Problems with the knitting 
When you buy a knitting machine, you are usually told that it will run easily, i.e. that you do not need to use force. This is actually true, provided that there are no problems with the yarn, that it is not too thick, and not uneven. Of course, if a knitting machine is demonstrated to you, the shop will use problem-free yarn. But in practice, you will probably use yarn of many different types. As referred to above, it helps a lot to wax the yarn with a stump of a stearin candle. Some machines have a little peg meant for a bit of wax along which the yarn can slide. Personally, however, I do not think that this helps sufficiently. When you wind the yarn on a yarn ball winder, you may simultaneously let it slide over a stump of stearin candle.
A carriage should be moved like you move an iron. You press a little on the hind end, depending on how easily the yarn runs. It is a good idea to hold both hands on the carriage; it is hard to your arms if you use only one hand. It is also important that you sit at the right level. If the chair is too low, you put a strain on your shoulders, and if it is too high, you put a strain on your back. For some machines, a motor is available, but that is an expensive investment, and the knitting does not run faster, far from it. The only advantage with the motor is that it spares your arms.
If you get problems with the carriage getting stuck, you will first have to control if there are knots or mess in the yarn, causing it to tighten, or if a needle should have become trapped. If these things are not the cause, you must try carefully to winkle. Different machines each require their own way to be winkled. You will gradually learn this, when you become acquainted with your machine. In some machines, the carriage has to be pressed somewhat harder down towards the needle bed, some have to be winkled a little out and in on the bar, but always with care. With a machine that does not use weights, you may pull down the knitting. However, if none of these attempts help, there is no other way than taking off the carriage. Maybe there is some mess under the carriage; maybe a needle has been trapped after all, which you just could not see because of the carriage. If you use force, you may bend or break needles. A number of spare needles are always included when you buy a new machine; but if the needle is not too badly damaged, you may yourself try to straighten it out carefully with flat-nose pliers, the needle being fixed in a vice. Also, the latch may have become wry. This can usually be corrected with the pliers, but if you are too violent, there is a risk of breaking it. However, you have to be aware that needles that you have straightened out yourself, may in certain cases cause problems; but it is nice to be able to cope with the situation at a pinch.
If the machine has been standing out of use for a long time, you could oil the moving parts under the carriage, the bar on which the carriage slides, and the needle feet. You do not need to do this very often. A knitting machine is easily kept up; you just need a little brush to cleanse off dust. But in case there are problems with the machine, it may sometimes help to oil it. If you have bought a second-hand machine, you may cleanse it thoroughly, by taking off all needles and putting them in kerosene.
I have experienced that my machine could not be used together with the ribber, it blocked in several places. It turned out that the needles were sitting too high; they have to lie flat down on the machine. The cause was that the needle holding bar was worn, i.e. the rubber below it was worn down, and therefore it did not press down the needles sufficiently. So, the needle holding bar had to be changed, and the needle bar to be cleansed. By the way, this machine had been bought second-hand; it had been used for demonstrations.
You may often have the problem that some loops get stuck in the gate pegs; and after you have knitted a few rows, the casting-off system does not function with the needles that are nearest to them. This may especially happen if you have unpicked, or carried out something manually with the knitting. What happens is that the thread between the stitches gets inside the gate, and then it remains there. Therefore, it is important to look carefully, after having unpicked, that all loops go outside the gate. There must never be anything inside. But that may be hard to see. Once you have begun, it may go on to be tricky. The cause is that, once you lift off some loops from the gate, new loops will easily get in instead. You can avoid that as follows: After having felt with your hand behind the knitting and discovered where something is wrong, you have to put several of the needles around that place in resting position, which allows you to lift off the loops with the crochet hook, or to nudge them up with a finger, without causing anything to happen with the rest.
If you are knitting with two or several threads of machine yarn, you may get the problem that now and then the machine takes only one of the threads. This, too, may easily cause some loops to get stuck in the gate pegs. The cause may be that the machine needs oiling. It may also be that you are knitting to loosely. Sometimes it is sufficient just to reduce the stitch size by 1/3 number; that will not be visible in the knitting, or make any greater difference in the knitting sample. For safety's sake, you may knit a few additional rows.
If you knit with several threads of machine yarn in different colours, it may give an interesting effect. If you simply take the threads directly from the cone, the knitting will come in random stripes, varying according to how the yarn lies. Sometimes, one colour is at the bottom, sometimes another. But if it occurs that you unpick and wind the yarn jointly, it will become twisted, and the knitting will become speckled instead of striped. If you have wound the yarn before you knit and afterwards have to unpick, it will be wound in another way, it becomes twisted an extra turn, and the specks will look differently. So, you have to wind the threads separately.
If you have some remnants of yarn, or somebody has given it to you, and you do not know if it is wool or artificial material, you may carry out a burning test. You place a small bit of yarn in an ashtray and add a lighted match. If the yarn melts into a small clump or ball, it is synthetic; but if the ash keeps its shape and smells of burnt hair, it is wool. If it is a mixture, some of it will behave like wool, and some will melt. This may be hard to see, however, if there is only little wool in it. There are many different mixtures.
Cotton is recognized by making a thread wet; thereby, it will become stronger. You may first try to break it when it is dry, and afterwards make it wet. But cotton, too, may be mixed. Then, it will still be stronger when it is wet. But you may also try to carry out a burning test. The synthetic part will make it shrink, but there will still remain a thread. It smells quite differently from wool, rather like burnt straw, but cotton too keeps its shape.