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Author Topic: Stuart Models Twin Oscillator steam passages  (Read 497 times)

Southern Sailor

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Stuart Models Twin Oscillator steam passages
« on: September 05, 2021, 09:10:16 pm »

Good day, I am converting the plan of the Stuart Twin Oscillator steam engine from imperial to metric dimensions. The steam ways are tiny and I want to make them larger diameter to reduce the possibility of breaking the drill. Does it matter if the diameter of these steam passageways is enlarged? Any advice please? Regards, Brian
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Bunkerbarge

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Re: Stuart Models Twin Oscillator steam passages
« Reply #1 on: September 05, 2021, 10:32:28 pm »

Enlarging the ports will affect the timing and duration of the steam being admitted as well as the exhaust being discharged, although the exhaust side is not a concern.


Admitting the steam earlier will at the least affect performance and efficiency and, if you go too far, at the worst stall the engine so it will not turn.  I would recommend staying with the plan dimensions.
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Southern Sailor

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Re: Stuart Models Twin Oscillator steam passages
« Reply #2 on: September 06, 2021, 09:13:13 am »

Thanks Bunkerbarge. So it's down to studying the recommendations on drilling small diameter holes! Oh well, things are not appreciated if you get them too easily! Cheers. Brian
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Bunkerbarge

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Re: Stuart Models Twin Oscillator steam passages
« Reply #3 on: September 06, 2021, 09:31:55 am »

Very slowly Brian with very gentle pressure. 


Either lightly centre pop the hole to stabilise the drill tip or, better still, mark the surface gently with a small centre drill with the job set up just before drilling the actual hole.  This will ensure the tip does not wander off centre and flex.  I would also put the drill deep into the chuck to make it a little more rigid.  Finally frequently back off to clear the swarf.  It might also be worth doing a test drilling first in a piece of scrap to be sure your set up is perfect.



Good luck.
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Circlip

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Re: Stuart Models Twin Oscillator steam passages
« Reply #4 on: September 06, 2021, 10:49:17 am »

And assuming the castings are bronze, back off the rake of the leading edge of the drill, stops grabbing. O0


  Regards  Ian.
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belli

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Re: Stuart Models Twin Oscillator steam passages
« Reply #5 on: September 06, 2021, 04:18:26 pm »

Altering the diameter of those will have no effect on your steam engines performance.
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Bunkerbarge

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Re: Stuart Models Twin Oscillator steam passages
« Reply #6 on: September 06, 2021, 07:35:26 pm »

Altering the diameter of those will have no effect on your steam engines performance.


Yes it will
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Southern Sailor

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Re: Stuart Models Twin Oscillator steam passages
« Reply #7 on: September 06, 2021, 07:51:09 pm »

Guys, the designed diameter is just under 2mm so there is really no problem. Sorry if I have raised the subject unnecessarily. Thanks for all the good advice. Cheers.  Brian
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belli

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Re: Stuart Models Twin Oscillator steam passages
« Reply #8 on: September 06, 2021, 08:08:56 pm »

I am quite sure that the question was "Does it matter if the diameter of these steam passageways is enlarged?".  This is quite different from 'if the steam ports were enlarged.'
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Bunkerbarge

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Re: Stuart Models Twin Oscillator steam passages
« Reply #9 on: September 07, 2021, 08:43:05 am »

Brian, You should be OK with a 2mm drill as long as you take the precautions mentioned above.  I would recommend that you get hold of a small centre drill however as they are perfect for spotting a surface prior to drilling to ensure the drill does not wander before it starts to cut.


I also came across this, which I know is a single but the procedure is the same and it might just give you something to think about.


https://www.model-engineer.co.uk/forums/postings.asp?th=104201


Then I also found an interesting exchange regarding the twin which you might also find interesting reading:


https://www.model-engineer.co.uk/forums/postings.asp?th=116721


I also think you will find it interesting to have a look through this thread.  While this is scratch built from plans the drilling process is obviously identical to your kit.


 https://www.rcgroups.com/forums/showthread.php?1616211-Building-a-Stuart-V-Twin-oscillator-Boiler
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Bunkerbarge

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Re: Stuart Models Twin Oscillator steam passages
« Reply #10 on: September 07, 2021, 08:47:29 am »

I am quite sure that the question was "Does it matter if the diameter of these steam passageways is enlarged?".  This is quite different from 'if the steam ports were enlarged.'


My apologies, I have never come across an oscillator with the steam passages of a different diameter to the port so naturally assumed they would always be the same.  I did make that assumption in this case however as I am familiar with the Stuart Twin oscillator.
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belli

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Re: Stuart Models Twin Oscillator steam passages
« Reply #11 on: September 07, 2021, 04:00:44 pm »

This little engine has been on my build list for a long time, I have a piece of 3" round bar set aside for it.   I would like to see If I can get all those holes in the correct places and the cross drillings without having  to make a second one....

The RCG thread is great, I think 'pattern maker' has passed on but what a good job he made of it!

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Circlip

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Re: Stuart Models Twin Oscillator steam passages
« Reply #12 on: September 08, 2021, 09:56:10 am »

  "I would like to see If I can get all those holes in the correct places and the cross drillings without having  to make a second one...."


  Perhaps you need a bigger piece just in case the second one doesn't work? Many seem to have been able to work to Stuarts dimensions.


  Regards  Ian.
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belli

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Re: Stuart Models Twin Oscillator steam passages
« Reply #13 on: September 08, 2021, 07:50:44 pm »

I don't think I will need a bigger piece, just more of them...


I've had to take more than one shot at most things in my life, school, drivers license, marriage, etc but I seem to get there in the end. 
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