If I ever have the opportunity to make a version 3 of my cnc I would make several changes to it.  I thought it was time to document some of those tweaks now, while they are fresh in my head.

I would get rid of these 12 mm rods and go with a 16 mm rod on the bottom and either a 12 mm or 16 mm rod on the top. It will increase the cost a bit and make it a bit harder to source parts but it would allow me to make this larger and make things a bit stiffer as well.  I have a pair of 16 mm rods and bearings to test out, it is possible that they won't be as stiff as 4 12 mm rods.  I will need to test them out to see.

With new stiffer rods I can make the x axis wider and use the full width of the underlying board.  I like this size base, it is just small enough that I can easily move it from inside the house to the garage without too much trouble.  Going any larger would make it too heavy to lift and to large to make it through the door.  However I could use the full 600 mm width of the board by moving the electronics to the bottom of the board.  If I add some supports under the base board I can also use a thinner piece of wood and that may save a bit of weight.

By raking the Y risers back a bit I can bring the spindle closer to the center of the axis and reclaim more of the working area of my y axis.  I could potentially get another 50-100 mm of travel in the y direction this way.

It would be good to use a more symmetric and logical pattern for the hold down bolts under the spoiler board. Mine follow no logical pattern and that makes them less useful for future upgrades.  I would guess that a pattern on 100 mm centers would be a good idea.

The limit switches were a bit of an afterthought on the original plan.  I placed them because they were easy to put on, but if I moved them to the other side of each axis I would end up with fewer wires that need to move.  In this case the Y limit switches could be moved to the base and not move at all.

The Z limit switch could also be moved to the x carriage so that the X and Z limit switch are attached to the same moving part, requiring only one bundle of wires to come back to the control box.

I did not capture a picture of it, but the Y stepper motors could move to the rear of the machine and a knob could be fitted to the end of each of the lead screws.  That would make it slightly easier to adjust the position of the gantries when doing maintenance.  I don't know that this is all that important.

The dust shields on the side are too short, they could come up quite a bit higher.  I could also add a removable dust shield on the rear of the machine that attaches with magnets for quick removal.  Those together would go a long way towards making things cleaner.  A full enclosure would be even nicer but that takes us away from a portable machine.

All the 3 mm heat set inserts could be replaced with captive nuts.  A dab of glue may be enough to keep the nuts from falling out, or a bit of 3D printing creativity could help.  I'm torn on this, on the one hand I really love the heat set inserts, but on the other hand they are difficult to source since every brand seems to be a different size.

The 3 mm heat set inserts on the motor standoffs could also be replaced with captive nuts.  

The motor clamp is not well made and I'm sure I could come up with a better solution. This is a poor compromise that makes all my other attachments sloppy because I'm trying to work with the stock clamp.  The clamp should attach solid to the motor separate from its attachment to the machine.  It would also be good if it was lighter, this is a very heavy part.  I have tried in the past to make this out of PLA but it was prone to deforming as the motor heated up. I would need to make this out of PETG and come up with a better way to register it precisely with the Z carriage.

The Y base is a bit wide, I could shave some material off of it and recover a bit more range on the x axis.  This is a small win, it may not be worth the compromise to the rigidity of the machine.

The Y uprights are beefy but not as beefy as they could be.  More material could be placed here.  And with a bit of work I could come up with a way to clamp each of the bars rather than just clamping the top bar.  Using captive nuts rather than heat set inserts for the 5 mm bolts would be nice as well.

There is no way to really synch down the nuts for the bar clamps.  I had a set rattle loose the other day mid cut, fortunately the bar itself was still held captive and the cut was not lost. These have a lot of flex to them so it is hard to make them clamp tight, it is possible that with a bit of better engineering I could come up with a stronger clamp.  Another idea would be to use lock nuts, or Loctite on the bolts.

Anyway that is all I could come up with so far, I'm sure there are other ideas that would be good to look at as well.  I will try to keep this up to date as new ideas come to me.