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
7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)
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 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.
7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)
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
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.
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
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...
7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)
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
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
Bugger Greater Brisbane is locked down until Monday Night - so will have to go Tuesday. Peter
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
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
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...
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
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
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.