Re: techniques for capping steel tube?
- From: utahparx <redbird@xxxxxxxxxxxx>
- Date: 20 May 2007 09:05:59 -0700
It depends,
you did not give us the wall thickness of the tube?
do you want a flat end with sharp square edges?
or do you want the edges softened and with a rounded edge?
IMHE, the object in fab fitting is to design the joint so there is room for
the weld puddle to fill and not be forced to sit on top above the surface
level. IMHO, the better the weldor and the joint design, the less grinding
will be required.
If you want to have sharp square edges then any of the other suggestions for
fitting the cap material inside the tube are good but I would suggest you
use some combination of bevel and/or gap to give the weld someplace to fill
so the surface will be reasonably flat, but without undercut. Using a
thicker capping material will make the job easier as this will tend to carry
the excess heat away and reduce any tendency to burn through and leave
holes. IMHO, this will be the easiest joint to make and if the tubing wall
is very thin will be the best.
If the tubing is heavy walled and you want to have a rounded edge, then I
would suggest the cap plate be a thickness just slightly smaller than the
tube wall and be fitted to sit on top of the tube and be only slightly
larger than the tube inside. This is the classic outside corner weld, this
joint will require more control of weld shape and the choice of rod size is
more critical, smaller rods (3/32-1/8") and lower heat will make it easier
to control the puddle shape and prevent the puddle from bulging excessively.
The edge of the nicely convex bead should just reach the edges of the tube
and the cap plate while still fully filling the corner. If done properly
and depending on how smooth you desire the finish to be, this joint should
require a minimum of grinding to clean up. IMHO, This joint is more
demanding of operator skill, and the best weldors will do it with only
minimal cleanup as the weld itself is a demonstration of the weldor's skill.
If the tube wall is thin and you desire rounded corners, then a combination
of these joint designs may be best. Here I would suggest using a thick cap
plate cut to fit tightly inside the tube and driven inside so that the top
of the plate is the same distance above the tube end as is the tube wall
which will also result in a classic outside corner weld.
your point about cap thickness is well made-
my first efforts involved a cap that was much thinner than the tube
wall and as I made the corner weld, i kept burning the cap away. more
material (and possibly a flatter drag angle) would have made it way
easier.
IMHO the worst joint design would be to cut the cap the same size as the
outside of the tube and to bevel the tube end or the cap or both and then
weld around the outside of the tube. This joint design will be difficult
for all but the best weldors to make visually appealing.
Good luck, YMMV
thanks for the great post.
.
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