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    Cool Thor

    So not sure if this should be in the EG section or not, will place it here and see if mods move it. The construction of this will be done with concrete using 52.5R grade, sand, stone (basalt) and superplastifier to assist the mix / flow. Estimated weight of the machine will be around 2 ton when done.

    Some initial reading material of how the design came to this can be found here - BUILD LOG: Thor, or should that be Zeus?

    Since then, the design has changed many times, pics below. For reference, I have put some of the pics of the rails and ballscrews for size reference. Spindle options are still being considered. Currently its drawn with a 4KW Chinese spindle. No ATC. This may change. The other design goal was to run this from 220V @ 32A single phase max. Motors will be 1.5KW for Y, 750W Panasonic Servo for Z and X.

    Thoughts / comments / concerns welcome.











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    Default Re: Thor

    Looks pretty cool.
    Very nice looking parts. The design looks great.
    My first question is how will you mount those rails?

    Lee


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    Default Re: Thor

    Quote Originally Posted by LeeWay View Post
    Looks pretty cool.
    Very nice looking parts. The design looks great.
    My first question is how will you mount those rails?
    Good question :-)

    Ill be making a flat surface using DHW putty (DIAMANT DWH: potting epoxy & casting compound for machine construction) and then once that has set, Ill be drilling into the concrete, thru the putty and epoxy nuts in the concrete. The 'flat' will be created by lowering a surface plate onto the area or some form of reference surface to be made out of steel.



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    Default Re: Thor

    Holy linear rail and ballscrews! Is that stainless tape over the top of the rail, or are those rails rear-mount?



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    Default Re: Thor

    Quote Originally Posted by louieatienza View Post
    Holy linear rail and ballscrews! Is that stainless tape over the top of the rail, or are those rails rear-mount?
    Stainless cover. Top mounted.



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    Default Re: Thor

    So this weekend I turned some spacers on my newly acquired (old) Boxford A lathe. Ive also spent a bit of time with the initial layout for the control panel.





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    Default Re: Thor

    Really nice design Chazaxl and nice renderings. It looks like a pretty good size machine with those rails and ball screws.

    I think the structural design of your machine is very good. The only problem as I see it is the material to select. With the kind of heavy rails and ball screws you have it has the potential too be a very heavy duty machine. The structure you have would lend itself to steel or aluminum construction in my opinion but that would make it extremely expensive and perhaps too heavy for a DIY machine.

    I'm not sure the concrete approach will give you the rigidity you desire for this heavy duty machine unless you fill all of those spaces with concrete. EG would be a better material for this but would still need an approach similar to concrete. The problem with concrete is that it's only stong in compression and needs extremely large cross sections to compensate. The same essentially holds for EG except it has better dampening. The structure would seem to lend itself best to steel reinforced EG. But the problem with steel reinforcement in both concrete and EG is that a little bit of rust on the reinforcement causes a breakdown in the bond between the reinforcement material and the EG. This starts to happen in only a few years. One approach is to use stainless steel as reinforcement members but this makes the cost go up a great deal. With stainless the system can last about 100 years before it starts to go bad.

    A good approach might be to built the structure from EG as you have designed it and then fill all of the holes in the frame with cheaper concrete. Or better yet. Cast the void shapes in concrete first and then put them in the mold cavity so that the epoxy will bond to them in the mold.

    Just some thoughts. I'm sure it will work with plain plastisized concrete or EG but it might not measure up to it's full potential.

    Another approach might be to make the structure with a skin of epoxy fiberglass about a half inch to one inch thick and then fill the core with glass fiber reinforced EG. The thick fiber reinforced skin would make it almost as strong as steel and the fiber reinforced EG core would add both high dampening and some added strength in all directions due to the random placement of the glass fibers.

    Paul

    Last edited by Hezz; 04-24-2016 at 06:45 PM.


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    Default Re: Thor

    Quote Originally Posted by Hezz View Post
    Really nice design Chazaxl and nice renderings. It looks like a pretty good size machine with those rails and ball screws.

    I think the structural design of your machine is very good. The only problem as I see it is the material to select. With the kind of heavy rails and ball screws you have it has the potential too be a very heavy duty machine. The structure you have would lend itself to steel or aluminum construction in my opinion but that would make it extremely expensive and perhaps too heavy for a DIY machine.

    I'm not sure the concrete approach will give you the rigidity you desire for this heavy duty machine unless you fill all of those spaces with concrete. EG would be a better material for this but would still need an approach similar to concrete. The problem with concrete is that it's only stong in compression and needs extremely large cross sections to compensate. The same essentially holds for EG except it has better dampening. The structure would seem to lend itself best to steel reinforced EG. But the problem with steel reinforcement in both concrete and EG is that a little bit of rust on the reinforcement causes a breakdown in the bond between the reinforcement material and the EG. This starts to happen in only a few years. One approach is to use stainless steel as reinforcement members but this makes the cost go up a great deal. With stainless the system can last about 100 years before it starts to go bad.

