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.John S -
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...
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.
John has we all know I'm not a fan of Chinese unsupported round rail or that matter supported but not because of strength. ? It's the quality that let's them down badly.
Push the machine remotely hard for any length and they soon become sloppy.
Same goes for rest of machine has well, the build quality is piss poor and has you know the devil is in the detail and these machines are thrown together in the cheapest possibly way.
It's the small details like ball screw end fixing just using cheap nasty deep Grove bearings, totally defeats the point having ball screws if they are going to float like a turd.
It's these small details that soon raise there ugly head when machines pushed.
Now to me the whole point to CNC machine is accuracy and repeatability and why woud you want to buy machine where you throw half of it away, has in the electronics, only to be chasing the slop out of the other half and scared to push machine for fear of turning it back to slop. ?
IMO even the mid priced machines are not worth the trouble.!
So I need to get you to build me a 6040 for about £1500 then without all the faults ?
Hypothetical question really seeing as I have recently bough a high quality MDF router off Geoffrey
Next question is will it do alloy at 27528 metres / min ?John S -
my recent machine including all the electrics apart from the spindle was £2k. About half of that was spent on aluminium!
Last edited by Jonathan; 24-11-2013 at 06:49 PM.
The machine you built While being a nice strong thing built with care and thought and a credit to you, I wouldn't exactly say it pushes boundaries either.? It just does the Job it was designed for and doesn't do anything special or better than any other machine correctly built and designed to do a job.!! Also you say 2K material costs which I don't disbelieve for minute but what your not saying is the hours of work that's needed to machine and Assemble it. Add this to the Mix and you'd probably need another 2K to make it worth your while.?
By itsmillertime in forum Machine DiscussionReplies: 11Last Post: 06-01-2016, 12:45 AM
By cncJim in forum Welding, Equipment & TechniquesReplies: 4Last Post: 20-02-2014, 12:25 PM
By cncJim in forum Machine DiscussionReplies: 22Last Post: 01-11-2013, 02:23 PM
By John S in forum Machine DiscussionReplies: 6Last Post: 12-09-2013, 10:35 AM
By John S in forum Milling Machines, Builds & ConversionsReplies: 13Last Post: 01-10-2012, 06:18 PM