIRE WITH YOUR WRONG ASSUMPTIONS?
     
  4. Jan 22, 2012 #64

    tel

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    I don't think anyone is making assumptions, the fact of the matter is that when you are parting off you want the end of the workpiece free and clear, so it can fall away as it should, NOT get impeded with a centre hanging it up, or, worse still, the pressure pushing it onto the tool and thus the rotating stub of the workpiece. It's certainly not good practice at best, and downright dangerous at worst!
     
  5. Jan 22, 2012 #65

    mcostello

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    It has not been mentioned here since I have been coming here, but now is the time to bring it up. I have a 14" South Bend Lathe which one would suppose is a bigger lathe than a small or Modelers lathe. It is not the most solid machine, which is going against it's size and appearance. I took some advice from another forum and made an upside down parting tool. It works great, with no problems, people with a threaded spindle have to be very careful not to unscrew things. I have a threaded spindle and part carefully and it works.
     
  6. Jan 22, 2012 #66

    Mike N

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    I have been in the Tool & Die industry since 1971. I have operated metal lathes since I was in High School (1960's). Until I read this thread I have never heard of anyone using a parting tool with a tail stock & live center. This would be equivalent to milling a piece of bar stock in half when its clamped in a milling vise! I use my lathe for making small parts for my model engine hobby. I chuck my stock close to the jaws & part off small pcs. & catch them with my fingers with a light squeeze. Of course I would not do this with large heavy cutoffs!

    I only have the parting tool sticking out a far as needed to make the cut. I use a .040" parting tool for my small work & .093" is the largest parting tool I own. I have Aloris tool post holders on all 3 of my lathes, I have shimmed up 2 of the tool posts so all 3 of my lathes have the same center tool height. I can share all of my tool holders between the lathes without setting the center height every time.
     
  7. Jan 22, 2012 #67

    MachineTom

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    Where is the OP Hauk, in all this discussion??
     
  8. Jan 22, 2012 #68

    Hauk

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    Right here!
    I have not been able to use my lathe for everal months due to the crash and some anoying delays in getting a replacement part. Wabeco has been very helpful, and has replaced the part without charge, but it has taken a bit too long.

    I have also bought what I hope is a good parting tool

    And I am soaking up all the advice I can while mustering the courage to start machining again.

    I Will keep you posted on my progress!
     
  9. Jan 22, 2012 #69

    stevehuckss396

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    I have not seen it discussed here but there is a good possibility that the casting failed causing the trouble. If I were you I would consider making a replacement part instead of installing another possible failure. I have in the past done the same thing you have done and the blade snapped long before a casting on the machine.
     
  10. Jan 23, 2012 #70

    Mike N

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    When taking heavy cuts or using a parting tool if the compound is set parallel with the crossfeed I think there would be less stress on the dovetail. From the first photo it appears the compound was set at 90 degrees to the crossfeed.
     
  11. Jan 23, 2012 #71

    90LX_Notch

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    Regarding parting off: I didn't see mention of it (or I missed it), but locking the carriage is key. Another thing that I have found helpful is to pause and let the tool dwell every so often. Also, as mentioned earlier, keeping the tool sharp and on center are also key.

    Regarding part catchers: The red tubes from WD-40 cans are great for this. You can bottom them out in a blind hole and offset them downward in a tailstock mounted drill chuck. This setup causes the part to ride the red tube away from the parent material once it breaks free. You can easily add more tubes to strengthen the setup for heavier parts.

    -Bob
     
  12. Jan 23, 2012 #72

    Hauk

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    I must admit that I had several minor dig-ins before the big one. So I am absolutely certain this was a an operator error.

    As I am a jack of all trades kind of modeller, I have not been sitting around looking in awe at the lathe all these months. What has delayed the return to machining is a time-consuming effort to master the art of airbrushing brass models. A learning curve just as steep as machining, but fortunately with a much less risk of crashes & damaged equipment. No compressor explosions so far!
     
  13. Jan 23, 2012 #73

    stevehuckss396

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    I don't know all the rules but using a phrase like this without posting photos has to violate a rule or two. ;D ;D ;D
     
  14. Jan 29, 2012 #74

    hobby

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    Just to clear up, that the gentleman was trying to make very clear, That a Chuck was used to hold the part steady, while parting off with the tailstock.

    Now with all due respect to the gentleman,
    -----------------------------------------------------------


    This is intended to be:
    @ Hauk, and to other new people to this hobby


    Here is a way to look at that controversal situation when trying to do a proper cutoff method.

    The workpiece locked into position in the chuck jaws.
    Gravity has no effect on this workpiece.

    The tailstock live center has its bearing point with due force on the tailside of the workpiece, the workpiece will not feel the effects of this preasure, due to the supporting of the chuck jaws.

    As the cutoff tool enters the workpiece, the workpiece is feeling all the effects of the chuck jaws holding it in position, as the blade cuts deeper into the workpiece, there will come a point where the force of the tailstock will begin to start having influence on the tailstock side of the workpiece.
    That is not good.

    As the blade comes to full depth the chuck jaw side of the workpiece is fully secured, there will not be any drop from its horizontal position, HOWEVER the point that all the professional machinists are trying to convey to you is this,

    It is not the drop of both sides of the workpiece that will cause a problem, since the chuck side stays stationary, they are trying to point out with as much patiance as they can, it is the drop from the horizontal position of the tailstock side of the workpiece, that due to gravity will inherently drop in the direction of the cuttoff tool, because a fulcrum effect is established as a pivot point with the tailstock live center point in a divet in the workpiece

    The loose workpiece will drop and wedge with the pivot point at the tailstock holding it..

