Dating wertheim treadle sewing machine
When the machine was running it most likely was quite noisy because the shuttle moved forward and backwards at great speed, at times it made the machine vibrate.
Its bobbin had to be inserted into a bobbin case, then the case was inserted into the machine vertically to the left of the needle.
The tension unit was directly in front on the needle which in turn threaded from right to left.
The slide plate (to access the bobbin) had a small oblong hole which aided whilst sliding the slide plate to the left to view the bobbin.
The 66K has a bed size of 14-1/2" so is much wider than the 99K The Singer 28K had what was called a vibrating shuttle or boat shuttle or bullet shuttle...
the long bobbin/shuttle was inserted into its case which looked like a bullet, then the case was located into the machine and lay in a frame that looked like a boat hull.
Search for dating wertheim treadle sewing machine:
Here the image shows a lovely 66K about 1920, originally may have been hand, electric or treadle operated.