[peteeng]

Morning All - Milli No3 has had two variations so far. I made the columns bigger and I added a 100x100x9 steel frame to the base. That made a big delta. As I have to make a stand I may as well use the stand stiffness if possible. So the top frame could be bonded onto the 50mm or 75mm base. But still not stiff enough so will have to upsize things again. Not by much current stats are X 14 Y 14 and Z30 N/um. The fixed gantry moving table has some wasted space & I still donl;t like the drive screw down in the muck.... Mud suggested putting the Z axis at the rear but with my bridge it would collide. Maybe the bridge can go but I expect not. Will run it with the bridge removed next time. Lukahr has started a large moving column design with similar issues. I'm thinking maybe going steel shell (laser cut tab and slot assembly welded, then finish machined) then CSA filled. But laser cut parts won't give me the curved shapes I want ultimately. May have to do some simple beam tests to compare. Onward Peter

[ardenum]

How about rotating the bed by 90°and making the whole thing longer but narrower? Do you prefer a square footprint?

You could add a silicone seal to telescopic covers so no coolant goes on the bed mechanics.

I really like this setup to not get any crap on the precision parts.

http://www.pillevaran.com/images/rezin02.jpg
http://www.pillevaran.com/images/rezin01.jpg

[peteeng]

Hi Ard - The intent of the machine is a benchtop machine. Wider is preferable for a benchtop then deeper. Its a bit big and heavy for a benchtop at the moment but I'll par it back once I get the config and concept right. seals and covers are Ok just would be good not to have to deal with that stuff. I do prefer a stationary part, still wobbling between the moving column and gantry configs. And even going back to a wide std gantry with Z axis design, now concrete has been understood it offers solutions not prior in the mix.... Möbius x100 Peter

[ardenum]

Hi Ard - The intent of the machine is a benchtop machine. Wider is preferable for a benchtop then deeper. Its a bit big and heavy for a benchtop at the moment but I'll par it back once I get the config and concept right. seals and covers are Ok just would be good not to have to deal with that stuff. I do prefer a stationary part, still wobbling between the moving column and gantry configs. And even going back to a wide std gantry with Z axis design, now concrete has been understood it offers solutions not prior in the mix.... Möbius x100 Peter

Nothing stopping anyone from putting it on the bench sideways, that way its wider and not deeper.

[peteeng]

Hi Ard - True I'll have a think. Peter

[catahoula]

pete, I like where this is headed, this is a cool layout. But i would be a little concerned here with the difficulty in aligning the twin columns. I guess one could stand a surface plate on edge to find a common datum, but it seems like a pretty fussy process. Probably less an issue if the Z figure was smaller so the columns could be more rigidly linked, or with a very massive bridge and columns. You could extend the bridge down the back half of the columns at least as far as the bottom of the gantry, so there was less unsupported length, too

[catahoula]

Or move the bridge to between the columns instead of on top? that would definitely improve the lateral stiffness of the gantry and not reduce any Z

[peteeng]

Hi Cat - Yes I have been looking at that. But the bridge is now stiff enough I have to upsize the gantry.. Takes time to digest a result, then rebuild CAD then get it into FE...

Lukahr published a Mori moving gantry machine video that has me wondering. Mori saddle has the cars on it not a rail for Y like Milli. This means the moment is always within the kern of the bearings (no third bearing like I have needed). I have a bottom up philosophy to the build ie you can build the machine incrementally from the bottom. But the Mori arrangement means the saddle has to be built and squared prior to assembly onto the X tracks. Also means those bolts are buried and to reset have to pull down the machine so they are critical to get right....

But its a superior arrangement. Will have more thoughts about that as I prefer the moving column non moving part arrangement... Peter

will try to find more images on the Mori structure

[peteeng]

Hi Cat- I think I'll have some large angles machined or a custom jig machined for alignment. The bridge can't come down too far as it gets into the part space...I'm thinking of reducing the Z spec to 350mm vs 450mm at the mo makes things easier. I'll jump the alignment thing when the time comes I've been looking for economy laser alignment devices if anyone knows of such a thing... The 20N/um has been a huge hurdle. maybe unrealistic for a bench machine...Peter

Aligning columns is same issue on routers. Always a bit of a fiddle. Squares aren't big enough, important things are in air. Ultimately its tuned by cutting and measuring and adjusting. Would be good to have the right metrology stuff...

