Dental burrs & wheels

This month’s blog is about dental burrs (also spelled “burs”) and thick disks, known as wheels, the latter of which are mercifully rarely used by dentists on patients!  They both consist of a head, neck and shaft or shank – all pretty self-explanatory terms.
 
The abrasive is generally diamond, but may be silicon carbide (carborundum).  This is either applied to the surface of the head in an electroplating process, or set in sintered bronze or other alloy.  The first are cheaper and wear out more quickly than the second - which can be much more aggressive.  You can, and should, buy both the burrs and wheels with different grades of abrasive – eg 80, 150, 220, 325 & 600 grits are to be easily found - as you can reduce the amount of necessary grinding and polishing later-on by using the finer grades after initially forming with the coarser.
 
These are good accessories to have as you can use them for an amazing range of operations.
 
A word of caution: do not bother buying the tungsten steel burrs, which have teeth and are designed to cut softer materials, as opposed to the diamond ones which are meant to abrade harder substances.  The former are not suitable for use with jade.
 
My selection of burrs, bought from a variety of sources around the world, have the following range of shaft diameters – 1.0, 2.34, 3.0, 3.14, 5.8, 6.0 and 10.0 mm (see Picture 1 below).  The small ones I mount in the Dremel, the larger ones in my Jacobs chuck.

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Picture 1 on left shows a variety of burrs and wheels in a range of shaft diameters.  I've found it is  hard to have too many different styles - they each have a use which I may or may not have yet discovered.

When using them, you need a drip or mist of water to keep them, and the work, cool – it extends their life and saves the stone from heat damage.
 
Assuming you use the small ones in your Dremel, as always, you hold the tool firmly but lightly with one hand and apply a minimum of pressure to the job, holding that with the other.  Clamping the workpiece is generally unnecessary.  But beware of the tool running-away from you by grinding against the direction of rotation on the work, and bracing your hand or wrist on something stable.  The grinding action can sometimes result in “bouncing” of the tool (I wonder what the official term is for that?  Someone please tell me!) but you will have to overcome that as best you can.  You may also notice a snarling sound sometimes if you are boring a hole and the tool is threatening to bind all around its contact surface.  To minimise this, pull back slightly and exert gentle pressure on only a portion of the hole through a circular motion from your hand – one reason why using tapered burrs is good for boring holes.
 
Some of the myriad of shapes available are:

• balls
• points
• cones or tapers
• truncated tapers
• reverse cones
• cylinders with flat or round noses
• flames
• footballs (I guess they mean rugby balls?)
• round, cheese-shapes which can also be thought of as wheels if they have a large enough diameter (see Picture 2 below)
• and many, many more
  

Picture 2 on left shows a 75 mm diameter x 5 mm thick wheel I had made up.  The sintered diamonds are wonderfully coarse and I can remove a lot of material in a short time when necessary.  The shaft is 10 mm diameter.

I’ll also mention the following two types of tools for completeness:

• slitting disks are very thin wheels which are generally used for cutting rather than grinding
• diamond drills, which are very useful in some circumstances

 
What can you do with all these tools?  Well, you are only limited by your imagination and the accessories you have!  Below are some processes available to you (and see Picture 3, below):
 

• boring holes
• grinding slots and grooves
• rough-shaping concave and convex surfaces
• smoothing ridges and removing tool marks
• cleaning up faces
• reducing high, hard spots in a surface
• cutting all sizes of features
• introducing texturing (you don’t have to polish the whole piece unless you want to)

Picture 3 on left shows a range of burrs on 6.0 mm shafts.  They work well mounted in the chuck on larger jobs.

I’d suggest you use them at the relevant stage of work on your piece (ie use a 150 grit burr when you are coarse-shaping with other 120 – 240 grit tools) because if the tool slips you will have to go back and polish out the marks - and that can be a real pain if you are at the polishing stage!
 
Hole-boring is a very important carving skill and deserves its own write-up which I’ll go into in a future article.
 
So what are you waiting for?  Happy carving!