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  1. #41
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    Default Re: Thor

    Putty done, levels look good. I am using a surface plate upside down as a table but also to get alignment of the ballscrew / mounts before I putty the level for the bearing holder.







  2. #42
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    Default Re: Thor

    Looks good, how did you get the putty flat. Did you lap it with that surface plate?

    It looks like you have a nice roll around steel stand for it. Maybe you should consider making the upper gantry and side beams out of steel and then fill them with cement. It will be much stiffer and very well damped.

    Overall the project is looking good.



  3. #43
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    Default Re: Thor

    Quote Originally Posted by Hezz View Post
    Looks good, how did you get the putty flat. Did you lap it with that surface plate?

    It looks like you have a nice roll around steel stand for it. Maybe you should consider making the upper gantry and side beams out of steel and then fill them with cement. It will be much stiffer and very well damped.

    Overall the project is looking good.
    No, the flatness is created by pouring the DWH epoxy and then lowering a reference surface onto it like a mold. Once its lifted, it 'copies' the shape. So in my case I used a large 'block' of metal which is flat as my reference. Ill find more pics of this.

    Ye, the stand was a must, not only for levelling but the bottom structure is around 750kg, so not easy to handle.

    I was thinking of that, easier than making another concrete structure but in the same breath, I dont want to cut corners on the design either.

    Does anyone have a view on steel with concrete filled in versus a thick concrete structure?

    Thanks for the comments.



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    Default Re: Thor

    Quote Originally Posted by Chazaxl View Post
    No, the flatness is created by pouring the DWH epoxy and then lowering a reference surface onto it like a mold. Once its lifted, it 'copies' the shape. So in my case I used a large 'block' of metal which is flat as my reference. Ill find more pics of this.

    Ye, the stand was a must, not only for levelling but the bottom structure is around 750kg, so not easy to handle.

    I was thinking of that, easier than making another concrete structure but in the same breath, I dont want to cut corners on the design either.

    Does anyone have a view on steel with concrete filled in versus a thick concrete structure?

    Thanks for the comments.
    I was thinking about heavy steel members filled with the high performance concrete. Not small tubes. 6-8mm sheet steel fabricated and internally braced to the shape that you had designed. Basically, my idea was to make the mold out of reinforced steel and It would out perform the concrete unless the concrete was made at least four times bigger or so. If it's steel reinforced in the center it's even better. It is so strong and stiff they use it for earthquake reinforcement on concrete bridges. Of course, this is your project and only you know what your budget and fabrication capabilities are. I don't mean to tell you what to do. The problem as I see it is that concrete does not flex very well without failure. And you will have to make your mold very precise to get the gantry just the right width to bolt it to the base. If there is a gap and you tighten it it may well crack and fail. There just isn't much room for manufacturing error in your design. But with a monolithic steel mold weldment you would have just a little flexibility and a good surface for lapping or grinding to get flat way mounts and

    Actually, I'm kind of the opinion that real heavy mass on the upper part of the gantry is not a good thing. For the base it's a good thing because it's a very rigid box type of structure, but the gantry is not and is prone to all kinds of vibration and resonance. And once this happens the mass is not in your favor. Once the gantry starts to vibrate the mass is a big problem. Stiffness and dampening and low to moderate mass I think are the most important features of a structure that is prone to vibration and resonance. The ideal gantry might be a structure that is steel skin on the outside and heavily braced with cement or EG fill near the bottom of the vertical uprights that attach to the base. But as you go up it might be better to have more bracing and a light weight sticky expanding foam or a EG constrained layer damped structure that limits the mass.

    Just my two cents. I'm looking forward to what you are going to cook up for this project.



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    Default Re: Thor

    Quote Originally Posted by Hezz View Post
    I was thinking about heavy steel members filled with the high performance concrete. Not small tubes. 6-8mm sheet steel fabricated and internally braced to the shape that you had designed. Basically, my idea was to make the mold out of reinforced steel and It would out perform the concrete unless the concrete was made at least four times bigger or so. If it's steel reinforced in the center it's even better. It is so strong and stiff they use it for earthquake reinforcement on concrete bridges. Of course, this is your project and only you know what your budget and fabrication capabilities are. I don't mean to tell you what to do. The problem as I see it is that concrete does not flex very well without failure. And you will have to make your mold very precise to get the gantry just the right width to bolt it to the base. If there is a gap and you tighten it it may well crack and fail. There just isn't much room for manufacturing error in your design. But with a monolithic steel mold weldment you would have just a little flexibility and a good surface for lapping or grinding to get flat way mounts and

    Actually, I'm kind of the opinion that real heavy mass on the upper part of the gantry is not a good thing. For the base it's a good thing because it's a very rigid box type of structure, but the gantry is not and is prone to all kinds of vibration and resonance. And once this happens the mass is not in your favor. Once the gantry starts to vibrate the mass is a big problem. Stiffness and dampening and low to moderate mass I think are the most important features of a structure that is prone to vibration and resonance. The ideal gantry might be a structure that is steel skin on the outside and heavily braced with cement or EG fill near the bottom of the vertical uprights that attach to the base. But as you go up it might be better to have more bracing and a light weight sticky expanding foam or a EG constrained layer damped structure that limits the mass.

