Saturday, February 18, 2012

Universal Circle Jig Table

Last weeks post was about a Wooden Platter I made this summer using a router and circle cutting jig (the Universal Circle Jig from Lee Valley). To assist in determining how the circle jig should be set, I built the table below (after the jump). Basically, it is used to quickly find the relationship between the size of the routed circle and the jig setting for three common router bit sizes.

The jig attaches to the base plate of a router. It works by pivoting on a 'pilot pin' causing the router to trace a circle centred on the pin.

The table is broken into two parts: Hole Diameter and Disk Diameter. Which side of the table to work from is based on what the desired goal of the cut is. If the goal is to create a hole in a piece of a certain size, the Hole Diameter size is used. Correspondingly, if the goal is to create cut an object out and have the object be a certain size, the Disk Diameter is used. These are different because there is wood lost to the router bit during the cut.

The 'reading' is a radial measurement and is taken from the centre of the pilot hole to the edge of 'T' cross groove closer to the pilot hole.

The Lee Valley description of the jig has the statement: "For quick reference and set-up, the surface is machined with an intersecting center and radius benchmark calibrated to produce a 7" disc and 7-1/2" opening with a 1/4" straight bit". This is illustrated in the first row of the table (in the 1/4" bit columns).

For example, say a disk 10" in diameter is needed. If a 1/4" straight bit is installed on the router, the reading needed is 1 1/2".

If a hole 12 3/4" in diameter is required and a 1/2" straight bit is installed on the router, the reading needed is 2 1/2".

The jig can be used for circles 6" to 40" in diameter and the table covers this full range.

The picture below shows a bit of on old tape affixed to the jig to assist in measuring the readings. This picture shows four pilot holes that have been drilled in the jig. As noted above (and evidenced by the placement of the tape), the reading measurement is taken from the edge of the cross grove closest to the pilot holes. The four readings here are 3/8", 7/8", 1 3/8", and 1 7/8". As I was using a 1/2" bit, these resulted in "holes" of 8 1/2", 9 1/2", 10 1/2", and 11 1/2" in diameter.






