A little light engraving

To see how accurate the beast is now, I opted for a light weight task and mounted my low cost multi-tool with a sharp point bit. 

I then grabbed an offcut of plastic  ( a block of Delrin that I bought a while ago) and tried engraving a little.

(I also experimented with spraying some white paint on the black Delrin and then sanding it off again to improve contrast... mixed results...more experiments needed)

The multi-tool is clamped by a block that I attach to the main tool support. The main tool support is made for my Blank&Decker router. 

Very impressed!

Looking at this, I should also be able to do PCB isolation milling as well which I've always wanted to try. 

Eureca!

Big deep breaths.....

I disconnected the link to the x dive so that I could slide the z assembly across. 

Yuck!!! It is grinding and not right at all. 

Suspicious of the top rail, I gently slid the rail out so the the z assembly was just on the bottom rail - still binding. 

Put the top rail back in and remove the bottom rail..... Smooth as silk!!! 

I removed the z assembly and could see that one of the bearing blocks was just slightly off centre - maybe 0.5mm too low. nothing wrong with the block, i had drilled the holes in the wood in the wrong place. Ok time to be bold!

I removed the offending bearing block and the thing is wobble free with two bearing blocks at the top and one at the bottom. 

Reassemble (including strengthening the attachment to the drive on the x axis) and... Oh my... It trundles smoothly back and forwards. 

Quick grab a router!

Bitter disappointment

Oh my goodness! 

The x-axis chugs across like an old train!

I tried different feedrates etc but this is truly horrible. It's jumping across in about 1-2mm steps. 

I can actually see the wooden construction flexing on the x-axis linkage. 

Time to stop and think....

Partial rebuild

And so the change begins. 

The old x rails (two pieces of wood with bits of curtain rail profile attached) are removed from my old machine and the z-axis assembly extracted. 

Although the old x-axis only used 4 skate wheels, I had added another two wheels to reduce wobble with moderate effect. 

The old and new x-axis rails/bearings can  be seen in the following photo:

The two wooden bars had adjusting screws that allowed me to tweak the alignment:

The trick now is to get the new rails attached to the x-bridge and the linear bearing blocks to the z-axis assembly with the rails being perfectly parallel so that nothing binds. 

The x-bridge is stripped clear ready for the operation:

The new blocks are fitted to the back of the z assembly and ready to put back on the bridge, rails placed and attached to the bridge. 

It looks good but doesn't slide as smoothly as I had hoped. Not too bad, maybe it will settle and loosen after a few runs. 

Now for the attachment to the x drive. I have a simple anti backlash construction. The main bit of wood (on the right) has a T screw in it and this piece of wood will be attached to the z assembly. On the left hand side a second strip of wood with T but is also fitted to the threaded rod and wound around until it is close to but not quite touching the main piece of wood. Two bolts then attach the two together and allow me to squeeze these slightly so that the backlash is eliminated but the threaded rod can still rotate. 

Now add the top of the Z-assembly that connects to the x drive. 

...and now.... Power it up!

Modify or rebuild?

One year after my first real build, my linear bearings have arrived!

Now the big question: do I modify my existing machine to use the new bearings or build a new structure from scratch?

The new rails for the x-direction are a bit longer than my old travel and certainly have a significantly taller profile than a skate wheel. If I just mount these on the front of the x-bridge structure, this will push the z-axis structure even further forward. If everything was perfect, this wouldn't matter however any wobble in the bearings and link to the x-drive will be amplified. 

One solution would be to try to move the x-axis motor and bearings forwards but I would have to modify the wooden structure a bit for this. 

The alternative is a major rebuild with a new design to make full use of the new bearings. This is possible but then I need to work out the new design properly and ideally I'd like a CNC machine to get all of the holes etc it the correct place. 

The third alternative is to have a half way mod to the existing machine and hope that the resulting tolerances are significantly improved and good enough to allow me to CNC the next gen machine :)