    Just my two cents. I'm looking forward to what you are going to cook up for this project.
    Thanks. Appreciate the comments / input.

    I am a bit limited with respect to doing 'big' steel type of work. I dont have the ability to cut and move large plates easily. That said, food for thought. The concrete gantry would be placed in place and then 'bonded' with epoxy to make up the gap to ensure that I do not 'flex' anything when using rods / bolts. I have some 100 x 100 x 5 lengths left over from the build of the metal frame, not sure if there is any benefit in trying to create an 'A' Frame (side view) from it.



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    Default Re: Thor

    Quote Originally Posted by Chazaxl View Post
    Thanks. Appreciate the comments / input.

    I am a bit limited with respect to doing 'big' steel type of work. I dont have the ability to cut and move large plates easily. That said, food for thought. The concrete gantry would be placed in place and then 'bonded' with epoxy to make up the gap to ensure that I do not 'flex' anything when using rods / bolts. I have some 100 x 100 x 5 lengths left over from the build of the metal frame, not sure if there is any benefit in trying to create an 'A' Frame (side view) from it.
    I think that there is a great benefit in building the side frames and gantry out of steel and then filling them with your concrete mix. Although I would fill the gantry with lots of bracing and expanding foam instead. If you make a kind of A-frame out of the 100 x 100 mm tubes with the thickest steel plate in the middle that you can work with you can make a system that will be a lot easier to align and be even stronger than you first intended. It can also be made to bolt to the base instead of being permenantly glued so it can be shimmed and moved forward and back and up and down a little bit.

    I'll make of quick mockup to showl you the idea. But of course it is only for your consideration.

    Attached Thumbnails Attached Thumbnails Thor-cement-steel-mill-quick-mockup_1-jpg  
    Last edited by Hezz; 09-03-2016 at 07:48 PM.


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    Default Re: Thor

    Quote Originally Posted by Chazaxl View Post
    No, the flatness is created by pouring the DWH epoxy and then lowering a reference surface onto it like a mold. Once its lifted, it 'copies' the shape. So in my case I used a large 'block' of metal which is flat as my reference. Ill find more pics of this.
    Thanks for the comments.
    What did you use?
    Show me



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    Default Re: Thor

    Quote Originally Posted by danande View Post
    What did you use?
    Show me
    Sorry, been busy.

    Place epoxy, (ignore the paper towel, the consistency was too liquid, but we created a dam for the epoxy). Then lower a reference surface (the 400 kg block used), let it dry, lift. The surface is not smooth (it copies the structure that leaves an imprint) but its flat.







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    Default Re: Thor

    What is that big thing?

    The surface you used looks like it's been ground. But what you did was make a negative of the surface on the block. It's enitrely possible that the surface of the block has pits and scores, which will be high points on your epoxy surface..
    I've thought about this too, but ended up getting my surfaces blanchard ground for my rails.
    I think ideally you should have transferred the negative of that block onto something like a stiff 50x50 shs and then use that negative to create a flat surface.



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    Default Re: Thor

    Quote Originally Posted by danande View Post
    What is that big thing?

    The surface you used looks like it's been ground. But what you did was make a negative of the surface on the block. It's enitrely possible that the surface of the block has pits and scores, which will be high points on your epoxy surface..
    I've thought about this too, but ended up getting my surfaces blanchard ground for my rails.
    I think ideally you should have transferred the negative of that block onto something like a stiff 50x50 shs and then use that negative to create a flat surface.
    Agreed, its not perfect but from what I can do at home, its reasonable. The aim is to improve the machine as I go and aim to get better and better with the tools / machines I have available.

    I bought a 600 x 600mm surface plate which I was going to use but I needed 1.2m which the steel structure gave me most of (900mm +-).



