Building a CNC - Improving backlash in cheap chinese RM1605 (ball bearing threads)

I've been struggling to get the CNC moving but the time and place are just not there.
I just needed some time off to finish this but I won't get any time soon so...

In these dead times I've been studying the BF12 block of the ball bearing threads.
This comes with a lock nut but when I use it it rubs against the rubber seal which causes a lot of friction and makes the stepper motor life harder.

BF12 bearing thread block

So to do if I can make something of it I disassembled the BF12 block. OHHH MMYYY GGOOODDD. Has expected this was poor pissed machined. This is what you get when you buy cheap Chinese crap. Just lock at the state of those two screws in the photo. The thread is completely worn out, because the holes where misaligned. The problem that causes the rubbing is the size of the spacers (bellow the ball bearings) that are just to short.

BF12 block disassembled (poor quality chinese product)

The way to fix this is to make a couple of new and longer spacers.
If the hole for the bearings is too deep (resulting in unwanted space and backlash) there is an additional method for preloading and it's a cheap and easy trick. Use an useless plastic card and make a washer to put between the bearings.
I'll show the final idea with a drawing:

Existing parts in blue and new ones in red

Preloading forces to ensure near 0 backlash

Now the fabrication part. If you are like me and don't have a lathe (oohh I wish...maybe I'll try to build one too :-P), you have too options.

1. Pay someone with a lathe to make it.
2. make a very rudimentary lathe like-thing with a power drill.

Since I don't want pay for this task I'll show you how you can make some lousy crafted (almost Chinese quality like :-P) but usable spacers and a trick to preload the bearing inside the BF12 block.
First the preloading plastic washer. Drill the card with a 12mm drill bit and cut with a scissor to make a crude plastic 1mm thick washer.

Drilling the plastic card

Put them between the two bearing and close the BF12 block again. Has shown in the earlier drawing, the pressure from the front plate will make the outer ring of the ball bearing go in and the washer will make the inner rings go out. This removes the backlash from the bearings.

For the spacers I use the power drill as a crude lathe. I cut a peace of 14x1mm steel tube and put it inside a M12 screw. Next I tight the end of the screw in the drill chuck and turn it on. To remove metal from the exterior of the tube I use the sharp edge of a drill and move it along the tube. I just need to remove about 0,5mm of steel. I finish it with a file and a peace of sand paper. To cut it put a saw against the tube to make an almost perfect perpendicular cut. Size doesn't matter that much. I just have to make sure it's bigger but not too big. And voilá. The new spacer.

Crude lathe in the drill press	Using a drill bit to grind the tube
Using a saw blade to cut the tube in almost straight line	A couple of spacers and a plastic washer

Original bearing in the left and new on the right.

The reassembled bearing thread is now virtually backlash free.
This is solution a-la-Macgyver but it works just good enough...lolol.

Building a CNC - Z-Axis

This week was all about building the Z-Axis frame.

For this one (since it is a lot smaller) I went for a couple of SBR16 linear rail guides.
It's made of two parts:

Z-Axis front plate (left) and back plate (right)

The back plate (smaller plate) is where the X-Axis bearing system is fixed. This is also where the RM1605 ball bearings nut will be attached. The mechanism is similar to the X/Y-Axis interface I built, but instead of two 608-ZZ bearing clamping the rail, this is a single aluminium peace directly screwed to the plate.

The front plate is a peace of metal sheet where both the SBR16 rails and the KF-12 and KB-12 (RM1605 ball bearing screw support blocks) are attached.
The front plate will accommodate the engraving/printing head of the CNC.

Here are a couple shots of the Z-Axis.

I've already made the motor mount support that I will place in my next iteration.
For the paint job, I went for spray paint this time. It is a hole lot better. Easier to apply, thinner layers and more homogeneous coating, and much less time to dry.
I'm actually considering repainting the hole machine, with different colors for the different axis components.

I just wish I had more time to finnish the machine. These lunch hour builds are 50% working and 50% preparing and cleaning up. Efficiency killing...

Building a CNC - Y-Axis - part 4

Finally some progress.
I've been working on the movement transfer interfaces between the CNC arms.
This is the binding element between the X and Y axis.

I've made it with some pieces of rectangular tube aluminium profiles from my previous CNC.

Here are all the elements individually.

X-Y arm interface

The larger holes where made with a circular drill bit.

I've made 4 spacer also with aluminium tube. These spacers will keep the structural shape of the rectangular tube when I tight the nuts that hold it in the ball bearing nuts.

Here are a couple of shots that show the assembly of the X-Y interface piece.