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Big Blue Saw Blog General Updates

Thin features on waterjet cut parts

It's true that waterjet cutting doesn't put much stress on the sides of the material that it's cutting compared to, say, milling. But vibrations from the cutting process can cause problems, especially near thin features. We created a couple sample pieces from aluminum 6061 to show just how thin you can make waterjet cut features. The photo above shows on the left a piece made from 1/4 inch (6.35 mm) thick material, and on the right you can see the same design cut from 1/16 inch (1.6 mm) stock.

You'll notice that the thinner material has one fewer bar. That's because the beefier material can hold thin features better than its skinnier counterpart. Thinner material is weaker for a given area and so it's more likely to vibrate when cut. You can see in the closeup below where the bar broke off. This bar was drawn to be 0.018 inches (0.46 mm) thick.

Even the thicker material had some trouble with a bar this thin. You can see that on the top face (the side where the waterjet stream first enters the material), the bar is missing some of its thickness and is just barely attached.

Below is a CAD drawing with the thinnest 3 bars. They are 0.0566, 0.0372 and 0.018 inches thick, respectively.


 

Keep in mind that these bars are only suspended from one side to the main body of the part. Connecting them to a bigger piece on both ends would help keep them stable when cutting. Also, different materials will behave differently when waterjet cut.

To summarize: narrow areas in  your design under 0.018 inches (0.046 mm) will probably not work out. Keep feature thickness to 0.037 inches (0.95 mm) and above. If absolutely must have thin features, use thicker material.

 

 

Load Holding Fixtures Using Waterjet Cutting

Fresh out of my e-mail inbox comes this fixture from a customer who wishes to remain anonymous. 

(Of course, at Big Blue Saw we keep your designs confidential. We also keep the fact that you're even a customer confidential as well. Many of the things we make end up in finished products, and our customers see Big Blue Saw's service as a competitive advantage. [Many are happy to provide testimonials, thankfully.] )

The structural pieces  were waterjet cut by Big Blue Saw from 1/4 inch thick aluminum 6061 and assembled by the customer using off the shelf hardware. The design uses tab-and-slot with the pieces held together with through bolts as in tensioned plate construction.

The customer says:


These are medium-load holding fixtures.  Using BBS for these type of fixtures saves us 50%+ on traditional tooling and also allows us to build instrument & medium load machines in a clean office!  (No welding, milling, sawing, etc - -just a few fasteners and counter-sinks.)  These fixtures are doing the job of machined 1/4" Al C-channel assemblies.


Got any parts you would like to show off or want to tell us how we are doing? Let us know!

Bitmaps Embedded in Vector Files

Our online quoting and ordering system works best with files in the DXF or DWG format. That's because these two file formats have nearly universal support in CAD software as well as in the waterjet and laser cutting world.

Significantly, these file formats are vector formats. As a quick recap: image files generally fall into one of two types -- vector files and raster (AKA bitmap) files.

Raster files consist of a regular grid of pixels, each of which has its own color. Think of a mosaic picture made using only square tiles of the same size. Or coloring in the squares on a sheet of graph paper.

Popular formats for raster files are JPG, GIF, and PNG. These files are typically created by digital cameras, scanners, and software like Windows Paint, Gimp and Photoshop.

 

A raster image is made up of pixels filled in with colors. In this image, the area in the red rectangle on the left has been zoomed in on the right so that you can see each pixel.

Vector files, on the other hand, create an image from a set of precisely defined lines and curves. Vector files are produced with CAD software like AutoCAD, DraftSight, etc. as well as by drawing programs like Inkscape and Adobe Illustrator.

A vector image is made of curves and straight lines. In this picture, you can see the end points of the lines as well as the control points that make up the curves.

One nice thing about vector files is that they can be zoomed or scaled and the lines look just as smooth. When you zoom in on a bitmap embedded within a vector file, this is not the case.

Unlike a raster image, a vector image can be resized or zoomed without losing any detail. The letters on the left look round even when made much bigger, as shown on the right.

When it comes time to make parts using waterjet cutting or laser cutting, we need a vector file because this gives the exact outline of the shape and a path for the cutting tool to follow. Astute users of our service will notice that uploaded GIF and PNG files are converted to DXF by a tracing process on our servers when the quoting process begins.

