Re: Cam making....

Well thanks everyone for the excellent advice, what a great group!
Summarising there is a technique for reverse engineering existing
cams;
Rotate in 5 degree intervals, measure with a dti and tabulate then
input to CAD as a series of lines
A technique for working from a hand drawn cam;
Import a scan of the drawing on top of a template made up of radial
lines at degree intervals using OSNAP intersection to find the points
To create the cam outline it is recommended to use arcs wherever
possible then use polylines to fill the gaps.
To smooth the polylines use the fit command.
The ideal method though is to draw the cam directly in CAD.

My next step is to get the first sample cam drawing from my colleague
and see what we are starting with, this is going to take a few days
though as he is away for a while. I will also investigate CV mode, I
assume this is CV mode in Mach 3. I have a bit of an issue with my
DXF conversions of JPEGs coming out as 3D polylines, I need to
explore converting them to 2D polylines before I can use the fit
command.

Just out of interest, the plan is to cast the cams in wax then
assemble them in the wax at the appropriate angles before committing
to casting. These are for JAP V twins where the inlet and exhaust
cams share the same shaft.

Dissappointed I didn't see the CNC cam grinder in Ebay, I would have
put in a bid!

I will give you an update when I get a real drawing to work with.

Thanks again

Ian

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Alan KM6VV <KM6VV@...> wrote:
>
> Hi Ian,
>
> Just a thought, if you have the CAD program, draw the cam
directly!
> What do the curved surfaces look like? Are some of them simple
parts of
> circles? Are there simple tangents between the arcs? All simple
enough
> to draw. Even if you have to approximate arcs with curve fitting;
I'd
> think you'd be able to very accurately draw the shape of the cam.
After
> that, I'd suggest using a rotary table and milling the outline of
the
> cam as a rotated surface.
>
> Cams for the model V-8s and other small gas models rely on a cam
> following fixture to grind cams. they use a grinding wheel in the
last
> steps to finish off the hardened cam.
>
> I'd suggest checking with the I.C. lists, or BAEM. I'm no expert
on cams!
>
> Alan KM6VV
>
>
> xj5373 wrote:
>
> >Firstly, many thanks for all the help with the ELCB problem.
> >
> >My miller spends a lot of its time making patterns for lost wax
> >casting parts for obsolete engines mainly associated with Morgan
> >Three Wheelers and now and then the odd exotic motorbike.
> >Latest idea is to make cams. A colleague is planning to draw the
cams
> >5 times life size on paper (probably a bit of magic goes into this
> >step....) so step one is to scan the drawing into the PC and get a
> >JPG. I then want to convert to a CAD file so have come across
IMG2CAD
> >which allows me to convert the scan to a DXF file. This then is
> >loaded into my copy of Autocad LT. The cam shape is a 3D polyline
and
> >if you zoom in it is pretty bumpy. The plan then was to scale the
> >drawing back to normal size then feed the DXF file into Mach3 to
> >generate the G code. A dry run indicates that all this works but I
> >would like to smooth the polyline in Autocad LT before sending it
to
> >Mach3.
> >My knowledge of Autocad is limited at best and I have had a poke
> >about looking for a command that will allow me to smooth the
polyline
> >but so far no luck.
> >Does anyone have any advice on smoothing my scanned polyline cam
> >profile in LT or even a better idea on how to go about this?
> >Thanks
> >
> >Ian
> >
> >
>