Useful information for new users of the Dremel rotary tutorial
Written by Roberto Muscia. Reproduced with permission.
Diamond and CBN Bits
Abrasive and Polishing Bits
Metal Bits and Cutters
Important Information About Cutter Usage
Something About Hardness of Bits
Increase The Life of Your Bits
Other Helpful Tips
Working On Aluminium
Working On Materials That Easily Melt
Cutting Soft Material And Still The Bit Gets Dull
This tutorial is written for those who are just starting to use the moto-tool and the bits. This tutorial also contains some helpful tips that could be useful to more experienced users. I posted this info because users quite frequently do not find the books which came with the tool very helpful to get started. The people who are new to the rotary tool often get lost with the number of different bits that are available nowadays or they just give up using this great versatile tool (actually: there is a versatile collection of bits available) after they do not achieve the expected results after reading the manual and playing around with it for only a short time.
I also would like to take this opportunity to thank those who passed on some recommendations and extra info to me after reading this or a previous version of this tutorial.
Grinding stones are available in many shapes, sizes, grits and grades, and in two common materials.
The two available basic materials are: Silicon Carbide ("carborundum": green bits - very hard (hardness 9.5) and Aluminum Oxide ("emery"/"korund": brown, orange, pink and grey bits - a bit softer but still very hard (hardness 9)).
Grinding stones are generally used to remove material from or engrave hard materials such as like iron, steel, stone, ceramics and glass. There are many shapes available to cater for different jobs. However, grinding stones will wear in time, especially when used at low speeds and the bit will loose shape. In order to restore the shape of a grinding stone or to create your own shape use the Dressing Stone from Dremel. It is simply a small bar of Silicon Carbide.
To dress the stone set your tool to about half speed, hold your rotating grinding stone to the Dressing Stone and simply reshape or clean your grinding stone. Grinding stones should normally be used at high speeds for the greatest effictiveness.
Pure aluminum oxide is white and silicon carbide is black. The aluminium oxide will take on a grey colour when it contains impurities. To "color-code" the grit of the grinding stones and to bind the grinding particles together manufacturers may use additives. The more pure grit has a quality called friability; that is it easily fractures along crystal faces. This causes the grinding particles to maintain their sharpness but it causes the stone to wear more quickly. This is because the edges of the exposed crystals wear giving them round edges and on the more pure stones (used to achieve sharper edges on the ground piece) the worn crystal faces flake off exposing the sharp edges. However the grey aluminium oxide wear more slowly and produces more heat and creates a rougher finish.
Diamond and CBN Bits
There are two types of coated bits available, diamond and CBN (Cubic Boron Nitride).
Diamond is used as an embeded coating onto the surface whereas CBN is usually applied as a bonded coating but these are similar in use hence why they are grouped together.
The cheaper diamond and CBN coated bits only have a thin layer of material which wears out quite quickly but the higher quality bits have a deeper layer and will last much longer.
On the cheaper bits the layer is not very saturated with diamond or CBN particles and the carrier material and production process is of lower quality. (The particles are not held into it very well). Diamond is extremely hard (hardness 10) and without wearing fast they can be used on almost all materials (materials that easily melt excluded). The diamond-coated wheels often have gaps and holes in the wheel. This allows better cooling (and saving diamond coated area to reduce production costs.)
The CBN bits are slightly less hard than diamond and act more like a conventional abbrasive than diamond since CBN is friable whereas diamond is not. However due to the hardness of these two materials they can be grouped together by appliction.
These bits are available in many shapes and they can be used to remove material or for engraving. They are especially good at cutting and shaping very hard materials such as Tungston Carbide and stone. They are however less effictive on softer materials such as mild steel, brass and copper. These bits work best at medium to high speeds.
Sanding disks are disks of sandpaper with paper or linen backing and coated with grinding particles. They are available in different grits (=size of the particles: low grit = course sanding, high grit = fine sanding). The expression "grit" also is used for grinding stones and grinding powder. The grinding particles of sanding disks are made of hard material but there is only a thin layer of sanding material on the disk. After the layer of sanding material is worn the disk becomes useless. Lower quality sanding disks have lower quality grinding material. They may use emery instead of carborundum, they may contain particles of varying grits, as well as using lower quality glue so that the particles do not stick to the paper or linen as well which causes them to wear faster.