The Confusing Thing

Strangely, files can contain both bitmap AND vector data! This happens commonly when exporting to a vector format from a bitmap-oriented editor. When a vector file contains an embedded bitmap, the embedded bitmap does not have the exact outline of the shape and a path for the cutting tool. It's still a bitmap and shares the limitations of all bitmaps.

DXF, PDF, and SVG all support embedded bitmaps to coexist with vectors.

How to Tell If Your Vector File Has an Embedded Bitmap

Zooming In

One way to tell if a file has an embedded bitmap is by zooming in. You will be able to see the jagged edges of the pixels in the bitmap image once you zoom in far enough.

An overview of a CAD design in Inkscape. It looks just like a vector drawing at this zoom level.

Zoomed in, you can see the telltale jagged outline of an embedded bitmap.

Outline View

Another way to check for embedded bitmaps is to use the outline view mode of your editor. In Inkscape, that's done by choosing View > Display Mode > Outline from the menu. An embedded bitmap will then be shown as a plain rectangle with an X in the middle. In this view, true vectors will be shown with their original path, but with alll styling (colors, thickness, etc.) removed.

Outline view in Inkscape.

The same design as a vector, zoomed in.

If you need free or low cost software that will create vector files for your design, take a look at our list of recommended software. Then learn how to format your CAD files for our online quoting system to make custom parts from aluminum, steel, plastic, and more.

Pemdas's Custom Keyboard with Waterjet Cut Plate

Our customer pemdas wrote to send us a photo of the keyboard he created with some help from Big Blue Saw.

The top plate was waterjet cut by Big Blue Saw from 0.063" thick aluminum 6061.

Here's what he had to say about our work:

Everything was perfect. Will definitely be using your services again for my future projects!


You guys made this so much easier than I thought it was going to be when I first started planning this project.


I keep thinking I should've ordered more than one just for the savings.

Pemdas also gave some details on the build:

I used vintage cherry blacks for the switches because I had a bunch of them laying around. They are linear switches and very smooth.



The outline was the easiest part! I used a tool made by a forum member named swill. I believe you guys worked with him as well for the water jet services.



My controller was the standard teensy 2.0 using the tmk firmware made by the another user named Hasu. That base plus a guide made by user matt3o made making the firmware super easy! No pcb meant handwiring which wasn't as bad as I thought it would be.



As for the keycaps in the picture they are a key set called Retro DSAs. They were from a group buy held many years ago. Sadly the only way to get them now is to purchase or trade for them second hand.

 
Thanks! And if you're interested in making your own custom keyboard, check out the Swillkb Plate & Case Builder and our custom keyboard example parts.

Advantages of Waterjet Machining, from the Expert

The information below comes from Carl Olsen's website waterjets.org. Whenever a customer comes to me with a very technical question about waterjets or waterjet cutting that I can't answer, I refer them to waterjets.org and Carl. If he doesn't know the answer, he knows who does.

 


With Carl's permission, I thought I'd post some of the great information he's written concerning the advantages of waterjet cutting.
- Simon Arthur

"If you need a machine and don't buy it, then you will ultimately find you have paid for it but don't have it" - Henry Ford.

There is a reason that waterjet machining has rapidly grown in popularity since the mid-1990's. Actually there are a number of reasons, listed below, but they mostly come down to "versatility." A waterjet is a versatile and flexible machining tool. You can cut a wide variety of material efficiently and cost-effectively and can create a wide variety of parts.

A two-dimensional shape

Machine any two-dimensional shape with one tool

Cut virtually any material

Because waterjets cut using water and abrasive, they can work with a wide variety of materials. These materials include:

  • Copper, brass, aluminum:
  • Pre-hardened steel
  • Mild steel
  • Exotic materialss such as titanium, Inconel and Hastalloy
  • 304 stainless steel
  • Brittle materials such as glass, ceramic, quartz, stone.
  • Laminated material
  • Flammable materials

One of the few materials that cannot be cut with a waterjet is tempered glass. Because tempered glass is under stress, as soon as you begin to cut it, it will shatter into small fragments—as it is designed to do.

[picture dragon artwork machined with an abrasive waterjet]

Pictured here is a dragon machined from 1" (2.5 cm) thick bulletproof glass, and inlay of marble and granite

Fast setup and programming

With waterjet machining, a flat piece of material is placed on a table and a cutting head moves across the material (although in some custom systems, the material moves past a fixed head). This simplicity means that it's fast and easy to change materials and that no tool changes are required. All materials use the same cutting head, so there is no need to program tool changes or physically qualify multiple tools.

