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IndustryArena Forum > MetalWorking Machines > CNC "do-it-yourself" > Milli a new composite mill kit
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  1. #541
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    Re: Milli a new composite mill kit

    Quote Originally Posted by peteeng View Post
    Hi Guys - We are discussing the proverbial cat problem and there are many solutions. Lets move along to the next hurdle... Peter

    https://www.bnd.com/living/liv-colum...20inside%20out.

    "Correct" that is what I said in my post from what I could find out about that company they are using a Mineral Cast insert just a different cat same end result but most likely could be cheaper to do it this way
    Mactec54

  2. #542
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    Re: Milli a new composite mill kit

    Morning All - I extended the pocket/subplate concept to the arm. I also put in an extra rail under the column to see if that helped. The stiffness stats are X 18 Y 22 and Z 22 in N/um so thats encouraging. The subplate approach allows bolt access and adjusting of geometry so that's good. The arm is now big so the BT30 is fine,,, everything's travelling in circles... So I'll figure out what needs to happen to get X stiffness up a bit then can move along... Peter

    Edit - Ran it without the middle rail and its stats are X 18 Y 20 and Z 18 so maybe a good thing to have for now....

  3. #543
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    Re: Milli a new composite mill kit

    Hi All - I think I'm getting close. The column is showing signs of local distortion so I'll work on that. Tuning up some materials and geometry and it will be the best it can be... Peter
    Attached Thumbnails Attached Thumbnails column lozenge.jpg  

  4. #544
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    Re: Milli a new composite mill kit

    Evening All - Latest news...

    I made the base and column solid plus added the steel frame base back into the model. The frame was to reduce the part weight a bit. No8 weighs 271kg which is not too bad. The X axis is still slightly under the target stiffness. The main parts are CSA at E=40GPa and the rest are aluminium. The base frame is steel (100x100x6 SHS). My view now is that in such a small machine 20N/um is a very high stiffness target. The main parts are made from low stiffness material E=40GPa and if made from aluminium at 70GPa or cast iron at 110GPa would fly in. The next step is to change the arm pockets from the top and bottom to the sides to allow easier access and that's it for now. I think I need to do some material testing to prove the CSA at 40GPa is doable and hopefully I can get more stiffness then 40. I'm puzzled why the European company has an international order enquiry process yet won't freight me E80 UHPC material. So we know that E=80GPa is possible in concrete and this would then allow the design to fly past the target stiffness. So onward to some material testing to increase the project certainty a bit... Peter

    Oh yes No8 stats X 19 Y 26 and Z 26 N/um. if I make the saddle steel it gets >20 all axis...

  5. #545

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    Re: Milli a new composite mill kit

    You could make the Z axis saddle as wide as the spindle headstock, I know you made it like this to make bolting the carriages easy, but maybe there's a different solution that doesn't weaken a component.

  6. #546

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    Quote Originally Posted by peteeng View Post
    My view now is that in such a small machine 20N/um is a very high stiffness target.
    Yes, though keep in mind you're trying to squeeze a bit more work area per overall size than most mills of this layout do, and that's why it's difficult.

    If the overall size of the machine, low modulus materials, and the resulting stiffness are the critical parameters, it's more straightforward to reduce the work area until you can achieve them. Which is prioritized?

    Or go back to a gantry layout and comprise on your Z travel. I don't think there's a magic layout to be found, it's just geometry, modulus, and mass. I went with steel and a fixed gantry layout and had no problems getting a large work area to size ratio and fairly high stiffness, but I sacrificed to 200mm Z.

    But it's fun following along. Cheers, and happy new year from the Rocky Mountains!

  7. #547
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    Re: Milli a new composite mill kit

    https://kapamilyachannel.ru/
    https://shandaarravivar.com/
    https://hoverboardsonly.com/
    The way you portrait the blog is outstanding like your work

  8. #548
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    Re: Milli a new composite mill kit

    Hi Ard - Up until Milli-ER No7 the saddle has always been the width of the bearings. This arrangement neglects the issue of how to bolt the cars to the saddle. It can be done by using flanged cars and bolt from the rear but in this case and others requires holes in the column to allow long wrenches to be inserted from the rear. Not a great solution. I don't like the current solution as the cars are on "air" but I think its a workable compromise using the subplates.

    Hi Cat - I don't think its the work area its definitely the Z height. I'll run it at half height to see the delta. Which would be more like the usual max Z. I have been in and out of the gantry layout a few times (in this thread and others) and come back here.... you say "fairly high stiffness" can you measure the actual stiffness? Thats the only way to understand the difference. Or if you can machine steel with a big cutter and tell us the parameters...

