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Hi guys, making a little valvless and just had a query. I recently bought myself a mig, and i have a stickwelder. Though I'm now thinking that I should have a TIG welder. Does the tig allow you to weld really thing stuff without blowing holes in it. I'm still blowing the occasionaly hole in .5/.8mm steel with the mig (Though its alot better then the stick welder for sure) I think i'm doing ok here with the mig though can anyone advise on a few little tricks or techniques to get a good bead without putting gaping hole in my rolled pipes. For instance - using the mig at a high angle of attack, faster wire speed? I've noticed if you put the tip of the trigger gun right on the overlap you can get an effective tack weld, though dont know if you should sustain the weld with torch tip in contact with the metal all the way along your pipe. Any little tips for the mig I would appreciate.
Mangy (47)

Here a few photo's of my first valvless pj. Nevermind, the answer is just a hefty amount of time and caution extreme. When its finished i'll gring off the excess to hopefully leave an "ok" looking engine.
I took what i have so far, plugged one end and filled it with water...
the water does eventually leak out but its very slow to do so and doesn't trickle anywhere (just starts looking wet along some places.) Yhere seems to be good pressure in there, will this be ok (as its only a test engine) or will i need to grind it down and go over it again. I just want to get the thing working not to fussed about lbs thrust at this stage... made from a paint tin too. The pipe and CC also ever-so-slighlty overlaps inside. I hope thats not going to make it not function. Will this stop it from working.

It's been ages since I miged anything together, but you appear to be welding over edges that aren't clean on both sides. Yep I know that the paints on the inside but it does contaminate the weld and make for poor welding. And yes when welding steel patches up a stuffed light truck I owned I welded over every thing. Mastic, paint, dirt, rust, wasn't pretty but it held together for another 6 months on the road. So you are doing OK for a first time on dirty metal if its not leaking.
Take some nice new clean metal and run some beads while you mess with wire feed and amps. Quick learning experience.
One other point welding outside with a MIG gas sheilded rig is a pain in a wind as it blows the sheilding gas away. Manky welds guarenteed.

Thanks for you reply because I learned something I didn't know... leaving paint on the inside = BAD! Thanks! The welds -seem- ok and only light trickles are poping through when filled with water, and blowing through it gives fairly good compression. Its a gasless mig, and its not too bad for this thinner stuff, gotta be hell careful though. Here is how far i've come thus far. Should it still work even if its not water tight?
Slight modifications have been made but meh I'm wingin this one! LOL I had stupid ass metal from old paint tins to start off with.

I do not know which kind of quality MIG welder you are using, but my (somewhat cheaper one) would not work nicely with sheet steel below 1.0 mm. Okay, I'm not an experienced welder, but anything near and below below 0.8 mm is more likely to be TIG welded.

Using stainless steel usually makes things wose, due it does not transfer heat as good as mild steel.

Of course, seting up the welder properly, e.g. current and gas flow, is important though.
You may also try different steel wires. I think 0.8 and 0.5 mm wires are commonly available.

So, for an unexperienced welder, I would suggest sheet metal of 1.0 mm thikness and 0.8 mm wire. For me it makes for the best compromise.
Then there is only left practicing.


Note: This topic might be moved to "Tools and Constructions".

It has been reported by Steve Bukowsky and others that TINY holes don't seem to keep a pulsejet from starting and running.

To me, the single most important thing to try for is the smoothest possible interior side of the welded joints, ESPECIALLY at the narrowest points in your pipe. Naturally, this is the hardest thing to achieve, and even the hardest thing to inspect for!

Oxyacetylene forever !!! ;-)

L Cottrill

Hey larry, thanks for finally answering my question... once again your the man! Anyway, i just did this, took one look at it and burst out laughing... i'm going to call it the "El-natural" ROFL!!! Muahaha

AND "Dolphin Friendly", too!

L Cottrill

Number47 wrote:Any little tips for the mig I would appreciate.

check out this post.

http://www.pulse-jets.com/phpbb2/viewto ... ght=#38584

Just noticed this - don't know why I didn't see it before. Just in too much of a rush, I guess:

Number47 wrote:The pipe and CC also ever-so-slighlty overlaps inside. I hope thats not going to make it not function. Will this stop it from working.

The overall impact of this depends on the direction and smoothness. It is FAR better to have the pipe overlap the outside edge of the cone than vice versa. This is because the overlap is in favor of the high speed of the blast mass leaving the cone. It's awfully draggy the other way, and at the worst possible spot in the engine.

However, even if the latter is the case, don't despair - I'm sure you will still have a running engine. AND, over the first few minutes of running time, the engine may itself smooth out this wrinkle by high-temperature oxidation. Just don't get behind this engine looking in, without a good full face shield !!! You may be surprised to see what comes out of there (at near Mach speeds), the first time you really let her run.

L Cottrill

Actually there is an even better way of doing things rather than leaving an over lap anywhere, and its really quite easy. Flare the pipe inside of the cone, slide the pipe down and then weld. You get a material overlap thats easier to weld, and no lip that hurts flow in any direction.

Eric

Not too bad for your first welds...

The #1 most important rule for welding is to make sure your materials are absolutely clean. Not doing this is probably the most common and biggest mistake made by people learning to weld.

Grind everything down until it's shiny clean, and then wipe it down good with some solvent, acetone is my favorite. You will instantly see an improvement.

Just about to try n get this puppy thumping, just need to know if I heat up the CC with the blowtorch first, then initiate gas and put the blowtorch down the air inlet is this a typical starting proceedure? or would I be better lighting it from the tailpipe? As you can see there is no sparkplug. I can also light a sparkler and toss it down there if it has to be started from within the cc.

Bastard wont start... into the bin she goes!
Was a good effort though and I learned alot about welding and got some good practice. Thanks for all your help, hopefully, my next attempt will be more fruitful. From your information I have some much needed insight and thanks to eric for that excellent tip for flaring the inside of the CC.
I thoroughly enjoyed giving it a go, and appreciate all your tips n hints. I'm really glad you guys took the time to answer my questions.
Best regards,
Mangy

....I'm off to play with my ramjet for a while! LOL!

Number47 -

Hmmm ... now, let me get this straight. You're giving up on your first pulsejet after spending less time trying to start it than you spent building it? And, without a single question as to what might be wrong?

As long as your engine is built reasonably close to the correct diameters and (especially) lengths, and isn't full of holes, AND has the fueling point located properly, it should absolutely YEARN to start up and run for you!

At the very least, go to my 'Audio FAQ Page' (which I still haven't taken down), put your headphones on, and listen to these two questions:
Aren't valveless pulsejets notoriously hard to start?
What starting method is used for valveless pulsejets?
You should listen to the second one enough times that you can hear it every time you close your eyes. The page is at
http://www.cottrillcyclodyne.com/index_Audio_FAQs.html
There is also a hokey 1-minute film of an early start of my Elektra I engine here:
http://www.cottrillcyclodyne.com/Elektr ... -14_Lo.wmv
This shows a little of the technique of "feeling around" with your blower and fuel for the right conditions for startup. Note how far the blower is from the intake! An FWE type design will take even less air than that for starting - just a whisper of air, really.

Obviously, you will need to use something for ignition besides a spark plug - I think both Mark and Eric have successfully lit them from the tail with something like a propane torch flame. But if the engine is well put together, there should be NO reason you can't get her running.

You're giving up WAY too soon, considering this is the first valveless pulsejet you've ever tried to run. It CAN be done! Go for it!

L Cottrill