"Fat Boy" 12/118 thrust engine

[racket]

Hi Gavin

I initially used a 2 inch A section V belt pulley in the vice jaws to get a fair bit of the circle bent but then used a section of pipe to continue bending around , the fairly thick 1.6mm wall section of the tubing helps as it acts more like solid bar than tubing .

Once I had ~400 degrees of bend , 40 degrees of overlap , I fitted the tubing in the vice and squeezed the overlap against each other and slit through using the side grinder with a thin 1/16" disc to produce a 360 degree "ring", make sure you cleanup the ID of the tubing ends prior to twisting them into alignment.

By slitting this way both ends are relatively parallel when they are fitted together for welding , some "massaging" of the ring is necessary to get everything into alignment , but if the ring is held in the vice to squeeze the ends together a reasonable welding scenario is created.

I only TIGed the inner half of the joint before fitting the ring in the drill press vice and drilling the 1/4" hole for the supply pipe to be welded over , a bit of work on the supply pipe end is needed to get a good fit between parts prior to TIG'ing together .

Cheers
John

[htevo80]

Dec 4, 2019 15:32:11 GMT -5 racket said:

Hi Gavin

I initially used a 2 inch A section V belt pulley in the vice jaws to get a fair bit of the circle bent but then used a section of pipe to continue bending around , the fairly thick 1.6mm wall section of the tubing helps as it acts more like solid bar than tubing .

Once I had ~400 degrees of bend , 40 degrees of overlap , I fitted the tubing in the vice and squeezed the overlap against each other and slit through using the side grinder with a thin 1/16" disc to produce a 360 degree "ring", make sure you cleanup the ID of the tubing ends prior to twisting them into alignment.

By slitting this way both ends are relatively parallel when they are fitted together for welding , some "massaging" of the ring is necessary to get everything into alignment , but if the ring is held in the vice to squeeze the ends together a reasonable welding scenario is created.

I only TIGed the inner half of the joint before fitting the ring in the drill press vice and drilling the 1/4" hole for the supply pipe to be welded over , a bit of work on the supply pipe end is needed to get a good fit between parts prior to TIG'ing together .

Cheers
John

Thank you John this will help alot hopefully I can stop kinking the tubing.

[racket]

If using thin walled tubing, kinks are a problem unless you fill the tubing with "sand", "plaster" or solder to make it "solid" , then it behave more like a solid bar , but the use of an appropriate tube bender is still a good idea.

Making my spray ring wasn't a job I was looking forward to doing especially as it was only going to be 3" in diameter , larger diameters are easier.

Annealed tubing should be easier than hard drawn stuff .

I've never tried heating the tube, but would imagine a red hot tube would bend easier

[htevo80]

I might try sand the wall is only 1 mill thick 3/8 inch tube
What hole size and amount would you suggest for the A/B ring?
Thank you
Gavin

[racket]

Hi Gavin

1mm - 0.040" holes are probably about as small as is easily drilled , I used them in the GT6041 jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart?page=9 , it used 16 holes but flowed 50% more air than your engine , so maybe 10-12 holes for your spray ring , maybe 3 or 4 pointing to the centre and the rest to the outwards of the ring , it'll depend on the "area ratio" , we need as even a coverage as possible

Cheers
John

[racket]

Hi Guys

Everything is ready for another test run , just waiting on the weather , need some rain to make things safe to fire up , don't want to be the guy to start the next bushfire especially when we're having Total Fire Ban days at the moment , already >600 homes destroyed in the State over the last coupla months along with >5 million acres burnt , we've still got a couple of mega fires burning leaving us blanketed in smoke most days with toxic air outside , so hiding away in the aircon unable to get in my shed.

Today I've finally been able to at least do some work on the gearbox pinion shaft and freepower coupling piece ,............ I hate having to machine the coupling piece's internal keyways in the lathe, especially into this high tensile steel thats not good machining quality , two hours of frustration but its done .

Next job is to turn up a mandril in the lathe and mount the coupling piece to it via the pinion shaft bore so that I can machine the turbine wheel bore spigot and mounting face true to the shaft .

