The later Jones Spool machines had reverse – there’s reference to it in the manual for those machines.
With a bit of jiggery pokery, you can get older machines to have a limited reverse function too.
The stitch length is adjusted by means of a lever next to the handwheel – up for longer stitches, down for shorter. What happens inside the machine as you raise and lower the lever is that a slotted track rotates. Inside that track is a roller on a pin that’s part of the feed connecting rod. All the time you’re stitching forwards, the track is tipping the same way, but tips more or less, which in turn pushes the connecting rod more or less offset from the centreline of the machine. When it’s more offset, the effect is for the eccentric to move the bottom of the connecting rod more – and you get a longer stitch length.
If the track is rotated right past the horizontal to tip the other way, hey presto, you get reverse. It’s not quite as simple as that though, because there are one or two other factors that come into it:
1 The existing end stop for the stitch length needs to be modified.
2 The slot in the stitch length adjuster has to be long enough to keep the roller under control.
3 The feed dog mechanism and needle plate need to be able to accommodate their strange new movements.
Point 1 is easily overcome. The stitch length lever has a cut-out in it for a pin fixed into the body of the machine.
Simply make that cut-out a bit less than twice the size, allowing the lever to be rotated down further when it’s on the machine.
Point 2 – The slot isn’t that long, but we don’t want to stitch backwards more than forwards, so this isn’t a problem.
Point 3 – is more of a problem. When set to achieve a nice long stitch length going forwards, the feed dogs strike the needle plate for a long stitch in reverse. My solution to this is simply to limit the stitch length in reverse so the feed dogs stay clear of the needle plate. This means the reverse isn’t any more than a “back tack” function – not really controlled.
There’s a grub screw on the front of the machine to lock the stitch length. On my machine the stitch length control is a bit loose for short forward stitches. This screw is useful to ensure there’s a bit of friction to stop the stitch length adjusting itself.
There’s a bit more friction in the mechanism when back tacking, but I think it’s acceptable.
Please don’t try this on your museum piece machine. My machine cost £2 and has been well used & loved, so I’m not so worried. For my purposes it makes the machine more usable – which is a good thing in my book.