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  1. #61
    Thanks for that, I guess that would be more than acurate enough considering the runout/bend of the ballscrew could be more than that.
    Cheers, Charlie

  2. #62
    Quote Originally Posted by CharlieRam View Post
    Does this bed design look better? It is still made using 1 off 80x40x4mm 7.5mm long and 2 off 50x50x3 7.5m long steel.
    I keep going back to my bed design and I'm wondering, for a novice welder (zero experience!) will I need to add adjust-ability into the X rail supports, I have allowed for 5mm thick epoxy but I am just a bit concerned about welding the frame only to find it is twisted or out of square?? If I were to make the X box section bolt on to the bed frame rather than welded would it be strong enough and would I be able to skim the 80x40 seating face acurately enough to bolt the rail directly without the need for epoxy.....I think what I am asking is 'how flat does the seating face need to be? less than 0,01 or is it more forgiving than that?
    Also if I go the epoxy route I have read people say drill and tap after applying the epoxy, could I do that with a standard drill or would I need something like a magnetic drill press? I was thinking to drill and tap the holes and coat some bolts with molten wax and then fix them in place before pouring the epoxy, would that work or not?
    Cheers, Charlie
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    Last edited by CharlieRam; 23-09-2014 at 09:09 PM.

  3. #63
    You want to try to avoid welding directly to the X axis box section. You can weld a 10mm plate to the top of each upright along the X axis then bolt through that plate into the X axis box section.
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    Last edited by IanS1; 24-09-2014 at 06:13 AM.

  4. #64
    This is what I had in mind, There will be aluminium blocks in each end of the X box section tapped to accept the the two bolts through the legs?
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  5. #65
    Nothing will happen if you weld carefully, tack everything together, don't make stitches bigger than 5cm, use your brain to figure what to tack before so it would not twist and most of all be patient. It really takes a lot of time welding a CNC frame.
    What you suggest is alternative but people go further this way and don't use epoxy at all / only at the shims/

    Anyway, most of all you should care for your top 2 rails to be more or less in the same plane. On paper the epoxy to spread the force needs to be minimum 3mm thick, so basically that's your limit. You can pour more than 5mm if needed.

  6. #66
    My prefered way is to use adjustable top rails and shims as it's more foregiving and can be better tweaked. It's does take longer much longer than epoxy with lot of time needed to get perfect but when done thats it. Also if the machine frame releases any stresses overtime you can adjust this out if need be which you can't with epoxy.

    I'll repeat for the million'th time but build in has much adjustment as possible and brace the hell out the frame and you'll have very very strong machine that's foregiving to those with limited means or engineering abilty. Silyavski as said everything regards welding except spread the heat around and don't weld in one spot for too long. Take breaks and it's a bit like eating an Elephant.? Lots Small bites.! . . . .. This goes thru out the build take it in small bites don't rush just to get it done or the machine will suffer for it.!

  7. #67
    Quote Originally Posted by CharlieRam View Post
    This is what I had in mind, There will be aluminium blocks in each end of the X box section tapped to accept the the two bolts through the legs?
    As Jazz as pointed out, the more adjustability you have, the better. Cutting and fixing the ends of the X box section the way you have drawn could make the adjustability more restrictive. Also, bolting through the end uprights may cause the frame to warp as you tighten the bolts.

  8. #68
    Your frame is similar to mine, this is what I did;

    http://www.mycncuk.com/threads/6565-...2425#post52425
    But I also welded matching 10mm 'pads' onto the underside of the X box section, http://www.mycncuk.com/threads/6565-...4294#post54294
    That was a mistake I think ! http://www.mycncuk.com/threads/6565-...4024#post54024
    I always intended to use epoxy as well.

    Instead of welding to the underside of the X box section, I would glue a piece of flat bar inside it using Gorilla Glue, similar to this ; http://www.mycncuk.com/threads/6565-...4981#post54981
    because it increases the wall thickness of the box section allowing a secure fastening through the plates welded to the top of the legs.
    Last edited by EddyCurrent; 24-09-2014 at 09:04 AM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  9. #69
    Quote Originally Posted by JAZZCNC View Post
    I'll repeat for the million'th time but build in has much adjustment as possible
    This is why I revisited the frame but what about the rail mounting surface, would it be accurate enough to skim the top face on a milling machine and bolt the rails directly to this or do you still recommend the epoxy and if I go the epoxy route would I be able to seal all the threaded holes by covering the screws in molten wax or will the epoxy melt the wax while setting?
    Just to say, I am a competent machinist and I'm quite confident in my skills, it is the welding that I will struggle with but I'm sure it will come good!
    Cheers, Charlie

  10. #70
    Yes skimming surface will be fine and all that's needed. Then just shim the rails onto same plane if needed.

    Welding at this level is simple just practice on some scrap and you'll be fine. Where not welding oil rigs here so bit of pigeon shit is fine and it all cleans up with a grinder.

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