Monkey

There are a lot of people who see CNC machines and figure that with one they’ll be able to do something faster, or more accurately, or have it do something they can’t do by hand. These are wonderful goals, and they are achievable, but like all things in life there are tradeoffs.

First, I’ll say flat out that there’s a big difference between owning a CNC machine, and programming and running a CNC machine. It sounds simple, but lots and lots of people fall into this trap. The machine isn’t magic, and it won’t know anything that you don’t know. It’s up to you to decide how to create your part, and then to program and test the machine. Sometimes it is in fact a whole lot harder and more time consuming to get a CNC machine to do something than it is to just go do it by hand.

First consider carefully whether or not a CNC machine will be able to cut the parts you want to make. A 3-axis CNC machine moves a spinning cutter in 3 dimensions while holding the cutter perpendicular to the work surface. Can you make your part with that, or do you need to tilt the cutter? (5-axis machines exist which would allow tilting, but they are significantly more expensive.) Will you be able to make your part by just cutting one side, or will you need to turn it over? If so, how will you ensure accurate placement of the part when you turn it? How will you hold the part down during the machining process? Can you clamp, screw, or glue the part to the table, or do you need a vacuum table? Do you need multiple cutters to create the part, or just one?

Next consider how you will program the machine. The first step is typically to draw what you want to machine in a Computer Aided Design (CAD) program. After this is complete, you need to create tool paths that specify how the machine moves the cutter in order to create the part. This is called Computer Aided Machining, or CAM, which is why you often hear the term CAD/CAM. It is extremely rare that a part you create in a CAD program can be automatically converted by a CAM program in to tool paths to run a CNC machine. It typically requires someone with experience machining using the cutters and materials to carefully guide the CAM program to construct the correct tool paths, accounting for work holding, the capabilities of the cutter, and the order in which the cuts should be made. This can be a surprisingly time consuming part of the process, and it is often error prone. A mistake in programming here can result in real damage to the machine, because the machine doesn’t know the difference between your raw material, a clamp, or even its own frame. And good CAM software usually costs a few thousand dollars.

Finally, consider whether or not you actually need a robot to cut the part for you. There are three primary advantages to using a CNC machine: accuracy, automation, and repetition. If you need 20 of something, then taking the few hours to program and test the machine may make a lot of sense. If you need 1 of something, then the only advantages the CNC brings are accuracy and automation. So do you need the accuracy? If not, then a CNC machine is likely overkill. Is the part you want to make so intricate that it would take hours for you to make by hand? If so, then it may be reasonable to take a few hours programming it, then let the machine take four more to do the work while you do something else productive.

That’s a lot of factors to consider, but with a little practice and experience they become simpler and simpler. Running a CNC machine really involves a combination of your normal craft (i.e., woodworking) with CAD and CAM, and for a time it will require an equal investment in each.

CNC machines are really great for lots of things. I use mine for the following:

1. Cutting snowboard cores. Here accuracy is king, and the effort to program the machine is completely worth it because, honestly, you just can’t get the accuracy you need doing this by hand, even with templates to help out.
2. Cutting mold parts. These are simple shapes, usually cut out of 3/4″ MDF, but I usually need 21 of each one. It it’s a big win to take the time to make a program to cut 21 of these out of a sheet of MDF while I do something else in the shop.
3. Table saw zero-clearance inserts plates. I cut them out of nice Baltic birch plywood usually 4-6 at a time. I spent an hour measuring the plate that came with my table saw and tweaking the program. Now I can make more of these disposable items anytime I want, and have a few more ready to go in 20 min tops.
4. Complicated one-off projects, like ornate wall brackets, templates for cutting other shapes, etc. Again, these end up being worth it due to the complexity of the shape. I usually start these in a CAD program anyway, and if they’re 2D then it’s usually reasonable to convert these to a few simple tool paths and let the machine do the cutting for me.

