View Full Version : Contest submission--missed deadline

08-26-2000, 01:42 PM
This was my submission to the Vector contest, but
I missed the deadline (I called and was told it
had closed already). I didn't want all this
information to go to waste.

As for all the pictures, I am only linking the
last one. If there is enough request, I will
upload the rest.

Bruce Clark

My Shopbot is primarily used for signage and store displays for my family business. When talking to customers in the store, fishing always seems to make its way into the conversation--we live on an island after all. The conversation almost always works its way to sharks and do they "catch any" in Port Aransas.

In our store we sell a fair amount of shark teeth necklaces. We also have on display a couple of 5" Megaladon shark teeth and dried/cleaned shark jaws. These in themselves are always a great topic of conversation. Customers really like the display and it helps sell shark teeth necklaces.

So, this project was "born" after watching a program about Megaladon sharks, the largest of all prehistoric sharks, I got the idea for creating a LARGE tooth. The program mentioned that the largest Megaladon tooth ever found was only 7" tall. Now, a 7" tall tooth equals about a 50 foot shark. Another thing about prehistoric shark teeth is that they are dark gray or black (like fossilized wood). So it is easy to tell a prehistoric tooth from a "recently deceased" shark, which teeth are white to a cream color. Plus the top part--the root-- is a matte finish while the enamel is a glossy white color.

The wheels were turning in my head. All I had to do was beat a 7" tooth, make it "white" which would mean that JAWS was swimming somewhere off the beach of Port Aransas! All, I had to do was find the material and make a MONSTER tooth. My original idea was to make a tooth 24" tall. This would mean that there was a shark more than twice the size of the largest Blue Whale. Image swimming in the Gulf of Mexico (or the ocean of your choice) with a 200 foot long shark on the loose!

Well, reality set in. First off, there was not room in the case for a 24" tooth in the display case we have. Second, almost NOBODY would believe that there is really a 200 foot shark alive today. Even JAWS was not this big or even HALF this big. Second, I didn't have material large enough to make this tooth. It would have required over 4" thick material, extra long tooling, and MANY hours to cut. Time is not something that I have a lot of right now, so I had to make compromises.

My original plan was to digitize a Megaladon tooth from our store display. Then import that data into my CAM software. At that same time, I got an offer to beta test a new STL to G-code program called STLWork from IMService. [MillQuick was the BETA name for STLWork. You can find out more about STLWork at www.stlwork.com.] I like to try new programs and the fact that this one just happened to fit PERFECTLY with my project was a bonus.

So after watching the program on August 13th, I borrowed a 5 inch Megaladon tooth from the display case to digitize it on a Roland Picza 3D digitizer. That took approximately 22 hours. Looking back, I could have used a lower resolution to speed up the digitizing, but was afraid I would loose too much detail when I scaled the tooth up to my "original" 24 inch size.

So, the project really took off on the 15th. My original intention was to use Precision Board, which is a high density urethane that holds fine details very well and would have been an excellent candidate for this project, but my local plastic distributor does not keep this in stock so it would have to be ordered in and I would have to purchase a full sheet of material. Anyway, if you look into this material, be sitting down when then tell you how much a 2" thick 4' X 8' "board" of this material is. So, plan "B".

I had cut some letters out of blue insulation foam about a year back and had a sheet of it left, lying around somewhere. It turned out to be 2" thick and that was fine for this first project, though storage had not been too kind to the surface of the material. That did not matter as most, if not all of the surface would be machined away. So, my material had been selected.

Now, I needed the tools to cut my model. My router bit collection includes a .500" diameter ball end
cutter, but the bit only cuts on the ball end. This was not going to work very well for cutting 2" foam. A trip to my local tool crib had just the bit I needed. A 2 flute.500" ball end mill that had a cutting length of 1.375". [See Photo MVC-010F.JPG]. Initially I was going to use a separate roughing tool, but decided that this cutter would work fine for both roughing and finishing passes.

Next was actually making the tooth toolpath. Since STLWork is a beta program, there was the learning curve to over come. Second, since it is BETA software, there were a lot of little "bugs" or quirks that I had found the "hardway". I initially had problems with my models being "gouged" while "roughing" out most of the excess material. So, four teeth later, I had the correct "path" and was happy with the results. [See Photo MillQuick.jpg].

