5 Tips for Prototyping from Cardboard to CAD

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Of all the expensive and fancy tools that can be used in metal fabrication, even the most professional, experienced builders still reach for a simple piece of cardboard to help them design their parts. That’s not an exaggeration. If you’ve spent any time around a fabricator (or watched them on TV or YouTube), you’ve likely heard the joke “I’ll design it in CAD, Cardboard Aided Design”. 

All sorts of inexpensive materials can be used to help get the shape of a part right before any metal gets cut. Cardboard just happens to check all the right boxes, being cheap (even free!), easy to work with and modify, and rigid enough to hold its shape. Once you have the shape, it’s relatively simple to flatten it out and cut it from metal, or snap a pic of it and trace it out in CAD to have SendCutSend cut it for you.

Why Not Skip Right to Metal?

For simple parts, you probably can jump right into the final piece of material and skip any prototyping. As in all areas where some skill is involved, having some experience can make it easier getting it right the first time. But when parts get more complex it can actually be faster and cheaper to make your mistakes on a cardboard prototype. How can doing it twice be faster and cheaper? Let us explain.

  • Cost – Cardboard is cheap, if not free. Those boxes that get delivered to your door with cool stuff inside… they’re made of cardboard that you’ve probably been recycling. It doesn’t take up much space to just flatten out a couple of those boxes and slip it behind a cabinet or workbench. If you accidentally cut a piece of cardboard too small and leave a gap, there’s no expensive wasted material. Just grab another piece and try again. You can’t say that about cutting a piece of stainless steel too small.
  • Easy to Work – Getting precise fits on custom parts can take a little trial and error. Cardboard is rigid enough to hold its shape as you trim it. It can also be folded to simulate bends in sheet metal. In fact, a lot of complex sheet metal shapes are prototyped by taping pieces of cardboard together to form the flanges. Taped seams can simulate a bend line or even a weld seam. A sheet metal bend line that’s off by just a couple degrees can leave you with gaps and seams that don’t line up.
  • Peace of Mind – If you’re not confident in your CAD skills, it can be stressful to order parts (from places like SendCutSend) and wonder if the part you drew is going to fit. Even worse if you want to make a large quantity of parts. You can always order a single part to test fit, make any needed changes, then order another, but even as fast as we turn around parts, that’s still going to take time to iterate. With a cardboard mockup you can test fit your part to be sure it fits before pulling the trigger on ordering. 

Useful Tools

We’ll assume if you’ve read this far, you’re convinced of the benefits of prototyping in cardboard. Or you’re at least curious. Read on and we’ll take a look at the materials and tools that can be useful to get nice looking parts quickly.

Cardboard

Obviously you need some cardboard, right? Maybe not. Cardboard is great, we’ve just spent the first half of this article singing its praises. Turns out for some projects, a simple sheet of paper can be just as good. If you have some graph paper, that can be useful later on in the process. SendCutSend’s new design services enables you to send their design team a graph paper sketch of your part and they’ll design the CAD for you.

When it comes to cardboard, there are options. Usually people think of the corrugated stuff when they think of cardboard. That’s what most shipping boxes are made from. Even your last SendCutSend order came in a cardboard box.

There’s also non-corrugated cardboard. Think cereal box. This stuff can be great too. It’s thinner than corrugated, just a single layer. It cuts clean and easily and can still be rigid enough to form 3d shapes.

If you have a template of your project on any type of cardboard or similar material, you can even send that in to SendCutSend and get your CARD file made by a member of their design services team.

Tools

We’ve looked at the material, now let’s cover some simple tools. You may not need all of these tools, but we’ve found them to be useful on projects in the past.

