Author Topic: By Jupiter  (Read 40180 times)

Offline 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
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Damned ijjit!

Offline 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

Offline 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!

Offline Vixen

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Re: By Jupiter
« Reply #293 on: May 01, 2019, 08:19:12 PM »
The next part to be made is the all important Propeller Hub.

It was standard practice back in the 1920's to mount the two blade or four blade wooden propeller onto a steel hub which, in turn, is bolted directly to the propellor shaft extending from the reduction gearbox at the front of the engine.

The first photo shows a sectioned engine in the factory museum in Bristol. It's best to ignore the garish red paint job on the propellor hub. The reduction gears can be seen inside the sectioned housing.




This drawing shows most of the detail of the propellor hub. Ten large bolts sandwich the wooden propellor between the steel backplate and the front plate, the parallel splines on the front of the propellor hub allow the front plate's position to move, to cater for different widths of wooden propellor. The engine torque is transmitted from the propellor shaft to the propellor hub via the tapered splines towards the rear. A single large diameter nut and tapered collet, secure the hub to the propellor shaft




I started by machining the internal taper cone for my propellor hub from EN3B grade steel. EN3B is an unalloyed low carbon mild steel with good machining properties. I wanted to get the taper splines done before attacking the external details of the hub. My plan was to use a standard key way broach to produce the 18 slots of the female tapered spline. Each slot was to be 2.4mm wide (3/32") 1,0 mm deep (40 thou) and just over 12mm long (0.5 inch). The exact depth of the spline slots was critical as this feature decides where the hub is positioned on the propellor shaft tapered splines.




I machined a tapered broach guide to match the propellor hub taper. A single guide slot was machined to the required depth. It was then intended to index the tapered broach guide using the polycarbonate index plate to cut each of the 18 female tapered spline slots.

The brand new 2.4mm keyway broach needed to be reduced in length to 8 cutting teeth, otherwise it would have collided with the tapered collet feature at the front of the propellor hub. The remaining 8 cutting teeth would increase the depth of the keyway slot by 14 thou on each pass. I therefore needed to make a set of shims in 10 thou increments to adjust the depth of cut of the broach. I made steel shims of 30 thou, 40 thou, 50 thou and 60 thou thickness, to allow the spline slots to be cut in 4 passes.



Here you can see  the setup. The tapered broach guide is positioned inside the propellor hub at the first index position. The thinnest shim has been inserted so that the broach can make it's first cutting pass. I used my drill press to force the broach vertically through the hub. I was surprised at the amount of force that was sometimes required. I realised that three teeth were in contact with the hub, each cutting a 1.5 thou slice out of the steel. Some passes seemed to need more force than others.



I cut the first tapered spline slot without too much difficulty and indexed to cut the second spline, starting back with the thinnest shim for the first cut.  Something went wrong after the second shim was in place. For some reason the broach appeared to take a larger than usual bite and the cutting force increased substantially. I could not pull the broach back so had to continue applying more force, resulting in a loud bang and a completely destroyed keyway broach. You can just make out the two chip curls in the second slot, I guess they are more than the 1.5 thou I expected




Now what do I do? The plan to use a keyway broach seemed a reasonable way to go. In the past, I have successfully cut many parallel keyways in EN1A steel which has similar machining properties to EN3B. The difference this time being a very slight offset angle due to the taper. The taper angle is very shallow, less than 2 degrees. I can only assume that this slight taper was somehow responsible for the occasional high cutting forces. I assume the applied force is forcing the broach against the upper face of the propeller hub taper, as a result would sometimes take a lager then usual bite out of the hub, resulting in higher than normal loads. Sufficiently high to buckle and smash the broach.

Now I know how not to do it. I only achieved one of the 18 taper spline slots and have no intention of attempting another go with another  new broach using the same method.

The big question is how should I have set about producing tapered splines in the first place?

The idea of using a shaper or a shaper attachment springs to mind, but I have neither available. I don't much like the idea of using my light Emco F1 milling machine as an impromptu shaper.

I am open to all good ideas and suggestions, or offers of help. This is an essential item of the engine, it won't run without some means of attaching the prop.

Deep gloom in Fareham.

