I have been wondering, both before I got into Festool and since, about how precisely one can make cuts using a TS and the guide rail using only a pencil mark and eyesight to line up the mark and edge of the guide rail.
So, tonight I conducted a little experiment. I wanted to make repeated cuts based on pencil marks at a standard distance, then compare the actual length of these cuts to evaluate the precision of the method. Here's exactly what I did:
1. Ripped a piece of 5/8 white oak into an approximate 3" x 24" section and checked it for square. It was.
2. Used a 24" steel rule and a rule stop from Lee Valley to set an exact and repeatable length for marking (see picture).
3. Made a mark using the rule and rule stop on the end of the board.
4. Using an MFT, TS 55, and guide rail, I lined the mark up with the edge of the guide rail, and made the cut. I didn't fuss over this, and tried to replicate the time and care one would normally take for such a cut. I placed the board on the table, lowered the guide rail, repositioned the board so the mark appeared to just touch the rubber strip on the rail, and made the cut.
5. I repeated this 10 times, labeling each block.
6. Used a Lee Valley electronic caliper to measure the length of each cut off at its center.
7. Analyzed the data.
This is what I found:
1. The average length was 0.9161 inches in length.
2. The pieces ranged from 0.9075 to 0.9340 in length (range = 0.0265).
3. For you real nerds, the standard deviation was 0.00809.
Of course, I'd like to do this 40 or 50 times, but I was getting bored. But, I think the data are enlightening nevertheless. I found the mark and align method of cutting to be pretty darn precise, with only 0.0265 difference between my shortest and longest cuts (about 1/38 of an inch for you fraction-heads). Not good enough for some things, but plenty good enough for lots of things. And, I suspect that with just a little bit of care, one could always keep the error within this range or smaller.
By the way, the mark and align method is not only precise, but pretty accurate as well. I measured the kerf width of the Festool blade at .0920. I had placed the rule stop on the 1" mark of the ruler. Adding the average piece length (0.9161) to the kerf width (0.920) gives us 1.0081. So, on average, I was able to cut within .0081 (1/123 inches) of my intended length. Not bad!
So, tonight I conducted a little experiment. I wanted to make repeated cuts based on pencil marks at a standard distance, then compare the actual length of these cuts to evaluate the precision of the method. Here's exactly what I did:
1. Ripped a piece of 5/8 white oak into an approximate 3" x 24" section and checked it for square. It was.
2. Used a 24" steel rule and a rule stop from Lee Valley to set an exact and repeatable length for marking (see picture).
3. Made a mark using the rule and rule stop on the end of the board.
4. Using an MFT, TS 55, and guide rail, I lined the mark up with the edge of the guide rail, and made the cut. I didn't fuss over this, and tried to replicate the time and care one would normally take for such a cut. I placed the board on the table, lowered the guide rail, repositioned the board so the mark appeared to just touch the rubber strip on the rail, and made the cut.
5. I repeated this 10 times, labeling each block.
6. Used a Lee Valley electronic caliper to measure the length of each cut off at its center.
7. Analyzed the data.
This is what I found:
1. The average length was 0.9161 inches in length.
2. The pieces ranged from 0.9075 to 0.9340 in length (range = 0.0265).
3. For you real nerds, the standard deviation was 0.00809.
Of course, I'd like to do this 40 or 50 times, but I was getting bored. But, I think the data are enlightening nevertheless. I found the mark and align method of cutting to be pretty darn precise, with only 0.0265 difference between my shortest and longest cuts (about 1/38 of an inch for you fraction-heads). Not good enough for some things, but plenty good enough for lots of things. And, I suspect that with just a little bit of care, one could always keep the error within this range or smaller.
By the way, the mark and align method is not only precise, but pretty accurate as well. I measured the kerf width of the Festool blade at .0920. I had placed the rule stop on the 1" mark of the ruler. Adding the average piece length (0.9161) to the kerf width (0.920) gives us 1.0081. So, on average, I was able to cut within .0081 (1/123 inches) of my intended length. Not bad!
