While waiting, I went into the shop wanting to find out what's the run-out of the lathe spindle and how much is added to that run-out when the ER32 collet chuck is mounted. Proxxon indicated the run-out of the spindle bore to be 0.005mm on their website without chuck mounted. My setup to measure the run-out may be flawed but this is what I got:
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| I wish it was parallex error I'm registering but it is not. I'm clocking 0.015mm run-out, 3 times more of what Proxxon advertised, on the 0.01mm mike. |
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| Adding the ER32 collet chuck "enhanced" the number to almost 0.03mm. |
Anyone?
5 comments:
Hi Wong, I assume that the lathe was cold. Run it for ten or twenty minutes and then test again. There is always some slack in a cold machine.
Run out of the machine, collets, and chucks have the same effect, whatever is chucked in them will have run out on its outside surface until you make a cleanup cut on it. From then on it is just as with the three jaw chuck,all your work will be concentric until you remove and re-chuck your part.
When you use collets it is usually a second operation where the out side has been turned to finish size and now is the reference. In this case the run out of the system would affect your results. If your center drilled and bored the part the bore would be off center by the amount of the run out.
I hope that is clear, if not just ask and I will try again.
GeneK
Thanks for your input. The lathe has not been started for the past few days. I'll try warming it up and do the test again.
The intention for using the collet chuck is to allow the parts to be re-chucked. At this stage, i often removed the part from the 3-jaw chuck only to realize that I've to put it back for another ops. Got to improve on that. Also the collet chuck allows me to go closer to the chuck without the fear of hitting chuck jaws.
Wong, I have a friend who likes to say that a four jaw chuck is a necessity and a three jaw chuck is a luxury. I gave up on three jaw chucks a long time ago, with the four jaw I can re-chuck and dial back in pretty close.
geneK
Gene,
Is run-out of 0.03mm bad enough to screw things up? I'm planning to turn down a short section of 1/2" diameter silver steel rod for 5/16 BSF thread to make a 1/2 center for the set-over center tool. A small section in the middle (between the 60-degree point and the 5/16 BSF thread is show as 1/2" on the plan.
Regards,
Wong
Wong, that is about one fourth the thickness of a sheet of paper.
In relation to the taper center you are making, any run out of the point of the center can only affect the out come by either raising or lowering that end of the part in the case of the final position being offset in the vertical plane. If the offset happens to be in the horizontal plane, the error will be adjusted out as you align the taper with the offset screws on the adapter.
One thing to think about is that "drill rod" is usually centerless ground and is not perfectly round. It tend to have 3 or 5 lobes due to the grinding process. Normally I would turn from a larger rod the 1/2" and the 5/16" thread part in one set up. Then when turning the part around to form the point I would have only the run out of the collet to deal with.
GeneK
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