Die grinder

Dremel is really a brand name, but is widely used to mean a small high speed rotary tool of any brand. Typically these take tools of upto just over an inch diameter with 3.2mm shank.

Tools

Many types of tools are used with these machines.

Drill bits

Upto 3.2mm

The thinner drill bits are very weak, sideways force or movement should be avoided

Grind stones

of various shapes, compounds & grades.

Use depends on the material and shape

Diamond coated engraving bits

For engraving glass

Metal wire wheel

For removing rust & paint

For creating 3d grain in wood eg for moulding.

Metal wire cup wheel

As above, but less powerful and more able to get into corners

Nylon brush wheel

Cleaning

Removal of soft materials

Removal of loose paint

Nylon cup brush wheel

As above, but less powerful and more able to get into corners

Cutting discs

Various compounds and grades

What they cut depends on compound and grade of the disc

See safety notes re non-reinforced discs.

Felt polishing pads

Polishing metal, plastics,

Use with polishing compound

Rasps

aka High speed cutters

Fast shaping of soft metals, plastics, wood etc

Sanding discs

Sandpaper discs are used with a flexible backing pad.

Screw mandrel

These hold felt pads

Tool Maintenance

Grinding stones can clog with metal. This can be removed either by a wirebrush or a coarse abrasive.

When grinding soft metals such as aluminium and copper, clogging can become a real problem. Rubbing the disc or stone firmly with chalk first may reduce the clogging to some extent.

Performance

Linear speed of a 1" 30,000 rpm tool is around 70% of that of a 4.5" 10,000 rpm angle grinder tool. Also angle grinder discs & brushes are more robust. Thus more speed and force are available from an angle grinder than a Dremel type machine.

The prime advantage of Dremels lies in their tiny size, which enables access in restricted spaces, and makes fine work with miniature tools practical.

They are also generally much quieter than angle grinders, which can be an advantage in some situations.

Finally more types of tool are available for Dremels than angle grinders.

Usefulness

How useful are they is a question often asked. Personal experiences follow.

1. I rarely use mine, but when I do, nothing else will do.
2. I last used one for cutting out some bearings. I don't know any other tool could have done the job.
3. They can be used for cutting pipes in awkward places.

Speed

These tools operate at extremely high rotational speed, and one should check that the tools used are rated for the speed of the machine. There are tools available rated at below typical machine speeds, and these should not be used above their rated speed on safety grounds.

Reducing speed

Some machines can be set to reduced speed to enable lower speed tools to be used, some can't. For machines with no speed control there are some workarounds for speed reduction.

• Running the tool off a 110v transformer gives a max speed of 110/240 x the usual run speed
• When no better alternative is to hand, running a lightbulb in series with the dremel tool reduces the voltage and thus speed. A multimeter is used to measure the offload voltage and thus calculate max speed. The downside of this arrangement is that as the tool is loaded its speed will reduce at a greater than usual rate as load increases.
• Low voltage tools can be run off a supply of lower voltage to reduce speed.

Speed = voltage/rated voltage x rated speed.

This holds true for both mains and low voltage machines.

Safety

The main risk with these machines is explosion of the tool due to breakage at very high speed.

Speed rating of machine and tool are important, the tool should not be used at above its rated speed. Running over speed can cause tools to shatter explosively.

Cutting discs for these machines are in some cases non-reinforced, despite the fact that they run at very high speed. This means that if they break in use they will explode. They are also typically very thin, thus having low force ratings, and meaning that a single intergrain bond failure has a greater likelihood of causing disc failure.

Wire brushes are prone to shedding bristles. These shed bristles come off at high speed, and are dangerous.

Eye protection is a must with these tools, and one should always stay out of the plane of spin of the tool.

A second risk results from high speed, tool inertia and absence of guarding. Catching a spinning tool on something can yank the machine forcefully. The machine should be held firmly, hands kept out of the way of the tool, and force on the workpiece should be kept light.

Tools that cause vibration should be retired. These have become unbalanced, and are much more liable to fail dangerously in use. They also put high stresses on machine bearings causing premature failure.