| The Right Tool for the Job
By Neal Immega |
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| Cabs are good for jewelry but when you have a display specimen, you want to polish it flat. You can get a surface sort of flat with our normal grinders, but you have to be better than me to not leave grooves in the surface from the edges of the wheels. The answer is to use a lap plate. I know --- a lap plate is used with silicon carbide and hardly high tech --- but it really works fast and is the right tool for the job. | |
| I have noticed a number of people trying to grind things on a wheel that would be much better done on a lap, i.e. people trying to finish the edge of an 18-inch square slab of granite. A heavy slab will bounce as you try to grind it, scraping the diamond off a $180 plated Diamond Pacific wheel. This is just not going to be allowed at any time. The edge of this slab could be finished in 5 minutes on the lap, with no grinding marks. | |
| A close call | Another more serious case is the one last week where a user had a rock get away from him and become jammed between the bottom of the saw and the wheel. This created a perfect example of an irresistible force meeting an immovable object. What happened this time was that the grinding arbor was torn from the base, pulling the mounting bolts right through the board. Scary. |
| If this had happened on the much more ruggedly built Rock machines, the wheel would have exploded, potentially causing serious damage to the operator. We are not going to do this anymore, are we? By the way, this is not just an operator training problem: in the last year it has happened twice, to a new member and to one of us who should have known better. | |
| "If this noise
were
coming from your your car, you would have good reason to be concerned." |
Everyone is going to get a refresher on the lap plate, so let me start on you. If you are doing a slab, then dop or glue a hand hold on it. A scrap of lumber is excellent (do not use oil soaked pieces that have been in the oil saws --- nothing sticks to them). You will find 3 grit sizes (80, 220, 400) in plastic squeeze bottles and if you need to make up more the recipe is to add dry grit + a little soap + water. Turn on the motor, turn on the water drip, shake up the grit bottle and squirt a little on the lap, put your rock on the lap and keep it moving. When you stop hearing a grinding noise, add some more grit. If you are having trouble holding the rock and the bottle at the same time, then grab the rock in both hands and ask someone to dribble grit for you. You do not need to put a lot of grit on the wheel to get that good gritty sound. If this noise were coming from your car, you would have good reason to be concerned. It is much easier to move a rock around on the lap plate than the grinder, particularly since Tony and I have been putting as many wheels on each shaft as we can. |
| Safety first | Remember: the grinders are for cabs, not rocks. When one of the shop
foremen comes around to give you a hands-on refresher on the lap plate,
please remember that this is for your own good. If you cannot remember
that, then remember that the HGMS board is 100% behind us having safe shop.
The lap plate does a better and faster job than a grinder – lets use it.
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The one thing that is missing from the flat polishing process is a prepolish step. We need to use a 600 and 1200 grit resin wheel between the lap step and the new domed polisher. It will have to be specially built to have enough clearance below the wheels. Please contact me if you have time to help me with the repairs to the shop machines. I am sure I can accommodate you schedule – weekdays or weekends are fine. I particularly need your help if you can weld up the frame for the new machine. |
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---adapted from Neal's article in the November
2002 Backbender's Gazette
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