25' Double Eagle aluminum build (placing stringers)

Discussion in 'Metal Boat Building' started by Northeaster, Mar 10, 2014.

  1. Northeaster
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    Northeaster Senior Member

    Really want to acknowledge and thank you experienced and knowlegable guys for helping me out here. Although some of the points you guys have discussed are over my head, or at a minimum, will require a 3rd or 4th read, I have learned alot already.

    I know this seems dumb, but I think I just missed something simple as I am building upside down and the gunwales are down near my feet, so just not in view. I didn't notice how the gunwales and all lines should sweep up (if right side up).

    If you don't agree with what I have typed below, let me know but I think, that because of or in addition to my inexperience - this is how / where I went wrong.

    Now that I think about it, if the hull were rightside up, the design of this hull, like many similar boats has the gunwales fairly low and near flat near the stern - then gently rising along the sides of the boat, then taking a more significant rise nearer the bow, to end in a quite high stem / bow roller location - to bust through the waves.

    It seems obvious now, that if I were building right side up, I would have expected the long stringers to sweep upwards nearing the bow in a similar fashion to the gunwales. But, as it was upside down, I just didn't view or grasp this.

    I plan to lay out battens tomorrow, and see were my stringers should land nearer the bow.

    Kevin- I only tacked a few of the stingers to frames, in a few spots each, to keep the frames level and at proper distances apart. I guess in hindsight it may have been better to use temporary bracing under the frames to achieve this and not use the stringers themselves.

    As it is though, I would say only 10% or all stringer to frame locations have been tacked or welded. Now that I am aware of the need to have drilled "mouse" holes at the inner end of the slots in the frames, I will have to do some work on these anyway- may just brace / tacl other suppoerts under the frames, and cut all tacks when I relocate the stringer slots near the bow. I am aware of the need to weld teh hull sheets together, before welding the longs to the hull or the longs to the frames.
    I was / am aware of the need for limber holes where the keel and chines meet the hull.

    As always, I appreciate any further advice or clarification. If one or all of you confirm that above is what likely caused my issues, and that re-running the stringers to trend now down (as still upside down) is the best approach I would appreciate it.

    Kevin - when you say "Your stringers as laid out and notched seem to me a headache you cannot overcome as they ARE NOT on the same surfaces as the frames." - Can you elaborate a bit on them being NOT on the SAME SURFACES as the frames? I believe (when building upside down) I have in error curved the longs up towards the keel/stem, nearing the bow, and I now believe they need to curve down towards the chines (and lower side ones toward the gunwales) instead.
    Is this a good enough understanding, or am I still missing something?

    I believe that the stringers are Ok in the aft and mid boat, until I start t ocurve the wornd way, as they are fairly straight there, and I went by measurements at frames 0 and 4.
     
    Last edited: Mar 14, 2014
  2. Kevin Morin
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    Kevin Morin Junior Member

    Framing the Eagle

    North,

    good idea and it may help find which relocation will help most?

    Yes that seems accurate.

    please don't confuse two different references- drilled holes as the radius inside of a notch and 'mouse hole' or limber hole as we have used them and you have been shown, please reread posts your statement indicates conflation of two terms.

    Illustrating this would take time I cannot now spare so I'll try some more words. The frames as you show them photographically will have some surface that will lay to them. So you should take the thinnest metal in your inventory and drape the forefoot area on one side of the keel to the chine.

    This surface, described by the lines of the transverse frame edges, is ONE surface. When you hold a thin sheet of metal over these frames' edges, you can look under the sheet with a light under your frames, and you will see the frames roughly touch this sheet material.

    (DO NOT USE THE HULL PLATE for this quick experiment of the work will be to high to waste.)

    If you have 0.080" or even some other thin metal sheeting it will lay to the frame edges. BUT the longs you show will be a long way from that surface. The surface of the frame edges is part of a cone, even if that is not obvious it is true. The surfaces your flat bar longs have on their outer edges is not this same conic section.

    Because the Body Plan location of the notches of the longs in your frames are not where they belong: They describe another surface below/inside/short of/"not common to" the same conic surface of the frame edges.

    This may have to be read more than once, this is a true but not obvious answer to your question.

