Author Topic: Stentor  (Read 60016 times)

Offline Brian Rupnow

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Re: Stentor
« Reply #15 on: August 18, 2014, 12:58:43 AM »
Jo--Nice work, and a very interesting model. I have seen pictures of two strokes similar to the one you are working on, but have never actually seen a "real" one.  I will follow your build with interest.---Brian

Online Jo

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Re: Stentor
« Reply #16 on: August 18, 2014, 07:37:19 AM »
Thanks for following along Brian  8)

I must be honest this type of engine would not have been my first choice but my supplier convinced me that it is a nice easy  :noidea: engine and I need a runner. It is supposed to be practise for when I do my other two stroke the Falcon, which is a two cylinder version of this engine:



And whilst I mention flat twins a very, very nice man tells me he has a set of castings for me for my birthday which will let me make one of these:





 :whoohoo: One can never have too many castings  8)

Jo
 
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Online sco

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Re: Stentor
« Reply #17 on: August 18, 2014, 08:50:28 AM »
That flat twin is nice - difficult to get the scale of it though - what size are those head bolts?

Simon.
Ars longa, vita brevis.

Online Jo

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Re: Stentor
« Reply #18 on: August 18, 2014, 09:05:33 AM »
The Falcon has smaller cylinders with a 25mm bore, 19mm stroke.

The Aeronca is 37cc, with square cylinders of 28.5 bore and stroke. (The bolts holding the cylinders down are 4BA) For scale that should be a 20" prop it is sporting ;D.

Both will have cranks that are just under 150mm long.

Jo
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Offline steamer

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Re: Stentor
« Reply #19 on: August 18, 2014, 10:38:03 AM »
Nice looking build Jo!

Dave
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Damned ijjit!

Online Jo

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Re: Stentor
« Reply #20 on: August 18, 2014, 11:59:10 AM »
Thanks Dave, I am ever hopeful that this one might run  :embarassed:

The crankshaft is shown on the drawing as being made in EN24T which I do not have any of  :disappointed:. Having enquired  around I am being encouraged that I might as well make it out of EN1 as it is not as if this is going to be used for racing.

I do however see a need to make it as a one part crank rather than a two part one for strength (the web is only 3.18mm thick) but then again if I did it as a two part crank I could make a separate pin out of Silver steel and harden it  :noidea:

Jo
« Last Edit: August 18, 2014, 01:22:36 PM by Jo »
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Offline Jasonb

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Re: Stentor
« Reply #21 on: August 18, 2014, 01:17:41 PM »
Actually having just looked at the drawing again the web is a bit on the thin side for a pressed in pin maybe better off with one piece from EN24T or EN8, whats EN25 when its at home :headscratch:

The other bit you want to know what you are using is the conrod which will need HE15 or 2014 not a suitable lump of something likely ;)

Online Jo

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Re: Stentor
« Reply #22 on: August 18, 2014, 01:24:20 PM »
Corrected the typo  ;).

The other bit you want to know what you are using is the conrod which will need HE15 or 2014 not a suitable lump of something likely ;)

As all the stuff I have is best flight grade Durallium I suspect it will be ok  :naughty:

Jo
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Bluechip

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Re: Stentor
« Reply #23 on: August 18, 2014, 01:43:19 PM »

whats EN25 when its at home :headscratch:


IIRC the trade name was 'Vibrac' ... Vincent Con-Rods made from it I think.  I used to get off-cuts of it for nowt. Machines quite nicely for alloy steel. Although that may have been due to the degree of temper I got ...  :)

Dave

Offline bp

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Re: Stentor
« Reply #24 on: August 19, 2014, 08:37:59 AM »
Corrected the typo  ;).

The other bit you want to know what you are using is the conrod which will need HE15 or 2014 not a suitable lump of something likely ;)

As all the stuff I have is best flight grade Durallium I suspect it will be ok  :naughty:

Jo

Some months ago I was about to make some conrods for some 2.5cc diesels.  The accepted material for these is 2024 T3 or better Al. Alloy.  At the time I couldn't get any at a sensible price.....US$100 postage on $40 odd dollars worth of material isn't sensible in my book.  So I sat down and did a bit of research.  I had been told that the reason that 2024 is preferred is because it retains its properties at "elevated" temperatures, and it is probably the best material, machines beautifully, wears well, etc etc.
So I plotted the yield strength of a variety of al.alloys at various temperatures.  Some of the books from my working days have been retained!  About the only guess made was the temperature range, I assumed that the combustion chamber would be the hottest area for which the only temp that I have heard talked about is 250 degrees C, hopefully the conrod won't be exposed to that very often!
Anyway, attached is the graph produced, which to my mind confirms the "accepted " preference for 2024, but I felt that the far more widely available 7075 T 5 or better would be suitable.  This has since been confirmed by several users.
Sorry to have rambled on, but I get excited by material selection, sad isn't it??
cheers
Bill

Online Jo

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Re: Stentor
« Reply #25 on: August 21, 2014, 01:07:17 PM »
Bill, I understand  8) I was lucky enough to have an  :old: friend drop by the other day and go through my alloy material collection with me so I now know better what I have got. And the only bits of soft stuff like HE30 I have are those I purchased for the S&P that I later did not use, all the other is HE15 or better so all good for conrods :pinkelephant:

The crank is coming out of a piece of steel and one of the things that has in the past puzzled me is how to get the offset centres in line. Tricks I have used include starting from a bit of square, clamping in Vee block or 5C collet in a block. This time I came up with a new wheeze:



Using one of my toolmaker vices clamped around the bar to keep everything square end to end  8) So now it is off to the lathe and take out most of the centre:



This is to lighten the piece of metal before I offset it to turn the crank pin  ;)

Jo
« Last Edit: July 13, 2017, 09:09:05 PM by Jo »
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Offline Jasonb

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Re: Stentor
« Reply #26 on: August 21, 2014, 02:21:19 PM »
Not seen it done that way before, most people turn the main shaft first and then just hold by that in a keats plate or similar homemade jig to turn the pin/form pin hole, far easier than working between two webs an no need to drill pairs of ctrs at each end of the bar.

What steel did you decide on in the end?

J

Online Jo

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Re: Stentor
« Reply #27 on: August 21, 2014, 02:28:53 PM »
Not seen it done that way before, most people turn the main shaft first and then just hold by that in a keats plate or similar homemade jig to turn the pin/form pin hole, far easier than working between two webs an no need to drill pairs of ctrs at each end of the bar.

I am following the instructions by a Snr A Morin, in his publication "L'usinage des Moteurs Models Reduits".

What steel did you decide on in the end?

I decided to make my crank out of the same stuff Eric made his out of, with green paint on the end.

Jo
« Last Edit: August 21, 2014, 02:32:26 PM by Jo »
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Offline Jasonb

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Re: Stentor
« Reply #28 on: August 21, 2014, 03:01:18 PM »
So he does, I take it you have therfore decided to go with a one piece job rather than a separate pin and will drill the weight reducing hole as one of the last operations?

I've got a few lengths of green stuff too but mine does not have the brown down the sides ;)

J

Online Jo

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Re: Stentor
« Reply #29 on: August 21, 2014, 03:17:38 PM »
Yes a one piece jobbie, I did consider doing it using a keat plate or even in a 5C collet but part of the reason for doing one of these tiddlers is to learn if and why machining them might be different than bigger engines and if there is any advantages or disadvantages of those techniques.

The protective brown stuff shows that it is vintage :naughty:

Jo
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