Reading machinist's drawings?

[TNHillbilly]

I am confused over reading decimal dimensions! I have -I thought a machinist's small rule, reads in 32nds and 64ths. For example, how do you measure 3.236? .2362 converts nearly to 6mm. So, am I supposed to measure 3" + 6mm ....... The few times I've done this before, the decimal number equaled something like 3/8th, 1/16.... Got a set of plans for a Swivel Breech, and getting confused already!

 

[Roy]

Get a set of digital calipers :thumbsup:

 

[sundog]

Oh boy , A set of dial calapers will help you. You do not convert anything, machine drawings do not use fractions.

 

[Blizzard of '93]

machinist drawings are usually noted in '100ths' of an ". sometimes all measurements are 100ths. most all dimensions and diameters are in 100ths.

 

[Stophel]

Other than hole drilling, there's not much anything on a flintlock gun requiring that much precision....not so that you can't convert to the nearest fractional size if necessary. Most of the time, for drilling holes, you're going to need a numbered drill set. I have an old index that has the numbers and also has the decimal measurement marked on it, which helps a lot.

To find the decimal equivalent of a fraction, just divide out the fraction. 1/4=.250 1/16=.0625, etc.

For measuring the fine dimensions in thousandths of an inch, you just have to have calipers. I have a cheap $20 set I got from Midway years ago that work just fine.

By the way, what dimension is "3.236 inches"?

 

[TNHillbilly]

If it has a hole drilled .3750, I look at a chart and whip out my 3/8th's bit, etc. I don't think I ever saw a .3750 drill bit in the store! As for the dimension 3.236, it's from the center hole of the main spring clevis block, to the front of the lock. The digital calipers make sense, but how'd they do it before digital? Guess I just never thought much about it. The few times I've used these, my chart would convert to something I could measure.

 

[Stophel]

Wow, I don't even know what a mainspring clevis block even is.

Before calipers? They didn't worry about it. Things were fitted by feel, by eye, and with comparitive calipers.

 

[TNHillbilly]

It's kind a strange! There are a few places where he gives a standard hole size like 3/32. This swivel system (double barrel flint if you will) has a lock basically made in 2 parts, front and back. Back portion is essentially a 'back action' lock with a shorter Ms held in a block instead of the tradiditional 'U' or 'V' spring. Front is basically 2 frizzens/pans, one up-one down, with 2 plates in the middle that turn. Clear?

 

[Vaino]

3.250"{3-1/4"}-.0156"{1/64"}=3.2344"{3-15/64"} which is close enough. Calipers are handy whether dial or digital. All this "figurin" is a good example why the metric system should be instituted in the USA in lieu of the illogical English system we presently have. How a high tech country such as ours is saddled w/ the archaic English system is beyond comprehesion. Our auto industry has used the metric system for many years because it's much easier to use. A MLer can be built w/o using even a caliper and mostly I just use a scale...Fred

 

[sundog]

There is a good reason to NOT use Metric measurements in machine tools. Metric numbers especially when they are used for very small measurements EX 3/10,000 of an inch become gigantic and combersome. When we had to program a machine tool to do metric work it was always converted from Metric to English.

 

[Stophel]

Egad, I hate the metric system.

There is nothing "illogical" about standard English measurements.

 

[Vaino]

Most of the WORLD uses the metric system and only because of our egocentricity, the USA does not. There's no comparison between the logical metric system and the archaic English system. Most critics of the metric system haven't really used it at all in spite of the fact that it's a very easy system to learn. Talk about a mental block! All the industrial countries of the world use the metric system.....I wonder why?.....Fred

 

[TNHillbilly]

Thanks for the education! I bought a digi calaper, it'll look good next to my metric mikes! Since it's all hand made/fitted, I'll make it work. Just looked at the plans, and thought: I am that stupid, or what? I guess having foreign cars way back, I got used to metric and also find it easier than putting down my 9/16's socket to get an 11/32, or was it 5/8's? I guess, too, if a guy was cutting parts with a CNC, deci's might be easier. I use a lot of 'eyeball' and 'squint' calipers. The 'touchy feely' method works good for fitting stuff together too. Can't figure how those old timers built this stuff without digital calipers though?

