Announcement

Collapse
No announcement yet.

USA vs UK & Europe

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Richard P Wilson
    replied
    Originally posted by thaiguzzi View Post
    Forgot, another old turner's fave, was leaving the top slide 5.7 degrees off parallel. A thou on the dial was a tenth of a thou cut. Or, put another way, 5 thou on the dial was a half a thou cut. Sharp tool recq'd...
    Yes, thats how I have my topslide set. I don't think many do, but it suits me. I've got cataracts forming, so its easier to feed 10 divisions on the topslide than it is to feed 1 on the cross slide. Also thats why I can't use a vernier any more, can't read it now so I use a digital calliper for rough work, (99% of my stuff) and break out the micrometers when I'm doing something accurate like fitting a piston to a bore.

    Leave a comment:


  • old mart
    replied
    I think that there is room to put a scratch mark on the Smart & Brown if the toolpost is temporarily removed. Actually I would like to try the technique. Today, I cut two 1" X 6tpi acme internal threads, the starting bore was 0.837" and the first was in aluminium as a test before the bronze was done. The aluminium turned out to be more trouble to thread than the bronze, even with lubricant, the bronze was done dry. I plunged straight in and had to reduce the cuts to 0.001" for the last 15 thou. There was noticeable flex, I thought it was the 16mm threading bar at first, but it is most likely the saddle moving as the lathe has a lot of wear in the ways.
    After sectioning the test piece, it fitted the leadscrew beautifully, the old nut threads have 0.015" backlash. Neither thread has any chatter so I must be doing something right.

    With such an old lathe, I have to back off the tool each time and wait for the number to come up on the threading dial, also I would rather not use reverse with a screwed on chuck, but I'm not in a hurry so it doesn't matter much.
    Last edited by old mart; 03-22-2018, 05:16 PM.

    Leave a comment:


  • Hopefuldave
    replied
    Originally posted by Baz View Post
    Set top slide to required angle using protractor, sine bar, calculation etc and just scratch a line where the scale should have had a mark. If you are happy to use the plunge technique at least sometimes then the setting of the 29.5 degrees does not have to be that precise. The actual thread angle should be set by the tool bit.
    30/60 is fine for Americans to do UNC and Metric but us Brits have to contend with Whitworth too. Split the difference?
    I think the concept of the set over was started when lathes and tools were more fragile and threads bigger, for big steam engines. The set over allows a better tool geometry to cut rather than scrape.
    Metric / UN Vs Whitworth/BSF - and not forgetting BA, buttress threads and....

    I've always used the set-over whether 29, 27, 23 or whatever suits the thread, the reasoning I was taught is that it ensures the carriage always has the cutting force applied consistently in the same direction, pre-loading the leadscrew/halfnuts to take out any backlash all the way through the threading train - and it's a good way to pick up threads when you've removed the job from the chuck, e.g. for trial fittings you can't bring the other part to (first example to pop up, internally metric threaded steering head nut for a motorbike without taking the forks out).

    As mentioned earlier by others, I leave the halfnuts engaged and do the demented-octopus-sending-semaphore jig:

    cross-slide quick retract at the same time as clutch lever from slow to brake (stopping the carriage travel);
    motor lever into reverse;
    clutch lever to fast and carriage back to the beginning five times as fast as the cut;
    lever to brake to stop carriage;
    motor lever into forward, cross slide return to battery and put the next cut on with the top slide;
    clutch lever from brake to slow to set the carriage moving;
    and repeat until...

    when threading - simpler than it sounds and it works, for me anyway, and becomes ingrained in muscle memory after a while...

