[peteeng]

Hi Ard - You need to build a dummy spindle and tool so the applied load is at at typical tool load point. make the tool very stiff so that is out of the equation for now. I have a "rigid" setting in my materials. Its an infinitely stiff material and I set the tool to that. The spindle can be steel as it is steel.... some images would help. I apply the load to the bottom of the tool surface. Peter

The dark blue parts are "rigid" the yellow arrow is where I'm applying the load usually 1000N. The post and cone are there so when loads are applied you can see what is happening at the tool.

As a general design point - The static stiffness of a machine is not what happens in practice. This is called the dynamic stiffness. The tool and the job and the cutting point is intimately connected. If the tool moves so does the job either by deflection or by material removal. If the tool is doing its job it chomps away happily at the material and it must be a small oscillating motion. If its skipping and missing cuts then its chattering. Plus the force of operation is not at the tool. The tool as we model it is a reaction not an action. The force is applied by the motion system and has to find its way to the cut site. So in summary the static stiffness physical test is an approximation that is easy to do to establish the apparent stiffness of the machine. We know that machine stiffness and performance are connected but we maybe testing it the wrong way, but its what we have at the moment...

[klaas123]

Milli always seems a bit over sized/weight, so why not go all the way and transform it into a "floor top" machine?

[peteeng]

Hi Klaas - I thought about that the other day actually. But it gets away from my customer base of DIY/Makers etc. And it starts to compete with "real" mills so I think its scale down not up. I'm about to review the whole thread, collate the good and bad bits and have a deep re think... Stay tuned. Peter

Hi Klaas - Its actually undersize & underweight for the size of the table when you compare to commercial mills. I do like machines you can walk on. Maybe a new class of Maker grade mills "walk-in" size.... or jumbo Maker class. In printers they have "large scale" printers but the "scale" keeps changing. Its all getting bigger and bigger.... if I went to FLOOR SCALE I think I'd go back to a gantry machine. Take up a car space??? They say to always think BIG. Peter

[peteeng]

Evening all - Moved the LHS stuff to the painted RHS side today. I sanded the painted side with my 5" orbital just knocked the pips off. Tomorrow paint the LHS. Then get some infusion VE or may use my infusion epoxy to do the topcoat. Didn't like the laminating VE, too thick. But it works in the end. Plan to have everything on wheels... Peter

[peteeng]

Hi All and Sundry - Up early to do the floor before it got hot. But stopped early as I ran out of resin. The pail says 20kg but I only got 18.3kg out of it. Have to talk to the supplier next week. Upsetting, that puts me behind schedule to get the floor finished.... Peter

[klaas123]

Bummer Peter, OTOH be glad with your new shop, I can only dream of such a space.

[peteeng]

Hi Klaas - Yes I'm very lucky to have a spot like this. I rechecked my resin tally and its correct. I did not carry over a couple of figures correctly in my weighing tally so I actually used 19.7kg and there's a smear of 400g in the pail. So will finish the floor asap... Will look at moulds for the CSA tomorrow can do some casts while waiting for more resin. Peter

[peteeng]

Project Summary

Milli Initial thoughts (Metal Mill)
BT-30 spindle, 500x500x500, 20N/um model stiffness, target actual stiffness >10N/um
composite for superior damping, make as many parts in-house as possible, benchtop mill

Milli-No1 lifting gantry config – too complex
Milli-No2 – moving column fixed table
Milli No4 – moving column moving table 650x300x450
Milli No4 lifting gantry
mucked about 15mm rails vs 20mm rails. Should go to 25mm rails

Milli No5 – moving column moving table – seemed to be firming up

Chasing cast material stiffness – need 70GPa plus EG too low
What spindle speeds and power to use? Lots of discussion here. Decided on 750W and 1000W AC servo. Small frame 80mm

Milli No6 tombstone column - moving table

So far its been a struggle to get torsional stiffness inot the column. This struggle continues

Ralph chirped in with his actual machine stiffness and machine model much appreciated....

back to basics – and some generative design. Sdtill no breakthrough. Discussion onh FE modelling cars and rails

Milli No8 – moving column -moving table. Quite big machine now

Milli No9 – mainly base development. Got thicker and thicker. The column got bigger and bigger

Milli No10 – moving column moving table -hit the stiffness target – maybe this is it and I just kept going?

Much discussion on materials

Milli-AL a plate model - moving column

CSA shows up. 2020-11-19

Milli-No13 lots of work on materials, damping and fibres

Milli No14 CSA spindly column moving column. Column rosional stiffness is the key and it continually is the common theme and hurdle

Mili No15 moving column moving table with saddle fixed table

Milli No16 shapely column CSA
Milli No17 worked on getting the bolts in and assembly logic correct
Milli No19 moving column on saddle 3 rails...

