Re: [CAD_CAM_EDM_DRO] Re: CNC division

I believe there is an EASY way to provide the number of turns you require to
achive 11, 13, 366 degrees, etc.

If your using an A axis set up using a motor driving the input shaft
(normally a hand crank) on a divinding head, the procedure would be as
follows:

Assuming a 90:1 ratio on the dividing head, the crank will index 4 degrees
for each full revolution of the crank. So, to arive at 11 degrees motion,
all you need to do is advance the input shaft 2.75 full turns. For 13
degrees rotate the shaft 3.25 degrees. For 366 degrees, rotation is 10.5
turns (9 turns for 360 degree plus 1.5 turns for the extra 6 degrees).
Using this method of indexing, you can achieve virtually any rotation you
need.

You should be able to set up a looping program fairly easily using this
technique. Also, if you set up the program to always turn in one direction,
you won't need to worry about backlash.

Smoke
-----Original Message-----
From: Ian Wright <Ian@...>
To: CAD_CAM_EDM_DRO@yahoogroups.com <CAD_CAM_EDM_DRO@yahoogroups.com>
Date: Friday, April 06, 2001 2:35 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: CNC division

>----- Original Message -----
>From: <rab@...>
>
>
>> I'd have thought that using any ratio of wormwheel and / or pulleys
>> that will divide up cleanly into 360 should be a good start, so that
>> a specified number of steps will give you exactly one whole degree.
>> I'm testing a 120 tooth wormwheel with a 200 step motor to turn a
>
>Hi,
>
>This is really the point I was making - most divisions DON'T divide cleanly
>into 360. Wheel counts which I often have to divide include 7, 11, 13, 17,
>54 and 366, none of which divide cleanly into 360. I appreciate that, by
>drawing the wheel out in a CAD program, it should be possible to generate
>g-code which minimises errors but I actually want to do something a little
>more complicated than the norm and was hoping there might be a way to
>separate the division from the cutting. I'll explain - What I am wanting to
>achieve is cutting unusual, specialised tooth forms by generating them. If
>you can imagine a disk with 13 maps of Italy sticking out from the edge

this

>will give some idea of the shape of a watch escape wheel. To cut such a
>wheel normally involves buying or making 4 or 5 special cutters at a cost

of

>around 40UKP each - not very realistic for a one-off. So, I reckon that,
>with a bit of clever maths, it should be possible to persuade a little cnc
>mill to generate the form by coordinated movements of the A, Z and Y axes
>while running the thin, round edged slitting saw cutter back and forth with
>the X axis. I haven't yet found any software which would seem able to
>produce the g-code for this from a dxf file (unless you can suggest one)

and

>so am almost resolved to coding it manually, in which case, having a method
>of producing a 'loop' to do the tooth shape and a separate 'loop' to index
>from one tooth to the next would seen to be easier than coding the whole

lot

>as one long file.
>
>Perhaps I am wrong, I have been before - it was Tuesday I
>think.....196x..... ;O) <g> Any sugestions or observations would be very
>welcome.
>Thanks to everyone else who has replied on this thread.
>
>Ian
>--
>Ian W. Wright
>Sheffield UK
>www.iw63.freeserve.co.uk
>
>
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