Skipjack by michael mott - 1/8th scale - SMALL - 19 foot open launch

[Bedford]

Am I to assume from the pics of the real engine that it has a total loss lubrication system, ie the oil pot on top of the engine?

 

If so I imagine that would simplify things too because it won't have an oil pump.

[michael mott]

Carl, Steve thanks for stopping by.

Steve I think that you are correct but I need to learn more about these old engines. This site has some interesting engines the one I linked to has cylinders that are 3/8th bore by 1/2 stroke which is very encouraging.

 

Michael

[Bedford]

Looks like there will be a wealth of knowledge there.

 

Will you make your own spark plugs? I have a contact of a bloke who sells them, not sure if they are small enough though.

 

Steve

[captainbob]

You should have lots of fun building that engine.

 

Bob

[michael mott]

Hi Steve, yes I am going to make my own, yesterday I went to the city to a large model supply store, I was disappointment with the answers to the questions I had regarding spark plugs and basic information about model engines. I also asked about book and was told that there is this thing called the internet. I did save the trip by purchasing some 3/8 dia 6061 aluminum alloy and some 1/2 inch diameter stainless steel rod. came home and looked up "how to make miniature spark plugs" on the web   that was how I found that model engine site.

 

I stayed up way too late reading as much as my eyes would allow but now feel much better about the decision to build a proper engine for Skipjack.

 

Thanks for all the likes.

 

Michael 

[michael mott]

Hi Bob I must have been writing when you posted. Yes it will definitely pose a few challenges but isn't that what these hobbies are really all about. Research, figuring out how something was built, testing  materials for our models, choosing a method to make some small item, sharing our discoveries. the joy of completing a part that meet our expectations.

 

While I have been researching this engine piece I have been ruminating in the back of my mind the specific choices and way that the ribbands will be made, even though they will be temporary they need to be strong enough to withstand the pressures of the bent ribs.

 

One thing that I am contemplating is to use thinner ribbands but laminate a few layers, because the outside dimension can be larger as long as the inside one conforms to the inside shape of the planking. If they are too flexible it will make fitting the ribs much more difficult. 

 

In my "Boatbuilding Manual 4th edition" by Robert M Steward  book, in the section that covers the preparation of the molds for building the hull it recommends that the ribbands be full length of the hull if possible and only use a join if needed at the least curved part of the length.

 

My ribbands can be cut from material that is only 32 inches in length so the joining longitudinally is not an issue. I do not want to put a lot of bending stresses on the thin plastic bulkheads so by making them thicker by laminating layers might prove to be the best option. I will be tying them to the bulkheads with very fine copper wire which should not interfere with the layers. 

 

Michael 

[captainbob]

I would have made the bulkheads smaller and bent the ribs on the outside of the ribbands.  I don’t know how to plank with the ribs on the inside.  I’ll have to watch and learn.  I do that a lot.

 

Bob

[michael mott]

Bob my understanding from Steward is that as the planks are going to be placed the ribbands are removed one by one as the planking proceeds. the link is to a series of pictures showing the method.

 

Michael

[captainbob]

That’s an interesting method, I’ll watch and see how you like it.

 

Bob

[Bedford]

Making the spark plugs and all, you're a better man than I Gungadin !

[michael mott]

I have been doing some research into the whole engine building aspect of this little launch. I made the top part of the engine this evening it still need a bit more work to add the top plat to seal in the water cavity the spark plugs will thread through the plate into the main body thereby allowing water to circulate around the part that goes through the cavity.

 

This drawing shows the section through the engine and sections through the cylinder head.

 

 

Buffalo 3HP sheet 1.pdf

 

this is the top part of the head

 

 

Buffalo 3HP sheet 2.pdf

 

And the brass part I made today

 

 

 

 

Michael

 

 

[Bedford]

Impressed Michael, very impressed!

[captainbob]

I know it is 1:8 scale but I didn’t expect it to be so small.  Fine work.  The guys on the model engine forum are very helpful.

