Author Topic: By Jupiter  (Read 26282 times)

Online Vixen

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Re: By Jupiter
« Reply #285 on: March 28, 2019, 08:52:06 PM »
Thank everyone for calling in. You are always most welcome.


The Hand Turning Gear on the Jupiter Mk VIII was a direct drive from the winding handles direct to the crankshaft. It was not a flywheel starter like the Tiger Tank starter in Art's video clip. The overall gear reduction was approximately 25:1. Therefore to turn the engine over at say 400 RPM required the hand cranks to be turned at about 16 RPM, ie. once every 3.5 seconds. The Jupiter had a displacement of some 27 litres, so it was obvious that two strong mechanics were required, especially with a cold engine in cold weather. when the oil drag was considerably higher.

The hand cranking gearbox was connected to the engine's crankshaft by a dog clutch, which automatically disengaged when the engine fired. An enormous coil spring, within an over centre mechanism, ensured the dog clutch was fully engaged before the start-up procedure commenced  It was also essential that the ignition was in the fully retard position during the hand cranking. Any kickback would surely wreck the hand cranking mechanism and probably injure the wrists of the starting crew.


The next parts to be made were the control levers for the over centre mechanism. The model does not actually use the dog clutch or the over centre mechanism. Instead, I will be using a cordless drill, in low gear, to apply the starting power through the jaw coupling I made earlier.

The side profile of main control arms was milled from 10mm alloy plate. I did an extra arm as an insurance policy, just in case. The individual arms were cut free and bolted onto a stepped fixture so the outside profile could be milled. The fixture plate was then angled over in the machine vice so the center could be relieved to produce the required "I" section, cross section.









I then machined a two copies of the central control arm. This arm was becoming progressively more difficult to hold as more and more was machined away. The final cuts were made with the arm supported on a single 3mm bolt through the pivot hole.







I cut the splines for the control shaft, which passes through the main body, with a 1.0mm woodruff cutter using my 4th axis unit to index the shaft. Below, you can see the control arms assembled.









The cap for the big coil spring was made using both the mill and the lathe for parting off. The square section coil spring produced it's own fun and games. It was made from a length of square section spring found in the 'come in handy one day' box. I annealed the spring so that it could be compressed to a realistic pitch and for the end faces to be turned square. The first did not go exactly to plan, as you can see. Fortunately I had enough to make it's replacement











The top cover for the gearbox was an interesting exercise in reducing most of an aluminium billet into chips, while leaving just a little bit for use on the engine.









Finally, here is a trial assembly of the over centre mechanism to check that it will all go together, just like the drawing




I will finish the last few parts and the assembly of the Hand Turning Gear in the next installment.

Stay tuned.

Mike
It is the journey that matters, not the destination

Offline steamer

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Re: By Jupiter
« Reply #286 on: March 28, 2019, 10:51:14 PM »
Hey Mike....how did you cut the ID splines?

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Online Vixen

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Re: By Jupiter
« Reply #287 on: March 29, 2019, 08:34:05 AM »
Hey Mike....how did you cut the ID splines?

Dave

Hi Dave,

No, I ainta gonna tell you how I cut the internal splines.



If you zoom in and look closely, you will see the reason why. On the model this linkage is non functional, so I just made the arms an interference fit on the outside of the shaft.

It still looks realistic enough and much nicer than a plain shaft

Cheers

Mike  8)
« Last Edit: March 29, 2019, 03:08:43 PM by Vixen »
It is the journey that matters, not the destination

Offline fumopuc

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Re: By Jupiter
« Reply #288 on: March 29, 2019, 11:02:33 AM »
Hi Mike, similar the fakes, sometimes made in a small workshop close to Munich. I like it and another step forward at your Jupiter build.
Kind Regards
Achim

Offline Baner

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Re: By Jupiter
« Reply #289 on: March 29, 2019, 12:03:48 PM »
Just found your thread Mike. Incredible work.  :ThumbsUp:  :ThumbsUp:

Dave.

Offline Roger B

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Re: By Jupiter
« Reply #290 on: March 29, 2019, 04:52:44 PM »
Still following along and enjoying  :praise2:  :praise2:  :wine1: A CNC 4th axis certainly make cutting the starting dogs easier. I ended up hand filing mine as there was not any simple milling set up.
Best regards

Roger

Online Vixen

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Re: By Jupiter
« Reply #291 on: April 08, 2019, 06:34:29 PM »
Yesterday, Sonia and I celebrated our Golden Wedding Anniversary, Wow.. 50 years, that's a long time.   :wine1: :wine1:
We did not have the planned celebration party, due to a bereavement of a family member. A very sad time, when we wanted to be happy.



I thought you would like to see the progress on the Jupiter's Hand Turning Gear.

I intend to start the engine with a cordless drill running in low gear. An extension shaft from the drill engages with this Jaw Coupling. There is a further 2:1 gear reduction between the starter's lay shaft and the engines crankshaft







The Hand Turning Gear on the full size engine had a double bevel reduction gearbox between the input shafts and the layshaft. I do not need these on the model engine, because I will be using the cordless drill's reduction gearbox. I still needed to model the input shafts and the spring loaded clutch throw out linkage, of the full size engine, because they are such a prominent feature. The ball couplings on the input shaft were made by using loctite to temporarily bond some steel stock onto a short length of scrap 6mm rod. The ball coupling was 'ball' turned on the lathe. Then, with a little heat applied, the sacrificial shaft was pressed through the turned ball into the loosened off collet, without leaving any mark on the ball coupling. Sorry, I forgot to take a photo.
 










The Hand Turning Gear is mounted on the Accessories Cover at the rear of the engine, between the two Magnetos and above the Pressure and Scavenge Oil Pumps. It's getting quite busy at the back of the engine now. The dummy Turning Gear neatly hides the Jaw coupling.  Otherwise it's a near identical copy of the real thing in 1/3 scale.











I can swap the one way Jaw Coupling for a simpler two way coupling so I will be able to turn the engine over in either direction to set the timing, adjust the tappets, check the oil flows etc. when the time comes.

One more part completed. Still quite a few to go.


Mike, Signing off




« Last Edit: April 08, 2019, 10:48:46 PM by Vixen »
It is the journey that matters, not the destination

Offline MJM460

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Re: By Jupiter
« Reply #292 on: April 08, 2019, 10:55:05 PM »
Hi Mike, congratulations to you and Sonia.  Itís a great achievement and worth celebrating. 

I understand you point about celebration and sadness.  After fifty years, the celebration will be just as good if you have it in a while. 

So well done to both of you and may there be many more anniversaries to come.

Oh, and I continue to be amazed by your skill in workmanship on the model.  Never miss an update.

MJM460
The more I learn, the more I find that I still have to learn!