Originally Posted by
handlewanker
Hi, for what it's worth, I think the bogey of welded structures is very over rated in that it appears that if you weld something then it walks around as it twists and bends......for some reason.
I worked in the industry making linear transfer machines for the car industry......they are long machines that have, in the one I worked on, 21 stations, each station doing a separate operation....total machining time for the job passing through the machine is determined by the slowest station operation, which in this case was the inlet manifold for a Holden 4 cylinder engine......40 seconds.....a raw aluminium casting is robotically loaded and unloaded in 40 seconds totally finished machined.
The various stations were ALL built up from welded plate material and aligned separately in the manufacturing facility.
These machines run for several years and I don't think they have weldment distortion problems during that time.
When a structure is welded it DOES get stresses locked in, but they only become apparent when you subsequently machine chunks out of the structure and the contained stresses pull the frame out of wack.
The worst you can do is to clamp a welded structure and twist it before machining.
It is advised after welding a structure to mill all surfaces that require to be connected accurately with another part.
Provided you don't remove significant amounts of material then distortion is not a problem.
Therefore, when you proceed to machine a welded structure, use packing material under the points that sit on the table to keep the structure in it's finished welded state, then you can machine it without the frame twisting back after the clamps are released.
Practically all the distortion I've seen in welded structures is caused by incorrect clamping prior to machining.
On the subject of the X2, it's not a bad mill as mills go, made down to a price etc, but it does give you a basis to start with when you want to improve it by extra work and fitting........the extra cost is minimal if no new parts are added.....labour is only a figure for accountants to worry about when you are being paid to do the work.
I think I could state correctly that if the dovetail slides are not accurate in their surfaces then it probably was so when the castings were machined and the finished machine part was released from the clamping forces.
If you have to apply manual alignment for setting up a casting on a machine prior to machining the raw casting, as opposed to just putting it into a jig and clamping it wherever it sat, then the cost would double if not more.......and I think most if not all of the time the person doing the machining will be an operator who just loads the part to a jig and presses the green button whatever may be the state it gets clamped in.
This is OK for an economical machining cost factor, but totally hopeless if you want to have a precision machine that is good to go from the box, but it's a good starting point as long as the initial purchase is cheap.
You wouldn't want to take a precision manual mill that cost 2 or 3 times a much because it was precision, and then hack it about to retrofit it for some CNC purpose.
Ian.