Mike  :thinking: :thinking:



« Last Edit: May 03, 2019, 09:55:41 PM by Vixen »
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Offline Elam Works

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Re: By Jupiter
« Reply #294 on: May 01, 2019, 08:35:42 PM »
Mike,

Did you fixture the work so that the broach was vertical? It may be that with the work vertical and the broach at a slight angle, some of the vertical force from the press was encouraging the broach to lift away from the shims, taking a deeper bite than it ought to. Enough perhaps for it to 'dig in'. Generally the cutting pressure should keep the broach firmly against the shims.

Or (or a contributing factor) could be that end of the broach, not being square to the press (applying the force to one side), was causing the broach to flex towards the work. This could also make the leading teeth engaging the cut to dig in deeper. If the cut were complete, this would have manifested itself by the bottom of the keyseat being curved or bell-mouthed at the entry. As you have probably noted when pushing broaches, they do flex and squirm about a bit; though obviously they have their limits!

-Doug

Offline Vixen

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Re: By Jupiter
« Reply #295 on: May 01, 2019, 09:50:45 PM »
Hello Doug

I am sure you are correct. I did not use any special fixturing. I simply put the flat bottom of the hub, flat on the bed and pressed on the end of the broach with the chuck of my drill press. I guess there was nothing much to stop the broach lifting off the shims and taking a bigger bite out of the slot entry, than it should have. Once it has taken a big bite, the broach is then committed to taking that oversize chip all the way through. The broach was brand new and razor sharp, just wanting and able to take that deeper cut.

I could make a 2 degree angle plate for the hub, this will get the broach truly vertical. But as you said, push broaches do flex and squirm, so will there be enough support, at either end, to stop the broach flexing and taking another big bite at some time. As you can see from the photos, the hub is a tall piece of metal and it's a very thin broach. 18 slots each with 4 passes each, will provide plenty more opportunities for it to happen again. These broachs are only intended to cut a single keyway slot, in one pass.

One thing is certain, I will need to get hold of something more rigid and robust than a cheepo Chinese drill press to control and push that broach.

There must be a better way.

Mike

« Last Edit: May 01, 2019, 10:01:39 PM by Vixen »
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Offline Vixen

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Re: By Jupiter
« Reply #296 on: May 02, 2019, 12:48:07 PM »
Thank you, to everybody who has looked in and to Doug who helped identify the failure mode with the keyway broach method.

It is clear that the use of a keyway broach to cut an 18 tooth taper spline may not be the best method.

I was hoping that someone out there could point out the correct and more reliable method to produce this tapered spline.

It could be a show stopper for the project, if I cannot find a way to make it

Mike



It is the journey that matters, not the destination

Offline Jasonb

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Re: By Jupiter
« Reply #297 on: May 02, 2019, 01:20:03 PM »
Missed this one last night, I often do tapered keyways for tapered gib head keys just as you have described and not had any issues, often the keyway is 30-40mm long in a cast iron flywheel hub. 3/32" and 1/8" I can do on my drill press, larger I use Jo's hydraulic one, both methods I don't tilt the work.

removing the teeth from the bottom may not have helped as the area infront of the first tooth acts like the sole of a plane riding on the surface and stops the teeth digging in.

Before I had broaches I always did it on the lathe, planing the carrage back and forth, these four 3/16" keyways are in steel and 1" long, worked OK for me. For the tapered version the topslide can be fitted with a lever inplace of the leadscrew and set over to required angle.

We know someone with a slotting head ;)

« Last Edit: May 02, 2019, 01:25:31 PM by Jasonb »

Offline Roger B

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Re: By Jupiter
« Reply #298 on: May 02, 2019, 01:42:43 PM »
I had a similar problem trying to use a 3mm broach where the plain piece at the begining was broken off (operator error on the previous key way  :facepalm: ). I thought it should still work but like for you it cut a couple of keyways correctly and then suddenly cut deep and jammed. It seems that the plain section at the start controls the depth of cut  :thinking: without it there is nothing to stop the first tooth digging in.

I have seen pictures of various hand operated shaper type tools that fit in the lathe toolpost for doing this sort of keyway cutting but tried one. This is the Hemingway version:

http://www.hemingwaykits.com/acatalog/Keyway_Slotting_Attachment.html
Best regards

Roger

Offline mikemill

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Re: By Jupiter
« Reply #299 on: May 02, 2019, 01:52:46 PM »
Mike

I believe you have a CNC mill, place the shaft in vertical rotary table, support the other end in a tailstock if you have one or use packing.

Write the appropriate code to cut the angled slot, then finish with with your original set up, should do the trick

Mike