[pippin88]

Hi Pippin - A better description is to use "geometric inertia" where its needed, sometimes mass and inertia are not related.... if you are comparing different materials with different densities... What FE are you modelling in?? Peter

Totally correct, I was coming back to edit the post to say "use material where it is needed"

Solidworks

[pippin88]

If you were to optimize an EG structure to reduce weight but keep the properties beneficial, I argue that, the added cost for a complex mold would probably offset any gains you'd get from smaller EG volume. EG optimizing is done slightly differently. The universal way of doing eg. criss cross in your example is not the proper way to do it(I do realize it's just an example). You do it for your specific electro-mechanical setup. Here's an example.


I would not want to be the one to design(or make) a mold for something like that.

I'm not convinced that a large solid is better.

A diagonal grid can be achieved by using polystyrene foam inserts.

A diagonal grid is a very stiff structure. What else would you propose?







Unrelated:
The Schneeberger page has some reasonable info:
https://www.schneeberger.com/en/prod...orecompetences

[peteeng]

Hi Pippin - Does SW have generative design like Fusion 360 or Inventor? I use these occasionally and the generative results are interesting. Peter

Ard - Its actually easier then you think to design something like that in a parametric solid modeller. You start by placing all the required bits as blocks in space in their correct place then join them together as needed. Plus add things that need clearance and check that they do not interfere. It sort of falls into place like a jigsaw does once you place a few bits in.... My hat is off to japanese engineers 25+ years ago that did small video machines and cameras on paper... a staggering exercise and achievement. 38 years ago I was doing steam pipe runs on battleships on a 5m long drawing board and that was brain draining enough.. Peter

[pippin88]

Hi Pippin & others - I worked through the Durcrete video and they made some maths errors. Plus I've never thought that grading works. Firstly grading apparently works because the concrete people want to use the largest stones possible because these are the cheapest stones, you can see the gaps so its logical to try to fill them. The smaller the stones the more grinding and grading has been done so the cost goes up. In the case of spherical particles hexagonal close pack or square pack gives you a solid ratio of 74%. In the case of the video if the inside dimension of the container is not a module of 40mm then you can't achieve a close pack arrangement so the efficiency is low. In the video they got 50% solid which is expected. Silica sand achieves 57-60% solid by itself. This is an industry accepted number for cartage, they work on 1500kg/m3 bulk density. The video bottle test they got 54% and I think they could have done better. In their last shot with the balls and sand they incorrectly calculate the solid ratio. 0.31/0.72=43% water ie 57% solid. They could have achieve this by filling with sand directly and wetting correctly. Now the cartage bulk density for alox is 2400/3900= 62% solid.

Anyone trying to make aggregate at greater then 65% solid ie chasing the theoretical 74% and some claim 90% plus solid are chasing straws. In the perfect spherical or elliptoidal world where we can fit smaller and smaller bits into smaller and smaller spatial quanta its fine on paper but viscosity, friction, rough particles, segregation, gravity and many other factors keep the actual figures around 65% best solid. So use a small particle that is much smaller then the thickness of the part you are making and its simpler and just as good as "graded" systems....

Some people put forward the small particle, more surface area theory with the addage that more surface area equals more resin,. This is totally incorrect. It comes down to the volume ratios of the constituents, no surface area involved. Most EG DIYers do not add enough resin to fully wet out the mix so they have porosity which is fine in the application. The water balance test is an easy and useful exercise for those interested in EG graded or not graded systems. Peter

I know you've posted about grading / single aggregate before Peter. As a mug (untrained individual) I'm not sure what to believe.

I see what you are saying about industry wanting different sizes because of cost. But many research papers that I've found show changes in strength and stiffness with different packing.

In the video:
Volume of jar 1.45L
Volume of balls 0.73L, therefore volume of void / water = 0.72L (..I agree with you that they have biased the demonstration by using a large aggregate compared to the size of the container and were never going to achieve optimal packing with the balls).
They add 0.72L of sand (which will have ~ 46% void as per their test)
They are then only able to fit in 0.31L of water
0.31/1.45 = 21% water (or 21% void in the ball and sand mix)
Isn't that right???


https://www.hindawi.com/journals/ace/2019/5732656/
This paper shows minimum void ratio when using 40% fines AND there is a large difference in size between coarse and fine aggregate. (Void ratio is higher when aggregates are closer in size).



