AusVarmint

Can anyone tell me how to accurately measure the spacing between two holes using a vernier?

I know, it should be simple.... spacing between the edge of the two holes plus the diameter of a single hole...should give me center to center.

I want to fit a rail to a drilled and tapped receiver and, need to drill the rail to suit the exact spacing. Last time I did it, I screwed it up being hasty...

Also, any suggestions for an easy way to cut out the rail for the ejection port? No, I don't have access to a lathe or mill so, at best I can dremel or drill press.

This is for an old .22LR, nothing fancy like a precision bench rest rifle.

The most accurate way I found of doing that was in a mill and zeroing the readouts at one hole then moving it along so the drill bit fitted into the second hole. But using verniers the only way I would think of would be take the measurement from inside to inside of the two holes then add the diameter of one hole- that way making the entire measurement correct. You may want to do it a few times to make sure its right and your not getting a one off dodgy reading.

after you've done all your measurements, try drilling the holes in a piece of wood and see if that fits before you drill your rail

Brad Y wrote:The most accurate way I found of doing that was in a mill and zeroing the readouts at one hole then moving it along so the drill bit fitted into the second hole. But using verniers the only way I would think of would be take the measurement from inside to inside of the two holes then add the diameter of one hole- that way making the entire measurement correct. You may want to do it a few times to make sure its right and your not getting a one off dodgy reading.

That's what I tried to do the first time. I admittedly rushed that attempt as I was eager to see the results.

I'll measure a lot before any drilling.

trevort wrote:after you've done all your measurements, try drilling the holes in a piece of wood and see if that fits before you drill your rail

Now that's a great idea! So obvious I never thought of it!

Yep I drill into something else first, if you use steel and its perfect you can use it as a template.

If I thought about it more....

Perhaps a simple paper template over the receiver would allow me to more easily replicate the exact spacing.....and then test drill a mock piece.

Just shows you how easy it is to get all technical when some basic techniques will solve the problem quicker.

Template is the go but also make sure you scribe and centre punch the hole. If you dont the bit can skate over the workpiece (even with a template). Dont forget you will need to countersink the bolt head too.

Bidgee wrote:Template is the go but also make sure you scribe and centre punch the hole. If you dont the bit can skate over the workpiece (even with a template). Dont forget you will need to countersink the bolt head too.

Agreed! I plan on doing all that.

Next trick is to figure out the correct thread size so I can source some suitable screws. The hole/threads are larger than the screws supplied with the rail. Are there 'standard' sizes for rail screws? Mine would definitely be non-metric (Sportco).

for the cut out in your rail just take to it with your bench grinder. just face off the stone first so its flat and square.

i found measuring the distance between two centres with a vernier easier (provided that they are both the same diameter) by measuring from the inside edge of one hole and the outside edge of the second hole.

Definitely redoing the rail now. Went to Springvale range and found the scope was sighting in a couple of suburbs away (miles too high). It's now fine but I've run out of windage adjustment.

Lesson learnt, don't do a dodgey rail mount...take your time and get it right.