I machined a new adapter plate for a 5” diameter 4-Jaw chuck for use on my 7” swing lathe. The adapter was made from 0.75” thick by 6 “ diameter hot rolled steel plate custom cut and available through eBay Buy-It-Now. There were challenges with machining the adapter: 1) six inch diameter steel is at the outer limit of the lathe’s capacity and 3/4 horsepower; and 2) the steel plate was cut out with a plasma cutter which left a very hard slag crust; and 3) the wavy plasma cut edge produced an interrupted cutting surface. I used TiN coated carbide inserts of the TT222 style for my cutting tool. If I had to do it again, I would have started with a brazed carbide-tipped tool bit with a C5 grade to handle the interrupted cuts and switched to the carbide inserts. Getting through the slag when the lathe could only handle 0.005” depth of cut was difficult. I used the product Energy Release P011 Cutting and Tapping Fluid for this hard material and then switched to using Rapid Tap Heavy Duty Cutting Fluid. After removing the slag, the cutting was very easy and the “rough” cuts had almost mirror-like finishes as shown in the photos. I do not know the steel alloy except that it machines extremely well. The adapter spindle recess and chuck boss on opposite side were machined to within the 0.0005” limit of the lathe precision but I did this to allow taking the chuck on and off with the parts left in the chuck for other operations off the lathe. The adapter plate attaches to the lathe spindle with hardened M6X1 screws and the chuck is mounted into bottom taped holes using 5/16X18 bolts.
I had the same worry when I bought the Bison 4-jaw chuck in 1993 (you can see the "93" date stamp in one of the photos) and then kept it off this lathe due to concerns you mentioned. However, in the last few years I have seen many examples of the larger chucks on the 7" swing lathes and no mention of damaged bearings. However, the first time a spun the large chuck up to higher speeds I thought wow there is a lot of momentum and hence a large force release potential (in terms of my geophysics background). Thanks for your concern.
My biggest concern with bearings is knurling operations using conventional side knurlers rather than the scissor action type on these smaller lathes and unintended impact on alignment and bearings.
Ok! Yet it is better to observe clearances (dial indicator) over working hours to see if not to damage ..
Thanks Randy, but I think that will change for me in January and won't have to worry as much. I good friend of mine, who is the owner of large equipment fabrication shop (very large swing Mackintosh-Hemphill lathes, slant bed Mazaks, etc.) was surplusing several old pieces of equipment and offered me the smallest lathe in his shop. It is a 12" swing x 36" between centers gear-head gap bed lathe. That has to be my best Christmas present in many years. He will deliver it to me January. I am already putting together a wish list of improvements for the new addition. Best regards, Paul
Yes, I have been considering replacing the original bearings with taper roller bearings but have not done this. I have been reading up on the technique and watching YouTube on the subject. However, I keep procrastinating the re-work because of my previous lathe headstock/tailstock realignment work. A few years ago I used the RDM (Rollie's Dad's Method see MiniLathe Alignment) to align the headstock within +/- 0.001" at the end of a 10" precison ground test bar and then had to align the tailstock. It is well worth the extra effort and I image the same is true for the tapered roller bearings. I highly recommend doing the RDM alignment process for the smaller 7" swing import mini lathes.
By the way, the main reason I decided to mount the 4-jaw chuck on my lathe was for machining small parts to a model compound steam engine built from bar stock instead of castings. Attached is a photo from tonight showing the 4-jaw chuck in action while I am machining the low and high pressure cylinders support entablature. The plans for the this compound steam engine is from vol. 1 of "The Shop Wisdom of Rudy Kouhoupt". When finished the marine steam engine will weigh about five pounds and be approximately 6"Lx5"Hx4"W.
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