Making new shafts for SU H2 carburettors and skimming original butterflies

#machining #lathe #classicmini
Needed custom spindle shafts for H2 carburetors, so I made them.
00:00 Turning
05:11 Milling (slotting)
16:02 Making a tool to thin down H2 and H4 butterflies
21:23 Thinning down original butterflies
23:49 Making new screws

[@1crazypj]

For as long as I can remember, Japanese carbs have had the butterflies machined on the outside edge for the closed angle of 27 degrees.
It means they are not actually circles but very slightly oval.
I've been planning on making a fixture to hold plates at 27 degrees but, as with a lot of things, haven't got around to it yet
That was a very neat fixture you made to get thickness correct and also the one for centre drilling.
I believe the 'slabbing' of throttle shafts was a common 'racing' mod as I read about it in 1970's.
All out race use, TIG weld butterfly in place and thin shaft further (but of course, then you pretty much destroy it when taking apart)

[@nbrworks]

Thank you. Yes, these SU butterflies are also oval and the top and bottom edges are at an angle, 15º from what I can tell. Having the possibility to remove them if needed was something I wanted to retain, hence the slotted screws. My plan is to use loctite, gently open the ends of the screws and then cut the excess off.

[@terrygreen5225]

Worked as a toolmaker for zenith carburettor company. Butterflies were produced in a press tool at an angle to fit the bore of the carburettor when the throttle was shut. Very difficult to get right as no c n c .

[@1crazypj]

That's interesting. I knew they were stamped but didn't realise the dies were made on an angle (makes complete
sense as soon as you mention it)

[@samrodian919]

That was very well done sir!

[@jobkneppers]

Nice job. I would end with the slitting saw so I have maximum strength for milling, drilling and tapping. Maybe you should explain to your audience why you changed the angle of attack for the drill you used. I know and own a complete set just for the grabby materials but I guess that the average home machinist doesn't have a clou what you're doing here. For the turning of the precise diameter of 7,5 mm I would start with 12 or maybe 10 mm bar. Check my center alignment at the front and back of the part and adjust my tail stock when needed. Then I would cut to 7,5 mm in one pass. No steady rest needed and therefore quicker. For turning precise thin washers/parts I use a soft collet. Bored to size as a first using blocking pins when tightened. Remove the pins and mount the "washer" part and turn to final thickness. I bought like 30, 30 years ago, and used wisely, they last for more than 25 years now. They're quite cheap new also and when used in one set-up they're rally accurate. When you turned the small end of the shaft in several steps I could see the deflection and I know the far end diameter was bigger because of this. Use the strength of the uncut material like Michelangelo did when he made the finger for David; Calibrate your lathe (shallow cut and establish diameter cut) and then go to the final small diameter in one go (if your machine is in good condition off course). Maybe it scares you at first but this approach works like a charm. No steady rest needed, no filing to correct the taper. Spot on in one go. These are just a few different ways to Rome. No nagging, maybe some advice. One nag though, sorry, measuring the size of a countersunk screw twice with a micrometer? That's for sure unnecessary. Best! Job

[@nbrworks]

Thanks Job. I really appreciate this kind of feedback and advice. Like I said in the expanding arbor video, I've only been using the lathe for 1 year (give or take) and these shafts were the very first parts I made. Today I would've done a few things differently, including leaving the slot to last.
I'm really curious to try the 'one pass method' you described.
For other readers:
«What I did to the drill was to (try to) set the cutting edges with a neutral rake angle (0º) because in soft materials normal drill bits tend to grab and lift the part. Being a thin/long brass part, I thought it was adequate.»
My first videos had no voice over, as I was still trying to figure out if I was capable of speaking in English :D I guess some text would have been helpful, but again, first videos... no experience. Today I'm trying the voice over, it's not perfect but it's getting better (I hope) and have also been adding some text as suggested by viewers, like units conversions.
People providing proper feedback means a lot to me, so again, thank you.

[@jobkneppers]

@@nbrworks Thank you for your kind feedback. Your voice over is excellent. Becoming a mechanical creature like I think I am now took a long time (30 years+). Creativity was my starting point; I need that part but how do I make it... And then you start cutting and trashing parts until you succeed. Frustrated in the meantime and talking to people in the trade I knew how to approach the completion of a complicated part (in the beginning I struggled with cutting threads in stainless or quite basic problems). I think the 10.000 hour rule applies her too. Pick up a saxophone and try to be a jazz player in one go? No way Jose. I don't know who you are and what your mission is here but if it is about making nice videos for TH-cam and learn in the meantime; you're right on track. If you want to earn a living as a machinist; you have to become more agile when making parts. Competition is fierce especially competing against cnc shops. If you do this as a living; prototyping (one offs) is still a way to earn appropriate money on manual machines, Stephan Gotteswinder does comparable jobs as I do and the knowledge, tempo and quality still pays the bills. Quite an elaborate answer from my side but I hope you get something out of it. Good luck and all the best! Job

[@typographicus4526]

Subscribed!
Great video.
From which book is the page shown at 15:45?

[@nbrworks]

Hi, welcome aboard. The book is 'Tuning the A-Series Engine' by David Vizard (second edition, 1989). ISBN: 1859606202

[@typographicus4526]

@@nbrworks Ok,
tnx

[@Spetet]

Nice work. What is the virtue of shaving the butterflies?

[@nbrworks]

Thanks.
I tried to improve a little bit the original shafts. Originals are straight rods with a diameter of 7.9mm (0.311").
That means theres a significant restriction on full throttle, especially in a small carburettor like this.
By skimming the butterflies and thinning the middle section of the shafts I was able to reduce that "diameter" to 4mm (0.157").
I could go further and remove the top half of the shaft and bolt the butterfly straight to the bottom half, but... I also had some considerations about reliability and safety.

[@rallymax2]

Enjoy the video.
Try to move the mic so it doesn’t pickup your heavy breathing, it’s very distracting.

[@nbrworks]

Hi, thanks for the feedback. This is something I've been trying to work on and hope to improve in the next videos. Thanks