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Rotary Tool Tutorial

Useful information for new users of the Proxxon, Dremel, or other rotary tool
Written by Roberto Muscia. Reproduced with permission.

Introduction

Defining The Grit of Abrasives

A Note On Safety

Grinding Stones

Diamond and CBN Bits

Sanding Disks

Cut-off Wheels

Abrasive and Polishing Bits

Polishing

Brushes

Metal Bits and Cutters

About Cutter Usage

Engraving

Hardness

Increasing Bit Life

Other Helpful Tips

Working On Aluminium

Working On Materials That Easily Melt

Cutting Soft Material And Still The Bit Gets Dull

References

Introduction
You will find many different brands of tools and bits and the general adage that you get what you pay for generally holds as true in this area as any other. There are several popular brands of tool and by and large the more expensive tools will have better motors, bearings, electronics, and more accurate mouldings. If you only want a tool for the odd weekend job then one of the cheap big box kits may be fine for you. However if you are wanting a tool that will be used often and for long periods then you will be advised to spend the money on a quality tool.

Simarlarly bits vary in price. My advice here is to stay away from those bargain bin cheap bit sets. The adhesive used in the cheap stone bits is quite poor and they will disintegrate as soon as you power the tool up. Also carbide, steel and embeded particle (diamond and CBN) will wear out in the first use. So as for bits, stick to name brands. I have found some good priced German bits on eBay that are often much cheaper than your local hardware store.

This tutorial is written for those who are just starting to use the rotary tool. 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.

A Note On Safety
Safety is of critical importance and should be uppermost every time you go to turn on your tool.

In the case of a rotary tool you need to protect your lungs and your eyes, and in some instances any exposed skin. The danger comes in several forms. You tool can potentially run up to several tens of thousands of RPM and despite its small size can impart a lot of energy into a shattered bit or stray particle..

The stomes and disks are quite fragile and can burst apart. This can eject pieces with a lot of kinetic energy that can seriously harm your eyes. Brushes can also eject wires which can pierce the skin, but even more dangerous, can pierce the eye which will result in a trip to emergency and potentially cause infection or permenant damage. When you are removing material through abrasion the fine dust can get into the lungs and cause damage to the mouth nose and lungs. If you are using brittle bits such as Tungsten Carbide or grinding then you also need to protect your skin from hot particles which can cause burns.

First you need a good face mask. There are many excelent choices but I find that the 3M 7502 is an excelent choice. It is confortable and the outlet points downward thus not fogging up your goggles. It uses clip on dual replaceable filters for different types of protection and both the mask and filters are easy to find online at palces suchas as Amazon and eBay. You also need to wear wrap around eye protection. Make sure it meets your local standards to ensure adequate potection. If there is a danger of skin damage wear long sleeves, and maybe even gloves and a face shield, especially when using wire brushes. Finally make sure you do not wear any loose clothing that can get caught in the rotating tool.

Grit
The grit nof an abrasive is a designation of how course the abrasive is. A lower grit is coarser and a higher grit is finer. A lower grit would be used for rapid removal of material and a higher grit would be used to give a finer finish and very high grits used to give a high polish.

There are numerous standards used to designate the grit numbers[1] but in general the lower grits are pretty muchg the same across all standards and begin to vary significantly over about 200 to 300 and over 1,000 are completely different. Threfore a 1,000 grit stone or paper from one manufacturer nmay have a completely different grit size from another manufacturer. You may even find varions in grit designations from different products from the same manufacturer, for instance between coated products and stones.

It suffices to say that 16 or 24 grit is extremely coarse and the particles are mm in size. By the time you get to 120 grit the particles can only be seen with a magnifying glass by all but the keenest eye. Once you get to over 1,00 grit you would need a microscope.

Grinding Stones
Grinding stones are available in many shapes, sizes, grits and grades, and in two common materials, silicon carbide and aluminium oxide.

Silicon carbide, also known as "carborundum" is typically green and very hard with a hardness of 9.5. Aluminum oxide, also known as "emery" or "korund" may be brown, orange, pink, grey or white. Aluminium oxide is a bit softer than silicon carbide but still very hard with a hardness of 9.

Pure aluminum oxide is white and silicon carbide is black. The aluminium oxide will take on a darker colour when it contains impurities or as a result of a darker binder. The more pure grit (lighter colour) 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 whereas on the more pure stones the worn crystal faces flake off exposing more sharp edges. The grey aluminium oxide is less fiable and has a harder binder meaning that it will wear more slowly and produces more heat and creates a rougher finish.

Therefore select a white aluminium oxide stone for sharpening knives and sharp edged tools and a darker grade for rough material removal.

Grinding stones are generally used to remove material from or engrave hard materials such as iron, steel, stone, ceramics and glass. Silicon carbide would generally be used for stone ceramics and glass since it is harder and aluminium oxide used fror metals since it is slightly softer.

