another welding thread

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RobP1
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Joined: Tue Sep 19, 2017 3:09 pm

another welding thread

Postby RobP1 » Wed Sep 20, 2017 2:43 pm

I started welding at age 17 some 40 years ago. Over the years I've experienced just about ever application there is with a stick mig and tig. From mil spec certs. to bridge certifications. Recently I bought a Lincoln square wave 200 tig. I had never welded with the newer inverter machines before. Now I'm looking at building an aluminum jet sled. I know aluminum mig would probably be the best application for this project. But I have always avoided aluminum mig like the plague. ( Give that job to the new guy I'll go over here to my tig, let him suck that smoke). With the new frequency controls and pulse I'm wondering if I should go ahead and give the little square wave a try at this project. First thing I did with the welder was change the torch to a water cooled torch. I like it much better. I would like some feedback on what some of you think about tackling this project with a tig ? I'm thinking with the new controls of the arc and proper sequence of applying weld to the hull I might be able to keep the distortion to a minimum. what do the pros think? thanks guys

Kevin Morin
Posts: 612
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

TIG Hull Seams

Postby Kevin Morin » Wed Sep 20, 2017 11:47 pm

RobP1, first idea is there are many threads here and on welding forums as well as generic metal boat forums where you could do some research and get a wider feedback- Glen-L has some great aluminum designs in the Catalob- but the bulk of the boat work here is non-metalic.

So, the conversation is likely to be limited to a few loyal Glen-L' rs who weld and build metal boats?

As one of these metal-Glen-L fans I'll restate my case that TIG is fine if you can put down proportional beads, with discipline. If you can keep the bead in the 1.1X to 1.2X range the parent metal being joined (?) AND you have some idea of the contraction from slower seam welds and the resulting parent metal expansion and contraction?

I usually reserved TIG for ends, tie-ins, corners, tanks and details and MIG welded most of the boats in my shop when I built full time (in the last century). However, I've increased my TIG work in several more recent boats and will say they worked OK. With that said: bead planning and control is the entire 'ballgame' as regard contraction/distortion and fair hulls welded with TIG over MIG.

It only takes a few over eager 10% oversized beads out of sequence to wrinkle or warp topsides as they're almost 'flat' aft the master section.

cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 612
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: another welding thread

Postby Kevin Morin » Thu Sep 21, 2017 1:10 pm

RobP1, the most challenging aspect of using a TIG torch exclusively for a boat hull build will be tacking.

The seams are most often outside fillet- inside edge to edge fits. I have some building method posts on the Metal Thread that will show some tacks. Also, an entire post on tack handling and some on the Tanks' thread where I discuss welding through a dressed tack and other details.

What is not shown (that I recall) and what will be the absolute most challenging IMO, is tacking in the "field" not along edges of parts. An example is tacking a rib, longitudinal or other structural element into the flat of a sheet's interior- not along the edges of the sheet.

Keel, chine, sheer are all one type of joint cross section but.... longs, rails, bulkheads, ribs, and other interior pieces only have one edge the other side of the joint, which are T -Fillets, is flat sheet.

Tacking on the structural elements before weld out is needed to avoid distortion, the interior longs, ribs and bulkheads all contribute to the hull sheets laying fair. Tacking holds everything in place- as you'll know from your welding experience.

But, TIG takes a few seconds to create a puddle- MIG's puddle is "sprayed on" so the parent metal side/bottom/cabin side/ or other sheet surface is almost instantly 'glued'/tacked/fastened to the frame/structure/interior pieces - that short time in MIG is much longer in TIG.

Unless you have a very strong, agile and probably custom made set of clamps to reach the middle of a bottom sheet from the chine- or the middle of the topsides from the sheer? it will be hard to clamp the structural elements to the insides of wide sheets of the hull panels- so TIG tacks will allow the sheet metal to bulge out from the tack site- as the tack puddle is started.

To complicate this- aluminum is very weak in the semi-molten state- so tacks will also pull apart during their cooling state- because the sheet metal will still be expanding due to the conducted heat of the tack's puddling - or heat of fusion.

Mig somewhat overcomes this by reducing the time allowed for conduction of the heat of fusion outward- reducing the expansion forces and chilling to hardened state faster due to the lower wattage delivered in a shortened time.

So, TIG will be the most difficult to use to tack up- one of the most crucial stages of building a fair hull. I think you'll find the clamp set needed is more expensive than an entire MIG (spool gun not push-pull) so the MIG is justified by the tacking stages alone?

Just wanted to add that idea into the consideration - TIG may handle all the seams and field stitches (with prep and planning?) but will be a bear cat to manage in tacking up without some exotic clamping.

cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Kevin Morin
Posts: 612
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

TIG tacking and clamping

Postby Kevin Morin » Thu Sep 21, 2017 6:32 pm

RobP1,

in order to give some exact visual reference to my discussion about TIG tacking versus MIG tacking I've decided to post this image and discuss an aspect of one hull that illustrates my point. This is an external Long- a hull topsides outside unequal leg angle that acts to form the primary panel reduction of the topsides - and a spray rail at the same time.

I tend to lean toward hull framing as almost exclusively longitudinals, as opposed to more wood boat inspired transverse frames- but the results are not much different in 'net' strength- what is different is the methods I use to build.

[FULL DISCLOSURE: I do not sell boat plans, and the images shown are for procedural education of prospective welded aluminum boat builders- only. I'm attempting to make a pretty fine point as an answer to a reasonable exploration by a Glen-L poster about the potential to use a TIG torch to build his hull.]

