Materials to Know: Medium Density Fiberboard

MDF is the cheapest and flattest wood you can buy at local hardware stores. It’s uniform in thickness, and easy to work with. It’s no wonder that it shows up in a lot of projects. MDF stands for Medium Density Fiberboard. It’s made by pressing materials together along with some steam, typically wood, fibers and glue. This bonds the fibers very tightly. Sometimes MDF is constructed much like plywood. Thinner layers of MDF will be made. Then those layers will be laminated together under glue and steam.The laminated MDF is not as good as the monolithic kind. It tends to tear and break out along the layers, but it’s hard to tell which kind you will get.

Proper way to attatch a fastener to MDF.
Proper way to attatch a fastener to MDF.

MDF is great, but it has a few properties to watch for. First, MDF is very weak in bending and tension. It has a Modulus of Elasticity that’s about half of plywood. Due to its structure, short interlocking fibers bound together by glue and pressure, it doesn’t take a lot to cause a crack, and then, quickly, a break. If you’d like to test this, take a sheet of MDF, cut it with a knife, flip it over, and hit the sheet right behind your cut. Chances are the MDF will split surprisingly easily right at that point.

Because of the way MDF is constructed, fasteners tend to pull out of it easily. This means that you must always make sure a fastener that sees dynamic loads (say a bearing mount) goes through the MDF to the other side into a washer and bolt. MDF also tends to compress locally after a time, so even with a washer and bolt it is possible that you will see some ovaling of the holes. If you’re going to use screws, make sure they don’t experience a lot of force, also choose ones with very large threads instead of a finer pitch. Lastly, always use a pilot hole in MDF. Any particle board can split in alarming ways. For example, if you just drive a screw into MDF, it may appear to go well at first. Then it will suddenly jump back against you. This happened because the screw is compressing the fibers in front of it, causing an upward force. The only thing pressing against that force is the top layer of laminate contacting the threads. The screw then jumps out, tearing the top layer of particle board apart.

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Bartop Arcade RetroPie Powered Laser Cut

[hhtat] wanted to build an arcade cabinet since his days in high-school. Only recently have the tech planets aligned. Looking into the night sky he saw a laser cutter, the Raspberry Pi, and lowering prices on key components and thought, “this is the year.”

Much like an arcade cabinet we posted earlier, this one sits on a counter top. With full controls and a nice screen, it provides a lot of the experience without the additional explaining to the SO why the living space should house a giant decaled MDF box.

The frame was designed in SketchUp and vectors were made in Inkscape. The frame was lasercut out of MDF and Acrylic. Decals were printed and applied. The resulting case, build from tab and slot construction, is attractive.

The internals are simple. A Raspberry Pi with a fast SD card acts as the brain. Rather than make it difficult on himself, [hhat] bought a pre-made controls kit from eBay. Apparently there is a small market for this stuff. He also purchased an IPS screen with built in controller. The IPS panel gives the arcade cabinet a desireable wide viewing angle.

The final product looks like a lot of fun and we can see it turning at least one person into an unintentional loner at any house party.

Materials To Know: Tooling and Modeling Board

I was in a fit of nerd glee the first time I used tooling board. I’d used MDF for similar purposes before, and I doubt I ever will again. Called Renshape, Precision Board Plus, or that green stuff people on another continent buy; it’s all the same extremely useful, unfortunately expensive, stuff. It’s hard to pin down exactly what tooling board is. Most of the blends are proprietary. It is usually a very dense polyurethane foam, sometimes by itself, sometimes with a fine fiber filler.

What makes tooling board so good is its absolute dimensional stability and its general apathy to normal temperature swings. (It even comes in versions that can go through curing ovens.) It is impervious to humidity. It has good surface finish, and it machines perfectly without wearing down tools.

The CNC set-up I coaxed precision molds out of.

This stuff is really tops as far as machining goes. I got super precise molds out of a very basic CNC machine at the LVL1 hackerspace. Renshape cut easily at a high spindle speed, and put practically no load on the machine. Climb and conventional milling were equal load wise with no immediately perceivable difference in finish. In the end I hit the precision range of my cheap digital calipers: +-.005mm, when the temperature is right, the battery is a charged, and the planets align.

I like to do resin casting when I get serious about a part. If you are making a master mold, there’s nothing better than tooling board. I’ve used both Renshape 460 and Precision Board Plus. Both impart a very light matte pattern, equivalent to a light bead blast on an injection mold. There’s no finishing required, though I mistakenly bought Renshape 440 at first and had to sand it a little to get the finish I wanted.

Tooling board is great for masters in metal casting, and is often used in the industry for just that, especially if quick and accurate prototypes are needed. It’s also tough enough to last through a few rounds of metal stamping in the home shop.

If you are doing lay-up for carbon fiber, fiberglass, or leather, this is also a very good choice. It will be unaffected by the chemicals, heat, and vacuum you may use in the process. It is tough enough hold alignment pins for proper set-up without premature ovaling. It is also a very good choice for vacuum forming.

