New O/A setup

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Thinking about a getting a medium duty O/A rig. I've got a plasma, mig, stick and soon to have a dc tig setup. But I find myself needing pre-heat for some stick and tig applications as well as using some torch heat to assist with bending metal. What size bottles should I get? I'm not worried about regulators, hoses and torches right now.Miller CST280Millermatic 251Cutmaster 42DeWalt StuffPlans are worthless, but planning is everything.  - D. Eisenhower
Reply:Some of your post doesn't really make sense.What are you welding right now that you find you need to preheat? The reason I ask is that your question is fairly basic, and most newer welders don't have any need for preheat, unless they are doing basic things completely wrong, like trying to weld heavy material with an undersized machine.  Usually preheat doesn't help beginners as much as many think it will, it simply helps hide the fact you are making poor welds. On the other hand if you are welding things that truly need preheat, that means you are welding fairly heavy weldments, and this significantly changes your cylinder requirements.You need to look at the tip size you want to run and what gas you will be using. Acetylene has withdrawl rate issues. 1/10th is the current recommendation, but 1/7th was the traditional withdrawl rate for years. A 75 CF acetylene cylinder is borderline with anything but the smallest cutting tips as far as withdrawl rate. If you plan to use a rosebud for any length of time, you need something larger even with the smallest rosebud sizes. To run large rosebuds you may end up having to manifold several large acetylene cylinders to get above the withdrawl rate. If so you may need to go to propane. Large heavy weldments often are heated with big propane weed burners. Usually the WPS doesn't call for you to heat the material super hot, only up to maybe 350-400F.Also regs tips etc will make a difference if you have to go to propane or some other fuel gas for heating.A 75 cf Acetylene cylinder is fairly typical for the average hobby user who only needs to cut a few things and heat a few bolts etc. It's usually matched with an 80 or 100 cf O2 cylinder. If you need to cut or heat more, then you start needing to look at larger commercial sized cylinders or propane, to deal with the withdrawl rate issues of Acetylene. This isn't some place where you can make a tiny set of torches do the job of a full sized set. Over drawing acetylene is very dangerous.From your comments I'm guessing you are new at this and are trying to get away with underpowered equipment already, probably to try and save money. This is a very bad place to try and do this. You need to get the right gear. You need to look at the big picture and size your equipment accordingly. You may have to limit yourself in project size if the equipment you can afford won't allow you to do some projects. That or just rent larger stuff when needed and eat the extra cost.Here's a tip chart.http://www.hoopersupply.com/tipchart.htmlLook at the far right side of the chart. You will see it says fuel gas and SCFH ( cubic feet per hour) If you use the 1/7th rule, a 75 cf acet would let you draw almost 10 cf /hr. That would limit you to the smallest sizes of cutting tips. Use the welding brazing tip instead, and that limits you to a #3 or smaller. Note the Heating tip section at the bottom a #5 starts at 7CFH at the very minimum and goes up to 25CFH, almost 3-4 times the allowable withdrawl!Last edited by DSW; 12-27-2012 at 04:33 AM..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:How many choices of gas bottle, as you call them, sources do you have to choose from.  How do they operate as to what they will sell you and what they will only deal in with a lease contract.  Is the lease five years for a certain size first one full cash and no credit check or is it a yearly lease for any size bottle, a detailed credit check and all gas first and subsequent fills billed separately. Find out what the policy is about getting a different size next time around, it might not matter all that much if  you can switch easily later.   Is portability important?  You would seem to be in need of argon, oxygen and acetylene.  Air propane as DSW suggests with the weed burner or things used by folks in the roofing trades might keep your need down to one argon cylinder.  There are compressed air/propane stuff good for up to 100,000 btu per hour if you have a big enough compressor, these things rather expensive new don't seem to have much value used.I get the biggest oxygen they have in the neighborhood of 300 cubic feet on a lease.  As for the preheat and welding  Dsw above is kind of in line with my thinking.  For mig spoolgun and aluminum a bit of heat before welding helps with my antique stuff.  Preheat aluminum and tig but you need ac tig for that.  The acetylene is supposed to work in a way that you soot up your piece of aluminum then heat it until the soot goes away and bend.  Kind of neet but doesn't seem hot enough to bend at that point to my liking.  Propane is more water in the flame and not as shielding but really quite sufficient for heat.fran
Reply:I have preheated 4130 prior to welding to help keep it from cracking along the weld. I've been using a rosebud quite a bit to work with small gauge steel to build roses and other neat stuff. I wished that I had a torch to heat up some material to bend it easier. I also need to weld to cast for axle trussing and bracketry so some preheat and nickel rod will be in order there. I have a small plasma, so an oxy rig that can cut 1" material is also handy. I also have the occasional brazing project. I was looking at a acetylene tank somewhere in the range of 110cf or so. How do I size my o2 tank? For rosebud work I was thinking of 1.25x the acetylene tank. So I would get an o2 tank sized around 140cf. I could draw down on the tank at 15 cfh without much risk. That would enable me to do quite a wide range of work with the tanks. I want a set of tanks that I can own. No renting or leasing. I don't work with crappy tools. I would rather not do the work if that is the case. I have been using someones oxy rig to do a few things, but it is time that I put my own together. Sorry that my post was a little confusing, I was pretty tired last night.Miller CST280Millermatic 251Cutmaster 42DeWalt StuffPlans are worthless, but planning is everything.  - D. Eisenhower
Reply:Originally Posted by gpnI was looking at a acetylene tank somewhere in the range of 110cf or so. How do I size my o2 tank? For rosebud work I was thinking of 1.25x the acetylene tank. So I would get an o2 tank sized around 140cf. I could draw down on the tank at 15 cfh without much risk. That would enable me to do quite a wide range of work with the tanks. I want a set of tanks that I can own. No renting or leasing.
Reply:Sounds good. I don't know what sizes I can actually get. The last time I picked up a bottle of acet for work there were size 4 tanks ranging in fill from 100-115 cf. They apparently had a rate based on the cf in the actual bottle. I might end up with completely different sizes, but I was trying to figure out how to match the o2 to the acet.Miller CST280Millermatic 251Cutmaster 42DeWalt StuffPlans are worthless, but planning is everything.  - D. Eisenhower