| Art Project |
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| Model Making |
| Written by Derek Goodwin |
 Art is the basis of Industrial Design, it is as important as technology in communicating design intent and the ability to imagine “What might be”
Kristrun Hjartar imagined eating utensils that would bridge the gap between Eastern and Western Tradition. Story We used Mastercam to write the programs and machined the utensils on a Fadal CNC machining center.
The first step was to create a material block and prep it so that it could be bolted down to a sub plate. Whenever you are making a blended part with a two sided flip, it is much more accurate to clamp to a plate, with locating pins than to hold it in a vise.
 Four clearance holes in the corners were used to bolt down the material and two .250 holes served as locators with ¼” dowel pins.
We used the silhouette boundary chook to create containment boundaries around each component, the boundaries allow for cutter containment within designated areas.
View silhouette boundary video Next we created surface tabs to help hold the part in the material block while we machine out the rest of the part. surface tabs are small areas of surface geometry, placed so that the cutting tool skips over that area and doesn't completely cut out the entire part until later. View surface tab video We were now ready to apply toolpaths, The first step was to apply a series of surface rough cuts using a ¼” ball end mill, we cut each component separately using the containment boundary and included the surface tabs in the geometry selection, so that the tool skipped over the tabs and didn't cut that area. View Surface Rough Pocket video
Once the material was roughed down half way, it was time to apply finish cuts. It’s often true that there is not just one finishing strategy that will get you to the desired result, so experimentation is required.
A surface finish contour toolpath will do a nice job on the near vertical walls, however there was a lot of excess material left over from the roughing pass so we added a semi finishing pass with a larger step down, followed by a final contour finish pass with a 1/8” ball end mill a tighter tolerance and smaller step down.
The problem with finish contour cuts is that they leave a poor surface finish in areas where the geometry is close to horizontal so we added parallel cuts and controlled them with cut depths & boundaries to have them cut in just the areas that we needed.
View Surface Finish Parallel video  Before flipping the part for the final op, we took advantage of the part being captured in the rectangular block, to stand it up in a vise to do the logo work on the end.  We were now ready to flip the part and add the toolpaths to the opposite side to finish the part, however even with the surface tabs connecting the parts to the material block, once we remove the material from the other side, there would be a lot of vibration on the part, which could cause it to break out of the block pre-maturely or cause a poor surface finish.
To solve this problem, we added “Bondo” metal filler to the machined side. Once the bondo dried it created a cradle for the work pieces, and tied them into the material block until we were ready to break the pieces out.
We wiped a very thin layer of Vaseline onto the part surface before applying the Bondo, this made it easier to remove the bondo from the part later, it helps to wipe the Vaseline off with alcohol & a clean towel in a few strategic locations to add gripping power.
Caution! The part will stick to the bondo, but not with enough holding force to machine the part held with bondo only. You must have some tabs or some other work holding method in place. Skim off any extra bondo that might get in the way of proper locating.
 We then ran the parts from the opposite side, using similar toolpaths, with some minor adjustments to cut depths, notice in the final verify that the part is still connected to the material by the tabs, and although you don't see it in the verification, it is still seated in the Bondo
 The final machining procedure was to remove the surface tabs to break the part out ofthe material block and of course, a little elbow grease to polish the parts. Skim Surface Tabs If you would like to receive our Newsletter via email, with our latest articles and tips, please register on our homepage, if you would like access to our full educational database please subscribe; one low fee full access. Thanks    |
Comments (1)
tutorial
1
Friday, 17 October 2008 14:51
Tom Hemphill
Good tutorial very informative Always good to learn new methods
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