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    Default Re: Milli a new composite mill kit

    Hi Ralph - Thanks again. I agree. Its just the machine has grown way past what I wanted in terms of size. I'll try to cut it down a bit when I get to it again. Got to get some work done on YaG, Xmas is nearly here!! Open sections are not stiff in torsion and that's what your probably experiencing... Peter



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    Default Re: Milli a new composite mill kit

    Hi All - Been looking at some benchtop machines like the Dyna Myte series. This is more the size I was thinking of. I'm not keen on developing the aluminium machine too much as I want to build a composite one. I do work for a company thats into various materials one of which is CSA concrete. Very small shrinkage and does not crack like portland cement. Very strong (80-100MPa compression strength) although strength is not the issue here stability is... The supplier assures me it's very stable compared to normal concrete ... Been looking for its modulus and it will be 30-40GPa could add my steel fibres to it.... or go to my stonemason and buy a slab of granite...Peter



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    Default Re: Milli a new composite mill kit

    Morning All - Had another go at the column in aluminium. Scored in N/um X 15 Y 84 and Z 38 easy to get bending stiffness. Will have to look at bigger or round column for torsion stiffness. Will have a deeper think... I even filled the column with CSA at 35GPa but didn't help much only a couple of N/um better. Geometry wins. So make it much bigger. Target is 20N/um plus.

    I've attached an article on steel reinforced concrete. Just be careful with the conclusion that the fibres don't improve the stiffness. They only added 1% by volume so would only make a few GPa delta as expected. I thought they would have used a much higher Vf for the fibres but they were interested in crack prevention I think more than improving stiffness like I want. But at least it shows 40GPa is possible with neat CSA that's pretty good... Peter

    By the way these stiffness values are with the column bearings held rigid. So even less when these are released...

    Attached Thumbnails Attached Thumbnails Milli a new composite mill kit-x-axe-jpg   Milli a new composite mill kit-y-axe-jpg   Milli a new composite mill kit-z-axe-jpg  
    Attached Files Attached Files


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    Default Re: Milli a new composite mill kit

    Hi Guys and Gals - I've gone back to the Milli No10-2. This is solid bits of infused FG at 30GPa stiffness. This is a lot of epoxy and epoxy is many $$$. So I've decided to go with FG "skins" about 15mm thick (this will be heaps for drilling and threading if needed) then backfill with CSA cement (E=30GPa or 40GPa) I'll probably put in steel fibers in the CSA to lift this a bit. This gets back to my original concept but the CSA will be cheaper then the epoxy backfill and potentially stiffer. So Milli No10-2 stats are in N/um X 28 Y 30 and Z 48. This is with 30GPa material so the FG/CSA maybe stiffer. I have not used CSA before so will get some and have a play. Onward and upward Peter

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    Last edited by peteeng; 11-21-2020 at 03:19 AM.


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    Default Re: Milli a new composite mill kit

    Hi All - commentary on the Mill-AL line of thought. 1) I didn't get it to the stiffness required 2) mainly because of local flexure of many bits involved. My aim was to minimise bits and cast as few a parts as possible 3) The column became the crux and although I made Dia225 dia275 and Dia325 the biggest one was still not much stiffer then the little one. This was because the section was changing shape. 4) I added a pure bending load of 1000N to the column and it deflected the column 0.5x the tool load. So half the deflection was bending and half was torsion. 5) I was going to use a geometry that put the "crank" through the h=shear center of the column but decided to flick all of those gymnastics and go back to the original general concept. 5) I have only come across CSA concrete in the last 2 weeks as I had a meeting with a client and they were using it on a project. CSA shrinks 1% initially then grows 2% as it cures, so at 3 days it has grown ~1%... Sounds good... I'll get some and have a play... Ptere



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    Default Re: Milli a new composite mill kit

