Stainless back purging for tacking

[Mike Wilson]

I'm wanting to make kitchen table legs out of 50mm stainless (304) box tube it'll be about 2mm thick. The top will be wood (I'm trying to get bowling alley floor past the wife but she thinks its a bit too quirky) and the legs will be a trapezoid frame that will join up in a loop.

Something similar to this:



I'm using stainless for aesthetics rather than its corrosion inhibition properties. So I guess eliminating sugaring isn't critical but I'd still like to exercise my skills and try to do best practices.

This will be my first stainless project, so I have a couple of questions:

Do I need to / should I try to do back purging whilst tacking together?

Once tacked I guess I use foil backing tape to eliminate too much gas escaping from the edge I'm not welding?

On my last joint (I'm intending on making a frame) I suspect I need to make an inconspicuous argon supply and drain hole for back purging?

Should I use aluminium foil to create the dam and leave the foil in the frame?

Thanks in advance Mike

 

[Richard.]

At 2mm thick for what it needs to do and where it's going to go you would simply be wasting gas purging that. I'd be looking at good fit up and part penetration on the joints. No need to purge it at all just weld it. The trick/skill is how well you finish it. Reinstate your grain, pay particular attention when regraining your mitres.

 

[hotrodder]

Like you say it doesn't really matter for a kitchen table, if you want to purge it for the practice or whatever then from a best practice POV thicker wall stuff that has a root gap for complete joint pen really needs a purge in place for tacking. Thin wall tube doesn't need gapping making it easier to tack up without a purge (without coking it), think small autogenous partial pen tacks

While foil tape is tough it's usually not designed to release cleanly i.e. results in a right sticky mess when removing it. Especially if it's gotten hot in which case it doesn't always stay stuck very well but somehow usually makes everything in the vicinity sticky.
All joints want taping up while estabilishing the purge, if fit up is good can remove the tape one joint at a time without the purge failing. Thicker wall stuff with gaps the tape is more commonly removed in sections, more so with larger dia stuff for obvious reasons.
Regular masking tape is what i'd use, a higher temp/outdoor flavour or some powder coaters masking tape (more ££ but designed to release cleanly after being baked) is better if you need to weld near it

If you wanted to use dams to reduce the purge volume then 2 of the joints can be tackled individually and the dams fished out. Mounting holes for the table top could be used for purging the final welds. That said a 1m length of 50mm dia 2mm wall square tube has a volume of ~2 litres. If this was something that needed purging there's not much point messing about with dams as the total volume isn't gonna be large ... cut, fit and tack everything then purge and weld. In reality, as Richard said, this job is more about finishing and regraining. From a welding POV no undercutting on 3 sides and a small neat fillet on the other is the goal

 

[Shox Dr]

I'd be more worried about movement than sugaring. Any discolouration, will be removed when regained anyway.

As said fit up is paramount esp' if you want all the angles to turn out the same, I would decide on how you are going to tack and then weld and do every one the same, that way any distortion should be hidden.

I would have a 1.6mm rod in hand just in case but all but the inside can be done without... Subject to good fit up.

(I've just bought some 1.0mm Multi-Strike Tungstens, to see if I can get a very small bead on some Stainless, so I dont need to refinish)


Practice, then practice some more. Welding Stainless Steel can be very rewarding, it can also ruin your day. Not to mention the work peice.

 

[Richard.]

I'd be more worried about movement than sugaring. Any discolouration, will be removed when regained anyway.

As said fit up is paramount esp' if you want all the angles to turn out the same, I would decide on how you are going to tack and then weld and do every one the same, that way any distortion should be hidden.

I would have a 1.6mm rod in hand just in case but all but the inside can be done without... Subject to good fit up.

(I've just bought some 1.0mm Multi-Strike Tungstens, to see if I can get a very small bead on some Stainless, so I dont need to refinish)


Practice, then practice some more. Welding Stainless Steel can be very rewarding, it can also ruin your day. Not to mention the work peice.

I don't agree with this shox
I would be using filler on the whole thing (baring the tacks)
Inside corners without filler are just wrong imo. Undercutting and lack of reinforcement are more than likely and I'd still be removing the tint on an inside corner even though the weld would be left in tact. Butt welds would be taken down and the grain reinstated again these fully filled as undercut would show up like a sore thumb.
Outside corners are a maybe and can be done and finished well from an autogenous weld but as it's going to be taken down I'd fill them any way to be sure.

 

[Shox Dr]

True but Its a kitchen table.

Besides I've lost count how many pan racks I've built, I've not had one come back yet.

(Corners; please reread my post)

 

[Richard.]

Not for a second would I suggest your work is not good shox.

I read the post clearly no need to read again. The part I didn't agree on was doing any of it (inside or outside) with out fill.

I think it's better to always use it for full runs especially if those welds are been taken down.

