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PostPosted: March 24, 2010, 6:35 pm 
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Welders and Fabrication Techniques 101
Selecting the best welder within your budget is essential when constructing a frame. The frame is the foundation of your vehicle it must be both strong and light. The building process requires good welding techniques along with the correct welder set up and settings. With a little patience and planning you will be rewarded with both a strong and dimensionally correct frame.

Welding Equipment
Most home builders will be using a small 115V gas metal arc welder “MIG or GMAW” for the Locost frame fabrication. There are several limitations with these welders that are usually in the range of 100 to 135 Amps. For steel this means that these basic welding units will be adequate only for steel that is up to 11 gauge or 1/8” thick. One needs to be aware of the limitation of the thickness what one can safely fused together. Another limitation is the duty cycle. Most are only rated at 10% to 20% which means that you can only weld 2 minutes out of every 10 minutes without over heating the unit. If you are looking to purchase a welder, look for a fan cooled unit which is only a few dollars more and avoid the flux-core units. Most of your welding will be around 90 Amps at 19V.
If your shop has 220V service and your budget allows it, one should consider a machined rated at 175 to 200 Amps which would permit you to weld up to ¼” thick steel. If your budget is sufficient for a top end 115V welding unit, look for a welder that has an all metal wire feed body. Another option is the used market, which typically has good prices on these small welding machines. If you purchase a unit with a plastic wire feed drive body, be careful not to over tighten the tension mechanism. These plastic feeds should have the tension released after you have finished welding for the day. Under constant tension they will exhibit plastic creep, which can cause the drive to twist making it more difficult to adjust the feed. They may even required local reinforcing around the drive wheel or idler wheel lever arm to reduce deflection.

Welding perishables
Most of these smaller welding units will be set up to run .023-.025” Diameter wire. General ER70S5 or 6, wire will be adequate for welding low carbon steel tubing, which is what most Locost builders will be using. I strongly recommend using an Argon/CO2 mix Vs straight CO2 gas. You will get slightly better penetration with straight CO2, but using a 75% Argon – 25% CO2 mix will produce a lot less weld spatter, making clean up much easier and it will also give you better wetting of the bead and a better weld face to the base metal when using the argon/CO2 gas mix. Do not get the small disposable gas bottles, because it will cost you a fortune to weld a complete space frame. I would go so far as to suggest that a 40 lb bottle is the minimum size one should consider buying. Other welding items you will need: anti-spatter agent for the nozzle, which comes in gel or spray, plus a wire cleaning bush for the nozzle. You will need weld wire cleaning pads. I would recommend Chem-Tec pads. These are cleaning pads that you clamp over the wire to remove any of the drawing lube that is still on the wire. Because most of these welders only have a single drive wheel any oil on the wire causes slippage in the wire feed. You will also need spare gun tips and nozzles plus a good pair of wire dikes. If there is a Tractor Supply near you, or other farm supply stores, check them out for these perishables, they have much better prices then welding supply centers and Tractor Supply carries Hobart weld wire is .023 -.025” size. Be careful of off band weld wires. Some are notorious for drawing the wire size down to quickly, which causes variations in the wire diameter. If you can run your fingers over the wire and feel any change in diameter, the wire is junk. Do not use it, you are just asking for wire feed problems.

Welder set-up
These 115V welders are made to a price point, and most can use a little adjusting to optimize their functioning. If you buy a used welder, clean “blow off” all the internal dust and dirt that has collected on the transformer, Clean is cooler running. While you are cleaning also blow out any build up inside the wire inner liner. It is a good idea to do this every time you put on a new spool of wire. Check the alignment of the wire spool to the input wire guide and shim or make adjustments. You will have to do the same for the alignment of the drive roller to the output guide and then to the inner wire liner. The best method is to use a straight piece of wire that can be use as a reference to set both front and rear guides and roller drive wheel so every thing is perfectly straight through.
Last keep the drive roller CLEAN. 90% of all your welding problems are not the welder, but the weld wire and drive slippage. Make a permanent note on the top of the welder, “CLEAN DRIVE WHEEL”. This should be part of your regular maintenance just like dipping the nozzle in anti-spatter, use alcohol and a Q-tip to clean the roller and drive wheel surfaces. If you are using the larger 10 to 12 lb spools of wire, make sure you do not have a lot of rotation friction. These small drive motors some times have trouble getting that larger mass moving. I have found that some of the plastic spools have two ribs on the inside diameter of the spool, at the mold parting lines. Removing those makes a world of difference in getting a consistent and dependable wire feed rate.

