Author Topic: Little Wall  (Read 2657 times)

Offline Jasonb

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Little Wall
« on: March 18, 2022, 06:57:51 PM »
This engine is based on a design by Elmer Wall that was published in "Model mechanics and Inventions" and despite asking around I have not been able to find an upto date photo of one, the best is a rather grainy image from scans of the original magazine article.



There was some talk of the old patterns having been bought, reworked and a limited run going to be produced but again I can find no sign of any of these casting sets if they were ever actually done nor mention of the original castings that Wall produced.

In redesigning the engine I opted for my usual 24mm bore which makes scaling the imperial sizes down to metric quite straight forward using the ratio of 1/16" on the original = 1mm on my drawings. At this size the original 36cc capacity comes down to 11cc. The parts were all 3D modelled in Alibre and assembled there two which allows for checking that things will fit and rotate rather than find problems during the build. This is something I have taken to doing with all models now as you can sort out legacy errors which saves headaches down the line, it is also a good way to get to think of how you are going to machine the parts.





I decided to make a start with the crankcase which was from a block of 6082. After squaring up the block and marking the crank and cylinder positions it was held in the 4-jaw to bore out to diameter for the end plates and then an HSS tool was used to enlarge the cavity to clear both the crank webs and deeper still in the middle to clear the conrod big end.



The block was then repositioned to bore the piston clearance and a larger recess to locate the cylinder liner.



For the external shaping of the crankcase I decided to make use of teh CNC, the following photos show it taking shape after each of the various stages of machining.

An adaptive clearing path was used first to remove most of the material using a 5mm 2-flute carbide cutter specifically for aluminium.



I then changed to a 6mm 2-flute ball ended carbide cutter and did a coarse "steep and shallow" path to remove most of the remaining material but leaving 0.2mm for finishing with a 1mm stepover



The same tool was then run again with a 0.3mm stepover to get a finer finish



At the time this was done I had not quite got my Z axis movement smooth so there are a few more steps than there are now but nothing a little needle file work could not sort out.

I probably showed this video in the CNC section but won't hurt to post again


Offline Johnmcc69

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Re: Little Wall
« Reply #1 on: March 18, 2022, 09:08:48 PM »
 :ThumbsUp:
 That's very nice Jason! It's nice to see some of these "obscure" kind of models being brought to light, I couldn't imagine how many there might be. I hope you have some clearer photos, or the magazine article to work from.

 I'll be following along,

 John

Offline Art K

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Re: Little Wall
« Reply #2 on: March 19, 2022, 01:59:41 AM »
Jason,
I am familiar with a lot of the Elmer Wall engines but not this one. I do recall a guy at the NAMES show who collected them this one doesn't look familiar. Looks to be a great project.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Jasonb

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Re: Little Wall
« Reply #3 on: March 19, 2022, 07:13:36 AM »
Yes I like to fine the old ones that are not about any more and enjoy the challenges of redesigning particularly the ones where I don't even have any drawings.

That is the only photo of the engine, there is another poor one of the assembled carb which was in a second article. Drawings of the engine are not too bad but the carb drawing is difficult to read.

Art, that seems to confirm what I have found or rather not found, it seems a very obscure engine unlike ones such as the Water Wizard and the other 4-stroke designs

Offline Zephyrin

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Re: Little Wall
« Reply #4 on: March 19, 2022, 09:04:57 AM »

Offline Jasonb

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Re: Little Wall
« Reply #5 on: March 19, 2022, 10:22:13 AM »
I assume so as I only have scans of the particular article. It's the CS ending not X but could still be the same mag which could have altered it's name

Offline Alyn Foundry

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Re: Little Wall
« Reply #6 on: March 19, 2022, 11:46:55 AM »
I see you’ve found a use for one of those flywheels you made the pattern for Jason….  ;)

Offline Jasonb

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Re: Little Wall
« Reply #7 on: March 19, 2022, 01:01:00 PM »
Oh no I haven't. They might just have done for the full size engine which was 4 1/2" dia  but the flywheel on this one is 74mm dia. No castings were hurt in the making of this engine ;)

Offline Jasonb

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Re: Little Wall
« Reply #8 on: March 25, 2022, 04:14:16 PM »
Once the CNC work was done on the crankcase it was then just a case of treating it like any other casting and doing the easy bit of drilling and tapping the various holes and also milling a couple of clearance notches at the sides of where the cylinder mounts to allow the transfer of the air/fuel mix.



