[peteeng]

Hi Spot - You maybe doing some stuff right and that will come out when you have a machine running. I only point out stuff that is clearly incorrect in your language, understanding and explanations of stuff so you and others can move forward towards the goal without going down rabbit holes. There is no perfect material for machines (i kind of like Beryllium or printed gyroid titanium at the moment) you have to pick your poison and go for it.. Peter

[G-Spot]

Hi Spot - Again sorry - the fibre composite industry has very specific definitions of weaving, knitting and tape laying,. I have been involved in all of these. The machine in the video is a tape layer. The tape is prepreg epoxy and carbon fibre. The resin is formulated for a specific "tack' so it is heated via an infra red element that you can see the glow from. It comes off the roll and is just like sticky tape. There is no stitching thread (sewing) or intertwining of fibres (knitting).

I suggest you read up on mechanics of solids... There is enough weight of evidence that Portland cement cracks and that every civil design code is based on the concrete cracking so the code has to mitigate the cracking issue with "reinforcement" which is a poor descriptor for what it does. FEA is only as good as your assumptions used and the interpretation within those assumptions. A manual calc is as good for something simple...

I have tested many materials personally or at labs. Concrete or grout - I have various samples that I have used for stepping stones around the place... some are quite expensive! steps...

Your saying that 0.25m3 is $35 USD and that 91.2kg od steel is $105 USD. So take your concrete at 2400kg/m3 is 600kg so concrete is 0.058 $/kg and steel is $1.15 per kg.

around here concrete cost around $250/m3 laid so thats 0.25 $/kg. At the hardware 20kg of cement costs $8 AUD so that makes 26kg of concrete so thats 0.31 $/m3

I'll use $0.10 USD / kg and steel at $1.00 USD/kg so the maths is easy.... Peter

This is just arguing over semantics, they were using weaved mats before, it's obvious, to sane people, that they just cut out some steps from the existing process. I think everyone here has wrapped an awkward shaped Christmas present with a straight roll of wrapping paper and are aware of the difficulties involved..we dont need to read anything on surface dynamics.

I suggest you go make some actual Portland cement in thickness greater than 300mm and find out it doesn't crack, big cracks, microcracks, etc. It especially does not crack when being used to support a power tool. I mean a 500 x 500 column of concrete will hold up a freaking discotheque but you seem to think it cant deal with a 3Kw power tool.

I've tested the limits of human endurance, personally, in an actual airplane. Inverted, weightless, in a stall turn 150ft off the ground. I have many stories of flying in unregulated airspace.

The take away from that should have been "there is a quality to quantity", you missed it, you should Google it, and the story behind it.

[peteeng]

Hi Spot - I have several slabs around my house for garages and sheds etc they are 200mm thick and have cracked since laid say 2 years old & I thought the contractor used a lot of reo in them. Here's a calculation showing that a 300x300 square beam of E40 GPa concrete is the same rigidity as a 300x300x8.3mm steel section. The steel is considerably lighter as well. As I have put fwd in the past the geometry of machine parts should be the maximum size possible in the space available, this means a concrete beam and a steel beam will be the same envelope size for any of the parts. I think your concrete cost is too cheap but using your figures the concrete is cheaper. I expect when adding form costs, inserts etc it will leap up in cost. Plus steel will get heavier as the 8mm plate will need secondary structures along the way. I expect they will work out similar in cost yet steel will be lighter and cheaper... I'll leave you to your journey and I look fwd to seeing your machine in action. Peter

300x300 solid concrete = 300x300x8mm thick steel in rigidity
concrete beam 216kg/m steel beam 78kg/m

using spots $/kg
steel costs $78/m and concrete is $22/m

using my concrete cost around $70/m

I pick steel

edit - since I like aluminium I calculated the beam for a that. its 300x300x28mm thick and weighs 84kg/m. I can edge bolt it don't have to paint it and not welding it will not distort....Being thick it solves the thin structure problems of secondary members so that's a good candidate as well...

[G-Spot]

around here concrete cost around $250/m3 laid so thats 0.25 $/kg. At the hardware 20kg of cement costs $8 AUD so that makes 26kg of concrete so thats 0.31 $/m3
]

No it doesn't, see attached pics it costs $130 cubic metre there and here it costs $108 a cubic metre

Don't make me waste any more time checking your error prone calculations, like the time you got confused dealing with Nominal Pipe Bores and had the pipe thickness wrong, I note you didn't take the time out to admit your error so that people can get the right information. As that is so important to you.

And you know full well nobody building a machine is getting a contractor in to lay the cement. You know they buy it in bags and mix it themselves.

Almost doubled your cost in concrete to call me out as a liar.

Then for a wood and concrete wizard you seem unaware of the formwork needed to cast concrete, walls expensive, columns cheap.....it's to do with the shape Peter, keep trying you will get there.

I value well reasoned and calculated peer reviews and not ridiculous appeals to authority.

[G-Spot]

]
edit - since I like aluminium I calculated the beam for a that. its 300x300x28mm thick and weighs 84kg/m. I can edge bolt it don't have to paint it and not welding it will not distort....Being thick it solves the thin structure problems of secondary members so that's a good candidate as well...