Sanding disks are generally used for shaping soft materials or for cleaning, finishing or preparation the surface of wood or metal, or to remove a coating (e.g. paint), or to grind soft stones, etc. Sanding disks, as well as grinding bits are very inefficient "tools" to rapidly remove material since the particles have random shapes and orientation. Cutters are much more effective and fast. However, because of their inefficiently these disks are great for detailed work because the material is removed relatively slowly. Often there are no cutters available for cutting hard materials so grinding bits, wheels, or discs are the only option.
The grit of sanding drums from Dremel can be determined visually. The sanding disks also have numbers on them (80 = 80 grit (coarse), 120 = 120 grit (finer), etc. The numbers on sanding discs are printed on the back of the disks. Sanding disks generally are used at medium to higher speeds.
TIP: When using sanding discs it quite often occurs that you need to have the sanding side at the "bottom" of the bit instead of at the top. If you place two disks onto the mandrel (one facing up, other facing down), you will not have to turn the disc all the time.
TIP: Sanding discs with differing grit are hard to distinguish from each other. You can code the the screw head on the mandrels to indicate which grit is on the mandrel. Use the two sections of the screw head either side of the slot in the screw head. To mark the bits simply mark one or both of these half circles either side of teh slot:
For easier identification color the coarse areas with moddeling enamel.
- Coarse grit disc - grind the top of the screw to make it rough.
- Medium grit disc - grind one half of the top of the screw and polish the other half.
- Fine grit disc - polish the top of the screw.
Note: The sanding disks available from Dremel are "close coat" as opposed to "open coat". Close coat disks have more grit per unit area and are better for harder material and produce a finer finish. The open coat is better for softer material because it clogs less easily due to the sparseness of the grinding material. You can use a soft rubber sheet (like the rubber soles of worn shoes) to unclog clogged sanding disks. Rubber sandpaper cleaning sticks are also commercially available. They are simply a cheap generic polymer and can extend the life of the sanding paper many fold.
Side note: I have been using this technique many years after I was desperately trying to clean resonous pine shavings from a sanding disk. I am not sure what prompeted me to use the scrap of plastic from an old shoe sole but it worked a treat and I have been using it ever since.p>
Cut-off wheels are available in different diameters, thicknesses, and base materials. The two base materials are non-reinforced and reinforced. The non-reinforced wheels (brown) are made of solid grinding material in a binder (looking at the color I think they are made of emery), they last longer but are quite fragile. The reinforced wheels (black) are a mix of grinding material (looking at the color, probably made of silicon carbide) and fibreglass reinforcing with a resounous binder. They are less fragile, somewhat flexible and they do not last as long since they are harder but with a lot of fibers. The very thin cut-off wheels can only be used to cut through materials. The thicker ones also can be used as a "thin" grinding stone for fast grinding. The thinner ones cut faster than the thicker ones. Besides cutting through materials they can also cut slots, for example the head of a rusted screw. Cut a slot in the head and use a flat screwdriver to remove the screw. They can also cut slots in security screws if you can get access to the heads to cut the slot. All cut-off wheels cut fastest and last longest when used at high speeds. The reinforced wheels should not be used on the sides as you would a "grinding stone" or whole layers of fibers will be destroyed and the wheel could disintegrate.
A special type of cut-off "bit" is the mini-saw attachment. The actual cut-off wheel is a small thin saw blade, made of HSS (high-speed steel). This attachment is very effective for cutting soft materials (that don't melt easily) really fast, leaving a very smooth cut. Use the mini-saw attachment at higher, or highest speed and make sure the saw blade is continously cutting. Do not allow the saw blade to rotating against the work piece without cutting since it will wear and overheat. The mini-saw attachment was originally designed to cut wood. However, it may be used on other soft materials such as perspex, wire netting, thin aluminium and copper. Make sure that the saw blades' teeth are pointing in the right direction. Also check that the tooth direction is correct on a new cutting assembly before using it for the first time. Note that it is normal for attachments which are based on a flexible core (Flex-Shaft, Mini-Saw, Right Angle, etc) to produce a weird and possibly loud noise but is nothing to worry about.