    Dave H. (the other one)

    Leave a comment:


  • jdedmon91
    replied
    I leave mine at 29 degrees, but manny years ago I was just taught that way. If my memory serves me correctly that is so you didn’t have to rotate the compound for threading


    Sent from my iPhone using Tapatalk

    Leave a comment:


  • danlb
    replied
    Originally posted by old mart View Post
    I have just thought of a slight problem with the 29.5 degree compound slide angle used for 60 degree threads. This 29.5 degree angle is anticlockwise from the axis of the cross slide, right? So as lathe compound slides are normally marked zero when they are parallel to the lathe axis, the actual figure should be 60.5 degrees rotated clockwise.
    The problem I have is the scales on my own 7 X 12 and the Smart & Brown only reach 45 degrees. I would have to have a close look at the S & B to see if there is a way of adding another zero mark.
    This is quite correct. Some lathes are have the compass parallel at zero, others have it perpendicular. Either way, the idea is to have the trailing edge of the cutter just a touch off from being parallel to the movement of the compound so that it does not drag as you cut the thread.

    The solution to your particular problem is to set the compound using a compass and then make a second index mark.

    Dan

    Leave a comment:


  • Baz
    replied
    Originally posted by old mart View Post
    Any suggestions relating to post #38 would be appreciated.
    Set top slide to required angle using protractor, sine bar, calculation etc and just scratch a line where the scale should have had a mark. If you are happy to use the plunge technique at least sometimes then the setting of the 29.5 degrees does not have to be that precise. The actual thread angle should be set by the tool bit.
    30/60 is fine for Americans to do UNC and Metric but us Brits have to contend with Whitworth too. Split the difference?
    I think the concept of the set over was started when lathes and tools were more fragile and threads bigger, for big steam engines. The set over allows a better tool geometry to cut rather than scrape.

    Leave a comment:


  • old mart
    replied
    Any suggestions relating to post #38 would be appreciated.

    Leave a comment:


  • thaiguzzi
    replied
    Originally posted by Rich Carlstedt View Post
    Lathe Top Slide
    Having it at an angle ( ie 29.5 Degrees) does several things.
    1. faster setup for single point threading.
    2. No interference with Cross-Slide Handle or Handwheel
    3. No interference with Tail Stock
    4. No interference with a Steady Rest or a Follow Rest ( in most cases)
    5. Angle allows "tweaking" a cut on a Diameter OR a Face , particularly when re-picking up a parting groove.

    That's what I was taught and have always used .

    6. And don't forget breaking an ID or OD edge (chamfer) when finishing a cut, without changing tools !
    Rich

    PS. Setting up a machine to efficiently handle the tasks at hand is the smart thing to do.
    Many employers have machine "Protocols " that really are dumb and set up by those not aware of maximum tool effectiveness
    Setups MUST be safe ! After that you want it to be effective in performance with no wasted time.
    Example, you have the chuck key at the drill press, not in a drawer !
    Good post.
    1. Correct. But then tool post is generally moved square, sod's law i have the wrong angle threading tool in a holder. Change some levers on the box. So when screwcutting, it's not a wham bam thank you m'am instant procedure anyway. Always a couple of minutes involved in set up.
    2-3. Top slide on my lathe does not interfere with either.
    4. Possibly yes.
    5. Yes, top slide set parallel to the ways only tweaks face, not OD.
    6. Have chamfer tools in holders for the QCTP. 5 second change.

    Leave a comment:


  • old mart
    replied
    I have just thought of a slight problem with the 29.5 degree compound slide angle used for 60 degree threads. This 29.5 degree angle is anticlockwise from the axis of the cross slide, right? So as lathe compound slides are normally marked zero when they are parallel to the lathe axis, the actual figure should be 60.5 degrees rotated clockwise.
    The problem I have is the scales on my own 7 X 12 and the Smart & Brown only reach 45 degrees. I would have to have a close look at the S & B to see if there is a way of adding another zero mark.

    Leave a comment:


  • Rich Carlstedt
    replied
    Lathe Top Slide
    Having it at an angle ( ie 29.5 Degrees) does several things.
    1. faster setup for single point threading.
    2. No interference with Cross-Slide Handle or Handwheel
    3. No interference with Tail Stock
    4. No interference with a Steady Rest or a Follow Rest ( in most cases)
    5. Angle allows "tweaking" a cut on a Diameter OR a Face , particularly when re-picking up a parting groove.