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    Default Re: Thor

    It's possible to buy granite straight edges of various lengths for "affordable money". They seem to get expensive quickly past 1m / 3 foot, but I wonder if there are chinese ebay equivalents? These would seem to be fantastic for moulding like this. eg use something like precision parallels to support the straight edge, fill below with resin. It would seem possible to do multiple 1m lengths pretty accurately using only a 1m edge, start in the middle and work outwards (or otherwise shim the outer supports to be inline with the first 1m section)?

    I would be interested if this gives better precision (or is easier) than simply relying on gravity to spread everything easily? I realise you are still left needing to get each individual rail to the same height/in the same plane, compared with a solution that has a channel between each rail... Problem?



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    Default Re: Thor

    Quote Originally Posted by the_wildgoose View Post
    It's possible to buy granite straight edges of various lengths for "affordable money". They seem to get expensive quickly past 1m / 3 foot, but I wonder if there are chinese ebay equivalents? These would seem to be fantastic for moulding like this. eg use something like precision parallels to support the straight edge, fill below with resin. It would seem possible to do multiple 1m lengths pretty accurately using only a 1m edge, start in the middle and work outwards (or otherwise shim the outer supports to be inline with the first 1m section)?

    I would be interested if this gives better precision (or is easier) than simply relying on gravity to spread everything easily? I realise you are still left needing to get each individual rail to the same height/in the same plane, compared with a solution that has a channel between each rail... Problem?
    I believe the gravity / flow method does not work. As we know there is a 'layer' which will always not be 100% flat. If you fill a glass, you see it on the edges. You can cut the edges off.

    The method I use here (lets assume the block / granite) is perfect, works. Shrinkage is minimal.

    This shows the same idea, albeit with Moglice (which is a surface which it runs on but it 'copies' the structure perfectly.



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    Default Re: Thor

    Quote Originally Posted by the_wildgoose View Post
    It's possible to buy granite straight edges of various lengths for "affordable money". They seem to get expensive quickly past 1m / 3 foot, but I wonder if there are chinese ebay equivalents? These would seem to be fantastic for moulding like this. eg use something like precision parallels to support the straight edge, fill below with resin. It would seem possible to do multiple 1m lengths pretty accurately using only a 1m edge, start in the middle and work outwards (or otherwise shim the outer supports to be inline with the first 1m section)?

    I would be interested if this gives better precision (or is easier) than simply relying on gravity to spread everything easily? I realise you are still left needing to get each individual rail to the same height/in the same plane, compared with a solution that has a channel between each rail... Problem?
    The problem with the Chinese stuff (lets assume quality is good) is shipment cost (to the UK) as well as import cost. I did look at it. I paid £200 for a decent granite block 600mm x 600mm. This goes up to £900 for anything that is a meter long, then there is the weight of moving the damn thing.



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    Default Re: Thor

    Yes, there will be a "meniscus" wherever you have a liquid meet another solid surface. However, I'm not sure that this is a problem, you will need to cut it off for sure, or arrange that you make the resin pad wide enough that the meniscus doesn't effect the central area where you want to install the rails

    Won't we have exactly the same problem with the press method as well? You need somewhere for the excess to go? I see you could have it squeeze out the long sides, but then you will get something similar to a meniscus. Or you could get complex and have some way is squeezes out the short ends, but that sounds problematic to arrange (and you still have a bit to chop off)?

    Seems the simplest is to make the pad wider than needed and ignore or chop off the edges? How have you handled squeeze out of the excess?

    Note, ebay occasionally has affordable (second hand) large granite plates going for sale. I would assume they are pock marked and well used, but it seems these could be sliced up to make the actual rails or gantry for a machine (or even a whole table), ie you get one flat side on a thick granite slice (at worst with some low points)? One issue is that the most common large size is 3 x 4 feet, I think you would want something a bit larger for a whole table or gantry (big arse machine)? Definitely seems like an interesting option for a smaller machine though. There is a chap on youtube with a micron accurate lathe, built using a bunch of cheap (in the USA) granite parallels. The bearings are all air bearings and he claims the machine accurate enough to make air bearings. I can dig it out, but probably it's well known? Anyway, I pondered if the basic design would allow for a fairly simple build and somewhat affordable cost for a high end accuracy and stiffness mill machine.... (I see a number of significant challenges though)



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    Default Re: Thor

    Quote Originally Posted by the_wildgoose View Post
    Yes, there will be a "meniscus" wherever you have a liquid meet another solid surface. However, I'm not sure that this is a problem, you will need to cut it off for sure, or arrange that you make the resin pad wide enough that the meniscus doesn't effect the central area where you want to install the rails

    Won't we have exactly the same problem with the press method as well? You need somewhere for the excess to go? I see you could have it squeeze out the long sides, but then you will get something similar to a meniscus. Or you could get complex and have some way is squeezes out the short ends, but that sounds problematic to arrange (and you still have a bit to chop off)?

