Simulating a Bevel Effect Using Stacking

At Big Blue Saw, we occasionally get requests from customers to put a bevel or chamfer on the edge of a waterjet cut sign or control panel.This is usually done for aesthetic purposes, to allow the piece more to show more highlights and shadows.

While we can’t put a bevel on the edges of parts using the waterjet, we can create a similar effect using the stacking technique.

Let’s take a look at how this works with a simple example created in Inkscape. The techniques shown here can be replicated using almost any vector drawing or CAD program.

Using the text tool, we will add a number “8” to the drawing.

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Next we will turn the character “8” into a set of curves by selecting it and choosing Path > Object to Path from the menu. We want to see the curves, so we choose View > Display Mode > Outline from the menu.

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We then make a copy of the figure using the Copy and Paste commands.

To make one of the figures into the skinnier upper layer, we use Path > Inset on the menu or Ctrl+( on the keyboard a few times. If you’re doing this, be careful that you don’t make the thin areas too thin to be cut by the waterjet.You can also try making the lower layer larger using Path > Outset or Ctrl+).

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If we were going to mount this number using adhesive, we would be done at this point. We could just save the file as a DXF and upload it to Big Blue Saw to be cut.

However, for this example, we will make mounting holes so that the numbers can be mounted with screws or nails.

We need to make sure that the mounting holes align on both parts. We select both figures and align them using Object > Align and Distribute on the menu. The shapes need to be aligned both horizontally and vertically using the buttons in the Align panel shown below.

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Now the two outlines will look like the figure below. This gives us an idea of how the final parts will appear.

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Let’s add a couple circles for mounting holes.

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We duplicate the entire drawing using Copy and Paste.

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And finally delete the outer outline from one of the copies, and the inner outline from the other copy. Now the drawing has both parts with the mounting holes correctly aligned.

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Finally, here are the assembled parts with the simulated bevel waterjet cut from 0.135 inch (3.4 mm) thick stainless steel, ready to be mounted.

 

Numeral 8 With Simulated Bevel

 

Waterjet Taper Details

Here are some photos showing taper in a piece cut from 0.25 inch thick 6061 aluminum. Note that the taper is not at a constant angle through the entire thickness of the part.

The part is compared to a machinist’s square and a flat granite reference surface.

 

closeupTaper0.25aluminum P1010210 P1010212

 

 

Locating Marks for Secondary Operations

Returning to the clamp example from the previous post, let’s take a closer look at how the  bolt holes were made through the side of the clamp.

In the photo below of the two clamp halves, you will notice that the clamp has indendations along the cut line where the bolt holes go. This makes it easier for a drill press operator to precisely locate the position of the holes.

The two halves of the split clamp before the bolt hole is drilled in the cut edge. Note the indentation which indicates where the bolt holes will be located.

The two halves of the split clamp before the bolt hole is drilled in the cut edge. Note the indentation which indicates where the bolt holes will be located.

Drilling a bolt hole in the cut edge of the clamp with a drill press. The indentation in the cut line helps locate the correct spot for the hole.

Drilling a bolt hole in the cut edge of the clamp with a drill press. The indentation in the cut line helps locate the correct spot for the hole.

A similar indentation in the cut line can be used to mark the location of blind holes or other features created by secondary operations.

Custom Clamps

One common application of waterjet cutting is to make custom clamps to hold pipe or tubing in place. You can see an example of such a part in the photo below.
Note that the bolts holding the to halves of the clamp together pass through a hole in the cut edge of the part.

 waterjet cut custom clamp holding two poles together.

waterjet cut custom clamp holding two poles together.

Bending/Braking Waterjet Cut Parts

For parts where t-nut construction won’t work, you may consider bending flat parts in a sheet metal brake.
Be aware that getting precise results from bending can be difficult. There are many factors to consider, including the bend radius of the material, the amount the material will stretch, and so on. Wikipedia has a brief overview of the subject.

Typically, an experienced brake operator will perform several practice bends on test parts in order to get the setup and bending procedure just right for accurate production parts. Thus, you should have several extra parts made and plan on your final accuracy being no better than +/- 0.01 inches in a small production run. You can compensate for this inaccuracy by, for example, elongating mounting holes in the part.

If you plan to use aluminum in a part which needs to be bent, you should use 5052 alloy instead of 6061, as 6061 is prone to cracking when bent.

Waterjet cut aluminum 5052 parts before bending on a sheet metal brake

Waterjet cut aluminum 5052 parts before bending on a sheet metal brake

 

The same parts as above after bending on a brake.

The same parts as above after bending on a brake.

 

The position of the ends of the bend line can be indicated by indentations along the cutting line. In addition, the material can be made easier to bend by cutting narrow reliefs along the bend line. A drawing of such a part is shown below.

 

Drawing of flat  piece to be bent.

Drawing of flat piece to be bent.

The photo below shows the part waterjet cut from 0.08 inch thick aluminum. The reliefs on this piece are large enough and the material thin enough that this was able to be bent accurately by hand. For added strength, the length of the reliefs should be reduced.

0.08 inch thick aluminum 5052 piece bent (left) and original flat piece (right)

0.08 inch thick aluminum 5052 piece bent (left) and original flat piece (right)

 

Help Deciding on a Material Thickness

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In a previous post, I showed you a little bit about how to choose a material. I’ve found in my work at Big Blue Saw that many people have trouble deciding on a thickness as well.

If you don’t have a set of calipers or a micrometer with which to gauge the thickness of the material you would like to use, you can use common household objects instead. Use chart below to get a feel for various thicknesses. You could also use any of these objects to measure existing parts.

For thicker measurements, stack several parts together. For example, 3 CDs are 3 X 1.2 mm = 3.6 mm or 0.142 inches thick.

Inches Millimeters
Dollar bill 0.0043 0.1092
#9 Standard Razor Blade 0.009 0.2286
#12 Heavy Duty Razor Blade 0.012 0.3048
Credit Card 0.030 0.76
CD, DVD, or Blu-Ray Disc 0.047 1.2
US Dime 0.053 1.35
US Penny (Cent) 0.060 1.52
US Quarter 0.069 1.75
US Nickel 0.077 1.95
Canadian Polymer Banknote 0.004 0.091
Canadian 10 Cents 0.048 1.22
Canadian Cent 0.057 1.45
Canadian 25 Cents 0.062 1.58
Canadian Dollar 0.069 1.75
Canadian 5 Cents 0.069 1.76

Table of material thicknesses

 

Exporting from 3D Modeling Tools for Waterjet Cutting

Waterjet quoting and final cutting is driven from 2D vector format files. However, many people use 3D modeling tools for their designs. Popular software packages in this category include Pro/Engineer, Sketchup, SolidWorks, Inventor, Geomagic (Alibre) Generating an appropriate 2D file generally means going though an export process to get the correct projected version of the parts to be made.

ViaCAD part export, zoomed out

ViaCAD part export, zoomed out

The biggest stumbling block here is that many 3D design tools will add perspective information, such as hidden lines, to the final output. Lines in the drawing to indicate perspective simply confuse the waterjet software. Below is an example of this problem. The original design was exported as a 2D drawing from ViaCAD (though this problem is by no means unique to that package. When zoomed out, the part looks like a simple outline.

ViaCAD part export, zoomed in on the problem area

ViaCAD part export, zoomed in on the problem area

However, when you zoom in on the upper right hand corner of the image, you can see that the software has drawn the front and back of the part in perspective, plus a middle line. The extra lines will simply confuse the waterjet software, as there is no real indication which line represents the outline to cut.