[suspension]

This model made of 60 E gives 77, 238, 227 stiffnesses in X, Z, Y directions respectively. This seems good. Any thoughts?
It's column is a shell made of 100mm granite.

[ardenum2]

you are confusing me, what are you trying to do? just find a c frame you like and copy its shape, no need to reinvent a structure that's been done for decades. heres one mr maw designed, theres plenty of other c frames on grabcad

https://grabcad.com/library/cnc-1100-600-600-1

[suspension]

you are confusing me, what are you trying to do? just find a c frame you like and copy its shape, no need to reinvent a structure that's been done for decades. heres one mr maw designed, theres plenty of other c frames on grabcad

https://grabcad.com/library/cnc-1100-600-600-1

Yes thats an option I have, but I am trying to find the best balance that works for me given the prices/availability/size/stiffness/etc.
The c-frame you linked to is too complex for example. The C frame of Alex may take too much material. And C-frame of Stef's may not give the stiffness I need, etc.

[ardenum2]

Yes thats an option I have, but I am trying to find the best balance that works for me given the prices/availability/size/stiffness/etc.
The c-frame you linked to is too complex for example. The C frame of Alex may take too much material. And C-frame of Stef's may not give the stiffness I need, etc.

if you want to maximize stiffness for the least amount of material you have to forget the c frame. if you are hellbent on a c frame make it as big as possible and make it hollow, 60-80mm wall thickness, you'll do this by casting with eg. polystyrene foam cores inside

[suspension]

if you want to maximize stiffness for the least amount of material you have to forget the c frame. if you are hellbent on a c frame make it as big as possible and make it hollow, 60-80mm wall thickness, you'll do this by casting with eg. polystyrene foam cores inside

Thant's exactly what I did based on input earlier. Apart from making it a shell, I made the column a pyramid to reduce more material without sacrificing too much stiffness. For example, this column only need 380Kg of EG compared to a rectangular shell column (100mm) which is 720Kg. The stiffnesses of this column are : 98.03921569 238.0952381 120.4819277.

[peteeng]

Hi Sus - you still don't have cars. bolts etc... the starting stiffness is good so now move along to the other design elements and review static stiffness later...

Hi Sus & others - To put the Portland thing in perspective:

Portland cement requires more water to be added to it then the chemical reaction requires, so it is workable & flowable. This excess water eventually desorbs from the mass and this leaves micro voids in the mass that leads to shrinkage. This shrinkage creates stress that cracks the mass. There are 3 sources of shrinkage with concrete. 1) initially the mass gets hot due to the reaction (as its exothermic) it gets bigger than its ambient size so as it cools the mass restraint creates internal stress 2) the solidification reaction happens in cells and each cell is different, they pull and push each other creating internal stress as it solidifies. This is called the plastic stage and additives can be used to help even this process out 3) drying stage - water desorbs from the mass creating shrinkage

CSA cements do not require excess water for workability. Just like epoxy its mixed at the exact ratio required for the reaction. Still have to be careful with exotherm and plasticity but the really big issue of excess water is solved.

There are similiar mechanics involved in resins - polyester and vinyl ester resins are supplied with excess styrene in them for transport reasons (6-8% by volume) and when cured this excess styrene desorbs from the mass and the mass shrinks (8% shrinkage typically) this is why we do not use these resins in machine parts as they change shape over time. Non solvated epoxy is mixed in exact stoichiometric ratio so there is no solvent to desorb and the resin/hardener react in ratio so the volume change is nearly zero and we just have to deal with the exothermal growth and shrinkage. Epoxy has a very small modulus so it takes up small strains better as the mass cools down. Plus plastics can relax and reorient as they are strained slowly in the cool down so end up with very little internal strain once cured. The curing crystal structure in the concrete are very stiff minerals which have no plasticity so they can only crack to relieve the curing strains.

Metals are the same when cast - they are very hot so they are much larger then their ambient size. In their plastic stage each cell pushes and pulls so when cooled the billet has a large internal stress due to cooling and solidification strains. The billet has to be annealed to remove these strains. Then it could be cold worked putting more strain in it. Plus internal metallurgical reactions (which change internal volumes - like alloys moving out of the grains into the grain boundaries) take a long time to settle down. So then we weld it, more strain. So then we stress relive it before we machine it... Lecture ends here...

Oh then theres granite and other stones its done all of this, but it did it 30 million years ago, so enough time has passed for it to stress relieve itself and settle down to a comfortable stable condition... So you could make your machine in any way you like, wait 30 million years and then you could machine it???

