Saw blade questions.

I see no need to take the arrows when it comes to figuring out what blade to use- use what people who make their living in lapidary use. The blade of choice for most of these people is the MK series. For MK, continuous rim blades are used in smaller size saws, segmented blades in larger saws. This makes sense, as the segmented blades dissipate heat better, therefore are probably more dimensionally stable. A large blade has a high surface speed, and is removing a lot of rock and generating a lot of heat. The 36" blade, for example, is grinding a 0.200" swath through the stone. That's a lot of meat and a lot of heat.

In segmented blades, the segments are laser-welded to the core. The segments have synthetic diamonds bonded to a metal core using metal powders. That process is called sintering.

Older is not always better. These are not your grandfather's blades. The processes and sophisticated manufacturing used to produce these blades didn't exist a generation ago. I have read articles in rock magazines about some codger with a block of wood and a mallet saving a bent blade. Not likely with these blades. You might get it close, but it will never cut like the original. As the guy at MK told me, the core of modern blades are so tough the only way to straighten them is to re-heat treat the piece. That cannot be done without destroying the blade, because the temperature used to heat treat is higher than the temperature used to furnace braze the metal/diamond mix onto the blade segments.

The price of a 303 may be steep, but don't be fooled into thinking a cheap blade is an acceptable alternative. You may get lucky and find a Chinese blade that works ok for you, and depending on what your end product is, maybe so. But if you are cutting medium to large wood and agate slabs with the intent to put a quality polish on them, you will quickly find you get what you pay for in a blade. I have seen cuts from cheap and/or dull blades that render the slab unpolishable.

Dressing a blade, whatever type you end up with, is important. I'm going to step on some toes here. Many think running a blade through this or that is a good way to dress it. Those useless white blocks, grinding wheels, red brick, fire brick, concrete, obsidian, etc. I have a seperate post on this forum detailing what I believe to be the optimal way of dressing a blade. Remember, these aren't your grandfathers blades, and what has traditionally worked may need to be re-examined in light of today's production techniques.

tims,
I guess "unpolishable" is a subjective term. A cheap, bent or dull blade can leave marks and grooves in the face of the slab that take too long to economically remove. I cut and polish commercially, so when I have a slab like that I often don't have the time to repair it. A dull lapidary blade behaves just like a dull blade in a Skilsaw- they wander.

I'm sure you have been to rock shows and seen slabs of material in tubs of water. Sometimes you are tempted to buy the slab and finish the work on it. Before you do, run your finger across the face of the rock. If you can feel a groove, you are in for a lot of work- maybe too much work. Often those slabs are sold unfinished for a reason- the grooves are so deep they cannot be saved in any reasonable length of time.

After cutting, I grind off the nub and fill the cracks. Then the slabs go onto a rotating flat lap for an hour or so, which is sufficient for most smaller slabs. Bigger slabs may take more cycles. Then to a bull wheel, then to another rotating lap for polish. The flat laps may not be practical for a hobbyist- they are big and expensive. But they are cool. If I had had my act together, I would have purchased these machines from the beginning of the hobby. They run pretty much unattended, and I can grind or polish 50-75 slabs per day(not including the bull wheel work).

As with any hobby that you end up getting serious about, one blows a lot of time and money along the learning curve, and I certainly have done that.

I assumed they were referring to the expense!