    A good approach might be to built the structure from EG as you have designed it and then fill all of the holes in the frame with cheaper concrete. Or better yet. Cast the void shapes in concrete first and then put them in the mold cavity so that the epoxy will bond to them in the mold.

    Just some thoughts. I'm sure it will work with plain plastisized concrete or EG but it might not measure up to it's full potential.

    Another approach might be to make the structure with a skin of epoxy fiberglass about a half inch to one inch thick and then fill the core with glass fiber reinforced EG. The thick fiber reinforced skin would make it almost as strong as steel and the fiber reinforced EG core would add both high dampening and some added strength in all directions due to the random placement of the glass fibers.

    Paul
    Many thanks for your response.

    My mechanical design skills and knowledge is limited. Most of what I have come up with is based at looking at other machines as well as getting advice from the person that has supplied me with the rails etc. By no means is this a perfect design.

    I am interested in how it can be improved however. I have bought the plastisizer but none of the concrete materials yet. So open to suggestions.

    In terms of weight. My understanding is that there cannot be too much weight. Weight helps with rigidity. Now, there must be a point at which its just 'too heavy' for practical reasons. Is the comment regarding weight related to the ideal of using Concrete?

    I looked at EG. I could not find a suitable mixture that would work. Perhaps there are too many variables. Costs compared to Concrete? My current costs indicate around £750 ish I think to make this from Concrete. The DWH putty etc additional.

    In terms of the 'holes'. My understanding is that a hollow object is stronger than a solid. If you look at many machine designs, they have ribbing or they have a 'pattern' of hollowness. I am not sure how the logic works to now fill these in with something. Can you please explain this, perhaps some reference pics of other machines?

    In terms of making any of this from steel. It was considered. Ive seen many examples where people try this and are still welding / grinding (months) later. Suppose the cost of the material goes up quickly then too. In all the cases I have looked at here, they then add concrete (or similar) after to give weight / ridigity. Certainly pouring concrete into a steel structure is arguably easier than making molds. I think (please confirm) that anything made from steel needs to be stress relieved? I dont fully know what it means but this isnt something I can do in my garage.

    Please dont take any of my responses as being defensive. I'm keen to learn and before I spend any more of my hard earned pounds .....

    Many thanks.



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    Default Re: Thor

    A hollow object is not stronger than a solid. A larger section is stiffer than a smaller one.

    If we have limited material, we can maximise stiffness by increasing the size of the section.

    structural steel & oil field suppliers,channels, sections, angles, sheets, bars & gratings, beams, flange beams, columns, is of interest.

    Have a look at some of the smaller tubes and compare to the larger tubes. In particular pay attention to the kg/m and the moment of inertia

    For example, 100x100x10mm tube weighs 27.4kg/m, with a moment of inertia of 462cm4. 150x150x6mm weighs 26.8kg, with a moment of inertia of 1174cm4. That's 2.5 times stiffer for the same amount of material.

    The hole doesn't make it stiffer, it's having more material in places that oppose the force.

    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)


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    Default Re: Thor

    Quote Originally Posted by pippin88 View Post
    A hollow object is not stronger than a solid. A larger section is stiffer than a smaller one.

    If we have limited material, we can maximise stiffness by increasing the size of the section.

    structural steel & oil field suppliers,channels, sections, angles, sheets, bars & gratings, beams, flange beams, columns, is of interest.

    Have a look at some of the smaller tubes and compare to the larger tubes. In particular pay attention to the kg/m and the moment of inertia
    Thanks. Ill go through this tonight. Are you saying then that a 'bunch' hollows is a lot better than a single one as there is more 'wall'. Difficult to explain ...



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    Default Re: Thor

    Sorry, I've edited the post. See above for more.

    It takes a little while to get, but the principle is very simple. You need material to oppose forces (cutting forces, gravity).

    Think of a soft drink can. It is very thin walled, but the walls are tall. You can crush it in from the sides with very little force. However (if undented) a person can stand on top of the can and it will support their weight (so long as the force is applied in the direction there is a lot of material).

    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)


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    Default Re: Thor

    Quote Originally Posted by pippin88 View Post
    Sorry, I've edited the post. See above for more.

    It takes a little while to get, but the principle is very simple. You need material to oppose forces (cutting forces, gravity).

    Think of a soft drink can. It is very thin walled, but the walls are tall. You can crush it in from the sides with very little force. However (if undented) a person can stand on top of the can and it will support their weight (so long as the force is applied in the direction there is a lot of material).
    Ok, that makes sense. In my case, with 1180mm rails (45mm wide), what would you change or is that 'vague'? Any pics of what you refer to in the sense of an ideal structure? Pics are useful :-)



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