[suspension]

Hi Sus - you still don't have cars. bolts etc... the starting stiffness is good so now move along to the other design elements and review static stiffness later...

Hi Sus & others - To put the Portland thing in perspective:

Portland cement requires more water to be added to it then the chemical reaction requires, so it is workable & flowable. This excess water eventually desorbs from the mass and this leaves micro voids in the mass that leads to shrinkage. This shrinkage creates stress that cracks the mass. There are 3 sources of shrinkage with concrete. 1) initially the mass gets hot due to the reaction (as its exothermic) it gets bigger than its ambient size so as it cools the mass restraint creates internal stress 2) the solidification reaction happens in cells and each cell is different, they pull and push each other creating internal stress as it solidifies. This is called the plastic stage and additives can be used to help even this process out 3) drying stage - water desorbs from the mass creating shrinkage

CSA cements do not require excess water for workability. Just like epoxy its mixed at the exact ratio required for the reaction. Still have to be careful with exotherm and plasticity but the really big issue of excess water is solved.

There are similiar mechanics involved in resins - polyester and vinyl ester resins are supplied with excess styrene in them for transport reasons (6-8% by volume) and when cured this excess styrene desorbs from the mass and the mass shrinks (8% shrinkage typically) this is why we do not use these resins in machine parts as they change shape over time. Non solvated epoxy is mixed in exact stoichiometric ratio so there is no solvent to desorb and the resin/hardener react in ratio so the volume change is nearly zero and we just have to deal with the exothermal growth and shrinkage. Epoxy has a very small modulus so it takes up small strains better as the mass cools down. Plus plastics can relax and reorient as they are strained slowly in the cool down so end up with very little internal strain once cured. The curing crystal structure in the concrete are very stiff minerals which have no plasticity so they can only crack to relieve the curing strains.

Metals are the same when cast - they are very hot so they are much larger then their ambient size. In their plastic stage each cell pushes and pulls so when cooled the billet has a large internal stress due to cooling and solidification strains. The billet has to be annealed to remove these strains. Then it could be cold worked putting more strain in it. Plus internal metallurgical reactions (which change internal volumes - like alloys moving out of the grains into the grain boundaries) take a long time to settle down. So then we weld it, more strain. So then we stress relive it before we machine it... Lecture ends here...

Oh then theres granite and other stones its done all of this, but it did it 30 million years ago, so enough time has passed for it to stress relieve itself and settle down to a comfortable stable condition... So you could make your machine in any way you like, wait 30 million years and then you could machine it???

This is great info Pete, thanks for the explanations.
I will detail out my model. As Ard says MrW's model looks good and probably is very stiff, but it is too big and also too complex for me to make. But I can certainly learn new things from it.

Also would 150mm shell thickness enough if I cast this with some sort of UHPC or grout?

[peteeng]

Hi Sus - 150mm is heaps. You will sort that when you start adding cars etc...

[hanermo]

Guys .. the nr 1 issue is column size, not thickness.
A 30 x 30 cm column is VASTLY more rigid than a 15 x 15 cm column.

Likewise, a 200 mm free length at end of column vs 400 mm is 8 x less rigid, not 2x.
It´s length power of 3.

Original bridgeports had about 30 cm columns, and they are very floppy.
A modern haas is about 40 cm, but lots of internal stiffeners, but only about 10 mm thick cast iron.
It´s decent.
A modern japanese machine is about double the mass, with bigger columns, and thicker skin.
It´s very good (expensive).

[suspension]

I asked about the thickness due to minimum thickness requirements of UHPC/Grout/EG.

Regarding stiffness of linear carriages: I can see that HIWIN has given the stiffness value for linear guides in the datasheet. For the model I am using it is 539. Being in the higher side, this might not affect overall stiffness of the machine. However it is great if I can incorporate this information properly during FEA. I guess this is not easy/straightforward?

[peteeng]

Hi Sus - The cars have different rigidity in different directions. If you search the site I discuss how to model this in a couple of places. Briefly it means you model a car as a multi material part. Then you tune the sides of the car so the modulus crates the correct transverse stiffness. Similarly for vertical loading. see attached diagram. But up front just make the cars aluminium and the rail steel. Thats close enough at this point in your modeling. Also when you quote numbers always quote the units with it. Otherwise readers have no clue what you are describing.... The grout I use can be cast at 20mm thick... Peter

You also have to be mindful that cars have a sliding direction. So in this direction the drivetrain is what resists the loads not the car. Early modelling you bond the cars to the rails but once the drives are in you can allow the car to slip in the correct direction. This will load the drive train correctly...

Hi sus - I looked at the contacts in fusion and you can attribute a stiffness to the contact. This is easier than the multi material method. You can also attribute it to slide so play with these settings....