Now, STLWork is very similar in function MillWizard. Matter of fact, if I did not use STLWork, I would could have gotten the exact same results (and probably a lot quicker--that is the trade off with BETA software) with MillWizard. While I am at it, I want to commend IMService for providing me rapid fixes to problems I found in the BETA STLWork program. I would report a bug and would get a fix the next day. This rapid fixing made it so could continue to use this STLWork on this project.

As in life, there are compromises to be made. The compromise I made was between cutting time and hand finishing/sanding. I chose a quick machining time and a little more hand sanding in this setup. If I had to do it again, I would probably lean more towards less hand finishing time, as I have found the blue insulation foam, while VERY easy to sand and work with, is VERY gouge sensitive. I think the less handling of the foam the better until there is a good coating of paint or other sealer on it. The cutting time for this file was approximately 40 minutes. Sanding also took about 40 minutes.

As a suggestion for sanding this material is to drag the paper only. The foam is so soft that the paper backing can easily gouge the foam, making it a nightmare to sand. On this particular application, there was no flat surface, so I could not use a sanding block--I tried. The technique was to use a single finger applying pressure and drag the paper in one direction. I used 220 grit paper for sanding the bare foam.

The output of STLWork is G-code only right now. So a quick run though the G-code converter that Shopbot provided results in a perfect ShopBot file. I am told that STLWork will support the ShopBot language directly, but right now the emphasis was getting it "working" correctly before doing a lot of postprocessor work. I can understand their position.

A little bit about my machine before I go on. My ShopBot is a PR96. It has a steel table and was an original cable drive until it was upgraded to rack and pinion in 1999. Best thing I have ever done to my Shopbot. Made my router a completely different machine!

I added a homemade vacuum table to my router to assist in a specific job I was doing this past summer. It was cheap and it worked so well that I have not bothered to take it off yet. The vacuum table is a whole other project in itself. Needless to say, it works GREAT for holding down this Styrofoam insulation. The motor for the vacuum table is a common 5 gallon Shop-Vac. Now, the vacuum table is only 4 foot by 4 foot, so my sheet of Styrofoam insulation had to be cut down. One of those retractable snap-away "tile" knifes works great at getting through the 2" foam in a pass or two.

Once loaded onto the vacuum table and all other uncovered vacuum holes are covered up, it is time to set the toolbit depth. [See Photo MVC-001F.jpg]

I want to point out, cutting wood is one thing, but cutting this blue Styrofoam insulation is a mess in itself. Not only does it break down into its individual "cells" but is also clings to anything and EVERYTHING in the shop. Even if you have a 99% effective dust collector (don't think about
machining this without SOME sort of dust collector), I still recommend you wear a dust mask. The static electricity created by cutting this stuff makes it cling to everything from your computer to you.

I tried two different vacuum attachments to collet the "dust" being generated. Neither one worked very well and finally decided that I would wait outside (in August heat in South Texas) while it finished machining. Still, my shop has a layer of blue foam dust everywhere (and remember I am using a dust collector). Also, the rack and pinion gears especially need to cleaned after each job, as this blue "dust" stuff builds up quickly. So be warned.

As I mentioned before. I ended up cutting about 5 teeth total. These did not go to waste. I used the early "samples" to test different finishing techniques. The very first one was painted with Tempera white. While this was color was close to an actual shark tooth, it did a poor job of filling the open cells and hiding the blue color of the foam--the tooth has a blue tint to it.

To simulate the enamel, I used a Minwax "Polyacrylic" gloss finish that was sprayed on. This worked pretty well, but still not quite the look I wanted.

So, I went to my local "Home Labyrinth" hardware store to buy some exterior white latex paint. This time I chose a semi-gloss. The next tooth was painted with this by brush. Color was good, but a little "yellow" tint would have made it "spot" on. The problem was with the brush marks left by the paintbrush.

The third tooth was sprayed with thinned down latex paint. This has the reverse problem of not being thick enough to fill the pours and make the surface smooth. So I compromised on the forth and final tooth that I was able to finish.

The forth one was first painted with a brush, making sure that a good layer was put down to fill the pours and smooth the surface. After it dried, I then sanded down the brush marks as best I could then sprayed a final coat. This worked the best.