The concrete on steel was giving distortions that would stop you achieving the accuracy of a 100N/m machine, I predict the heat distortion from aluminum on steel would be more than the distortion from the forces on the spindle.

Did you attach the steel rails to the aluminum tube? what possible distortion did you get from heat differences ?

Did you carry out vibration analysis of the tube? how will you deal with the vibration on a steel tube and and aluminum tube?

You will probably want to fill them with something that will absorb the vibrations..

[G-Spot]

Did thermal analysis of shapes.

Made a simulation that simulated the concrete being at the max possible temp where I live, then the air temp around it drops to the minimum possible temp where I live.

10 degrees centigrade to 40 degrees centigrade.

The takeaway is that having non symmetrical shapes leads to large distortions and stresses.

The distortions will be the same no matter what material the shape is made from, just the magnitude changes.

The L-Shape warps and you can see from the stress analysis where it would crack.

The donut shape does not warp and you can see from the stresses it would not crack.

Therefore a portal type machine which has symmetry will be much more resistant to thermal changes than a C-shaped one.

I can now design the concrete core so it will not crack. I can also see why machines which use concrete have cracked.

Going to go for the same design as the Octabeast but using concrete and using a circle/donut and not an octagon.

The donut shows uneven distortion, more at the top, because it is being supported at the bottom. If I supported it in center, if that was possible then the distortions would be symmetrical. Easy to see with videos but I cant post them here.

[G-Spot]

I only point out stuff that is clearly incorrect in your language, understanding and explanations of stuff so you and others can move forward towards the goal without going down rabbit holes.

In case anyone is thinking of going down the 300x300x28mm box section of aluminium with 35mm steel rails rabbit hole then you might want to reconsider as you will get deflections of up to 0.2mm on your rails as can be seen from this FEA.

One pic is the simulated temp gradient of splashing cooling liquid at 10degC onto the Aluminium tube where the rails are, the other side of the tube is at my typical ambient.

The other pic, is the deformation that would happen because of that temp gradient.

A 0.2mm deflection is what you would get on a machine whose overall stiffness is only 5N/um

[G-Spot]

Here I discovered the best way to attatch rails to the concrete.

If you constrain both sides of the concrete with through bolts, then the force constraining opposite sides will be equal, so you don't have to add the same amount of metal to both sides, you just have to apply the same constraining force to both sides, which through bolting achieves.

So I am only going to use 10mm thick plate on the opposite side which saves a lot of money.

Will use direct optimisation to make the end bolts thicker to stop the ends from curling.

You can also see that the ideal place to mount the actual rails will be in the middle section of the top plate.

Concrete and steel work really well together as long as you don't let the steel get cooler than the concrete.

[G-Spot]

Here's a concrete only frame, no steel that can do 100N/um and is only 1 cubic meter of concrete for a cost of $108.

The inside circle diameter is 800mm so if your spindle post is 300mm you would be looking at a 500mm x 500mm x 500 working area.

It wont crack or distort because of its symmetry.

Don't believe me, put it in your FEA inner diameter 800mm outer diameter 1800mm.

Top inside face of 200mm with 1000N applied, bottom inside face of 200mm fixed support.

[G-Spot]

Refined and checked the mesh, the 1 cubic meter of concrete shaped as a Torus is actually 125N/um stiff.

I've attached the step file for anyone who wants to check the simulation in their FEA.

You will find 2 faces opposite each other inside the torus, put 1000N of force on one face, and make the other fixed support.

I also found that it would not crack until 15000N was applied on the same face. And then it was the surface shearing, with through bolts and steel it will be a lot higher.

You could comfortable machine in a 500mm x 500mm x 500mm in the centre of this torus because its inside diameter is 800mm.

The cost of this cubic meter of cement has already been established as $ 130 max.

I'm challenging Peter to submit a design using steel only with a value of $130 to back up his comments.

[G-Spot]

Well I seem to have cracked it

This is the torus with 2 steel plates either side.

Simulated as just stuck to the concrete using regular adhesion giving 500N/um Stiffness.

I know from my previous concrete design that the stiffness leaps up when you mechanical lock to the cement.

The end plates are 40mm thick so I can bolt the inner machine faces to them, and not the concrete so all machining forces go through the steel and not the concrete.

I just have two huge plates 600Kg each that I can just need to be cut and the inner edges milled for the rail mounts.

I am probably going to reduce the thickness of the plates and size to get the same stiffness as my 35mm rails.

The cost for the steel and cement for this would be $1500

I've attached the Drawing File, this time there are 3 inner faces at the top where you need to apply the force and 3 inner faces at the bottom which you can make fixed.

Don't believe me, find out for yourselves.

[G-Spot]

Added the bolts, it is still 500N/um because when you add the force to the 3 faces you effectively constrain them together.

The thermal analysis was excellent because all the distortion is on the outside of the torus.

I once again simulated worse case thermal shock, concrete at outside temp, pour water on the steel.

