[Rockhounds] Color of Minerals (now: need saw blade recommendation)

[jb]

DonH wrote:
> Kris Rowe wrote:
>
>> I'm currently converting an 18" saw from oil lube to water. 
>> Thankfully, the
>> saw is equipped with greasable bearings, rather than sealed, and can 
>> be used
>> with water. A full circulation and filtering system is being 
>> installed and
>> will hopefuly work! (Mumbling my prayers ...)
>> I'd love to get some opinions and recommendations on blades for this saw
>> before spending the precious dollars. What say you, dear list 
>> members? Buy 1
>> top quality (expensive) blade, or start with cheap import blades and 
>> simply
>> replace more often?
>
>
> Greetings!
>
> First, by way of helping out, notice that I modified the subject.  You 
> will definitely find on this list that not everyone reads every 
> thread, and if you need help with a specific thing, it's a good idea 
> to post a new message with a new subject... in this case, it would 
> have been good to say "help needed with 18" saw blades."  There are 
> several people on this list who have quite a bit of related 
> experience!  I hope this logic makes sense and it is helpful to you in 
> the future.
>
> Now, as far as blades, my experience is limited to 10" and less. 
> However, I can say with certainty that I have always received what I 
> paid for.  Now, I can't compare dollar-for-dollar and brand-for-brand, 
> but in general, as groups, the name brand and more expensive blades 
> perform better, last longer, and warp less than the cheaper ones I 
> have bought.
>
> However, I can also say that quality control in developing countries 
> such as China and India is improving by leaps and bounds.  It may well 
> be true to that a Chinese blade of a certain edge style and kerf, 
> though costing 1/3 less, may perform as well as one of the big names.
>
,,,,
> Good luck,
> Don
>

As noted elsewhere, the MK-303 blades are about the best for general 
lapidary cutting. They have a consistent thin kerf, cut very smoothly, 
and last a long time. I have used all manner of blades in the past 
decade or so with all manner of self-collected (read 
bashed-up-real-world) materials ranging from serpentines to corundum, 
and the original "Black Blazer" that came with the saw and the MK series 
have been the best performers. I think the MK series are better as they 
are sintered.

For cutting of bulk materials, a good blade to use is the Harbor 
Freight  7 or 10 in. diamond blade. They are good and cheap and they 
last a very long time. They are intended for cutting tile but work well 
on my lapidary saw. The disadvantage is that they have a thick kerf and 
"waste" a lot of material. For example, it might take three turns and a 
little more of the screw advance on the rock vise to cut a 1/4 in slab 
with the Mk-303, but it will take six turns to cut the same slab with 
the H.F. blade. And the H.F. blade cuts a much rougher surface, which 
translates into more time at the grinding wheel. The Houston Gem and 
Mineral Society shop has made very effective rough grinders for large 
spheres, etc. by mounting eight or ten of these together on the same 
shaft; imagine a 10 in. diamond grinder for about $350.

Use the MK-303 for your better materials, and the H.F. blade for cutting 
bulk or splintery material into usable slabs. The H. F. blade is 
excellent for beginners to use as it is much harder to destroy it as it 
is so heavy.

That being said, the principal cause of blade loss is not mis-alignment; 
nor is it wear. The principal way to lose a blade is by not securing the 
rock in the vise enough. Any movement at all of the rock in the vise 
will bend, warp, and otherwise damage the blade, and it might not be 
apparent to you, the user, until a few slabs later when it starts to 
"not cut right". So don't be afraid to cut some of the sharp edges off 
the rock before you attempt to mount it in the vise. Have handy an 
assortment of wooden spacers and wedges to make sure that the rock 
really is secure.  Test and test again to make sure that the rock will 
not move. Test it again. Only when you are sure it is secure do you turn 
on the saw.

Sometimes a rock will break during sawing from a hidden crack or flaw. 
It happens. It is good shop practice to provide pretty close observation 
to cut things off when it does happen. You may not be able to save the 
blade, but you certainly won't if you don't keep track. A *lightly* bent 
blade may be straightened by tapping on it on a smooth flat surface with 
a hammer in a spiral motion from near the center to near the edge; do 
not go to the edge as it may bend the diamond carrier slightly out of 
vertical to the blade body. Not good. I sometimes can recover blades for 
more use with a lead-filled dead-weight hammer. In any case, the runout 
on the blade (or side-to-side motion of the edge while running) should 
not exceed a half mm. or so. If it's more, the blade will bind and drift 
in its cut about half way into the slab, and cause heat, mist, and 
eventual shutdown. Incidentally, ordinary concrete floors are not 
usually smooth enough to use in "repairing" the blade.

Another thing to watch out for is eccentricity or having a blade that is 
just a bit out of round at the edge. You can tell by the sound of the 
sawing. There will be a little "pulse" in the sound as the  bite into 
the rock varies.  This is caused by not having the blade perfectly 
centered, usually by some kind of bearing wear or bad machining or worn 
spacers where the blade mounts to the shaft. And don't forget to make 
sure that the flange is centered and secure. It is very important in 
damping vibration and keeping the thin blade from destroying itself.

It does not pay to try a professional repair on a blade less than 18 in. 
Just replace it if it is bent too far out of shape.

All of this assumes, of course, that the arbor, blade, and vise have 
been perfectly aligned to begin with. Pay very close attention to 
alignment, especially if the arbor has been repaired or replaced. Being 
off by a few thousandths at the center of the blade translates to 1/8 mm 
or more at the rim of a 10 in. blade, even more for the larger blades. 
And make sure the vise is really at right angles to the blade and is at 
the same distance  from it along its entire length.

Good luck, and enjoy your saw.


john