Suggested method of machinng

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charkmandler
Posts: 14
Joined: Sat Apr 29, 2017 8:11 pm

Re: Suggested method of machinng

Post by charkmandler » Tue Jan 01, 2019 6:05 pm

A late reply due to family illness. In the end I was unable to get any rectangular bar stock of the specified material that wouldn't have needed a fair bit of milling to size and deemed that it would be faster to make from circular material. I used a 3mm profiling tool that had a small radius (can't remember spec) on each side and turned as one and then parted off. I then made a jig to hold the parts to mill off each side 10 at a time. The surface finish doesn't look great but were actually pretty smooth when running a nail across the surface - I am pleased as EN8 isn't the nicest to turn. All turned to within a .0005" tolerance with only one wasted due to brain fade. Photo is of the parts bagged up (parts still have milling swart on them) as somehow I lost the other photos.
I did have an odd occurrence in the middle of the run. For the first 9 parts the DRO remained accurate with the turned diameter, but for the next 6 parts each diameter was about .006" more than the reading and the last cut. This then took time with more measuring / checking. I changed the tool insert after this happened with 3 parts and still got the same moving reading for the next 3. After this had been happening for 6 parts I got consistent readings and diameters (just as for the first 9) for the remainder of the run.
Nothing changed through the whole run and I used the same tool throughout so did not remove it from the holder - odd.
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pete
Posts: 1696
Joined: Tue Feb 10, 2009 6:04 am

Re: Suggested method of machinng

Post by pete » Tue Jan 01, 2019 8:04 pm

If ALL the lathes assembly was unquestionably tight from the carriage to the tool tip during that run of parts then I'd suspect a loose component holding your dro scale or reader head if you were seeing inconsistent readings and results. If it's a decent dro proven in the past it can be trusted then somethings obviously not quite correct.

charkmandler
Posts: 14
Joined: Sat Apr 29, 2017 8:11 pm

Re: Suggested method of machinng

Post by charkmandler » Fri Jan 04, 2019 2:52 pm

DRO is good and continues to be. I'm really at a loss as I have not had the problem since and have been on the lookout. Hopefully, just one of those things.

Harold_V
Posts: 17690
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Suggested method of machinng

Post by Harold_V » Fri Jan 04, 2019 4:53 pm

This experience is one where one would have been wise to compare the DRO against the screw. It would reveal whether it was the DRO, or not.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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