Abrasive and Polishing Bits
There are Emery Impregnated Polishing Wheels, Emery Impregnated Polishing Points, Abrasive Wheels, Abrasive Points and Abrasive Buffs. All of these bits have a different grade of polishing. The results can even vary depending on the material on which it is used. For the impregnated bits the harder the bit the longer it lasts. The more flexible bits (stiff - flexible: Abrasive Wheel, Points, Buffs) are more convenient to use but have differing results. Abrasive Wheels and Points are great for de burring, pre-polishing or to roughen up a smooth surface to be painted for instance. Abrasive Buffs are great for smoothing out irregularities or removing swirls produced by other bits on surfaces. The latter are available in two grits which are coloured dark for medium and sand for coarse. In general it is best to use these bits at medium speeds.
There are several felt and cotton wheels to be used with polishing compound. To put the polishing compound on the bit just run at low speed and push the bit gently in the compound. The compound will melt and the melted compound will flow into the felt or cotton. Once the bit looks uniformly red you can start polishing the work piece at a moderate speed. You may need to re-coat the buff regurarly in order to maintin an even coating of the polising compound.
TIP: While polishing some spots of compound may appear on the work piece. Lightly run over these spots until they dissappear. If the polishing compound seems to have disappeared and the surface looks uniformly shiny then it is time to stop or to get some more polishing compound onto the bit for the next run.
After polishing you can remove the residual polishing compound with a dry soft cotton cloth. Some weak solvent such as alcohol can be helpful to remove the remaining polishing compound and grease base. Polishing works best on low to medium speeds since the soft polishing wheel should be able to adapt its shape to the shape of the surface being polished.
Brushes are available in several shapes and materials. Depending on the material to be brushed you can choose from brushes with bristles made of Nylon, Brass, Stainless Steel or Carbon Steel. In this order they vary from soft to hard. To distinguish Carbon Steel brushes from Stainless Steel brushes Dremel uses a gold colored shaft on the Stainless Steel brushes.
TIP: DO NOT use Carbon Steel brushes on stainless steel. The brush can alter the surface chemistry of the srainless steel causing it to be prone to rust. This layer which WILL rust in a humid environment and the extremely thin layer WILL most certainly become visible!
TIP: Brushes can be used together with other polishing materials, for example polishing compound. If the material of the brush is softer than the material to be brushed the the polishing compound may give you a polished surface. Different brushes loaded with different fluids or pastes will produce different effects on different materials. Experiment with different bits and compunds on different materials and you will be surprised by unexpected and different results.
TIP: When metal brushes have been used for a while the wires will end up facing the same direction. As a result the effectiveness of the brush is greatly reduced. To restore the brush just use it in a low speed device such as a battery powered screwdriver, rotating it in the reverse direction applying the brush to scrap material.
Metal Bits and Cutters
These are also are available in many shapes, sizes, and materials and some are specifically designed for particular jobs. Cutters are normally used at higher to maximum speeds. Run the cutter at lower speeds if the material to be cut is soft or if it melts easily but they last much longer at high speed, especially on harder materials.
There are two materials commonly used for tool bits. High speed steel (HSS) Cutters (made of the same material as ordinary drill bits) and Tungsten Carbide (sintered carbide) cutters (harder than steel but still softer than materials such as flint or quartz). The Tungsten Carbide bits are designed for harder materials since they have a higher hardness.
HSS cutters (Router bits also are made of HSS) are used for removing material from or engraving wood, soft metals (low carbon steel or softer), plastics (if not melting) and other materials that are not very hard. Tungsten Carbide cutters can also be used on harder metals (like bearings, moulds, spring steel, etc.) and other hard materials. Some of the special purpose cutters (like the tile cutter) have large teeth and can be used for fast cutting in bricks, glass or greenware. Initially they may appear to be quite similar but it is not difficult to learn the difference. By the weight, colour and tooth pattern. For example the Tile cutter, Tungsten Carbide cutter, Drywall, Multi Purpose bit, and Grout Removal bits.
