Building a CNC - Frame modifications and (re)assembly

Now for the frame.

First I had to fix a construction misalignment (explained in the picture bellow), that caused the the stepper motor axis to collide with the linear rail bar and twist and rotate eventually breaking the coupler in two.

I did it by cutting the corner stuffing (inside the cutted tube and over the corner) a metal bar that I had laying around (and was pretty much the height I needed), and then weld it and cut it to the desired length. The picture gives a clear idea. The fact that the bar entered in the tube also acted as an reinforcement. I was quite happy with the result.

Modifying/fixing the rail angle

One other thing I didn't liked in the initial design was the bottom bars in the frame. The initial idea was to put the bottom plane over these bars. But any millimetric offset would mean that the "floor" of the CNC would be like bump or a dip. So I removed the bars, used them to reinforce two of the sides (for the axis that clamps on the top side. The bottom side would probably cause collision problems) and the corners in the bottom square.

Modified Frame

 To finish I gave it a black paint cover and the axis a red tone as you can see bellow.

After the paint job

Finally I reassembled the CNC and gave it a spin. It's a working machine. OHHHHH YEAHHHH.
The picture bellow was taken before all electronics were in place but the machine is all now fully loaded and tuned.

Assembled Axis and Frame

Now I must thing of a name for my baby/beast CNC..hummmm
More modding is on the way. Electronics are next. So stay tuned...

Building a CNC - X and Y axis modifications

I've been working on changing some less well thought/crafted parts.

The way the RM1605 ballscrew thread was mounted/fixed on the X and Y axis was one of them. The fact that I was depending on some rubber pads to align it with the stepper motor shaft was not ideal and was a source of alignment issues.

To fix that, I rotated the BK and BK block by 90º, so it would stand on it's side. These block are 60cm wide (aprox. the same as my NEMA23 stepper motors) and allowed an almost instant misalignment free position.

Here is the new supports welded to the X axis.

New supports

X-axis fully assembled

To be continued...

Building a CNC - The end (a new beginning)

After a 8 months break I restarted to think on my CNC and the away I could put this puzzle together since I didn't thing the design all the way through.
It toke me about 4 hours to come up with a plan the result was a working CNC :-P.

I actually had to undo a couple of parts I have showned in past posts, and replace others. To make the last parts and since no welding was needed, I used aluminium rectangular tubes (easier to work with).
I've also relocated all the electronics to an old Pentium II PC that I had laying around, and now have a neat single tower PC/Controller solution that I will also show.
In the next posts I'll try to show what I've done to assemble the CNC, what I've accomplished in terms of results, and some of the problems I've encountered and I'm currently fixing/working.

To be continued...

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.

Building a CNC - Y-Axis - part 3

Yesterday, I started mounting the Y-axis ball bearing transmission to the arm.
First I had to deal with the transmission block vs stepper motor shaft difference of heights.

To address this situation I used an 0,80€ pencil rubber that I sliced to act as anti vibration pads beneath the linear transmission blocks. It's cheap and it does the job well. I'm hoping it will help me cope with the noise caused by the vibration of the steppers running, against the steel structure.

Next I made a steel plate that will act has the stepper mount plate, and weld it against the arm.

But when I mounting the arm in the CNC cage ...WTFFFF...
The ball bearing thread hits the linear rail of the Z carriage.
Fortunately I only made alignment welds. I had to cut them put the rails of the Y arm higher and re-weld them into place.

Has you can see there is now a very small gap between the Z-rail and the Y-thread, but I should suffice.

To be continued...