I'd mentioned above the time duration of a TIG tack versus a MIG tack- I'd hoped to suggest that TIG is a great weld process but... usually involves a longer time interval during which the sheet aluminum (in this case the topsides) would be heated and expand from the heat of the TIG arc. I'd mentioned that the MIG process takes much less time so that MIG tacks are much more functional for field or 'mid-sheet' tacks of longs, frames and bulkheads to mention a few structural elements that are connected in T-Fillet welds.

Image

What is in the picture. The boat is LOA 25' or so, this boat in mounted on a rotisserie fixture to allow me to reach welds in positions I can achieve in high quality at my age (60's) that would be compromised if I had to kneel down and and weld below my knees in the bilge.

The side rail/spray rail/hull topsides long is being tacked on using TIG. The picture is of a clamping tool that (starting at the top) has a bar with cupped interior upper end to hold onto the bar tacked to the inside of the guard deck/sheer clamp/gunwale plate horizontal at the top of the sheer.

This pivoting bar (bolted through the 2" sched. 80 -6061-T6 pipe) allows the lower length of the pipe to swing inward toward the chine when pulled by the ratchet strap winch pulling from the center beam of the rotisserie fixture. Orange strap at the bottom of the image.

The 4x3"x1/4" angle has been cut to 4"x2" and the outer edge or apex has been rounded over using a 3hp router and 3/8" radius roundover bit and lots of generic frying pan spray to lubricate the cut. The result was then dresses length wise with a belt sander and Scothbrite (tm; 3M Corp.) belt to create a smooth surface that includes the rounded outer edge.

This photo shows the process of TIG tacking the 1/4" angle to the 5/32" (0.160") 5086 topsides. The angle has had 60deg. bevels inlet into the two legs' outer edges so the welds will be narrower root face but will have a gouged or cut root face V. This improves the use of TIG for a hull weld (stitched welds as shown by tacks in the image) so the weld can be installed very hot (300 A) but with a narrow face and deep joint -root face penetration.

The weld pattern is 4"- skip 4" -opposite side 4" and skip 4". All the bevels or joints are cut before the angle/extrusion/spray rail are in place for the tacks. All cut, dress, and surfaces are cleaned with Acetone and then wire brushed VERY carefully close to the weld zones only.

[The mill scale has been 100% removed from the topsides prior to this entire operation by running them through a 50" drum sander.]

There is a sliding collar that mounts another pivoting leg allowing the tool to adjust to the various angles between the topsides and gunwale plate/guard deck/sheer clamp- and this feature includes locating the clamp leg below the angle/spray rail so it's held against the side tightly.

The pipe clamp forward of the current tacks lifts the extrusion "the hard way" along the 4" vertical leg.

This is the extent of clamping/planning/fixturing required to use TIG to tack longs in the field. I'm not attempting to suggest this is the only means ? This is just what I came up with to do this job alone; in full control; and with no hurry to get the tacks "tight"

What is not shown is a 2x12" Plank of fir- inside the hull expanding the topsides in to an outward camber in order to further stress the topsides panels and by adding cylindrical or conic 'bulges' I'm attempting to reduce the final weld heat contraction so the topsides come out fair- even when a field tack and weld is required to add this structural element.

Image

This rail followed the sheer downward (near the stern) then swept up with the sheer toward the bow. So tack up control was absolutely critical.

Image

Rigging to get the rail on in a 'clean' manner by myself. Lots of clamping, fine adjustment and holding power if I wanted to use TIG to do the work?

Image

TIGged hull seams are fully possible but they do require more planning and discipline than MIG for the same boat.

Image

She turned out OK, and fair, but.... this was not my in my first 100 skiffs either. Hope to make this point clear: you can do a skiff hull with TIG but MIG is easier. RobP1, happy to help answer any more questions, and to clarify my replies here to the original inquiry? Please let me know how I can help your research- if I can?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

RobP1
Posts: 3
Joined: Tue Sep 19, 2017 3:09 pm

Re: another welding thread

Postby RobP1 » Fri Sep 22, 2017 8:25 am

Thanks Kevin, That was a tremendous help. It helps me understand what I'm getting into. It seems the most logical approach would be to fit and tack everything with the mig and then try the tig on the seam welds. If push comes to shove I can always do the greater part of the welding with the spool gun (guess I better brush up on my step and pause or as us old timers called it whip and pause technique) with the spool gun. Love that hull clamp where did you come up with that? I'd love to see the details. Thank you for taking the time to help this novice boat builder out. Robert

Kevin Morin
Posts: 612
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: another welding thread

Postby Kevin Morin » Fri Sep 22, 2017 11:04 am

RobP1, you're welcome for any suggestions I can make about welding aluminum boats.

The MIG gun could be used to weld out as well. However, a caution that whipping with an inverter does require some practice and settings to avoid 'fighting' the power supply's very fast reacting control circuits- depends on brand, mode, settings. All much different than the older transformer based power supplies with their analog controls. Machine beads or 'drag' (even though you lead the weld!) beads are common with inverters- there are several brands and models that make whipping a challenge.

The clamp was just something I imagined to do this job as I couldn't find another -portable- way to get the rail trapped firmly to the side for TIG tacks. A huge C or other inside outside clamp that would add the force needed was just too large, even hanging from the overhead monorail crane in this rental shop.

This clamp worked because the skiff was mounted on the rotisserie with a box beam under the skiff as strong back for the rotisserie (Davis Skiff Jig) fixture.

Good luck with planning your build.

Cheers
Kevin Morin
Kenai, AK
Kevin Morin


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