I agree a bit of porosity doesn't matter in a DIY epoxy granite machine tool base. What matters is modulus of elasticity, workability, cost etc. Adding more epoxy just to fill porosity is not really beneficial as it is costly and does not increase the stiffness.

[peteeng]

Hi Pippin - Yes I went back and my math is incorrect. If their water addition is correct they get 79% by volume solid. I dispute that they put in enough water. But if you went with those figures (and the epoxy I use has a density of 1050kg/m3 so may as well be water) then I expect you get porosity and so be it. My point is whether you get 65% or 75% solid it doesn't really matter as long as you know the real number not some theoretical number. DIYers do these things then don't test (thats fair enough as well) so don't know what they actually get. Being a designer I need to know real numbers not estimated numbers...

Plus its easy to do small scale stuff but some of these things don't scale well, they segregate and you can't vibrate them as well as a small batch etc etc. If someone does tests to prove otherwise then publish please, willing to learn... Hopefully will be able to get across the border next week to get some CSA and resin... Queensland border is closed again....Peter

[ardenum]

Hi Pippin - Does SW have generative design like Fusion 360 or Inventor? I use these occasionally and the generative results are interesting. Peter

Ard - Its actually easier then you think to design something like that in a parametric solid modeller. You start by placing all the required bits as blocks in space in their correct place then join them together as needed. Plus add things that need clearance and check that they do not interfere. It sort of falls into place like a jigsaw does once you place a few bits in.... My hat is off to japanese engineers 25+ years ago that did small video machines and cameras on paper... a staggering exercise and achievement. 38 years ago I was doing steam pipe runs on battleships on a 5m long drawing board and that was brain draining enough.. Peter

I despise jigsaw puzzles with passion. If CAD didn't exist, I'd be carving wood animals in front of the TV.

[ardenum]

I'm not convinced that a large solid is better.

A diagonal grid can be achieved by using polystyrene foam inserts.

A diagonal grid is a very stiff structure. What else would you propose?

Unrelated:
The Schneeberger page has some reasonable info:
https://www.schneeberger.com/en/prod...orecompetences

Depends on your specific configuration(rails, ballscrews), where they are in respect to each other, what loads they need to carry, etc.

Usually I'd put minimal viable structure under each of them separately, and then see if I need to connect the structures with basic geometrical shapes. I'll be casting a 2 ton bed for my project and I'm only doing cutouts here and there for cables to not stick out of the machine.

Once you put things like anchors, cooling pipes, into the cast, you're left with awfully little space to actually be able to optimize anything, worth noting I'm also keeping a minimal wall thickness rule inside the cast too, so min 80mm(for my particular EG blend) between anchors and between the outer walls around the anchors.

Also I'm not too sure about copper pipes, I was thinking of using PP pipes instead, but haven't done any actual research yet though. I'm building this to last for life(that's why EG and not CSA in my case)so I have to be sure nothing happens to the pipes in 10-20 years.

Doing a frequency FEA is also vastly more helpful when it comes to EG.

[peteeng]

Hi Ard - I think for a big cast like that you should look at infusion. Much easier to dry stack a mould and let the vacuum do the work. If the pipes are for cooling using a plastic (insulator) seems to be the wrong thing. Copper is traditionally used in composite moulds for heating and cooling. They will last your lifetime and more. Annealed stainless steel (hydraulic lines) is another option....Peter

[ardenum]

Hi Ard - I think for a big cast like that you should look at infusion. Much easier to dry stack a mould and let the vacuum do the work. If the pipes are for cooling using a plastic (insulator) seems to be the wrong thing. Copper is traditionally used in composite moulds for heating and cooling. They will last your lifetime and more. Annealed stainless steel (hydraulic lines) is another option....Peter

Ah thanks for that, of course it has to conduct heat. Silly me

[pippin88]

Depends on your specific configuration(rails, ballscrews), where they are in respect to each other, what loads they need to carry, etc.

