Re: [CAD_CAM_EDM_DRO] Renishaw, digitizers

Jon,

I'm working on a controller that can use a MaxNC type G61 (G31)
instruction, and save the point read. My initial thought is to define a
scan path with Gcode, and output the points. Later designs could use
envelope and pitch parms directly. Yes, I'd like to see your design! I
don't have a clear idea how the Heim works or what it is.

The counter sink holes you suggest for the balls is a good solution for
my "hemispherical" hole requirements.

Any software I write will initially be "Sherline sized", with either
4-phase or step/dir outputs using MaxNC pinout. With a little help,
other machines can be accommodated.

Alan KM6VV


Jon Anderson wrote:

>
> Something to keep in mind when digitizing. If you plan to scale the part
> down, any errors in the scanning will be reduced by the scale factor. I
> have done some very small (microscpic) detail work with a Deckel
> pantograph at 10:1 reduction. It's amazing how sloppy (relatively
> speaking) one can get with the pattern and not be able to see the errors
> in the finished part.
>
> I like the concept of the Heim joint idea Pete suggested.
> Since the one project I plan to setup scanning for will involve
> conductive parts, I came up with this:
>
> A rod is fitted to the Heim joint with clearance so that it just will
> slide freely. Snap ring on the upper side retains rod. Top end of rod is
> fitted with ball or polished full radius.
> Heim joint is fixed inside end of tube. On top of the ball is a plug
> closely fitted to the ID of the tube and spring loaded against the ball
> with the ball sitting in a shallow tapered socket. A straight axial load
> will allow the rod to slide up through the Heim joint, returned by
> spring pressure. Radial deflections are allowed by the Heim joint, the
> ball being returned to center by the tapered socket. At the measuring
> end of the probe, different styli could be threaded in place, matching
> the contour of the cutter that ultimately will be used to reproduce the
> part. If the end product is to be reduced, the probe tip profile is
> increased by the inverse of the ratio. By matching probe profile to
> cutter profile, one does not need to worry about generating a true
> surface from the point cloud.
>
> Since I only need electrical contact, I simply insulate the part being
> probed. One side of a circuit is connected to the probe, the other to
> the part being digitized. What this allows is a fast approach until
> electrical contact is made, reversal until circuit breaks + some small
> amount, then approach for the second signal at a much slower rate.
> I'm interested in a fair amount of speed with this. My Ducati engine is
> out in the shed, but from memory, the clutch side case would require
> probably an 8x10 envelope to digitize. Working on .020 centers, this is
> 200,000 data points. If it takes 5 seconds per point, this would be 277
> hours! Of course, I would not need to scan the entire case at this
> resolution, but digitizing for fine resolution can be time consuming.
>
> I spoke to a fellow at Ahha recently about using Ahha to digitize. It
> would be fairly easy to write a program that could do all this, with
> variable fields to define the envelope being scanned, probing increment,
> etc. However there is no function available to write axis locations to
> disk. However, it turns out they do have something tucked away that
> would allow this with a second PC. It would interface to the Ahha card
> and monitor steps sent out for position (assuming of course that no
> steps are lost anywhere), and writing axis positions to a file.
> He says they are playing with it, and might consider bringing it to
> market. No cost estimate yet.
>
> Outside of this, I'm not aware of any programs for digitizing on PC
> based controls except for MaxNC, and if one goes that route, one would
> probably just use his probe anyway. If anyone here is planning on
> writing a PC based digitizing routine, I'd like to hear what you think
> of this approach. If it looks workable, I'd be happy to draw up the
> probe as I envision it.
> I've thought this out to answer my needs, which is to digitize
> motorcycle parts to produce scaled miniatures, probably not workable for
> someone wanting to digitize non-metallic parts.
>
> Jon