Author Topic: Alyn Foundry Sphinx  (Read 5911 times)

Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #15 on: April 17, 2019, 01:24:19 PM »
Hi Ray.

Hmmm, must be getting old.... I'd completely forgotten about the Brass ring and seal assembly!

I wouldn't Loctite the open end as the liner will expand as the engine warms up. And as a footnote I've always preferred to use Acetate cure clear Silicon for all gaskets on my engines. If your mating faces are good a light smear and a tightened bolt will seal even exhaust fittings.

Regarding your PM, sadly I don't have a replacement " Starwheel " casting. May I suggest making one from some mild Steel round bar?

Cheers Graham.

Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #16 on: April 17, 2019, 01:41:15 PM »
Damn.

The gas bottle man arrived just as I was finishing.... Totally missed the jacket question.

Having just measured that rough new one and another from 30 years ago they both are 4 and 5/16" long so it seems Ray you're the first to point out that the drawing is in error!! I think it should read 4 and 1/16" long as machined.

The cylinder liner casting is a MK 2 version and was made a little longer than the original so that it protrudes through the base a little more than previously.

Jason.

I chose Brass for a reason. Theoretically it shouldn't corrode onto the Iron liner making disassembly impossible in the future.

However, a thick bead of Acetate cure Silicon to fill the gap is a very cheap but suitable alternative and these days I'd probably just do that! As I'm getting lazy.... The thin " O " ring at the front is a good idea.

Cheers Graham.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #17 on: April 17, 2019, 01:52:04 PM »
Thanks again Graham and Jason for your thoughts. One thought I had is to machine a recess for a ring at the end of the jacket where the four lugs are and Loctite that in. The lugs are plenty long enough to allow this.This would provide a larger surface area for the cylinder flange to seal against - particularly necessary if reducing the diameter of the flange to recess in the cylinder head.
As regards the open end, as far as I can see, the o-ring seal as shown on the plans would only work if the cylinder was a snug fit into the hole in the front of the main body casting, otherwise the o-ring would tend to deform and be squeezed into any gap when the barrel retaining bolts were tightened.
Perhaps an o-ring groove on the inner face of the brass ring would provide a better seal?
Ray

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #18 on: April 17, 2019, 02:47:53 PM »
Ray, if you need to file up a new star wheel this drawing has the radii and ctrs of the arcs that I think will give the right sort of shape. I think I would cut the flat faces with a thin slitting saw then rough hack saw the curves before filing to shape.

I'm not sure if I can use my casting but it would give me an excuse to play with the CNC. I think a 4mm cutter would be as small as I would want to go so the corners would need clearing up but may give it a go.


Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #19 on: April 17, 2019, 06:48:14 PM »
Many thanks Jason, that will be very helpful. I did 3D model the wheel in Fusion 360 and created the radii by eye. I am going to see if the casting is usable, but looks as if I may need to make one manually.
« Last Edit: April 18, 2019, 07:45:42 AM by RayW »
Ray

Online crueby

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Re: Alyn Foundry Sphinx
« Reply #20 on: April 17, 2019, 09:29:00 PM »
Thats a very interesting shape on the star wheel - if I follow the video correctly it holds the arm up away from pushing the rod every other time around. Clever stuff!

 :popcorn:

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #21 on: April 18, 2019, 06:43:56 PM »
I decided to CNC a Star wheel from scratch just to get some more practice with the KX-3, more details in the "going over to the dark side thread"

http://www.modelenginemaker.com/index.php/topic,8882.msg199296.html#msg199296



« Last Edit: April 18, 2019, 06:50:03 PM by Jasonb »

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #22 on: April 18, 2019, 06:57:43 PM »
That looks really good Jason.A perfect demonstration of the benefits of CNC. Just one observation.- I think the central recess should be on the other side so that the teeth are facing to the right.
Would you be willing to make a star wheel for me please? I would, of course, be happy to pay you for your trouble.
Regards
Ray

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #23 on: April 18, 2019, 07:25:09 PM »
Yes that is the back of the wheel, I photographed it that way as all the machining shots were from the same side. Buy cutting it that way up I could get the nut lower down which meant less of the 4mm dia cutter sticking out of the collet to avoid crashes.

Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #24 on: April 19, 2019, 12:23:38 PM »
Hi Both.

The recess in the back of the Starwheel is to accommodate a " double flat Grover washer " more commonly known as a spring washer these days.

The idea is to reduce the possibility of the wheel being dragged as the pawl retracts. I noticed on the picture that Jo posted earlier the builder had fitted a neat vertical flat spring to keep the Starwheel from going backwards.

Cheers Graham.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #25 on: April 19, 2019, 02:18:15 PM »
Oops!
My apologies to Jason for thinking that he had put the recess on the wrong side of the wheel! I had mistakenly thought from the drawing that the spring washer was located between the bolt and the wheel, not between the wheel and the main body. It was only when I looked at the exploded view that I realised my error.
Ray

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #26 on: April 19, 2019, 05:03:20 PM »
Don't worry Ray, I have a second one cut this afternoon which has the recess on the outside that may suit your way of thinking :Doh:

I got distracted while doing some alterations to the CAM and forgot to flip the part over, never mind I'll make use of this one as I had been thinking of putting a recess on the visible face that could be painted to look like a casting so you won't have any filing to do on yours.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #27 on: April 19, 2019, 05:27:48 PM »
Thanks Jason. I have just realised that, by putting the spring washer between the head of the bolt and the wheel, I will need to put a short spacer between the wheel and the engine body to stop it rubbing, which would not be a problem with the washer on the inside. I'm sure either will work fine.
Ray

Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #28 on: April 19, 2019, 06:06:16 PM »
Thanks Jason. I have just realised that, by putting the spring washer between the head of the bolt and the wheel, I will need to put a short spacer between the wheel and the engine body to stop it rubbing, which would not be a problem with the washer on the inside. I'm sure either will work fine.

Hi Ray.

Just make sure it's made of Brass !  ;)

Cheers Graham.

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #29 on: April 19, 2019, 07:51:20 PM »
The modified cutting sequence included some 2.0mm holes at the root of each internal corner that made it easier to file out the waste that the 6mm milling cutter could not get to. I have also enlarged the incorrect recess on mine with a round nose tool and will paint the recess.