    NOW... the next test is to lay a piece of plywood between ANY TWO forward frames. Notice this is a FLAT PLANE, and it will come close to the surfaces of the longitudinals you show tacked in to the frames.

    Therefore: there are two surfaces; one Conic on the outer frame edges; and second a series of nearly flat planes like Cylinders between the frame's edges.

    Your terminology is too confusing to make clear in regard the questions but I will make a few statements that I think you can use.

    The sheer and chine, IN PROFILE keel down, turn up forward. The long's should do the same but the distance between the sheer and the chine or the distance between the chine and keel are not exactly evenly divided to locate the hull longs at each station.

    The hull long notches in your design could be battened/drawn/laid out/marked on the hull by using a 1-1/2" x 1-1/2" x 1/8" angle or perhaps moving down to 1-1/4" legs if the previous is too stiff.

    The flat leg of the angle is laid/clamped/fitted to the outer edge of the frames. Aft where the hull is a prism, these are all straight lines to provide parallel buttock lines. However forward where problems are- the angle has to be pulled to the frame edges without kinking/hogging/permanently bending the angle.

    What this does is work as a layout tool for the notches to carry the bar longs. The angle will lay flat to the both the after cylinder AND the forward conic surface and TELL YOU WHERE TO NOTCH!!!!

    If you bend or kink the angle you will not have fair longs: if you allow the angle to lay to ' the frames it will show you where each notch will be fair to carry a flat bar on the same surface as the conic development of the outer edges of the frame.

    So, if you will give this a try, you'll find out where the longs need to be. Imagine the angle extrusions' leg that is on the frame edges as a PIECE OF THE BOTTOM SHEET. If you'll do this carefully so you don't over bend the angle, or reduce its cross section should it end up bending permanently (indicating it is too stiff a batten for the curve) then you will find that by moving the angle inward toward the keel/bow stem AND simultaneously toward following the (down now) lines of the chine and sheer, you will find a location INSIDE the same plane as the bottom for the longs to be notched.


    Once these notch edges are laid out on the frame edges, a small try or machinist square can be sued to line out the notch. Then at the center tip drill that hole so the notch can be as tangents.

    Hope to have helped?

    Cheers,
    Kevin Morin
     
  3. Northeaster
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    Northeaster Senior Member

    Absolutely that helps. Very well explained as always. Many thanks Kevin. With any luck, I will have some time to work on this tomorrow. Hopefully, I will have some improved pics to post in a couple of days.
     
  4. Barry
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    Barry Senior Member

    To AdHoc
    Re my comment that I would not build a boat with less than 1/4 inch. The topic at the time was the concern about using 1/8 bottom. Our boats were always 1/4 bottom between 18 to 40 feet with the sides at .125 to .188.

    Your comment.
    "The moment of inertia of the plate should not be an issue."

    If you are welding 3/16 inch stringers onto a 1/8" bottom the bottom will pucker due to the thinness of the bottom . Of course you can turn the heat down but the root of the weld will not be deep enough to provide the necessary strength.
    If you are welding a 3/16 stringer onto a 1/4 inch plate bottom, you can achieve good depth penetration and the thickness, stiffness or the moment of inertia of the plate not affected by the bead will keep the plate quite flat.


    You provided a coast guard vessel picture, are you saying that this boat has 1/8 sides and no distortion from frames/bulkheads being welding vertically on the sides of the hull?

    Northeaster is building a boat that I expect that he might paint. I would not build the hull as he is doing but that is where he is at. We would have built steel frames that the plans provided, installed a keel, chine and sheer piece a few stringers flush with the frame to stabilize the set up, and plated the sides and bottom. Then pulled the shell, flipped it right side up, installed angled longitudinal stringers from the transom to the bow, stepped near the front, then installed some cross braces between the stringers not touching the floor and we would have been done.

    Talking about the sides now.
    So back to the paint issue A glossy painted boat will show every imprint and plate deformation that is in the boat. Ourselves and our competitors normally paint the boats and the goal is to get a boat that you can sight down the side and see almost no deformation. As we tack in side stringers, that have a sheared line and are stiff, 4 or 5 inches by 1/8 inch, the sides are fair.


