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Big Blue Saw Blog General Updates

Stopping a Cobra with Custom Stainless Steel Brackets

Rick Johnston was working on his  Factory Five Racing MK4 AC Cobra replica (shown above) and wanted an upgraded braking package. His solution: custom brackets waterjet cut from stainless steel by Big Blue Saw.

Once he's tested out the parts and worked through any bugs, Rick plans to make the designs public. For now, here's a sneak peek at the custom braking package partially assembled.

 

 

Rick gave us some technical details on the how and why of his design.

The design is modular and covers both the front and rear brakes. The outer bracket you see on the rear brakes is also used in the front. This is why there are 2 additional “outer brackets” (“L” shaped) in the part outlines [shown above].

 

 

This allows the mounting of front brake packages to the rear. Cobras are different than most production cars that the kit industry borrows parts from. Cobras have a typical front to rear weight balance of 55% - 45%. Additionally the center of gravity height is MUCH lower than a typical production car measuring approximately 15” in height. Also the tire Diameters remain quite large for such a low CG height. This means that this kit needs a lot more rear brake than the standard parts provide. My equations (not proven yet) should reduce the pedal force needed from around 150 lbs to about 40 lbs to lock all 4 wheels in a balanced manner (fronts locking slightly before the rears). I am working on another design very similar to this one, that would allow standard production 13” Mustang Cobra brake components to be used that would further reduce cost to builders.

 

And one more look at Rick's ride.

 

 

Note that when Rick ordered, he took advantage of our best tip for saving money on waterjet cutting: putting several designs into the same file. If you've got many parts all made from the same material and thickness, it's most cost effective to put them all into the same file before uploading them to the online quoting system.

Making Polycarbonate Parts Any Color

Unlike acrylic plastic, which is available in dozens of colors and styles, it's difficult to color match polycarbonate plastic. Polycarbonate sheet is generally available in small quantities in one of only a few colors: clear, gray, bronze, white, and black.

Above is a photo of my robot "Big Blue Saw Presents Flipper 720". You may notice that the top is a lovely semi-transparent blue. It's waterjet cut from polycarbonate for extra toughness. How did I create the top without buying an entire truckload of blue-tinted polycarbonate? Read on.

I wanted a robot that would stand out from the typical metal and plastic creations of Robot Battles. A blue top would help with that. After some research, I learned about several common techniques for coloring clear plastic:

  • Coloring with a permanent marker
  • Applying window tinting film
  • Dying with clothing dye
  • Spray painting

Spray paint seemed like the least fuss way to go. It turns out that Tamiya, the plastic model kit and RC company, makes spray paints specifically for polycarbonate. They typically sell to hobbyists painting polycarbonate shells for RC cars. It's available in a large variety of colors and styles, including metallic, transparent, and irridescent hues.

I ordered a can off of Amazon in an appropriate color, "Translucent Light Blue", part number PS-39.

Here's a closer look at one of the smaller pieces after painting.

I'm quite pleased with the finished product. It leaves the inside of the robot visible while adding the flair of a bright color.

My tips for using spray paint:

  • Make sure the surface to be painted is clean.
  • Paint in a well ventillated area away from dust or wind.
  • Begin spraying next to the piece to be painted. Starting the spray with the can pointed right at the workpiece can lead to clumpy or uneven paint.
  • Move in a steady, even motion across the workpiece. Follow through and stop the spray only after the end of the stream is off of the part.
  • Apply in layers and use less paint than you think you need on each layer.

Sizing Errors When Using Drawing Apps

We often see parts come out slightly smaller than the designer expected when they're designed in a vector based drawing tool like Inkscape, Illustrator or Corel Draw. These parts show up smaller in the online quoting tool than they do in the drawing software. This is due to the stroke width of the part. Let's take a look at how this can happen.

In Inkscape, we'll resize a square with rounded corners to be 5 inches by 5 inches and export the design to a DXF format file.

When uploaded to our online quoting system, the size is only 4.902 x 4.902 inches!

What's going on here?

The secret is that Inkscape counts the stroke width as part of the object's size. So if your line is 0.098 inches wide, this increases the overall width and height of the part beyond the center of the line by 0.098 inches (0.049 inches on each side). Our online quoting tool (and most CAD programs) measure from the center of the line, rather than the edge of the stroke.

The solution is to set a very small or 0 line width before resizing. Let's set the line width to be 0, then resize to 5 x 5 inches, and export again.

Now when the part is uploaded, the dimensions are correct.

 

Tough and Transparent Sale: October 17-19

You have seen parts from Big Blue Saw being used for robots, lighting fixtures, signs, car parts, electric vehicles, and more robots. But you may be having trouble deciding which material to order. During our Tough and Transparent Sale from Monday, October 17 though Wednesday, October 19, you have two great materials to choose from. And you can save on both of them.

 

 

All of Big Blue Saw's polycarbonate and aluminum parts are made using waterjet cutting, which allows us to turn flat sheets of solid mateiral into real parts based on the designs you upload to our online quoting system.

Polycarbonate is a plastic with a high tensile strength of 8000 to 16,000 psi. 

Being a polymer, it is lightweight. And it's transparent to boot.