With that part complete I turned my attention to the end covers which are almost identical, the only difference being that one has a parallel area that the ignition timing disc can rotate on and the other at the flywheel end is as "cast". The first thing to do was bore out for the bronze bearing, turn the OD and also cut a spigot to fit into the crankcase.



Having previously carved out similar details for the Stuart Lightweight on the manual machines I again took advantage of having the CNC to shape the external pockets leaving the webs that support the bearing housing. First roughing out



Then a finish cut with finer stepover



When doing the CAM I had set it to leave 0.3mm on the bolting face so the part was returned to the mill and skimmed to finished size, as this surface was going to be left as bear metal the turned surface looked a bit nicer than the CNC milled one.



While the mill was covered in aluminium chips I also made the base, this was just drilled and tapped twice from below so it could be held to a smaller block which in turn was held in the mill vice. This allowed for easy access all round the part. Not so easy to see but the outer edge has a draft angle machined into it to more closely represent a casting.






Offline Jasonb

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Re: Little Wall
« Reply #9 on: April 12, 2022, 06:40:33 PM »
The cylinder started life as a piece of 50mm dia steel bar, faced and ctr drilled for tailstock support so that the waste above the mounting flange could be removed. I did most of this with a parting tool then switched to a 1mm radius end grooving tool so that I got some fillets left in the corners as it was brought down to final size.



I then roughed out the cooling fins with the same parting tool and finished with the groover, this took a bit of setting up as due to the change in length of the fins the angle of each changed slightly as the spacing remains constant.



I used the CNC to cut the shaped holes for the inlet/exhaust boss and the simpler shaped transfer block



I also made use of it to cut the profile of the blocks on the ends of a bit of round bar, these were then cut to the undersize  inner radius of the cylinder using a boring head





A trial fit showed that the CNC had done a nice job with close fitting parts that just needed one or two strokes of a needle file and then they could be lightly tapped into place with a small nylon hammer.







Happy with the fit the parts were cleaned and fluxed before silver soldering together. After machining the inlet/exhaust boss to finished length it was back into the lathe to Finish bore the inside to accept the iron liner. Once that was done and there was no more need for a chucking piece the top of the cylinder was turned to profile and the M10 x 1 plug hole drilled and tapped. You can just see the every thin line of silver solder around the joint from the inside





The last bit of machining was t mill the slots for intake and exhaust and tap two holes M3 to hold the combined manifold in place.



Lastly I grit blasted the outside to remove any discolouration from soldering and give a good key for the stove paint I had planned for it.












Offline rklopp

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Re: Little Wall
« Reply #10 on: April 12, 2022, 07:01:48 PM »
Nice work!

Offline RReid

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Re: Little Wall
« Reply #11 on: April 12, 2022, 08:23:35 PM »
That's some fancy fin work! Sharp little beauties (literally).   :ThumbsUp:
Regards,
Ron

Offline Hugh Currin

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Re: Little Wall
« Reply #12 on: April 13, 2022, 05:05:44 AM »
Jason:

Very nice work. I'm awed by the 3D contouring one the crank case. Cylinder came out great also.

Thanks.
Hugh

Offline fumopuc

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Re: Little Wall
« Reply #13 on: April 13, 2022, 06:42:27 AM »
Hi Jason, nice progress.
CNC does allow to think about the making of parts in a complete different way.
I do like it very much.
Kind Regards
Achim

Offline Roger B

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Re: Little Wall
« Reply #14 on: April 14, 2022, 09:15:52 AM »
That's some excellent fabrication  :praise2:  :praise2:
Best regards

Roger