    To Kevin
    Re the curve of a sheet.
    You say that you have been told that the natural bend is from the cooling at the mill.
    Almost all of our material comes from a mill in a coil, certainly up to 3/16, (I doubt 1/4 as I cannot recall a curved 1/4 inch sheet and it is to late to check), and ends up in a distributors outlet. Most of the big distributors have a coil line that take the coil and uncoils them through a multi roll set up that takes the deformation caused by the aluminum being in the coil out.

    If the guy on the roller is not careful, he will not get all the curve out. We have had 10 foot long by 5 foot wide by 3/16 sheets, as it sounds like you have, that would have a curve of over 2 inches over the 10 foot length.

    The tig weld in the bow locker looks like butter was poured in and without deformation, Sweet
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    The 33m CG vessel, correct...ops just converted those imperial units (i'm not familiar with them). 1/8 = 3.125mm. No, i'm saying it has 5mm...whatever that is in old imperial units??

    You can see for yourself in the image.

    It all depends what throat thickness you are using. It should be based on no more than the thinnest scanting.
     
  6. SukiSolo
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    SukiSolo Senior Member

    3/16" = 4.8mm, a tad under 5mm which is approx 13/64". At risk of being shot down but I do find metric and SI units easier to work in generally. Especially doing quick weight/volume back of the hand stuff.
     
  7. Northeaster
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    Northeaster Senior Member

    Kevin - forgot to mention. I had planned, and still may - to set it up like a rotisserie, and be able to flip almost, if not completely over. That is why I went with a heavy duty 4"x4" steel jig, instead of using a wood jig as many home builders do. Was planning on using tripod type points at each end, but now am considering just lifting one or both ends a bit from shop ceiling rafters with chain falls and setting down after. Also have backhoe heer to hold up one end if required.
    Just haven't got around to welding up some form of lifting point at each end - would like them to be vertically adjustable, so that i can chneg the CG as the weight is added on, to keep it stable when flipping.

    Barry - I appreciate hearing how you would would build a similar boat, including sequence and hull thickness. However, and please correct me if I am wrong - is the sequence you describe not normally "reserved" for production builders with some special jigs, etc that would likely not be worth it for a one-of home builder to invest time and/or money in building? At least from my plans and alot of reading I have done, I think the way I am doing it, upside down, frames on a jig, then stringers, then hull plate, followed (hopefully) by correct welding sequence is the common or preferred approach for home builders.

    re: bottom thickness - my plans, or more specifically, an accompanying writeup from the designer, says to resist the urge to "build stronger" by using heaving hull sheet/plate. Instead, it suggests adding more long stringers, if more 'strength' is desired. I know this does not help with distortion due to thin sheeting, or ease of welding, but that is what it says.

    One of my problems is that I can have to pay an expensive roll change charge when ordering long sheets i.e 4' x 20' or 5' x 20', in different thicknesses. So, I don't mond ordering 4 large sheets of 1/8" or perhaps even 4 large sheets of 3/16", but it woudl not be economical to order 2 sheets of each, ie 3/16 for bottom and 1/8" for sides. Unless I order mosly long sheets and make do with shorter sheest for the other thickness i.e 4'x8', but that means butt welds across the boat, which would like to avoid by using longer sheets.
    Also, this is not a river boat, and other than light beaching, it will not be "on purpose" run into rocks at 30mph. It has a keel and skeg protected prop and rudder, but is not a river running, rock hitting design.

    I do NOt plan on painting it, or at least only painting the bottom. It will be used in salt water and brackish water (my dock is on a tidal river, with fiarly low salt content, but it's only 0.5km to the bay / ocean).

    Appreciate all of the great advice!
     
    Last edited: Mar 15, 2014
  8. Barry
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    Barry Senior Member

    5mm is .197 which is above 3/16 (.188) and I would have few worries welding the frames vertically to the side with proper sequencing and bead width, heat etc.

