Measuring for dummies

[The Raven]

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.

[Brad Y]

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.

[trevort]

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

[The Raven]

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.

[The Raven]

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!

[stinkitup]

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

[The Raven]

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.

[Bidgee]

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.

[The Raven]

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).

[andrewk]

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.

[The Raven]

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.