Anti-backlash Upgrade


#1

I have been testing the anit-backlash nut which is on ebay.

This was something I always wanted to design but never got around to… well someone has finally done it and exactly as I would have.

I tried to measure the back lash of the STD nut on the thread. I don’t have a dial indicator just digital verniers but it looked like 0.2 to 0.3mm back lash… certainly feels like a lot. With this setup there is well none.

Here it is installed on a Wilson II I build for a friend.

What I did was cut 2 coils off the spring as it was way to long and the preload was a bit much. You could go a little more but I found this did work.

They fit together better one way, so once you workout the way mark them.

I found the threads a little tight. I got a battery drill, put some tape around the end of the leadscrew to protect it and put it in the chuck. On slow, I ran the nuts with spring assembled with some light machine oil up and down quite a few times till it felt nice and smooth.

After assembly I ran it up and down in Z and found it still a little tight. I stopped and checked my alignment and made sure all looked good. I bumped the Vref voltage to about 0.9v (I run DRV8825 drivers) I added more oil and run it up and down quite a few time… like 20 times.

Once happy I started a few random prints and it seemed good, so I stopped it.

I ran the Cube Torcher Test but in S3D I set Retraction Verticle Lift to 1mm so every retact it lifted 1mm and down 1mm and then scaled the test to 150mm.

It ran well I kept an eye on the motors and drivers but they never got warm despite the amount of Z lift every retract.

I would call that a win.


#2

Great result @ant0ny! I have looked at these on eBay and wondered whether they could be incorporate into the Wilson II. I will order some up this weekend so that I can fit them before I take my assembly too far.


#3

No probs. Just make sure you have everything right. if there is any issues this may try to jam one leadscrew. This is the issue with making things better, it means the tolerances on everything else are more critical.

I can’t quantify if the results are better with or without but I know in theory there should be differences when doing lift on retraction and this is one thing that gives you a nice top layer finish without the scaring.

If you cut the spring but find you have cut the spring to much, just make a spacer and add back the tension.

Someone will work this out and make the bottom nut with a thread over bottom section with a nut and you would wind on the tension needed just like a coil over suspension on a race car.

I miss having access to a lathe.


#4

Here is the anti-backlash nut fitted to my Wilson II.

One thing I have found is the the spring fitted varies in strength depending upon who you buy it from. On the ones that I purchased the spring was quite weak so I have not cut any off. The axis moves quite easily with very little increase in effort. There is no detectable backlash in the leadscrew.


#5

I’m having trouble visualizing how these work, does anyone know of a gif/video which might explain it to me?


#6

OK, found this, not a gif but does explain it in a way my brain understands:

I also notice they have a coil over style nut like @ant0ny was suggesting, and the concept looks like one that could be printed using 2 standard nuts.


#7

The Anti backlash nut has been around for our dinky CNC machines since the early days. In real CNC the issue is well documented and sorted.

There have been a couple of nice setups on various forums and Thingy but nothing that was a “bolt on” for the Wilson design. I had drawn up a few versions exactly like the one I posted but just never got round to doing anything. All I did to combat the issue was buy extra nuts from china and swap them out once the backlash got too much.

For the LulzBot I even bought a 10x2 Tap in intention of making a anti back lash nut setup for it but again time.

Here is another simple idea I had bookmarked using 2 brass nuts http://www.thingiverse.com/thing:1369262

I didn’t like the way it was on top of the X reducing travel.