Minimum acetylene tank size for frame building?

[Alistair]

Hi,
Im aspiring to build my first frame and Im interested in an oxy acetylene setup. Ive concluded that bigger=better (provided I can transport and store them safely). That being said Im having a hard time finding large tanks in my local market and small acetylene B size tanks seem to be a dime a dozen. My concern is that I can't find a definitive answer as to the acetylene withdrawal rates during frame building and accordingly how big of a tank i need to keep acetylene use within the 1/7th withdrawal rate rule. Ive seen users here (or maybe on mtbr?) citing use of B cylinders and even MC cylinders but the tank size discussion seems centered around cost and refill intervals, and not withdrawal rates. Are these smaller tanks suitable for the more gas intensive processes like fillet brazing, fork crowns etc.?

FWIW Ive used oxy-ace in the past, just never for frame building and I will probably setup an oxy-propane rig as well to see what I prefer. Leaning towards a victor j-28 torch if that matters.

Lars H.

I have a #3 Acetylene tank, which is 75 Cu. ft. I consider it to be a handy size. Big enough to do a few framesets, easy to move around and exchange at the LWS.

Recommended max draw for that tank is (75/7) 10.7 SCFH. Victor lists the flow rate of it's no. 3 size tip (for Acetylene) at 8 - 18 SCFH, over the range of the recommended operating delivery pressure. Flow rate for a No. 4 tip is 10 - 25 SCFH.

From that you can see that a No. 3 tip is probably the largest you'd want to go with that size of tank. Maybe you could drive a No. 4 off it if you really wanted to, I don't know. You would run the risk of drawing Acetone into your regulators, generally not good. Multi port rosebud tips aren't going to work well off a tank of that size eithr (according to the Victor numbers. Never tried it myself).

Alistair.

[Lars1]

Sounds like maybe my concerns over small tanks and withdrawal rates are not so relevant in practicum but there seem to be a lot of votes for tanks in the 60ish-80ish cu.ft. range. I guess Ill shoot for something around 75 cu.ft. since it seems like a safe size from a technical standpoint and will minimize the 40mile drives to my local air gas. Thanks for all the input guys.

[jclay]

I just ran into some updated withdrawal information reportedly from the Compressed Gas Association. They've apparently revised the withdrawal rates for acetylene down from 1/7 cylinder capy per hour to 1/10 for intermittent use and 1/15 for continuous use. The short article is worth reading.

Fuel your safety knowledge - TheFabricator.com

I realize that heretofore I had been exceeding the old recommendations, never mind the revised ones. A 300 cf cylinder, difficult for me to transport, is what I'd need for the largest tips I use. That's the reason I recently decided to switch to LP for lugs, crowns, BB shells. My 75 cf Acetylene cylinder is only for the smaller tips and frame items now.

[Ken Holmes]

I use 40 cf cylinders, the B type. I have consistently gotten nearly 3 fillet brazed frames out of them, usually using up the acetylene before the oxygen. I would have 80cf if I could to save on fills, but transport is more of a pain for me. I bought mine outright years ago, which has certainly paid for itself and reduced headaches around rental fees.

[EricKeller]

the total capacity is important because of how many frames you can make with it, but also because of how fast you can remove the acetylene. My LWS was reluctant to rent me tanks, and I ended up with the largest they would sell me. I think it's 80 cu ft. I did the calculations once, the largest tips that fit on an A1WA will draw gas at a higher than recommended rate. This is mostly useful if you are brazing lugs with brass. The standard AW 205 tip will not overdraw the tank. That's plenty big for fillet brazing a bottom bracket or dropout.

[jon_norstog]

I used "B" tanks for years, because that's what I had. I could build 4-5, sometime 6 frames with one tank of acetylene and have O2 leftover. They were nice for jobs where I had to hump them in on my back. It's an expensive way to buy gas. I've got bigger tanks now. Whatever you get, own your tanks.

Good luck!

jn

"Thursday"

[edoz]

I started with the smallest size tanks the welding supply store carried (they litterally both fit in a 26l backpack) , and I was able to fillet braze just fine. I got a bunch of practice joints and my first couple of frames out them, then I traded up when they were empty.

[jclay]

Bumping this thread because many are unaware of the safety implications related to use of acetylene cylinders that are too small for the fuel demands made of them. I definitely operated outside of recommended safe practices for years.

Posts 15 and 17 accurately summarize the older and current recommendations. In post 10 I noted that a Meco #5 was OK for use with my AC3 (75 cu ft stamped) cylinder. If adjusted properly (soot just disappears from flame prior to addition of oxygen) it would consume acetylene at an excessive rate and risk aspirating acetone into the regulator, hose and torch. That could damage the diaphragm and hose, and in extreme cases cause them to rupture. Now I know why the flame from the #5 and 6 Meco tips occasionally started getting dirty, different and rough, as compared to using the 3 or 4, when driven hard; acetone was bleeding through and igniting along with the acetylene. The flame was distinctly different and uncomfortable so I dialed it back or used a smaller tip, but I didn't know why or what I was risking.

The Smith (now Miller) O/A instruction book and catalog have consumption rates for their tips which, when used in conjunction with Mark Stonich's tip size chart, can provide guidance for other tip brands:

Welding Tip Size Comparison Chart