Using a Micrometer

[DavZee]

I am working to learn the new micrometer I purchased in a set with a caliper. I purchased some manual ones because I don't trust the electronic HF caliper I have. The Micrometer is vernier. There's some great YouTube videos that show how to read them. On the back of the mic there's a ratchet that opens the spindle. Is it supposed to open or close it? Can you change the direction? This set didn't come with any product descriptions at all.

[oneokie]

The ratchet should ratchet in one direction, when you are closing the mic onto the object you are measuring. Supposedly to give you the same applied force each time. It should not ratchet when you are opening the mic.

[DavZee]

Bummer, mine ratchets the spindle open :groner:

[Stephen Cohen]

When I was taught to use one, I was told you must always use that spindle. or as you say ratchet to open or close, however that ratchet sound you hear on closing should not be heard on opening IMO. an interesting thing to try is use the body to make ajustments when miking a bullet then use the ratchet and I bet you get two different readings.

[DavZee]

Ah Ha! Now I get it! Thanks Guys! :2_high5:

[MBTcustom]

Yes, in the old days before the ratchet, It was up to every machinist to learn to apply the correct pressure to his own micrometers in order to achieve the correct reading. Unfortunately, there were too many who just didn't have "the feel" for their tools. That, coupled with manufacturing tolerances being tightened while being sped up to ludicrous speeds, it was necessary to have a method of using that tool so that ten machinists could all measure an object and come up with 10 answers that matched within .0001. The ratchet is how they achieved this. Some use the ratchet, some use a friction thimble (my preference) but they all do the same thing.
In case any of you dont know, the way to check zero on a micrometer is to close the anvils lightly on a piece of clean white paper, and pull the paper from between the anvils. use the rathcet to tighten the anvils together in the same way as if you were measuring something. The zero line should match perfectly! If it does not, send me a PM (that is an offer to any of you who read this) and I will try to help you calibrate it the correct way, or you can send it to me and I will handle it personally. It is a delicate operation and you must be very careful to never spring the beam of your micrometer, its the same as scratching a telescope lens.

[Bret4207]

One way top learn to use the mic is to get a standard or some object you are sure on the size of and practice closing the mic on it. Sierra bullets, IME, run very close to advertised diameter, but your mic should have come with a standard to set it with. Practice closing the jaws so you get consistent readings, use the thimble or the ratchet or both and see what works better for you. DO NOT spin the anvils closed quickly! These are precision measuring instruments, not toys.

[theperfessor]

Don't know if this will be of any help. It's a link to a program I wrote years ago. Not all the sections are there, it was meant as a framework that could be added to and expanded. But if you click on the button that says Measuring Tools you will get a page that lets you open illustrated instructions on how to read an inch basd micrometer and also an inch based vernier. It's all just HTML code and can be printed out for reference if desired.

http://www.usi.edu/science/engineering/machasst/machasst.htm

Feel free to poke around in it, there are some (maybe) helpful tables of data, etc.

[DavZee]

This was a fairly inexpensive set I got from Amazon.
I know the zero line does not line up with just using the ratchet. I have to use the spindle and some pressure (not a lot) to line them up. I know there are much better quality tools but I'm only using it for loading. Perhaps I'll take GoodSteel up on his nice offer of helping me adjust it but maybe they are just junky and I got what I paid for.

http://www.amazon.com/Anytime-Tools-Professional-Machinist-Inspection/dp/B000HDF8N4/ref=sr_1_sc_2?ie=UTF8&qid=1341584833&sr=8-2-spell&keywords=dial+calier+micrometer

[C.F.Plinker]

It looks like your set has an adjusting wrench. Close the spindle just using the ratchet and notice how far the index line is from the zero on the spindle. Open the spindle several turns and line the index line back up with the reading on the spindle where it was stopped by the ratchet and lock the spindle in place. There is a small hole on the back of the index arm. This is for the little projection on the jaw of the wrench. Use the wrench to turn the index arm until it lines up with the zero on the spindle. Now release the lock and turn the spindle back in until the ratchet clicks again and see if you are still off. Fine tune the adjustment as necessary.