There are many shapes available to cater for different jobs. Ginding stones will wear or clog, especially when used at low speeds and the bit may loose its shape. In order to clean the stone, restore the shape of a grinding stone, or to create your own shape use a Dressing Stone. It is simply a bar of Silicon Carbide with a resin binder. You can get minature dressing stones for use with the small stones used in rotary tools. You can also get diamond dressing stones which are designed for bench grinders but may also be used for dressing stones used in rotary tools.

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. The diamond dresser could be held in a soft jaw vice while the bit is moved over the diamond impregnated face to dress the stone. Grinding stones should normally be used at high speeds for the greatest effictiveness.

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.

Also 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 and the particles are not held into it very well. Diamond is extremely hard with a hardness of 10 and can be used on almost all materials with minimal wear.

The diamond-coated wheels often have gaps and holes in the wheel. This allows better cooling, and will use less diamond thus reducing 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. Neither diamond or CBN should be used on materials with a low melting point.

These bits work best at medium to high speeds.

Sanding Disks
Sanding disks are disks of sandpaper with paper or linen backing and coated with grinding particles. They are available in different grits. 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 binders which will wear faster. Lower quality disks may also use emery instead of carborundum and they may contain particles of varying grits.

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. 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 for removing material. However, because of their inefficiency 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 may also have the grit printed on them, 80 for coarse, 120 finer, and so on. The grit of the 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 you may need the abrasive side on the "bottom" of the bit instead of on the top. If you place two disks onto the mandrel, one facing up and other down, you will not have to turn the disc and thus sand from both sides.

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:

You can also color the coarse areas with moddeling enamel to make them easier to see.

Note: The sanding disks are typically "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: Many yeas ago I was frustrateds that while sanding resonous pine the sanding disk rapidly became clogged. I saw the plastic sole from an old shoe and on a whim pressed it into the abrasive which at once became as good as new. 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.

Cut-off Wheels
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 but 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. The thicker ones also can be used as a "thin" grinding stone for fast grinding. The thinner ones also cut faster than the thicker ones. Besides cutting through materials they can also cut slots, for example the head of a screw with a damaged slot. Cut a slot in the head using a non-reinforced disk and then 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 when attaching it to the tool. 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 quite normal.

Abrasive and Polishing Bits
These may be in the form of abrasive impregnated polishing wheels, polishing points, abrasive wheels, and abrasive Buffs. These bits may have different grits. The results can also vary depending on the material on which they are used.

For the impregnated bits the harder the bit the longer it lasts. The more flexible bits, points, and buffs, are more convenient to use but have differing results. Abrasive wheels and ponts are great for de burring, pre-polishing or to roughen up a smooth surface to be painted for instance. Abrasive bffs 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.

Polishing
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
Brushes are available in several shapes and materials. In order from soft to hard brush material may be Nylon, Brass, Stainless Steel or Carbon Steel. Brush selection will depend on material and purpose. 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 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 which are 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) low grade stainless steel (lower nickel and chromium content), plastics and other materials that are of lower hardness. 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. Tungsten carbite is quite brittle and chips easily so should be used with care. 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 or 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.

About Cutter Usage
Always make sure that the bit is alwys cutting and never rubbing. If the bit rubs against the work piece without cutting it will cause the bit to overheat and may 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. Slowing the speed of the tool may cause the cutter to be less efficient, 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. 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 or hard materials. By the way, this applies to any bit which have certain names and they come with a purpose description. The user may use any bit that is most suitable for the job at hand. For example the tile cutter can be used for cutting tiles but they also work really well on hard wood, glass or hard metals. 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 will do a great job. When you are new to the tool the results of this approach may not be as expected but when you get it right you know it.

Engraving
Engraving looks as simple as handwriting but it takes a lot of 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).

It is a good idea to find a piece of scrap to practicve on before attempting to engrave your finished piece.

Hardness
There are a number of typs of hardness and hardness scales[2] but in this case we are talking about scratch hardness. The usuall scale is the Mohs Hardness scale[3] which is typically used in geology to detirmine the hardness of minerals. The scale starts at 1, talc and goes to 10, diamond. The idea of scratch hardness is that a harder material will scratch a softer material but a harder material will not scratch a softer material.

In the context of rotary tools and bits, the bit being used must be (by definition) harder than the material being cut, polished or engraved.

With this in mind the following applies to the use of bits.

The list below shows some of the more common abrasives and their hardness.

The abrasive needs to be harder than the material being abraded but depending on the exact chacteristics of the abrasive and material you may not always choose the hardest abrasive. The choice may depend on whether you are abrading low melting point materils, rough material removal or sharpening.

Increasing Bit Life

Other Helpful Tips

Working On Aluminium
Aluminium is quite difficult to work with since it is very maleable and easily clogs most bits. 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 embeded with much harder particles such as 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 sometimes use carbide, CBN or diamond bits.

References

Happy Dremeling :-)
Roberto and John

 

 

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Last updated: June 23 2017