My new 6040 improvement plan.

[magicniner]

I don't think replacing the x axis rails with supported rails will yield much benefit.

Cool, let us know how ignoring horribly flexible machine components goes :D

[PaisleyPCdoctor]

Zee flyboy,
I appreciate your input. Here my thinking.

If you push on spindle, the axis shafts flex. The pivot point is the ball screw, top rod flexes forward, bottom rod flexes back. Vice versa if you pull on spindle.

During this motion, the gantry stays stationary.
The backplate is attached to gantry.

Imagine the gantry didn't need to move left/right on x axis. If I placed a piece of metal from top of z axis to backplate and bottom of z axis to backplate- it would support the spindle and it wouldn't flex. Assuming of course back plate was rigid.

To allow x as is movement- Ill use wheels on the supports.

It'll work.

[Zeeflyboy]

Yeah but in your example of the Z-axis bolted to the gantry, it can't pull away... a wheel isn't attached to the gantry it just rides on it. Sure it can't push into the gantry (well, beyond what degree flex of the wheel allows) but it can pull away from it. That's not even getting into the problem with swarf getting trapped under the wheels and wearing down the relatively soft aluminium surface.

What you need is something that can't push towards the gantry or pull away from it - ie a supported rail. Round supported rail however has the drawback that the shitty bearing becomes the weak point (even shittier than a fully round rail bearing is)... enter profile rail. Now you come full circle to what I was saying in the first place which is that the unsupported round rail is just inherently inferior to profile rail for milling anything substantial.

Honestly, what you are suggesting is a waste of time - imo the improvements will be minimal if noticeable at all. Combine that rear plate with proper linear rails and now you have a substantial improvement but are at the mercy of the next weak link. And onwards the chase continues.

Listen to me or don't, but I would sincerely suggest you just get cracking with your machine without any major effort/changes and take it from there. I would say after a few mods and chasing your tail you will come to the conclusion that it's better to just chalk it up to a good entry machine for learning/playing around and decide to build your own one rather than constantly trying to work around the inherent weaknesses of the design. Either that or you will decide that for whatever your intended purpose is, it's just fine.

Note that when I say the inherent weaknesses of the design, I'm not just talking about the unsupported rails... there are MANY issues with these machines and to address them all you would effectively end up building a new machine anyway - which is what I am now doing myself.

Just trying to save you some time and money in the process. Up to you if you want to heed that or not.

[PaisleyPCdoctor]

I see what you mean about it moving away from wheels, but that would take a lot more force and I don't see how it would happen. The workpiece can only push from the very bottom.

The supported rail was my plan, but I seen the guy on YouTube done it and it didn't help at all. Maybe with the fat backplate though. The way the ballscrew is attached to the bearings just now make it look like a big job. I'll need to have a good think how to do it though.

BTW, I'm still using the machine in between mods. I did specifically buy it with intention of modding it and learning. I knew the weaknesses when I bought it, if anything it was a lot better than I'd expected. I didn't get disappointed. It's a hobby machine. I'm hobbying.

[PaisleyPCdoctor]

I could possibly ADD a really fat supported rail on the other side of backplate, mounted to z axis assembly over and under the backplate.

hmm.

[magicniner]

Just trying to save you some time and money in the process. Up to you if you want to heed that or not.

Save your breath, it's a brilliant machine with some little shortcomings which can be resolved with a hex key.

Or Not :-)

[Zeeflyboy]

I see what you mean about it moving away from wheels, but that would take a lot more force and I don't see how it would happen. The workpiece can only push from the very bottom.

I think you underestimate how little it takes to produce chatter

The supported rail was my plan, but I seen the guy on YouTube done it and it didn't help at all. Maybe with the fat backplate though. The way the ballscrew is attached to the bearings just now make it look like a big job. I'll need to have a good think how to do it though.

Again, the supported rail that you are thinking of is not what I suggest. Supported rail is barely better than round rail... What I am suggesting is profile rail. Everything else you do without doing that is just really little more than pointless.

BTW, I'm still using the machine in between mods. I did specifically buy it with intention of modding it and learning. I knew the weaknesses when I bought it, if anything it was a lot better than I'd expected. I didn't get disappointed. It's a hobby machine. I'm hobbying.

Good, and I applaud garden shed engineering - it's quintessentially British. Even so, there is limited value in repeating the mistakes of others that have gone before you. One of the great things about our species is the ability to progress based on prior learnings of others rather than being doomed to constantly be stuck in a cycle of repeating the same failures... There is a reason why anything above the absolute most entry level machines use profile rail across hobby/industry and it's not because they weren't creative enough to come up with weird and wonderful solutions like wheels.

[hanermo2]

Excellent thread !
I very much like the OPs grit-n-go attitude, esp. considering actual measurements re_ flex.

Very Well Done ! keep at it.

The major value to the OP is learning about rigidity, motion control components and actual needs of machine tools in cutting apps.

All others reading this may learn a lot about what is flexible and or sloppy (backlash, jitter, bend aka flex) in these machines, and by about how much, and what happens when you change one part at a time.

The vast majority of people do not ever measure stuff like the OP did re:flex.
The vast majority also give up, usually soon.

I am not giving advice here ... (tend to do too much of that..).

There is a big body of evidence that more or less all machines will do upto about 5x or 500% "better" with some tune-up, mods, and very carefully controlled cutting parameters- for a single specific tuned job when optimised for the machine and tools available.

This applies to the chinese 6040s, bridgeports, small lathes, big lathes.

[Zeeflyboy]

]very carefully controlled cutting parameters

That part is the most significant by far imo... I've always said the most productive "mod" I ever did for the X2200L was learning to use Fusion360 and figuring out how to best use/tweak adaptive machining for my machine.

[PaisleyPCdoctor]

Okay, I'll look at profile rails.
In your opinion, what are the Chinese profile rails like? Their prices look fine, but most of the branded ones I've seen are just far far too much for me.