Tungsten Carbide cutters are darker grey than other bits and their shaft is shiny and polished. Tungsten carbide is also slightly heavier than HSS. Other cutters are lighter grey, have a less shiny shaft, and have a worse finish. Except for the structured teeth tungsten carbide cutters they have a really matte shaft, as the shaft itself is not made of tungsten carbide. However, they are easily recognizable due to the extraordinary look of the cutting part which looks like a bunch of "large spikes" near to each other. Structured Tooth Tungsten Carbide Cutters have a silver color and the Structured Tooth Shaping wheel is gold colored. Structured Tooth Tungsten Carbide cutters are not the most effective cutters because they consist of random shaped and orientated spikes. However, they can cut soft materials rapidly because of the relatively large spikes. An example of a material that can be cut fast with these bits is "thermohardened" plastic such as Bakelite. Plastics come in two basic types, thermohardened (also called thermosetting) and thermoplastic. The former are plastics that produce powder when being cut, the latter get peeled off (with a knife/ cutter for instance), and are relatively soft and melt easily due to friction (when being ground, sanded, or cut). An example of products that often are made of thermohardened plastics are power sockets and other electrical products around the house.
Listed here are some differences between the bits.
- Tilecutter - has sharp small individual teeth all the way to the top.
- Tungsten Carbide cutter - cutting edges which are close to each other, and spiraling all the way to the top.
- Drywall cutter - has more open spaced cutting edges not all the way to the top. Near the top the spiraling stops, and the top looks more flat.
- Multi Purpose cutter - has open spaced cutting edges all the way to the top like a drill. But an ordinary drill hasn't such narrow shaped cutting edges (ordinary drills are produced by twisting a slotted wire and only the top is sharpened. The Multi Purpose cutter has completely been cut or ground to its final shape).
- Grout Removal Bits - have a long shaft (to be used at an angle with the attachment) and only have a short cutting area (grout always is only a thin layer).
Important Information About Cutter Usage
Always make sure that the bit is alwys cutting and never rubbing. Do not allow the bit to rub against the work piece without cutting since this will cause the bit to overheat and blunt. There are always some variables that need to be adjusted depending on the material to be cut; rotating speed, pressure, and speed of the cutter movement. Just play around with these variables and you will build your skills in order to produce the most efficient cutting. This especially counts for routing. It is not hard to determine, it is just a matter of playing around and trial and error. If you have problems with cutting too far using a continuous cutting motion (you might accidentally cut too far into corners, or detailed curves) you should use a pulsating motion which may give you more control over the tool. Continually vary the force applied to the work piece. Do not simply slow down the speed of the tool otherwise the cutter will cut less efficiently, and if you cut too slowly your bit may rapidly dull and the work piece may dis-colour, or it may even burn and smoke.
High speed Cutters and Engraving Points are just High speed Cutters. Engraving points are named so because their shapes are most practical for engraving jobs. You may also engrave with High speed Cutters. Some Tungsten Carbide cutters also have small tips and are suitable for engraving detailed work on soft as well as hard materials. By the way, this applies to any bit: they have certain names and they come with a purpose description. It is up to the user to use whichever bit is most suitable for the job. For example the tile cutter can be used for cutting tiles but they also work really well on hard wood, glass, hard metals, etc. It's just a matter of trial and error: if you feel a particular bit would work for a particular job you have in mind, just try it and often the bit actually does a great job. When you are new to the Dremel the results of this approach may not be as expected but when you get it right you know it.
Engraving looks as simple as handwriting but it definitely takes practice to achieve satisfactory results. Engraving is the ultimate in doing detailed work, and requires concentration and the comfortable use of tools. The Flex-Shaft can assist in engraving. Using the Flex-Shaft your hand can hold the comfortable slim grip near the bit and you will not have to carry the weight of the tool all the time (tired hands can not do detailed work).
Something About Hardness of Bits
- Diamond coated bits can be used on all materials without getting dull immediately since diamond is one of the hardest known materials.
- CBN Cubic Boron Nitride) is a little less hard that diamond but is harder than any other grinding material. In almost any instance it may be used instead of diamond.