Usually I'd put minimal viable structure under each of them separately, and then see if I need to connect the structures with basic geometrical shapes. I'll be casting a 2 ton bed for my project and I'm only doing cutouts here and there for cables to not stick out of the machine.

Once you put things like anchors, cooling pipes, into the cast, you're left with awfully little space to actually be able to optimize anything, worth noting I'm also keeping a minimal wall thickness rule inside the cast too, so min 80mm(for my particular EG blend) between anchors and between the outer walls around the anchors.

Also I'm not too sure about copper pipes, I was thinking of using PP pipes instead, but haven't done any actual research yet though. I'm building this to last for life(that's why EG and not CSA in my case)so I have to be sure nothing happens to the pipes in 10-20 years.

Doing a frequency FEA is also vastly more helpful when it comes to EG.

2 ton is a next step up. I'm hoping to keep mine in the easier to handle range. Parts (base, columns) less than 500kg can be handled with an engine hoist or similar.

Pipes etc in the casting do increase the difficulty, that is a good point. I'm not decided on pipes for temperature control yet. Ultimately my machine will never be in a climate controlled environment.


The search for the holy grail is not easy. We want stiff enough, damp enough, cheap enough, light enough, workable in a home shop...

[spumco]

Ah thanks for that, of course it has to conduct heat. Silly me

Copper has better heat transfer than stainless, of course. It also is better for anti-bio fouling - less likely to get critter growth over the long term depending on what you're running as a coolant.

If you're going to go with thin-wall copper (for bends/returns inside the cast), you might consider plugging one end and filling with dry sand before placing it in the mold and casting. Last thing you want is for the tube to collapse from a chunk of aggregate or some other unexpected thing while you're in the middle of casting.

Getting the sand out is messy but easy - small plastic tube attached to a garden hose used like a hydraulic drill.

-R

[peteeng]

Hey All - I got my border pass for Monday!! So its off to get some resin (coating workshop floor and some test blocks) and 25kg CSA for trials. Peter

[peteeng]

Bugger Greater Brisbane is locked down until Monday Night - so will have to go Tuesday. Peter

[peteeng]

Morning Al - Have been watching videos of people struggling with EG machine parts using engine hoists etc ( MYCNCUK ) and this reinforces my initial concept of benchtop size. Parts must be <50kg. I'll have to cut Milli down considerably. Today I'm off to get some CSA at last!! Peter

[peteeng]

Hi All - Picked up the CSA today. Have to make a mould and start testing it. I also picked up the resin for the floor today. Start painting the workshop floor tomorrow.... So much to do... Peter

[peteeng]

article on creep of UHPC - Peter

https://www.maschinenmarkt.vogel.de/...tten-a-706058/

and I do like big machines. I do like the the doors and windows on this one.

I have been looking for laser alignment instruments but haven't found anything under $25k AUD yet...

[ardenum]

article on creep of UHPC - Peter

https://www.maschinenmarkt.vogel.de/...tten-a-706058/

and I do like big machines. I do like the the doors and windows on this one.

I have been looking for laser alignment instruments but haven't found anything under $25k AUD yet...

There's definitely a system for about EUR 2,000. I can't remember the name though, the smaller the distance that a system measures, the cheaper it probably is.

[peteeng]

Hi All and sundry - Painted out half of the workshop today. Used a resin I have not used before, will go back to infusion resin for this sort of thing... Will finish out first coat with this resin and top coat will go back to infusion resin. This one is VE laminating resin and its too thick. I brushed this floor...I know why the EG guys have so much trouble with thixotroped (laminating) resins!! Will soon be able to get into shelving, new benches and get all my tools in... Yeh!! Peter

[peteeng]

Hi All - 3D printed UHPC building bits. Very organic. Perhaps can do this with Milli and ALOX....I'm upgrading my Rhino CAD to RH7 so I can play with Grasshopper to do this sort of thing...Peter

[ardenum]

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" ???

peteeng which surfaces do you apply forces to? I've started doing FEA for the spindle mounts and frankly it doesn't look right, I'm applying it to the hole the spindle cartridge sits in but the deflections are 'local', they deflect the surrounding volume but don't seem to carry over to the mounting surfaces.