Welding Safety
With MIG welding you have several elements that you need to be constantly aware of. First there is a bottle of highly compressed shielding gas, an electrical power source, arc flashes, and hot metal. Always think safety and keep a fire extinguisher handy “just in case”. I would recommend that you attach the fire extinguisher bottle to your welding cart, if you have cart and you should, because it is too easy to knock over a bottle of shielding gas. You will need a good pair of leather gloves and a welding jacket or a pairs of cotton welding sleeves. Last, the price for self darkening welding helmets is now so low that there isn’t any good reason not to have one. If you plan to do a lot of welding at one time, cover your skin with sun block. If moving your small welder around to different areas of the frame or shop and you will, make sure that the electrical extension cord is rated for a min of 20 Amps and more is better.

Fabrication Techniques
I’m not going to explain how to weld, it takes more then just a few paragraphs, visit the Miller, Hobart, and Lincoln web sites. Lincoln and the American Welding Society “AWS” both have excellent welding books and teaching aids. Also check out the local library plus your friendly local welder. Then practice on a few small projects first or scrap metal if you are new to welding. You could make that welding cart! Remember your life depends on the frame structure you will be building.
Locost fabrication techniques: When welding the thin wall tubing typically used for these frames one has to be careful of not introducing stress raisers or reducing the tubing wall thickness. You can be penned or bent in the tubing side(s) where you will be attaching the aluminum body panels. This slight relief will allow you to grind the weld seam down for fitting the aluminum panel but it will still provide more of the filet material at the weld joint. I would highly recommend that you just tack weld all of the main frame tubes together before completing any individual welded joint in the structure. The only time you should weld a complete section, is when it is needed to dimensionally stabilize the structure. Do not weld all of the tubes joints in one location at one time. This will cause the structure to distort. The key to welding this type of space frame is to clamp as much as possible during the tacking process and only weld one or two short seams at a time and then try to weld on an opposite side of the tube or area that will counter act or balance the previous weld’s built in stress cause by the weld shrinkage.
A 90 degree buck or fixture would be very helpful during the early stage of the building process so you can clamp the tubes to the buck while tack welding them in place. Once the frame is fully tack welded together you should have minimal weld distort if you balance your welds during the final welding. Rule number one, 99% of the time the weld will shrink and pull in the direction or to the side that the weld is placed on. So planning your welds is another key element in building a dimensionally correct space frame. I would go as far as suggesting that after you have tack welded the frame completely together, use a simple rotisserie “an Engine stand” that allows easy access to all the tubes weld seams to complete the welding. Do not just clamp the frame down and weld one side of the frame, this locks in all the welding stresses on that side of the frame. Using a rotisserie reduces the distortion and the tendency to weld all one area or one side of the frame at a time, before turning the frame over to weld the other side which will lead to pre-loaded frame sections and distortion. Being able to rotate the frame makes it much easier to balance the welds. That is in fact how prototype frames are made in the auto industry. If you are careful, using this technique, you will end up with less then 1mm of distortion over the length of the frame.
Your build goal should be all suspension mounting points within 1mm of design nominal. The frame tubes do not have to be within a millimeter, but the suspension mounting points should be. If they are not, modify or cut the bracket off and try again. When welding in your triangulation tubes, if you have the option, design the joint so each of the three or four tubes central axis insect at the center of the joint, Vs a joint where the triangulating tube is offset to the front or back of the joint. When welding various brackets or gusset, one should not weld right to the edge of the gusset, but stop the weld about 5 or 6mm from the end. This reduces the stress concentration at the end of the gusset and also reduces the chance to notching the gusset. If the bracket is highly loaded, such as a control arm mounting bracket, weld all around the bracket or gusset so you do not have any interruptions in the weld or any skips which could cause a stress raiser. If this is not possible, then make a “J” weld around the end of the gusset. You can also extend the weld 5mm or more pass the end of the gusset, but you must change the angle of your gun as you reach the end of the gusset to more vertical position to prevent notching when extending the fillet or making a “J” type weld. I would avoid this technique if you are a novice at welding, without first practicing the technique. If placing a gusset on square tubing, such as a corner brace, position the gusset on the inside or outside of the tube’s web corner and not in the middle of the web. The center is not as stiff and the flexing under load will cause the weld termination to crack in the heat affected zone. For round tubing the gussets should not be place on the middle of the tubes but on the inside or outside center axis of the tubes. What is the neutral axis of the tube when the tubes are loaded; because again there will be less flexing when the joint is loaded on the neutral axis which will prevent cracking. Other highly loaded gussets such as the lower control arm gusset should always have a fish mouth design, “a curved contour” which spreads the load out, Vs a straight across edge that concentrates loads right at the end of the gusset because of the large change in section area between the tube and gusset. If you plan to bolt on various components through the frame tubes, use an internal spacer tube to prevent the main tube from collapsing and weld both ends of the internal spacer tube. If it is lightly loaded attachment then a small tab may be the best option.
Last it is very important while inspecting all your welds, to look for weld filets that have undercut “A melted groove that is below the surface of the parent metal”. With such thin gauge tubing it must be avoided like the plague. It must be repaired. Note that you typically get the best filet and penetration when the weld gun is around 45 degrees to the surface and pushing the weld Vs pulling it, which is very helpful with low amp welding machines. If welding plated steel, to be on the safe side, and grind or sand the plating off the steel before welding, and do not try to weld through paint and oil. If you have any question about getting good penetration on heavier gauge material, prep both sides with a “V” in the filet area. If you end up with porosity in your welds, a dirty nozzle, grind out the weld and try again, do not weld over it. Porosity can also be caused by welding in a breeze, which blows away the shielding gas or welding with to much wire stick out “the distant from the tip in the gun to the metal” which prevents the shielded gas from covering the molten puddle.
Always think about safety while welding, Dave W