 

Bob

[michael mott]

Thank you for all the likes, And Bob and Steve for your comments, its been a long couple of days fiddling with some finicky numbers, I had to make a couple of small modifications to my Mill Drill so that I could use some dial verniers as read out dials for the table travel. I had already set up the depth one a few years ago and because I have slip dials on the mill I have been able to manage up until now . However machining these tiny dimensions with a centre Zero was challenging to say the least. so now I can clip in the vernier and use it as a poor mans DRO (digital read out, only this is an Analog read out )

First I cut a piece of 1 inch square brass and then re cut it to 1.375 x 1 x .625 inches the first task was to bore the main holes to form the inside of the water jacket shell these are .625 diameter and almost 5/8 deep. then bored the holes that will mate with the combustion chamber in the top piece. After the big hole were machined I flipped it over to reduce some of the metal and then machines the small holes for the valves and water passages to the top part of the head.

Next I made a couple of support keepers out of some 3/4 diameter brass rod to fill the bore holes and reduced the diameter at the top to use as location stubs for the top part this also allowed me to thread some 10 - 32 cap screws through the spark plug holes  to hold the whole shebang together. after the inlet and exhaust ports were machined which seemed to take forever, I was finally able to get on with some finish filing.

 

 

 

I like to have a ground safe edge on some of the files it really helps to keep things square

 

 

The parts are beginning to look like the top of the engine.

 

 

The valve rods will be fabricated from some largish sewing needles these are .046 inches in diameter which works perfectly, they obviously need some work yet.

 

 

Time for a break.

 

Michael

[Bedford]

How do you get the brass so smooth after machining?

[michael mott]

Steve just plain old "elbow grease" files , wet and dry 400, 600, and steel wool. The files are what do bulk of the work. The hard brass might also contribute. 

I notice that some brass is more yellow and gummy. This brass is nice to machine and work with hand tools.

 

Michael

[mtaylor]

Sweet machining.  This is right up there with the goodies at:  http://www.craftsmanshipmuseum.com/index.html

[Jack12477]

Nice job of machining Mike.

[EdT]

Very impressive, Micheal.  Very impressive.  I can't imagine working to that precision on something so small - or even something large.

 

I am catching up a bit with your posts.  I agree very much with the idea that satisfaction comes from working out solutions to the many different problems we face in this craft.  If it were not for those challenges in research, planning, testing ideas, etc. building these models would be much less engaging - for me at least.

 

I agree with the person who recommended ribbands in one long length.  I pieced the ribbands near the stern on YA and regretted it.  Its very easy to introduce discontinuities into the curve.  One piece, uniform thickness, straight grain - important factors.

 

Laminating the ribbands should give their curve more set - ie make them stifferand less resistant to flexing.

 

Great work. Fascinating.

 

Ed

[michael mott]

Thank you all for the likes.

Brian, Jack, Mark  thanks for the kind comments.

Ed the more I think about laminating the ribbands the more I like the idea.

 

I discovered that at this small scale there is little room for error. When I removed the support plugs today after finishing the shaping and a few more holes for the water inlet and inspection hole in the front side, I saw that the port holes had in fact penetrated the wall of the water jacket. the space inside the jacket is large enough that I decided to add a plate that will get sweated in place.

 

the first picture shows the two crescent shaped holes from the port drill breaking through the wall.

 

 

The sleeve insert is machined from some  hard 3/4 brass rod the wall thickness was .020"  I sliced off two rings then cut those further to just fit enough that the curve is slightly greater than half the diameter inside. By doing it this way they are snug enough that they do not fall out.

 

 

The next picture shows the inspection hole which still need cleaning up and the cylinder liner positioned to show the water circulation cavity. I will make the base plate before the liners are finalized. It has occurred to me that I will need a pretty good filter system to keep any debris out of the water system.

