G0768 workpiece finish issue

T

TDuff

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Hello again everyone. I have been playing around with my recently acquired (used) G0768 and find that I cannot get any kind of decent surface finish on aluminum or steel regardless of feeds or speeds. By this I mean the surface of the work piece ends up looking like a finely threaded surface - not smooth at all despite traversing the compound VERY slowly. My uneducated suspicion is that the compound slide assembly/carriage is probably not rigid enough although I can imagine that a loose spindle could also be a potential problem area, but that seems good with no apparent play. Mmy suspicion is with the carriage assembly/slide assembly. Is there any good way to trouble shoot this before I simply start disassembling things? I have worked with tightening gibs and cross slide lead screw nuts but I end up with slides too stiff to operate when I attempt this. I have not found anything on-line to guide me on this model. Any suggestions?

As an aside, the tail stock operation was really stiff and "non-friendly" so I tore it apart and found the quill was very slightly bent. Bought a replacement, put it all back together, and it works like butter. So it seems like there is potential for the rest of the machine. Please let me know if my expectations are too high for this machine.

Thanks for any input!

Terry
 
try rounded tooling.
too sharp of a tip or a non-existent radii , will cut a thread form into the work
a rounded tool should produce a better surface finish
 
Yes I agree with Ulmadoc; you say nothing about cutting tools that you are using, that is likely the root of the problem.
 
Thanks for the suggestion. I went ahead and changed over to a cutter with about a .030" radius tip and of course it is much improved, but still has grooves one can see and feel. Much shinier finish though. Forgot to mention in the original post that this is not the case for a facing cut, even with the smaller rad cutter tip, which is a Grizzly indexable carbide tip cutter (set G5639). I'll see if I can get some pictures posted for reference.

Thanks,

Terry
 
A slower feed rate when finishing, and use of a cutting oil like TapMagic may help, and also a touch with a bastard cut single cut file and emery cloth will give you a nice finish; filing in the lathe is normal practice and used for final fit and finish.
 
TDuff said:
Thanks for the suggestion. I went ahead and changed over to a cutter with about a .030" radius tip and of course it is much improved, but still has grooves one can see and feel.
Click to expand...

Feed < tip_radius / 3
 
Thanks for the Feed info. I have the gears set up for the finest feed, which is .0037" per rev.
 
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