New Machine Build- Drum Shell - Rotary Indexer?

[EStegall]

Hi Guys,
Anyone have ideas for a rotary indexer addition to a small 3 axis machine? (Excitech 2'x3' table) My hands are crapping out on me, a side-effect of MS. I'd like to drill drum shells for hardware and edges. I am thinking of attaching a second, horizontal spindle to the Z axis, using the indexer off the end of the table (Y axis.)

Thoughts?

Thanks Guys.

[CarveOne]

In my mind's eye I'm seeing something resembling a large Lazy Susan style plate that is driven from a vertically mounted stepper motor via a timing belt from off to one side of the rotating plate. The whole affair is assembled on a single rectangle or square base plate that is removable from the CNC machine table top. The rotating plate could have clamps of some sort on it that allows mounting various size drum shells. It would need to be designed to be as low to the table as practical. If the rotating plate is made on the CNC machine it could have teeth around the edge of it (like clock gears) and the teeth would need to closely match the timing belt teeth.

The motor could also be mounted so that the timing belt pulley faces downward and is aligned with another timing pulley that is under the rotating table.

I think it is possible to build one to do this job, but it will be some work to get the drum shells centered and well supported for the drilling operations.

You may want to build some trial mechanisms from plywood or MDF and the largest Lazy Susan base you can find that will do the job. Some sort of home brew radially mounted skate bearing support may be less wobbly.

CarveOne

[EStegall]

Good thinking there. Really good. I have one shell-holding fixture figured out, It's kind of a jamb chuck setup. Would it be a nightmare figuring out the degree rotation of the "susan?" - The indexer came with a tail stock, a jaw chuck mounted to the planetary gear head, then the stepper. As far as centering, I made a Z-zero touch plate. I was thinking of using it for identifying center of the indexer.

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More and more I'm thinking of the whole works being fixed horizontally along the short axis/end of the router, and using the tail stock. What if the shell fixture actually had a "cap" that centered on the tail stock? Kind of a captured shell, thing. I'd need to fab risers for the indexer to clear the diameter, but that's accomplished easily enough.

Thank you for your ideas here. I appreciate it more than you know.

[CarveOne]

What I was thinking of would not use an indexer at all, and the drum shell would be mounted with an open end facing upward. That was due to your mention of a horizontal spindle. I took "spindle" to be a CNC spindle motor with the drill bit in it mounted horizontally on the Z axis to locate the drill vertically on the side of the drum shell.

Using a stepper motor to turn a Lazy Susan plate would give 200 steps per revolution (1.8 degrees per step). Using micro-stepping would give finer steps for more resolution.

So, it looks like you already have the CNC indexer and tail stock and will mount the shells so that they would roll like a Ferris wheel. Consider making a round plate that mounts onto the indexer chuck, and a similar round plate for the other end of the shell. Both plates would have a channel or V groove that the shell fits into. The plate at the tail stock would have a ball bearing at the center of the plate that the tail stock center fits into. This bearing would be pressed into a pocket in the plate. (I assume that the tail-stock does not have a live center that rotates.) The point of the tail stock would fit into the center of the ball bearing's hub and support the shell while it is rotating, and the indexer will drive the shell while drilling operations are done. Tail stock pressure is to be snug enough to keep the shell held firmly in place between the two rotating round plates.

You could have specific plate sets for every diameter of drum shell you need to drill, or you could also have multiple channels or V grooves for different size shells in one set of plates. I think the V grooves will automatically center the shells better.

If the tail stock has a live center (has a rotating point) then a brass or aluminum insert with a machined tapered pocket could be substituted for the ball bearing in the tail stock plate.

The Z zero setter would need a stationary metal reference plate that could be used for setting the Z height to the desired position for drilling. The gantry (Y axis?) would move the Z assembly to each end of the shell for drilling , and the indexer then rolls the shell to the next radial position.

Is this anything like you are thinking?

CarveOne

[EStegall]

Love the idea of using one plate with several radii v grooves. Excellent.
I'm still going with your orientation, with the shell facing upward; only keeping the indexer off the table itself. So the plate fixture would still be hanging over the table space.

Yes, horizontal spindle attached to Z. So the Z axis would position from edge to edge of the shell (top to bottom,) the X axis would control depth of cut.

Now I just have to get it configured...

[CarveOne]

Originally Posted by EStegall Love the idea of using one plate with several radii v grooves. Excellent. I'm still going with your orientation, with the shell facing upward; only keeping the indexer off the table itself. So the plate fixture would still be hanging over the table space. Yes, horizontal spindle attached to Z. So the Z axis would position from edge to edge of the shell (top to bottom,) the X axis would control depth of cut. Now I just have to get it configured...

Very good. Let's see some photos of the results when you have it built. Maybe even a video. An arrangement like this could be useful for other things besides drum shells.

One other thing, if your normal router mount has a detachable plate maybe you could design a new mount that allows removing and remounting the same router/spindle 90 degrees from vertical to horizontal on the one Z assembly. That way you don't use up gantry travel with a second Z assembly.

CarveOne

[EStegall]

Now making the spindle "flip" 90 deg is a fantastic idea...

Wow!

E