Author Topic: By Jupiter  (Read 41282 times)

Online Vixen

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Re: By Jupiter
« Reply #30 on: December 12, 2017, 07:45:04 PM »
Thanks Mike,

When I saw the valve gear on top of your Scorpion, I was envious. So when the 1/3 scale Jupiter became available, I could not resist.



Here is the 3% oversize inlet manifold pattern against the Jupiter cylinder head so it does not quite fit.  Lots of interesting valve gear on the Jupiter

Looking forward to the Bristol show in August, also hope they can do something at Guildford but on a smaller scale than before

Mike

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Online Vixen

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Re: By Jupiter
« Reply #31 on: December 12, 2017, 07:50:05 PM »
Hello Jason,

The silicon resin is heavy and quite runny. It is a 24 hour cure so the air bubbles, which are inevitable when you stir the mix, have time to rise to the surface. The molded surface is clean but there are some bubbles under the top surface of the mold box. If I had a bell jar and a vacuum pump, I would use them, but unfortunately.........

Mike
« Last Edit: December 12, 2017, 07:59:06 PM by Vixen »
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Online Vixen

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Re: By Jupiter
« Reply #32 on: January 18, 2018, 12:27:47 PM »
Before christmas I completed the two silicone rubber moulds for the core and main waxes. The time has come to get serious and create the wax models before sending them to the foundry for the hot work.




This first photo shows my 'kitchen chemistry' approach to melting and injecting the wax into the moulds. My wax injection pump is a modified cookie maker which has quick connect bayonet end caps at each end. I made up a new aluminium piston with an O-seal piston ring and a conical nozzle. The wax inside the cylinder is heated in a Bain Marie style water heater made from an old coffee tin. This ensures the wax temperature remains constant and never exceeds 100*C.




Here you can see the 9 soluble wax cores and the silicone core mould






Here is the core wax positioned inside the main silicone mould after the red (non-soluble) wax has been injected and allowed to cool.




The waxes are placed in cold water overnight to dissolve out the soluble wax core. The wax model is now ready to send to the foundry for the hot work. At the foundry they add wax runners and risers to my waxes before placing them in a casting flask filled with special investment plaster. The wax in burned out of the casting flask in an oven at red heat before being transferred to a vacuum caster where the molten aluminium is drawn into the flask.




I sent two sample waxes to 'Just Castings Ltd' a specialist foundry located in the famous Hatton Garden Jewelry district in London. So I now proudly say that I have two lost wax inlet manifolds cast by a jeweler by Royal Appointment to Her Majesty. They kindly added a few candy sweeteners with the order, to soften the blow of the cost.  The cost of an individual casting is not that bad, but nine castings to which must be added the dreaded 20% VAT tax, is a different story.




Here we can see the different stages. The master patterns for the manifold and the core, the finished wax model and the final investment cast item in aluminium. Sometimes there is no substitute for an expensive bespoke casting, when the internal shape cannot be machined out of the solid.

« Last Edit: January 18, 2018, 06:38:23 PM by Vixen »
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Offline Ramon

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Re: By Jupiter
« Reply #33 on: January 18, 2018, 01:03:33 PM »
Expensive they might have been Mike but what a result from all the input you have put in to get the finished item. Way beyond my best intentions, that's model engineering at it's best - well done indeed :praise2:

Tug


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Offline b.lindsey

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Re: By Jupiter
« Reply #34 on: January 18, 2018, 01:15:02 PM »
Most impressive Mike (excellent pictures also) and the results speak for themselves. Somehow I'm thinking the two candies didn't soften the cost a lot but it was a nice gesture none the less.

Bill

Offline Jasonb

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Re: By Jupiter
« Reply #35 on: January 18, 2018, 01:25:23 PM »
They look to have turned out really well Mike, good to know the company were able to do them.

Couple of questions:

1. Were you able to indicate where the runners should be attached? If so I assume they went onto one of the mating surfaces that is going to be lightly machined.