    But Northeaster is using 1/8 on the side and as a first time builder, this can cause problems. Several years ago we tendered on a government boat, 30 feet in length. The plans that came had frames, 24 inches on center, welded vertically to 1/8 sides, 5 inch skip welds on both sides of the frames, chine to gunwhale without longitudinal stringers.
    We got the bid, and got in touch with the appropriate people and told them that we wanted to make a change to horizontal stringers to minimize distortion which of course they denied. Said the naval architect knew what he was doing, so just do it as per the plans.
    While we did everything to minimize the distortion, we still ended up with about a 1/8 inch curve between the frames. The purchasing department, as per the tender, came down and approved the boat prior to painting, and approved the boat.
    When the paint was applied, the distortion flashed out and a major head to head occurred. We had covered ourselves so the fix was to the government expense, install horizontal stringers in between frames to get rid of the distortion and of course a repaint.

    I guess for my input, just trying to make the point to Northeaster to be careful if he is considering vertically welding frames to the 1/8 side plate
    And of course the use of 1/8 material for the bottom, 1/4 might be a little heavy with the number of stringers that he is using, by it is my opinion only that 1/8 is a little to light. Certainly, you can install more stringers, as someone suggested to him, which is the fix but more stringers means more weight, work and expense.

    Adhoc,
    your comments on welding over welds lowers the strength of the weld. How do you butt weld the plate that you say that you work up to 20 mm ( 3/4 inch) to 70mm
    ( 2.75 inches) on a single or even a double pass ( ie from both sides) without multiple passes. Just curious here

    Northeaster
    re the sequence. I have seen many plans similar to the one that you are using with
    frames and small stringers and certainly they will work. Many of these multi framed small stringer designs come from plan suppliers who had originally designed the boat using wood and then converted them to aluminum. If you have small stringers, you need more support and hence the requirement for more frames.

    With thin skinned aluminum boats you need to control flex and plate thickness is one way to do it multiple stringers is another.


    Re the length of sheet. We have never had an issue of getting 20 foot lengths of material in 1/8 to 1/4 inch in most marine alloys. Again try Ryerson, can never remember an upcharge. Sometimes for making the shipping skids but it is minimal

    When welding the plate, insure that when you stop a weld, before beginning another that you take a skill saw and cut back the end point maybe and inch as there is a big potential for crevice cracks that can occur and every weld termination due to the contraction of the weld as it cools. And of course back cut the first weld when making the second opposing butt weld to sound material.
     
  9. Kevin Morin
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    Kevin Morin Junior Member

    Double Eagle building

    Barry,

    I didn't make myself very clear that's for sure. The coiling operation happens when the heat of rolling is still in the material so the coil mass cools from the outside in. The huge mass of the coil insulates the inner areas of the future sheet materials but the outer edges are (thereby) allowed to contract slightly in relation to the inner areas.

    When we stand a 5' or 6' (1.8m or 2m) wide 20' (6 to7.6m) or 25' long sheet of 0.125", 0.160", or 0.187" on edge- on the shop floor they almost always form a cupped sheet. This is from top to bottom; they are bowed or cambered or cupped about 1" or so. Lengthwise the sheet will bow/cup/warp/curve a 1' (.3m) or more along the long axis.

    I was told by a supplier one time in the 1970's that this was the result of being rolled into a coil while 'warm' and then stored and transported in that coil until 're-rolling' in to sheets and sawed/sheared for size and delivery.

    I was remarking about the definite advantage to the builder of putting this naturally occurring convex tendency of the native material to use; by orienting the sheets' bow or cup- outward in the build.

    Barry, semi-automated TIG is really a great way to weld aluminum, and with the newer inverter power supplies and their digital arc control features ; dialing in the arc provides pretty much ideal welds every time. Thanks for the compliment on the bead- more machine than me in all truth.

    AdHoc, Barry, in regarding welding heavier section longs to a thinner skin; in aluminum MIG I would turn up the weld amperage so the wire would 'wet' the root face at higher rate, and then increase the travel speed to minimize the weld puddle cross section.

    I would use 0.045" (1.14mm) dia. wire at higher than normal voltage and much higher travel to leave a bead that was only 0.125" (3.17mm) wide on its face and I'd bevel the 3/16"-.0187" (4.75mm) by at least half its thickness so MIG bead was more under the section of the bar than outside the bar's lower edge.