Now, one thing that I did before the painting was to make "under cuts" with my razor knife to simulate the curvature of a tooth. These curvatures give the illusion that the underside is also "carved" out. This undercut was also painted white, but not as much attention was given to getting all the brush marks removed.

As mentioned above, I needed a glossy "enamel" look for the tooth. While the Polyacrylic was OK, I saw something that I thought would work better. While in a Michael's looking for a plaque to mount my tooth on--time was getting tight and I did not have any material on hand to make this plaque out of as it would have been REALLY easy to do on my ShopBot--I saw a thick spray on glaze by PLAID.

I tried this on the first latex painted tooth and it gave the look I wanted, but it attacked the foam (the label said it works on plastic--go figure). This was the same results I had with urethane. My solution was to paint the entire tooth with the latex paint to seal off the foam. So, my final tooth was painted on the back side with a brush.

So, three layers of spray glaze on the tooth gave the look I was after. Now, all I had to do was sand the areas where the spray had landed but I did not intend to leave glazed, such as the root. Since this glaze layer was thick, I ended up using a 180 grit paper to get the glaze down to the latex paint. It also left the latex paint with a real nice matte finish, which was the look I was after.

As I mentioned above, the backing plaque was premade. All I had to do was sand it down, stain it and put a satin spar urethane finish on it. This plaque was a very inexpensive pine. I choose a red stain, thinking this was good for a shark tooth background (red=blood). I used Bartley's Pennsylvania Cherry. This is a gel based stain that give a more even stain on softwoods such as pine. I used spar urethane to protect the finish from sunlight and UV rays because we use a LOT of fluorescent lights in the store and they can fade just about anything, thus I used exterior latex paint and spar urethane.

The tooth was bonded to the plaque after it after the urethane dried. I used an all-purpose white glue. This was to make sure it did not attack the foam and dry clear.

That about wraps it up. [See MVC-007F.jpg]
I had it in the store today and I got a lot of comments on it. The best one was "Is that a real shark tooth?" I then asked, "Does it look real?" Yes was the answer. Proof enough of a job well done. It was a shame that I had to tell them the truth that my giant Megaladon was only a piece of blue insulation foam.

Bruce Clark

08-26-2000, 11:11 PM
That's ftp://ftp.shopbottools.com/incoming/mvc-007f.jpg (ftp://ftp.shopbottools.com/incoming/mvc-007f.jpg)

08-27-2000, 12:17 AM

Thanks for providing the correct link.

Also, I forgot to mention that final over-all size
of the tooth. It is about 11 inches tall and
about 6 inches wide. Here is a picture from left
to right of shark teeth for comparison.

Left is one of the ones I made (an early "color
sample"). The middle one is the actual 5"
Megaladon tooth that was digitzied. The last one
is the "average" size tooth from a modern day
shark. This tooth was used to base the colors on.

Click here for a picture of the different shark teeth (ftp://ftp.shopbottools.com/incoming/Mvc-003g.jpg)

The rule in the picture is to give you an idea of

Bruce Clark
bwclark@centurytel.net (mailto:bwclark@centurytel.net)

09-27-2000, 12:12 AM
For you guys who have your HEAD IN THE SHOP
and havent done FTP yet ...

Here's a how to.

Go get an FTP program from tucows or downloads.com
and similar site. The WSFTP95 is great and I use
it for my web pages etc. as well in this example.
Install it per the accompanying instructions.
It's easy and not a big deal.

Next ... What to put in the "boxes" ???

Hopefully this pic will show up with the correct entries next ...


Note the ShopBot site and it's login entries.

Now ...


The rest should be fairly self evident since
YOUR files appear on the left.
the TARGET ( at shopbot) will appear on the Right
and allz ya gotta do is highlight the files
that you wnat to transfer and click the Right Arrow.

Retrieving files is just as simple by
Highlightingh files on the RIght and clicking
the LEFT arrow button.

Wheee, let the sharing begin :-)

09-27-2000, 12:17 AM
Sorry for large pIX !!!

But hey, we wanna see some Shopbot Camp Pix


So keep us posted

david allen
09-27-2000, 08:36 AM
you can also download files by pointing your browser to:
right-clicking on the file,
then selecting the 'copy to' function.


09-27-2000, 09:56 AM
I'll snap a few pics at "Camp" and post them.

(that is as long as I remember to bring my camera with me!)