Yet another 'right way' to assemble 1310 cnc router anti

Oct 06, 2023

I have seen so many articles and videos on the ‘correct’ way to assemble the anti-backlash nuts on the various small cnc routers that are available for hobby use, particularly ‘1310’ units, and possibly their slightly larger ‘1419’ types cousins.

And so many of the articles and videos are partially right, or even just wrong, and plenty of sources complain about how the supplied spring is not stiff enough – and there are plenty of subsequent ‘fixes’ that go on to advocate stronger springs or lumps of rubber as springs.

What is not widely shared (ok ok, I have not found an example yet) is that there is no need for a spring. Instead, some careful adjustment is required. That said, the spring is certainly useful during assembly, and provides one way of low-complexity (if low-accuracy) assembly for those who are not familiar with fine adjustment.

For more detail, scroll down, but the short story is:

Assemble the nut as the top picture, but with the locking part of the nyloc nuts hardly engaged (not as far on as in the photo).

In this situation, the spring is providing weak anti-backlash action – move the moving part of the machine back and forth by hand to feel how much backlash there is, it will be a fraction of a millimetre: hardly visible and ‘good enough’ for non-precision use, but too much slack for accurate machining.

Turn each nyloc along its long bolt until is just kisses the back of the brass nut (note: this is why the spring is useful, as it gives this starting point for the fine adjustment). Backlash felt by hand will remain the same as it was with the nyloc nuts hardly engaged.

Now, very carefully – eventually a tiny tiny fraction of a turn on each nut at a time – tighten the nylocs.

The first thing to be noticed is that the leadscrew gets easier to rotate as the spring-pressure-induced drag on the shaft is been removed.

The next thing is to be noticed is that the backlash will diminish – you will feel it more than see it (And you might hear it, as the mechanism ‘clonks’ quietly at the ends of movement).

Once you have gone too far – probably well under a half of a turn of the nylocs in total – the leadscrew will rapidly get too stiff to rotate by hand.

Somewhere between ‘just-kissing’ and ‘too-far’ (oo, er, missus), is a sweet spot with no human-detectable backlash as well as a leadscrew that rotates more easily than it did with spring tension on the anti-backlash nut.

Just for reference, the photo left shows heads of the long screws that have to be held still while the nylocs are rotated (or vice versa) to do the backlash adjustment. Also visible are the ends of the threaded holes for the bolts that are used to attach the ‘fixed’ half of the anti-backlash nut pair.

What is going on?

The spring pushes the two halves of the anti-backlash nut apart, pushing against two inner-facing surfaces of its screw thread (sorry for the lack of diagrams, dear reader) – taking length-ways slack out of the system until forces are such that the spring is compressed. Folk add stronger springs to delay this compression point, but this increases friction, making it harder to rotate the leadscrew at all times – remember, the leadscrew is rotated by a tiny NEMA17 stepper motor.

Doing the nyloc nuts up pulls the anti-backlash nuts together against the spring, lifting the anti-backlash nuts away from the face of the leadscrew, noticable because the leadscrew is easier to rotate.

Doing the nylocs up further, brings the anti-backlash nuts together until they push against two outer-facing surfaces of the leadscrew’s thread, strongly increasing the effort required to rotate the leadscrew.

When adjusted properly, there is almost no pressure against these two outer-facing surfaces (so the leadscrew rotates easily) but also almost no slack in the system (and so no backlash).

Anatomy of a low-cost anti-backlash nut

Leadcrew: heavily-threaded long silvery rod

Anti-backlash nut: Two (brass in this case, gap between the two just visible in photo right) internally threaded nuts, often held apart by a spring, with some means to prevent them rotating separately (in this case – photo below –, holes in the nut flanges through which the adjusting bolts pass through).

The long bolts are the adjusting bolts, with the nyloc nuts partly threaded on (nyloc nuts are bulged on one end and are designed to keep their position on a thread once adjusted.

One small Allen headed bolt can be seen retaining the ‘fixed’ nut of the anti-backlash nut pair to the (red) structure being moved by the leadscrew. The second retaining bolt is out-of-sight.

In this case, none of the four holes in each of the anti-backlash nut halves was threaded, and only two of the holes in the frame were threaded. I have heard of other combinations. Most other combinations can be made to work without drilling any threads out.