CAD/CAM, the DIY Builders Best Friend

February 8, 2014
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If you are building a custom electric bike, you really need to know about Computer Aided Design (CAD), and Computer Aided Manufacturing (CAM). These things only sound complex and difficult to learn, but if you break them down into bite-sized pieces, any average person can do this. I know, because…I recently drew a part on my laptop computer screen…and then ordered the part from a water-jetter. The parts were perfect! They arrived at my house in a small box a week later, and they were all precisely identical.

The thing that gave me the final push to attempt this is that I have personally hand-made custom plates from fairly thick aluminum in the past (as I will again in the future), but…I dread working with steel plate of any significant thickness. Stainless Steel is even harder to work with than common steels, and stainless has a very professional and desirable look to it, that I would love to be able to use in a design.

(I was able to cut thick aluminum plate up to a 5mm / 0.200-inch thickness with a large 6-amp jigsaw using Bosch T118A steel-cutting blades)

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First Step…Drawing the Part

Before you invest some of your personal time into learning something new, you first need to determine if the new skill will be able to do what you need. The shape of part that you imagine in your head can be drawn with any one of several free programs, but…you must be able to convert your drawing into an exportable file type that your chosen CAM vendor can use. So you have to start at the end, for planning purposes.

1. Determine what material and cutting method you will use to make the part you want.

2. Find a vendor that you want to do the work for you. (price per part, shipping costs?)

3. Ask them what file types their process can use (.stl/ .dwg/ .dxf/ etc)

4. look for the easiest and least expensive program that can draw the kind of part you need and will be able to save the file in the desired “file type”.

 

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The Big Blue Saw CAD drawing program is free and easy to learn if you need a water-jetted part.

 

Just to help you get started, if you plan to do this often, and are willing to pay extra for a comprehensive program that can pretty much do ANYthing you may ever want to do the rest of your life (including 3D color graphics)…the “go to” professional program in industry is Solidworks. Our friend Miles at endless-sphere is fond of Alibre. I’ve also been told that Rhino is a great mid-priced program that definitely makes .dwg files for cutting 2D flat shapes. Another popular 2D program is Adobe Illustrator.

The best free program is Google’s Sketchup, and be aware that there are free “plug-ins” that will expand the capabilities of the basic version of Sketchup. If Sketchup is a little daunting for a simple flat 2D part, try libreCAD, which is a free CAD program that already has the ability to export files as a 2D .dxf file.

If this all is starting to look and sound very intimidating, just remember that you will likely only need to learn the most basic functions in order to draw a two-dimensional shape, which will be cut into wood, plastic, or metal sheets. Plus, there are many free tutorials on all of these programs on You Tube.

Here’s a late addition: from ES member “Mattyciii”. He used emachineshop, and they have a simple and free 2D/3D CAD program (along with a beginners tutorial) that you can download and use anytime (not just when you are on their website). The cost for one part is pretty pricey, but if you order more…the “per piece” price drops quite a bit. He actually drew his custom clamping drop-outs on this program, but had them made by a local vendor to save on shipping.

Here are possible file-types to look for: .stl/ .dwg/ .dxf

I actually used scissors to cut out the shape I wanted from a large manila office folder (to work out the shape that would fit on my frame), then I transferred the dimensions and shape onto the CAD drawing program. I have even seen builders cut their prototype shape from thin and stiff 1/8th-inch thick fiberboard, which can be cut by a razor-knife.

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Water Jetting

The only process from this list that I have personally used is water-jetting, and I am very happy with the results. I chose a company called Big Blue Saw (BBS). I didn’t know how to use Solidworks or the free program Sketchup (yet!), and BBS has a free proprietary CAD drawing program that is very easy to draw shapes on. If you want, you can supply them with a CAD file drawing from somewhere else, but they realized that many potential customers only needed to draw a simple shape, so they created an easy program with a video tutorial to get you started.

 

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This particular water-jet vendor can cut stainless steel up to 3/4-inch thick

 

If you draw your part on their easy proprietary .jpx program, you will not be able to export that drawing to use with another vendor, but it is free and there is no harm in just experimenting with it for an hour or so to see if it’s something that would work for you.

BBS has wisely included a page on how to download the “plug-in” that allows a Sketchup drawing to be converted from their .svg file into a .dxf file that just about anyone can use. This is because Sketchup is so popular, but most industrial machines don’t use Sketchups’ .svg  files. Of course this knowledge benefits anyone who will use any of the methods listed below, not just water-jetting at BBS.

 

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Here, an electric skateboarder needed an aluminum pulley in a particular size that nobody stocks, so he ordered them from a water-jetter. This build can be found here.