 

 

 

Polycarbonate happens to be one of the tougher plastics around.  Impact toughness is the ability of a material to absorb energy and plastically deform without fracturing. To put some numbers behind it, polycarbonate has a notched Izod impact strength of  5.71 ft-lb/in² or 12.0 kJ/m². That's over 7 times tougher than acrylic (Plexiglas®) plastic. So polycarbonate can take a beating without shattering or cracking.

 

 

  

 

Meanwhile, if you need something much tougher, you could try aluminum alloy 6061. It has a fracture toughness (ability to resist breaking completely after cracking) of 29.0 MPa-m½ or 26.4 ksi-in½.

Aluminum 6061 also provides fantastic stiffness for its weight, making it an ideal material for frame parts, trusses, bearing blocks, and the like. It also is corrosion resistant, weldable, and looks good too, which makes it a great choice for a variety of other applications.

If you're looking for stiffness of aluminum or the transparency and light weight of polycarbonate, Big Blue Saw makes the custom parts you need.

 

 

 

During the Tough and Transparent Sale, waterjet cut parts ordered online made from aluminum 6061 in 0.25 inch thickness and polycarbonate in 0.125 inch thickness will automatically receive a quantity discount. This means that when ordering as few as 1 part,  you'll get the same discount as if you had ordered 10 pieces. Depending upon the design, you will save as much as 70% off your order.

Upload your design now to our online quoting system to get started.

Fixing the Error "You have areas inside the part which cross each other."

"You have areas inside the part which cross each other."

You may have seen this error when uploading a design to Big Blue Saw's online quoting system. Let's take a closer look at what this error means and how we can correct the problem.

This message indicates that the online quoting system is able to find the outside outline of the part, but you have holes or other features within that outline that cross over each other.

If you're just beginning with Big Blue Saw, it's important to understand two things:

1.  What kinds of parts you can make with Big Blue Saw. We can make parts using waterjet cutting or laser cutting. This means that all parts are cut from flat stock. The flat stock is cut completely through on every pass of the laser or waterjet.

2. Your uploaded design should contain only the outline of the part to be made, scaled 1:1. Read our guide to formatting CAD files.

With those 2 basics in mind, read on for help diagnosing and correcting common mistakes.

Where to click to get a diagnostic view.

When you get an error when uploading a design, you should begin diagnosing the problem by clicking the link for the Diagnostic View of the part. This will show incomplete lines and highlight problem areas.

Diagnostic View

If you haven't already, review the DXF or DWG file in software which is specifically intended for working with these files, like DraftSight, LibreCAD or QCAD. We have a list of free and low cost software for working with DXF files. Sometimes when you export from an application which is not specifically designed for DXF files, the export won't be completely clean. Zoom in on the areas where the online quoting system finds a problem. Sometimes you will need to zoom in quite closely to find the mistake.

Here are 5 common causes of the error "You have areas inside the part which cross each other."

1.  The line in the drawing was intended as a cut line, not the outline of a part.

Drawing of a puzzle with common cut lines.

Box for laser cutting with common cut lines.

This is often the case for jigsaw puzzles and designs with pieces intended to fit together after laser cutting. Every part should be outlined individually to work with the online quoting system.

It can sometimes be practical for us to do this type of cut. Contact us if you really need this type of waterjet or laser cutting.

2. You have duplicate overlapping lines due to a 3D projection error.

3D part incorrectly projected into 2D

If you have created the original drawing with a 3D drawing tool (SolidWorks, Sketchup, OnShape, etc.), make sure that your export to a 2D drawing does not include any hidden lines. The drawing used with Big Blue Saw should be a single outline of the face to be cut.

Often lines from a 3D projection will be closely overlapped and may be hard to see without zooming in closely. You may have to try selecting lines and deleting them to find closely overlapped lines.

3. You have duplicate overlapping lines due to a stroke path.

Outline from a doubled stroke path.

When using a vector based illustration tool like Illustrator, Corel Draw, or Inkscape, make sure that the export procedure you used exports a single line for the outline of your part. These tools can sometimes export a stroked path as two separate lines: the inside of the stroked shape, and the outside of the stroked shape.

View the drawing in outline mode (View | Display Mode | Outline  in Inkscape or View | Outline in Illustrator) to see the outlines which make up the shape.

Normal view on left in Inkscape of a shape with a complex stroke path, outline view on right.

Delete any outlines other than the ones which show the exact outside outline of your parts. Remove any lines or paths which cross over other lines or paths.

4. You have visible objects in the drawing which were not merged correctly.

Outline view of a part with incorrectly merged holes.

Like #4, this problem is also commonly seen when using drawing applications like Illustrator, Corel Draw, or Inkscape. You have multiple objects in your drawing which appear to be the a single object because they overlap and are the same color.

Again, view the drawing in outline mode (View | Display Mode | Outline  in Inkscape or View | Outline in Illustrator) to see the outlines of the shapes in the drawing. Merging the shapes before exporting should fix this problem.

Normal view (left) and outline view (right) of a part with incorrectly merged holes.

5. Your drawing includes a sheet format or information other than the outline of the part to be cut.

Some CAD software will create a grid for you to enter information about the creator of the file, date, material, and so forth. The solution here is to delete everything in the drawing other than the outline of the part to be cut.

If you have gone through all of these steps and still can't find the problem with your file, please contact us and we'll do what we can to get your design working.

 

 

 

 
 
 
 
 

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Big Blue Saw
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Waterjet and Laser Cut Custom Parts.
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Phone: (678) WAY-SAW4 (678) 929-7294