Welding panels before or after?

Steel and aluminum boatbuilding. See: "Boatbuilding Methods", in left-hand column of the Home page, for information about alloys.

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Rdeleurme
Posts: 2
Joined: Wed Oct 10, 2012 1:29 pm
Location: British Columbia

Welding panels before or after?

Post by Rdeleurme » Wed Oct 10, 2012 1:41 pm

Hello there, I have recieved the aluminum Scrambler plans recently and I have a general question. For transportation and storage reasons I'm looking at purchasing 8ft panels for the sides and bottom and welding them together to make the length needed. My question is should I weld them to length on the floor fully, before placing them on the frames? Or should I place them on the frame and cut to fit in the smaller pieces?
Thanks for any advice, I'm new to aluminum welding but doing tons of practicing and getting ready to start building

Wearl
Posts: 27
Joined: Sun Jul 01, 2012 12:27 am

Re: Welding panels before or after?

Post by Wearl » Sat Oct 13, 2012 8:14 pm

That is a great question. I just finished my scrambler, and was new to welding aluminum too. I hauled full 20 ft sheets across town on top of my pickup. I would think you would butt weld them to size before...you need the full length so you can tack weld front and curv it from front to back....


Wayne

Rdeleurme
Posts: 2
Joined: Wed Oct 10, 2012 1:29 pm
Location: British Columbia

Re: Welding panels before or after?

Post by Rdeleurme » Wed Oct 17, 2012 10:05 am

Thanks for the reply. I've started the frame and the more I think about it, the more likely I am just going to get the full 20 footers, just have to figure someway to get them to the shop. Maybe rent a 20 uhaul or get someone who can deliver them to the machine shop near my house then drive them home from there on the roof of my truck or something.
By the way, I thought both the scrambler builds here were great and I can't wait to have something worth posting for pictures.

Wearl
Posts: 27
Joined: Sun Jul 01, 2012 12:27 am

Re: Welding panels before or after?

Post by Wearl » Thu Oct 18, 2012 5:37 pm

Rd,

Sounds like a good plan, it is a fun learning experience. Look forward to seeing some pictures.

Wayne

mcmbuilder
Posts: 106
Joined: Fri Apr 22, 2005 11:56 am

Re: Welding panels before or after?

Post by mcmbuilder » Sat Oct 20, 2012 6:25 pm

If you do have to weld any full length panels together you will better off to use some type of stiffeners on the back side or weld them to the frames first. If those options are not practical then be sure to leave a gap between the plates (~.125), and stagger the welds, otherwise you will have huge problem with warpage. By staggering the welds I mean to weld the plates on each end then the middle, then 1/4 way then keep welding until you have the plates welded solid. You will definitely be happier using the 30' lengths

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

Re: Welding panels before or after?

Post by Kevin Morin » Mon Nov 24, 2014 1:01 pm

Another older topic that has a great subject for welded aluminum builders so I'll add some remarks hopefully to increase the utility of the posts already here?

Aluminum alloy sheet/plate stock (some folks use the term sheet for thinner materials but doesn't seem to be an agreed cut off thickness between plate and sheet?) is most often sold in 12 or 20' long lengths, but in many locations coil lengths are available sometimes for a small premium cost over the market cost per pound for stock sheets.

When aluminum is made/rolled from billets into sheet or plate there are two main types of lines or rolling mills. One cuts sheets at 12 or 20' as the material comes off the final rolls and the other coils up the sheet/plate into huge rolls of material. The roll stock may be store or transported as rolls and then 're-rolled' or straightened in a series of cold rolling operations and that is where longer or 'coil length' sheet and plate stock come in.

A coil length of material is hundreds of feet long so cutting a re-rolled plate or sheet to 25 or 30' is 'doable' where stock 12' and 20' material has to be welded at some time during the build if the LOA of the boat means the hull panels are longer than stock. Another alternative is to buy the longer pieces but this usually takes more effort all up and down the supplier's chain of vendors, including increased shipping and handling all along the delivery stream to your shop/site/home.

Depending on where you live, the local metal supplier will have familiarity with these market facts. However it's important to note that many locations' vendors, often farthest from smelters and mills, will tell customers what I've just said is not 'true'- you can't get this or that size, this or that alloy and there are no sheets longer than 20' anywhere.

