Measuring patch thickness

[Billnpatti]

There have been several postings about measuring patch thickness. I will tell you how I do it. First, you will need a micrometer like this one: http://en.wikipedia.org/wiki/File:Micrometer_caliper_parts_0001.png. It does not have to be a high dollar micrometer, one of the cheaper ones will do. You are not measuring parts for a space shuttle so even one of the Chinese made micrometers will do for measuring patch thickness. You will need one that has a ratchet on the thimble so that you make your measurements the same every time.

There are two measurements to be made on a piece of fabric. The first is the un-compressed thickness and the second is the compressed thickness. The compressed thickness is a measurement of how thick the patch will be when compressed between the ball and the inside of the bore. The importance of the un-compressed thickness is that the greater the difference between the two, the more compressability the fabric will have and the better will it be as a gasket forming the important seal around the ball when the gun is fired. As an example, let's assume that you are shooting a .50 caliber rifle and loading a .490 ball. Let's further assume that you have found by experimentation that a .010 patch works best in that rifle. So, you go to the fabric store and find two different 100% cotton fabrics and both give a .010 compressed measurement but one has an un-compressed thickness of .015 while the other has an un-compressed thickness of .018. The fabric with the .018 un-compressed thickness will provide a better seal than the one with the .015 un-compressed thickness simply because it will compress into the rifling better and form a better seal.

So, how do you make these two measurements with your micrometer? First, you have to be able to read your micrometer. That will take a bit of reading and practice. It can be pretty confusing at first but don't give up. If you have one of the micrometers that are made in China, you can usually forget the instructions that come with it. In most cases it is poor toilet paper at best. You can find tutorials on the internet or you can get a machinest's book from your local library.

Okay, let's assume that you have figured out how to read your micrometer and have taken it to the local fabric shop. Just be sure that it is clean and free of any oil that might get on the fabric. You select your first fabric and place it between the anvil and the stem of your micrometer. Then you grasp the ratchet portion of the thimble using only the tips of your thumb and index finger and and tighten it down until it contacts the fabric and starts to click. Give it exactly 5 clicks and then read the un-compressed thickness. Do this at several places on the fabric to be sure that you have the correct un-compressed thickness of that fabric. Use a pencil and discretely write this measurement on the end of the cardboard tube on which the fabric is wrapped. Now, you will need to make the measurement of the compressed thickness of the fabric. This requires a bit more practice since it relies on the feel of the amount of compression that you are using when making the measurement. A micrometer is a delicate instrument and can be damaged if you tighten down on the thimble like King Kong. You need to develop a feel for "snug" when you tighten down on the thimble. Again, when making this measurement, you will be using just the tips of your thumb and index fingers to tighten the thimble. This is so you won't over tighten the micrometer and spring it. Doing so will ruin the micrometer.

So, you have a feel for what the term "snug" means when making a compressed measurement on a piece of fabric. You simply tighten down on the non-ratcheting portion of the thimble until it feels good and snug and the material is well compressed but not crushed. This is your compressed measurement. Write it on the cardboard tube next to the un-compressed measurement. Write small so the sales staff won't take umbrage at you writing on their fabric tubes. After you have measures several pieces of fabric, you can go back, look at your notes on each tube and select the piece of fabric that best fits your needs.

After you wash your fabric, make the measurements again so you can see how much washing has affected the thickness. Usually, the compressed thickness will not change but the un-compressed measurement will have gotten larger. This is because when the sizing is washed out of the fabric, it tends to fluff up a bit. If this happens, it is not a bad thing, all it means is that the fabric will form a better seal when the patched ball is pushed into the bore. Sometimes, you may find that the ball is a tad bit harder to start but once started, it will seat with minimal additional resistance.

Some of the more popular fabrics are pillow ticking, cotton "drill" and denim. Some folks have even used linen. The important thing to remember is that the fabric needs to be a natural material such as 100% cotton or linen. Most synthetics will melt and make a mess in your bore that is rather difficult to remove. The fabric also needs to have a tight weave. Loose weaves are no good as patching material.

 

[FishDFly]

The best writing on how to measure patch thickness as I have seen. You have done a nice job, thanks.

Needs to be a sticky, I have seen this 100 times in the past, how do I measure.....

My initial thoughts are, how did the United States go to the moon in 1969 and folks still not read a micrometer and be able to measure fabric and they are allowed to handle loaded guns?

Our education system is not doing well.

 

[M. De Land]

Good job Bill! I never thought of counting clicks on the mic clutch for more consistency. Always something new to pick up and I've been using a mic for many years in home machining.
I will add that a mic or caliper should always be checked for zero when cleaning the anvil and stem or jaws before taking the measurement. Mike D.

 

[necchi]

What is the difference between compressed but not crushed?
What then is "crushed"?
Why does a person always need to use the "ratchet portion" of the micrometer and not the shaft?
Do people realize that the ratchet will not be damaged if the actual shaft of the micrometer is turned with direct contact of your fingers?

 

[Billnpatti]

"What is the difference between compressed but not crushed?
What then is "crushed"?
Why does a person always need to use the "ratchet portion" of the micrometer and not the shaft?
Do people realize that the ratchet will not be damaged if the actual shaft of the micrometer is turned with direct contact of your fingers?"

The difference between compressed and crushed is a matter of feel. When the micrometer is closed on the fabric and the operator feels the stem to be closed firmly but not overly so, that is "compressed". But when they use undue force to really tighten down on the thimble, that is "crushed". How can you tell the difference? Other than to say "common sense and a matter of experience" I don't know.