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PostPosted: March 24, 2010, 9:21 pm 
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Super job Dave. Maybe you could do a few more specific tricky bits with pics of your setup and before after shots. I'm a well experienced professional automotive technician with welding skills to match. That means I can get by with lots of cleanup time required.

I often have issues staying in a straight line "seeing" what I'm doing. I have a good darkening helmet, but I still mess up sometimes. I've thought about getting a 500watt work light to see if it would help, what do you think?


Geoff


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PostPosted: March 24, 2010, 10:58 pm 
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Thanx, very good write up. I've bookmarked this thread.

I used to weld for a living. Being a welder was the pinnacle of the shop work ladder. They didn't really have to work (or at least that's what I thought) so it was a position to be strived for. It didn't hurt that they made more than me.

But I went inside and out of the shop and have only gotten back to welding recently. It's amazing how much you forget. The old axiom of if you don't use it you lose it is very true.

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PostPosted: March 24, 2010, 11:09 pm 
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Geoff,

A strong light from over the shoulder opposite the weld hand; ie: if you hold with the right and guide the tip with the left, have the light coming over your left shoulder. It should be off to the side enough that it doesn't illuminate the inside of your helmet.

If you have an adjustable auto-darkening, you could try and adjust the "shading"; not the reflex speed.

Also don't block your puddle with the tip.

Tom

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PostPosted: March 25, 2010, 7:57 pm 
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Tom,
I'm getting the steel sheared for my motor mounts next week and soon after that I'll be back to welding again. I'll set up with the light (mig by the way - left handed too) over my right shoulder and practice a few passes.

I'm using a low voltage mig that I've had decent luck with so far. It's close to ten years old and has done a good few projects, so I'm not ready to sideline it. I'm also almost out of gas, so I need to get a fill before going back at it. Do you think there's any measurable advantage getting 85% over 75%?

If I'm welding better for the next session, it'll be your fault :cheers:

Geoff


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PostPosted: March 25, 2010, 8:22 pm 
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Geoff,

I don't know the difference between the 70% and 85%. I use 75% and it works fine for me. Just remember the golden rule of Mig welding: Cleanliness is next to good weld bead-linness.

Tom

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Sometimes, I'm as confused as a baby in a topless bar.

My short term memory is absolutely horrible and so is my short term memory.

https://www.youtube.com/watch?v=sG16m2e4O6I


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PostPosted: March 26, 2010, 6:50 am 
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Dave, thanks for taking the time to write this up. I have read what I thought were pretty good articles about welding, but many of the points you raised were in none of them.

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PostPosted: March 26, 2010, 8:23 am 
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Geoff
Yes I agree 100% on the 500 watt light, In my younger days I could weld with one eye closed and still see the seam. Now I'm blind in one eye and can't see out of the other. For use old guys, most welding shops have cheater lens that you clip inside the helmet. If you are over 50, thats the way to go.
I'll make up some drawnings of the gusset welds and post them at the bottom.

Dave W


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PostPosted: March 26, 2010, 9:22 am 
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A comment on visibility-
1) if you do the shop light, be sure that it's not shining into the back of your helmet, or you'll have glare.
2) if you have trouble seeing where you're going, sometimes you have to "zoom out" and look at the big pictures to see where you're going. One thing that really helps stray in tees is watching puddle angle- it shifts as you move off to one side.