[ardenum]

All mori machine renders are on their youtube channel https://www.youtube.com/c/DMGMORI/videos

[peteeng]

so simple and clean !! Hmmm

[peteeng]

Hi All - So Milli-G has been re-imagined and here's what its end shape should look like. I think it will work well. BUT I still don't like the job moving and the drive down in the grunge... so much grunge. I have a story about an apprentice that cleaned up a mill some 35 years ago in my care with a household vacuum cleaner. We did a lot of aluminium stuff and used kero for the lub. I came in and he was merrily sucking up kero and swarf with some smoke coming out the back of the vac that he didn't see. I grabbed the extinguisher but luckily no fire!! Stern words and explanations needed...

Any how... the Mori vids (thks Ard) where interesting and they have several configs that I have not seen before. The take away is to make the rails as far apart as possible and their Monoblock sure does do that. So I'm going to work up a Mori tribute from the Milli23... S'pose its Milli-M Peter

[lukahr]

Yes DMG mori videos give you plenty of ideas, i have watched them all frame by frame into details
I'm trying to go with moving column because i dont want to have ballscrews and rails lower than milling table - so no mess and needed protection there.

[catahoula]

I'm trying to go with moving column because i dont want to have ballscrews and rails lower than milling table - so no mess and needed protection there.

Lukahr, many fixed gantry machines use an open machine base with the rails mounted on parallel, separate tubes, which allows coolant and swarf to drain out the bottom. Usually a simple sheet metal cover for the ballscrew is utilized. Edit: which is not to say the elevated rail moving gantry layout isn't also clean and stiff. But for DIY machines meant to have real accuracy I find one screw per axis to be very nice and a bit cheaper

[catahoula]

Interesting that these modern Mori machines are utilizing relatively thin plates with so many holes cut in them. From a basic standpoint it seems all the free edges and thin sheet would be hell for vibration, but maybe there's so much form rigidity it's offset? Or not better to have a bunch of holes in a tubular/skinned structure than to have it solid and be one big bell?

[peteeng]

Hi Cat - The holes are not lightening holes they are "prints" The sand core used in the casting has round protuberances sticking out to attach and centralise the core to the mould. So when the sand is shaken out it leaves a hole. I think you would find they are quite thick. These machines are large and castings have to be a certain thickness to not warp. I'm sure they have done the math!! Yes if its stiff enough it won't vibrate easily...Peter

[peteeng]

Evening All - I think I may have arrived.... I put together this from parts in the story to see what it would be like. It has 300x600 table and it looks brick **** house material to me. The job and table are separate so it can be easily changed to rotary or trunnion. Once sorted I don't think stiffness will ever be questioned. So now to tidy the geometry, trim some rails and get the FE going... Peter

[ardenum]

I think your way beyond your weight limit but you can hollow it out from the back. Can you tell us more about the spindle setup? Does the customer want a bt30 cartridge or is that just a placeholder?

[peteeng]

Hi Ard - There was a lot of discussion about the spindle further back. DC, induction, steppers, axial, power ranges, speed ranges. I have reduced it to a 90mm servo 750W or 1kW option with a 2:1 speed up . The customer can play with ratios or put on a high speed spindle.... or a bigger servo. I'm sure now that Milli will take heaps of power once I settle it down a bit. And yes the headstone will need to be hollow!! There is no fixed customer. But I have had enquiries and I am working around their wish lists and mine... Peter

[lukahr]

But for DIY machines meant to have real accuracy I find one screw per axis to be very nice and a bit cheaper

Yes also for me that is one of main points why i'm trying to avoid gantry build.
With two screws everything must be perfectly synchronised and align.
I have gantry machine in my workshop and i see how quickly machine can get out of squareness.
If i have 1 motor and ball-screw per axis i have one problem less to worry about.