    Quote Originally Posted by peteeng View Post
    Hi All - commentary on the Mill-AL line of thought. 1) I didn't get it to the stiffness required 2) mainly because of local flexure of many bits involved. My aim was to minimise bits and cast as few a parts as possible 3) The column became the crux and although I made Dia225 dia275 and Dia325 the biggest one was still not much stiffer then the little one. This was because the section was changing shape. 4) I added a pure bending load of 1000N to the column and it deflected the column 0.5x the tool load. So half the deflection was bending and half was torsion. 5) I was going to use a geometry that put the "crank" through the h=shear center of the column but decided to flick all of those gymnastics and go back to the original general concept. 5) I have only come across CSA concrete in the last 2 weeks as I had a meeting with a client and they were using it on a project. CSA shrinks 1% initially then grows 2% as it cures, so at 3 days it has grown ~1%... Sounds good... I'll get some and have a play... Ptere
    You can get CSA fiber reinforced as well

    Mactec54


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    Default Re: Milli a new composite mill kit

    Hi Mactec - Yes can get it in many flavours and additives. Will need to talk to a concrete chemist and find the one that gives best long term stability. I know epoxy gives very long term stability (been using it for 35 years) just don't know much about CSA yet. I have confirmed that the 80MPa CSA has an E=40GPa so that's impressive. Don't want it to severely micro crack some time into its life. Plus I shall have to figure how to couple it to the epoxy "skin" Probably after making the skin, wet out the inside then place some fluffy FG on the inside providing a key to the CSA. The thermal co-efficient of expansion is similar, FG to CSA both are about 10-12e-6/degC so that's good news as well. I have to build a benchtop for the sink for my new shed so shall make a terrazo top as a test from the CSA. Will learn a little from that.... I'm still looking for a good local short fibre CF supplier but I'm happy with the steel fibres I have....Peter

    shrinkage - CSA does not shrink much compared to portland as the excess water added is completely used in the CSA chemical reaction. Portland has excess water to create a slurry and the excess water desorbs out over time. This shrinkage creates internal tensile stresses and as Portland has very low tensile strength it cracks over time. We know we want zero or very low internal stress in a machine part so this rules out Portland as a good material. But CSA seems to offer the best value in the cement area as it has small internal stress due to the complete utility of water in the reaction ie low volume change and you can get very low exotherm versions so the casting temperature stresses are minimised.

    There are concretes based on portland and plaster of paris that look interesting too... slightly expanding and very stiff.....

    https://www.timbermate.com.au/concremate/



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    Default Re: Milli a new composite mill kit

    Quote Originally Posted by peteeng View Post
    Hi Mactec - Yes can get it in many flavours and additives. Will need to talk to a concrete chemist and find the one that gives best long term stability. I know epoxy gives very long term stability (been using it for 35 years) just don't know much about CSA yet. I have confirmed that the 80MPa CSA has an E=40GPa so that's impressive. Don't want it to severely micro crack some time into its life. Plus I shall have to figure how to couple it to the epoxy "skin" Probably after making the skin, wet out the inside then place some fluffy FG on the inside providing a key to the CSA. The thermal co-efficient of expansion is similar, FG to CSA both are about 10-12e-6/degC so that's good news as well. I have to build a benchtop for the sink for my new shed so shall make a terrazo top as a test from the CSA. Will learn a little from that.... I'm still looking for a good local short fibre CF supplier but I'm happy with the steel fibres I have....Peter

    shrinkage - CSA does not shrink much compared to portland as the excess water added is completely used in the CSA chemical reaction. Portland has excess water to create a slurry and the excess water desorbs out over time. This shrinkage creates internal tensile stresses and as Portland has very low tensile strength it cracks over time. We know we want zero or very low internal stress in a machine part so this rules out Portland as a good material. But CSA seems to offer the best value in the cement area as it has small internal stress due to the complete utility of water in the reaction ie low volume change and you can get very low exotherm versions so the casting temperature stresses are minimised.

