Wet & Dry sanding mandrels

​Following on from last month’s blog on diamond wire saw blades to cut through otherwise very hard to reach areas, the story continues here with cleaning up the cut faces of one of my recent pieces of work.
 
The matau had a narrow slot through the curved mid-channel of the piece.  I now had the choice to use a grinding wheel to open it out, or else a diamond file.  In the event I decided to widen the slot with an abrasive wheel which neatly followed the saw cut, then use my 100 grit medium sized half-round file to follow the groove around the arc to clean up on one side and then the other.  The circular culmination of the channel, the centre of the koru, needed a round file of the right size to clean it up.

​Picture 1 - the tight curves can be cleaned up using a small brass mandrel with some Wet & Dry paper wrapped around it

​​I used a mandrel with a piece of Wet & Dry paper (W&D) wrapped around it to sand the smaller radius curves down and remove the coarse tool marks from the files.  I began with 240 grit paper and followed with 600 and finally 1000 grit paper.
 
For the larger radius curves I used a sanding block wrapped in W&D by hand.  I hesitate to show you the next picture as this is not what you are supposed to use a stainless steel rule for, but I didn’t press too hard and it worked very well in the situation with no damage to the rule!  As a carver you will often need to improvise and there is everything to be said for it!

Picture 2 - it was just the right size for the job!

​​It came out quite neatly.

Picture 3 - the end result of the sanding down was smooth and quite pleasing.

​​But let’s talk a bit about the different tools you can make up or buy to perform this task:
 

• Brass rod is a useful material widely available in a range of diameters and easy to cut to length.  You can file off the ends to the shape you want in your drill - remember to move the file slowly back-and-forth whilst doing this to avoid overheating it. Cut a lengthwise slot to take the end of the W&D.  The mandrels can be straight, slightly tapered or any profile you want – it’s up to you to decide.

 
Most importantly, bearing in mind your electric drill or point carver normally turns to the right viewed from the body and looking towards the tip of the tool, you need to wrap the paper around in the right direction.  A band of rubber is good to secure the outer edge of the paper

Picture 4 - a brass mandrel showing the cut and the homemade rubber disk

​

• You can also just use friction to secure the paper, not cutting a slot in the rod, but using a band again.  This works well when grinding dry by hand.  The band can be a proprietary rubber band, or a flat disk cut with scissors from an old bicycle inner-tube and then the hole made using hole punches
• Proprietary stainless steel mandrels – good for smaller sizes where tolerances are tight
• Tapered mandrels with no slots and using a band – those shown are made from mild steel rod
• You can even use a piece of steel or brass rod glued into the centre of a piece of dowel, with a slot cut for the paper end.  You would need to turn the tool in your drill and carefully sand it down to make sure it is perfectly round and centred before use

 
You can see the selection I use in the picture below.

Picture 5 - showing the range of mandrels I  use for various jobs, both using power tools and by hand.  In the top row, the fone on the right has no slot but the remainder do.  In the bottom row, the two proprietary ones on the left have slots and the other three not

​​When sanding using power tools you need to keep your work cool to avoid overheating and the appearance of white flecks in the stone, so moisten the paper and work occasionally, and when it becomes dry again from the friction, dribble a few more drops of water onto the workface.  The W&D is sufficiently robust to take it, and to form itself into the shape of the tool.  If you have several turns of paper they will gradually wear away, but not before you complete most jobs.
 
A final thought is to keep each mandrel tagged with the grain size of the W&D paper that is on it so you may be able to use it again for the next job.
 
Happy sanding!