Reading Hole Diameter Disk Diameter
1/4 Bit 1/2 Bit 3/4 Bit 1/4 Bit 1/2 Bit 3/4 Bit
0    7 1/2 7 3/4 8    7    6 3/4 6 1/2
 1/8 7 3/4 8    8 1/4 7 1/4 7    6 3/4
 1/4 8    8 1/4 8 1/2 7 1/2 7 1/4 7   
 3/8 8 1/4 8 1/2 8 3/4 7 3/4 7 1/2 7 1/4
 1/2 8 1/2 8 3/4 9    8    7 3/4 7 1/2
 5/8 8 3/4 9    9 1/4 8 1/4 8    7 3/4
 3/4 9    9 1/4 9 1/2 8 1/2 8 1/4 8   
 7/8 9 1/4 9 1/2 9 3/4 8 3/4 8 1/2 8 1/4
1    9 1/2 9 3/4 10    9    8 3/4 8 1/2
1 1/8 9 3/4 10    10 1/4 9 1/4 9    8 3/4
1 1/4 10    10 1/4 10 1/2 9 1/2 9 1/4 9   
1 3/8 10 1/4 10 1/2 10 3/4 9 3/4 9 1/2 9 1/4
1 1/2 10 1/2 10 3/4 11    10    9 3/4 9 1/2
1 5/8 10 3/4 11    11 1/4 10 1/4 10    9 3/4
1 3/4 11    11 1/4 11 1/2 10 1/2 10 1/4 10   
1 7/8 11 1/4 11 1/2 11 3/4 10 3/4 10 1/2 10 1/4
2    11 1/2 11 3/4 12    11    10 3/4 10 1/2
2 1/8 11 3/4 12    12 1/4 11 1/4 11    10 3/4
2 1/4 12    12 1/4 12 1/2 11 1/2 11 1/4 11   
2 3/8 12 1/4 12 1/2 12 3/4 11 3/4 11 1/2 11 1/4
2 1/2 12 1/2 12 3/4 13    12    11 3/4 11 1/2
2 5/8 12 3/4 13    13 1/4 12 1/4 12    11 3/4
2 3/4 13    13 1/4 13 1/2 12 1/2 12 1/4 12   
2 7/8 13 1/4 13 1/2 13 3/4 12 3/4 12 1/2 12 1/4
3    13 1/2 13 3/4 14    13    12 3/4 12 1/2
3 1/8 13 3/4 14    14 1/4 13 1/4 13    12 3/4
3 1/4 14    14 1/4 14 1/2 13 1/2 13 1/4 13   
3 3/8 14 1/4 14 1/2 14 3/4 13 3/4 13 1/2 13 1/4
3 1/2 14 1/2 14 3/4 15    14    13 3/4 13 1/2
3 5/8 14 3/4 15    15 1/4 14 1/4 14    13 3/4
3 3/4 15    15 1/4 15 1/2 14 1/2 14 1/4 14   
3 7/8 15 1/4 15 1/2 15 3/4 14 3/4 14 1/2 14 1/4
4    15 1/2 15 3/4 16    15    14 3/4 14 1/2
4 1/8 15 3/4 16    16 1/4 15 1/4 15    14 3/4
4 1/4 16    16 1/4 16 1/2 15 1/2 15 1/4 15   
4 3/8 16 1/4 16 1/2 16 3/4 15 3/4 15 1/2 15 1/4
4 1/2 16 1/2 16 3/4 17    16    15 3/4 15 1/2
4 5/8 16 3/4 17    17 1/4 16 1/4 16    15 3/4
4 3/4 17    17 1/4 17 1/2 16 1/2 16 1/4 16   
4 7/8 17 1/4 17 1/2 17 3/4 16 3/4 16 1/2 16 1/4
5    17 1/2 17 3/4 18    17    16 3/4 16 1/2
5 1/8 17 3/4 18    18 1/4 17 1/4 17    16 3/4
5 1/4 18    18 1/4 18 1/2 17 1/2 17 1/4 17   
5 3/8 18 1/4 18 1/2 18 3/4 17 3/4 17 1/2 17 1/4
5 1/2 18 1/2 18 3/4 19    18    17 3/4 17 1/2
5 5/8 18 3/4 19    19 1/4 18 1/4 18    17 3/4
5 3/4 19    19 1/4 19 1/2 18 1/2 18 1/4 18   
5 7/8 19 1/4 19 1/2 19 3/4 18 3/4 18 1/2 18 1/4
6    19 1/2 19 3/4 20    19    18 3/4 18 1/2
6 1/8 19 3/4 20    20 1/4 19 1/4 19    18 3/4
6 1/4 20    20 1/4 20 1/2 19 1/2 19 1/4 19   
6 3/8 20 1/4 20 1/2 20 3/4 19 3/4 19 1/2 19 1/4
6 1/2 20 1/2 20 3/4 21    20    19 3/4 19 1/2
6 5/8 20 3/4 21    21 1/4 20 1/4 20    19 3/4
6 3/4 21    21 1/4 21 1/2 20 1/2 20 1/4 20   
6 7/8 21 1/4 21 1/2 21 3/4 20 3/4 20 1/2 20 1/4
7    21 1/2 21 3/4 22    21    20 3/4 20 1/2
7 1/8 21 3/4 22    22 1/4 21 1/4 21    20 3/4
7 1/4 22    22 1/4 22 1/2 21 1/2 21 1/4 21   
7 3/8 22 1/4 22 1/2 22 3/4 21 3/4 21 1/2 21 1/4
7 1/2 22 1/2 22 3/4 23    22    21 3/4 21 1/2
7 5/8 22 3/4 23    23 1/4 22 1/4 22    21 3/4
7 3/4 23    23 1/4 23 1/2 22 1/2 22 1/4 22   
7 7/8 23 1/4 23 1/2 23 3/4 22 3/4 22 1/2 22 1/4
8    23 1/2 23 3/4 24    23    22 3/4 22 1/2
