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| David Jupp:
--- Quote from: PekkaNF on May 08, 2012, 03:11:21 AM ---Three prongs/legs? Or a cunning plan to get all level and square? PekkaNF --- End quote --- Or turn the whole thing as a profiled disc on an axle (like toy gyroscope) - an infinite number of legs better than 3 ?? |
| BillTodd:
Yes, the cross-section view can be a bit misleading. It is, as David suggests, a disc with a torus around the edge. :) It might make a simple edge detector but, because to the non-linearity, it would be only be suitable to a fix sized probe I haven't abandoned the ball slide idea just yet; While sitting on the throne this morning, contemplating the weightier of matters of state, I started to wonder where the errors are creeping in... First up is to test the DTI. Then, just to see where the 50um/2thou" on the Z axis has gone, test the upper taper section with out the lower taper or ball in the way. At the moment, I cannot account for all the missing 80um/3thou" in the XY plane; The play in the vertical slide is << 1 thou" and by playing with it (pushing and pulling it ) the ball-slide has <10um according to the dial. |
| PekkaNF:
--- Quote from: David Jupp on May 08, 2012, 05:30:51 AM ---Or turn the whole thing as a profiled disc on an axle (like toy gyroscope) - an infinite number of legs better than 3 ?? --- End quote --- I think that accuracy needeed for that would be such that very few of us could reach it. On that front my only bet would me to use something massproduced part that has to to have that accuracy, like ball bearings and preloading them such way that clearances don't accumulate on measuring direction....which is ofcourse harder when there are many degrees of freedom on movement. I'm really tool-envy on that lathe. Nevertheless would it be possible to double check that the measurement method and/or device does not introduce it's own set of variables. Can you affix 3D indicator on the mill or something and test 3D indicator reading agains micrometer anvill movement and possibly to verify it with a micron dial gauge or such? Even better if there were no oilfilm anywhere (spidle/slides/you name it). PekkaNF |
| BillTodd:
--- Quote ---Nevertheless would it be possible to double check that the measurement method... Can you affix 3D indicator on the mill or something and test 3D indicator reading agains micrometer anvill movement --- End quote --- That's a good idea Pekka , and I have a 1/10000" micrometer head that would be ideal for it :) ATM the lathe is a convenient way to quickly test bits. I found a hour yesterday to test the DTI etc. The DTI is OK within a few microns (i.e. within readable limits) When I tested the Upper Taper alone. I discovered that there is a small difference (~15um) between one direction and the other. That is, going IN to zero on the DTI will give a different reading on the DRO to moving OUT to zero. I think this is caused by the motion of the ball in the right-angle hole and this maybe due to my use of a non-flat tip on the end of the DTI, so I'll have to make a flat tip and test it. I'm now fairly sure that the major cause of the other errors is the angle of the tapers: The upper taper shows a error of ~50um over 2mm (middle taper was cut at the same time so will have the same error) . The lower tape was cut in something of a hurry so is likely to be even worse! When I recover from this mystery back strain that has been giving me grief all day, I'll set up the top-slide with a sine bar and re-cut them. Bill |
| PekkaNF:
I am soo happy :D you are back on track :clap: It happens me all the time - I'm so absorbed with the problem in my hand that I overlook procedural complications. Once I spent some time trying to figure out where the error comes from. And I was using simple DTI! Long story short: Everything I tought being square was not square and the "balls" where so small that even a little offset from theoretical measurement axis introduced error....the object was straingt but my measurement wasn't. Spindles, bearings and slides never stop to amaze me. Move them and when you stop them they "sit". You can measure that, but they lift when you turn or mill. How on earth anything gets done with any predictability....I get massproduction, but one-offs! PekkaNF |
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