    Seems the simplest is to make the pad wider than needed and ignore or chop off the edges? How have you handled squeeze out of the excess?

    Note, ebay occasionally has affordable (second hand) large granite plates going for sale. I would assume they are pock marked and well used, but it seems these could be sliced up to make the actual rails or gantry for a machine (or even a whole table), ie you get one flat side on a thick granite slice (at worst with some low points)? One issue is that the most common large size is 3 x 4 feet, I think you would want something a bit larger for a whole table or gantry (big arse machine)? Definitely seems like an interesting option for a smaller machine though. There is a chap on youtube with a micron accurate lathe, built using a bunch of cheap (in the USA) granite parallels. The bearings are all air bearings and he claims the machine accurate enough to make air bearings. I can dig it out, but probably it's well known? Anyway, I pondered if the basic design would allow for a fairly simple build and somewhat affordable cost for a high end accuracy and stiffness mill machine.... (I see a number of significant challenges though)
    Thanks. Well aware of the micron lathe, source of inspiration. In the UK, these components are a lot less common than the UK. I looked at using air bearing components but the cost of new is too expensive for me. I also looked at building machines from solid granite blocks, this has merit but also has its own issues.

    In future, I'd probably look at building a custom metal form, casting into it and having professionally machined 'reference surfaces' that can be lowered to form templates against.

    Agreed on the excess. In my case one side was done intentially to come out the side and make a side layer which I later chiseled off. The rest did not come out and the 'end' of the putty is always lower. There is enough width in the 'centre' to support the rail. The rails are 45mm wide, the putty was 55mm.



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    Default Re: Thor

    Any updates on Thor?

    CAD, CAM, Scanning, Modelling, Machining...


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    Default Re: Thor

    Quote Originally Posted by mcphill View Post
    Any updates on Thor?
    A few but slow going :-(

    Ive cast the gantry, waiting for it to fully cure so I can move it. Hoping to get some momentum back into the machine building asap.



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    Default Re: Thor

    Been a long time since an update. I tend to update a thread on our UK Cnc forum.

    So, an update.

    I managed to epoxy the gantry to the main body. Scary stuff this. Will some 'glue' hold an estimated 750 kg weight? Seem it does.



    Next step was to rotate the mass and remove the table as I needed access to the rails.

    Ignore the loose rails in the middle of the lower part.





    I then, with a lot of effort, lift my 300 kg 'reference' onto the rails, align and mount so that I can use this to get the epoxy set against the gantry.




    The nett result is that I have something that moves forwards and backwards that is aligned to the bottom rails and should therefore be square once moulded. I should be doing the epoxy pouring this weekend.



    Some of you might note that the reference part is only 50% of the width of the gantry. I dont have a larger reference surface and using it on its side means it will be too low.

    So two options. I can either mould this width and then use a surface plate that I have and basically overlap until I get the full width.
    Second option (and what I have gone for) is to basically put 100mm wide (the rails are only 40 but I need some extra height for the adjustment up and down) 30mm thick alu tooling plate (Eco Cast). I know its not perfectly flat but I am hoping this will be reasonable. Ill bolt this to the reference square and see how this looks.





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    Default Re: Thor

    Mounted the tooling alu, a quick sweep tells me it looks to be accurate to within 0.05mm. Not ideal but not bad for a garage job.

    Around 6 coats of carnuba wax later, we are ready to pour the epoxy.









    The epoxy takes 24-48 hours to set but will leave it for the week and remove the reference table / plates to see the result. Then it will be a case of drilling holes and mounting the rails which is a pain in the backside. Not sure yet how Im going to epoxy the nuts in yet - when doing it from the top, gravity helps. On its side, not sure.



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    Default Re: Thor

    Success!

    Apart from some places that remained a bit unmixed, the rest has gone hard and is mirror smooth.

    Removed the reference frame, alu still 'stuck' to the epoxy.



    Then, a bit of prying with a crowbar and both parts are off.

    The remaining epoxy is smooth and even has the tooling marks that transfers across from the plate.

    A quick test with a straight edge confirms all is good. A quick test with the rails indicate they arent perfectly straight (This will be fixed as they get bolted down).







    Next step is to drill two holes, around 1/3 from each side and mount, get basic alignment, using reference piece for X travel height calibration. Marking the rest of the holes, drilling, then mounting with another alignment test. This takes ages as I need to go to around 26mm from memory and there are many to drill into this hard concrete.



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