Tools: End Mills, Drill Bits, V-bits
Materials: Wood, Plywood, Brick, Foam, Copper Clad PCB Board, Leather, Steel, 3D Printed ABS, Delrin
There are a million and one tools that you can attach to a dremel to cut with, but here are the three that Bar has been using the most and some thoughts on how to work with them.
An end mill is a bit which is designed to cut in as it moves through material in any direction. End mills are useful for cutting out a shape by cutting all the way through, or to create pockets or slots by cutting only partially through the material. The general rule is that an end mill should only cut to a depth of about 1/2 to 1/4th of it’s diameter, with each pass, so a 2mm end mill might step down 1mm with each pass. Another good rule of thumb is to set the step down no larger than the flutes on the mill.
Large holes can be made by using an end mill to cut a circle of the desired size, but to make small holes you need a drill bit. These can be had in practically any size.
V-bits are mostly useful for engraving text or routing circuit boards. V-bits are nice because they leave an attractive v-shaped groove and they are typically much cheaper than an end mill of comparable size and material. The tungsten carbide ones are worth the extra money. You can find these on eBay pretty easily.
Wood is one of the best materials out there. It is strong, light, easy to work with, beautiful, readily available, and inexpensive. Wood is a broad category ranging from balsa wood to iron wood, so you will have to do some experimenting to see what works best for any particular wood. In general, wood will yield accurate and beautiful objects and can either be cut or engraved. When cutting wood it is important not to burn the wood or your end mill. Rotary tools often can be set to very high speeds (30,000 RPM or higher). These kinds of speeds will cause your end mill to heat up rapidly and burn the wood you are cutting. To prevent this from happening, when cutting wood, use a lower spindle speed in conjunction with a relatively high feed rate (feed rate is how fast the bit is moving laterally) and a small step down (a step down is how much deeper the bit cuts with each pass). This combination lets you maintain accuracy without burning your bit.
Plywood is useful because it has similar properties to wood but it is available in large flat sheets which makes it easy to design with and cut. Similar to wood, you want to keep your feed rates up and your step down small when cutting plywood. We normally keep a stack of plywood “blanks” next to our machine so that if we think of something we want to cut out they are ready to go. It’s useful when cutting plywood to put a sacrificial piece of foam underneath so that when you cut through the plywood you don’t cut into the bed of the machine.
For brick use a high spindle speed in conjunction with a low feed rate and a small step down (we used .2mm). This means that it takes a long time to cut, but it cuts cleanly.
Foam is an interesting material with some useful properties. It combines light weight with reasonably high strength and soft surface texture. We recommend fan-fold insulation foam which is available in big sheets at any home improvement store. Fan-fold foam has small pores which makes it ideal a range of applications from mold making to lost foam casting to RC airplane parts. The downside to foam is that it makes awful dust when you cut it. You can cut foam at any feed rate and spindle speed because it is so soft. There are a lotof types of foam out there, almost all of them produce dust which is toxic and some produce harmful gasses when cut as well. Always work in a well ventilated area and take the proper precautions to insulate yourself from harmful dust and gasses when working with foam.
Copper Clad Printed Circuit Board (PCB)
Copper Clad PCB Board is made from a sheet of FR4 (fiberglass) sandwiched between two sheets of thin copper. Copper clad board can be found online or likely at your local electronics supply store. It is used to make circuit boards through a chemical etching processes or by cutting away the copper to isolate traces. Making PCBs at home has long been one of the holy grails of digital fabrication. FR4 is toxic so we recommend working with FR1 which is a non-toxic alternative.
We hope to have a complete circuit board cut soon, but we have been unable to do a full board because we are having trouble getting heeksCAD (CAM software) to read our digital circuit files. Preliminary tests look good however. Because of the exceedingly high accuracy required to make a PCB you must put love and care into doing it right. To cut copper clad board you can use a v-bit which costs only about dollar, or use a tiny end mill which can cost as much as $25. Using a small end mill results in a noticeably cleaner cut, but they are obviously much more expensive. To cut copper clad board, you want to use the maximum spindle speed of which your dremel is capable, and a low feed rate. There isn’t a low-end on how slow you should go, the slower you go the better the board will look. Backlash becomes a big issue when cutting PCBs because slight inaccuracies in the router’s movements can result in small pieces of copper remaining connected.
When cutting a circuit board, depth is crucial. We recommend moving the bit close to the surface of the material and then stepping it down in .1mm steps until it just hardly cuts through.
You will need to find and cut any uncut connections before a PCB can be used. So how small of traces can you make? We're not sure at this point. We would say that DIP (through-hole) part are viable with no problem and SMD parts as small as 1206 and MAYBE 0805 parts are reasonable to try to hope for, but packages like the SSOT16 will be impossible on this type of mill.
Leather can be either cut with an end mill or engraved with a v-bit. The spindle speed varies with the type of leather and the bit being used.
Our router won’t cut steel, but it can drill very precise holes in it. This is mostly useful for making solder masks for PCB production. Because the bit is only moving vertically while it encounters the material, backlash is not an issue resulting in very precisely drilled holes
3D Printed ABS
We were asked about the possibility of cutting a part which had already been 3D printed in ABS so we tracked down a print that had gone awry from a friend's printer and tried it. We were a little worried that the router bit would bind up because 3D printed ABS is formulated specifically to melt, but it cuts great. We would recommend using an end mill with decent sized flutes to remove the chip.
Delrin is a hard plastic which is known for machining well. As expected, it does.