People frequently ask me if they should build their own CNC machine like the one I’ve built or just buy one. I don’t necessarily want to discourage anyone, but it really comes down to how much time and energy you want to spend building the machine vs. how much time you want to spend making use of the machine. Presumably one wants a CNC machine to help them perform some interesting task after all!

Building your own CNC machine is fun, and you learn a lot doing it. But you should go into the endeavor with your eyes open regarding what you’re getting into.

First, I’m going to assume that you want to build a large table CNC router that is on par with the reasonable low-end of CNC routers on the market today, like the base model Shopbot. There are lots of other options, though, like desktop machines with smaller cutting areas, or much lower precision machines built out of MDF and plastic that are great for many projects and a good way to learn about CNC at a low cost. I have no experience with either of these alternatives, so I’ll limit myself to precision CNC routers.

My goal was a machine that is accurate with repeatable positioning to within +/-0.005”, and which will stand up to years of use with reasonable maintenance. It should be rigid enough to cut half inch MDF or poplar at a reasonable rate, say 100 IPM, hold a 2-3hp router, and spin bits up to 1.5” in diameter. You should first establish similar goals for yourself: determine what precision you need, what materials you want to cut, and how fast. Use specs on commercial CNC machines as a guide.

It’s not necessarily that much cheaper to build a good CNC machine than it is to buy a good one from outfits like Shopbot. It cost me just under $6,000 to build my machine in 2003, and at the time I could have bought a machine from Shopbot that was just as accurate, and a bit faster, for a little less than $8,000. Frankly the difference in price was justified: the Shopbot had a more rigid frame, larger motors, etc. I also saved a reasonable amount of money buying some of the parts off of eBay. The components that go into it are not cheap, particularly the stepper motors, linear slides, and the framing material. These are 3 areas that you should not skimp on at all if you decide to build yourself, but they are the 3 that I frequently see people try to save a buck on, which only makes them sad later.

Building an accurate, rigid CNC machine takes a lot of time and precision metal work. At some point you will require the help of someone with at least a manual knee mill to flatten various mounting plates, and drill very accurate holes in key areas. The more precise you attempt to make the machine, the more precise you must be in machining the parts. Many materials are not actually flat when you get them, even though to the naked eye they might appear flat. Quality linear slides must be mounted to very flat surfaces or they will warp when the bolts are tightened down, the bearings will bind, and nothing will move. Thus some background in precision machining is essential to constructing a good CNC router.

You’ll also need some background in basic electronics. These machines easily draw 30A at 220v between all the motors, drivers, and controller. You should be comfortable working with both high voltage AC and low voltage DC.

If you do decide to build your own machine, then I highly recommend two things:

1. Look for a precision machining course at a local community or technical college. I took two courses in precision machining in the evenings at Lake Washington Technical College, which were excellent. Without them, I surely would have failed to build my first machine.
2. CNC Zone. This is a fantastic community of DIY CNC builders, with resources for materials and components, advice on design and construction, etc.

Today I moved all of the snowboard construction content from the main Happy Monkey site over to posts in this blog. This will make it more convenient for me to organize and add to it. None of the content posted before this post changed today, it was pretty much just a copy.

The purpose of the Making a Monkey posts on this site is to provide information on exactly how I built snowboards at Happy Monkey Snowboards, Inc., so that others may learn from it. This will not be a comprehensive treatment of all the different ways to accomplish these tasks, but rather just the ways that I have personally done it that have yielded success. For alternatives to these techniques see SkiBuilders.com and GrafSnowboards.com, where they have collected detailed how-to’s on how they and others build boards, and have extensive and active forums with even more information on alternatives.

• The Basics category has posts that should give you a good overview of the process from beginning to end.
• The Advanced Techniques category contains the rest of the details, including part numbers, suppliers, materials, tools, etc.

If you have any questions that aren’t answered in these posts, or clarification on something that is here, please don’t hesitate to contact me and I will do my best to help you out. I’m constantly answering questions and helping out other small builders, so don’t be shy. There is a thread at SkiBuilders on our process that may be helpful as well.