One uses the ratchet when making measurements because when the stem meets the anvil or the object being measured, it begins to click telling the operator that the stem has met the object and no further tightening is necessary. Not all micrometers have this feature. It is not absolutely necessary if one is an experienced operator, it is just a nice feature that is an aid in making accurate measurements. I am not a machinist or gunsmith so I can give no better answer than that. My micrometer has this feature and I find it to be quite useful.

You are right in saying that the micrometer will not be damaged by using the fingers to tighten the thimble. This is true in most cases but there are people out there who believe that if tight is good, tighter has got to be even better and if you really romp down on it, that has to be wonderful. While the average person may not do any damage when tightening the thimble, there are those who can damage an anvil with a feather duster. Those are the ones I worry about.

If you are asking why I say to use the ratchet when making the un-compressed measurement, it is because when using the ratchet, the ratchet starts clicking just as soon as the stem contacts the fabric and provides a more consistent measurement of the uncompressed thickness.

This technique is what I find gives me the best measurements and is consistent with the teachings of Dutch Schoultz. I share this technique because it is what has worked for me. It is simply for the amazement, amusement and edification of the reader. If you have a way that works better for you then that is the way you should do it. :hatsoff:

 

[Billnpatti]

"Why does a person always need to use the "ratchet portion" of the micrometer and not the shaft?"

I failed to properly address this question. You misunderstood what I was saying when talking about using the ratchet portion of the thimble. I didn't mean to indicate that the ratchet should always be used. When measuring the thickness of patch material, the only time you need to use the ratchet is when you are measuring the un-compressed thickness. When you measure the compressed thickness, you use the thimble to tighten the micrometer to a good snug tightness but not so tight that you spring the micrometer.

 

[ohio ramrod]

As a long time machinist I was taught long ago that a micrometer is not a C clamp! Therefore I always use a "light feel". What you are after is a comparison rather than an absolute measurement. Therefore consistency is the most important thing. As long as you do it the same each time you will get good results. :idunno:

 

[hanshi]

I agree. And it matters not how or with what tool material is measured as long as it is done consistently.

 

[necchi]

Good answers Bill and thank you, Something like this should be up in the resources section so we could refer folks to it as this topic comes up frequently.

The real trouble is we're trying to establish a nation/world wide standard and we really can't because as you mention different folks have a different idea of what the feel is. The only way we could do it is to have a designated sample of fabric that could be mailed to each person so they can determine what kind of pressure to use, even different ratchet type micrometers vary from each other.

I think the biggest misunderstood aspect of fabric thickness when someone is experimenting with different types and thickness,,
isn't what fabric measures compared to what the next guy measures. It's what/how each person measures and does it the same way each time so they can see the difference in the fabrics they are trying.

 

[azmntman]

Uh huh I agree. Cept nobody gonna wanna play postmaster! :shocked2:

 

[Billnpatti]

Yep, you are dead on.

 

[Billnpatti]

You are absolutely right about the "light" feel when measuring hard things such as pieces of metal. However, when measuring fabric and wanting to obtain the un-compressed and the compressed measurements of the fabric, you will need to do it the way that I was speaking of. That is because, unlike metal, fabric is soft and compressible and, according to Dutch Schoultz, both of these measurements are valuable knowledge. However, as you said, "a micrometer is not a C clamp". For this reason, obtaining the compressed measurement requires a bit of feel and common sense to do it without damaging the micrometer. :hatsoff:

 

[Billnpatti]

"it matters not how or with what tool material is measured as long as it is done consistently."

I absolutely agree with the idea that these measurements must be made consistently, but with what instrument other than a micrometer could one make these measurements with any degree of accuracy? We are talking thousandths of an inch. How can you make these measurements with another instrument? What would you use? :idunno:

 

[necchi]

A Dial Caliper.
Yes, there is a difference because of how much of the fabric is held by the jaws of a caliper vrs the anvil/shaft of the micrometer,
But it still doesn't matter to the individual person making the measurement because his measurement is the only one needed for comparison.

 

[Billnpatti]

Yes, a dial caliper will work for obtaining at least a single reading for the thickness of a patch but if one is going to do it like Dutch says and get both an un-compressed and a compressed measurement, I am not sure how well a dial caliper would work. I have one but have never used it for measuring patch thickness. Since I have never tried using a dial caliper to make these measurements, I will not say it can't be done. I'll have to admit that in the right hands measuring both the un-compressed and the compressed thicknesses of patch material consistently with a dial caliper is plausible. But........I'm sticking with my micrometer for these measurements because it is what I know. :hatsoff:

 

[hanshi]

I use a dial caliper with excellent success. I would not, however, recommend doing it with a 12" ruler. :grin:

 

[ohio ramrod]

Actually there is a special instrument that is ideal for measuring cloth. In the rubber mills they use what my dad called a "spounge mic" instead of a simple rod and anvil tip approximately 1/4 inch thick they have two disks about one inch in diameter one for the anvil and one on the "stem". This allows for more force since the force is spread over a larger area. :idunno:

 

[roundball]

Speaking for myself, a dial caliper has worked perfectly for me for 20+ years now...IMO measuring patch thickness isn't rocket science.
My findings have been that the thickness of commercial precut / prelubed patches is apparently measured without compression. When I random sample patch thickness from bags I occasionally order, if they're labeled .020" I get a .020" reading when caliber contacts the material, not compressing it.