VT-50 Jr. Dragster (kindof)

[Feathers]

The EGTs when running are actually just fine, around 400-450*C.

I was just worried about the integrity of the turbine wheel folowing the invitable hot starts its been through.

I'll post more pics as things come together.

[sven]

Thats what I meaned, sorry my english dosent make sence all the time

cheers
sven

[Feathers]

I just ordered an omron E3X-A11 and an E32-D24 2M fiber kit.

This will output some square wave signal corresponding to revolutions per second...

What I'm looking for, is some simple circuit to divide this signal by ten, so that rather than have an LED pannel display reading 0-80,000 RPM, I could use an automotive gauge reading 0-8,000 RPM...

I suppose I could do this with an arduino, but I'm wondering if there is a simpler way to achieve the frequency division.

[wolfdragon]

convert the square wave into 5V max, put that into a decade counter, the carry over pin (count 10) will go to reset the counter and will be your DIV10 signal source, scale back up to 12V or whatever the Tach wants to see

100% hardware solution

[Feathers]

That sounds fantastically simple.

One further question,
Kicking the output back to 12 volts I can do in a blink with a mosfet.
But if I were to use an LM7805 or similar regulator to reduce the signal voltage to 5 volts for the counter, would it accurately reproduce the signal out the other end? I'm not sure wether or not those regulators were designed to operate at 1.5KHz...

Thanks for the input!

[Feathers]

Did some more searching on that counter, and it looks like it will work entirely on 12 volts.

Thanks wolfdragon!

This project just turned into some free time to work on other things...

Like finals...

[wolfdragon]

a voltage regulator is meant for more steady state operation, if the counter didn't want to see 12V, you would use a "level shifter" circuit to knock the 12V into 5V

even a very crude one that just clips the top of the signal down to 5V would be just fine this application

BUT, you found a good high voltage one, so go nuts!

[Feathers]

Alright!

Just got an Everlast Powertig 185 Micro,

I'm sure the welder works great!

I just have half an idea what I'm doing .

After a day of practice, I decided to try and tackle the nozzle. I'd bought a 16 gauge 5"OD to 3"OD reducer, 4 inches long.

I'd also bought a Burns Stainless exhaust flange, and a cheapo ebay 5" stainless v-band clamp.

Unfortunately the inner diameter of the joint on the flange, was just about equal to the outer diameter of the reducer, so I had to space them a little over 1/8" in order to avoid a distinct "step".

So for my first tig welded part, I'm tackling thin stainless tubing with a large gap and no back-purging.

Thank god I'm good with a grinder.



The "v" in the clamp was a little small, but some work with a hammer and some sore knuckles later it fit perfectly.



I also disassembled the combustor to check for hot spots and wear. Heres the evap system:



Some spots look "frosted", like little flakes of burnt sugar.

Not sure what to think, but they've survived so far!

And Racket, I did this just for you .

[sven]

Nice thrust nozzle, I bought myself also Tig welder, but havent try it out so far.First have to buy some argon gas, then learn some skills. So far Im welding with Mig(gasless setting).


Cheers

Sven

[ernie wrenn]

Purge the inside of the tube with a inert gas.... argon...co2..(This will stop stainless from sugaring inside the wield).

Before wielding let the torch vent your gas mix at the wield site. Also let it "post " purge to keep it clean till the red hot area is cooled.

ernie

[Feathers]

Ernie,

I have a 1 second pre-flow, and 5 second post-flow set up on the torch,

I also would have liked to purge the backside, but I don't yet have the equipment...

Stole a trick from Johansson, and covered the backside in aluminum tape.
It smells a little bit, but did just fine.

Need to plumb up a purge line!

Started welding aluminum the other day, just amazed at what a noob like myself can do with a decent machine and a little practice!

[Johansson]

Good to hear that the tape trick worked for you, inside small diameter tubes you need back purging but for larger objects it has worked fine for me.

Looking forward to another video!

[wolfdragon]

More appropriate times for pre/post flow are better determined by how long the weld is still hot.

Your 1sec preflow is too short to actually purge the line, needs to be at least 5, I use 15 seconds. Just give the pedal a nudge when you reach for the torch, by the time you have gotten situated, the line is clear and your work area has a good blanket on it, so you are actually ready to strike the arc.

Post flow accomplishes 2 things. First, keeping the hot (read: reactive) weld area within an inert atmosphere until it cools. Second, unless your torch is water cooled, it cools off the torch. You should be higher than 30 sec, I use anything from 30-120 sec depending on the amperage used to weld and my duty cycle of welding.

Case in point, when making a stainless grill grate set for my grill...
24"x28" overall 1/4" rod outline, two stringers for support, and 1/8" runners every 1/2", twice over since there are two grates... That was basically 8 hours straight of welding with only stops when the torch head was hot through my glove. Argon was flowing for the entire time, keeping the welds from sugaring and keeping the torch cool.

Obviously you don't want to try to go over the rated duty cycle of the welder, but cutting off the post flow too soon will force you to derate your equipment or risk damage.

Shielding gas, even Helium is cheap in comparison to replacing torch heads that have melted.

[Feathers]

I haven't run my torch over 70 amps and have had no heating issues, nor have I had any oxidation/sheilding issues...

120 seconds post-fllow sounds kindof excessive, no?

I can't imagine that, in the ~10 sec. between welds for a typical job, diffusion would let more air into the line than a second of preflow would purge...

The welder and torch are rated for 185 amps, I don't think I'll hurt anything with 70.

[wolfdragon]

The 120 postflow is what I use when running nearly full power on my 200A welder, it was just a range for values sake, at lower power yes it is a bit excessive.

As for your setup, it (like all welders) has that rating for a 10% duty cycle over 10 minutes. At 70A, you are looking at a rating of no more than 50%, so in 10 minutes you should only have the arc on for no greater than 5 minutes...

From the way you worded your last, I doubt you do long continuous welds, so your actual duty cycle is low, thus no hot torches.

For general purpose thin welds (50-75A), I use a 10-15 preflow and a 15-30 postflow. You could shave a few seconds off of that, but gas is cheap and a bad weld can cause lots of problems.

I know it sounds like I'm doing X-ray quality welds, but those require even more stringent practices far above and beyond a little extra shield gas.