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

[fifa]

Sorry I am not native English speaker, therefore I can be easily misunderstood.

X rails: pre-machining rails do not count due:
- rails must be parallel - your design is frame from 4 profiles. Forget on straightness (you are assuming this will help with using expensive profiles.) think about other two elements which are connecting both profiles.
You have 2 plates - potentially nonparallel, two profiles Mitsumi + two profiles catted and machined by... as I said check the stiffens of the bearing, lets assume the total error of non-parallelism is 100 microns, and that half of this error must be compensated by bearings, the other half by brackets. This means 25 microns per bearing - now check the stiffness and you will see the load which is in the "system". If you wish to remove error, you need to do machining in the assembled condition...

Check the I (Area moment of Inertia) of profile and plate, most likely 25 mm thick plate is stiffer than 50 mm profile or it is close to it. And whatever will you do: If the profile and plate are not planar, when they will be assembled the result will be non-straightness of the rail "bed" surface.

Y gantry: problem is torsional load not the bending - check the I and calculate displacement applying 100 N force at the end of the tool
The second problem is: Y gantry length must meet X rail width - within micron range otherwise you are facing with additional load to the X bearings... Not mentioned that both side surfaces must be parallel, - if not additional load on X bearings again

Regarding the idea of setting the true angles with bolt - by definition this means you are incorporating elasticity in relative stiff system. Means also you have nice oscillation.

You are right system is relatively rigid. I am escalating problems caused G&T and consequences of those.

regards

regards


,

[njhussey]

Well I think that compared to my machine, which is welded steel frame with a bit of epoxy for levelling the rails and some 20mm tooling plate for the gantry, this is far more of an engineered and well thought out solution. Thought has gone into how to assemble the machine and the OP is very realistic with respect to the area they want and what they want the machine to do.

I think gents that everyone is getting a little too nit picky (which, don't get me wrong, can be a good thing) and getting a little bit too bogged down in ultra precision engineering and forgetting that this is a hobby machine..............there is nothing here in this design of machine which couldn't be sorted with the help from a few beers an assortment of shims and a bloody big hammer

[1Jumper10]

Absolutely agree. There may be some minor adjustment needed at the end but there would be with ANY machine (except possibly a Datron). It looks more well planned than most other DIY machines that have turned out just fine.
ZeeFlyBoy your skills with Fusion 360 are incredible.

[Zeeflyboy]

Thank you chaps! Neil I think you summed up my thoughts quite eloquently - especially the beer and hammer part lol.

I am of course after critique, it was the main purpose of sharing this design before starting to build it rather than vice versa - and I am extremely glad I did.

The complete change to the Z-Axis for example is not something I would have thought of but I can definitely see the benefits... but ultimately yes, one needs to keep sight of the fact that this is a hobby machine to go in the Man Cave, not an industrial interferometer calibrated machine.

I am confident that the design as it now stands will fall within the alignment error ability of the linear rail carriages, and with some tweaking I think I can get probably get it to within my ability to accurately measure.

Jumper - Thanks but I'm still just an amateur with Fusion, but I do find it refreshingly easy to use for the most part!

[Zeeflyboy]

Sorry I am not native English speaker, therefore I can be easily misunderstood.

X rails: pre-machining rails do not count due:
- rails must be parallel - your design is frame from 4 profiles. Forget on straightness (you are assuming this will help with using expensive profiles.) think about other two elements which are connecting both profiles.
You have 2 plates - potentially nonparallel, two profiles Mitsumi + two profiles catted and machined by... as I said check the stiffens of the bearing, lets assume the total error of non-parallelism is 100 microns, and that half of this error must be compensated by bearings, the other half by brackets. This means 25 microns per bearing - now check the stiffness and you will see the load which is in the "system". If you wish to remove error, you need to do machining in the assembled condition...

All profiles are going to be from the same place (mitsumi now, given I want the milled stuff) actually, given that they almost certainly should be cutting the bracing profiles one after the other without re-positioning the cutting gate they should be very, very close.

They can always be massaged with my current machine which will happily repeat to substantially better than your stated 100 micron example (as confirmed by some fairly expensive glass scales mounted to both X and Y axis). It should be fairly easy to get them to within 10's of microns rather than 100's...

Check the I (Area moment of Inertia) of profile and plate, most likely 25 mm thick plate is stiffer than 50 mm profile or it is close to it. And whatever will you do: If the profile and plate are not planar, when they will be assembled the result will be non-straightness of the rail "bed" surface.

Y gantry: problem is torsional load not the bending - check the I and calculate displacement applying 100 N force at the end of the tool

This is a bit beyond me, I have never used any simulation software and not sure where to start.

I'm simply going on the basis that common sense Garden Shed engineering tells me a combined total of 32mm of solid aluminium plate and 40mm of heavy profile that makes up the gantry cross section is overkill for a 550mm span gantry on a relatively light duty table top machine. Certainly it is at least as beefy as most DIY machines of that scale that I have seen.

The second problem is: Y gantry length must meet X rail width - within micron range otherwise you are facing with additional load to the X bearings... Not mentioned that both side surfaces must be parallel, - if not additional load on X bearings again

I don't really see this being an issue as long as it's longer rather than shorter. All it requires is to try inserting a shim brass sheet of various thicknesses between the gantry arm and mounting plate until you find a thickness that slots in snugly.

Regarding the idea of setting the true angles with bolt - by definition this means you are incorporating elasticity in relative stiff system. Means also you have nice oscillation.

How is it incorporating elasticity? Once the angles are set the bolts on the respective parts are torqued down clamping everything rigidly in place... you aren't relying on the part just resting on an eccentric bushing. Where does the elasticity come from?

You are right system is relatively rigid. I am escalating problems caused G&T and consequences of those.

You've lost me again lol - what's G&T when it's not in a glass with some ice?

[Boyan Silyavski]

I dont see a problem, as far as your face and back plate are actually machined on a mill.


Not that we are getting picky, but when some one sees that machine design, its obviously to a higher standard. So in order to maintain that standard and result to be incredible machine, one should aim high.

I said once somewhere, you may laugh but the most imprecision in a build comes from not wiping the dust correctly from rails when mounting, when you are alone and tired, in a rush and no one to help you.