This is just a reflection of their experiences as my purchase of 6'x30'x1/4" & 8'x25'x1/4" plates delivered to rural Alaska reflect my past experiences buying aluminum.

So; joining sheets to fit your boat's LOA can be an important building question at the materials ordering stage- the building stage in handling, layout and tack up- and, of course, the consideration of a butt weld of two sheets together.

I'll group the theories of sheet joining into two main methods for the sake of discussion. First, is the weld together before; Second is weld together on the boat, or after tacked up and framed.

The primary problem with any sheet to sheet butt joint is cooled weld contraction ending up in a length wise wave, wrinkle, distortion of the sheet material at the location of the weld. Builders use one of the two methods to solve this potential hull blemish, and the two camps seem to be firm in their arguments for their own preference?

Welding is going to result in the parent metal expanding as it is heated. The edge of plate that expands will tend to cup the plate and when that expanded metal is cooled it may contract more than its original length due to the weld metal added contracting in addition to the original/parent metal.

One method, welding before the sheets are on the hull and frame, is to weld the seam using MIG at as high a speed a possible for the welder, with as long a weld as the welder can reach. The idea here is to reduce the time of a 18 or 24" weld (long by most MIG standards) to a few seconds time, at extremely high voltage in order to reduce the net heat added to the edge of the, and to reduce the deposited wire in the weld. Both of these factors do work to reduce the weld contraction of a sheet to sheet butt weld.

Beveling the sheets/plates is another method used; often in conjunction with the method above. Also welding one side fully then turning over the two joined plates and back chipping (cutting out the weld 'sag' or penetration to clean parent metal) and re-welding following similar technique.

Others following this same general routine will flip the sheet back and forth, putting welds in different locations along the seam to operate as an 'opposing' contraction to the weld on the other side. Still others will follow this general method and stagger or step the welds insuring the weld contraction is not concentrated in one segment of the seam before other areas are welded to counter act the contractions.

When welded off the boat, one advantage not as easily used by those who put the plates/sheets on th hull is the hammer fairing of any contractions. By using a dead blow hammer and a wooden anvil tapping a cupped area on the inside will lengthen the contracted surface and allow the sheet material to lay flat, but this is about as skilled a metal working craft as welding and not as widely recognized today as in the past. But it works, and works well if the hand on the hammer is skilled. Therefore pre-assembly welding and post weld fairing can result in a very uniformly joined pair of sheets and a fair hull panel.

[One note for new builders is weld size in proportion to parent metal thickness; it is my experience that most weld contraction problems come from MIG bead size being too large for the joint and material. This is a subject of an entire separate topic/thread/discussion but needs to be mentioned in any weld joint thread.]

Next group of builders- put the sheets on the hull frame or if using an outline only build method, cut the panels out and tack them up (including tacking the butt joint together) then tack up the boat and then add the butt weld in sequence to the overall weld out.

The primary idea here is to add weld contraction in a slow, steady and controlled amount to the entire boat instead of one panel as a blank. But the big draw back is correcting any final contraction - it is much more work to do if this second method is followed. If a plate has framing near the joint, or added framing to the joint, each of these frame elements can work to reduce weld contraction in one or another direction.

Further, if the welds are added in a pattern over the entire hull, the contraction can add up but less often results in a single location of contraction that wrinkles and cups a given hull panel. For example if the butt joint is backed by longitudinal framing (?) those bars, angles or other shapes' stitch welds will work to resist cupping or distorting at the butt joint.

Some builders add a full backing bar to a butt joint, The weld joint edges are beveled at the outer two plate edges and the weld is performed along the entire butt joint relying on the longitudinals and the backing bar (longs are notched for the weld back up bar) to create a weld zone that is fully welded from one side (backing bar is just stitched inside) with the backing bar and longs stitch welded to the two plates holding the entire area flat or fair.

I know this is a long post, but I think the topic needs to have some explanations for new builders considering the variables to their boat? Sheet size availability in the Puget Sound may be different than farther from the mills. Methods to build have to adapt to what material sizes are available, and the method of adding the welds to a potentially tricky hull seam also needs some 'pro and con' type of discussion.

Hope this helps others consider some of the aspects of deciding how to handle sheet-to-sheet butt joints in welded aluminum boats?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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