    Note: a gantry machine it wastes a lot of rear space due to the gantry/saddle/Z axis stack. This machine is intended as a benchtop machine so compact depth is a priority. I looked at running the machine "along" the bench as well.... Peter

  9. #549
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    Re: Milli a new composite mill kit

    HI All - One aspect of this machine is vibration and damping. The machine is intended to be made in composites for their excellent damping characteristics. So far I have neglected vibration or modal analysis and since we have a "real" machine to look at I decided to run some vibs today. All thin column machines tend to wobble fwd/aft or sideways as the first modes. In Millis and Skyfires case this is so. Milli does this at 252htz and Skyfire is at 123htz. This is good for Milli. Millis next is at 416 then at 600htz etc. Skyfire goes 123, 147, 203 and more. Skyfires table has many wobbles from 561htz up.

    Ralph if your watching did the Skyfire have any noticeable operational wobble points? Would you describe the Skyfire as a mini mill or a benchtop mill?

    Skyfires frame weighs 341kg and Milli-ER No8 is 271kg so I'm happy with that. Skyfires footprint is about 700x700 same as Millis. Peter

  10. #550
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    Re: Milli a new composite mill kit

    Hi All - Since Ralph has supplied a "real" model of a machine and we have a test I figured its worthwhile looking at it a bit closer. I looked at the loading photo and realised the load was being applied to the machine not to the tool so I reran the model with this taken into account. Ralphs test calculates the X stiffness at 8.8N/um yet the model is only 6.5N/um. The model uses CI E=116GPa but it could be up to E=150Gpa depends on the alloy used. 1.3x6=7.8 which maybe correct. Anyways if all things are correct the model is less stiff then reality. Which mans my Milli model will be stiffer then calculated but I won't hang my hat on that. Lets just say that the order of magnitude is correct.

    I looked up the Skyfire M stats and its envelope is about the same as Milli. So its not a bad benchmark.

    Skyfire M
    X 420mm Y 220mm Z 400mm nose up 450mm nose down 50mm from bed
    table 760x240mm
    BT30 spindle 300-6000rpm

    about 600kg weight including covers and enclosure

  11. #551
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    Re: Milli a new composite mill kit

    Peter,

    Mini-mill vs benchtop...? "Mini" meaning toy, like a Sherline, or "Mini" like a Haas Mini-mill?

    Assuming 'mini-mill' means 'toy', I think my mill could be classified as a benchtop mill, but barely. It's really too tall for a bench, and I believe a fair amount of stiffness/damping/whatever comes from the cast iron stand. It certainly isn't suitable to just plop on a bench. Size/travels, it's about halfway between a Tormach 770 and the larger 1100 series. Smaller travels than a Rong-Fu RF-45 (and PM-940, and other variants) by a bit, but the base and column castings are about the same size as the RF-45.

    Put it this way - if you set it on a normal working-height bench, the table top would be halfway up your chest. Way too tall to be lifting vises or heavy stock, although if Milli has no sadle/table stack it'd be fine on a bench - just need ceiling clearance for the spindle motor.

    Mine is more like a Syil X7 type machine - similar travels, linear rails, etc. Mine is older and much less refined than the new(ish) X7, especially the brand new one with the EG base/stand, but basically the same class.

    The Skyfire/Syil probably have better fine positioning capability than the Tormachs due to the rails, but have no damping effect from a giant oil-slathered dovetail way surface. I suspect this may be why the 'typical' Tormach feeds & speeds for index mills and fly cutters never worked out on my mill.

    I've not noticed any odd harmonics or resonances that weren't due to the stepper motors. I have (already binned) really cheapo stepper drives and they had the typical hum/groan at about 10-20ipm. Also remember that though the current Skyfire has a BT30 spindle, mine pre-dates Skyfire and has (had) an R8 using the TTS toolholder system. I think this also contributed to chatter & vibration.

    It certainly cut better in Y than in X during hard or aggressive cuts. Due to my semi-permanent trunnion table I tended to face stock in Y passes to avoid running in to the trunnion ears, and I think this also helped.

    NOTE - the extension required to tighten the cars through the column (and base) is not really a problem. A 12" hex drive extension is easily inserted through the holes and a torqe wrench is used to run them down. On the head, the outboard screws are accessible with a standard hex key, and just two holes are needed for all eight inboard screws. The head is moved up and down to access the screw pairs, and the holes are large enough to insert a proper 3/8" drive hex socket. Same-same on the saddle lower trucks - extension through eight holes in the base, but those holes are small enough that I'll have to use a hex extension and not a ratchet/socket assembly.

    And you only have to do it once, hopefully. Only oddballs like me disassemble their mill down to primals.

    If I can offer any other vague opinions or ramblings, just let me know

    -Ralph

  12. #552
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    Re: Milli a new composite mill kit

    Hi Ralph - Yes descriptions are difficult. The Skyline M is described as a mini... here's another mini (yes its a toy IMO) In a few days I can get some CSA and do some test bricks, then do some modulus tests to see what I get, then I can get back to Milli. Need some hard data for the design work...

