Cutting slabs from large rough -- one saw or two?

That is some nice looking rough holajonathan

I would think the bigger saw would give some nice slabs. You could use the smaller saw to slab what is left over. I have a lot of pieces that are now too small to clamp in my 16” Covington.

I'm glad I'm not the only one who was considering the loss of material when cutting.

I like your "combination" approach and it is likely the way I would go if I had the two saws available.

I also like @hookedonrocks approach to the whole matter. The rough would definitely sell...and even if you take a small loss (financial - not material) on it, just consider it a "rental fee" you had to pay to check them out.

Halojonathan, I think the more important question is orienting the first cut so that it might give the best chance for a window that shows great designs and not worry about saw kerf loss. Sometimes a face cut is used to mount the remaining portion to a mounting block.

holajonathan I like the question you are asking because is shows an analytical mind trying to maximize the rough you have and figure the best way to proceed. This is exactly what the RTH is for and many on here have done the same before one way or another.

From my point of view: Lets say the average "rock in the box" above cost you $6.00/lb and there are 45 pounds. Your total cost for the pile of rocks is 45lb*$6/lb=>$270. If you waste 32% in the saw kerf, then when you get done you will have 45lb-14.4lb=> 30.6lb of slabs. If we take the loss at $6/lb*14.4lb=> $86 is the cost of lost rock. If the other method results in 18% loss the 45lb*.18=> 8.1lbs of lost rock. That means the difference between the methods is 14.4lb - 8.1lb => 6.3lb*$6/lb=>$37.80 in incremental loss. What is missing is how long will it take you to slab the 45lb of rock with the big saw and how long will it take to slab with the small saw. If it is 1 hr then you have saved $37.80 in an hour and you can say I am worth $37.8/hour. If on the other hand it will take 4 more hours then that number is down to more like $9+ per hour. So what is your time worth?

The issue of waste is more important when selling slabs to maximize the yield. I only slab to make cabs and estimate the yield taking waste into account. I also am willing to leave a few slices on the board that can be cut at a later date.

rmf

Thanks for adding this.  We think alike.  I was doing this exact analysis in my head when I made the original post.   I didn't want it to get too long and cumbersome, so I limited it to the issue of material loss with different width blades.   I was also thinking about the variable cost of different size blades, wear and tear on the saws themselves, and cleanup time with the two saws... but I have to draw the line somewhere.

There is 62 pounds of rough in that photo.  My weighted average cost is around $5 a pound, which lowers by 16% your calculations of what my time would have to be worth to use the smaller saw merely to save money by reducing waste.  If I assume I would save at least 2 hours on the larger saw (it is probably much, much more), and at $5 a pound for the rough, it makes sense to use the large saw if my time is worth more than $15 an hour.  More precisely, if I value time NOT spent slabbing rocks at $15 an hour, which I do.  In other words, the opportunity cost -- what I could be doing instead of slabbing rocks -- is worth more than $15 an hour to me.  

Taking into account your refined analysis, here is my plan:

1.   Window each chunk on two ends using the big saw to see what's inside.  If I don't like it, sell the rough and cut my loses (although there may be no loses).  Considering the amount of time I will ultimately spend turning this rough into cabs and the thousands of dollars I have invested in equipment, the cost of the rough is a tiny part of my overall cost.  As a result, it makes no sense to proceed with slabbing rough unless I love it and will enjoy working with it.

2.  If I like the rock enough to keep it, I will slab it out on my big saw in quick order.  My big saw will slab 6 inches at 3-4" thick in 3-5 minutes, at least 10 times faster than a true lapidary slab saw / blade.  The material lost from the wider curf is more the offset by how much I value the extra time with my wife and her -- I mean our -- cats.   

3.  If there is something spectacular about a a particular piece of rough, it may be worth my time to maximize the yield from that particular piece, and I will proceed with the small saw.  Your analysis, which is the correct way to think about 99% of decisions that involve something costing more or less depending on the amount of time invested, does not apply as neatly if a rock is so special that it is not easily replaced or replicated simply buying more rough.  Using economic terminology, I am talking about goods that are not fungible either because they are unique or have non-economic (sentimental) value.  

This last point is related to a general limitation of this sort of cost-benefit analysis: the value of time saved depends on your personal feelings with regard to the particular activity and with regard to the products or goods (in this case, rocks).  We all have personal preferences about what we enjoy or do not enjoy, and which goods or products we value more than anyone else would be willing to pay us for them.   There is nothing wrong paying more than our time is worth to avoid things we hate doing, and working for less than our time is worth if we get some type of personal reward or enjoyment from the activity.  Stated differently, what your time is worth depends on what it is you are doing, what you could be doing instead, and how you feel about those two activities.  

Here is a personal, non-rock example: I heat my house with a wood stove in the winter even though I have a natural gas furnace and natural gas is cheap right now.  If I consider how much I paid for the wood stove, chimney liner, and installation -- and I add the cost of the 100+ hours a year I spend cutting down trees, splitting and stacking firewood, moving the firewood to the garage and later inside the house, loading the stove, maintaining the stove, etc... then heating with wood is a massively dumb  economic decision.  I won't even get into the many thousands of dollars spent on chainsaws, log splitters, and firewood racks....  Even if my time were worth nothing, it would take 10-15 years of heating with wood just to pay off my investments in the stove and firewood-related equipment. And who knows if the stove will even last that long?  And if even if my time were worth only $5 an hour -- what I got paid to shovel manure out of horse stalls when I was 15 years old -- I would probably never break even in 30 years of heating with wood.  But I do not consider heating with wood to be a bad decision, because I enjoy it, even if it makes bad economic sense.  

To bring this long, rambling post full circle, I do not enjoy slabbing rocks enough to work for $5, $10, $15, or even $20 an hour doing so, when I could instead be sitting on my couch listening to my wife talk about what my spoiled-rotten cats did all day.  As a result, my choice is to slab up the pieces I love with the big fast saw, get rid of the pieces I don't love, and use the smaller saw only if I run across a piece that I consider to be truly special.

Amen.    

True that ... and congrats on your  amazing fornications.  


 

holajonathan thanks for the kind words and the reply. Just to let you know I also heat with wood when it is below 32deg F.
we have and electric heat pump and wood is cheaper than the extra E-heat below 32F. We bought a fireplace insert 40 yr ago figuring we would not use it much. I was not going to buy wood. I love to split it by hand and I have all my wood from our property. I figured break even in 10-15 years now going on 40+ How wierd is that?

BTW that is real wood not petrified wood:)