Steel drops to 10 degrees concrete stays at 35.

Also attached is the stress map with 500 metric tons on the z-axis, acting as a press.

The red,orange,green areas are where the base is constrained to the fixed support, so the edges of that area will have infinite stiffness which is why the stress is so high.

Also the top bolt hole is too close to the edge which is showing that it would fracture at the bolt hole.

But with a top hole mod this machine could safely press 500 metric tons.

Attached is the updated drawing with concrete and steel drilled out and bolts added.

[G-Spot]

Did my first full simulation using HWIN 35mm rails.
Optimised the rails and cars first.
Then attached them to the frame.
Reduced the steel and size.

I wanted to see what total stiffness I would get with all the axis fitted.

Made a frame for 300 x 300 x 400 and I got 222 N/um

That was with only 1286kg of house cement ($50)
And the total steel was only 800Kg ($950)

Also I used the old 300mm x 300mm x 10mm tube for my spindle, which is were all the deflection is coming from.

Best thing is this design can be made within a month and the cement is unlikely to crack because it is symmetrical. The cement is only attached to the machine through the plates and through bolts. No other part of the machine contacts the cement. The size of this machine also means that should the cement crack it is only 5 bags of cement $50 to try again.

One thing I know is fact from more than 40 hours a week for the last 3 months of FEA.

Your rail spacing is the most important factor. Forget looking at your machines outer dimensions and trying to improve on that. The biggest leaps in stiffness happen when you move your rails further apart. Of course once you get them to their limits then you have to increase your outer dimensions. But if you are looking for smart design to give you better stiffness than other similar sized machines then that is the best area to focus on. I am also going to fit 4 sets of rails to my Z axis because with this design that gives a huge increase in stiffness because you are linking both plates either side of the cement together.

Also the saddle problem should, in my opinion, be solved by using two 20mm plates bolted back to back and not by changing the location of the bearings, with 35mm bearings you will be losing like 30mm of your track spacing, and that kills your stiffness. It is cheaper to use another plate bolted back to back than it is to try and increase your other machine sizing to get more stiffness.

First I got a frame as stiff as I could afford and then I tried to keep my tracks as far apart as possible.

[G-Spot]

Beefed up the spindle.

Then simplified my x and y axis to the more traditional setup.

Wow the previous unconventional setup is a lot stiffer than the conventional.

This time even though the spindle is no longer the max deflection area, it is only 200N/um

[G-Spot]

Sorted out the Y axis deflection problem.

Y axis is now 250 N/um. So I only gained 10N/um from doubling the thickness of the spindle column to 20mm. But I get 40N/um from spacing the tracks another 40mm.

So it looks like from the designs I have tried so far that you can pick up a N/um for every mm you increase your track spacing.

Tested the other axis and was surprised to find the X axis was the weakest at only 120N/um but I can fix that by beefing up the top, which I was planning to do because I want to pretension the concrete up there.

Z axis was hundred ton press stiff

[G-Spot]

Refined it further, the mesh and the dimensions.

Spaced my rails another 100mm apart on the Y axis which improved the X-axis results by 50 N/um.

I think it would have been up to 100N/um but I removed a 100Kg plate that it was bolted to because I can use the steel more effectively in another area.

I am aiming to get both x and y up to 200N/um then I will start trying to manually confirm the FEA and get actual stiffness data for the bearings and screws.

This is looking like a very promising design as I want to use it for milling which is predominately movement on the x and y axis, and those axis only weigh 100 kg.

Should be able to mill at high acceleration rates compared to moving a beam and z axis and spindle motor etc around weighing 300kg plus.

The machine still weighs 2000Kg of which 1240Kg is cement. That is with a 20mm thick spindle tube and 30mm thick plates on my axis

800Kg steel is half what I was expecting to have to purchase so I am very happy and then engineers who will cut and mill the plates gave me excellent rates.

Hoping to order bearings and screws before the end of this month.

[G-Spot]

I now have both x and y over 200 N/um

Now to find some suitable screws.

I am now confident that what ever bearings and screws I purchase, I will be utilising their maximum stiffness.

Which I think is somewhere about 50 N/um for 35mm bearings and rails, will find out in the next few weeks.

Super confident that I can make a better milling machine than a Bridgeport which I think is only about 20 N/um, it's hard to get exact figures.

[metalmayhem]

what sized end mills are you planning to use

[G-Spot]

what sized end mills are you planning to use

That will depend on the power of the spindle motor I choose and the actual stiffness I achieve.

I want to use this machine to make a much larger outdoor gantry CNC for welding/3D printing boats, I nearly bought a small manual milling machine but after seeing so many up close I figured I could make one for a few thousand dollars more but a lot better and If I bought a manual mill then I would also need a lathe. Also want to use concrete on my outdoor machine and this small machine would prove a lot of unknowns without having to break up huge amounts of concrete if there is a problem.

What sized end mill and type of motor would you go for?

[metalmayhem]

What sized end mill and type of motor would you go for?

depends upon the application and the parts being machined at the time