Also, a note on machine care-
if you have your welder very long, you will get dust in the gun liner. you'll want to blow the cable out with compressed air.
keep your tips clean- if they're fouled up, they can cause a bird's nest inside

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PostPosted: March 26, 2010, 11:04 pm 
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Dave w, I thanked Tom inadvertently instead of you for the info. Tom, no disrespect intended. .....good weld bead-linness.???? :cheers:

Dave, I hope you'll expand on what you started. If you're not sure that your information is valuable, just ask the group. I'd be happy to supply the top 10 "situational welding" questions and ask the group to add theirs.

Here's my first few:

In a few weeks my engine - GM 3800 Supercharged - will be sitting in place. The oil pan will be lower than I want it so I'm going to shorten it by 2". The pan will be cut down with a lazer so the edges will be perfect. I'll be having a friend bend up the metal with 2" side-kickouts.

i what gauge do you think is most suitable?
ii is there any particular grade/type of metal that would suit the purpose more than others?
iii using my 120v mig, what settings would you suggest I practice with to do the welding?
iv I would like to have wide weld beads for both looks and effectiveness, any suggestions?
v can I prevent distortion by keeping parts of the assembly cool in water while welding elsewhere, or?
vi is there something before / after the weld to help the new assembly last longer?

This MUST have come up 100 times before and guys are then doing it for the first time. Most of the time the final product will be rubbish and that's why there are companies that supply this kind of stuff.

Dave.........Explain "cheater lens" please.............Over 50? I have underwear older than that

Geoff




Hope I'm not being too pushy. I figure when I have a resource like you, get what you can when you can :hail:


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PostPosted: March 26, 2010, 11:41 pm 
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Geoff,

A cheater lens is a Fresnel lens that sits behind the splatter shield but in front of the tint glass of the helmet. It's like wearing reading spectacles, only cooler. I have one in my cutting goggles also. You can also just wear your reading glasses inside your helmet too; that is what I do now.

I'd use a minimum of 14 guage for the new bottom of your oil pan if you're not going to brake the edges up to become sides. I like to have a sturdy base for oil pans in low cars. Weld in a threaded bung for a drain hole in the side of the pan extension. If the plug will be the lowest point on the pan and suceptable to hitting speed bumps, put it on the passenger side so that the speed bump wont loosen the plug, or, weld a protector pipe arond the bung.

Tom

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Sometimes, I'm as confused as a baby in a topless bar.

My short term memory is absolutely horrible and so is my short term memory.

https://www.youtube.com/watch?v=sG16m2e4O6I


Last edited by Off Road SHO on March 27, 2010, 11:41 am, edited 1 time in total.

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PostPosted: March 27, 2010, 9:21 am 
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I have one of those el-cheapo HF self darkening welding hoods. I guess I've lost the book if it ever had one (in english). I hadn't welded in a month or so and now it doesn't darken as much. It's much too bright. I looked for a battery in that thing but didn't find one. Should I just trash that one and buy another one or does anyone know the solution. I remember Dave (blinded by the light) Hempy having probs with his here while back.

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PostPosted: March 27, 2010, 10:19 am 
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Yup. Mine just wouldn't darken at all...or maybe it was slow (1/4 second?)...I don't remember. For $50 HF, I just bought a new one. I can do this every other year.

If you haven't welded in a while, it doesn't hurt to set the helmet in the sun or under a strong light while you're getting your work ready. I don't know if these units actually have some sort of battery/cap, or if it all fires directly from the solar panel voltage.

You can download all the user manuals from the HF web site. Just find the product page, and look for a link at the bottom, near the price.

-dave

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PostPosted: March 27, 2010, 10:20 am 
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my hf auto darkening helmet has worked well for me, had it about 2 years, the first one i had had a small issue when i first got it and did not want to risk having problems, so i bought another one. better not mess around when it comes to sight

(i guess hempy beat me to it)


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PostPosted: March 27, 2010, 9:26 pm 
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Tom,
Thanks for the continued info. Is a Fresnel lens something I'd get at a welding supply house? I already wear reading glasses, I found that helped a lot.

I'll be talking with my fabricator friend next week to plan the oil-pan mods. He has some pretty sophisticated equipment. 14 gge sounds right to me, I'll share what he tells me is best for strength, accuracy etc. The idea currently is to bend the bottom, sides and top (kick-out extensions) in one piece, with a very small radius (not a sharp corner). Then laser cut the top to match the pan. The ends will be laser cut/formed and welded to the cut-down pan.

I'm planning on some kind of "trap"* to keep oil around the pickup too. There is an oil level sensor that I don't really need but I think I should make a flange for it on the side of the pan and use it anyway. I'll put the drain on the lower, outside corner close to the back, so I can get 99% of the old oil out with minimal effort.

*I learned on a Pontiac site that arranging hinges around the oil pickup that only swung in the direction of the pump created an effective oil dam. Any thoughts from the group?

Geoff


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