[nanuk]

I bought a SAE mic, Frankfort Arsenal

JUNK! Absolute JUNK!


My mitutoyo Metric is very nice... and $10, the price was right. Metrics measure to about 1/3 of a "Tenth"

[dragonrider]

While you are practicing with you micrometer DO NOT watch the spindle as you do so, this will influence your results. Do it blind, eyes closed, or hands under a table or behind your back. Get it to where you think it feels right, then open your eyes and look. You will develope a proper feel very quickly.

[MBTcustom]

Before you adjust anything, you had better have done the paper cleaning like I told you to. Also, I have run into a few "junky" micrometers, but they are few and far between. If a micrometer has flat, parallel anvils (clean with paper and close until you just barely feel the anvils touch each other and hold it up to the light, if you cannot make out a light gap no matter how you turn it in front of a light source, then you are good) and if the threads are reasonably tight, I can measure to .0002 accurately and consistently every time. I had to do this for years, because the cheap Chinese micrometers were all I could afford. I certainly upgraded as I got raises, but I made about half a shipping crates worth of parts with the cheapos. Calipers are a different matter, you get exactly what you pay for.
Another thing I might add, is that when you go adjusting your micrometer, don't just grab the little spanner wrench that comes with it and go yanking on it. It works if that's the only way that it was designed to be adjusted, but it puts undue force on a precision screwthread. I have fixed many a micrometer that a guy was cussing trying to get it to turn, by simply taking the ratchet off the back via the conveniently located flat head screw, raising the thimble, finding the conveniently located hex-head set screw, and simply putting the thimble where it needs to be on the barrel and lightly tightening the set screw to lock it in place, then comes the inevitable "oh" from the guy that was doing the cussing a few minutes ago. It never ceases to amaze me how many people are afraid to take something apart to see how it works, but have no quams twisting and yanking on the same delicate precision piece of equipment. There are lots of different designs of micrometers, the one described above is only one (but very common) configuration. Just relax and treat it like you would a vernier creedmore sight, or a spotting scope, or any other blessed thing you care about being perfect, and you'll do fine.

[Char-Gar]

I have Starret micrometers with no ratchet, with ratchet and with the "friction thimble". I have found that when clean, properly adjusted and used properly they all give the same reading. I learned to use a micrometer with no ratchet/friction thimble and tend to use all of the with just finger pressure.

[DavZee]

I've got it zeroed now and my reading are getting more consistent the more I use it. After spending some time with it, I find the numbers are easy to understand and quick to read. Now it seems my bullets do not have a consistent circumference at all even after sizing them. Using the ratchet technique and measuring at 3 points using the mold line as a reference spot, I'm getting variations from .4535 to .4557. These bullets were cast from a Lee 6 cavity .452 mold. They were sized in a Lyman 450 lube sizer with a .452 sizer. I don't think I have the perfect nose punch for this bullet. Could they be going through crooked and that is causing the difference?

[oneokie]

Is your vairance on boolits from the same cavity each time? Or is the variance from cavity to cavity?

Measurements should be taken on the parting line and 90° to the parting line on the same driving band.

How consistent is your alloy?

Lyman sizer dies are known for being mis marked as to size, or your alloy is not the same as the alloy they use for checking.

[Char-Gar]

If my math is right, your bullets are more than .002 out of round AFTER going through the Lyman sizing die. If I have that right, and if you have measured right, there is something out of whack.

I would not be suprised to see a Lee bullet .002 out of round as cast. But I would be suprised to see a Lyman sizing die .002 out of round.

A less than perfect nose punch won't account for a bullet that much out of round after sizing. What I would do is.

1. Check your mic and mic skill by measuring a round object of a known diameter. A jacketed bullet will not be very much out of round. A jacketed 30 cal bullets will be .308 pretty much all around and so forth.

2. Take a good look at your sizing die. Are you misreading the number. Could it be something larger than .452.

3. It just may be a communication issue. Tell us again what your issue is.

[bob208]

i still have my starret 0-1 mic i bought in 68. i also have starret mics up 6". now when i was learning tool making the shop i worked in all 4 of us could mic something and get the same reading even if we used eachothers mics.

as stated don't look at the mic while you are closing it on a pic. do it by feel only.