 

BBS can water-jet aluminum and common steel up to a one-inch thickness (24mm), and can cut stainless steel up to 3/4-inch (0.750-inch / 19mm). Although I am using BBS as the water-jetting example, they also stock a wide variety of materials that will laser-cut, such as leather, thin wood, and plastics.

If you are cutting a part that is very thick, carefully consider if you need the sides of the cut to be perfectly perpendicular. Common water-jetting results in a slightly tapered/flared cut, but it is not noticeable on thinner parts. If a thick part needs an unusually straight edge, you may need to pay a little more to specify a “low taper” cut

 

These parts

These parts are one-inch thick 6061 aluminum, and were drawn and ordered by Mattyciii for his custom build, found here.

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Laser Cutting

A method of CAM that seems to be very popular recently is laser-cutting. Check around for a local shop that does this and get a quote to see if this is better for the part you need, or if water-jetting might be better. If you don’t find a local shop you like, several endless-sphere members have used polulu.com. This web-based laser-cutter uses .dxf files, so any CAD drawing must be converted to .dxf before they can use it.

Click on this link to see a laser-cutter in action.

 

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ES member jimnasium drew and ordered these parts to be laser-cut out of thin plywood. They assembled into a battery-box that fit into his E-bike frame. If someone else wanted the same, just get a copy of the file and order another…it only has to be drawn once!

 

Our friend Mike (ES username LightningRods) was impressed by the motor on the GNG 1,000W mid drive, but the rest of the kit has many weak points. He decided to develop the best possible mid drive kit from this motor, which has been found to be capable of 72V X 30A = 2,200W (roughly 3-HP). The bracket shown below could have been water-jetted, but Mike found a local shop that would laser-cut the steel, and then also perform the precision-bending that he needed.

 

This is the mounting bracket for the motor and jackshaft of the LightningRods kit we will be testing soon.

This is the steel mounting bracket for the motor and jackshaft for the LightningRods kit we will be testing soon.

 

Some custom E-bike builders still want to use a rear hub-motor. If you want to use a LOT of power, then a common torque-arm is not strong enough to hold the axle. A popular solution is to make a clamping torque-plate, which attaches to the frames stock rear drop-outs. Since the best material for this is thick steel, this is the most common E-bike part that is water-jetted or laser-cut. The pic below is an especially professional example designed and made by ES member “kiwi“, and it allows an owner of a Giant DH Comp to use a very powerful rear hub with complete reliability.

 

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These clamping drop-outs for a Giant DH Comp bicycle were designed by ES member Kiwi. Since he needed a 3D shape from stainless steel, he laser-cut three layers of flat sheet-metal, and then had them welded together. They also could have been water-jetted and then welded together.

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CNC Milling

Computer Numerically Controlled (CNC) is one of the first ways that computers were used to make machine shops more productive. Instead of having one high-paid machinist per mill or lathe, making dozens of the same exact part over and over…one machinist could set-up and run three CNC mills (or more!).

The pic below is a custom pulley being cut from thick aluminum for a mid drive E-trike by an endless-sphere builder called Trilska. If a friend (or a customer) requested the same exact part, you have only to email the file to a CNC shop that you like, and a complex part will be precisely cut and then shipped to your house. This particular pulley was very large, so it was cheaper and easier to make it in two identical halves.

CNC used to be the way to cut both 3D and flat 2D shapes, but since the advent of water-jet and laser-cutting, the higher price of CNC milling is typically only used for 3D now. The .stl file-type is the common one for 3D shapes.

 

The white liquid from the 3D CNC milling machine cools and lubricates the cutting bit.

The white liquid from the 3D CNC milling machine cools and lubricates the the high-RPM cutting bit.

 

The custom Paul Brodie eBee mid drive has many parts that were drawn in CAD, and then CNC-milled, for a very professional “production” look.

 

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Here is a CNC mill cutting out one of the sideplates to mount the motor on Paul Brodies NAHBS “eBee” mid drive. This part was just cleaned, and now the CNC mill is about to start another series of cuts.

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3D printing

The last CAM method I want to talk about is very exciting, because this last year they have gotten so inexpensive that the average builder can actually afford the entire system if you want it bad enough. It is a RepRap 3D printer (Replicating Rapid prototyping). It is a machine that can make complex 3D shapes out of plastic.

You purchase a roll of plastic string (called filament) to feed into the machine, and the nozzle heats it up and extrudes out many thousands of tiny dots that fuse together. A simple bracket that RepRap can produce, can function well with the coarse “orange peel” texture that is the raw result from the affordable models, but be aware that there is also a technique called “acetone vapor smoothing” that can convert your part into having a very smooth finish (if you are using ABS filament).