Disclaimer: some of the information in these posts can be dangerous. Use common sense, and if in doubt, consult a professional directly. Neither myself nor Happy Monkey Snowboards, Inc., can be held responsible if you injure yourself or damage your equipment through use of the information here. Proceed at your own risk.

Note: if you right click a thumbnail in any of these posts and select “Open link in new tab” or “Open link in new window” then you will get the images full size, rather than scaled for the normal picture viewer. All images are 1280 pixels wide and hopefully detailed enough to help you see everything you need.

This is a detailed overview of my press, complete with part numbers where applicable. All part numbers are for McMaster-Carr unless otherwise specified.

Steel

The press is designed to handle boards up to 200cm long with ease. It’s built out of steel I-beams that are 12” high, 8” wide, 9’ long and weigh 40lbs/ft. There are two beams side-by-side on the top and bottom for a cavity width of 16”. The top beams are supported by two 16” long beams turned on their sides for a cavity height of 12”. That puts the total weight of just the I-beam material in the press at 1,547lbs.

Many question the use of I-beams turned 90 degrees as the separator between the two layers, and yes, in the limit, there is the possibility of minute deflection allowing bowing of the upper and lower beams. In practice, however, this is simply not an issue.

Assembly

The press is assembled with 1/2″ Grade 8 nuts and bolts. This is a simple, cost effective way for anyone to put a press like this together and get a reliable joint. Welding is another option, but it takes a very skilled welder to produce the proper joint to withstand the pressure generated by the hose. If you’re a good welder, or know one, then that’s a reasonable way to go, and is a lot less drilling. But if you’re not, then a weekend’s rental of a mag drill (less than $100, including the drill bits you’ll chew thru) and $35 for the nuts, bolts, and washers is the solid way to go. Part numbers: 91257A748, 94895A825, and 98023A033.

I put the press on casters, and although the final weight with everything in it is right around 2,000lbs, it’s easy to move. Part numbers 22955T42 and 22955T36.

Pneumatics

A little time spent on the air system pays off in simplicity and reliability in the long-term. There’s a little bit of soldered copper piping in the system, but that’s really just for the long runs, and it’s completely optional. The rest is made up of standard brass fittings put together with a little Teflon tape. (Tip: get the yellow stuff designed for natural gas applications. It’s a little thicker.)

Airflow to the bladders is controlled with a hand-operated lever air control valve, 4-way, 3-position, closed center. Part number 3368K26. It’s hooked up so that when the lever is in the center, no air flows. When the lever is to the right, air flows into the bladders, and when the lever is to the left air flows from the bladders out the exhaust.

The exhaust is muffled with a simple sintered bronze exhaust muffler, part number 4450K2. It’s about $2 and completely worth it to save your hearing.

Overall pressure to the system is limited to 90psi with a simple brass pop-safety valve, part number 48435K72.

There is a pressure gauge and pressure regulator on the input side and a gauge on the bladder side to monitor the actual bladder pressure when the valve is closed.

There’s a quick connect on the input side that matches the rest of the air tools in the shop, so a standard shop air supply hooks up to the press. There’s also a similar quick connect from the press frame to the flexible hose for the bladders to allow the bladders to be removed when necessary. This also hooks directly to shop air, just in case.

Bladder connections

People usually have a lot of trouble constructing leak free bladders. They usually seem to end up with a lot of “goop” involved in an effort to stop leaks at the ends and at the through couplings. These bladders are essentially leak free to 90psi with only Teflon tape.

The ends are held together with standard 1″ angle iron from Home Depot using seven 3/8″ Grade 8 bolts: two on the outside ends, one in between the hoses, and two through each hose. They’re torqued down pretty snug, but we didn’t kill ourselves tightening them. No silicon sealant, plumber’s goop, etc., and no leaks.

