Replies

1. 
   StanleyNiemiec | May 15, 2002 03:24am | #1

   Jerry:

   There are non-cellulosic polysaccharides in wood (the 5 and 6 carbon sugars sometimes referred to as the hemicelluloses) that will begin to degrade (carbonize) at temperatures as low as 250 degrees F.

   There are also various extractives in the pines (pitch, turpenes, turpenoids, etc., etc.) that will degrade and/or volitilize at fairly low temperatures.

   If the temperatures generated in cutting are greater than 212 degrees F, any moisture in the removed kerf will turn to steam and therein "extract" some extractives and sugars. 

   With carbonization, volitilization and steam extraction you will get a mixture of vaporous, liquid "stuff" that is trapped in the kerf and gullet that will recondense on the nearest cool object.    Additionally, if you are creating a lot of very fine sawdust (due to a small tooth bite) that is sufficiently fine enough to escape (spill from) the gullet, it will most likely deposit the warmed, sticky parts on the part of the tooth/blade they come in contact with.  This gunk will reduce side clearance and might have a higher coefficient of friction than the saw plate steel.  As such, the more build-up you get the hotter the blade will run.

   There are a lot of frictional forces in machining wood.  These frictions generate heat.  The greatest temperatures are at the tip of the tooth (approaching 800 degrees C for router bits machining MDF) as the chip passes across the face of the tooth.  There is also a limited amount of wood springback from the compression that accompanies "cutting".  Friction (in the gullet and with spilling sawdust) can also heat the rim of the blade, such that if sufficiently great will cause the metal on the rim to expand.  When expansion reaches some critical level, the saw will lose its tension and begin to wooble.

   With reduced saw plate thickness, you obviously have less mass in the saw to absorb, transfer and dissipate this heat so the thin kerf blades are more susceptible to losing their tension.  Thin kerf saws are more susceptible to deflection and are therefore less accurate.

   Why use a thin kerf blade for cutting tenons?  Kerf loss is not an issue especially if the tenon cut-offs are scrap anyway.

1. 
   wooddog1 | May 23, 2002 06:12pm | #2

   Thank you very much for the information.  It would appear that you obviously have a little knowledge in the area!  It frustrates me that I really would like to become a "better hobby woodworker", but these little leasons keep coming up!  It is becoming painfully obvious that I need to keep on reading and experimenting!    Thanks again for your help. 

   Jerry

1. 
   StanleyNiemiec | May 23, 2002 08:08pm | #3

   Wooddog:

   The science and technology of wood and wood processing can be very complex and varied.  It is very much an applied science that is inherently messy because of the great differences in species and due to the general organic (and variable) nature of wood.   For many individuals it is a life-long effort. 

   There is a large volume of published information that is ancedotal and how-to.  The really technical stuff is obscure and spread out all over the place.   Some of the best information is old (but since wood and this or that process is unchanged), it is still extremely valid.  Unfortunately, this means that some references are not readily available.  A case in point is wood machining; Peter Koch published his book in 1963 (Wood Machining Processes) and it is virtually unobtainable at any price.  And it is not easy reading! 

   There is also a very real difficulty in taking germain parts of the available pieces and fitting it together into some understandable and coherent "picture".  You can study wood chemistry and if you cannot connect this with the dynamics of wood machining, you will remain lost.

   Do not be detered; the more you learn the more interesting wood will become to you.  Start with Hoadley's book Understanding Wood.  When you really know that information, start obtaining stuff from the USDA Forest Service.  And a full day trip to your state's land grant college/university's library could provide you with some very interesting reading.

   I wish the inter-relationship between artisan/craftspersons and the academics of Wood Science were better.  Part of the problem lies in each group  -- the artisans think the academics too high browed and stuffy, and the academics think that the artisans are not interested (and sometimes, incapable of learning).  There is also a propensity in academia to support (big) industry or focus only on "their" research area.

   Since I have had my feet in both groups, I run into problems straddling the gap.  Most crafties consider me too arrogant, technical and theoretical, while the academics consider me too "blue collar".  It gets really absurd because industry considers me too academic and the environmenatlists consider me overly oriented towards industry.  Sometimes you just cannot win.

   Be curious and read; I will help whenever I can. 

1. 
   DonStephan | May 26, 2002 09:10pm | #5

   Mr. Niemiec: More in depth information is greatly appreciated here. Sometimes I have to read several times to start to understand, but that is no reason to limit exposure to shallow overview. More information and understanding makes us more successful and efficient. On the occasion when an explanation is too detailed, I can easily move on to the next thread, as I'm sure everyone does. Thanks for your time and interest in sharing knowledge and experience with us!

2. 
   gerry001 | May 23, 2002 10:39pm | #4

   I'll skip the technical explanation which our friend has already offered, and comment on the surface effects, to wit:

   Yes, it is normal in some pieces of wood, especially certain pines. The next board probably won't do this.

   The blackening is normal from the above; no, it will not dull the blade; yes, you should clean it off. No, there's probably no hurry, unless it's very thick or you're very fastidious.

   It sounds like you're cutting 3/4 deep and probably through 2-5 inches, so I don't see where the thin kerf matters, nor if it's crosscut or rip. Either will make enough of a difference to matter.

   Gerry