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| Calculate thread pitch and feed rates... |
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| John Hill:
Hi John My first pass at the tables:- Longitudinal feed rates in MM with cog ratio 48:24 0.162 D2 SI 0.188 D4 SI 0.211 B5 SI 0.219 B1 SI 0.226 A4 SI 0.264 D5 SI 0.264 C1 SI 0.273 D1 SI 0.306 B3 SI 0.317 A5 SI 0.323 D2 SII 0.329 A1 SI 0.332 C4 SI 0.345 B2 SI 0.369 C3 SI 0.374 B4 SI 0.376 D4 SII 0.382 D3 SI 0.396 E5 SI 0.411 E1 SI 0.415 C2 SI 0.422 B5 SII 0.438 B1 SII 0.451 C5 SI 0.452 A4 SII 0.459 A3 SI 0.461 E4 SI 0.517 A2 SI 0.527 D5 SII 0.528 C1 SII 0.546 D1 SII 0.574 E3 SI 0.612 B3 SII 0.633 A5 SII 0.646 E2 SI 0.657 A1 SII 0.664 C4 SII 0.689 B2 SII 0.738 C3 SII 0.747 B4 SII 0.764 D3 SII 0.791 E5 SII 0.821 E1 SII 0.830 C2 SII 0.902 C5 SII 0.918 A3 SII 0.922 E4 SII 1.033 A2 SII 1.147 E3 SII 1.291 E2 SII I assume a practical thing would be to choose a dozen or so and put them on a reference card, please note I had to do a bit of interpolation and with rounding errors etc I expect some of these that appear very close are actually the same. |
| John Hill:
Now I am in a very grumpy mood as due to some error Excel changed all my calculated values to "#REF" when I saved the workshet... :( |
| John Hill:
John, re accuracy of the thread charts. I assume that is something that can only be determined by measuring the finished work? |
| bogstandard:
Thats right John. Cut 'em to 'by the book' size, then, if possible, try to find a commercial nut, or tap one myself (if I have a tap that size) and see if it fits ok. If it won't fit, that means you will have to make both the nut and bolt by single point threading, which defeats the object, as normally I do single point cutting to make a bolt to match say an old tapped hole. If you can get within a small part of a % on final pitch or TPI, you stand a good chance of it fitting anyway. But usually some of these cutting charts give such a large percentage error when the thread is cut, they will never fit the correct sized internal thread. That is when you need to start looking for non standard change gear sizes to get to where you need to be. John |
| John Hill:
Well John I suppose we can at least accept the screw cutting thread is accurate? I can think of ways of measuring the ratio between spindle and feed screw and if I get really interested I could fit a couple of micro switches or Hall effect sensors, one on the spindle and one on the feed screw and with a bit of software I could count the ratios and Excel could do the rest for us. If we think the feed screw is unreliable I could measure carriage travel against turns of the feed screw but that would require accurately measuring carriage travel over, say, 30cm. It wouldnt really be such a big job as once I have the first 25 ratios (A1..B5) the rest are software tasks including all the change gears you would care to imagine. Regarding the usefullness of the feed ratios, I agree with what you say but what annoyed me last evening was setting the parting tool going with the power feed then scratching my head and squinting at the chart trying to find which is the next fastert, combination. I think my initial table is worth it just for that especially if the close ratios are culled. Meanwhile, I am looking for a nice little brazing torch as everything I have is really too old and they wont fill that type of cylinder anymore. I need a bit of brazing for my gyroscope project. |
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