    There are concretes based on portland and plaster of paris that look interesting too... slightly expanding and very stiff.....

    https://www.timbermate.com.au/concremate/
    You can try it also by adding epoxy there are some users that have already been adding epoxy to CSA or mixes like this

    Mactec54


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    Default Re: Milli a new composite mill kit

    Hi Mactec - Do you mean using the dry "cement" as a filler or adding epoxy to wet cement? epoxy does not like water so I don't see how that would work. They are immiscible I expect. There are epoxies that will work under water but these don't mix with water so I don't see the benefit of the "mix". If you add dry cement to epoxy as a filler again I don't see the advantage as its just a low modulus filler. There's a saying in Oz, "Please Explain?" cheers Peter



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    Default Re: Milli a new composite mill kit

    Hi All - some data on CSA, settled on a 34GPa mix. Will pick some up asap... - Peter

    Attached Thumbnails Attached Thumbnails Milli a new composite mill kit-shrinkage-jpg  


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    Default Re: Milli a new composite mill kit

    Hi All - I boiled Milli down to 3 cast parts. Material 30GPa (FG and CSA). The column is 40mm thick and weighs 51kg, the base weighs 204kg (FG/CSA) which needs some work to reduce its weight or split it in two. its pretty much a chunk of granite 100mm thick someone said once before...

    I'm trying to keep parts to <50kgs each. But its static stiffness is good. In N/um X Axis 24 Y 43 Z 74 Milli No11 (Milli-AL is 11) should be No12 but we'll leave it at that. I want to simplify the column and then rationalise the envelope again then try to get to detailing level... Been thinking about a diagrid for the base to keep the audience happy Peter

    Attached Thumbnails Attached Thumbnails Milli a new composite mill kit-milli-no11-1-jpg  


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    Default Re: Milli a new composite mill kit

    Quote Originally Posted by peteeng View Post
    Hi Mactec - Do you mean using the dry "cement" as a filler or adding epoxy to wet cement? epoxy does not like water so I don't see how that would work. They are immiscible I expect. There are epoxies that will work under water but these don't mix with water so I don't see the benefit of the "mix". If you add dry cement to epoxy as a filler again I don't see the advantage as its just a low modulus filler. There's a saying in Oz, "Please Explain?" cheers Peter
    I saw it being used in a video to do the same as what you are doing, my be there was more to it than what the video was showing as it did not show any mix ratios, just said it was a special formulation of epoxy the cement was mixed then the epoxy was added, I will see if I can find the video it was some time ago that I saw it

    Mactec54


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    Default Re: Milli a new composite mill kit

    Hi All - I've been thinking about putting the rails on the sides of the columns so the action center goes through the shear center. So this morning I built a quick test model to see if its a good move. Turns out the thru Shear centre arrangement is about 7% stiffer then the front mount. So taking the assembly alignment issues into account I don't think I'll do it.... Keep making Peter

    By the way I used a forced deflection of 0.001mm so the FE calculated the force needed to move the edge 0.001mm. On centre was 48.4N and on front was 44.8N. The column was 200x200x30mm thick SHS aluminium.

    Attached Thumbnails Attached Thumbnails Milli a new composite mill kit-cad-jpg   Milli a new composite mill kit-centre-jpg   Milli a new composite mill kit-front-jpg  


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    Default Re: Milli a new composite mill kit

    Hi All you swarfers and chippers out there. Time to review Milli.
    1) I set out to design a FG composite benchtop mill and now I'm close
    2) I intended to use mostly infused fibreglass skins (E=20-30GPa) backfilled with epoxy steel or epoxy something
    3) Came across CSA concrete (E=30-40GPa) and this has opened up casting possibilities, cost down, performance up, not known about prior
    4) So I have rethunk a few things and it looks like Milli will be more like a mineral casting then an FG machine. The issue with this is post cast machining. One aim was to produce parts that could be machined post casting. I'm thinking through that now... So perhaps its epoxy steel fibres in the machining areas as I know that works and CSA in the bulk areas
    5) So maybe its Milli No13 after some deeper thought.. keep at it Peter



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    Default Re: Milli a new composite mill kit

    Hi All - Working on a diagrid for Pippin. I can used diamond shaped Styrofoam "voids" to create the grid....or make a proper mould and make a top half and bottom half then bond together...Keep thinking and making Peter

    Instead of a grillage I think I'll just add Styrofoam balls to the mix to make it lighter will think that through more... I have settled on Bluey HE80 CSA mix. Best stability and slight growth according to the CSA guru...

    Attached Thumbnails Attached Thumbnails Milli a new composite mill kit-diagrid-jpg  


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    Default Re: Milli a new composite mill kit

    CSA - is that what Slocum used in the concrete shear damper system?