    This will print through but minimize the weld distortion between frames and longs due to over-sized out of proportion welds which do not add to strength but do create deformity in smaller craft.

    [​IMG]

    Here is a little 14'er I skinned entirely of 0.100" (2.5mm) 5052 and 5086 and most of the welds are MIG. This view shows she was tacked up fair, without any framing so I started with a set of clean surfaces before adding the internal framing.

    [​IMG]

    She was eventually framed for a deck, foredeck and after engine well as a guard deck to avoid transverse full height frames. The heavier longs in her bottom are 0.125" and 0.187" (3mm & 4.7mm) cut sheet, that have little forward butt line rise along their lower edges.

    Forward the bulkhead, she was framed along her waterlines so all the bars were 0.187" (4.7mm) and 0.25" (6.3mm) 6061 flat bar extrusions held to flat lines of the waterplanes. [Easiest framing in the forefoot of small boats in my view.]

    [​IMG]

    The welded out skiff was fair and had no contraction wrinkles because the 0.125" and even 0.187" (4.75mm) longs and framing elements were beveled and the welds were put in at high speeds to reduce net heat and therefore minimize contraction distortion.

    So welding in heavier framing to lighter hull sheeting can leave a fair hull if the welds are #1 prepped correctly and #2 the weld technique is proportional to the site and #3 the welding plan is observed closely.

    I would not say these welds are for North's build because he's still getting his hand in. With more experience under the hood he'll have a better chance to make these beads with less distortion. (hot and faster than considered 'normal') So for his build the thicker hull will be more forgiving in final appearance and I don't a couple hundred pounds of added material will be a big deal on his hull.

    Last comment about the heavier frame element to a lighter skin hull panel is that transverse welds are all the above, but even more critical to these points.

    this little skiff was painted;

    [​IMG]

    The topsides finish coats are on, (done by auto body painters not me!) and the bottom below the bootline is etched and Allodyne rinsed; ready for bottom paint. But the side shows in reflection that a 0.100" (2.5mm) hull can be MIG welded fair - but it does require strict methods compared to a hull twice as thick.

    Also in these pics North, you can see my idea of bulging, the panels convex somewhat. If you look closely at the corners of the skiff you'll the bow stem is curved to give more curvature to the topsides forward, the after corners of the transom are curved from chine to sheer to keep the convex topsides all the way to the stern, the transom is also somewhat (slightly) compound and so are the bottom panels. No Body Plan station would show a straight line from keel to sheer, except the narrow guard deck or sheer clamp around the gunwale.

    I like all panels to have tension as much as I get in them without having to English wheel them. This helps, IMO, a tremendous amount in mainlining the hull surfaces fair in their post welded conditions. And this is where I take into account the sheet material's cup- as discussed above. I stand the sheet up, observe the 'lay' or relaxed state and try to do all layout and hull planning so that cup bulges away from the keel plane.

    Cheers,
    Kevin Morin
     
  10. Northeaster
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    Northeaster Senior Member

    Barry - I was surprised to find a Ryerson location only a 5 hour drive away, in my hometown of Saint John, New Brunswick. Will give them a call early next week.


    Kevin - Beautiful workmanship - I definitely am aware that my results are not going to lool like your's, and that my low skill level mean I should consider thicker material to increase my chances of sucess.


    Well, I used a 20' length of 1 1/4" x 1 1/4" angle, to "find" much better lines for my long stringers. Again, it seems so obvious now how the lines were supposed to go, but I had my myopic view of an upside down boat in front of me, focusing on tasks instead of observing what I was doing.

    The temporary angle clamped down well at all stringers locations, and I was able to mark new locations for my slots and cut them out.

    Now, my problem is that (near the bow where the curves are greater) my flatbar does not want to lay in the new slots nealry as easily or "fairly" as the angle did. Of course, they are flexing side to side between the fwd couple frames.

    I really liked how the angle sat as each location. I am very tempted to leave the flatbar in most stringer locations, where there is not much curve, and order either angle or something like 1 1/2" x 1" tee (the longer section being perpendicular to the hull for any stringers which have alot of curve near the bow.
    I would then cut my slots larger (box shape) to accomodate the new angle or tee stringers (using a die gringer or similar to round out the corners to prevent cracking).


