Conclusion

The proper blade to use will of course depend often on  carefully evaluating the particular technical context, but still , the choice is not often clear.  An example of this would be deciding which blade to choose  for sectioning lower anteriors. When the preparation's margins are close together the thin .007 width blade with its 25 teeth per inch would seem to be the ideal choice. 

However, our choice in this instance, may  also be problematic.  When small preps are close together the dowel pins (in the case of a pinned model) are in close proximity.  While the .007 is ideal for starting the cut, the blades lack of rigidity may make  continuation of the cut between the dowel pins more difficult.

The approach that would produce the best results may be to start the cut in the margin area with a .007 (25 TPI) blade to preserve the margin integrity (Fig. 13); then start another cut from the bottom of the die with a .010 (25 TPI) blade (Fig. 12) positioned between the dowel pins and precede to cut up until the two cuts come together.

In other circumstances considerations for the correct blade choice is more obvious.  If your models are processed rapidly and still retain a fair amount of moisture you may discover that when using the finer 25 TPI blades the gullets become loaded with the moist die stone dust and inhibit efficiency.  In this instance, consider drying the models or using the more coarse 18.5 TPI blade.

In general blades with more TPI ( IE:25 ) produce a less aggressive cut, with  less chipping and drag, making it more ideal for cuts in the areas of the margins.

Blades with fewer TPI  ( IE:18.5 ) produce a more aggressive cut by allowing the teeth to remove a larger portion of the die stone with each stroke, thus  increasing the possibility of chipping the margin area. The recommendation? Reserve the more aggressive blades, for the rapid sectioning of preps that have adequate clearance in the margin area.

This author  suggests that a well equipped model department  have several hand saws with different blades pre-mounted on them.  A good start would be to have three saws with the following blades:  #1 .007 (25 TPI) ;  #2  .010 (25TPI) and  #3  .010 (18.5 TPI).  Having blade options allows the technician to start the cut with  the blade least likely to compromise the margins, i.e., a fine cut blade, then switch to a more aggressive blade.

Ultimately, the empirical method determines which blade works best in any given situation; however, having knowledge of blade properties and access to a variety of blade configurations will speed up this process.

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Photos & Graphics by Vince Ferraro

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