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motorworks
04-24-2003, 07:51 PM
Good Day
I had to make several bushings over the past weekend and most had a figure 8 pattern inside them.
I tried to copy by setting the lathe at 1/2 thread per inch but could not get the exact pattern.
Any ideas
I did see this lathe on ebay that does just that.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=1272&item=2526053163&rd=1
thanks
e

Dave Opincarne
04-24-2003, 08:19 PM
The only thing I can think of would be some kind of cam, incramental cutting with a small rotary cuter held in the toolpost or just freehanding it in with a small die grinder. How precise do these oil groves need to be anyway?

Spin Doctor
04-24-2003, 08:36 PM
We've got one at work. Built around 1890 to 1900. The saddle is conected to the operating mechanism by an arm. Where the arm ataches to the is an adjustable post set-up. think an adjustable stroke device similar to a shaper. In addition the spindle rotation to saddle osilation is controled by a set of gears that can be changed to different ratios to derive different "twists" or pattens. There is also a dog clutch on the spindle that allows for mirroring the pattern inside the bore. The dog clutch can also be disengaged to allow the machine to act as a slotter. And God that is one ugly paint job. I didn't know Earl Schibe did machines http://bbs.homeshopmachinist.net//rolleyes.gif

Weston Bye
04-24-2003, 09:45 PM
Watched a german fellow cut a figure 8 grease groove inside a bushing with a hammer and chisel! Not quite as pretty as a machine-cut job, but just as effective.

Wes

Thrud
04-24-2003, 11:30 PM
motorworks:

This is your chance at "home Dentistry"! I use a flexshaft with a carbide or HSS burr - does not take long at all. The groves do not need to be too deep. To be honest, if you use good synthetic lubes and greases they are rarely needed even in extreme pressure applications.

CCWKen
04-25-2003, 12:48 AM
I made one from an old push drill. I have it mounted on a plate (drilling end up) with a homemade cutter in place of the chuck. I made a couple of supports/sleves that fit the bushings I had to do. I set it up under a shop press. Press the cutter through the bushing and Vola!
I'm sure there's some $30,000 machine that will do it perfectly, but mine worked on what I had to do. If I had to do this more often, I would improve on the design.

Forgot to mention, The drill is reversable so flip the switch and press again. You should only have to cut .002-.003 groves. The bushings I did were 1 1/2 and 1 1/4 and only .090 wall.

[This message has been edited by CCWKen (edited 04-25-2003).]

darryl
04-25-2003, 01:14 AM
Some years back, I made a pair of bushings from brass, for an experimental flywheel shaft. I didn't realize at the time that bronze bushings were what they are, oil impregnated, made to live a long life, with minimal maintenance. Anyway, I happened to spin one of the bushings, which, by the way, had two grooves lightly filed in them, and lo and behold, it just sat there spinning for a good ten secs or so. Then it suddenly seemed to catch a friction and stopped. I spun it again, same thing. Apparently, the grooves allowed air to be hydrodynamically sucked into the gap, creating a cushion that the bushing spun on. Further thinking about this led me to believe that the grooves should not have sharp edges to them, but instead be blended into the curvature of the bearing bore so a maximum ammount of lube can be drawn along with the rotating shaft, giving maximum support to the shaft. The figure eight pattern should be trying to keep the lube flowing toward the center of the bushing, from where there is no escape, probably giving better strength to the oil film.

Dr. Rob
04-25-2003, 02:09 AM
A-ha! Is this the same mechanism that cuts an eternity screw (XXX)if applied to a shaft?

BC21OSH
04-26-2003, 09:37 PM
The guys in the shop at work had to replace large bronze bushings in the punch presses and would cut the figure eight with a small Dumore die grinder with a ball end cutter. They would then relieve the sharp edges of the groove slightly.

Bernard