2. What is the dimensional accuracy like as that was a big issue with the printed options?

Lastly, don't let Jo get hold of your silicon and wax supplies otherwise her castings may start to multiply ;)

J

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Re: By Jupiter
« Reply #36 on: January 18, 2018, 01:46:40 PM »
Hello Jason

'Just Castings' were one of the foundries on your list of suggested suppliers. They were the only people to show any 'real' interest in the job. Most of the others did not bother to respond to e-mail questions. They are a professional outfit, they cast various metals (mostly precious metal) every day of the week and are incredibly well equipped to do the work. They are not a 'hobby' foundry.

I did indicate where I thought the runners and risers should go. I used the end flanges for the wax injection, you can see the stub ends on the red wax model. JC did it differently, they attached the runner to the outer curved surface, in full view. It turns out that they knew best (that's always a good sign) and their position for the runners was easy to cut off and file smooth. I was having some problems with the wax not completely filling the cylinder flange bosses. JC showed me how to build up the wax using a knife blade heated in a candle flame. The additional wax can be carved to shape once it has cooled.

I made the Master patterns 3% oversize to compensate for the various shrinkages. The finished casting ended up about 1% under size. Not a problem as I will drill and counter drill the flanges using a drilling jig plate, so the bolt holes will line up perfectly.

Jo or anyone else are more than welcome to make use of the silicone moulds to make their own waxes.

Mike
« Last Edit: February 16, 2018, 03:13:33 PM by Vixen »
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Offline mikecole7

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Re: By Jupiter
« Reply #37 on: January 18, 2018, 01:48:25 PM »

       Brilliant as usual Mike, I'm still having trouble working out the last casting stage.
       Really great work.

      Mike

Online Jo

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Re: By Jupiter
« Reply #38 on: January 18, 2018, 02:01:53 PM »
Looks very nice Mike  8)


       Brilliant as usual Mike, I'm still having trouble working out the last casting stage.
 

Maybe we should get him to bring it all along to Bristol so he can show all the members of ICEBG and we can all fondle his castings ;D

Jo

P.S. Still reading the Bentley book... might have to get Eric to pull his finger out and cast the required exhausts for that just in case I find the need  :embarassed:
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Online Vixen

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Re: By Jupiter
« Reply #39 on: January 18, 2018, 02:19:55 PM »
Hi Jo,

Good idea, I will bring the master patterns, moulds and some waxes to Bristol. I did similar (smaller) inlet manifolds for the 1/4 scale Mercury. I will bring them as well and you can get to fondle all those castings as well.

I promise not to tell Uncle Eric how much the Jupiter castings cost, otherwise he may get BIG ideas for casting the Bentley manifolds. I think he may have done the castings for Dan's Gold Medal winning Bentley from the same set of dies.

Keep safe

Mike
« Last Edit: January 18, 2018, 06:45:10 PM by Vixen »
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Offline Dave Otto

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Re: By Jupiter
« Reply #40 on: January 19, 2018, 12:19:34 AM »
Hi Mike

Thanks for the update, the manifolds turned out very nice. It is nice to know that this can be done with out an expensive wax pot.
Do you put the silicone mold in any kind of support structure when you inject the wax into it? It seems that just holding in your hand that the wax may want to squirt out of the part line?
Also I was wondering if you have any issues with air bubbles in the wax?

Dave

Online Vixen

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Re: By Jupiter
« Reply #41 on: January 19, 2018, 09:23:23 AM »
Hello Dave,

Half the fun is making do with what is available. I would love to own an expensive wax pot and a vacuum bell jar but I cannot justify the expense for so few castings.

The silicone mould is quite flexible so I support it in a four sided box, actually four separate plates and rubber bands, while I inject the wax. The secret seems to be to get the wax to a high temperature which makes it thin and runny, then there is less tendency to hydraulic the two parts of the mould appart.

When you make a batch of waxes, it gets into a one hour cycle. Inject wax, allow to solidify, open mould, clean up, reassemble mould and inject again. I found it better to keep the molten wax at temperature in the Bain Marie all the time. I can remove the handle and stand the cylinder full of wax, vertically in the simmering water pot. This has the added advantage of keeping the metal nozzle at temperature, so The wax does not cool and solidify in the nozzle during injection.

