JBEC router system UNDER THE BONNET

[Jonathan]

Applying a linear rail does not add the performance of the rail system if it is not backed up by the bed design, precision and stability.

Accuracy is just one advantage of linear guides though - the other important parameter is their high stiffness. On a lot of 'diy' builds you'll find linear guides not mounted to the specified manufacturers tolerances, however so long as the surface is reasonably accurate they will still make the machine more rigid and last a long time.

and the result is a good machine – the video speaks for itself.

Thank you for the comments about my friend's machine. We will post a video showing what it can really do in a few weeks, i.e. cutting aluminium over 10x faster than that.

I feel I should clarify a few of the points you have highlighted.

This has been clearly illustrated by the work required to align the rails on the machine and to align the machine for accuracy – tram and twist etc. It may well have been the most cost effective frame build in a DIY context but it is not sustainable commercially.

We did spend a long time getting a suitably accurate surface for the rails to mount on, however this was only due to trying so many different methods. In future I would just go straight to using epoxy, as it's quick and easy and as you can see from the reading I took it's plenty accurate enough.

Also the estimated price tag of 4-5k not including the time and extensive know how gives the general audience a feel for the cost and effort that goes into a “sufficiently stiff” CNC router.

Perhaps I wasn't clear, 4-5k was my estimate for a finished machine. The cost of all the parts (metals, rails, spindle, motors, control box etc) was just under £2500. The biggest purchase was about £950 in aluminium, which could perhaps be improved upon in a future build.

There is also the question of relieving the stresses in the welds and the long term stability of the bed.

I agree that was an oversight on my part - I should have got the bed stress relieved before pouring the epoxy. On the plus side I can check it again in a year with my surface plate and pour the resin again if it's twisted substantially. The frame did have about 6 months left outside after powder coating, so the thermal cycling there will have stress relieved it a bit, in the old fashioned way!

There is also the question of Mach3 lost position? Possibly due to missed steps perhaps due to some slight lock up – eliminated by the cleaner pulse trains from Linux giving more motor performance perhaps? Unless there is a software issue with Mach (not passing the driver test – or other quirk) then the software fix (move to linux) has potentially overcome what is actually a hardware issue? Perhaps there was a motion controller used with Mach3 and not a LPT - in which case the previously stated possible issues are invalid.

If you're referring to my experience when making the 'sufficiently strong' machine, then I'm certain it was not a hardware issue - otherwise I wouldn't have posted it. The only change I made which affected the problem was changing the software from Mach3 to linuxCNC, which I've stuck with since as it seems to be more reliable. That said, I don't think this is the place to discuss the virtues of mach vs linuxcnc.
Similarly if you've got any more comment on my build log, then I'd be interested in hearing them so feel free to post in the thread.