The nozzles can be sized for extrusion output diameters of 0.2mm,  0.4mm, and 0.7mm. The fatter extrusion nozzle will be faster, but the smaller extrusions will have a smoother finish and provide much finer detail.

 

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Here is a roll of the common 3.0mm diameter PLA filament, the other most popular size is 1.75mm diameter.

 

The dimpled surface of items made by a fast and coarse 3D printer can be smoothed-out by simply placing an ABS-based printed part in a glass jar with a few ounces of acetone on a warming plate. When heated to a temperature of 190F / 90C the acetone evaporates, but creates a cloud that is heavier than air (it will stay in the jar). The cloud surrounds the model and melts the surface; after a couple of hours for cooling and solidifying, the item has a mirror finish.

The most common starter filament is PLA (Poly Lactic Acid). It melts at a temperature that is slightly less than ABS, it is recycleable, and when heated to print, it has almost no smell. I highly recommend you select components that are capable of printing with ABS (it will still be able to print with PLA). The common filament for making mechanical parts is ABS (Acrylonitrile Butadiene Styrene). If you have ever seen childrens LEGO blocks, they are made from ABS.

PLA is made from plant sugars, and its faint fragrance is slightly sweet. It is great for in-home art projects. ABS is formed from petrochemicals, so when it’s hot, it has a “plasticky” smell (print in the garage?). The end product from ABS will have a harder “feel”.

If you are starting out with only PLA printing, you don’t need a heated base-plate/bed. But make sure that any kit you choose is upgradable to easily add a heated bed in the future, so you can print with ABS when you want. PLA will work better with a heated bed, but the bed must be able to run at a very hot temp to work well with ABS.

You may notice on some videos that a part will start with a thin and flat “mat” printed under the part, this mat and also the heated bed will help the part remain “sticky” and stay attached to the bed, so it won’t wobble as it’s being whipped around. Without matting and a heated bed, you will have to print items very slowly.

 

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The figurine on the left was 3D-printed using a fast and coarse printer that was one of the more “affordable” models. The one on the right is identical, but it was finished with an “acetone vapor smoothing” process. You can clearly see the many horizontal “slices” that the machine printed on the left.

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Cheapest fully assembled 3D printer?

If you can’t quite afford to get your own 3D printer, there are several services around the country that will accept your CAD drawing file (the most often used 3D file is .stl), and they will make your part and ship it to you. Even some Office Depots have this service, so you might be able to get your part locally, to avoid waiting or paying for shipping.

The most affordable complete and fully-assembled RepRap right now is the $200 QU-BD One Up, which can print a size of part that would fit inside a 100 X 100 X 125mm cube (3.9 X 3.9 X 4.9-inches). If you want a larger version, then for $80 more you can get the Two Up model with a 175 X 175 X 125mm print volume (6.8 X 6.8 X 4.9-inches). Also, for $80 above the printers base price, you can add a higher-temp capability so it can print objects using ABS (instead of the common PLA), which is a much stronger plastic.

If you only need to print one part at a time, the upgraded ABS-capable Two Up is a great value for only $360.

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Any DIY kits?

Here is a list of DIY RepRap 3D printer kits and open-source models. If you don’t have a clear preference, the Prusa i3 is well-regarded. For less than $40, you can buy all of the complex joints (which are made on a 3D printer, by the way!), which are then simply connected by all-thread rod that you can purchase locally to save on shipping. You would then also need to individually purchase the controller, the stepper-motors, an AC/DC power supply, printer extrusion nozzle-head, fan, and various other small parts. The frame can be bought (or made) from free plans found on the web.

The total price for a functioning Prusa i3 should be less than $180, and that is for a printer that has a higher-quality printing head than the QU-BD printers listed above, and it will be able to print a cube volume of up to 200 X 200 X 270mm (7.8 X 7.8 X 10.6-inches), and this is twice as big as the QU-BD One Up‘s print capabilities listed above. A larger print volume also means that even if you are printing small parts, you can print several at once, instead of just one at a time.

Here is a 2-minute video of a Prusa i3 in action. In this video, it is set to run very fast, and if you used a slower print-speed…it would provide prettier results, with fewer hair-like strings that look like fuzz that would have to be trimmed off after the part cools down.

 

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This is the starter kit of 3D printed plastic pieces that make up the core of the Prusa i3. The pic on the right is assembled using a single-sheet aluminum plate-frame (water-jet or laser-cut). An alternative is to make a DIY thin plywood “boxed style” frame.

