Replacement barrel for 1911

[Dave Sample]

Glad you got things worked out. The first time for anything is a learning process and the next time will be a piece of cake.

[Unclenick]

Echoing Dave here. The first 1911 I ever did took about 100 hours to get right, and I ruined two sears and a hammer and a bushing before I was done. The second one took about 30 hours, the third about 20 hours. You get the idea. You get faster both from learning and from buying or making special tools that speed the work up.

Dave, I love those inexpensive Chinese calipers, too. They're so cheap I keep separate ones in kits for different tasks. Tell me if the set you got from Harbor Freight does any better, but I find the inside measurement of a hole with my calipers is typically 0.001" to 0.002" smaller than the outside measurement of the chucking reamer I used to finish it. With little holes, the fact the tiny flats on the inside jaws bridge a chord in the circumference of the hole make it measure undersize anyway, but I get disagreement on larger holes too (1/2" range).

I should have made it clear that telescoping gauges are for those who want to split thousandths. You need a micrometer with a vernier scale or a digital that resolves two ten thousandths or finer to take advantage of them. Also, the telescoping gauges are only made to measure holes 5/16" and up. For holes in the range of 1/8"-1/2" you can use small hole gauges and a micrometer (http://www.use-enco.com/CGI/INPDFF?P...&PARTPG=INLMK3). For even smaller holes, use pin or plug gauges, verifying the actual O.D. with the micrometer (same page as the small hole gauges).

Nick

[Eghad]

WOW.....great thread. Got a 1911 I am interested in fitting a barrel.

[Shorts]

I picked up a 6" dial caliper from HF. Measuring on my feeler guages it dials right on. I'll have to see about larger ranges. I only measured .025"-.0015".

For consistency's sake, what's the proper way to position and hold the calipers when measuring? Do you hold the jaws clamped down on the object? How much of the jaws do I place on the object? I know the amount of space to work with determines that a lot, and the jaws should be parallel for all intensive purposes. Measuring the feeler gauges, I held the thumb tab down so that the jaws were snug. That gave me accurate readings. Is that proper?

[Dave Sample]

Uncle Nick will have to help you on this one, Shorts. I am not a machinist and I do very little measuring as most of my 1911 work is cut and fit, cut and fit , cut and fit. I like the calipers to check the lock up on barrel fits and to measure the parts before we start chewing on them.
That 100 hour figure rings true as our Online 1911 Students need about 100-150 hours to complete that first Custom 1911. Our students rarely ruin any parts, but if they do, they have to replace them and they soon learn that Rule One is Iron Clad.
" Metal is very easy to remove, but very hard to put back!"

Most folks who like to build a 1911 do it flying blind and with no direction or logical sequence of the order of doing the work. Building a Custom gun from Parts is a series of steps like the fitting of the Barrel, to name one. We take them through all of the procedures in a logical way that allows them to complete a wonderful pistol worth a lot more than their investment in time or money. It is almost Un-American to give them back more than they give! I do not allow anything but the very best effort that thay can muster up and we do not condone sloppy workmanship at all.

[Unclenick]

Dave,

Take pride in your lapping fit work. Lapping, scraping, and stoning are still the most precise practical machine fitting methods. I once annealed and scraped right corners onto three two-inch CRS cubes. I had a university lab measure them, and they were flat on all three faces to within 0.00002” (20 millionths), and the three sides were square within 0.00004” across the flats. I could tip one of these up along an edge on a granite surface plate, drop and push, and watch it skate across the plate on the layer of air trapped beneath it.

All that was done by the rule of threes, known from publications done in the 1600’s, and probably discovered and lost and re-discovered repeatedly since Egyptian times. It works on the principle that if three surfaces make complete overal contact with each other interchangeably (1 to 2, or 2 to 3, or 1 to 3), then, by definition, they must be flat. Nothing needed but a scraper and some high spot blue (smoke soot works pretty well, too). A friend of mine who once worked for Sheffield Tools said that by stoning after scraping, it was possible to get within 5 millionths (0.000005”) and that they did this on aerospace precision grinder beds not only for accuracy but to fit so tightly that grinding wheel grit particles couldn’t slip between the sliding surfaces and ruin them. These had to be used in temperature regulated rooms to stay within specifications. Too precise for use in a gun or anything else that changes temperature significantly.