[Silver Eagle]

Remember when storing calipers or micrometers (Or any measuring instrument) to leave them open a bit. Do not close them all the way and put them away. It is nicer on the measuring faces. Also prevents metal expansion and contraction from temperature changes from affecting the instrument.
There are a few threads on this forum concerning mics and calipers. They contain info on use, maintenance, calibration. Do a search and look them up.

Silver Eagle

[Bret4207]

I've got it zeroed now and my reading are getting more consistent the more I use it. After spending some time with it, I find the numbers are easy to understand and quick to read. Now it seems my bullets do not have a consistent circumference at all even after sizing them. Using the ratchet technique and measuring at 3 points using the mold line as a reference spot, I'm getting variations from .4535 to .4557. These bullets were cast from a Lee 6 cavity .452 mold. They were sized in a Lyman 450 lube sizer with a .452 sizer. I don't think I have the perfect nose punch for this bullet. Could they be going through crooked and that is causing the difference?

Okay, first off, and I don't care what any manufacturer says, you'll never, ever get a perfectly round boolit, even after sizing, except by pure luck. If you are measuring as cast boolits from a 6 banger then your results are well within the tolerances I've seen. If they are after sizing, then go back to step one and see what they dropped at. No matter what you do, you'll never get a .4535 boolit to measure .454 just by putting it trough a .454 sizer! You will also find that sizer dies can be as much as a couple thou off from their marked diameter. Usually it's not that bad, but IIRC I had one marked .310 that produced .308 boolits consistently, or something like that. So, first thing to do is measure the boolit before sending it through the die and then see what it measures after.

Another thing to consider is that some dies have a very narrow sizing band. A boolit will always follow the path of least resistance going through a die. So if you have a boolit that didn't fill out so well in one area going through that die, the boolit will "snake" it's way through there to an extent. Obviously with longer boolits this can become more of an issue. Off center sizers, top punches and sizer ram play and misalignment can also add to this mess.

Getting back to the variation in your diameter- Part of that is likely poor fillout. That can be caused by a cool mould, by oils gassing off in that area, by an alloy with high surface tension, by technique, by a cool sprue plate, by the way you part your hair and the type of socks you have on! Maybe not so much on the last 2 in that list, but the others surely come into play. IME most moulds, especially Lee moulds, often need 3-4 casting sessions or more before they straighten out and decide to start casting right. My theory is that it's oils in the cavities gassing off as they heat, I don't know for sure, but it seems to be pretty common. Add in that you have 6 cavities with their own variations and it becomes apparent that it's all going to add up. So, I suggest you start looking at that list and seeing if you can't get your casting reject rate down. If you want consistent diameter, you need the best possible fillout you can get. You have to start culling more ruthlessly, but don't throw the better looking rejects back int he pot. Do a test someday and you'll likely find those little variations in diameter mean squat for 80% of your shooting, they may even outshoot the "perfect" boolits!!! It happens.

Anyway, take a look at some of that stuff and see if something jumps out at you.

[DavZee]

Thank You all for taking the time to post your helpful suggestions. My latest thing to try has been to run bullets through the sizing die twice with a 180 or so twist. That seems to have helped a lot. Now I'm getting measurements between .452 and .4534 pretty much. My Lyman sizing die, .452, is used and looks like it has seen many many boolits passed through it. Not abused but it's been on the job for a long time. The Lee mold is new. I did the Lee-menting process on it and have it smoked real good but that was the first casting session and I thought it was going well until I had to leave the pot for a few and when I got back, the mold was cool and I snapped the sprue cam lever like a twig on the next pour. I got me a new steel one now from Kal so that won't be happening again. I do realize what happened to make that happen though. I was running the pot at 700 and it looks like I was getting real nice fill out. Of course there was some pretty funny looking "things" that came out of the mold but I got about 100 real nice ones before my newbieism caught up with me and I busted the cam lever. So now you guys have given me much to think about and ideas to work through. I'm really enjoying this and thanks again for all the help.