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Thread: Look at my bottom

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    Look at my bottom

    Ok, anything for a laugh.

    Thinking about the construction of my router base at the moment. I am going for a welded base of either aluminium of steel. I can weld steela bit but not ali and I can get either of them welded in the department however ali will take more setting up and the technician time is scarce enough without doing things for me so leaning to steel.

    Anyway here are a few ideas. I got some inspiration from a book called "Design of Weldments" by Omer Blodgett. The book is really good and describes how machine bases and other structures of superior stiffness and rigidity than cast iron can be made by welding steel providing the correct structure is formed.

    The basic way to get a really rigid box is to add gussets that run diagonally in a criss-cross nature. It seems that having these members at 45 degrees to the "box" is important and there is a great picture in the book of test structures showing this.

    There is also mention of adding slots for fixing things to beds. This reduces the strength of the bed unless the individual sections of the bed are tied together some how.

    Attached are a few possible methods of doing this, the u-channel one is much like the book, not as good as the gusset lattice but good. I am going for the one with the V channel (my own design), I think I can make this lighter than the other and just as stiff if not stiffer. I was going to make a stiff box and add aluminium t-slot material to the top but with this method I will end up with steel slots and also save some cash which I really need to do. The choice of V slot is based on availability, it makes the machining a tad tricky but not really that bad. I am not sure but I think the V may also be a bit stiffer.

    Sorry to waffle, just thought I would start the ball rolling on this subject.

    Cheers,

    Graham

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  2. #2
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    Oh, the big blocks on each end of the left most picture are to support my gantry rails (they may remain as beefy ali extrusion I already have).

    Graham



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    just curious .... you didnt mention the overall size of your table and I was thinking .... all the time and effort to weld up your table you will have a lot of heat in this and I'm not sure how flat it will be when you are done .... I looked at it and was thinking why not just make it out of solid stock Al or steel machine in your t-slots and be done? you would have a stiffer base with alot more meat to keep vibration and movement down ... just my thoughts

    Mark



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    The base is 730X730mm

    The cost of a solid base would be HUGE for equivalent stiffness, it needs to be very thick just to have enough meat for the t-slots. Then there is the weight, a solid block would be impossible to get into my attic where the machine will be kept and also increadably difficult to move about in general. I hope to make a base that is stiff because it is smart not just because it is fat

    Indeed it will warp during the welding process and this is where I am glad to have access to a huge milling machine to skim the surface. If you are getting serious then I think the frame should also be normalized in an oven however I suspect that will not be needed.

    Graham



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    Gold Member WeCheat's Avatar
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    Have you ever thought of using Epoxy and stitch wielding it?? 3m make some epoxy for auto/air craft construction that we have used to make thin gauged parts that would warp very easily if wielded all the way. We Just glue it all together like wood, just not where the stitch wields will be. We get real good result with this method and it is very very strong. Most of your car roofs are done in this manner. You can get the stuff at the auto parts store.



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    What do you mean by stitch welding? Do you just mean intermitant short runs of weld?



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    Graham S...use your approach...boxed members for structural integrity yet light in weight is cool.....more mass in the gantry section to minimize the effects of vibration is also good.



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    Gold Member WeCheat's Avatar
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    What do you mean by stitch welding? Do you just mean intermitant short runs of weld?
    Yes it will be very strong and have a lot less in the way of warping do to the low amount of heat put in to the part.



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    While talking to the guy who is going to weld it he mentioned stitch welding without my prompting, even without the glue it should work well. My book on weldment design also covers welding to minimize distortion, I think you essentially go around tacking opposite corners and allow the structure that provides the eventual stiffness to prevent the distortion. The opposite corner thing is also a little like tightening the bolts on a cylinder head, sort of balancing the forces.

    Anyway I have rough cut the steel, I get the plate for the top (which will be slotted after welding) tommorow, I now need to size the flats accurately and set to the task of making all of those V slots :O



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    Steel now sized and the central slots that allow the diagonals to interlock are cut, marked out all the other slots. Started to make a little template for hastle free marking of all those Vs.



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    Quote Originally Posted by Graham S
    Steel now sized and the central slots that allow the diagonals to interlock are cut, marked out all the other slots. Started to make a little template for hastle free marking of all those Vs.
    Pictures?



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    Will do, should have something worth picturing on tuesday.

    Collected the steel plate that will form the bed itself, it is 730mm X 730mm and 6mm thick, that's 28"X28"X1/4". I assumed being quite thick and expensive that it might be flat, oh well... There was a 3mm box in both directions and one corner even seemed to be turned over slightly. I have managed to get it a lot flatter by bending it on a fly press but it is still far from perfect. I don't want to clamp it flat for the frame to be welded to it as it will just build in stress, I can't mill both sides unless I want a 1mm thick piece of metal at the end that cost X6 as much as it should either.

    So I am going to build the reinforcing framework seperately, plonk the sheet on it and weld it, the weld will have to fill the gaps and epoxy could also be used as suggested earlier. Then after the final surface machining I should still have enough material left for a bed.

    Graham



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