    I would appreciate advice on the above idea, or others suggestions.
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Barry,
    May be it is an American terminology thing that's confused me, but what do you mean by "vertically welding"..??

    Classic case of mixing units. Me not understanding imperial units and you miss reading metric :D

    If you reread, you'll note I am referring to boats of length in the 20m to 70m range....metres since you're building much small boats under 10m, not millimetres of thick plate :p

    But up to 12mm will be a root and 1 cap on an edge prep joint.

    Kevin,
    Nice work..
     
  12. Barry
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    Barry Senior Member

    Northeaster, Samuel Metal has a branch in Fredericton, also a major supplier

    Understood about the coil heating etc but I am under the impression that the if you unwound a coil of say 1/8th, that it would be severely curved and the unrolling the coil requires the sheet to be put through a roller system to take the material past the yield strength, albeit minimally to make it straight.
    We received a 20,000 pound, order that had come off a rolling system with a huge curve in the sheet, we sent it back as much of what we were building did not require fitting to frames etc, and would not be straightened in the fab process. After that the suppliers never sent us any sheets that were not flat.

    Adhoc, by vertical I mean on between the chine and gunwhale

    and and and, yep misread the 70m as 70mm plate thickness , and thought wow, now that is thick plate haha
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Wow!!...may be this is different practices here. Whether we order large amounts or small amounts of aluminium, it is always, “O” temper, unless for whatever reason the client insistent on a different temper. As such, even the basic “O” temper has dimensional control and tolerances which must be adhered to. Since we’re always building to Class and as such the plate arrives in sheets either 2x4, 3x6m and is checked by QA dept. and is issued a cert by the mill.

    Curious why you buy in rolls/coils…is it a cost thing?

    Bear in mind some of the vessels I design have more than 100 tonne of aluminium in them, hence curious why you buy bulk in coil form.

    That’s kind of what I suspected. But, forgive me for asking such a silly question….if the frames are not welded, how else do you connect the frame and plate? Since everything is welded.

    What I’m trying to understand, is why you call it vertical welding…do you call the bottom frames to plate…horizontal welding??

    The only definitions to me that are important in defining difficulty to distinguish one weld from another, is ‘downhand’ or ‘overhead’…anything else is just a weld regardless of its location. Hence my curiosity where this term comes from.

    I am constantly caught out when quoted in imperial units. I simply don’t understand them…:confused:

    Mind you, having said that, we have used 50mm plate on the T-Foil ride control foundations and 20-30mm plate for the ducts of the waterjets.
     
  14. Northeaster
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    Northeaster Senior Member

    I am inetersted in what Barry meant by vertcial welding as well. I assumed that he was asking me, (on the topsides only) in addition to the welding of the hull sheet to horizontal / longitudinal stringers, would I also be welding the vertical sides of the frame to the hull.
    Although the plans call for it, I am leaning towards only welding the hull to the stringers and then the stringers to the frames of course. (floating frames as you guys call it) But, if my frame sides are very close or touching the hull I guess it would be best to weld them?? That is still a ways off.

    The small metals suppliers / metal resellers that i have been dealing with do not stock 5086 in sheet (or 5052 in anything larger than 4' x 8'), and it must be ordered and cut from a coil from the large suppliers that they buy from. Hence the roll change charges passed on to me.

    Barry-
    I will check on other suppliers as well. I lived in Fredericton for many years. Never heard of them, but bought my steel for projects from the local small steel supplier - Best metals.
     

  15. Barry
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    Barry Senior Member

    We do not buy them in coils but the distributor would by them from the aluminum manufacturer in coils. That way they have a Cut to Length which involves taking the coil unwinding it onto the roller system to straighten the built in curve that is a result of it coming off the coil, then cutting it to length. I guess it saves them money and for us if I need 6.5 meter pieces or 8.25 meter pieces, I can get them. While Samuel and Ryerson will have the standard lengths, 8 foot. 10 foot, 12 foot etc on the shelf for quick shipping, these also come off coils, or so I have been told


    Re the term vertical, I am not referring to welding direction, uphand, downhand, flat, or overhead.
     
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