- Silicon Carbide grinding stones are harder than aluminum oxide grinding stones.
- Sanding, abrasive, emerald impregnated bits, polishing points, cut-off wheels, etc. are based on substances with properties lying in between aluminum oxide and silicon carbide.
- Tungsten carbide (Structured Tooth) Tungsten Carbide cutters, all "special purpose" cutters like the Multi Purpose, Tile Cutter, Grout Removal, etc) are much harder than HSS (high speed cutters, engraving points, router bits, drills, etc.)
- From hard to soft brushes: carbon steel, stainless steel, brass, nylon. (Carbon steel brushes have a silver colored shaft and stainless steel have a gold colored shaft for distinguishing them more easily.)
- When using two materials on each other with the same hardness (e.g. aluminum oxide bits on ruby or ceramics) the bit will wear but the work piece will wear faster and loose the contest. This is because moving particles have more kinetic energy than material that moves less fast or is stationary. However, bits are usually chosen with an excess of hardness so they last much longer.
Increase The Life of Your Bits
- When using cutters always be sure that the bit is cutting at all times and not just rotating against the work piece without moving. In the latter case the contact area gets hot and when metals (including hardened metals or steel) get hot, they get softer and dull more rapidly.
- Lubrication also increases the life of the bit. This is especially useful when using bits whose effectiveness depends on the sharpness of the outer layer "particles" (coated bits, structured or sharpened teeth, etc.). As soon as the outer particles or teeth become worn these bits will not work. Lubrication helps the particles or teeth to remain cool. Water can used for lubrication. To help the water to stick to the work piece or bit you can add some soap (detergent) or some lubricating oil. This "oil" contains soap-like ingredients (emulsifiers) which cause the water and oil to form an emulsion so the oil and water do not reject each other and remain mixed. The latter type of lubricant prevents metal parts rusting when they are not dried or cleaned properly afterwards. A common lubrication for steel or brass is kerosene. A small amount may be applied to the surface being cut, drilled or ground. You can also purchase a sulphur based general purpose cutting compound from most hardware stores. This is a similar consistency to grease and can be applied to either the tool or the surface being cut. If you buy a small container of this cutting compound you can recoup the purchase many hundreds of times over in the extended life of your tools. Use a little of it every time you cut or drill and it will greatly extend the life of your tools. There are many lubricating substances available, all of which have differering properties and purposes.
- Never force the bit into the material, let the speed do the job. Make sure the tool does not bog down too much so there is insuffucient speed. Many people use ordinary cutters or cut-off wheels on a rotary tool the wrong way, pushing too hard in order to cut faster and they notice the wheel wearing faster. When you push lightly on the wheel and let the high speed do the job the motor hardly bogs down and running at high speed the sparks fly around and the work piece is cut like butter. After the job is done the cut-off wheel does not wear as much and thus remains larger longer. To avoid the wheel getting stuck in a deep slot you should swing the bit slightly as you cut. Swing in a direction parallel to the slot to be cut, making a long slot. This way the slot gets a bit broader than the wheel itself. This is because you can never make a perfect movement along the slot. The wheel will hit the sides of the slot in a slightly random off-angled way.
Other Helpful Tips
- Important! Tiny particles or objects fly around the area at high speed during the grinding, sanding, cutting (chips!), polishing (polishing compound!), or brushing (wires!) process almost continuously. In order to prevent your eyes being damaged by one or more of these objects you should always wear safety glasses, or goggles. When using Tungsten Carbide cutters on hard metals or bendable materials you also should protect bare skin. Whilst cutting there is a continuous stream of tiny sharp itchy, and annoying chips produced which can irritate your skin for days.
- When placing a bit in the tool do not slide it all the way in before tightening the collet nut. Keep some space underneath the bottom of the bit. This stops the bit binding against the bottom of the holder when you tighten the collet. After loosening the collet to change the bit again just push the existing bit down and it will come loose from the collet. If you do not do it this way the bit might still be held tight by the collet despite of the collet nut being loosened. The collet may also work its way loose since it may not be abled to be properly tightened if the bit is bottomed out in the base of the collet.
