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.

ATTEN 858D Repair


Yesterday I decided to repair my ATTEN 858D air gun.

This is a cheap chinese hot air gun to solder/rework pcb boards with smd components.

Disassembled air gun (broke pins place)

The first time I use it got broken. This hot air gun comes with 3 tips to focus the air flow that get jammed very easily. While trying to remove one of those tips I 've broken two plastic pins that hold the resistive part of the gun in place (signaled in green in the pic). The broken plastic pins made the resistance stand floppy and potentially slide out the plastic holder.

Refractory glue for fireplaces

 
Man, that day I even chipped my tooth trying to remove the tip in desperation. Since then I've never inserted those tips to the end, instead I just let them sit on the edge of the gun.

So how do you repair a hot gun that reaches temps well above 400ºC?? Some special glue must come in hand for sure. The answer: Refractory glue used in fireplaces and stoves.

The one I used resists up to 1500ºC. More then enough.
 

Standart PC case screw

The idea was simple. replace the plastic pins with to screws (those used in CD-rom drives or disks to fix the drive in the case are fine). I've started by dremel the remains of the old pins and dig a little deeper to make a bed where the screw head would rest in place (alignment) with the holes in the resistance of the gun. Then I applied the retractile glue in the void ring where the resistance rests. I've made it slightly higher so this ring of glue could work as a clamp. If too much glue is applied I would then remove the excesses with the dremel tool.As you can see the glue filled the ring completely. After trimming this ring to make a tight fit I've screwed everything in place.
 

Glued screw to the resistence support

Make sure the 12 hours of curing are respected (I didn't and the glue broke near the screw, and had to (re)glue them).

After that the resistance was tight in the holder and didn't felt flimsy any more.

Hurray ;-)