Tips on removing weld from inside of a pipe

Good evening. I know this sounds like something a kid would do but here goes nothing.

I'd like to remove the weld from inside a piece of 2" sch 40 steel pipe. The end result will be an air cylinder.

Before anyone says don't do it or buy some DOM, this has to be done on the cheap (read free!) I'll be making something like 5 or 6 of them to use on a "Mad Max" vehicle. It is more of a parade vehicle and the cylinders will not be used for holding, just for slamming something against a spring into a latch - so it does not matter if the piston seal is perfect. I'm looking at using 50-60 psi and welding in the ends in place. I might not even use an o-ring on the piston if I can get away with it.

I have a #1 Bridgeport, an old SB 9" lathe and a 13 x 40 jet with which to do this. I'm looking at a cylinder length of around 16" and would like some simple tool like a counterbore that I can put a shaft extension on and just run down the inside of the pipe. I know the pipe is not terribly round and if the tool surfaces a bit of it that would be OK as well. I do not want to use a boring bar - I do not have the $ for one that large and I don't need it that good.

I teach welding at our local HS and community college and the kids are really into this project & I hope to be able to get it done. Additionally, while I'd like anything I build to last forever - I doubt this thing cycles a thousand times in it's life.

As a last thought - after I get this process ironed out, I'm going to make a large one out of a piece of 8" pipe - 24" long, so keep that percolating on the 'ol idea burner as well.

Thanks in advance for your advice!

Mikey

While I appreciate "cheep" and "free" you might check Surplus Center for a cheep air cylinder, they are quite cheep. Probably cheeper than the hone your going to wear out.

Now to answer your question, build an bar with one cutting edge and one "foot" opposite the cutting edge. hone after with an extension.

are you sure that you need 16" travel? 2"@ pixrsquarex60= 188 pounds of force

silly boy piaren't square, piare round

Might be easier to line the bore with say pvc or brass pipe. turn the outer diameter of the pvc and maybe a shallow slot to clear the weld so it fits inside the steel pipe. any explosive failure of the pvc is contained in the steel shell. If the slot needs to be too deep maybe bed it in plaster of paris or silicone caulk so the slotted part is backed up by something solid preventing the pvc pipe from bulging out of round too far.
Bil lD.

Pipe is possibly the worst material you could try to make any kind cylinder out of, especially as a teaching exercise. Seriously, what they will learn is how to waste time on a fruitless endeavor. You will not be able to produce a surface even half as good as the ID on DOM tubing, which will seal with a fat o-ring as-is.

weld a long rod onto a drill bit and ram it down the hole, hang on to the some bitch though. It will eat the weld.

I needed to remove the weld from a piece of pipe to fit a bolt through. I know you said you don't want to use a boring bar, but it will work. I made a boring bar out of a piece of 25 mm bar out of my scrap bin. Might have been 304 stainless, not sure. I used a 6 mm square hss cutter bit. The pipe was mild steel, id 36 mm, length about 450 mm. I used a steady, taking light cuts and flipped it over half way. It worked for the purpose.

The 9" south bend probably won't fit 2" pipe through the spindle so you'll need a steady rest to do this but I agree with Piek that you should bore it by making a boring bar as he describes. This will also round out the tube so you can machine a piston that will fit nicely. Don't use O-Rings at all, just machine the tube and pistons to with say .003 and you're in business.

I teach undergrad engineers on co-op jobs and a we often do things "properly" to make the point that they need to learn to do things properly. Getting your kids to bore these things would be a valuable exercise in using old tools and cheap stock to do something really well by means of the application of skill.

line bore it, maybe?

If I were going to attempt this I would get a piece of 2" stock about three inches long. Cut a groove across one end with a 1/4" end mill almost 1/4" deep. Drill and tap a hole about 1/4-20 right next to the groove. Drop in a 1/4" HSS cutter and clamp it with a 1/4-20 cap screw and washer with just a little bit of the cutter sticking out. Drill and tap the other end to hold a 1/2" rod for the tailstock to grab with a beefy chuck. Grind the cutter so the 2" stock has to more or less enter the pipe before the cutter makes contact (think a backwards grind on the cutter with the cutting edge toward the tailstock). You might even be able to get away with not using a steady if the 2" stock goes up in the pipe far enough. Once the weld is cut away the stock should ride in the pipe and support it. Line boring basically with a homemade cutter. Not very elegant but I can imagine it working for the level of accuracy you are looking for.

crossthread said:

If I were going to attempt this I would get a piece of 2" stock about three inches long. Cut a groove across one end with a 1/4" end mill almost 1/4" deep. Drill and tap a hole about 1/4-20 right next to the groove. Drop in a 1/4" HSS cutter and clamp it with a 1/4-20 cap screw and washer with just a little bit of the cutter sticking out. Drill and tap the other end to hold a 1/2" rod for the tailstock to grab with a beefy chuck. Grind the cutter so the 2" stock has to more or less enter the pipe before the cutter makes contact (think a backwards grind on the cutter with the cutting edge toward the tailstock). You might even be able to get away with not using a steady if the 2" stock goes up in the pipe far enough. Once the weld is cut away the stock should ride in the pipe and support it. Line boring basically with a homemade cutter. Not very elegant but I can imagine it working for the level of accuracy you are looking for.

