rotary table issue

[tatlerParticipant @tatler]

help

I am trying to cut the spokes for a 1 gauge Green arrow driving wheels.

the wheel size is (old money values sorry) 2.530″ OD ,18 spokes ( so thats 20 degrees on the table) to finish at 0.055″ at the rim to 0.077″ at the hub.

At a loss on how to correctly machine the angle.

everything is centred and i can get the correct number of spaces but the angle has me stumped.

 

joe

[Clive FosterParticipant @clivefoster55965]

Basically you offset the rotary table centre relative to the cutter path to get the spoke width and tweak the actual angle setting to get the taper.

So using round numbers and assuming the cutter is of zero diameter to make it easier to see what’s going on. Think laser cutter I guess. If the spokes were parallel and 0.100″ wide you’d offset the RT centre by 0.050″ to one side and go round cutting one side of the 18 spokes. Move it over 0.100″ so the RT centre is 0.050″ offset the other way and cut the other side of the spoke.

As the spokes are tapered set the offset for the wide end and adjust the angle on the RT so the line of cut is deeper on the narrow end giving the desired taper.

In the real world you have to add a further offset of half the cutter diameter to get the cut line in the right place.

If your trigonometry and geometric visualisation is less than wonderful this is the sort of thing that is likely to net you a whisky bottle size hangover headache without the pleasure of emptying the bottle first.

Playing with CAD makes it all much easier.

Good idea to mock things up on paper with pencil or slender felt tip pen / sharpie in the spindle and a suitable backing board in the RT to support the paper. Draw out something simple, four spokes are plenty, and try to trace over it. When the penny drops after 3 or 4 goes you will wonder what the problem was. But until it does …

The trigonometry involved is fairly straightforward. I imagine Jason or one of the other CAD jockeys can easily show you that. My trig is well up to such things but I found getting the visualisation straight for the moves needed first time through tricky.

Clive

[Andrew CrowParticipant @andrewcrow91475]

The problem you have is that although your rotary table can achieve the spaces, your milling machine needs to have a universal table ie. one that can be set to the angle you require so that the longitudinal movement is at the required angle to the cutter. It can be achieved by calculating the angular offset required so that in your case you centre the rotary table the move the y axis by 11 thou plus .0385(half spoke thickness at the hub) to cut one side of the spoke then cut the other 17. After that reposition for the other side and repeat.

Hope that makes sense.

Andy

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