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Big Blue Saw Blog General Updates

Using Ball Bearings with Waterjet Cut Parts

A fellow robot builder once told me that using ball bearings in a waterjet cut base was "advanced waterjet mastery," which I thought was a little odd. To get ball bearings to work in a waterjet cut part isn't hard: just make a hole big enough to fit the outer race. It turns out, though, that there is a lot more subtlety to making this work the right way.

You see, without a precise hole to fit in, ball bearings tend to wear out early.  Choosing a fit is complicated, and depends on the type of load the bearings will see, among other factors. (See SBP's article on the subject and the MITCalc website), but typically what is known as an H7 fit is used. This would mean that, for example, that a the hole to hold a ball bearing with an outer diameter of 0.5 inches would need to be between +0 inches/mm and +0.001 inches (0.018 mm) oversized. This type of tolerance is impossible to achieve with the waterjet or even ordinary twist drills. You'd need a very accurate milling machine, lathe, or possibly a precision reamer in a drill press.

In practice, however, that kind of precision is often not necessary. For light loads, infrequent use, or short lived prototypes, you can get away with using a low-taper waterjet cut hole that's 0.01 inches oversized. Additionally, to fill in any gaps and hold the bearing more solidly, you can use a retaining compound like Locktite 638 or Devcon 68050.

I built the gearbox shown below for my fighting robot Jaws. The bearings for the larger shaft have a 3/4 inch inner diameter and a 1 5/8 inch outer diameter. The smaller shafts, at 1/2 inch inner diameter, ride on ball bearings that have a 1 1/8 inch outer diameter.

I used the more primitive technique for this: rather than going for an exact H7 fit, I oversized the hole and fit the ball bearing in place, holding it tight with retaining compound. You can see the robot in action in the video below. The ball bearing seems to run quite smoothly in this case, even though it has been placed under some brief, intense use. I don't know if I'd trust it to work under a heavy load for a year of continuous operation, though.

Let's take a look at how the waterjet cut pieces work together. The ball bearings in this case are 3/8 inch thick. Since the bearings are thicker than the main 1/4 inch walls of the gearbox they are held in place using 1/8 inch thick plates. At Big Blue Saw, we call this type of construction the stacking technique. I tapped 3 holes into the 1/4 inch wall for the screws to hold the stacked plates in place.

Here's a closeup of one of the the 1/2 inch shafts with the shaft collar removed. If you look closely, you can see there are two 1/8 inch layers stacked on top of the 1/4 inch wall: the inner layer supports the bearing much like the 1/4 inch wall. The outer capture plate layer keeps the bearing from sliding out axially. It has just enough clearance to allow the ball bearing inner race to move freely.

Here's the assembly with the outer capture plate removed.

If you're less worried about the efficiency of the rotating shaft and don't want to bother with getting a precise fit for a ball bearing, a bronze bushing is a good alternative. Bushings are also compact, light weight, and less expensive than ball bearings.

Find out how you can get free CAD software to start designing your waterjet cut parts with bearings today.

Building the Open Source FarmBot with Big Blue Saw


You may have heard of FarmBot, an open source robot for automatically growing and managing the lifecycle of plants. It turns out that the first FarmBots are being made with parts from Big Blue Saw. Here's what Rory Aronson of the FarmBot project had to say about Big Blue Saw:

At, we’ve been fortunate to work with a fantastic water jet cutting service provider named Big Blue Saw. Big Blue Saw is attractive for us to use because they are an online-first service that really caters to their customer’s needs. On their website you can upload a .DXF file of your parts, choose your material and quantity, and receive an instant quote for free. If the price looks right, you can place the order right then and there, and your parts will arrive at your doorstep within a week or two!




Here's the FarmBot in action. See if you can spot the waterjet cut aluminum parts.

You can keep up with the latest FarmBot developments on their blog, or follow the project on Twitter. They recently got FarmBot to plant its first seeds!

Turn a Logo Into a Custom Metal Sign

Many customers come to us wanting to turn their logos into signs or stencils made from metal or plastic. This ranges from small laser cut acrylic pieces to place on employees' desks to large outdoor displays meant to be visible from the street. Waterjet cut stainless steel and aluminum are both popular choices for metal signs due to their appearance and durability.

Let's take a look at how we turned the logo for Inkscape, a popular open source graphics editor, into real stainless steel and aluminum signs.

We started with the official Inkscape vector logo. When imported into Inkscape, here's what it looks like:

It's a pretty logo, but you'll notice right away that this design does not lend itself well to being waterjet cut as a sign or stencil. This design has several gradient areas and a waterjet cuts all the way through the target material, meaning that we need to reduce this logo to simple solid areas (positive space) and holes (negative space).

In Inkscape, when we do View > Display Mode > Outline from the menu, we can see many of the individual paths that make up the logo.

Deleting all but the paths that give us the black and white colors yields the outline shown below.

If you've read our article on turning a logo into a sign, you'll know that there are 4 general approaches toward turning a logo into a sign:

1. Logo as negative space, disconnected pieces

2. Logo as negative space, bridged pieces

3. Logo as positive space, bridged pieces

4. Logo as positive space, disconnected pieces

Sign types #2 and #3 allow the design to be cut and installed as a single piece. Type #2 is also a great choice for a creating a stencil. Types #1 and #4 require that the finished piece be set on a background for display, like a wall. In this article, we'll turn the Inkscape logo into both a #2 and a #3 sign.

The next step will be to resize the entire logo to be the final size that we want. In this case, we're making the logo 6 inches wide. (Note that this is not the final size of the overall finished piece in the type #2 sign, as that sign type requires a border.) We'll choose Edit > Select All from the menu to select everything to be resized.


