Only trouble is how easy "max" makes it look to get a perfect weld!! I was more than a little disappointed with my first couple of attempts!
I'll say it again just to be clear.!!. . So long has the welds are kept Short 1"-2" Max and Don't weld in one spot moving around the frame you'll be fine. Even just welding several short bursts and having a break to prevent heat form travelling if your unsure will help. . . . Remember it's DIY so there's no Rush it doesn't have to be done in same day.!
Milliput - The epoxy putty with a thousand uses in modelling, DIY and industry
Comes in sausage shaped cellophane wrappers. Easy to use just mix equal parts in your fingers just like mixing Play-doh. Then spread on Clean dry surface and sets like concrete in about 6-8hrs, packet says 3-4 but I've found it's longer and leave over night. Leaves a super flat surface it can be tapped, filled and ground just like steel.
Here's Where and how I use it. It's also why steel or frame distorting slightly is no big deal.!!
Most of the frames I build are a mix of welded and bolted like these pics below. ( Frame only here no Bed, it's adjustable) At the joints and where top rail sits on plates is where it's used.
When I'm all finished and welding up then I bolt frame together to get an idea of how far off things are.? Most the time they are hardly off at all and just a quick grind or tweak of mounting plates brings it near enough to call Ok.!! . . . Some times shims may be needed.
Remember the rails being parallel and on same plane are the important areas and because the top rail is Bolted we have complete control and adjustment of this. It also doesn't get welded so NO distortion happens, just choose the straightest unbent piece you can find. (We have ways around bent rails has well but won't get into that now.)
Now in most cases after shimming or grinding true and square I could leave it at this but I don't. I go one further and disassemble again this time rebuilding with Epoxy putty at each joint with cellophane between to prevent sticking together.
This gives me about 1hr to set the frame square and true, Doesn't matter if the welded frame isn't quite square or plates not perfectly flat etc because the putty is going to take up any slack. . . . . So long has the shims from first assemble are used then All that matters is that frame is SET square and uprights vertical Now because Putty's going to fill any discrepancy and when it's set solid over night you have perfectly flat and true surfaces. The shims can be removed or set left into Epoxy.
Now where not talking 5 -10mm thick epoxy pads here, there often just wafer thin just filling voids etc.
Drilling and pinning the joints with dowel pins helps make sure everything goes back in same place and makes assembly easier.
Again the main frame being 100% perfectly square isn't overly important, it's the top rails that matter.!! . . Can't stress this enough.
Now what can be more of a pain to deal with is Twist of welded sections from distortion but again depending on design etc this can be got round. Often it's just a case of forcing the twist out by twisting in opposite direction, if twist is happening then you can often see it has your welding so stop and twist it back. This is also why spreading the welds around is important.
The bed is the main area you need to keep an eye on distortion and even then again Epoxy can be your friend if really bad and with a bit of Brute force and epoxy if need be then the Bed can easily be sorted to within a knats cock. When spoil board is surfaced then it will be Cock On.!!
Now here's what the scare mongers, who probably have never built a steel framed machine are not saying.? . . . If at first you don't succeed just grind the bastard apart and re-weld or re-set that's one of the beauty's of steel is it's flexibility for having another crack at it.
Last edited by JAZZCNC; 11-08-2013 at 08:44 PM.
Ok - design progress time.
I've been focusing on the frame/table so far - its now at a stage where i'm pretty happy with it & I think i've added everything that I meant to.
red = 60x60x4 box
blue = 50x50x3 box
green = 60x4 flat bar
orange = 50x4 flat bar
Rails are sat on 50x10 ally flat.
Ignore the floating guide leadscrew for now - its just there as a vague reference as to where i'm planning to put the leadscrews at the moment. Also ignore the holes going through the outside of the legs, they won't be there when I make it.
The frame has the ability to be adjusted for square in every direction. The cutting surface can be positioned in 5cm increments down the legs.
Both the lower surface & cutting surface will be covered in mdf added further bracing.
Hopefully this will mostly get nods of approval so i can move on & start thinking about leadscrews, motor mounting & the gantry in more detail.
Ok looking much better.!! . . . Take it you have decided not to weld.? If so Not saying this is bad thing if that's what your most comfortable with but will be a lot more work and maintenance. Mixture of both works best IME.
Only thing I see and question is DO YOU really need that much adjustabilty of the bed.? If not then I'd raise the lower frame and increase the triangulation. Will just help stiffen the frame a little.
There are still welds in there - I think I need to see how I get on with the welding to see how accurate I am with it...then if I feel confident enough, i'll drop more of the bolts & weld instead (like the table surface). I do want to make it so that the whole frame can come apart into manageable sections for moving house etc in the future.
Regarding the height adjustment - I don't know is the short answer...I've seen that others do it & it might be useful for me at some stage - but I don't have any examples in mind. In reality I probably don't need that much. I'm also still playing with the overall dimensions a little - so i'll still be tweaking for a while.
The frame at the moment should be a decent height for me to work at - i'm conscious of making it too low & giving myself back issues (which I get from time to time)...more cross bracing can be added at a later date easily enough.
Most of the frames I build are a mix of welded and bolted like these pics below. ( Frame only here no Bed, it's adjustable) [/QUOTE]
Jazz, do you mind explaining how the bed adjustment holes work on the frame pictured. It looks like you have another tapped plate or something inside the RHS? Cheers
The main bed frame is heavy so there's 4 lead screws (2 each side) to help lift up and down and roughly get into position. Then there's 8 angle plates(4 each side) fastened to bed frame with 2 holes in each so 16 Bolts total that bolt into uprights with 10mm tapped plates inside.
It's simple and easy thou to be honest it's not something you do very often has usually you'll settle on a position that allows 90% of what you want to do.!. . . . It's just nice having the flexibility to do oversize things when needed.
Last edited by JAZZCNC; 13-08-2013 at 06:09 PM.
The Following User Says Thank You to JAZZCNC For This Useful Post:
Chaps - i'm dithering about with the gantry quite a bit...can't come up with an approach that i'm happy with yet.
I've been looking around at a lot of build threads on here & cnczone...I haven't seen a gantry design that seems to suit what i'm doing.
Firstly - do I need to be concerned about weight. ie, am I ok using steel box or is this something that I may regret later?
Secondly - Jazz, the mock up design that you posted earlier in this thread - the gantry on that has 2 lengths of steel box attaching to vertical end pieces. I assume this would have to be a weld - my concern here is alignment & the lack of adjustment. Is there another way of going about it?
I'm trying to keep the range of materials that need to be purchased down...i've been looking at using aluminium box with a vertical plate - but it starts upping the budget quite quickly.
I'll also drop in a note here that I also really like the simplicity of KingCreaky's gantry...cheaper than some options, but the ally rect box & front plate add up quite quickly.
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