Die grinder
A Die Grinder is a small high speed rotary power tool. Typically these take an array of tools of upto 1.5" diameter with 1/8" or 3.2mm shank.
Dremel is a popular make of die grinder, and the word Dremel is widely used to mean a die grinder (of any brand).
Tools
Many types of tools are used with these machines.
Drill bits
- Upto 3.2mm
- Bits to have 3.2mm shank
- Thinner drill bits are very weak, sideways force or movement should be carefully avoided
- Do not be tempted to use solid carbide bits in die grinders, in small sizes they are unsuitable and unsafe for handheld tools
Spiral saw
- 1/8" spiral saw bits can be used in die grinders, but their uses are limited.
Grind stones
- Various shapes, & a few compounds & grades.
- Aluminium oxide is used for most grinding stones, and is not good at grinding steel. These stones are light coloured.
- Carbide strones are good for steel. These are dark grey, and several times the price of alox.
- Use depends on the material and shape of the bit
Diamond coated engraving bits
- For engraving glass
- assorted shapes
Metal wire wheel
Metal wire cup wheel
- As above, but less powerful and more able to get into corners
Nylon brush wheel
Nylon cup brush wheel
- As above, but less powerful and more able to get into corners
Cutting discs
- The discs are very weak and break very readily
- Potective eyewear is needed with these non-reinforced discs.
Sanding drum
Felt polishing pads
Rasps
Sanding discs
- Sandpaper discs are used with a flexible backing pad.
Screw mandrel
- These hold felt polishing pads
Flap wheel
- Sanding flaps
Tool Maintenance
Grinding stones can clog with metal. This can be removed either by a wirebrush, a coarse abrasive or a spiked wheel.
When grinding soft metals such as aluminium and copper, clogging can be 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 2/3 of that of a 4.5" 11,000 rpm angle grinder tool. Also angle grinder discs & brushes are much more robust. So more speed and force are available from an angle grinder than a die grinder.
The prime advantage of die grinders 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 die grinders than angle grinders.
Usefulness
How useful are they is a question often asked. Personal experiences follow.
- I rarely use mine, but when I do, nothing else will do.
- I last used one for cutting out some bearings. I don't know any other tool that could have done the job.
- 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 die grinder 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.
See Droppers for more information
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 very thin and unreinforced, despite the fact that they run at very high speed. This means that when they break in use they fly apart. Being extremely thin, they break very readily.
Wire brushes are prone to shedding bristles. These shed bristles come off at high speed, often sharp point first. Some wire brushes have a reduced speed rating.
Eye protection is a must with these tools, and one should 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 always 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.