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Radial slot cutting

Maplehead

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#1
Hi All
Using a ball nose end mill, I need to make some radial cuts in a hemisphere.
Think of the slots as the five arms of a star. They eminate from the top of the hemisphere and then go down the outter edge to the bottom of the hemisphere. The ball nose is a 1/8" CD and the depth of cut will be 1/8".
What I am making is a guitar knob to be afixed to a solid shaft. So I'll start by drilling a shaft hole in the brass rod, cutting off the 3/4" brass to be rounded, placing this brass "slug" on a shaft in the lathe, cutting the hemisphere and then drilling a side hole into the shaft hole for a set screw.
With all that I should be able to take this hemisphere knob and afix it to my rotary table.
How do I cut my grooves from there?
 

Wreck™Wreck

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#2
Are you making hundreds of this part, a dozen or just 1? The quantity required will determine the fastest and least expensive method of producing them/it.

If only several parts then your approach is sound, for a single part the rotary table is overkill, I would just walk off the hole centers with the hand dials.

Good Luck
 

Maplehead

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#3
Two knobs per guitar. I'm not pumping out guitars right now as I have a full time job elsewhere. I have rotary table for other uses.
Can you explain your last sentence please?
 

RandyWilson

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#6
The only thought I have is to use the ARC function of a DRO, after switching the Y and Z scales. This way the DRO's X-Y arc would really be in the X-Z plane.
 

DAT510

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#7
It sounds like you want to cut the equivalent to the Longitude lines of a globe, running North - South?

They only way I can think of doing it on a Manual Mill is to mount a rotary table in the horizontal position. Some how mount your "Ball" perpendicular to the Axis of the Rotary Table, but centered on the axis. Then come in with the Ball End mill (Also centered in the axis of the Rotary Table and the centerline of you Ball Knob, such that the Ball endmill would cut a constant depth groove/slot in the Ball Knob, as you rotate the rotary table.
 

Maplehead

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#8
Hi DAT
Yes, just like the longitude lines.
I'll have to give your idea some thought. Mine was almost exactly like this but I figured the rotary table would need to be mounted on the vertical, (it's side).
 

DAT510

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#9
To make sure we are on the same page, by Horizontal, I mean the axis of rotation for the Rotary Table would be parallel to the Mill Table.
 

Maplehead

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#10
Hi DAT
I think we are saying the same thing then. Put another way, the rotary table is perpendicular to the mill table.
Now to figure out the rest.
 

easymike29

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#11
Unless I am not understanding the question I would clamp the knob in a Spindex mounted horizontally on a horizontal Rotary table. The Spindex would of course need to be mounted at the correct distance from the center of the Rotab.
Rotate the Rotab through the appropriate 90 degree arc, index. repeat.

Gene
 

Maplehead

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#12
I made a jig for my rotary grooved knobs. Here's the first to come out of it. It's not perfect as I have yet to at the groove end stops to the jig, so I just eyeballed how long they should be.
 

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