12X36 Lathe Machining Surface Improvements Using Anti-vibration Techniques

[Paul Jones]

I highly recommend trying these improvements if you are seeing a harmonic herringbone pattern in the machined finishes from your import 12X36 lathes. I have been able to eliminate the poor machined surfaces caused by motor vibration and did it for less than $20.

I have a 12" swing by 37" between centers geared-head gap bed lathe built in 1987 by Dar Sin Machinery Works, Ltd in Taiwan. It looks very similar in design to the newer Grizzly 4003 metal lathes. The Dar Sin is well made with extras like hand scraped surfaces on the cross slide and compound but the motor mount design needs improvement. My lathe has a Leeson 1.5HP 115 VAC 1740 RPM electric motor mounted to a hinged cast iron plate that is attached on the rear side of the lathe headstock. I always suspected the motor introduced the harmonic herringbone pattern on the machined parts while using the longitudinal or cross power feeds. I eliminated the majority herringbone pattern with homemade anti-vibration mounts (see Homemade Lathe Motor Mount Improvements ) and a Grizzly Power Twist 1/2-Inch V-Belt but this still had room for further improvement.

I found an even better way to achieve extremely smooth machined surfaces like I can machine with my 3" swing Unimat SL 1000 lathe. I recently purchased and installed four G1101046 Cylindrical Vibration Isolators (those with a stud and threaded hole for M8 x 1.25 bolts) from Zoro for $16 including shipping. I used the four anti-vibration mounts to isolate the motor vibration and also added three rubber washers (left over from a toilet tank repair kit) to further improve the vibration isolation on the back mounting to the headstock. See the attached photos.

The harmonic herringbone pattern has been totally eliminated on machined surfaces using 1018 Cold Rolled Steel as the test case. The 1018 CRS machined surfaces are excellent despite 1018 CRS having a machinability around 78%. As another experiment, the machined surfaces on 12L14 steel proved to be silky smooth and looks identical the machined surfaces achieved with my small Unimat SL 1000 lathe. I attribute the significant machined surfaces improvement to a combination of the Cylindrical Vibration Isolators motor mount isolation and the power twist drive belt. The only other future improvement would be using another three Cylindrical Vibration Isolators where the motor mount attaches to the headstock in replace of the three rubber washers (left over from a toilet tank repair kit).