The through couplings were more of a challenge. We went through a few tests before settling on what you see below. Right click the close-up and open in a new window for a full size view. If you look closely at the full sized image you’ll see a little soapy water around most of it. This picture was taken with the bladders at 90psi. Again, no goop. The secret here is the combination of the three kinds of washers, and the simple fact that the nut for the panel mount coupling is on the outside of the bladder. The washer configuration is repeated on the inside. The 1/8″ thick rubber washers are against the bladder, then the steel, then the Aramid/Buna-N between the steel and the brass nuts. The result is a great seal with the bladder, and a great seal to the nuts. This is not super-tight… just snug, with a little deformation in the rubber washer visible during assembly.

The steel washers are the standard 3/4″ washers from Home Depot. Here are the other parts and the McMaster-Carr part numbers:

• Med-Pressure Extruded Brass Thrd Pipe Fitting 1/4″ Pipe Size, Panel Mount Coupling, 50785K273
• 3/4″ Screw Size, 2″ Od, 1/8″ Thick Large-Od Extra-Thick Reinforced Rubber Washer (10), 90131A106
• Aramid/Buna-N Washer 3/4″ Id, 1-1/2″ Od, .0625″ Thick (5), 93303A317

These parts aren’t super-cheap, but they’re completely worth it.

Pressure

I press the average width board at right around 50psi. This presses the laminate completely into the mold, and results in good squeeze out without removing too much resin. I compute the fiber fraction of every board I build and carefully track this to ensure I’m getting the ratio of glass to resin we’re after. For especially narrow boards I drop the pressure proportionally. Pneumatic presses are capable of amazing pressures, but too much pressure is just as bad as too little. Too much pressure results in a dry laminate that is weak and prone to delamination.

Layers

All aluminum used for mold skins is 0.032” 5052-H32 aluminum that I get from Alaskan Copper & Brass Company here in Seattle. From bottom to top I have the following: the MDF mold, one aluminum skin, the bottom heat blanket, one aluminum skin, the aluminum base mold skin, the snowboard, the aluminum top mold skin, one aluminum skin, the top heat blanket, one aluminum skin, the 1” steel cat track bars, the bladder, the top MDF mold and 2×4 fillers.

Put another way, it’s the mold, the bottom heat assembly, the board assembly, the top heat assembly, the track, the bladder, and the top filler. This allows for easy insertion of the board into the press after wet layup.

Each assembly is held together with a very simple system: 4 holes are drilled near the edges of the aluminum skins, two on each side, and the two sheets of aluminum with either a heat blanket or the laminate are held together with small lengths of 12awg copper wire. You can see these poking out the sides in some of the pictures.

Cat track suspension

The cat track is suspended with simple bungee cord, bought in bulk from McMaster-Carr. 8858T21, 100’, red.

There are a lot of steps to building a Monkey. There’s lots of things to do to prepare the materials, and lots of stuff to get ready for lamination. I keep track of exactly where I am in a build via a simple one-page spreadsheet. I print one of these for each build, and keep it with the board from core blank thru to finished product.

SnowboardConstructionChecklist.zip (right click and select Save Target As…)

The press is heated with two custom silicon heat blankets from MEI, each one 14” x 85”, 2,083 watts running on 240v. They heat very quickly and evenly, are flexible, and they can take the pressure within the press. The temperature must be ramped up from room temperature to 175F over about 10 min, then held within +/- 5 degrees of that for one hour, and finally cooled before the board is removed from the mold.

The heat is controlled by a custom-built controller using a solid state relay, a PID controller with ramp/soak programming features, an contactor, a few fuses, and a couple of thermocouples. We’ve not taken the time to draw a schematic, but the circuit is pretty straightforward. Power comes in to the contactor, and from there is distributed to conectors for the heat blankets. One of the hot leads is passed through a solid state relay (SSR), which is connected to the ramp/soak PID controller. A thermocouple is connected to the PID controller as well, with the sensing end placed with the heat blankets. The SSR can switch may times a second if necessary allowing pretty fine control over how much heat is delivered via the blankets.

The blankets are connected with normal 240v 15A plugs. Being able to disconnect the blankets is helpful sometimes when working on the press. The thermocouples are also connected with plugs which allows us to place the thermocouples in with the blankets before loading the laminate, and to easily replace thermocouples if they get damanged.