A few pics of "progress??"







Cheers
John

[pitciblackscotland]

Hi John,
Yeah that would be a bugger of a job doing internal keyways. Mmmm i think i will have my local tool maker do some internal keyways for me he has a nice metal shaper in his home worshop. Nice work on the pinion shaft

Cheers,
Mark.

[racket]

Hi Mark

Yeh , thats the tool I'm missing , LOL, my old lathe has so much play in EVERYTHING that most jobs become a battle between man and machine which invariably end in a draw :-)

I'll hopefully get the rest of the coupling piece finished tomorrow , then a spacer between the two bearings so that everything can be locked up tightly

Cheers
John

[racket]

Hi Guys

Pinion/freepower bits made , just need to cut off the "extra" bit of shaft outside the gear , I left it till last job just in case I needed it .

The tubular spacer between the bearings was a mongrel to make using this crap high tensile steel, spent 3 hours "honeing??" out the ID so that its a smooth slip over of the shaft , made it long enough for ~0.004"- 0.006" endfloat of the bearings in the housings as the alloy housing could expand a bit during use.

The freepower's driving curvics has one curvic ground off for positive indexing of the wheel to shaft coupling piece , the whole lot is held together with a high tensile 7/16" UNF X 3 inch long bolt , I would have liked a 1/2" bolt but with the shaft keyway taking up some of the shafts 22 mm dia there wasn't a lot of "meat" left for the screw threads .

I'll remove the bearing's seals and wash them clean and do a rough balance test of the rotor , I did do a spin using the workshops compressed air and things felt OK , so probably not too far off .

It'll soon be time to start fitting the two gearbox halves together and seeing how the cogs spin :-)

A few pics of todays efforts







Cheers
John

[azwood]

I been wondering will the wheel run cooler when it's spins

[racket]

Hi Aaron

It will once the water spray fires up :-)

But yeh , a spinning wheel should run cooler because it won't be subjected to the "impact" of the gases that a stalled wheel feels , think of it this way .........normally theres an expansion of the gases in the scroll/NGV with a temperature drop , with a spining wheel the gases just sorta pass through axially without much interaction with the blades , but the stalled blades get slammed with high speed gases which "recompress" and "reheat" back towards their pre scroll/NGV levels ...........LOL, I guess theres lotsa variables at play which will create more or less problems ,

Cheers
John

[racket]

Hi Guys

Gearbox is getting close to completion , youtu.be/1hxJS4LHftE just need a couple of locating pins to keep the halves in alignment , I might need to do a trip and purchase them so that I can get it finished before Christmas arrives and everything shuts down for the holidays.

The usual stuffups encountered , whilst other bits went easy , I've given a bit of clearance "rattle" between the gears , it should be OK with some thick oil inside

Cheers
John

[turboron]

John, please summarize the gearbox details for us. The ratio, center distance, gear diameters and design horsepower etc are of interest. Are the gears from a supplier or did you cut them?

Thanks, Ron

[racket]

Hi Ron

To keep costs down I'm using off the shelf gears khkgears.net/new/spur_gears.html a SSS2.5-11 pinion and shaft combo feeding a SSS2.5-48J40 , so a 11 tooth to 48 tooth ratio of 4.3636:1, all the size info is on the PDF downloads , gear width of the 2.5 module is 25 mm.

The main gear worked out OK , but the pinion has caused a lot of unnecesary problems/work because of its shaft dimensions , both dia and length , I think getting a bespoke pinion gear/shaft would be the way to go so as to eliminate the turb wheel to shaft adaptor.

LOL......design horsepower .........mmmmm, I sorta worked on using a chunky gear similar to a large motorcycle gearbox gear I had lying around , the 2.5 Module seemed to fit the bill , pinion ~35mm OD, driven ~125 mm dia , centre distance ~75 mm .............cost for the pair of gears was ~$AU220 - $US150

I went with spur gears so that centre distances aren't as critical and costs are down compared to helical , I really don't need to worry about silent running :-)

Cheers
John

[turboron]

John, I love it. I have always liked high speed gears. I can't wait for you to test it with your engine.

Thanks, Ron