Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Frank1959 on January 18, 2015, 02:03:23 PM
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I mill big sculptural pieces of polystyrene foam on a home-built machine that is 4000mm long, by 2000mm wide, with a Z movement of 900mm, sometimes flat and sometimes using an A axis. An example of one of these A-axis pieces could be a human head. I fix the block for the head to the A-axis chuck using a flat cut at the neck, and if the piece is long, I give it some support at the top of the head, in a tail stock. I use DESKPROTO for G codes, wonderful for the job, working from .stl files from a DAVID SCANNER.
Doing things this way generates an AWFUL lot of waste, polystyrene dust that’s very bulky and difficult to dispose of ;-(.
There are companies that offer polystyrene milling machines combined with hot-wire cutters. They economize on both waste matter generated and on milling time by first roughing out the form (human head for example) using hotwire cutting, before milling, then classical A-axis milling to produce the finished article. A wonderful idea…..
I´m trying to figure out how MACH Lathe could be used to control a hotwire function, to cut profiles along the X axis with the A axis stationary, and once done, continue in the normal rotary milling way, to achieve basically the same.
How I see it is this: Somehow I generate let´s say 4 sets of G-codes for the four outlines of a human head: one for the (front) neck- chin-lips-nose-eyes-forehead-top of head, one for (side) neck-jaw-right ear-side of head-top of head , another for back of neck-back of head-top of head, and lastly one for (other side) neck-jaw-left ear-side of head-top of head: in a word, four silhouettes or profiles.
My question is, Could I then program MACH Lathe to “cut” each of these profiles, travelling along the X axis, having set up a hot wire cutter, but with the A axis stationary, not rotating, just to get a profile? I would leave maybe a 10mm skin in this roughing stage.
I would then do this another 3 (or even 7 more times to get a roughed-out octagon ) times, spinning my A axis 90 degrees each time (or even 45º) and thus removing almost all surplus material before milling to finish. Hope I´ve explained myself ; )
Anyone got any ideas? I´m getting fairly familiar to MACH Mill, but Mach Lathe is unknown territory for me so far.
Any input grateful, many thanks as ever,
Frank Norton.
www.franknorton.com
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I would not use TURN/Lathe mode as it sis too limiting to what you want to do.
Use a simple 4 axis Mill setup where A is the rotary axis similar to a lathe. Make Z The hotwire segment to do the rough cutting. Make a V shaped head to hold the hotwire rigid in Z. Then cut the rough profile from the top, left to right on the X axis rotate to the next segment cut,rotate,cut,etc,etc, When you have it roughed out then switch to a router bit and finish it as a normal 3D 4th axis application.
The trick will be getting the CAM portion correct for the roughout cuts . A hotwire CAM should do the job.
Just a thought, (;-) TP
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Thanks (at last!) BR for your suggestions, but the problem with that approach I think is that depending on the shape of the figure you´re doing i.e if it has a hollow area between two high areas, you run the risk of cutting material from these high areas because the formal milling aproach only "sees" the height of the material at Y=0, whereas the hotwire cuts everything left and right of this point...difficult to explain I fear....Im about to post a fairly detailed explanation from another approach: edit the g codes so as to only go on the highest Z value at any given X axis point.
Frank.
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That was the point of using a HOTWIRE cam it KNOWS where the low spots are compared to the high spots (;-) WITH any straight hotwire you will have the same issue even if you use your Gcode file. as it has no idea what is left or right of the centerline it is cutting on.
You would cut the front then back then left then right and then the diagnals (corners) to rough it. THen Router the rest. It only has to get close.
OR cut it the radial mode around A with the wire running parralell to A . just cut to the largest diameter of the part.
Just a thought,
(;-) TP
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Hi again!
The problem is, no Hot Wire cutting software I have checked is capable of working from .stl or .obj or other 3D files;-(. Do you know of one that can? Dxf is fine for "simple" shapes, lettering, profiles etc, but not for a human head, for example;-(.
In my other post of yesterday (http://www.machsupport.com/forum/index.php/topic,29935.0.html) I suggest what might be a workaround solution; use existing .stl-to-g-code software and "extract" the necessary X and Z coordinates, at say 0, 45, 90, 135 degrees, etc. Then combine hot wire and mill at those angles, using rotary A axis.
There is a video here of the way I need the software to rough out the foam.....
see http://www.hotwiredirect.com/
Thanks again for all your input.
Frank.
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Mach3 cannot do that it is just a CNC controller it has no Cad/CAM capability.
You could get close by rotating to A0.00 then follow X Z plus say .500" then rotate to 45 deg and repeat,repeat util you are done.
I have an idea send me one of your small files.
(;-) TP
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Maybe I explained myself badly..I dont want MACH to do that, I have it installed and working fine as a controller.
Heres an .stl file as requested...curious about your idea ; )
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sorrrry, for some reason I cant load the stl file...
Ive sent it to your email address ; )
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I am pretty sure you can use deskproto to create an extremely large diameter tool and subsequently use it to create gcode for an XY/Z-A mill.. You can then run the gcode in a standard hotwire XY/Z-A machine to take 80% of your material away before standard milling.
We've done something similar during the prototyping of our 5-axes Foamcube. (http://foamcuttingcube.com (http://foamcuttingcube.com)). If you want to we can look into it again. It's been a while.
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thanks guys! I really like your machine!
I tried what you suggest in Deskproto, but it didn’t work ; -((
I ended up using a Contour Only routine, this worked fine, thanks to an idea from TP (BR549).
I have tried INKSCAPE for generating g codes for HotWire cutting, but have achieved poor results. The piece is usually cut in half, as Ink doesn’t allow me to choose where I want the cutting to start. It usually chooses a node on the vector far away from origin X0Y0, so cuts the piece in half just to get there before starting ; - ((. Of course, it doesnt "know" its cutting, cause it "thinks>" its a milling routine with a Z axis. Any ideas??
Is there a preferred setting in Ink that works good for Hotwire cutting ? I use it for a plotter, and it works fine, but the plotter has a Z axis and it goes down to starting drawing anywhere on the line.
Thanks in advance and congrats with your machine!
Frank.
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We've had a lot of issue's too with "move" lines cutting up our foam. The solution is rather simple and annoying.
First off - our foamcube software actually shows the "move" lines in blue so we know ahead of time if our DXF will cause problems. Usually rotating the piece (if possible) is a quick solution.
Now the real problem is that the software actually does exactly what it is supposed to do. It moves from 0,0,0,0 to the first node in your .DXF file. Most people don't even realize there is a start and end node in a .DXF file but in inkscape they can be visuallised. Our blog post explains this in detail , hope this helps :
http://foamcuttingcube.com/prevent-move-cut-destroying-work-dxf-starting-point/ (http://foamcuttingcube.com/prevent-move-cut-destroying-work-dxf-starting-point/)
regards,
Pete
(http://foamcuttingcube.com/wp-content/uploads/2017/06/dxf-startnode-6.jpg)
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Understood, thanks Pete! I will be recommending your machine here in Spain. Rgrds, Frank