First of all you need a mold around which you are going to form your base. I usually use a plastic tube of a lip balm. It's circumference is 51mm and I am aware that it's a bit small when compared to other people's but it's the right size for my finger. You can use any cylindrical objects from markers to maybe a spatula handle and if you still cannot find a mold in right size, you can adjust the size by wrapping a piece of paper around it until it becomes a desired size.
Make sense to you? Okay, the photos above are not very clear to help understand. Let's have a look at next two.I reproduced the process with a piece of paper. You fold the one side of the end like this...
and wrap the rest of the bias binding tape around the mold like this. I taped the paper at the bottom side like this for the photo taking purposes. I didn't think it would still show after I trimmed the photo, but here it is. The correct way to tape the bias binding tape is put the adhesive tape at the centre as you see in the third photo above.
The core of the base I make is paper. Unfortunately I cannot tell you what paper I use or the thickness of the paper I use because I recycle ad fliers which come with daily papers, you know the glossy, heavy ad fliers, the one used for posh condos and fancy cars and such? Sometimes I recycle postcards and greeting cards but they are a bit too thick for my taste. You may find my thimbles too small and not sturdy enough, but this is the way I want them; sleek and pliable. Anyway, the choice is up to you, you want your thimble thick and sturdy, you need a heavier paper and you want them light and pliable, you need a lighter paper. Please bear in mind, however, that layering the light paper doesn't substitute the single layer of heavier paper. You can certainly achieve the thickness in size but the result is completely different and I think there is a reason why the paper is categorized by weight. Please experiment a bit until you get what you want.
Then fold over the edges of the bias binding tape so that the fabric covers the paper ring core snugly.
Now I stitch together the folded over edges. Do not make a knot when you start your thread because a knot makes a bump. Instead make a tiny stitch or two (avoid the overlapping part) and you are fine to go. Firstly stitch the underside edges together as you see above and below pictures,
then, go back a little and stitch the overlapping (upper side) edges together as below before you stitch all the way around. I find stitching the overlapping edges firstly before going around makes the finished base looks much neater.
I like to pull the thread really tightly all around until the lining (bias binding tape) becomes rather taut but how strong you pull is up to you. Some people like the lining fabric just covers the paper core unlike mine. You had better make a few to see what you want yours to be like. In any case, I would like to point out that the overlapping part becomes lumpy unless you pull the thread very tightly when you stitching together the overlapping part and a lumpy base makes a lumpy thimble. Another thing I would like you to know is if you pull the thread tightly like I do, the inner circumference tends to become a bit smaller than you originally thought it would be. It only 1mm or 1.5mm but it's a big difference when you need to make a thimble in a specific size. Please measure the size before you make the stitches with silk threads to be sure it's the correct size.
Now I finished all the way around. Because all these stitches will not be visible once the thimble is finished, you don't need to worry about your stitches not being very tidy. You can see the lumpy part I mentioned earlier? It's unavoidable but try to minimize the bump when you stitch the edges together.
To make a marking paper, measure the outer circumference of the base firstly. Mine is 63mm and when I use the same lip balm tube as a mold and same bias binding tape, same paper for core, and same sewing thread, my base always turns out in the same size so I cut the paper to 63mm width, draw the marking lines evenly (in this case I needed 8 segments so I draw 7 lines, and you can see the marking lines in the picture above although they are a bit faint) along the length and every 10mm across and cut it along 10mm line as I go, but you may want to measure the circumference every time you finish your base. Cut the paper 63 x 10mm and draw the marking lines EVENLY. I capitalized the word and in italic because your design accuracy solely depends on how accurate you are when you draw your markings. 0.5mm is big when you are using the thread equivalent to the machine thread for middle weight fabric. Now, you wrap the marking paper around your base and secure it with plastic adhesive tape as shown in above picture. You can see the lining fabric (bias binding tape) still peeking from the top and bottom of the marking paper, and it's important because you don't want to make stitches on the marking paper otherwise the edge of the paper would fray and the frayed bits and pieces may stick between the stitches you make.
Put the needle through the marking paper and wrap the thread around the middle of the body of the base like this. I skipped it today and therefore no photo, but I usually add two layers of light cotton tape before wrapping the thread around. You know the tape you sew together when you sew the bias fabric to prevent it stretch out? You can apply another layers as I usually do, or skip it as I did today. I like my thimbles small and sleek as I told you earlier and to achieve the lightness I keep the thickness of the paper core relatively thin so that the finished edges (both top and bottom) of the base is thin. However, the base still needs to be sturdy enough to use as a working tool. Applying light cotton tape around the body gives the base firmness without adding the bulkiness at the top and bottom edges because the width of the tape is narrower than the base's. This process is optional because yours may be already sturdy enough and doesn't need any additional layers.
Now we are going to apply the wadding to the base. I use silk floss wadding. It comes like a sheet of fiber like this (at least the one I use comes as a sheet and in the photo I folded it in half).
When you pull the fiber, any place you like, it becomes like this;
Uncombed silk floss formed like a sheet is the best description I can think of and because it's silk floss the fiber is really really really long.
Therefore it stretches well and you can apply the really thin layers little by little to form the shape you want. Remember the lumpy part? Of course you do, you cannot forget it when I repeatedly reminding you there is one. That lumpy part is not the overlapping top/bottom edges only, but the body itself too. Apply thin on the lumpy part on the body so that your finished base looks nice and smooth. Or try to.
This is just what I do to make a base and surely there are other ways, too, maybe a better way. I just wanted to share what I do with you is all. If any question, please let me know and I will try my best to answer it.