For the test samples I used some old, several times, recycled wax. It was contaminated and full of minute air bubbles. The resulting casting had a rougher surface which needed extra work to clean up and smooth off. Now that I know the process works, I will use virgin wax for the 'production' run.

I did have a problem with the wax not always completely filling the flange boss cavities. JC showed me how to build up the wax using a knife blade heated with a candle flame. The excess wax is easily carved to shape once it cools. It is always better to have too much metal in the casting than too little.

Here are some photos of one of the inlet manifolds roughly in position behind the cylinder head. The black delivery tube is some undersize plastic pipe from the scrap box. I have found some 22mm diameter, thin wall aluminium tube to make the real delivery pipes. The Bristol radial engines of this era were designed with style.

Mike







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Offline Dave Otto

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Re: By Jupiter
« Reply #42 on: January 20, 2018, 12:22:42 AM »
Hi Mike

Thanks for the additional information, do you think it would be possible to preheat the silicone mold to help the incomplete filling problem? It seems that you could put the mold in an oven and bring the temp up quite a bit above ambient to keep the wax from freezing so quickly?

I'm not sure what I would make but I would sure like to give this a try sometime.

Dave

Offline Jasonb

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Re: By Jupiter
« Reply #43 on: January 20, 2018, 07:21:55 AM »
Possibly air getting trapped in the bosses, a small vent would allow that out and the wax that enters the vent can just be trimmed off. A simple "Vee" cut with a scalple would form the vent in one of the mould faces.

Online Vixen

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Re: By Jupiter
« Reply #44 on: January 20, 2018, 12:10:45 PM »
Hi Dave and Jason

Thanks for your helpful suggestions, it is gratifying to know someone out there is interested.

Jason, the problematic flange boss is in the lower half of the mould, surrounded by the greatest mass of silicone. The boss in the top half where air would collect appears unaffected. The wax casting has all the characteristics of a chilled pour rather than bubble entrapment. I believe Dave is near the mark with his suggestion of pre-heating the silicone mould.

There are several grades of wax, I am using the 'red' wax, intended for injection moulding. The wax does not have a distinct melting or freezing point. At room temperature 20*C, it is a rigid solid. At 40 to 50*C it softens like putty. At 60 to 70* it flows like a paste. Above 80* C it is a slush and near 100*C it is a free flowing liquid. I have found that it is also a poor conductor of heat, so takes forever for the solids to melt into the surrounding liquid wax. I found it necessary to maintain the wax, all day, in the molten condition and to avoid adding fresh wax to the melt.

Producing the batch of nine waxes was an epic in itself. It required a complete take over of the good ladies kitchen and all it's facilities. Wax melting and conditioning started soon after breakfast. The first wax was produced just after lunch and the one hour, inject, cool, clean, rebuild mould, cycle began. The first moulds were injected with the silicon moulds at room temperature. The first waxes were the best quality.

Operations had to stop when the time came for the evening meal to be prepared. When the hostilities were over, I was able to continue, I wanted to complete the whole batch of nine in one day to avoid consuming a following day as well. I tried to reduce the one hour cycle time by cooling the injected wax mould in the fridge. It did take about 15 minutes off the cycle time. It was past midnight when the last wax was completed. It was only the next day when I discovered that the last few waxes were cast 'short'. So I tend to agree with Dave, a warmer silicone mould should prevent premature wax cooling and shrinkage. Will try harder next time and only attempt a smaller batch.

Dave, if there is no other alternative, then try lost wax. It is an exercise in frustration, time and expense. It's like opening your wallet and asking the man to take out whatever he wants. The patterns were made from materials in the shop, but took a long time to make. The two silicone moulds consumed 30 of material. The nine soluble wax cores consumed 25 of wax. The red injection wax was a further 20. The cost of each individual aluminium casting was 31 plus the dreaded 20% VAT tax. Not an undertaking for the faint hearted. If there is an alternative, use it.

Cheers

Mike
« Last Edit: February 16, 2018, 03:21:31 PM by Vixen »
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