The movement of the machining head is controlled by a computer, which greatly simplifies control of the waterjet. In most cases, "programming" a part means using a CAD program to draw the part. When you "push print," the part is made by the waterjet machine. This approach also means that customers can create their own drawings and bring them to a waterjet machine for creation.

Little fixturing for most parts

There are very low sideway forces with waterjet machining--cutting the material doesn't push it. The downward forces are also small, in the range of a few pounds. Typically, the largest force is from the water in the tank pushing back up against the material.

Fixturing is generally a matter of weighing down the material by placing weights on it. Small parts might require tabs to prevent them from falling into the tank.

The low side forces, means you can machine a part with walls as thin as 0.01" (0.25 mm). This is one of the factors that make fixturing is so easy. Also, low side forces allow for close nesting of parts, and maximum material usage.

Almost no heat generated on your part

What little heat is generated by the waterjet is absorbed by the water and carried into the catch tank. The material itself experiences almost no change in temperature during machining. During piercing 2" (5 cm) thick steel, temperatures may get as high as 120° F (50° C), but otherwise machining is done at room temperature.

The result is that there is no heat affected zone (HAZ) on the material. The absence of a HAZ means you can machine without hardening the material, generating poisonous fumes, recasting, or warping. You can also machine parts that have already been heat treated.

No mechanical stresses

Waterjet machining does not introduce any stresses into the material.

Machine thick material

While most money will probably be made in thicknesses under 1" (2.5 cm) for steel, it is common to machine up to 4" (10 cm). The thicker the material, the longer it will take to cut. A part made from material twice as thick will take more than twice as long. Some companies make low tolerance parts out of metal that is up to 5" to 10" thick (12.5 cm-25 cm), but it takes a long time and tends to be an occasional operation. Typically, most waterjet parts are made from metal that is  2" (5 cm) or thinner.

[picture of 2in ss304 machined with an abrasive waterjet]

Pictured here is a part made from 2" (5 cm) thick 304 stainless steel 

Are very safe

Obviously, you don't put any body parts in front of a waterjet machining head while it is on. Anything that can cut through 2" steel will make short work of flesh and bone. Aside from this, however, waterjets are very safe. A leak in a high-pressure water system tends to result in a rapid drop in pressure to safe levels. Water itself is safe and non-explosive and the garnet abrasive is also inert and non-toxic. One of the largest hazards is cuts from the sharp edges of material created by the waterjet.

Modern systems are now very easy to learn

Control of the waterjet head is complicated and requires careful calculation to get the proper speed that will give the best result. This means that the system needs to be controlled by a computer, which means that the user-interface for the system can be simplified and made friendlier. Modern systems are designed the same way as many other computerized CAD systems and are quickly learned.

Environmentally friendly

As long as you are not machining a material that is hazardous, the spent abrasive and waste material become suitable for land fill. The garnet abrasive is inert and can be disposed of with your other trash.

If you are machining lots of lead or other hazardous materials, you will still need to dispose of your waste appropriately, and recycle your water. Keep in mind, however, that very little metal is actually removed in the cutting process. This keeps the environmental impact relatively low, even if you do machine the occasional hazardous material.

In most areas, excess water is simply drained to the sewer. In some areas, water treatment may be necessary prior to draining to sewer. In a few areas, a "closed loop" system that recycles the water may be required.

The pumps do use a considerable amount of electricity, though, so there is some additional environmental (and cost) impact due to this.

No start hole required

Start holes are only required for materials that are difficult or impossible to pierce. A few poorly bonded laminates can fall into this category, in which case pre-drilling or other special methods may be used.

Narrow kerf removes only a small amount of material

The amount of material removed by the waterjet stream is typically about 0.02" (0.5 mm) wide, meaning that very little material is removed. When you are working with expensive material (such as titanium) or hazardous material (such as lead), this can be a significant benefit. It also means that you can get more parts from a given sheet of material.

When machining or roughing out expensive materials such as titanium, your scrap still has value. This is because you get chunks, not chips.

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Big Blue Saw
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Waterjet and Laser Cut Custom Parts.
Address for correspondence only:
3522 Ashford Dunwoody Rd NE #145
Atlanta, GA 30319
Phone: (678) WAY-SAW4 (678) 929-7294