Working with laps - an update and summary

Thanks to Greg for his query on grinding with laps.
 
To summarize:

• Wear eye protection
• Your laps need to be perfectly true and flat, and firmly attached to the point carver
• 1500 – 1750 rpm is fine
• Keep the flow of water low into the centre of the lap because otherwise you wear it – just one drip every few seconds is generally enough.  If the stone becomes too hot to hold then increase the flow rate
• Always grind points and sharp edges trailing on the Wet & Dry (W&D) paper to avoid their catching and flicking up in your face, as well as damaging the paper
• Grinding at the edge of the lap will naturally cause the stone to heat up more due to the higher speed there and more friction
• But use the paper in the centre of the lap too!  It is slower than using the outer areas but just as effective
• If you are grinding a large slab it seems to take forever to get it flat the first time.  But resist the urge to try to grind down high spots on your diamond belts first when using laps – I end up taking longer in trying to grind out the low spots afterwards than if I’d just kept going with the laps!
• Be gentle!  The harder I press the stone onto the lap the more it depresses the rubber facing under the W&D and then rounds the edges of the piece being ground – it also wears out the paper more quickly
• If the stone starts to slip out of my grip it’s better to let go rather than try to hold it by pressing harder, as it will eventually be thrown off onto the back of the splashguard and I run the risk of losing parts of my fingernails on the W&D
• Don’t rush the coarser grades of W&D paper (100/120 and 240) as these give you the basis for your form
• Rotate the pieces through 90˚ and move them across the lap continually so concentric arcs don’t form, which then take a lot of grinding out
• Turn the pieces over regularly to keep the piece square and even
• 400 grit W&D paper doesn’t last very long with nephrite, and 600 and 1000 even less.  Remember to add these costs into your calculations when pricing a piece of work
• As you reach the finer grades, scratches and grooves appear which can’t be seen with the coarser paper before, causing you to return to that coarser grade to remove them.  Get used to it!
• The quickest way to remove a scratch or tool-mark is to grind across it at right angles

 
 
Happy grinding!