El Beast - Initial design phase, comments and critique welcomed!

[Zeeflyboy]

Yeah yeah, just haven't had time to work on that part yet as i've been re-designing the x-axis gantry and the z-axis first.

Boyan - plan was to mount the rail to the 45x90 and then level it to the ecocast plate bed before tightening down all the screws, which would give alignment in the Z-axis. I suppose you are suggesting that the flatness of the extrusion will leave it slightly "wavey" in the horizontal axis?

What about mounting a 20mm ecocast plate to the extrusion and then the rail to the plate, similar to what i'm ending up doing with the X-Axis?

[Boyan Silyavski]

I am speaking about how you would level the long rails that gantry moves on them / Y/- in the Z plane to be on one plane and at the same time to be flat . I am not so worried about the flatness as you say you will be using Ecocast plate.

[Zeeflyboy]

Another potential option perhaps would be to re-design around this misumi milled profile? https://us.misumi-ec.com/vona2/detai...689340/?Inch=0

Not sure of the cost or availability however.

[Boyan Silyavski]

Seems alright. I would have done it same way. using straight edge you can make sure all is ok

[fifa]

Boyan is right

2 rails each side are nonsense. The result will be huge loads to the rail bearings due to thermal distortions, nonparallel cuts etc. General problems with gantry types is non-optimised stiffens. Torsional displacement of the gantry beam define the stiffens of whole system.
Everything is assembled from standard profiles. I-s are known, do the simple test and apply load of 100N at the end of the cutter.
Don't be surprised.

regards

[1Jumper10]

Looks like it will be an extremely high quality machine!

I have a question which you will probably find quite noobish but I am interested in your glass scales. Specifically, how do you use the glass scales in a feedback loop to control your position? Does the position from the scales get fed back into the motor driver and that corrects any error? Or is the position fed back into your break out board and on to your motion controller?
The reason I ask is if you have position feedback​ from a linear scale any backlash in your drive system wouldn't matter?? Then theoretically one could use c3 screws instead of c7 for instance. Or, standard gearboxes instead of low backlash units. Am I thinking correctly here??

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[Zeeflyboy]

Looks like it will be an extremely high quality machine!

I have a question which you will probably find quite noobish but I am interested in your glass scales. Specifically, how do you use the glass scales in a feedback loop to control your position? Does the position from the scales get fed back into the motor driver and that corrects any error? Or is the position fed back into your break out board and on to your motion controller?
The reason I ask is if you have position feedback​ from a linear scale any backlash in your drive system wouldn't matter?? Then theoretically one could use c3 screws instead of c7 for instance. Or, standard gearboxes instead of low backlash units. Am I thinking correctly here??

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I simply use the glass scales for calibration purposes. They were mainly the answer to my current machine's less-than-optimal screws - I simply adjusted the steps per unit to match the scales. In mach3 you can actually go deeper than that and map the ballscrew to compensate for variation along the screw itself too, but I never went that far.

Certainly it is possible to link a positional encoder such as a glass scale and a CNC controller to give absolute position feedback, but I haven't looked into it too far as for my needs the calibration was sufficient. I think linuxCNC has a way of using it.

It certainly would be a good way of compensating for lead inaccuracies and variation - I don't think it would do a great job of controlling excessive backlash though, but then most semi-decent ball screws don't have much backlash anyway. If you had a lot of backlash it would have to be very quick to arrest movement to stop chatter and poor edge surface finish, there is never really a good solution for backlash other than to remove it.

BTW I think you have the C's backwards, the lower the C number the more demanding the specification... so in your example it would more be a case of it allowing you to use c7 rather than more expensive c5/c3/c0. Of course good glass scales aren't cheap either so it's debatable as to how much saving you would make.

Edit - EMC2 can do it too apparently.

Edit 2 - also came across this quote which pretty much describes what I was thinking regarding it not being a cure for backlash:

But, a caution: Knowing position via the glass scales doesn't
eliminate the backlash problem. The real problem is that the
position of the table is not constrained in both directions by
the servo. it is only constrained in one direction at a time,
and the motor cannot hop from one side of the backlash to the
other instantly, therefore cutting forces and inertia can flip
it from one side to the other faster than the motor can
compensate. This can lead to messed-up parts, broken tools and
general foul language around the shop. So, don't think the
glass scales are some kind of panacea that allows you to do
precision work with sloppy leadscrews.

[1Jumper10]

Got it. Thanks!

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[Chaz]

Great build. Looking forward to seeing the end results.

What CAD software do you use out of interest?

Also, where did you get the foam from? I'm thinking of doing the same for my garage / setup.

Thanks

[Zeeflyboy]

Cheers,

Using Fusion 360, foam was from www.efoam.co.uk and I got the downcut router bits from www.cncroutershop.com