8 1/8 23 3/4 24    24 1/4 23 1/4 23    22 3/4
8 1/4 24    24 1/4 24 1/2 23 1/2 23 1/4 23   
8 3/8 24 1/4 24 1/2 24 3/4 23 3/4 23 1/2 23 1/4
8 1/2 24 1/2 24 3/4 25    24    23 3/4 23 1/2
8 5/8 24 3/4 25    25 1/4 24 1/4 24    23 3/4
8 3/4 25    25 1/4 25 1/2 24 1/2 24 1/4 24   
8 7/8 25 1/4 25 1/2 25 3/4 24 3/4 24 1/2 24 1/4
9    25 1/2 25 3/4 26    25    24 3/4 24 1/2
9 1/8 25 3/4 26    26 1/4 25 1/4 25    24 3/4
9 1/4 26    26 1/4 26 1/2 25 1/2 25 1/4 25   
9 3/8 26 1/4 26 1/2 26 3/4 25 3/4 25 1/2 25 1/4
9 1/2 26 1/2 26 3/4 27    26    25 3/4 25 1/2
9 5/8 26 3/4 27    27 1/4 26 1/4 26    25 3/4
9 3/4 27    27 1/4 27 1/2 26 1/2 26 1/4 26   
9 7/8 27 1/4 27 1/2 27 3/4 26 3/4 26 1/2 26 1/4
10    27 1/2 27 3/4 28    27    26 3/4 26 1/2
10 1/8 27 3/4 28    28 1/4 27 1/4 27    26 3/4
10 1/4 28    28 1/4 28 1/2 27 1/2 27 1/4 27   
10 3/8 28 1/4 28 1/2 28 3/4 27 3/4 27 1/2 27 1/4
10 1/2 28 1/2 28 3/4 29    28    27 3/4 27 1/2
10 5/8 28 3/4 29    29 1/4 28 1/4 28    27 3/4
10 3/4 29    29 1/4 29 1/2 28 1/2 28 1/4 28   
10 7/8 29 1/4 29 1/2 29 3/4 28 3/4 28 1/2 28 1/4
11    29 1/2 29 3/4 30    29    28 3/4 28 1/2
11 1/8 29 3/4 30    30 1/4 29 1/4 29    28 3/4
11 1/4 30    30 1/4 30 1/2 29 1/2 29 1/4 29   
11 3/8 30 1/4 30 1/2 30 3/4 29 3/4 29 1/2 29 1/4
11 1/2 30 1/2 30 3/4 31    30    29 3/4 29 1/2
11 5/8 30 3/4 31    31 1/4 30 1/4 30    29 3/4
11 3/4 31    31 1/4 31 1/2 30 1/2 30 1/4 30   
11 7/8 31 1/4 31 1/2 31 3/4 30 3/4 30 1/2 30 1/4
12    31 1/2 31 3/4 32    31    30 3/4 30 1/2
12 1/8 31 3/4 32    32 1/4 31 1/4 31    30 3/4
12 1/4 32    32 1/4 32 1/2 31 1/2 31 1/4 31   
12 3/8 32 1/4 32 1/2 32 3/4 31 3/4 31 1/2 31 1/4
12 1/2 32 1/2 32 3/4 33    32    31 3/4 31 1/2
12 5/8 32 3/4 33    33 1/4 32 1/4 32    31 3/4
12 3/4 33    33 1/4 33 1/2 32 1/2 32 1/4 32   
12 7/8 33 1/4 33 1/2 33 3/4 32 3/4 32 1/2 32 1/4
13    33 1/2 33 3/4 34    33    32 3/4 32 1/2
13 1/8 33 3/4 34    34 1/4 33 1/4 33    32 3/4
13 1/4 34    34 1/4 34 1/2 33 1/2 33 1/4 33   
13 3/8 34 1/4 34 1/2 34 3/4 33 3/4 33 1/2 33 1/4
13 1/2 34 1/2 34 3/4 35    34    33 3/4 33 1/2
13 5/8 34 3/4 35    35 1/4 34 1/4 34    33 3/4
13 3/4 35    35 1/4 35 1/2 34 1/2 34 1/4 34   
13 7/8 35 1/4 35 1/2 35 3/4 34 3/4 34 1/2 34 1/4
14    35 1/2 35 3/4 36    35    34 3/4 34 1/2
14 1/8 35 3/4 36    36 1/4 35 1/4 35    34 3/4
14 1/4 36    36 1/4 36 1/2 35 1/2 35 1/4 35   
14 3/8 36 1/4 36 1/2 36 3/4 35 3/4 35 1/2 35 1/4
14 1/2 36 1/2 36 3/4 37    36    35 3/4 35 1/2
14 5/8 36 3/4 37    37 1/4 36 1/4 36    35 3/4
14 3/4 37    37 1/4 37 1/2 36 1/2 36 1/4 36   
14 7/8 37 1/4 37 1/2 37 3/4 36 3/4 36 1/2 36 1/4
15    37 1/2 37 3/4 38    37    36 3/4 36 1/2
15 1/8 37 3/4 38    38 1/4 37 1/4 37    36 3/4
15 1/4 38    38 1/4 38 1/2 37 1/2 37 1/4 37   
15 3/8 38 1/4 38 1/2 38 3/4 37 3/4 37 1/2 37 1/4
15 1/2 38 1/2 38 3/4 39    38    37 3/4 37 1/2
15 5/8 38 3/4 39    39 1/4 38 1/4 38    37 3/4
15 3/4 39    39 1/4 39 1/2 38 1/2 38 1/4 38   
15 7/8 39 1/4 39 1/2 39 3/4 38 3/4 38 1/2 38 1/4
16    39 1/2 39 3/4 40    39    38 3/4 38 1/2