Laps

Laps are the most basic piece of carving equipment after sand and water!  They are ideally made of a 5 - 10 mm thick disc of steel machined perfectly flat, and 150 – 250 mm diameter.  They need to be rigid and heavy so there is a flywheel effect and they don’t slow down easily as you apply pressure.  They can be mounted on a Morse taper to insert into your point carver or have a suitable diameter plain shaft which can be gripped in a chuck.  A screw-in mandrel isn’t really suitable – the disc is too heavy and it needs to be completely “true” so there is no wobbling which would affect your work and wreck your wrists!

Picture 1 on left – this shows the lap with a disc of Wet & Dry paper attached.  It is 200 mm diameter and 10 mm thick, and mounted on a Morse taper.  A faithful workhorse!

I have glued a 2 mm thick disc of sheet rubber onto the steel with contact adhesive to protect the latter from wear, and then used 3M Spray Mount to temporarily fix discs of Wet & Dry paper (W&D) to the face (it’s a lovely product but hard to source outside NZ and the USA.  In Australia you can purchase a product called "3M 75" which is, I'm told by 3M, basically the same, though I have yet to use it).  To attach the W&D, I take a sheet, apply it to the rubber and cut around the edge with an old pair of scissors.  Be careful to cut it close to the steel disc because spinning W&D can give you quite a nasty paper cut if you aren’t careful.  I save the larger offcuts for small jobs around the workshop.  Start with 100 grit paper and gradually go up through the grades – 220, (400,) 600 and 1000 as detailed before.
 
It makes life easier if you have a number of laps – one for each grit size – and saves slightly-used sheets for the next job, so saving you money.
 
Be careful you don’t press too hard on the lap because the rubber “gives” a little and you will end up with slightly rounded edges instead of sharp ones - and you wear out the paper more quickly.
 
As the sheets wear they cut more slowly.  You will know when it is time to change them!
 
Safety note: do not lead in with a sharp point or edge against the direction of travel of the lap – it can catch, dig-in to the W&D and be torn out of your hand - and rocks flying around my head are not my favourite things!  It also means you can’t use that sheet of W&D any more.
 
I use my laps at around 1750 rpm for best effect.  But don’t forget you need a dribble of water, applied to the centre of the lap by your Loc-Line or equivalent (see Picture 1 from the splash boxes blog).  You can see how it sprays outwards in the picture, keeping the whole of the working face clean and moist – and you as well if you apply too much water!  The water also keeps the stone cool so you don’t burn your fingers.
 
So what can you produce using the lap?  Let’s start with flat surfaces, and shapes made up of those.  They’re OK to start with.  But you can also form cylindrical shapes (ie curved along one axis), and can go on to make convex-shaped pieces (ie cabochons – “cabs”) and surfaces with a bit of practice.  So they are very versatile.  And with experience you can turn out some beautiful curves.
 
Always check your work with a hand-lens to see there are no ridges or tool-marks and, as previously mentioned, grind twice at each grade, at right-angles to the previous operation to make sure you have ground off all the coarser scratches before progressing to a finer grade.
 
A few tips:

• You need to grip the workpiece firmly but lightly and roll your wrist/s to achieve a regular curve
• Watch your finger nails – W&D is unforgiving if you get them too close!
• Be careful if you run the piece across the centre of the lap (one reason you place the water feed centrally) – it will kick in your hand because the disc is rotating around the centre – so instead of pulling away from you in the bottom half it will be pushing towards you in the upper
• You can be the most careful and gifted carver in the world but bias creeps in - turn the piece around regularly so as to balance out any irregularities in your work
• If your point carver fan belt squeals when you start up your point carver (it’s normal – because of the weight of the lap), you can cure the noise by using some wax crayon on the running faces of the belt – but please keep your fingers away from the moving belt!
• You can use a lap dry as well, but it means the stone heats up quickly and you are forever dipping it in a bucket of water to continue working and to slow the inevitable dulling of the nerves in your fingertips!
• The quickest grind is produced at the edge of the flat face of the lap, where the W&D is moving the fastest, but at, say, $1 per sheet and with only a limited working life, you’ll want to use the whole sheet unless you have unlimited funds
• Regular pieces are more difficult to make than irregular ones
• It is very difficult to get a round sheet of W&D back onto a lap once removed – sharp edges will be sticking out somewhere

 
So there you have it – Laps 101!  Enjoy!