Milli No20 quite detailed and developed
Milli No21 started to consider metal inserts and other deatisl. Well developed....

More base development

UHPC apperaed 2020-12-10

Milli No22 more CSA but more steel – yuk
Milli No23 vibration analysis

Mill-G was a moving gantry design.. Much more discussion on materials

Milli-M M was for Moris config. Called it the headstone config. Lots and lots of materials discussion

2020-12-25 ralph provided step file of Mikinis machine very useful

I decided to make the machine smaller and use an ER17 power head. Machine still not small enough!!

606 posts and still no resolve on the basic design
Common theme is poor torsional stiffness of any of the columns designed. The smaller the machine to more , material stiffness is needed... EG has poor stiffness, need advanced cold casting material??? E80 is out there but available to me... rethinking in progress. Peter

[ardenum]

Make a proper cast iron part and work backwards from that. Maybe that will give you some ideas.

[peteeng]

Hi Ard - Cast Iron is out as I can't do that myself... cheers Peter

[joeavaerage]

Hi,
that's why God invented foundries, so you can cast stuff without having to do it yourself.

My experience is that it's not cheap but the result is superior.

Craig

[MARV]

Nice digs Peter!

[peteeng]

Hi Craig - Foundries are a dying trade. Not saying that they are wrong just in a few years printing will replace most of that and CI will die out from machine tools as well. Composites will replace them, printed or RTM or cold cast so may as well get on the bandwagon now. I could make Carbon Fibre parts cheaper then CI parts maybe if the volume was there. Have to look at that in more detail....Peter

Hi Marv - Thanks a few visitors have said they want to move in.... but sorry its a workshop not a batch. Peter

[peteeng]

Hi Ard - Here's a cast iron kit. I think you mentioned about buying a kit? Peter

https://allcncrouter.com/collections...mill-frame-kit

[ardenum]

Hi Ard - Here's a cast iron kit. I think you mentioned about buying a kit? Peter

https://allcncrouter.com/collections...mill-frame-kit

No, what I meant is once you had a cast iron part that meets(exceeds) your specs, with the same wall thickness all around the part, etc, you could work backwards from that to replace it with a steel assembly, for example. It would give you a hint where material is needed and where its not, of course you could do a generative/topology optimizations instead too, but that thing gives results that can't really be replicated with anything other then powder printing, but it would still give you a hint.

So cast iron but only virtually, is what I meant.

You also mentioned something about an ER motor? so out with the BT30? Got any particular one in mind?

[peteeng]

Hi Ard - The spindle has currently three options 1) ER17 2) BT30 and 2) high speed router spindle.... the ER and BT motor will be a 80mm (or 90mm) frame 750W or 1kW option AC servo. See images of power heads attached.... Peter

Since the column has been the hurdle so far my thoughts are to return to the gantry style to remove the column. The machine would run "along" the bench and be a lifting gantry design to remove the saddle. The columns would be fixed and it would have a moving table. The only negative I see is that the table drive is in the muck. Sort of been here before but that was also before CSA so need to sort out the CSA casting stiffness. Re Your comment about designing in CI then converting to steel. I have sort of been doing that. I design the geometry to what I think is needed then change the material from EG E40 to AL E70 to steel E200 to see what makes a delta. If steel doesn't do it then its back to changing geometry. A new possibility has arisen in that a customer of mine has mentioned he has a working 10"x5" commercial router in a warehouse doing zip. I can work contra to get access to it. This means making large aluminium parts (or machining lands on cast parts) maybe within reach at a reasonable cost. Early days on that possibility. Its a 2 hours drive away so means I need to learn its system and spend a good day to get value out of it... But maybe a good thing. Peter

[ardenum]

I've read bad reviews of those green cartridges so make sure you know what your getting into. There's a blue version from a different company that seems to be slightly better.

[peteeng]

Thanks Ard - I'm sure there is a quality grade per cost. Once I get the structure settled I can investigate that issue. So green is bad blue is good
Maybe a different one will show up. A round type or maybe Martec will build me a few blue ones. Peter

[ihavenofish]

Thanks Ard - I'm sure there is a quality grade per cost. Once I get the structure settled I can investigate that issue. So green is bad blue is good
Maybe a different one will show up. A round type or maybe Martec will build me a few blue ones. Peter

They are all pretty poor. they have radial bearings and most are good for 2000-3000rpm - a few say 6k but i wouldnt.
They are not what you buy when you go to the effort of building a nice machine frame. they are what you buy to bolt to a sheet a plywood to stick a grinding wheel on.

[peteeng]

Morning IHNF - Thanks for the heads up. Can you suggest a suitable supplier? Cheers Peter