My new 6040 improvement plan.

[magicniner]

Aren't those just grub screws holding the bearing cartridge in place? I don't see how those would do any adjusting on the bearings other than distorting the casing or possibly forcing things out of alignment slightly.

Tighten them enough and whatever is under them will eventually apply more pressure on one side of the rod, it isn't an engineering solution but if it works then the only remaining problems are wear and those floppy pesky unsupported rods ;-)

[PaisleyPCdoctor]

The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

When I loosen the grub screws, the gantry flexes as if it's on rubber mounts. Difference is remarkable.

I'm just left with the flexing of the 20mm unsupported x-axis shafts. There's a youtube video where the guy replaces them with supported rails, but improvement was MINIMAL at best. Waste of time.

I have a better, cheaper and easier solution. Just sketching out the plan and I'll post it.

[magicniner]

The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

Have you tried marking the rod with a marker pen to see if the contact is simply the screw against the rod? ;-)

[Zeeflyboy]

The main gain was in Y-axis bearings.

They are adjusters. When they are tight, there is no noticeable flex/movement on the gantry. I tighten til they stop, then quarter turn to nip up. Gantry feels rock hard.

When I loosen the grub screws, the gantry flexes as if it's on rubber mounts. Difference is remarkable.

But that simply isn't how these bearings work, there is no pre-load adjustment... they are just a few rows of bearings inside a tube. You are achieving a reduction in slop most likely by forcing them out of alignment and thus introducing an increased load on one side. It achieves the goal but the problem is that the load isn't evenly distributed and wear will likely be accelerated.

Whatever works for you, but they are retainer screws not adjustment screws.

I'm just left with the flexing of the 20mm unsupported x-axis shafts. There's a youtube video where the guy replaces them with supported rails, but improvement was MINIMAL at best. Waste of time.

I have a better, cheaper and easier solution. Just sketching out the plan and I'll post it.

Supported rail doth not equal profile linear rail. My current machine is effectively a 6040 with proper 20mm profile rails and the difference is very obvious compared to the old machine... I don't need a guy on youtube, I've extensively experienced both. Of course even with proper rails you are still left with the general somewhat lightweight design but it's still a significant improvement over the previous model I had with unsupported rails like yours.

I'm not belittling you, you are obviously keen to get stuck in and learn - just be aware that despite what you may think at the moment, those unsupported rails (and to a lesser extent the supported rail on the bottom) are a limiting factor in this machine which you will need to learn to work around and will limit the level of tolerance and finish you can ultimately achieve in harder materials.

[magicniner]

An engineer would understand that there is no way to adjust a linear bearing which has at least 4 bearing channels with a single grub screw.

I know you are hoping that you have found the Holy Grail that everyone else has missed but look at the way the system you are messing with actually works and you will understand that you are simply adding side load and wear in an attempt to resolve a problem with tolerance and clearance in the set of components you have unfortunately bought.

- Nick

[magicniner]

But that simply isn't how these bearings work.

Don't waste your time!
There are things we understand, there are things we don't understand and there are things which we don't understand why we don't understand them, we are dealing with the third circumstance here :D

[PaisleyPCdoctor]

If they are simply retaining screws, then fine- they weren't fastened when they built the machine and they are now in their proper location!

It's not like I've torqued them into the rod. Like I said, I screwed them in until they touched/reached resistance then gave them a QUARTER TURN.

The grub screws are obviously put there for a reason and being fully unscrewed (as they were) clearly serves no purpose whatsoever.

The bearings still run smoothly, no crunching or grinding.

The bearings were sloppy, now they are not. Moving on...

[PaisleyPCdoctor]

I don't think replacing the x axis rails with supported rails will yield much benefit. It looks more work than its worth so I'm going to try a simpler approach.

I'll replace the back panel (3mm aluminium) with 10mm steel plate or possibly 25mm aluminium.

At the top and bottom of my Z axis assembly, I'm going to fit a runner wheel (or 2), adjusted to run tightly along the back plate (rolling along the x axis direction). For the spindle to rock back or forth, it will need to flex the back plate as well as the 2x20mm rails.

I currently cannot see any flexing left and right, just back and forth.

The mod should be cheap, but I will probably need to pay someone to mill some components for me.

[PaisleyPCdoctor]

I also plan to mill the spindle mounting plate to allow a little tram adjustment left/right tilt. Back/forward tilt should be easy with shims.

But no point until I improve rigidity.

[Zeeflyboy]

I wouldn't bother tbh... just get it up and running. If you want to revisit ideas later on after having actually put some use on it then do so.

The biggest flex for me on the unsupported rails came from the ability for it to twist (eg apply a force on the bottom of the cutter which is after all where the cutting forces come from) pushing it towards the back of the machine. The top rail will bend forwards and the bottom rail will bend backwards. The deflection is very measurable (and even visible) with quite moderate loads. Your solution of the rear panel doesn't do anything to change that, nor does a single wheel. Two wheels would go someway to solving half the equation (the rail being pushed towards the back) but not the other half (the rail being pulled away from the back). Even then I doubt you would see much benefit with the wheel slop/flex/wear.

In the nicest way possible, don't try to re-invent the wheel on this one. Get your machine up and running, get some use on it and if you find you need to improve on it then feel free, but in all honesty you'll probably come to the conclusion that you are better off building a new machine than trying to improve the 6040.