    I started putting some drives on but thought better of it. I may put the column directly on the bed and go back to a moving table to see the difference, that maybe interesting. I call that the tombstone version. YaGs rails arrive this week and I can get it moving again yeh!! In my research for a laser alignment machine I came across this little number for modulus and damping will put it on the wish list..... Peter
    Attached Files Attached Files

  13. #553
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    Re: Milli a new composite mill kit

    Peter,

    You had me confused with "Skyline M"

    You're referring to the Skyfire SVM-2, which is the same basic machine as mine. I think they're marketing it as a "Mini-VMC" rather than what I (and it appears you) think of as a "Mini-mill". i.e. a toy.

    -R

  14. #554
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    Re: Milli a new composite mill kit

    Evening All - I dropped the column onto the bed and moved the rails out and put the table back on. The consequence of that is the column & Z would have to be 70mm higher due to the table and cars height. I didn't do that I just supported it the same as No8. I made the nose height 400mm as usual.

    The No9 stats are X 19 Y 46 and Z 37 N/um. No8 was X 19 Y 26 and Z 26. So the cars and rails provide some compliance. So 25mm maybe better even 30mm... but the X axis torsion is the issue and tombstone didn't change that at all!

    So onward to some material mucking and testing. Peter

    Hi Ralph - sorry yes Skyline is Skyfire and your SVM is correct.... "small vert mill" ???

  15. #555
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    Re: Milli a new composite mill kit

    In the latest configuration, is there some reason the base & column can't be cast as a single piece? One big L-shaped thing... would make getting the X and Y-rail mounts perpendicular a bit harder if post-machined, but not if the mounts are cast in place.

    In addition, this configuration screams out for side plates to triangulate the base & column. I can see a big "L", with cast-in screw holes on the sides, and a couple of aluminum side plates maybe 1/4" thick. Perhaps with cut-outs near the table for workholding or fixturing access.

  16. #556

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    Re: Milli a new composite mill kit

    Quote Originally Posted by peteeng View Post
    The No9 stats are X 19 Y 46 and Z 37 N/um.
    Those are really nice stats, the headstock is double T shaped, that shape is actually really bad against twisting. I don't think it should matter since its so short, but who knows.

  17. #557
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    Re: Milli a new composite mill kit

    Good Morning All and Sundry:

    Ralph yes it does look like a solid L casting would be good. The column would need to be deeper to bring the X stiffness up to the others. But this casting would be heavy. So it would need to be in a couple of pieces. Coming back to the machine objective its mean't to be a benchtop machine liftable by two people. Milli is not that light yet. So currently its a stand machine. One other rule is that parts are to be <50kg and the column is 100kg and the base is over that. Again its a stand machine...

    Other news - since I can't get the E80 material from Europe, which would solve several current issues I researched the aggregate more and sent an email request for info to the european importer HAMAG. They said it was not worthwhile sending durigid to Oz but look for some local calcinated alumina. I can get alumina but will figure out what the calcinated does/means. I also got a quote back from Brazil re modulus testing device and its $5500USD which is not bad for such a thing. I have a D&B project for a 16x8x3m concrete printer this year and will include that in the budget. Otherwise will get tests done at the uni I usually work with for materials testing...

    Back to the tombstone config. Its last negative is the drive screw will be in the muck which I was trying to get away from. It also means adding 4th and 5th axies will be harder. If I make the base in two pieces then it becomes a more flexible arrangement.

    Now I have the calcinated alumina clue this gives me hope of a E80 material vs the current E40 material... I was going to look at laminated metal again if I can't get higher then E40 CSA...Peter

  18. #558
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    Re: Milli a new composite mill kit

    Morning all - I've been researching calcinated aluminia and its what has been discussed in other threads. Commonly called alumina, ALOX, carborundum. Its E=300-375 GPa. So I can get 1.4mm grit from the local blasting suppliers. The durigid stuff is much bigger. So I figured that out about a year ago... I'll get some costs on the grit and go from there... Laminated aluminium is starting to look good again!! Peter

  19. #559
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    Re: Milli a new composite mill kit

    alo3 sandblast grit is what you'd use for the fine wear surfaces - like if you do actually mount the rails directly to the eg. Downside is you are not going to "edit" that surface after casting in any easy way. It could also be the fine filler between larger quartz aggregate. It costs a lot more than silica though, in the $1 a pound range over here.
    wotzBotz

  20. #560
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    Re: Milli a new composite mill kit

    Hi IHNF - Yes you are effectively making a grinding wheel in the shape of the part. Silica is only 70GPa so sand is not attractive if you want stiffness. I'm expecting ALOX to be expensive. But we shall see. The trick would be to add just enough to CSA to get to 70-80GPa. At 25% by volume Alox and 75% CSA you get E=97GPa. This would make it slightly less dense then Al 2600 vs 2700kg/m3 and its weight ratio would be 66% CSA to 34% Alox. Have to figure the cost out. Maybe back to the idea of a fibreglass shell and backfill with the alox. Or just go laminated aluminium. Al is cheap I can make laminated slabs then machine to finish. Do some costings then decide... Peter

    My new rails for YaG just arrived I can get that moving again Yeh!!
    Attached Thumbnails Attached Thumbnails rails.jpg  

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