    That's what I was taught and have always used .

    6. And don't forget breaking an ID or OD edge (chamfer) when finishing a cut, without changing tools !
    Rich

    PS. Setting up a machine to efficiently handle the tasks at hand is the smart thing to do.
    Many employers have machine "Protocols " that really are dumb and set up by those not aware of maximum tool effectiveness
    Setups MUST be safe ! After that you want it to be effective in performance with no wasted time.
    Example, you have the chuck key at the drill press, not in a drawer !
    Last edited by Rich Carlstedt; 03-18-2018, 03:11 AM.

    Leave a comment:


  • old mart
    replied
    I really need to practice more with threading on the Smart & Brown, up till now it has always been a nightmare with the huge amount of backlash, but things are about to improve somewhat. We have been replacing shafts and bushes in the apron, and even before the apron is refitted (next Wednesday, hopefully) the slop has been reduced. There was typically 30 degrees of backlash in the saddle traversing wheel before the rack gear started to move, now 3 degrees. The leadscrew clamping nut threads are worn enough to allow 0.015" end float, this will be fixed when I produce a new 1" by 6tpi acme nut which will be cut into three segments, one to use and two spares, another 140 years worth.

    I usually make use of the wheel on my Mitutoyo digital Vernier, the high quality construction keeps the jaws dead parallel, unlike the Chinese versions. When using it to measure a diameter of work in the lathe, I often use both hands and hold the jaws clamped with my fingers, while zeroing the readout.
    Last edited by old mart; 03-17-2018, 06:12 PM.

    Leave a comment:


  • Mark Rand
    replied
    As I discovered yesterday, with a Hardinge HLV:- If you have the top slide parallel to the cross slide, you can't use the cross slide feed, because the handle clashes with the top slide .

    Leave a comment:


  • MattiJ
    replied
    Originally posted by thaiguzzi View Post
    So top slide, sorry compound, placement is more of a comfort, routine, happy it's out of the way thing. Nothing to do with rigidity.
    Forgot, another old turner's fave, was leaving the top slide 5.7 degrees off parallel. A thou on the dial was a tenth of a thou cut. Or, put another way, 5 thou on the dial was a half a thou cut. Sharp tool recq'd...
    I use my own "metrificated" version of 2.2 degrees so that 1 thou on the dial becomes 1 micrometer cut. Even my tools are not that sharp but a 5 micrometer cut is more reasonable.

    Leave a comment:


  • thaiguzzi
    replied
    So top slide, sorry compound, placement is more of a comfort, routine, happy it's out of the way thing. Nothing to do with rigidity.
    Forgot, another old turner's fave, was leaving the top slide 5.7 degrees off parallel. A thou on the dial was a tenth of a thou cut. Or, put another way, 5 thou on the dial was a half a thou cut. Sharp tool recq'd...

    Leave a comment:


  • J Tiers
    replied
    The problem with the roller that is not easily curable by any reasonable degree of "care", is that the measuring point and the point at which the "measuring force" is applied, are wildly and drastically misaligned. The result is a form of Abbe error.

    It is made worse by the usual spring "gib" that restrains the moving part from tilting. Some looseness is necessary for the thing to move, and then it can tilt, which throws off the measurement. If you "baby" it sufficiently, you can do better. And, calipers are not used for accurate measurements, so that helps too. (except by some who claimed to interpolate between the marks with a magnifier).

    How much is the error? Who can say without checking? It is different for each caliper, and each measurement. The gibs may or may not be adjusted the same on any two calipers, and the point at which the part contacts the jaws is different for every measurement, so the force needed to make an error appear is different. All that can be said is that it exists, and contributes to the other issues existing with calipers (aka "guessing sticks" to some).

    Of course, if you use your fingers to close the jaws, applying force directly in line with the part, you eliminate much of the total error, and essentially all of it that is from misaligned force.

    The error does not exist, for instance, in a micrometer. There is no misalignment, and so that cause of errors is eliminated.

    Leave a comment:

Working...
X