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Once you have a computer and a 3D printer, the process is something like this:

  1. Create a 3D CAD model, and export it in the .stl format. Or, get a .stl drawing from the internet or a friend.
  2. Arrange one or more models on a virtual print plate with a “host” program (you can print just one part, or several parts at once).
  3. Slice the the virtual models into thin horizontal slices, and compute a path for printer head. This is done by a slicing software, which converts the model into g-code (g-code is the language a 3D printer speaks). “Slic3r” is a popular slicing program.
  4. Using the “host” program again, send the g-code to your printer, or copy the code onto an SD card, which you can insert into your printer (if your printers controller is SD-card capable). A popular program that combines both the slicer and host functions is Repetier.

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Random 3D Printing Notes

If you end up 3D-printing a huge volume of parts, it is possible to make a machine that takes raw industrial plastic pellets (bulk purchased at half the retail price of finished filament rolls), and extrude your own filament to feed your 3D printer. Some PLA plastic can even be purchased that glows in the dark!

And even if you never want to learn how to draw parts, you can now make (or buy) the first part with hand tools, and then scan it into a 3D computer model. There are even services that will scan a part that you send them, and convert it to a 3D .stl CAD file for you to use for CNC or a 3D printer.

If you are willing to pay anywhere from $500 to $3,000 for a higher quality and more capable 3D printer, check out this MAKEzine special edition on the latest selection of 3D printers that are available for purchase in 2014.

As a final note, just be aware that a 3D printed part may not be super strong (it’s just plastic), but…the 3D printed part can be the core to a silicone mould, which can then be used to cast metal-impregnated resin parts. You can also use your 3D printed part as as the core of a Plaster mould to cast custom aluminum parts.

If you are ever ready to upgrade to a more capable machine than the starter models that are discussed here, one interesting option is the ability to print with Nylon filament. It requires the ability for the extruder head to maintain a higher temperature of around 320F/160C, which is much higher than the common PLA/ABS 220F/104C (here’s a list of the differences between PLA/ABS).

There are many variations of each filament chemistry, in order to get various characteristics. When starting out you should stick with the most common, which is 4043D for PLA, and PA-747 is the standard ABS.

Here is an interesting article. It is about using a laser to sinter fine-grained titanium powder in order to “3D print” a bicycle frame out of metal. A titanium off-road full-suspension frame is their first attempt because they need a high purchase price to recover the development cost. It is unlikely that any shop that is set up to do this will take orders from the public for custom jobs, but it is fascinating so I thought I’d include it.

The very last link I put in this article is the most important one, so I will park it here at the bottom so it will be easy to find again. It is a set of 3D printing guides from Makerbot.

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Written by Ron/Spinningmagnets, February 2014

 

 

 

 

 

 

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas


7 Comments

  1. Nice article. Could you give some general ideas of costs for each method? I think some broad ranges could help determine what route to go based on the pros/cons outlined.

    • For waterjet or laser cutting, you can take a look at the Big Blue Saw website and click the “Find Out More” button to see several example parts. You can use these samples to find out the prices for various quantities and materials.

  2. This is an very impressive article and a great overview of modern machining technology. I’m glad the parts we made for you worked out so well.

  3. I enjoyed this article. I work and live in Sausalito, across the bay from sf and I have been obsessed lately with electric bikes. I own Marin Metalworks and we do prototyping for people with ideas. Our main tool is a 6′ x 12′ Flow Waterjet. Our machine has cut 5″ thick steel with no taper. It uses 87,000 psi of water pressure and it is the greatest tool in the world for designing things. We have made parts for Pi Mobility and Yuba bikes, both of which used to be based in Sausalito. I would love to make some cool stuff for you if you have any ideas, in exchange for advise with my bike projects. I have 3 moonlanders that I am trying to make work with a mid drive Bafang bbs02. I put Rouloff hubs and Gates drives on them but having trouble with the mid drive fitting the bottom bracket. I can’t stop designing cool bike stuff and would love to trade for some advise. Email me any time. Let’s make something.

  4. How does one calculate the exact profile for a belt pulley ? Are there add-on tools for this for for instance sketchup or LibreCAD ?

    • A ‘V’ belt?

      Visit your favorite search engine and search for “v-belt profile chart”. Don’t forget to look at the images it finds too.

  5. Also don’t overlook plasma cutting. I have one of these in my shop. I live in a small town and have several small welding fabricators around town. I know two of them have a plasma cutter. Mine is a PlasmaCam brand.

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