i want to mount a scout style scope or red dot on my tc black diamond which came with no rear sight. i will use the 2 rear sight holes with a tc weaver omega scope base, and no the omega base holes do not have the correct spacing, so i can only use one existing hole on the base. i emailed tc requesting the spacing and they came back with it is unknown. i measure .628“ center to center just looking to verify the spacing before i start to drill a hole.
tc black diamond sight spacing
- Thread starter dr1445
- Start date
You should measure the distance between the holes (inside edge). Then add 1/2 the diameter of the drill to get the location where to drill. I'd also use an edge finder to find top dead center on both areas (assuming the barrel is tapered). Then I'd use the readout on the mill to get exactly where I'd want it.
Since I am using calipers, 2 things.
1 the fat jaws do not fit in the small #6 holes. I had to use the thin jaws, outside to outside.
2 ½ hole will get you to the center of one hole, what about the other hole?
I did the layout on a scrap piece of aluminum, fit and function went ok so I was good to go.
1 the fat jaws do not fit in the small #6 holes. I had to use the thin jaws, outside to outside.
2 ½ hole will get you to the center of one hole, what about the other hole?
I did the layout on a scrap piece of aluminum, fit and function went ok so I was good to go.
Do you have a mill? You can use a gauge held in a collet and drop it in one hole. Set your zero. Move the mill and get a readout for the other hole. That's the distance apart those holes are.
Alternatively, if you have a complete set of drills, drop the smooth, uncut upper part of the drill into each hole. Make sure they don't wobble. Then take your calipers and measure the distance between them. You can confirm your readings by measuring the distance from the outside diameter to outside diameter of each drill rod. Then subtract the sum of the two drill rod diameters to get.
Alternatively, if you have a complete set of drills, drop the smooth, uncut upper part of the drill into each hole. Make sure they don't wobble. Then take your calipers and measure the distance between them. You can confirm your readings by measuring the distance from the outside diameter to outside diameter of each drill rod. Then subtract the sum of the two drill rod diameters to get.
no miller, just a drill press. i know 1 person with a miller and one with a jig bore who will do the job but i need to give them the center to center distance to pick up the 2nd hole. the test piece i made to check the c to c fit, so now i have the spacing and a sample to send along.
What Snyper said.
If you want to measure because you lack the transfer punches or a lathe to make them on, you can get a conical tip centerline attachment for the caliper for as little as $22, currently. Assuming the threads are not all the way to the top of the hole, that will work.
If the threads are all the way to the top of the hole, the top turn can bias a conical tip to the side. Same with a conical tip center finder. In that instance, take a set of number drills and find the largest size that still slips inside the thread all the way to the bottom. You use a second drill that same size for the second hole. Measure between the drills sticking up in the holes by measuring the outside space between them and also the inside space between them, and then average the result. Do it a number of times, using the smallest inside and largest outside numbers you get, as any error in jaw perpendicularity to the centerline between the drills will make the inside number larger and the outside number smaller.
My guess, though, with the 0.628" result you have now is that the actual spacing intended was 0.625", an even 5/8 of an inch. The 0.003" is a not-unacceptable cumulative tolerance error for holes to mount something like a scope ring. Also, it is easy for the eyes to be fooled about the exact location of the hole center by the top thread causing and minor optical illusion. It is also easy for calipers to be off a couple of thousandths in awkward measurements. I don't think I've ever owned a pair with inside jaws ground to perfect precision. I take the measurement, lock the jaws at that number, then measure their actual spacing with an OD thimble micrometer. The micrometer giving 0.002" difference from what the caliber readout says is not uncommon on inside jaws checked this way. Same for locking the micrometer at a fixed value and applying the jaws to measure the distance between its anvil and spindle nose.
If you want to measure because you lack the transfer punches or a lathe to make them on, you can get a conical tip centerline attachment for the caliper for as little as $22, currently. Assuming the threads are not all the way to the top of the hole, that will work.
If the threads are all the way to the top of the hole, the top turn can bias a conical tip to the side. Same with a conical tip center finder. In that instance, take a set of number drills and find the largest size that still slips inside the thread all the way to the bottom. You use a second drill that same size for the second hole. Measure between the drills sticking up in the holes by measuring the outside space between them and also the inside space between them, and then average the result. Do it a number of times, using the smallest inside and largest outside numbers you get, as any error in jaw perpendicularity to the centerline between the drills will make the inside number larger and the outside number smaller.
My guess, though, with the 0.628" result you have now is that the actual spacing intended was 0.625", an even 5/8 of an inch. The 0.003" is a not-unacceptable cumulative tolerance error for holes to mount something like a scope ring. Also, it is easy for the eyes to be fooled about the exact location of the hole center by the top thread causing and minor optical illusion. It is also easy for calipers to be off a couple of thousandths in awkward measurements. I don't think I've ever owned a pair with inside jaws ground to perfect precision. I take the measurement, lock the jaws at that number, then measure their actual spacing with an OD thimble micrometer. The micrometer giving 0.002" difference from what the caliber readout says is not uncommon on inside jaws checked this way. Same for locking the micrometer at a fixed value and applying the jaws to measure the distance between its anvil and spindle nose.
i have a workable # @ .628 to pass on to one of the guys with a machine, if it ever stops snowing and i see them at the range. my other problem would be locating the scope base center line but that is no problem once mounted in a miller or jig bore. for now i am just waiting out the weather.