There now exists some very fancy gear that can shave single atoms from things, and these could theoretically make a better fit if there were enough time to employ them on anything bigger than the point of a pin. The problem is that this is so tight that even fractional temperature changes would take the parts out of specification.

So, keep on lapping!


Shorts,

How to use the caliper? The main thing is consistency. The weak part of a sliding jaw caliper is the fit of the slide in its channel. To move, this can’t be a dead-tight fit. So, a phosphor-bronze leaf spring is usually used to establish a pressure bias toward one side. If you push the jaws so hard it overcomes this spring, the jaws will cant a little and throw your measurement off. You need to apply the closing force from the same point and in the same amount each time you measure, and not overdo it. The caliper isn’t a clamp. You need light, steady pressure.

To learn how much pressure to employ, place a small round steel object between the main outside-measuring jaws and measure it. The smooth shank of a drill bit works. After discovering that drill bits are usually undersize, note that if you apply light pressure, the measurement is larger than when you apply strong pressure. In the latter case, the measurement gets smaller because you are deflecting the jaws. Also note that this error gets worse the nearer the measured object is to the tip of the jaws. This is because you are applying more torque to the deflecting moment owing to the longer lever arm. The moment, or pivot point of the lever is where the jaws are bearing against the channel. Slowly cease applying pressure and the reading will come back out to its correct value if the round object doesn’t move at all with respect to the caliper. Use your thumb to see how much pressure you can apply before the false reading begins to appear. Use something that feels like about one third of that pressure for all your measuring.

Also, don't allow the object you are measuring to cant in the jaws. You may have to wiggle it slightly back and forth as you apply closing pressure and use the minimum reading that results. In general, try proceeding as follows:

1. Wipe the main outside-measuring jaw faces to clear any particles.
2. Close the jaws and zero.
3. Open and re-wipe and close again.
4. If you didn't go back to zero, repeat the process until you do.
5. Wipe the object being measured to clear any debris.
6. Make your measurement.

Notice the main jaws are beveled near the tip. The bevel creates a narrow flat for getting inside grooves or measuring a diameter at one point on an object whose sides aren’t parallel. However, this beveled tip is more easily damaged than the broader flats just inside the beveled area. So, use the broader flats whenever you can and save the more delicate tip area for when it is necessary.

You can test your measuring accuracy on a micrometer standard. This is a precision fixed-length rod with parallel flat ends. You can buy hardened or even carbide tipped micrometer standards, but I would just buy an inexpensive micrometer that includes one. Enco’s 600-0012 is such an item, currently $12 on sale. This will have a 1” standard for checking zero on the micrometer. English scale micrometer thimbles are good for 1” of travel, so you have to have a separate micrometer for each inch of measurement range you want. This one will measure between 1” and 2”, which is limited, but it resolves individual ten thousandths and has up to 20 times the accuracy of most calipers.

The inside measuring jaws are on the opposite side of the beam from the outside measuring jaws. These are placed inside a hole and the jaws are expanded until they stop. Again, gentle wiggling and tilting while applying measuring pressure is useful (but this time looking for a maximum reading). One of the problems with this is you are no longer applying pressure in the same direction as when measuring outside dimensions. This can introduce an error. Assuming you have a 3-way caliper which has a depth measuring stem that emerges from the back of the beam as you open the jaws, you may zero for inside measuring by placing the back end of the caliper beam on a flat surface and applying opening measuring pressure back against the flat. Also, if you have an object with a precision hole in it, you can measure inside it for comparison.

Most calipers now include that depth measuring stem. Placing the back edge of the caliper on top of a step while you extend the stem downward will allow you to measure the height of the step. Most commonly this feature is used to measure the depth of a blind hole. The back edge of the caliper is so narrow it is hard to use precisely in this way, but accessory T-bar bases to extend this flat are available (http://www.use-enco.com/CGI/INSRIT?P...PMPXNO=7911700). You close the jaws and zero the caliper against a flat surface, then slip the T-bar over the beam, flat against that same surface while you tighten its set screw.

Hope this helps,
Nick