    Any literature on CSA use for machine tool frames? Particularly as molded vs filling steel tubes/forms.

    I have been thinking about the use of styrofoam balls in epoxy granite for ages. Haven't found any literature / testing.
    Big balls (measured in tens of centimetres) arranged by some sort of wire grid / spacers OR small balls (measured in mm) chucked into the mix?

    For my design, weight and epoxy volume (major cost) are important considerations. Section size can easily go up for base and columns. Only saddle has major size constraints.



    From my untrained FEA, few larger diagrid members worked nearly as well as many smaller. Much easier to mold / form fewer larger ones.

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    Default Re: Milli a new composite mill kit

    Quote Originally Posted by peteeng View Post
    Hi All - Working on a diagrid for Pippin. I can used diamond shaped Styrofoam "voids" to create the grid....or make a proper mould and make a top half and bottom half then bond together...Keep thinking and making Peter

    Instead of a grillage I think I'll just add Styrofoam balls to the mix to make it lighter will think that through more... I have settled on Bluey HE80 CSA mix. Best stability and slight growth according to the CSA guru...
    Miculite or Perlite would be better than Styrofoam and would help with the weight, I have also been experimenting with different mixes and foaming agents for 2 years which I have some great results with

    Mactec54


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    Default Re: Milli a new composite mill kit

    Hi Pippin - Re CSA Slocum I don't know and for machine frames again I can't find any. Its a punt. But I think a good one from talking to concrete chemists. CSA is $2.40/kgAUD vs epoxy at $18AUD/kg so its a big cost down. Plus its at least E=25Gpa which is 10x stiffer then epoxy so another win. You either play with framed geometry (grillages) or use bulk materials. When you use lightweighting materials you dilute the modulus. Expanded minerals like perlite present a problem with CSA as they absorb water and this water will eventually try to get out due to temp changes and capillary action etc. So it will change the bulk material over time. Perlite in epoxy is fine but I would vacuum dry it first as it will have a high water content to begin with thats why they use it in agriculture to retain/control media or soil moisture.... . Cost vs stiffness vs weight is a tough balancing act. I think aluminium is the best value material all round. But CSA maybe a great answer we shall see. Pippin CSA with a high plastic fibre content maybe your answer. CSA density is 2200kg/m3 so lighter then Al but not as stiff. If its simple flat shapes then aluminium sandwich is the best I get so far. If complex shape requiring casting CSA is the go so far.... I'm rethinking Milli around straight CSA casts vs infused skins then backfilling.... Peter

    Mactec by foaming agents are these for epoxy? Epoxy foaming agents generate hydrogen so I hope your not a smoker!! Epoxy foam has poor strength as the foaming agent breaks down some of it but its a good foam. All lightweighting attempts dilute the bulk properties of the material. Ultimately geometry wins until we can use bucky balls or graphine these have measured stiffness in Terrapascals...and weigh nearly nothing... cheers Peter

    I have started Milli No12 its parts are cast CSA (E=35-40GPa) but its motion beds (orange parts) are machined aluminium, These are bonded onto the cast parts. I'll make jigs for alignment or may rough bond then final machine. Since the motion bed parts have to be machined anyway they may as well be final machined vs jigged.. a few more ZZZ's to ponder that.

    Pippin there are a few polypropylene fibre suppliers around in OZ. Its usually used as a shrinkage control and microcracking control agent in Portland cement. Used at low addition rates. But it would make a good lightweighting strategy in your case. CSA is effectively liquid granite to improve modulus use hard aggregate addition. Bean bag balls for lightweighting but reduced modulus....

    Attached Thumbnails Attached Thumbnails Milli a new composite mill kit-milli-no12-jpg  


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    Default Re: Milli a new composite mill kit

    Concrete-based Constrained Layer Damping
    Eberhard Bamberg Alexander H. Slocum

    There are a series of papers and a thesis

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    Default Re: Milli a new composite mill kit

    Hi Pippin - I'm familiar with these works. I think they used Portland? Constrained layer damping is a difficult design to execute and a difficult design to analyse. Prefer to use damp materials and do the best I can. There are contradictions in the thesis and I expect he knows about those by now, but worth a read every so often, lots of good info in there. Cheers Peter



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