The SSR is a Continental RVDA rated for 25A.

The contactor with panel-mount switch is part #SD1-025-RR from automationdirect.com.

The thermocouples are from Omega, part #5SRTC-TT-K-36-36 for 5 type K thermocouples, and #RMJ-K-S for the connectors on the control box. The thermocouples are 36AWG (0.005”), and are therefore small enough to be placed directly on top of the heat blankets without harming the blanket. I place one with each of the blankets, with the sensor end in the center of the blanket. The thermocouple on the bottom is conntected to the ramp/soak PID controller, while the one on the top is used simply to monitor the temperature differential between the two sides of the laminate.

So much of core construction involves the trusty router. The primary router I use on my CNC machine is a Porter Cable model 890 2 1/4hp router motor. The part number is 8902. For trimming sidewalls I use a Porter Cable Model 7301 laminate trimmer with a Model 7318 Tile Laminate Trimmer Base.

I greatly prefer bits from Amana Tool. A quality router bit really does make a big difference. They are well balanced, making the tool quieter, and yielding smoother cuts.

For cutting MDF for molds and most core cutting where a 1/4” bit is called for we use a two flute up-cut spiral carbide bit, #46102, running at 23,000rpm.

For profiling cores, I use a 1.5” two flute straight bit, #45452., running at 18,000rpm.

For placing alignment marks I use a 1/4″ v-groove bit, #45704, running at 23,000rpm.

For cutting base and nose/tail spacers, I use a 1/4″ two flute straight bit, #45208, running at 23,000rpm.

For sidewall profiling, I use a 1/4″ two flute straight bit with a top bearing running at 30,000rpm in the laminate trimmer. This is not an Amana bit… it’s an el-cheapo Home Depot bit that will be replaced with a good Amana bit when it wears out (which will be any day now by the looks of it.)

After the board comes out of the press we still have a lot of cleanup work to be done before it really starts looking like a snowboard.

More pictures of this process will be added later. I was pretty lax getting pictures of this the last time I did it… next time I’ll get my wife to shoot a bunch while I’m actually doing these things.

Trimming the flash

The first step is trim off the “flash”, which is the leftover material beyond the edge of the snowboard. This consists of extra fiberglass, cured epoxy, rubber, top sheet, nose/tail spacers, and sidewall material. I start by using a bandsaw to remove the flash from along the effective edge of the board. This is easily done by allowing the bandsaw blade to press against the metal snowboard edge. It is also possible to remove the flash from the nose and tail using the bandsaw, I chose to cut these portions away using a jigsaw with an abrasive bit.

Cleaning the edges

Now the laminate is starting to look more like a snowboard, but the edges are very rough. Both tools leave a rough edge, and in places there will still be a thin layer of excess material, usually PTEX sidewall or nose/tail spacer. An angle grinder with a 60 grit flap sanding disc is used along the entire perimeter of the board. Excess material is carefully ground away, and the full edge is exposed. I then switch to a 120 grit flap sanding disc and cleanup the nose and tail portions of the board completely. This will be the final treatment these parts of the board receive. This is a pretty delicate process. You can do a lot of damage to the edge of the board with an angle grinder and a 60 or 120 grit disc in an amazingly short period of time!

It is critical that you not overheat the edges while grinding with the angle grinder. I constantly move to another area even before the portion I’m working on is done. I spray liberally with clean water as I do, and check the temperature of the edge with my hand. If you can’t hold your hand on the edge, then it’s too hot.

Base grind

Next, the board gets its first base grind. I start with a coarse 80 grit belt to quickly remove the excess epoxy and a thin layer of base material, then switch to a 120 grit belt for the final grind. While the 80 grit belt is still in place, I cleanup the effective edge holding the board perpendicular to the base grinder. This ensures that the full length of the edge is smooth and even the length of the board.

