Velociraptor Project

[krfitz]

I bought MillWizard with our PRT96 2 1/2 years ago, and this is the first time I have used it. This foam male plug of a Velociraptor will be going to a museum in Pensecola, Florida. They are going to make female molds and reproduce the little critters en masse. Here is the link: http://www.oriondogsupply.com/dinosaur.htm
I am working on the head/neck/body/tail. The left side is done, and as noted in the gallery, I have to redo the right side. After that, I will machine all four legs out of foam as well. I will keep you posted on progress...

-Kevin Fitz-Gerald

[paco]

How do you design it? How have you been modeling it? And with witch software? Or was it a digitilizing?

I'll keep looking your project Kevin!

[krfitz]

Paco,
I downloaded the 3D model at TurboSquid.com. It was a 3ds format file. Next, I modified it with Rhino3D (www.rhino3d.com (http://www.rhino3d.com)) by removing teeth and tongue, and slicing it in half lengthwise to make left and right halves. Then I sliced off the legs. I then imported the model into MillWizard and generated the toolpath.

-Kevin

[paco]

I'm trying now RHINO. And I plan to visit TurboSquid.com

Thanks! 8-)

[Mayo]

Nice work Kevin.
Do you think you could have saved a considerable amount of cutting time if you had created an outline of maybe 2" all around the part to be machined, and only machined to within that 2" margin rather than spending all that cutting time cutting away non essential areas?

The 2" margin (or even 1" for that matter) would still allow placement of hold down screws if you needed them.

uhhm, are you packing it in... styrofoam for shipping? I noticed you had an abundance of packing material on the floor... :-)

[krfitz]

Mayo,

Glad somebody out there is thinking! Since this is the first time I have used MillWizard, I'm not familiar enough with it to create an outline. The only problem I see with an outline is that the router housing and the bottom of the z axis would be continually smashing into the uncut area outside the outline. I would think that this would make it lose steps, but I could be wrong.

I am going to have a special crate built to ship it. I wouldn't wish that foam dust on my worst enemy. Helpful Styrofoam cutting hint; in addition to the obvious need for a dust mask, wear googles that totally seal your eyes.

[gerald_d]

"The only problem I see with an outline is that the router housing and the bottom of the z axis would be continually smashing into the uncut area outside the outline."

We are not shy to use a hammer and chisel to remove this "uncut area" in large chunks (mostly while the SB is running elsewhere). This type of job has made us wonder if a chainsaw would be a useful addition to our toolbox.........

[gerald_d]

Were you not tempted to hack away all the areas that were only going to produce dust when you got here?:



2659

[robtown]

An electric chainsaw would be a great addition to the toolset there Gerald.

[Brady Watson]

Kevin,
If you are going to hack away the extra foam, the easiest ways are to either use a hot knife, score and snap or a Dozuki saw....or just chuck in your spoilboard bit and knock the high spots down.

The only thing that you really have to watch for is that the collet doesn't smack into the foam and move it. Other than that, you really have little chance of losing steps as a result of biting off too much in foam under 5lb density. I think I have lost steps once cutting foam at 3IPS. The router will hog through it at 9000 RPM with a 1/2" bit or a 1/8" bit with no apparent difference. Make sure that you are running the router at the lowest speed possible. There is no advantage to running it faster on a PRT through foam. It just creates more dust...remember the chipload formula. I get nice curled chips when cutting foam and only a small percentage of dust that naturally clings to the machine statically.

Another thing you might want to try is using thinner slices of foam. The biggest 1/2" ballnose that you are going to fit under the gantry with about 1/4" max safe pull-up is 3" cuting length on a 6" long bit. Make sure you set the safe Z pull-up in MillWizard so that it doesn't top out on the Z, and consequently lose your Z-zero.

-Brady

[krfitz]

I did think of removing some material before the bit got to it, but I was very unsure of what would appear where, so I pretty much left stuff alone until about the last pass. I was smart enough to use the slowest router speed though.

I have a very thick spoil board, and the longest bit I can use for this project is 4" long. I even had to do some customizing of the Z-zero routine to get it to work, like changing the pullup to 1/16". I also used 1mm as the safe z to avoid losing z at the top.

When I rerun the right side, I am going to use a much faster feed speed, and I am going to keep a sharp, long-bladed knife handy for excess material removal. Must be very careful to keep the X-Y force on the foam very small while manually cutting so as not to move the material relative to the table. I like the idea of a hot knife...hmmmm...maybe use my paint stripping gun to heat the blade? That should work...

[Brady Watson]

Kevin,
Your machine may be different than mine as far as losing steps go. I had to adjust ramping on mine when rastering at a high rate of speed. I had one file that would lose steps in the same spot every time at 3IPS, in mahogany. I slowed the speed down to 2,1 and it was fine. I normally run foam at 2.5 to 3 IPS with no problems.

Just make sure the bit's flutes are long enough to get everything in one pass. If it isn't, it will gouge the foam at the top of the part because only the shank will be touching at that part.

I'm not sure if you do a roughing pass on it or not. That would help out to clear out the big chunks and reduce cutting force. THere is an option in MW to put a border around the file. If you use this, it will help clear out the high spots as well. Use the largest end mill you can for the rough pass. If you only have a ballnose, tell MW that it is an end mill. MW takes forever to rough out if you tell it is a ballnose.

-Brady

[krfitz]

OK, I found the border option in MW. Please explain to me exactly what this does? Another MW question: when you run a finishing pass, does it only cut the area of the model itself, or does it also "cut" those areas that have nothing there?

[Brady Watson]

Kevin,
In the MW Manual "The border added is set to the last value you used, or the radius of the largest tool you have specified, whichever is the larger of the two, to ensure that you can machine around the sides of your object. You are able to change this value to zero if you wish."

Unfortunately, you are going to have areas where it is just cutting the flat area using MW. I think that there are options to just mill the 3D part in other programs like VisualMill and ArtCam. What I do is set up multiple toolpaths on one sheet of foam and position them as close as I can to one another. I either overlap the dead flat areas in Rhino with my STL or 3DS files or just eyeball it when defining my 0,0 on the foam to save material.

-Brady