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Home Forum General General LinuxCNC Questions Using image-to-gcode - tool diameter problem

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TOPIC: Using image-to-gcode - tool diameter problem

Re:Using image-to-gcode - tool diameter problem 21 Apr 2012 02:05 #19416

  • grey1beard
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Reinforced by coffee and toast, I think I now have an explanation of my problem.

First, the Corel program let me generate a greyscale map of what amounts to a Z axis only view of my model. This is a series of filled ellipses, going from white in the centre to black outside.
If the "blend" that Corel performs is made with no "acceleration", the result is a linear step size from each ellipse to the next, so the profile seen from the side would be a straight slope.
Having chosen a high acceleration to the blend, the resulting profile is a truncated bell curve, which is what I'm aiming for.

When the saved .gif file is opened by Axis, it requires a set of parameters to be input, and it then generates a display of the resulting tool path.

Two things have now occurred.

The first is that the tool path doesn't allow the tool profile( generated from tool diameter and tip shape input as above) to cut into the shape being generated. I've no idea how it does this at present, but just accept that it does !
This means, in my case, that if the surface being generated has a curve of smaller radius than the tool, which I suspect may be occurring near the bottom of the bell curve, the path will avoid this conflict.

The second is that the path shown on the Axis window appears to show the shape of the object.
It doesn't.
The image of the tool path looks very much like the finished object, but it will be "fatter" around the X-Y plane by an amount equal to the tool diameter.

I think these two effects merge together, and have given me the present problem.

As my judgement of the shape is purely an aesthetic one at this stage, because there is no reference grid available as a background, I have been taken in by the similarity of the tool path to the shape I'm trying to produce.

It seems to me now that the only course is to cast some wax, and get cutting.

This in turn now makes me wonder about the choice of "alternating" path when cutting wax.
Will it be liable to melt when the tool is cutting in the "wrong" direction ?

Ho hum. :unsure:
Last Edit: 21 Apr 2012 02:09 by grey1beard.
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Re:Using image-to-gcode - tool diameter problem 21 Apr 2012 03:30 #19417

  • cncbasher
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i presume your trying to produce in 3d , you would probably be better with a 3d drawing and then processing the stl file into gcode ...

which wax are you using ? , i tend to use ball end slot mills with wax , or in general slot mills , i use trycut wax

Dave
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Re:Using image-to-gcode - tool diameter problem 21 Apr 2012 06:23 #19420

  • grey1beard
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Hi Dave.
I'm using Corel as I have been using it for about 15 years, and feel a bit long in the tooth to start over !
As for wax, I've got about 20lbs paraffin wax with additives from days gone by when I used to make my own oval picture frame moulds.
I built a hand driven Archimedean oval lathe chuck about 2ft by 3ft, and used fixed profile tools to scrape the wax into the shape I needed !
So once again, I'd prefer to stick with what I'm familiar with.
It has occurred to me to do a first test with MDF anyway, but another problem has surfaced(sorry).
My ball nose mill hasn't got enough cutting length, so I recoded with a roughing pass.
Ho hum again.
John

Edit Just googled trycut wax - looks very nice - might well get some. Thanks for the idea
Last Edit: 21 Apr 2012 06:35 by grey1beard.
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Re:Using image-to-gcode - tool diameter problem 21 Apr 2012 07:20 #19422

  • cncbasher
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ha yes i know exactly what you mean , i dont have any problem with the wax melting as this stuff is quite stable ,
and used for lost wax casting etc , redundant prototypes get remelted into new blocks again using home made aluminium moulds
i use a deep fat fryer to melt the wax .
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Re:Using image-to-gcode - tool diameter problem 21 Apr 2012 07:23 #19423

  • grey1beard
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cncbasher wrote:
i use a deep fat fryer to melt the wax .

But what do chips taste like ?

:laugh:
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