Tooling board is, unsurprisingly, really good for tooling. It’s a great material for soft-jaws, alignment fixtures, and assembly fixtures, especially if you are doing delicate precision assemblies.

If you’re made of money, tooling board can be used for models, signs and props. It sands, shapes, and files extremely well. It bonds well to a lot of substances. It also takes paint very well with none of the absorption properties of wood or MDF. Most professional model shops will use it.
2015-11-05-10.34.01The one big flaw of tooling board is its price — this stuff is expensive. There’s no good DIY version that I’ve scrounged up so far. If you’re making a mold master, a fixture, or anything where you need tooling board’s properties and you are likely to get a few uses out of the board, then it’s probably worth it. Also, be careful of sellers selling plain “Renshape” it is probably going to be the lower grade Renshape 440 and not the more expensive Renshape 460 (or equivalent), where you start to really see the surface finish advantage of the material.

Tooling board is an industrial material. Typically you can call up a supplier and tell them what you’d like to do with it and they will be able to help. If you are making tools for carbon fiber quadcopter frame lay-up, let them know and they’ll have a formulation for that. If you are resin casting, there’s a formulation that gives superior surface finish.

It’s a pretty common material in the industrial scene, but I don’t see it a lot on the hobby scene. This is almost certainly due to its cost, as well as a shortage of small quantity re-sellers. (If someone starts selling assorted sizes on eBay for a reasonable price you have at least one buyer in me.) However, after using it in the niches it is designed for, I really don’t use anything else. I used to hack MDF to fit, but MDF is awful to paint, has no dimensional stability, and dulls tools really fast.

Are you a fan of tooling board? Have a good source? If you have anything to add, let us know in the comments.

MDF Omniwheel Uses No Metal or Plastic

What’s better than a caster? An omniwheel. These wheels are like a big wheel with little wheels at different angles that can roll in any direction. [Sonodera] built an omniwheel out of laser cut MDF. MDF–or Medium Density Fiberboard–makes up all the parts of the wheel. There’s no plastic or metal at all.

[Sonodera’s] wheel is more of a passive design like a caster. It would be possible to drive the wheel through the center in two directions, but the right-angle rollers are passive.

We’ve seen several robots with omniwheels before. In fact, this tripod-inspired robot also has passive rollers and the three-legged design takes advantage of them (the so-called Kiwi drive). Some schemes combine multi-directional wheels with conventional wheels (usually the standard wheels are in the center). There are other multi-directional wheel designs out there, including the Mecanum wheel. You can see a video of the MDF wheel in action, below.

Giant Spirograph Delights Children, Dwarfs Banana

giant spirographLate last year at a craft show, [hahabird] and a friend came across a laser-cut Spirograph and they both had a go at it. After mocking his friend’s lack of fine motor skills, [hahabird] was struck with the idea of making a giant-scale Spirograph that would (hopefully) be less frustrating for kids of all ages.

He generated the gears using an InkScape plugin, and then moved the project to Illustrator for adjustments. After nesting the inner gear drawings, he was able to print them out on one 3×3′ piece of paper at the local FedEx-Kinko’s. To make a template for routing he pieces that make up the eight-foot diameter outer ring, [hahabird] first cut it out of MDF and then bolted that to plywood. The outer ring’s size was dictated by the number of sections that fit on a 4×8 piece of plywood.

The challenge of the inner cogs was to make them move smoothly and still mesh with the teeth of the outer ring. [hahabird] solved this by mounting casters on raised platforms, which double nicely as handles. Each inner cog has a series of PVC couplers that take the 1″ PVC chalk holder insert.

So far, [hahabird] has cut 22-, 35-, and 44-tooth cogs, all of which are painted in nice, bright colors. According to his reddit comments, he will have a video or gif of it in a few days. We hope he makes the plus sign cog and the tongue depressor piece, too.

Roboceratops: A Robot Dinosaur That Defies Extinction

roboceratopsInspired by a childhood love of dinosaurs, [Robert] set out to build a robotic dinosaur from the Ceratopsian family. After about a year of design, building, and coding, he has sent us a video of Roboceratops moving around gracefully, chomping a rope, and smoothly wagging his tail.

Roboceratops is made from laser-cut MDF and aluminium bars in the legs. That’s not cookie dough on those legs, it’s upholstery foam, and we love the way [Robert] has shaped it. Roboceratops has servos in his jaw, neck, tail, and legs for a total of 14-DOF. You can see the servo specifics and more in the video description. [Robert] has full kinematic control of him through a custom controller and is working to achieve total quadrupedal locomotion.

Inside that custom controller is an Arduino Mega 2560, an LCD, and two 3-axis analog joysticks that control translation, height, yaw, pitch, and jaw articulation. For now, Roboceratops receives power and serial control through a tether, but [Robert] plans to add an on-board µC for autonomous movement as well as wireless, a battery, an IMU, and perhaps some pressure/contact detection in his feet.

The cherry on top of this build is the matching, latching custom carry case that has drawers to hold the controller, power supply, cable, tools, and spare parts. Check out Roboceratops after the break.

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