    This workpiece can only go one direction on this pivot, and that is toward the cuttoff tool.

    Thats why these professional machinists are against the tailstock method, with or without chuck being used.

    Any pivot towards the cutoff tool is not good practice, just as you never cut a 2x4 in half with both sides of the 2x4 supported at each end, unless the area of the cut is well supported too.

    Always a cutoff piece of material never should pivot towards the cutting tool.
    Its about kickback, or binding, that will occur in most cases.

    Maybe this will help clarify what the professional machinists are trying to convey to you and all the new people to this hobby, in this thread.

    These machinists are knowledgable as professionals in there field, so they know what there trying to make clear to the original posters, and any one else who is new to machining.

    So please all newcomers adhere to the advise given by the people on this board who have the credentials to make the statements they make concerning safety practices in there field of expertise.



     
  15. Jan 30, 2012 #75

    tel

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    Look Ma! No centre!

    Parting off 4" dia bronze in the Myford. This is one of those rare occasions when I had to part from the front.

    [​IMG]

    [​IMG]
     
  16. Jan 30, 2012 #76

    Peter.

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    There's been a lot of heat generated in this thread and some sign of pack-mentality too. I thought better of this place.

    Parting with a center isn't the most dangerous thing you can do in your workshop, the OP managed to make quite a wreck without using one, that piece of brass could make quite a dent in your head. Sometimes using one is preferrable to not, like last week when I was parting off spacer rings from a piece of acetal. That piece would certainly have climbed the tool and come out of the chuck but the center held it nicely.

    Quite often a person has to modify what they would normally do according to the situation, expecially when limited to home shop equipment. You wouldn't run across a 6-lane motorway at 4 in the afternoon but you could stroll across it at midnight.

     
  17. Jan 30, 2012 #77

    hobby

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    I am not a machinists, just a home hobbyist.
    Therefore my opinions are not professional advice by any means.

    However, looking at the logic of the situation, shows that it is a given fact in every construction field, that any material being cut all the way through should always fall away from the cutting tool.

    Unless both ends of the material is supported to keep them stationary, never should a loose work piece ever tilt in the direction of its cutter, wether it is a revolving cutter or a stationary cutter, other wise there is a chance of binding or kickback.

    Please understand:

    The professionals on this board are trying to keep the safety standards intact, there are situations for modifications of a method, but should always keep the safety factor top priority in using a modified method.

    It seems that a correct way to use a tailstock during parting is:

    1. part only part way through using tailstock, then remove tailstock to finish parting through.
    2. Use a tailstock chuck to hold the workpiece and part all the way through, that ensures that the workpiece cannot tilt and bind against the cutter.

    Please understand, the professionals on this board ,which I am not, are trying to teach the newcomers the correct way to acomplish these things, when a person learns enough about machining methods, then they can modify the correct ways to suit there needs, by that time they will have learned how to modify these methods within the safety limits.
     
  18. Jan 30, 2012 #78

    coopertje

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    I am in the same situation as Hobby, never had any education in machining at all, just learned by trial and error. I regret to see so much emotion in this tread, it is something that I am luckily not used of this forum. I believe that a good discussion is based on facts and that the emotions should be left at home (even though that can be difficult sometimes). Please, lets not call each other thoughts, ideas or way of working stupid (i believe doing that is stupid ::) ). Terms like "I strongly disagree", "for me it sounds really dangerous" etc trigger the beginners over here and sound much more friendly. Every body has the right of having his own opinion, that should be treasured over here and not being demotivated. However I really agree although that safety comes first, so in a way I can understand the emotional responses!!! I am not judging over here, if this way of parting off works fine for him its ok with me, however I personally will never try this method because I am scared of it and I prefer that the material falls away from the rotating chuck instead having it pressed towards it. However a video of greenie in action would be nice to see.

    Too bad to see your Wabeco brake down Haul, I would expect better from them, they are not cheap machines! Hope to see you back in business soon! By the way, what type do you have? I had a 6000D and was quite satisfied with it.

    Lets all have (save) fun overhere, regards Jeroen
     
  19. Jan 30, 2012 #79

    tombstone

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    For a tailstock to engage sufficiently with the part it would have to exert pressure on the part thus forcing it on to the tool while still rotating as it nears the end of the cut as Tel said with the chance of it either breaking the tool or forcing it into the bar stock or damaging the part off face of the part. Keeping the part off slot clear as it is created is obviously important as shown by the design of part off inserts ability to reduce the width of the swarf and allow it to drop clear.A common part off procedure with early cnc lathes was to part off down to about ¼” dia at normal speed and feed rates then reduce rpm to 100 with a feed of .001” per rev which let part drop down clear with out rattling round inside the cabinet.Some years later when twin spindle machining centres were developed the manufacturer found that when the 2nd spindle gripped the part in its collet it pushed it onto the part off tool and usually broke it their answer was to grip the part then move the 2nd spindle back .004” before starting the part off sequence this released pressure on the tool and was very successful.Personally I part off with a 3mm Iscar self grip tool mounted upside down in front cross slide at 500RPM and .006” per rev feed for everything and spray WD40 to lube chips for their release the part either falls into a box or pick it off by hand the current range has been 2” S143 stainless and aluminium down to 1/8” in similar and insert lasts a long time so far touch wood.
    Ray
     
  20. Jan 30, 2012 #80

    chuck foster

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    it would have to exert pressure on the part thus forcing it on to the tool while still rotating as it nears the end of the cut as Tel said with the chance of it either breaking the tool or forcing it into the bar stock or damaging the part off face of the part

    wow i never would have thought of that ::)

    chuck the ignored canuck
     

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