Next, the resize lock (1) should be selected to make sure that the file resizes proportionally. The units should be inches (2) and a width of 6.0 inches entered (3)

This resizes the logo way beyond the original size of the document, so let's fix that. Choose File > Document Properties from the menu.


The Document Properties dialog will appear. In this dialog, we need to set the default units as inches (1), and make the overall document size 8x8 inches (2 & 3).


We'll be moving the logo around as a single unit, so we must select everything again (Edit > Select All) and group them together with Object > Group.


Since we're starting with a type #2 sign, or stencil, we need to make a background frame on which the logo will sit. This is done with the rectangle drawing tool.

We can click and drag to draw  in the drawing area to make a rectangle. We will set the fill color of the rectangle to be white and the outline to black to make it easier to see.  You can access the fill and stroke style by selecting the rectangle in the drawing and clicking on the Fill and Stroke styles on the bottom right hand corner of the window.

This pops up the Fill and Stroke panel where you can set the appropriate styles.

We want our frame to be 7x7 inches. This can be set by selecting the rectangle and setting the dimensions in the area just above the drawing.

You'll notice that the frame rectangle is covering up the logo. You can fix this with Object > Lower to Bottom.

To align the logo in its frame, select everything and chose Object > Align and Distribute to open the Align and Distribute panel. We want to center everything in the page, so select Page from the dropdown (1). Then center horizongally and vertically using the horizontal and vertical centering buttons (2 and 3).

We now have a logo as shown below, centered in a square frame.

Since we want the white areas to be solid material, we'll need to connect them to the outer background areas. We can do this with rectangles that are 1/8 inch wide. These rectangles will have a solid white fill and no stroke outline.

We'll need a few of these to hold everything steady. The "lake" feature requires an extra long bridge.


Instead of bridging the highlights on the 3 ink drops at the bottom, we'll just expand the ellipse to touch the outer edge. This follows the appearance of the original logo which had a gradient effect in this area.


Longtime users of Inkscape or and Big Blue Saw will know that our bridges aren't quite right yet. We need the drawing outlines to reflect exactly the shape we want to cut out. Let's take a look at the outline view.

As you can see, the rectangles from the bridges overlap the outlines of the rest of the pieces. This means that when we save this design, we haven't provided an outline to cut. Fortunately Inkscape offers an easy solution for fixing this. (This technique was brought to my attention in a YouTube video by professorlooney). By using the fill tool, we can make all the white areas in the drawing a single path entity. Just choose the fill tool and click in the white area inside the drawing.

We've filled the newly created path with red and outlined it so that it's easier to see. We'll move the new outline out of the way and delete all the original objects.

Now we have just the exact outline that we want to cut. Looking at the drawing in outline mode confirms this.

Finally, we need to add mounting holes to be able to hang the piece on the wall.

This design can now be exported using Big Blue Saw's DXF Export for Inkscape or saved as EPS then translated to DXF with pstoedit. This gives us a DXF file for use with Big Blue Saw's instant online quoting and ordering system.

When this type of design is made from metal and placed against a dark background, it resembles the original logo. But what if we wanted to make this a different way: with the mountain made of metal and without the framing rectangle? This is possible as well.

This type of sign needs bridges as well, similar to what we've seen already, so I won't go over all the details of making the design. I will note that in the image below, I used curves with a 1/8" wide
stroke width to bridge the main mountain to the splotches of ink at the bottom.

Using the same bucket fill technique as before gives the outline for the final part shown below.


After cutting, the parts come off of the waterjet looking like the pieces below.

These aren't yet something you would want hanging on your wall. There are marks from the mill that produced the raw material, as well as from the waterjet and handling. This can be cleaned up, however. Big Blue Saw offers Basic Finish and Bead Blast finish to help parts look their best. I used sandpaper and a paper towel with denatured alcohol to clean up these parts.

Here are the finished parts in 0.06" thick stainless steel:

Also in 3/8" thick aluminum:

The materials are both grey metals, but aluminum has a brighter appearance. Choose the material that best meets the look you're going for. I will say that people tend to associate stainless steel with expensive products and associate aluminum with inexpensive, mass-produced products. The image below shows the color difference. Stainless steel is on the left, aluminum on the right.


Other metals work well in signs. Brass works especially well for a nautical, steampunk, or Victorian look. Copper is often associated with kitchens, though it can corrode or develop a patina. Carbon steel gives a more industrial look.

What thickness to choose can depend on how you're mounting the final piece, the lighting, and the effect you're looking to achieve. If you want the sign to really pop out of the wall, choose a thicker material. Again, the aluminum below is 3/8 inch thick, and the stainless steel is just under 1/16" thick, or 0.06", about as thick as a penny.

Get started by uploading your design to our online quoting system and turn your logo into a sign or stencil made from metal, plastic, wood, and more.

If you need help with creating a cuttable outline, adding bridges, or choosing a material, contact us and we'll be glad to help.


Two New Waterjet Cutting Videos

You may have seen our earlier video showing waterjet cutting in slow motion. Today we've got two more videos showing how the waterjet cutter works.

Many people assume that since the machine uses water, the waterjet cutting process is quite gentle. This is far from the truth. In actuality, a waterjet cutter uses a stream of water and garnet sand to blast through material at 60,000 or higher pounds per square inch. Here's what it looks like when the waterjet first starts.

Next, we've got a close look at the waterjet cutter in operation working on the same job in 1/4" thick aluminum 6061.

Read more about how Big Blue Saw can turn your designs into real parts made from aluminum and other materials using waterjet cutting.

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Waterjet and Laser Cut Custom Parts.
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