 

[Elnathan]

IIRC all other industrial countries run on some sort of socialist system or another, and change their constitutions every five minutes. :haha:

More seriously, we still use the old system 'cause we are cranky traditionalists at heart, even with all the emphasis on new stuff in our popular culture. The Canadian author Mark Steyn has pointed out that in some ways we Americans are very traditional - even our radicals spin their proposals around an 18th century document - and we are by far the oldest constitutional democracy on the planet (he comments that our constitution is older than all the constitutions of Western Europe combined). I can't help but wonder if there is some connection between our use of feet and fractions and our veneration of the Constitution, deep in our national psyche... :hmm:

Personally, I like the English system, and while I have been known to use centimeters, I find the lack of a counterpart to the English foot to be a mental block. Incidentally, metric is only more rational if you think in decimals, rather than fractions, I think.

 

[paulvallandigham]

The only benefit of using the Metric system is that it uses a base 10 for all measurments. We use base 12, base, 24, base 36, as well as base 10 for some measurments. Our weights are mostly base 16, but in lbs. we are base 10. Can we work with grams, drams, and drachmas? Yeah, but it really is not necessary.

The rest of the world just has found something that it can use to laugh at the most successful democracy, the oldest democracy, and the most successful free-market economy in the world. And, they hate the fact that they have had to turn to us in two world wars, and any number of dust ups since to save their bacon! Ever hear of any other country in the world celebrate an " American Appreciation Day?" The complain about our use of energy, but ignore the fact that we are by far the most productive country in the world, and that we produce both the food, clothing, shelter, and fuel to help out people all over the planet when natural catastrophies strike. No one else has the resources, or the transportation system to get it there. That is where all that energy goes. I didn't seen any aircraft carrier sailing up the Mississippi to help out American Flood victims in Iowa, and Missouri these past couple of weeks, but we sure saw them show up off the coast of Indonesia, and again off Burma( Myanmar) to help those victims, only to be turned away by governments that don't want any aid being given to the people that indicates its source of origin, making them look bad.

So to all you fans of the metric system, who love to hate the USA, call someone else where the poop gets into your air conditioner. We are no longer going to answer your cry for help.

 

[shortstring]

If you want to hear something sadder yet. I've been hanging around the world of machining so long that I'm the opposite. When I see 11/16 I think .6875, ect.

 

[Elnathan]

Okay. Just for the record, I do not think that the metric system is un-American. I was speculating that there may be a connection in our habits of thinking between our reluctance to change measurement system and our veneration for an 18th century document - that does not indicate that a dislike of the English system indicates a dislike for the Constitution!

I am sorry I ever wrote anything...

 

[sundog]

Most machine tool work iven in Metric countrys is done in the inch system. The metric numbers used in numericly controlled machine tools get positively gigantic , thus the error factor comes in. Yes you can program them metric but they convert it to english to operate. Try converting a measurement like 3.4555 +or- .0005 to a metric number and you will immediately see why machine tools use the english system.

 

[Zonie]

3.4555+-.0005 is 87.770 +-.013mm :grin: .

TN Hills: Glad to hear you got some digital calipers.
I think one thing you will find very useful is the part that measures "inside" dimensions.
If you coat your flat plate with blue dykem or a felt tip pens ink, then after making sure the readout says 0.0000 when the jaws are closed you can move the jaws to whatever dimension you want to mark. Then place one point of the inside measuring tips at the starting place and lightly swing the other tip across the plate leaving a lightly scribed line. It will be closer to the exact dimension than you can see.
Just make sure you don't bend or damage the tips.

 

[J.D.]

we are by far the oldest constitutional democracy on the planet

Folks, I gotta remind everyone that the United States does NOT have a democratic government. It is a REPUBLICAN form of government. The two forms of government are very different.

IMHO, the insistence by the media that we have a democratic government stems from the fact that simple suggestions, especially subliminal messages, bring people to accept that idea.

That same suggestion, in this case of anything democratic, can also influence one's acceptance of related categories, such as influencing listeners to vote democratic. Yeah, the libs know ALLOT about psychology, and they use it to manipulate the uninformed masses.

I am currently studying social psychology, BTW, and the topic of implicit associations is part of the course of study, so this idea is not simply a part of a great conspiracy theory...at least not from the conservative side.
J.D.