Chinese 6040 CNC Router Advise Needed

[John S]

There is a lot of crap written about unsupported rails.
Yes I know supported is better than unsupported but lets look at what were are faced with.
On the 6040 machine as an example the 60 which means 600mm travel is supported, it;s the Y at 400mm and the Z that are on unsupported rails.

The one I saw has 16mm rails fitted with 16mm ball screws. So taking the max length of the Y to be about 500mm can golden bollocks work out the MAX deflection of two of these rails ?
I would imaging it's very small.

These machines do have some drawbacks after seeing a few examples. So far what I have seen is often the motor mountings / bearings are kludged up. Seems to be on a haphazard basis as to where it was assembled as opposed to who's selling them.

Biggest drawback is the controller box with is absolute rubbish and an accident waiting to happen, however if you factor in a new BoB and three 542 drivers you still have a machine worth more than the sum of it's parts given that most of the mid priced ones have a high speed spindle and VFD included.

OK a custom build would be better, not necessary cheaper but many people can't or don't have the skills to do this but want a machine so that they can get working straight away. For them the end product is the goal, not machine building.

As regards cutting at high speed, they can't because they are not big enough to get up to speed before it's run out of room. Will they cut alloy ? yes but slowly but if you want to cut alloy you have chosen the wrong machine.

There is far too much emphasis on this forum about cutting speeds and cutting alloy to the extent that it's probably driving beginners away.

I have a little Roland 2200 engraver here, year dot, works by dragging the carriage on bowden cable on a plastic capstan. I have removed the spindle motor and replaced it with a diamond drag.
It's powered by a 24v Yoohoo board which was spare.

The whole thing is crap, it's slow, max speed is 3.2 furlongs per fortnight but it works and if I engrave some small letters in stainless [ Yes will do stainless ] then run the same program it doesn't double cut at all so accuracy and repeatability is spot on.

Thing is it does the job which is engraving gauges. If i posted this as a build on this forum I'd get shot down in flames but this is an example of the work.



That circle is 50mm diameter and the small script name is less than 1/2mm high.

[Jonathan]

Can only work out the deflection if you know the force, which obviously depends on what you're cutting and how you're cutting it. It's more meaningful to calculate the stiffness. You can do either with the spreadsheets that have been posted on this forum years ago...

The whole thing is crap, it's slow, max speed is 3.2 furlongs per fortnight

So 32mm/min .. that's about what my mill did when I first converted it using an old unipolar stepper driver!

Thing is it does the job which is engraving gauges. If i posted this as a build on this forum I'd get shot down in flames but this is an example of the work.

I certainly wouldn't do any shooting there, as an engraving machine is the right application for unsupported rails. The obvious reason is the cutting forces are low, so the appropriate size unsupported rail isn't too large. As soon as you require a bit better material removal rate, the required unsupported rails size is so large that it's much more economical to use supported rails. The problem is all too often people post a design with unsupported rails and expect it to work well at much more demanding tasks.

When someone (who will remain nameless) posts a machine with unsupported rails and calls it 'something more rigid that also has good performance' or says it 'will cut through a range of materials with ease and no chatter or wobble to be found', then then they really are asking for it.