 

[Shox Dr]

If he uses filler he will most certainly have to use a grinder to linish the welds down. It's far from easy to do this on an outside corner, and not get circular marks.

If he gets the hang of welding without rod, the weld will be flat or a little dished, no grinder no chance of marking. So his clean up will be greatly reduced. If he gets them right -colour and all- he might not want to linish them back.

 

[Richard.]

If he uses filler he will most certainly have to use a grinder to linish the welds down. It's far from easy to do this on an outside corner, and not get circular marks.

If he gets the hang of welding without rod, the weld will be flat or a little dished, no grinder no chance of marking. So his clean up will be greatly reduced. If he gets them right -colour and all- he might not want to linish them back.

I know what your saying but I do it a little differently. Each to there own but I would take them all down with a 80 grit flap disc.
I would then use a flap wheel on a battery drill along the grain to reinstate it. I mask off all my mitres on one side with thin sheet so that the grain follows as it should. Colours are a big no no for me I don't like them on nice ss fabs nor do I like linishing marks so I take care to get them out on regraining. Welds on show also a no apart from inside corners which still get buffed up to eliminate the tint but left as welded nice little tidy runs (fully filled). That's how I prefer to do fabrication that's going on show.

 

[Mike Wilson]

Grand, cheers all for your advice.

I think I'll leave the purge, save that for a job where I can tell the difference and go for a tight fit up with partial penetration.

I guess the talk of regraining is post weld finishing with abrasives in line with the metal to retire the aesthetics of the steel.

 

[Richard.]

Grand, cheers all for your advice.

I think I'll leave the purge, save that for a job where I can tell the difference and go for a tight fit up with partial penetration.

I guess the talk of regraining is post weld finishing with abrasives in line with the metal to retire the aesthetics of the steel.

That's exactly what it is.
Please ensure you put pics up of the build and finished item. Would be lovely to see with a nice wooden top on it.

 

[Mike Wilson]

Sure will do the, job may be a month or two off as its to go in a new kitchen that needs starting first.

Thanks again for the help

 

[Mike Wilson]

Right, we'll be starting this project in the next week, steel is ordered and kitchen is finished (including a complete new floor due to woodworm).

We've got some nice chunky hardware to bolt the tabletop to the frame
View media item 9332
and a design drafted out.

My next question for the project is how am I best cutting accurate angles for a good fit up? I have a grinder and a hack saw and some gauges for marking out accurate angles. I have in the past struggled cutting accurate angles I tend to wander off the cutting line I guess maybe more haste less speed (Ps I don't fancy cutting 50mm x 2mm box stainless multiple times with a hack saw).

 

[Brad93]

Right, we'll be starting this project in the next week, steel is ordered and kitchen is finished (including a complete new floor due to woodworm).

We've got some nice chunky hardware to bolt the tabletop to the frame
View media item 9332
and a design drafted out.

My next question for the project is how am I best cutting accurate angles for a good fit up? I have a grinder and a hack saw and some gauges for marking out accurate angles. I have in the past struggled cutting accurate angles I tend to wander off the cutting line I guess maybe more haste less speed (Ps I don't fancy cutting 50mm x 2mm box stainless multiple times with a hack saw).

Find someone with a chopsaw or bandsaw would be my advice. You're gonna really struggle getting good fitup with a load of cuts made with a disc.

 

[Hitch]

In the absence of an accurate saw, careful marking out is the starting point. once you've done that, use a good quality disc to cut the lines, cheap ones wobble and bounce around. Take it nice and steady and let the disc do the work.
Do a few test cuts to gain confidence. If they are a little off careful use of a flap disc will true it up.

 

[Richard.]

Right, we'll be starting this project in the next week, steel is ordered and kitchen is finished (including a complete new floor due to woodworm).

We've got some nice chunky hardware to bolt the tabletop to the frame
View media item 9332
and a design drafted out.

My next question for the project is how am I best cutting accurate angles for a good fit up? I have a grinder and a hack saw and some gauges for marking out accurate angles. I have in the past struggled cutting accurate angles I tend to wander off the cutting line I guess maybe more haste less speed (Ps I don't fancy cutting 50mm x 2mm box stainless multiple times with a hack saw).

Hiya Mike I've just looked at your location and it's a small world. I spent the first 24 years of my life from these parts and 10 of them in the next village (leeming bar).
Unfortunately I don't live anywhere near now. I was checking your location to see if you were close enough to come do your cutting on my saw. You would of been very close a good few years ago.

 

[Mike Wilson]

Thanks for thinking of me Richard, very kind. A small world, Leeming Bar certainly isn't far away from my house.

Thanks all for the advice, I'm currently looking into dry saw (metal chop saw, not sure of the correct term) options and if I choose to not go down that route I have a friend up the dale who may have the machines to help.