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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Mini-chuck repair
Hi,
Thanks everybody for you responses at my topic "Cupertino, CA - local lathe owner for small help?". I got lot of valuable information, I also got the invitation to use the lathe (thanks, skuke). Most important thing that I understood that what I wanted to do to fix this chuck was absolutely wrong. Nice article by brownsharp gave me some ideas what I have to do (yes, I also consulted with my brother who owns a machine shop - unfortunately 6000 miles away). Today I fixed the chuck by myself. There is what I did: Central hole has been bored already too big. So I removed jaws, made some pattern with 60 degree angle and filed all the jaws a little - so the tip width became only 1/16". My chuck thread is able to move those shortened jaws all the way forward so I recovered the ability to hold small parts. There is no reason to do precise filing as jaw's tip angle is not too important. Now when I am able to bring all the jaws as close as 3/32" I put the chuck on to the spindle (spindle TIR is 0.0005") and used the 1/4 drill rod as the probe. I indicated at three points where jaws contact the probe. It is better to reset the indicator at the highest point and then get the negative readings for other two points. Negative reading means that jaw is going too far and has to be shortened. I do not have granite/steel plate so I used sharpening stone (new, Japan made, big one). I build the prismatic 90 degree construction using the machinist square as the guide and pressed jaw against the stone by fingers. Electronic caliper has been very helpful - zero it on original jaw and then shorten the jaw by half of the indicator reading. Do it for two (or one) jaws and rebuild the chuck. Put it onto the spindle and repeat the process untill result is good. In my case I got too much to cut and needed additional filing for tip to keep tip narrow. So after 5 or 6 iterations I got TIR 0.0015" and could not move further due to quality of the thread. So my toy still be the toy but at least it is the decent toy now! I could use the collet for small sizes with TIR 0.0005" and for bigger parts current precision is enough. Anyway device saddle and crosslide lack the rigidity and precision but it means that I have something to do with it! There is the picture of the chuck fixed: http://s89568048.onlinehome.us/images/P1.JPG and it's original state: http://s89568048.onlinehome.us/images/044.JPG Thanks, Arcady |
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