Needles and threads, sizes that is

[Bugscuffle]

After having instigated a two page thread on sewing machine questions and doing several days of research on various machines, prices and filtering through the claims, some of which would embarrass a politician running for office, (No I don't believe that your portable Singer will sew through a manhole cover) I have had a brain fart and am contemplating starting a low dollar experiment to find a machine that will sew two pieces of 6-7 oz. veg. tanned tooling leather together and cost less than $150. Now here is where I need your help. Is nylon thread O.K. to use? If not, why not? What size thread should I be looking for? I understand that I need to use chisel point leather sewing needles on any machine that I end up with, but what size needle do I need to sew those two pieces of 6-7 oz. leather together? is size 18 enough or do I need a larger size needle? I get the impression from my research that needle size and thread size are interdependent. What size thread can I use with which size needles? Is there a good instruction book out there on the care and feeding of a sewing machine? All of the above will factor into which machine I decide to experiment with, but at the present, I'm looking at Singer model 66 machines with motors upgraded to at least 100 watts (1.0 amps). They are affordable at around $50 to $60. They are built like tanks with all cast iron bodies and all steel internal parts. They accept needles from size 9 through 21. (21 seems big enough to me) The parts and accessories are readily available, like bobbins (which are probably of too little capacity for practical use with the larger thread, but hey, you have to give up something. So I'll reload them more often, no big deal. I'm pretty sure though that this machine is NOT going to like waxed linnen thread. So it's going to have to be nylon and it's probably going to be lighter than what is normally used.
So, shoot some holes in my idea or I'll be forced to spend money that I can't really afford.

[Bugscuffle]

Here is an update in case anyone is interested other than me. I bought a machine that will for sure sew through two layers of 6 Oz veg tanned leather, my original requirement. It also sewed through 7/16" of denim and a Pepsi Cola can. No I don't know why he sewed through the Pepsi can. The machine will accept upto a size 22 needle and the size 22 needle which will sew with thrread up to size 207. This 207 thread size is also known as Tex 210 and Government Size 3-Cord. It has a 32 lb. (14.5 kilo) tensile strength; a 0.0200 in. (0.5080 mm) diameter; and gives about 2,000 yards (1,820) meters) per pound. What I don't know and will not know until the machuine arrives is, will the machine handle this thread? We'll see, I guess. As I said, this is an experiment. I have a liftime supply of size 98 thread. I got the size 98 thread because the manual says that it will handle up to a size 18 needle and size 98 thread is the largest thread that a size 18 needle will sew with effectively. I can find no information on whether or not the machine itself, not just the needle will handle the size 207 thread. I'll just have to experimwnt and see. I have concerns about things like the tension adjustments, the bobbin size (how much size 207 thread will the class 66 bobbin hold?). The presser foot has a maximum of 7/16" of clearance. That isn't a lot, but it will clear three layers of 7 Oz. tooling leather which is all that I need for my purposes. When the machine arrives I'll give you a complete rundown, successes and failures of the machine.

[TwoWalks Baldridge]

So what is the machine under discussion?

[Bugscuffle]

So what is the machine under discussion?

It's all in my original post. My goal was to find a reliable machine that will sew two layers of 6-7 Oz leather together aned cost no more than $150.00. The result is still pending on my little experiment. In fact the machine is still on the way.

[theshoer]

ya but what kind of machine is what he wants to know

[Bugscuffle]

The machine itself is a vintage Singer Spartan model. The Sparrtan is a model 99 only made in England. It is properly named. It is a 3/4 size machine and as tough as a Spartan being all steel and cast iron. It is also as plain as white bread toast with no butter. It doesn't even have a lamp on it.  This model was modified slightly. The motor has been upgraded from the usual 58 watt motor to a 165 watt motor, so it will have considerably more power. It now accepts leather needles as large as size 22. The only documentatiion that I couild find indicated that the machine would sew with size 98 bonded nylon thread, but that was with a size 18 needle and that is the largest needle that the manual (sometime in the 50's) said that the machine would handle, and the larger size threads won't work in that needle size. So all I can do now is wait for the machine to arrive and test it out and experiment with what I can and cannot sew.

[Massive]

Most sewing machines will sew leather to some extent.  In particular they will dutifully punch holes into leather.  Where it gets tough is in trying to get the required tension on the stitch.  The needle itself creates the tension both top and bottom, there are tension adjustments on both, but the thread is set in place by the action of the needle.  This means that the limit of tension is set by the lateral bending resistance of the needle.  If someone wanted to spend a fortune making a modern upgrade for old machines, maybe they would be able to do so with some new materials, say a carbon fiber needle.  We have much stronger super thin threads, and the old machines are colossal, unfortunately the needles limit performance a lot.  By the way, correct machine sewn tension is not all that high, but it can still be an issue.

The other issue you will face with any machine is that even medium experienced sewers have trouble getting their purpose built machines to sew.  I spent two weeks of very frustrating off and on work getting my sailmaking sewing machine to sew spinnaker nylon.  This is something it is know for, a main reason to buy it, it will stitch sails, but also flawlessly stitch 3/4 oz nylon.  I was going crazy.  Eventually I figured it out.  But my point is that had I been trying to make it do something it was not designed for, I am sure I would have packed it in earlier, even though a better tech might have sorted it easily.

[Bugscuffle]

Massive, thanks for the reply. Believe me any advice that I can get here is very welcome. The machine has still not arrived. In fact if it doesn't get here tomorrow the last day that the "estimated delivery" would be, I may just cancel the sale and start over again. I bought this particular machine because it came from an established sewinbg machine shop, it has been completely and professionally refurbished, the listing showed actual examples of the machine sewing two layers of 6-7 ounce veg tanned leather and a Pepsi Cola can. I guess he wanted to impress me with how tough the machine was. In any respect I saw that the stitching on both sides of the leather was even and balanced. This machine will also accept and work with size 22 needles. I have bought some size 18 and size 22 leather sewing needles and thread in sizes 98 (Tex 90), 138 (Tex 135) and size 207 (Tex 210). I can find no information of what thread sizes the Spartan will handle, but I have found the documentation that says that they will handle up to a size 22 needle. The size 22 needle is required for either the size 138 or 207 threads. I'll just have to experiment with the machine to see what threads it will sew with. I'll have two weeks to play with it to make that determination. If it works great! I will make my goal of sewing two pieces of 6-7 Oz. leather on a machine for under $150. If it doesn't work out I'll pay the return shipping and be out less than $28.00 . Wish me luck.

[Massive]

Sounds good, I would love to hear how it turns out.