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That's the way. Make a close fitting plug with a cutter to broach the bead, if that is an acceptable machining term for the application, and ram it through so it shaves some of the bead and repeat. I've done small sections with the tip of a file.
Another more labor intensive idea is to cut the bead out from the outside, squeeze the pipe back together and reweld from the outside. My idea so if you use it send money[emoji12]

Seiner said it right -- track down an air cylinder. If you ordered something today versus trying to successfully bore out a chunk of pipe, the purchased air cylinder would probably be delivered before the pipe was finished...

Otherwise, check out a scrap yard for some steel tubing drops. The price will be a whole lot better than buying new material, and the end result will be a lot better than cobbling something out of pipe.

If you absolutely want to use pipe, then line boring will probably give you the best results. It isn't done as often these days on a lathe, but w-a-y back, in the pre-WWII days, it was a lot more common. The easiest way would be to track down a Palmgren milling attachment for your lathe, but you can always make a one-time fixture.

rcoope said:

The 9" south bend probably won't fit 2" pipe through the spindle so you'll need a steady rest to do this but I agree with Piek that you should bore it by making a boring bar as he describes. This will also round out the tube so you can machine a piston that will fit nicely. Don't use O-Rings at all, just machine the tube and pistons to with say .003 and you're in business.

I teach undergrad engineers on co-op jobs and a we often do things "properly" to make the point that they need to learn to do things properly. Getting your kids to bore these things would be a valuable exercise in using old tools and cheap stock to do something really well by means of the application of skill.

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A 9 inch South Bend probably won't fit 2" pipe thru the spindle? PROBABLY won't? Do you have any idea what you're talking about? They won't be able to bore that long POS at all, let alone maintain .003 clearance for the piston. And without a seal, after five minutes it will have leaked enough compressed air to have paid for a tubing drop. This exercise is known as "trying to make a silk purse from a sow's ear." The undergraduate engineering students are not going to be able to do this on a 9" SB and my point is that they should not be given the impression that it is worth trying in the first place. It would be basically showing them that it's OK to waste time doing something inefficiently.

ON the SB9? Gonna need a L-O-N-G bed.

dian said:

line bore it, maybe?

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What you need has already been said... but in case your of the RED GREEN era....

git you self a mailing tube or a pc of plastic pipe of proper length and some plastic for end capsand a piston and some rubber floor mats from the old truck...ohh and one more thing...
a length of BROOMSTICK...

Using those and maybe a few hose clamps, ya oughta be able to cobble together what might pass for an air cylinder the RED GREEN way...

Lotsa luck, we're all pullin for ya..

Oldwrench said:

A 9 inch South Bend probably won't fit 2" pipe thru the spindle? PROBABLY won't? Do you have any idea what you're talking about? They won't be able to bore that long POS at all, let alone maintain .003 clearance for the piston. And without a seal, after five minutes it will have leaked enough compressed air to have paid for a tubing drop. This exercise is known as "trying to make a silk purse from a sow's ear." The undergraduate engineering students are not going to be able to do this on a 9" SB and my point is that they should not be given the impression that it is worth trying in the first place. It would be basically showing them that it's OK to waste time doing something inefficiently.

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Go back and look at the original post. He's not teaching engineers, he may actually have actually NO budget and he's not trying to hold pressure. It sounds more like he building a potato cannon than a cylinder. In this case, sure, the definition of "properly" is to get a cylinder so normally you'd have the students figuring out what cylinder to specify but clearly thats not what they're doing here. You're right the South Bend is possibly too short to do this and maybe it's worn as many of them are, but then again maybe it isn't.

Then again, schedule 80 plastic pipe would probably work well for this as many a potato cannon has been built of such stuff.

I've done it, like other have said make a bar and add a rider on the opposite side. I actually used three riders spaced out 120` and it ran smoother. Clean up the end normally , then use the bar once there's room for the riders.

I'd still rather find scrap cylinders and rebuild them.

Mikey D said:

...and the cylinders will not be used for holding, just for slamming something against a spring into a latch - so it does not matter if the piston seal is perfect. I'm looking at using 50-60 psi and welding in the ends in place...

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I did read the OP and it doesn't sound like a potato cannon. It's on a vehicle. Pardon me for taking it seriously, but are there possible consequences to riders and spectators if it doesn't actuate the spring and latch?

Oldwrench said:

I did read the OP and it doesn't sound like a potato cannon. It's on a vehicle. Pardon me for taking it seriously, but are there possible consequences to riders and spectators if it doesn't actuate the spring and latch?

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You're right there, and in particular if you don't have a normally sealed cylinder then it's going to be hard to control the speed at which the actuator operates so it might be hard to make the latches work. I was of coming at it from the point of view that sometimes you have to go into Cuban car mechanic mode with all the ingenuity but no funding, but this does actually sound like a pretty serious piece of design and if you're using actuators that big you should think hard about safety. unless perhaps you're using 10psi or something.

I suggest you go buy a piece of 2" rigid electrical conduit. Same size and thickness as 2" pipe, but with the inside weld removed. If you have a good hardware store near you, they may well have drops available so you don't have to buy a whole length.

It might be almost as cheap to buy some hydraulic jacks at Harbor Freight and take them apart and use their already-machined parts for your cylinders. Wouldn't be exactly 2" but then you'd learn a thing or two about hydraulic jacks.

metalmagpie

I'd use the shaper with a long poke tool to take the ridge off, then bore it.

Well, no, I'd go to the steelyard and sift through their drop aluminum and get some sch40 for $2/lb, and use that.

metalmagpie said:

It might be almost as cheap to buy some hydraulic jacks at Harbor Freight and take them apart and use their already-machined parts for your cylinders. Wouldn't be exactly 2" but then you'd learn a thing or two about hydraulic jacks.

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