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DFMiller
12-17-2010, 05:22 PM
I changed out the bearings on my Colt (Taiwanese) lathe.
It made a huge difference. I just cut a test piece and taper is 0.0015" per inch instead of the 0.010" I was getting before.
I also did some fine tuning on the spindle on the small bearing so I had a nice sliding fit. The shaft was interference fit. I am now able to adjust them and get some heating from the bearings. I will fine tune it. I might be able to snug them up a bit more.
Now I can look at ensuring lathe is level and if headstock is perfectly aligned. I did a quick check and the headstock might be pointed off a touch.
Looking for suggestions on how the best way to align a headstock? What I did was take a piece from my tap holder which is MT2 to straight set up a dial then traversed the feed. I measured a slight 0.001" miss-alignment over a couple of inches. It looks like my headstock is bolted with 4 bolts to the bed and has a setscrew to dial in the adjustment.
Thanks for all the suggestions on my original post.
Special thanks to Sir John for his offline pointers.
Dave

KEJR
12-17-2010, 05:54 PM
First level the lathe bed so that there is no "twist" to the bed. While the lathe beds seem rigid they are prone to twisitng on their own weight. This is one reason the behemoth monarch 10EEs are so nice is that the whole base is a rigid cast iron structure. There are many articles on there and other places so I won't get into it. The reason you must do this is that a twisted lathe bed can appear to be a misaligned headstock. You'll probably have to borrow a precision toolmaker level from someone.

Get a straight section of ground stock Check it with V blocks on a surface plate for straightness), maybe 8-10 inch long and indicate it in both at the chuck (first) and at the end of the bar (by lightly tapping with a brass block, etc). Do this by a stationary indicator and a rotating the chuck by hand. Don't turn on the lathe, a piece hanging out this far is probably prone to whipping!

Now your bar is aligned to the axis of rotation of the headstock. Check your test bar by lightly placing a DTI on it within 0.005" or so and have it ride with the carriage. I'd record what the reading was for every 0.5" or so. This will allow you to plot the runout in a spreadsheet program or something which will allow you to average out any dips or low spots on the lathe. If the headstock were out of alignment considerably I would expect to see a fairly straight line.

I'm not an expert, and there may be better ways, but this is what I'd try. Just make sure to start with a straight bar.

I was going to recommend turning between centers, but this will mask a problem with the heastock angle error since your tailstock will influence the alignment of the bar alot.

KEJR

lakeside53
12-17-2010, 09:00 PM
Don't go for perfection with your adjustment in the first few hours. My 14x40 has a more complex spindle bearing aseembly, but also has a break-in of (IIRC) 250 hours.. and not to exceed 1200rpm until so (max 2500).