  • Measuring tools – Rulers, tape measure, calipers, framing square. Anything you can use to take measurements (distances, angles, radius, etc) can be useful. What you need to measure will depend on your part.
  • Straight edge – Drawing a straight line by hand is a skill not all of us possess. A simple ruler or even a piece of scrap material with a straight edge works great.
  • Marking tools – You can use a pencil, marker, ink quill, even your finger rubbed in some dirt can be used to mark the material.
  • Cutting tools – Cardboard cuts much easier than metal, so hold off on the tin snips, angle grinders and plasma cutters. Scissors or a sharp knife can give you nice clean cuts.
  • Uncutting tools – Whether you cut too much, or just need to mockup a part that’s bigger than the pieces of cardboard you have, something to attach pieces together is handy. Tape is our go to here.
  • Printer – Think of it like a CNC pen. Certainly not necessary, but if you want to do a final check of your digital patterns before they’re cut from metal, a simple printout can be used to verify the fit. Print it, cut out the shape either just in paper or transfer back to cardboard and check the fit.

Simple 5-Step Process for Prototyping from Cardboard

Are you ready to build a prototype from cardboard? Follow along and we’ll show you how we do it.

Take Measurements

You’ve got to start somewhere. We like to take measurements of anything that our part will interface with. If there are any size restrictions, this is the time to figure out those measurements.

Rough Out The Shape

You probably already have an idea of what the part will look like, but if not a rectangle of cardboard is as good a shape to start with as any. Trim any edges to fit with nearby parts. Mark the locations of any holes. If you need any bends you can either bend/crease the cardboard, or sometimes it’s easier to cut a separate piece and tape them together where the bend will be. You want to capture any of the important features first. Depending on the complexity, you might need to iterate multiple times to get the fit just right. If you trim too much away, you can always tape more in place or get a fresh piece and transfer over your marks.

Don’t be afraid to include notes for reference. Directions and angles of bends, lengths of edges, distances between hole centers and hole diameters are all useful to have written right on the template.

Details

Once you have the shape roughly laid out on your cardboard, spend a few minutes to clean it up a little. If your original piece of cardboard is in good shape, you can use it, but don’t be afraid to transfer your shape to a fresh piece. Use a straightedge to make straight lines. Something round to trace out round features if needed. A straightedge can be used to put a clean crease in the cardboard for bending. This is also a good opportunity to add any cosmetic details you may want. You don’t necessarily have to cut everything into or out of the cardboard, but you might draw lightening holes or similar design flourishes.

If you have a part with bends, unfold those bends to get back to a flat pattern. If you’ve taped together multiple seams and you can’t unfold back to a flat, you may need to cut one of those seams open to allow unfolding. Complex sheet metal shapes can be a little bit of an art, but having the physical piece in your hands can help you figure out which seams to bend and which seams need to be open.

Make it Digital

Once you’re satisfied with the shape you’ve created and its flat pattern, it’s time to bring it into the computer. The easiest way to do this is you lay the piece out flat and snap a digital picture of it that you can import into the CAD software of your choice. When taking the picture, we’ve got a few tips that can make things much easier for you.

  • Get the camera as square to the surface as possible. If you take the picture at an angle, the edges closer to the camera will appear longer and the edges further away will appear shorter.
  • Include a known scale for reference in the picture. A framing square is great for this. Not only does it give you measurements, but it also provides a 90 degree reference. If you don’t have a square, a ruler works well. If your piece is small enough you can even lay it on top of a piece of graph paper to take the picture. If you used graph paper instead of cardboard you’re already a step ahead!  
  • When importing the image into your CAD software, get the scale on the image to 1:1. This will make it easy to trace the sketch right over your image. Most CAD programs have a simple tool to help you do this. In Fusion 360 for example, there is an option to calibrate after inserting a canvas.

via GIPHY

Import your best picture into whichever CAD software you’re going to use. You can adjust the transparency of the image to make it easier to see what you’re doing. You want to use the photo to create your part. Tracing out features and shapes. Take your time here. If the photo doesn’t look quite right, you can always measure your piece to get the actual dimension to input into the computer. You don’t have to match your template exactly, if you have the actual measurements, use them. 