 

 

The next photo shows the top of the cylinder with the head removed the holes still need to be reamed 13/32 for the stainless liners. I am still contemplating making these two parts able to be separated I think I have enough space to add some small long bolts up through the water jacked that way they would be hidden.

 

 

 

I think I need a break from metalwork and do a little whittling of the boxwood stem and sternpost.

 

Michael

 

 

[WackoWolf]

Beautiful metal work. Thanks for sharing this.

[Omega1234]

Hi Michael. I'm totally lost when it comes to building engines, let alone, anything to do with metal work. It's no wonder, therefore, that I have total respect for your skills and craftsmanship.

 

Well done!

[hexnut]

Looking absolutely beautiful, and the decision to go w/ jump spark and buzz coil should make it (relatively ) straight forward. 

 

Are you going to use Macor for the plug insulators?

 

One question: The bronze sphere on the 1:1 engine just aft of the block--is that a vacuum accumulator?

[michael mott]

Bob, I read somewhere that it is to reduce water hammering. i cannot find the reference right at the moment though.

 

Thanks to all for your kind remarks and for all the likes.

 

Michael

[hexnut]

Thanks!--found an air chamber reference--page 1217 of "Power and the Engineer" from 1910:

http://books.google.com/books?id=oMU6AQAAMAAJ&pg=PA1217&lpg=PA1217&dq=gasolene+launch+engine+water+hammering&source=bl&ots=76kaSZu2U0&sig=bLQQ_trmY5EsZkZ4N_XUdxSRiak&hl=en&sa=X&ei=0SRZVOfjOvPfsAT60ILwDg&ved=0CDQQ6AEwBA#v=onepage&q=gasolene%20launch%20engine%20water%20hammering&f=true

[popeye the sailor]

your progress is really awesome Michael!

[Twister]

Wow!!

 

What more can be said?

 

I've always liked the idea of building a small 4 stroke engine, so I'll be paying particular attention to this log. Having just acquired a lathe I think I'm rather a long way off having the requisite machining skills to attempt anything like this yet - I'm currently focusing on making huge amounts of swarf.

 

Your workmanship is, as always, superlative!

 

Regards,

 

Row

[shipmodel]

I expect that I will never build a miniature engine, much less a working one, in my modeling lifetime, but I am immensely enjoying following your work.  

 

That was a truly elegant and practical solution to your slip.

 

Dan

[cog]

Michael,

 

Looks stunning, as all your metal working has been here at MSW so far. I presume you make it a runnung engine ... any reason for using brass instead of iron, aluminium, etc?

[michael mott]

Denis ,Row, Dan, Carl, thanks for looking in and for the kind words. 

 

I am beginning to wonder about this engine business.

 

The three cylinder blocks so far!

 

 

The one in the middle was the first one I was getting more dissatisfied by the hour, because the little break through into the water jacket area was nagging at me all the time. It was actually the second of the things that was bugging me and the top part had its own error I realized the oval water area was too long. also I decided that the bottom mounting lugs needed to be an integral part instead of part of a plate that was going to be fitted to the bottom somehow?

 

So I started over and was merrily milling down into the water jacket area when saw the cutter making it way down the outside of the jacket....... yup I set the cuts on the mill from the wrong side of the block after working the outside dimensions.

 

you can see the clean little slot on the one in the back, right down the middle.

 

The one in the front is version number three, according to folk lore it should be lucky.

 

 

The most tricky part was drilling the inlet and exhaust holes (still a bit gun-shy after the first mistake) I had to set the block up with a compound angle, for each hole the inlet ones on the outside and the exhaust ones in the middle. Now the hand work filing the surface shapes is under way. I also increased the size of the valve heads to .125 from .093 inches. The bore of the cylinders is reduced to 5/16 from 3/8ths in order to get more space for water circulation.

 

 

Carl in answer to your question why brass instead of iron, it is because brass is easier to work and I have the material. I have noticed that some of the engines on the engine website are brass and they seem to run fine as long as there is a steel or iron liner and an aluminum piston. this is the route that I am following.

 

Michael