Hi Jeff
Just thought i would write a bit about combustors having read your discussions with Adam.
on stainless when you see two numbers first is chrome content, second is nickel a third number would be molybdenum
chrome at higher percentage can make steel brittle so they add nickel to make it ductile again .
all 300 series are about the same strength 347 has more post weld corrosion resistance.
the three number system is out of date now mainly used by the food industry for pans and cutlery.
18/8 304 can fall under the 18/10 category by increasing the 8% to 8.3% !
18/0 has no nickel and is magnetic.
Kurts book on the KJ66 the combustor material is listed as 18/10 which is 316 stainless at between 0.5mm and 0.3mm thick, stay at 0.5mm to 0.4mm for 304 stainless
I have only ever used 18/8 304 stainless which is very cheap stainless used as splash backs in kitchens or in urinals in pub's, also worth checking on stainless steel shim usually 316.
Have used 316 tubing for the sticks,it may eventually burn away just grind it off and spot weld another on,or try oven elements drilling the powder out.
best welded with a spot welder just overlapping the sheet by 4mm, there must be minimum gaps anywhere.move you hole pattern round to avoid the seam with any large swaged holes.
when spot welding the inner and outer wraps try a quick spot weld on one end check the diameter if not right just twist in to break weld, adjust and spot weld again,worth fitting a timer 0-5 secs
If the spot welder does not weld switch off and clean the stainless and copper points, do not try twisting or moving the stainless to make a contact as it can spark and blow a hole.
Always wear eye protection for above reason, you do get some splash out between the plates.
Aviation tin snips are better than normal tin snips you can cut through a full sheet without bending it to much,mine where just from the local DIY store B&Q own make,picture below just to show the right type,you can get ones to do left and right hand curves,oil on the blades makes it cut easy.
www.toolstation.com/shop/p20727304 at 0.5mm can be spun easy on a medium sized lathe,use a piece of brass with grease on as a push tool in your tool holder or make a ball bearing tool.
when spinning avoid going to the edge of the sheet until bent round corner or it will crinkle.
If you are not sure of the material heat it to cherry red and let it cool,it may go softer as stainless can be work hardened, 316 0.6mm mig welding wire can be made softer to use for wiring up.
Microwave transformers can be used to make a good spot welder,but you must use very thick wire to replace the secondary winding's, old jump start leads,car starter motor cable or welding earth wire cable works great as very soft multi strand.
Do not take the transformer lamination's apart,leave in one piece thread the new secondary through.
leave the shunts in ,steel lamination,s between the two primer and secondary coils.
Please read up on microwave transformers as used in the microwave they step up the voltage,high voltage kills and even DC gets dangerous at high voltage.
with the microwave transformer mod to a spot welder you are stepping in down to 2 to 4 volts A/C and increasing the amps.
video below is one of the better ones,you don't get old taking risk,s !
www.youtube.com/watch?v=RnjF5Hj2Udg If you don't feel safe about mains you could try this one it uses a 12v battery but may only work with very thin sheet.but the Arduino is worth looking at instead of a timer you would need to do your research ,they can be set up to send a small current to check the connection before the welding pulse.
www.youtube.com/watch?v=3RLVuy5PUKo&index=1&list=LLFwTc3LvYc5I7K9n6YFrtNw&t=8sI spot weld everything on a combustor, seams, sticks,fuel brackets all minimum distortion. people have altered the NGV to use all spot welding,no slots to cut !
drill holes for the sticks 1mm under size and punch to size, helps better support the sticks,I cut the tube and open to 4 petals spot weld on each petal.
If you are trying to make an ultra light engine the sticks can be turned down in wall thickness if 1/4 dia to 6mm, if your 3 jaw chuck is not to good, fit and turn down
a bar to slide fit in the inner i/d and use a live centre to push against the shoulder, that will be enough to turn it,take small cuts 5 thou,do the sticks in individual lengths + extra for weld tabs.
Try to keep to max 0.5mm wall thickness for the sticks.
I normally form the sheet over a tube just by hand don't have rollers,if you take your time and start by using a larger tube,tin or pipe and move to smaller dia ,
where the join is the last bit will need pushing round a smaller bar
A combustor will burn through inconel or any higher grade heat resistant metal if not burning right,the injector needles must be just right against the inner stick wall or liquid fuel will end up burning at the back of the combustor or NGV ,
I have seen burnt away NGV and cracks to ever blade on cast NGV and the large combustor holes made twice the size with all the area distorted .
you can tell you have vaporizing problems when on liquid as it will wash though at the 5 oclock or 7 o clock position depending on rotation (kj66 or FD3 ) making a hot spot.
really for discussion to help everybody I have been though some of the spot welding with you Jeff,a spot welder makes it a lot easier and worth taking time out to make one