- If the tool is obstructing the depth of cut, you can remove the collar from the tool. This is the nut employed to protect the thread that is used to mount attachments onto the tool. This will only reduce the thickness of the tool just below the bit (useful close to the edge of the work piece). Really helpful options are to use the Right-Angle attachment or the Flex-Shaft. Both are narrower and allow you to cut slots in any surface away from the edge of the work piece.
- If you need to work in poorly lit areas (e.g. underneath a sink, in a closet, in a narrow area, or underneath a windowsill) the Mini-Light attachment can be very helpful. When using another lighting source such as a flashlight, you keep hustling with space and shadows which really holds up the job. You can also get LED head lamps from eBay for abotu $20 which are also useful.
- If wish to mark your bits you could use colored tape. Punch holes in the tape (with perforator or hole pliers) and stick it over the holes where you hold your bits in the tray of your storage case. Next to the perforated holes you can write (with a fine water-resistant marker) a description of the bit which is stored there. You could also color-code your bits using small pieces of heat shrink tubing. Cut the heatshrink to about 3mm length and sleeve the tiny tube over the shaft to just below the actual wheel or grinding stone and shrink it using a hot air gun or a lighter. Make sure to cut short pieces otherwise bit will not be able to slide into collet of the tool far enough.
- To increase the versatility of your tool you should have a variety of bits. To keep things organized a storage case with an area or tray where you can separate your bits is highly recommended. If the bits are lying loose they can knock against each other and damage the cutting edges. There are also deigns online of bit holders made from wood blocks. Polishing wheels may be contaminated with grinding particles from other bits which may cause scratches in your work, and it becomes inconvenient using them.
- You can create your own bits for special purposes! Several mandrels are available on which you can mount a piece of any material. Before doing this make sure the piece is suitable for rotating. It should not be too large and it should be quite symmetrical and round. (e.g. piece of sponge, sandpaper or cloth). There are different mandrels available than just those from Dremel. There are mandrels with a slot along the length of the shaft. You can mount any piece of sheet material in the slot (e.g. sandpaper). This way you create any customised flapwheel. There are many web sites where there are may different bits, mandrels, accessories, etc.
Working On Aluminium
Aluminium is quite difficult to work with since most bits clogg when working with aluminum. Aluminum is soft and easily fills up the small spaces between the grinding particles or cutting teeth of your bits so that the bits cease to work. Cutters are hard to clean but can be cleaned using a stiff bristled brass brush. You can buy a cheap brass brush from an automotive supplier then cut the bristles short to make them stiff. Grinding stones can be cleaned with the Dressing Stone.
To cut aluminum you need a bit with more space between the teeth. The two smallest cylindrical Router bits work fast and great, but only on relatively thin work such as sheet aluminium.
Abrasive and polishing bits also work well on aluminum. Sanding bits may also work depending on the aluminum alloy.
It is a good idea to use a small amount of kerosene when using a cutter on alumuinium. It prevents wear on the cutter and helps to prevent it from clogging. Candle wax rubbed along the cut line may also be a suitable lubricant for cutting aluminium.
Working On Materials That Easily Melt
Use cutters or saw blades that have relatively large teeth and run at low speed. Preferably the speed should be lower than 10k rpm (minimum speed of standard Dremel Multi 395 and previous versions). The Digital rotary tool is recommended as it has a lowest speed of 5k rpm and it still has enough torque at low speeds. When grinding, sanding or polishing you always have to deal with fine particles and a lot of friction which generates a lot of heat. In order to prevent melting you should apply very low pressure and keep the bit moving quite fast if possible. If bit is held too long on a small area the material will soften or melt instantly. Small work pieces should be worked with short pulses so the cutting or grinding area is allowed to cool down between the application of the bit.
Cutting Soft Material And Still The Bit Gets Dull
At first glance some materials appear to be soft. However, often these materials are contaminated with particles of hard material like flint. Examples of such materials are grout and greenware (clay products) and sometimes-even metals, which weren't very well mixed while liquid during the production process. You can never avoid this and you just have to live with the fact that bits need to be replaced more often. In these instances you can use CBN or diamond bits.
Happy Dremeling :-)
Roberto and John