David Romano
06-17-2009, 3:55 PM
I'm trying to understand the relationship between TPI, board thickness and number of teeth in the stock at one time and also how this affect the quality of cut vs speed of cut. What I've learned so far makes sense for thin stock
TPI = board thickness x number of teeth in the stock
where more TPI = finer cut with the upper limit being overheating of the stock and/or blade
Miminimum recommended number of teeth in stock is 2 - 4 typically and so 6 tpi is popular for 3/4" boards
I use a bimetal blade with a 4/6 variable TPI, so that averages 5 TPI. The cut quality is really good but I find that 4" thick is a practical limit for stock thickness. This equals 20 teeth in the wood at one time. Going thicker slows the cut too much and burns the wood/clogs up the gullets.
If I apply this knowledge to 12" stock, I'd need about 1.5 TPI and the cut quality would be terrible. Yet, I see that it is popluar to use a 3 TPI blade on stock this thick. That would be 36 teeth in the wood. Why does the equation change? Is it the greater gullet depth at 3 TPI? If so, this leads to the next question which is: For a given tooth pitch, do all gullets for hook tooth blades have the same depth? Or do some blades have extra deep gullets?
I'm considering buying a bimetal 2/3 TPI blade for stock 4 - 12 inches.
David
TPI = board thickness x number of teeth in the stock
where more TPI = finer cut with the upper limit being overheating of the stock and/or blade
Miminimum recommended number of teeth in stock is 2 - 4 typically and so 6 tpi is popular for 3/4" boards
I use a bimetal blade with a 4/6 variable TPI, so that averages 5 TPI. The cut quality is really good but I find that 4" thick is a practical limit for stock thickness. This equals 20 teeth in the wood at one time. Going thicker slows the cut too much and burns the wood/clogs up the gullets.
If I apply this knowledge to 12" stock, I'd need about 1.5 TPI and the cut quality would be terrible. Yet, I see that it is popluar to use a 3 TPI blade on stock this thick. That would be 36 teeth in the wood. Why does the equation change? Is it the greater gullet depth at 3 TPI? If so, this leads to the next question which is: For a given tooth pitch, do all gullets for hook tooth blades have the same depth? Or do some blades have extra deep gullets?
I'm considering buying a bimetal 2/3 TPI blade for stock 4 - 12 inches.
David