Spherical/ball grind on end of 3/8" carbon fiber rod 3

[mtnaire67]

I have a need to grind a full spherical/ ball radius on the end of a 12" long 3/8" dia carbon fiber rod. The issue is that I need to build an automated feed grinding machine that can produce finished ground rods at a rate of 1 every 8-10 seconds. This is for mass production. My current machine is hopper fed, and the rods are picked up and rotated around a notched disc and fed through a grinding wheel with a half profile set at a slight angle to achieve a full ball radius. The problem is it is terribly difficult to maintain consistency. I'm looking for tips or ideas that I could incorporate into a completely new design. This kind of production grinding is hard to find information on. Any help or ideas would be greatly appreciated.

 

[Compositepro]

How accurate does the shape need to be? What is your consistency problem? Your current method sounds okay so maybe you just need to improve your fixturing. I assume you are flood cooling with water.

 

[unclesyd]

To get a consistent shape and finish you are going to have to rotate and arc the rod on against an abrasive disk or wheel.
There are a lot of similar machines as shown in the link below that would make a good pattern for a production machine. There might be a machine that will do the job.

http://www.tubefinishing.com/LE_rod_bar_chamfer_machine.html

 

[mtnaire67]

The shape just needs to be spherical ball end. No real tolerances that are real important or unobtainable. The main problem in consistency is in over grinding on sides as the part rotates around. That is, if you look at the profile and rotate the part there is an up and down kind of wavy look around where the profile ends on the straight shaft, if that makes sense. And yes, we are flood cooling. I looked at the LE machine. The belts rotate around a fixed shaft. It may be difficult for long, fast production but a good way of looking at it.

 

[Compositepro]

I was envisioning a grinding wheel where the outside diameter had a "U"-groove and the rods were fed-in perpendicular to the wheel axis. This would tend to self-center the rods. With the arrangement in your picture it seems that the handling of the rods becomes more complex and requires that the rods be very precisely rotated about their centers. Any wobble or slop will change the shape.

 

[unclesyd]

You might want to look at this too from Severance for rod end
forming.

http://severanc.brinkster.net/pdf/Rod End Forming Cutters.pdf

 

[Compositepro]

I've used diamond grit grinders similar to unclesyd's link and was initially going to suggest that. However, they are more suited for handheld work and low volume. The problem is that the surface speed of the cutter is zero in the center so it really doesn't cut there. This tends self regulate the depth of cut which can be good. Rocking the rod side-to-side will provide a little bit of grinding action at the rod tip. You may notice that such cutters are not a full semicircle to allow for this rocking.