How do you use V blocks to measure

[125JHP]

OK, I need some educationing on how to use my newly acquired 1 1/4" V blocks to measure things. Now I know I can't measure a 5 groove S&W bullet with these 90 deg. blocks but I should be able to measure a 4 or 6 groove one.

These B&S 750-A blocks (d1=1.250" top to bottom surface) and have a shallow and a deep V cut opposite each other with a square slot running down the V trough (d2=.560" between the V troughs).

In contemplating slugging a bore and measuring the desire bullet diameter, or when checking fired bullets (not deformed by impact) what are the best methods?

When a bullet is laid in the V, it's diameter determines where along the v the bottom is. It's easy enough to measure from the opposing v slot to the top of something in the supporting V (d3). What is the standard way to measure to the objects bottom to get its diameter (d)?

My initial guess is to use the parting blade side of the caliper to measure from the bottom of the top V up to the bottom of the bullet (d4) [but sometimes that is to close to get the caliper blades into], then measure from the bottom V (underneath) to the top of the bullet (d3) and then use a formula like d= d3-(d4+.560)... does this make sense?

Of course the grooves and lands would have to be aligned specifically to the measurement being sought.

Not being a machinist I never learned this skill. Any tips from the experts?

thanks
al

 

[Titegroups]

I don't know what you've got there but using a caliper to make measurements to the thousandth is not a good idea. Use an outside mic. for precise measurements. You can easily be off a thou. either way making it pointless.

 

[Lenny_D]

If I understand what you want you are looking for the difference of the diameter of a fired bullet between where the lands of the rifling have left their indentations to the full diameter of the bullet? If you're checking the projectile just use an outside micrometer and measure the bullet then set your bullet in your "v" block and use a dial indicator to measure the difference between land and groove multiply times two and subtract from outside diameter you measured to come up with the smaller diameter. I'm not clear on what you're looking for.
"V" blocks are really measuring and setup aids they, in themselves will not actually give you measurments.

 

[125JHP]

Hmm I guess I was going on some threads I read about how to use 105 deg V blocks for measuring S&W 5 groove slugs. The gist of it was that you can't directly measure the lands or grooves because of their offset so you need to use a v-block that is cut at a 105 degree angle and that (as I understood it) you would take measurements from some point on the block and use a conversion factor that was pre-calculated for the block dimension.

Not having all the details makes it murky to explain, but for some reason I also got the idea I could use a regular block for even groove configurations.

I don't have a dial indicator but ya know, your right I can use a mic directly

 

[125JHP]

Well, after fooling with it for a while, it appears there may be times when using a V block could be handy...

o- Like when finger holding an object for measurement becomes a fumble fest of thumbs and just securing it in the block is much easier - but now the block gets in the way of taking the measurement. Thus using it as a measuring aid as in my original question.

o- Like when the part to be measured is recessed or too narrow for a mic anvil to fit on it but the thin blades of a caliper will work and get the job done. +-001 is close enough for for my needs.

BTW has anyone noticed any reading variance or flex error between the cheaper digital calipers so common these days and the dial models from years gone by?

I noticed that if you use the thumb pad or wheel on a digital model to close on a part, that you can change the reading with the amount of thumb pressure used, but if you use your fingers to squeeze on the jaws instead, that you get a good solid reading.
I think this may be from flexing of the plastic digital housing which my SS dial caliper doesn't seem to do.

 

[Moonman]

CHEAP DIGITAL CALIPERS are just that, CHEAP.

Real Calipers and Micrometers are PRECISION INSTRUMENTS, please treat them accordingly.

Both of these instruments require practice and an Educated FEEL, they are in no way clamps or C-Clamps, though some people seem to use them like that.

Measuring a lead bullet grooves has to be done gently or you will compress and distort your reading.

American Handgunner magazine had an article on using the 105 degree v-block and conversion chart for 5 grooves several months back.

Good Micrometers, Calipers (I prefer DIAL ones over digital), dial indicator, travel dial indicator, V-Blocks and Precision Gage Plug Pin Sets will last more than your lifetime if cared for.

My machinist tools are still in fine shape even after being used for a 40 year machinist career. Many are Starrett, Mitutoya, Brown/Sharp, and Lufkin.

For testing the hardness of lead bullets, lead ingots, pieces of lead, I use a CABINE TREE hardness tester. The Cabine Tree unit is easy to use and accurate.

The tools now serve around the house and loading bench/gunsmith measuring jobs.

 

[125JHP]

Thanks for your insight Moonman,
I understand what you are saying and your sensitivity to the subject, Sorry, if my selection of wording was a bit ruffling and sounded misleading. Although I don't have your experience and don't know the nuances of the various brands, but I realize the market has been flooded with cheap copies and I try to buy quality tools when I can afford them and treat them with care.

I also don't know all the terminology specific to the trade, so was improvising my description to get an idea across. I know they are not c clamps and 'feel' is a technique learned. My point was that using a popular digital model utilizing plastic in its construction could induce error, dependent on the thumb pressure applied while a stainless dial version caliper did not. The tip on using fingers to close the jaws for an accurate reading with the digital version came from a machinist forum I happened upon while looking for info on my original Q.

I was only mentioning the differences because there seem to be a ton of new re-loaders on the forums that will read these posts and run out and buy a cheap unit and start using it without realizing the results may be inaccurate.

 

[ruffbird]

A few snaps with my crapy camera...

The lower part of the article, sorry it's out of focus somewhat....

Last part...

This is the book it came from...

Hope this helps ya....

 

[125JHP]

Thanks Very Much, that is the type of thing I was looking for. Now to adapt it for my blocks and use and then someday I will acquire a set with the correct angles for 5 grooves.

hmmmm.... Maybe Moonman could start a hobby service of selling custom angled V blocks to interested forum members.

 

[ruger-p94]

I was an instructor in the wonderful world of machining and the V blocks are used to lay an object on the get a good reading. Most of the time you will use the blocks with a granite table and a dial indicator. The best thing I ever invested in with my senior eyes is a good vernier digital caliper. You can do OD ID and inside measurements. You should be able to get within a few thousands of an inch if you follow the book closely.