[ardenum2]

you don't have to do that much simulation, you don't need to know the real stiffness values either, all you need fem for is to compare between iterations.

[peteeng]

Hi Sus - If you think 5mins is a bit much to wait - if you add in contact stiffness and sliding etc the solution time goes up big time. Right now apples to apples is good enough. You have a lot of work to do to get to a good GA. Plus you have to decide if your going grout/epoxy/steel /aluminium plate build etc. Peter

[ardenum2]

here's an example where I compare between different internal support in a column. I fused all parts together and applied a single material to it. 1000N load. I want to change my method in the future to apply infinite stiffness to the ram. It should isolate the load to only affect the column but requires more setup.

do you know why your new column is stiff yet uses half the material than the previous one? you now have proven what I was suggesting from the beginning and now you have made a mini double column.

[suspension]

Hi Sus - If you think 5mins is a bit much to wait - if you add in contact stiffness and sliding etc the solution time goes up big time. Right now apples to apples is good enough. You have a lot of work to do to get to a good GA. Plus you have to decide if your going grout/epoxy/steel /aluminium plate build etc. Peter

Based on current simulation results, steel is probably out. In here 24mm thick sq foot of mild steel costs 25USD. With Laser/Plasma cutting, welding and SR costs my guess is that it will be more expensive than UHPC.
I have emailed several Grout/UHPC suppliers including the ones you suggested, but none of them got back to me with elastic modulus information. I contacted a local manufacturer and they suggested epoxy (please see attached data sheet). That also does not specify YM but they are happy to send commercial samples if we can do a test.

Up until now, I have not been using the simulation effectively. You can add multiple load cases and do a single sim run to get results of all load cases. I thought it only simulate the activated load case. Now 5 minutes is manageable!

[suspension]

you don't have to do that much simulation, you don't need to know the real stiffness values either, all you need fem for is to compare between iterations.

Hi Ard, in this case how do you know that ultimate machine will give you say 50 stiffness?

[suspension]

here's an example where I compare between different internal support in a column. I fused all parts together and applied a single material to it. 1000N load. I want to change my method in the future to apply infinite stiffness to the ram. It should isolate the load to only affect the column but requires more setup.

do you know why your new column is stiff yet uses half the material than the previous one? you now have proven what I was suggesting from the beginning and now you have made a mini double column.

Hi Ard

Not sure if your result is in agreement with mine. In my case I didn't have any internal supports to the column. Following previous advice, I created a column that has the highest dimension (restricted by space constraints and to some extent aesthetics). Then I made a shell out of it. Then I shaped back and sides to give a pyramid like shape. This did not have any internal structures. In fact I did many other simulations and it was evident that above process seem to give best stiffness for a given mass. Are you suggesting having an internal structure like yours can give better return on stiffness for a given mass?

Thanks
Sus

[ardenum2]

how do you know that ultimate machine will give you say 50 stiffness?

I don't need to know that, I'm limited by weight, as long the part is within the weight limit I just strive for the stiffest I can get.

Are you suggesting having an internal structure like yours?

no, I'm playing with cast iron, I was only showing the best use case for FEM, to compare between iterations, real stiffness numbers don't really matter much to me. I'll end up with whatever my weight limit allows me.

that epoxy is not suitable for EG, it's viscosity is 15000 - 17000, you want something under 500

[peteeng]

Hi Sus - flooring system epoxies generally have a solvent component. This will lead to shrinkage as the solvent desorbs from the cast mass. The data sheet does quote the flexural stiffness. Assuming the material is isotropic then the tensile and compressive modulus is the same. Its interesting that as the filler component increases the stiffness decreases at high filler additions. The range is 8GPa to 5GPa not very good for a stiff machine part. Plus you'd have to ask them about thick casting. These systems are designed for thin curing so it has a very active hardener. If you cast too thick the exotherm will cook the epoxy... Peter

If you are designing "thin" parts you will need internal webbing to locally stiffen the section as it deflects. If the part is "thick" it maintains its shape at the desired max deflection. Thin and thick are relative. Early models are comparative only to gain insight and direction on how the part is best made. Depending on the manufacturing route will shape how the part looks.

[ardenum2]

I took a look at what's available in sri lanka, you have a domestic manufacturer siam city cement,

https://www.siamcitycement.com/srila...s/insee-cement
https://www.siamcitycement.com/srila...insee-concrete

some search results showed they also had holcim concrete but the website doesn't show it anymore, holcim makes a 100year uhpc called dynamax xrd. it's best to write them an email and ask about grouts