Sturdy and Fast all Steel CNC , my first build

[Neale]

Well, that's an obvious way to set up the epoxy on the gantry. You know, the kind of "obvious" that's only obvious when someone else says it!

I've been kicking ideas around in my head for the last week or two about how to align the Y rails for "constant spacing" if I put them on the top and bottom of the gantry bars for my new design. Easy enough to lay the gantry on its back and use epoxy to level the Y rails on the front face, but I couldn't work out how to do it where the fixing faces for the rails were not in the same plane. Easy enough if you have an accurate level surface to put the gantry on and do one rail at the time but how do you generate that initial level surface in a home workshop? So use one of the level surfaces you created when you used epoxy to set up the X rails! As I say, it's obvious once someone else has pointed it out...

In practice, any idea of how much out of true a typical length of, say, 50x50 or 80x80 steel tube would be? Are we talking about a mm or two, or significantly less than that? How much does the epoxy thickness vary, in other words?

[njhussey]

In practice, any idea of how much out of true a typical length of, say, 50x50 or 80x80 steel tube would be? Are we talking about a mm or two, or significantly less than that? How much does the epoxy thickness vary, in other words?

This should help http://www.parkersteel.co.uk/media/p.../JPSBS0010.pdf I was looking for it yesterday when I wanted to look at how "true" my beam might have been. Don't forget you're also at the mercy of the stockholder and transport to keep the steel flat and not to induce any additional bending/torsion etc...

[CharlesJenkinson]

Very interesting build, and good research for me. A weld bead causes shrinkage where it is deposited, so weld induced distortion is not so much due to the 'heat' that goes into the part, but is due to the fact that a weld, when solidifying, pulls on the adjacent parent metal. Apart from looking nice, I'm not convinced these types of bed frames, with massive members, need to be fully welded at the joints, from a stress point of view anyway - stitch welding would be perfectly adequate - having said that, the effect of inducing bending due to weld shrinkage is possibly only noticeable on smaller dimension square hollow section, less than 70mm say. The effect of weld shrinkage induced distortion may be mitigated where possible by welding to the perpendicular plane of the material, if that plane isn't as critical for flatness, and the design configuration suits it - I don't think it applies in this particular build case though.

Sorry to theorize in your build thread - being a noob, I guess I'm eager and this seemed an appropriate, and reasonable relevant place.

[JAZZCNC]

Apart from looking nice, I'm not convinced these types of bed frames, with massive members, need to be fully welded at the joints, from a stress point of view anyway - stitch welding would be perfectly adequate - having said that, the effect of inducing bending due to weld shrinkage is possibly only noticeable on smaller dimension square hollow section, less than 70mm say.

Charles Very true regards Stitch welding being plenty strong enough if done correctly but even larger dimension SHS will distort if the heat put into it is too great. Spreading the welds around and keeping the bead length down to a minimum is very much needed with any size material if distortion is to be kept to minimum.

I've just got my self a New 250A AC/DC Tig welder with pulse and I love it for just this reason as the heat is kept very isolated to small area. Fact I can weld thick Aluminium plate as well as thin Aliminium plate is lovely as well.

[Neale]

Any chance of some advice on best welding strategy for welding novices like me? Starting with the assumption that we are welding box section (I'm probably talking 50x50x3 in my case), what's the best way to get an accurate frame that's not going to distort as you add bits on? I'm starting to hear things like tack welds to hold it all together, then add more tacks/spots for strength, but continuous welds at the joints are not needed.
Specific example - you are welding two pieces of box section that meet as a Tee. Couple of spots on the "internal" corners so that you don't pull the pieces out of plane, then tack the sides, then add a few more spots for strength?
I'm guessing that all this is blindingly obvious to an experienced welder but I get the feeling that a lot of people cut their welding teeth for the first time building a router!

[CharlesJenkinson]

Erm, I don't have vast practical welding experience, but I'd say two decent 30mm long 3 or 4 mm leg fillet, i.e. one in the middle of each of the 2 flush butting sides of that joint should hold it good, for strength - just weld through (over the top of) any tack you've put down. I don't see any point welding round the corners or trying to fill the whole void in where the square cut end doesn't meet the radius edges of the mating member - doing this is just adding loads of extra heat and metal that isn't doing anything. The important point about tacking together is to set and maintain the WHOLE assembly geometry before laying heavier deposits down, so if you have any gussets orbraces supporting the ends of your T assembly, IMO they should be tacked in after the T is tacked together but before putting the structural welds down.

[njhussey]

I'm no expert (I seem to weld every 4 years or so) but what I did was cut the pieces to length, dry assemble the uprights and the main frame outer pieces then put either one tack or a couple of tacks on each piece.



Then I got a square and spirit level and made sure all was as good as I could get. I then tacked in the bed braces..



I then checked all was square again before starting to add the angle braces...



I then checked that the uprights were still square and all was good and then started welding the uprights. Now here I confess I didn't do it in small short runs spread out round the frame like I probably should have. I just did it in one or two runs per weld (50mm long welds as using 50x50x4 box)



I then checked to see if all was still square (otherwise the angle grinder would have to come out!) and then proceeded to weld up the rest of the welds. I didn't do it in any particular order (it was pretty random) and then after finishing the frame (but without the X axis rails welded on) I checked all the frame was still level and the uprights were still 90° to the bed.



I then offered one X axis rail up, clamped it with F clamps roughly level and then referencing off the frame rails and tacked it as parallel (using a digital bevel box) as I could. I then put lots of tacks on it, checking in between that it hadn't moved, and then once cool I welded over the tacks in one go.



I then did the same for the second rail checking for parallellness (is that a word?) in both directions with the first rail as a reference but also checking the second rail against the frame to make sure it wasn't out. I then did the same weld procedure for the second rail and it turned out pretty square and parallel....probably more from good luck than skill!

[Neale]

All pretty obvious, then - the kind of "obvious" you only see when someone's pointed it out!

Thanks for the idiots' guide (and I'm the welding idiot, just to make it clear!).

[njhussey]

All pretty obvious, then - the kind of "obvious" you only see when someone's pointed it out!

Thanks for the idiots' guide (and I'm the welding idiot, just to make it clear!).

I knew what you meant......I also class myself in the category of welding idiots. I just put it together and once I was happy it was square I wacked the welds on regardless of putting too much heat (see told you I was a welding idiot!!) in to the frame. I seem to have got away with it.....so far!!

[JAZZCNC]

To be honest it's not rocket science but the Welder your using does make a difference to some degree.

Arc or MMA welders put a lot more heat into the steel than Mig or Tig so it's a good idea when using Stick to keep runs shorter and spread them around but keep balanced. By balanced I mean if you weld Left side of material for 1 " then weld right side 1" at same time before moving to another spot.

For general steel work then Mig is best has it's relatively quick and easy to learn but it's not has cheap has stick to buy equipment.

Tig is best for controlled heat but it's slow and more specialised and expensive so I wouldn't use it for steel frame work. (unless using MMA option)

Just for building a one off frame and keeping costs down then MMA(Stick) is best has it's cheap to get setup and not too difficult to learn.

Just remember bird shit can be scrubbed away so tis is true with welding and grinder is your best friend. . Lol

Welding and Epoxy leveling make steel frames very easy and cheap to achieve.