Beveling the sidewalls

Next, the board is returned to the work bench where the sidewall bevel is applied. A laminate trimmer with a tilt base is used to run a flush trim router bit along the length of the effective edge. This gives the sidewall a perfect 10 degree bevel, and is the last bit of cleanup needed on the sidewalls. If you don’t have a laminate trimmer with a tilt base you can build a wedge out of wood and attach it to the base of your router to form the correct angle.

The key here is to move slowly and ensure that the base of the trimmer remains flat against the base of the board. Ease into and out of the cut at each end, and blend any sharp transition that might be left with a sanding block.

Exposing the inserts

Finally, the inserts are drilled out. I locate the inserts by using two small magnets that will stick to two 3/16” steel ball bearings that I placed in the guide inserts during preparation for layup. The guide inserts are centered along the length of the board, and 4cm from the first set of inserts. Using a guide I can quickly mark where the inserts are below the surface of the board, then drill them out in two steps. The first step is to use a 1/8” drill bit to open up the inserts, then a 45 degree counter sink to expose the full inserts and leave a nice bevel. The counter sink will self-center in the insert. Keep the drill perpendicular to the board to ensure an even, round hole. The threads are cleaned up with a M6 tap, and checked by running a binding screw down into each insert by hand. If the screw doesn’t feed easily all the way to the bottom, the tap is used again until it does.

Use a small pair of tweezers to remove bits of the mylar insert cap that get pushed down during drilling and counter sinking. Clear the inserts with compressed air before tapping and before running the screw down.

Go easy with the M6 tap. You don’t want to cross thread it and destroy the threads in an insert. You also don’t want to run it too far down and push out the base of the insert, which would leave a dimple on the bottom of the board. Most taps come with a point at the end. It’s best to grind this down to a flat bottom, as shown in the pictures below.

I press Monkeys in my custom built pneumatic snowboard press. The press heats both the top and bottom of the laminate to 175F with two 2,083 watt heat blankets that provide direct, even, controlled heat to the board to properly cure the epoxy. The combination of pressure and heat results in a very flat board on top and bottom, appropriate squeeze out of excess epoxy, and perfectly consolidated fiberglass layers.

The press cavity is 92″ long x 16″ wide x 12″ high. It is built with W12x40 I-beams. The long beams are 9′ long and weigh 360lbs each. Total press weight is right around 2,000lbs so far. There are two 5″ fire hoses which operate between 50-80psi depending on board surface area. There are two heat blankets, one on top and one on bottom, for a total of 3.5W/in^2. The blankets are 14″x85″, 240V for a total draw of 17.35A. It takes less than 5 min to heat a board from 70F to 175F.

The heater control has one PID controller with ramp/soak for controlling the heat of both blankets. Temperature is measured below the center of the board. It also has a second temperature sensor to monitor the heat transfer in other locations. It’s helpful to see the lag between the heat on the bottom and on the top of the board during pressing.

Air is controlled with a level in the center of the press. When off, no air flows, when on one position air fills the bladder, and in the 3rd position air escapes from the bladder thru a silencer. There’s also a pressure gague on the press to allow for fine control over the pressure.

The board comes out of the press with “flash” around the edges, which is the extra fiberglass, top sheet, sidewalls, etc. that extends past the edges of the board during layup. The flash will be trimmed off after the board has had a chance to further cure at room temperature for a few more days.

The mold is adjustable for different effective edge lengths, and different nose/tail lengths and rises. I tend to stick with a single camber block that has yielded good results for us over a broad range of shapes and lengths. I have an ever growing selection of nose/tail blocks. If a new block shape is needed for a particular build then I’ll design a new one and whip it up on the CNC machine.

Pneumatic vs. vacuum presses

The first few seasons of production at Happy Monkey were done with a vacuum molding system. This produced decent snowboards, but was a somewhat hit-or-miss process at times and presented some frustrating problems. We switched to a pneumatic press years ago and believe that it yields a superior product with fewer consumables used. The pneumatic press allows me to heat the laminate more thoroughly and consistently than did the vacuum system, and applies significantly more pressure which results in better squeeze out and a more consistent fiberglass layer.