Side Note: If creating the CAD is the part of the process that’s keeping you from building your parts, SendCutSend now offers Design Services. Send us your photo or physical template and we’ll turn it into CAD for you!

Final Check

It seems like you’re finished once the part is in the computer, but the final step we’d recommend is printing out the shape you’ve just created in the computer to check its fit. It only takes a couple minutes, but it’s much easier to fix issues at this point than after you’ve cut the part out of metal. Some of our customers with their own small desktop laser cutters will even cut the digital file on their laser in cardboard or a similar prototype material like MDF or plywood.

If everything fits, you’re good to go. You can use your files to get instant pricing and have SendCutSend cut your parts from whatever materials and finishes you choose.

For our example project we chose 5052 aluminum and textured black powder coat.

Problems to Avoid

Creating prototypes can have a few pitfalls you may need to dodge. With a little bit of forethought, you can learn to avoid any issues before they pop up.

  • Bend Radius – Each material and set of tooling used to bend it will produce unique bend geometry. Cardboard won’t have the same bend radius at ⅛” steel, but that’s ok. There are plenty of tools available to make sure your parts come out correctly. A lot of CAD software includes sheet metal tools that will do the calculations for you. All the materials SendCutSend bends have their properties listed (bend radius, K factor, minimum flange lengths, etc). If you’re going with a more manual approach, you can also use our Bend Calculator.
  • Flexibility – Cardboard is more flexible than most sheet metal products (depending on the thickness). It can be easy to bend a cardboard template slightly to get a perfect fit, but when you get the part cut from ¼” steel plate, it doesn’t flex as easily and may not fit. This is an easy one to avoid if you just pay attention when fitting up your template. Keep it flat where it needs to be flat.
  • Thickness – Cardboard comes in multiple thicknesses, and so do the final materials. It’s important to understand how the thickness of your template may be different from the real material while you’re shaping it.

Cardboard Aided Design!

Using an inexpensive material like cardboard to build a prototype/template from can be a great way to dial in the fit of complex designs. It can also be useful for testing your digital design files before you send them off to get cut. We hope this article provided you with some helpful tips to make the process as easy as possible. From cutting, bending and tapping to finishing we’ve got a range of services to help you get your parts quickly. With SendCutSends Design Services, you can even skip the CAD.

Whatever your next project, SendCutSend has the materials and services to help. Get your instant pricing today!

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We proudly use hardware by PEM

Flush Standoff, 4-40, .250" Zinc plus Clear Chromate

Aluminum: 5052, 6061, 7075 Steel: Mild, G30

SKUSO-440-8
Thread Size4-40 x .250″
Hole size in sheet (+0.003/-.0.000).168″
Minimum sheet thickness0.040″
Maximum sheet thickness.125″
Fastener materialSteel
Minimum distance hole C/L to edge0.230″
When determining the distance between two or more fasteners, you can calculate the distance by the formula, C/L to edge + 1/2 the diameter of the second mounting hole..345″
Recommended panel materialSteel/Aluminum
Coating typeZinc
Length.250″
Aluminum material ranges (5052, 6061, 7075)0.040″-0.125″
Steel material ranges (CRS, HRPO, HR)0.048″-0.119″

We proudly use hardware by PEM

Flush Standoff, 4-40, .250" Passivated

Stainless Steel: 304, 316

SKUSO4-440-8
Thread Size440
Hole size in sheet (+0.003/-.0.000).166″
Minimum sheet thickness0.04″
Maximum sheet thickness.125″
Fastener material400 Stainless Steel
Minimum distance hole C/L to edge0.230″
When determining the distance between two or more fasteners, you can calculate the distance by the formula, C/L to edge + 1/2 the diameter of the second mounting hole. Example shown with x2 of the same hardware..313″
Recommended panel materialStainless Steel
Coating typePassivated
Length.250″
304 Stainless Steel material ranges0.048″-0.125″
316 Stainless Steel material ranges0.060″-0.125″