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

[Jim Lad]

Just catching up after our week away, Michael.  Delightful work - as usual!

 

John

[michael mott]

 

As all fabricated components have dimensions, and dimensional and positional tolerances, did you conceive a plan for dimensional tolerance management ahead of commencing with the machining of the components?  Or are there few enough 'stacks' of components that you can control individual parts dim's/tol's to allow assembly?

Elia the short answer is Yes.

 

I began with the base external Dimensions of the Engine, as noted in the Buffalo catalogue. determined the bore and stroke based on a scaled version of original core dimensions such as the diameters and lengths etc. Some dimensions are absolutely critical, Gear meshing , piston fits shaft diameters and so on. I do have leeway over many ancillary dimensions though. for instance the outside diameter of the hub for the 30 tooth gear, I drew it at .250" I think the final finished dimension was .249" is doesn't matter and without miking the diameter it is impossible to see. it could just have easily been .235"

 

Without actually having the real engine in front of me to measure, and this is a model after all I certainly have taken dimensional liberties as well as material and design ones.

 

I have no way of knowing some dimensions and so they are guesses, there is enough "stacking " as you say that I can make some adjustments as I go along.

 

One of the most critical and challenging fits is going to be the smooth meshing of the gears, on the real engine the DP of the teeth is an unknown to me, I could have done more research and found out exactly no doubt but being impatient I scaled from photographs of the engine counted the number of teeth, in actuality the real gears are 64 and 32 a 2:1 ratio.

I do not have a proper dividing head or gears with those numbers of teeth to use as masters, only a rotary table albeit a good but very large one it can measure into degrees minutes and seconds.  The key information is the ratio of 2:1.

 

The camshaft had to be clear of the con rods, and I had some general dimensions based on the catalogue and photographs Gears are really no more than a couple of discs ( Pitch Circle) that rub against each other with teeth projecting from each so as not to slip. There are tables for all the standard tooth sizes these are based on the Diametral Pitch system which is the number of teeth in the gear for each inch of pitch diameter. lots of small gears use 64 or 48 teeth per inch these are standard ones that are sold through the commercial vendors.

 

On the engine that I am building neither of these pitches provided a pair of gears that were the correct ratio and the correct number of teeth to look scale or the correct Diameter(approx in any case ). I used the formulas to calculate from the diameters that were formed from the two circles on my drawing for the crankshaft and for the camshaft a set of gears that would give me 60 teeth and 30 teeth it worked out to 75 teeth per inch of pitch diameter.

 

A non commercial gear size, so using another set of tables in an article in a Model Engineer magazine, developed by model engineer D. J. Unwin, I made the tool to make the cutters for the 75DP gears.

 

Here's the rub, on paper they mesh perfectly ,I will find out soon enough if my machining tolerances are good enough for them to mesh perfectly in situ.

 

In the (unlikely   ) event that I need to make a minor adjustment I can make the camshaft bearing housing which are 3/16 diameter carrying a 1/8th inch shaft  (.18725" and .125" respectively ) I can make a second set that is very slightly eccentric which would allow for the camshaft to be moved to in order to have the best meshing. This is my fall back position.

 

I think that we always need to consider the fall back position when we are building our models because  "life is."

 

Apologies for another long winded answer, but a nice break from winding the table on the mill , only 30 teeth to go on the big gear.

 

Michael

 

 

 

[EdT]

Micheal, I'm with you on the risks in repetitive work.  I don't like it much because my mind really likes to wander.  Unfortunately, there is plenty of it to be done in this work. 

 

My hat continues to be off to you on this engine.  I can't wait to see a video of it running - I'm sure you feel the same.

 

Cheers,

 

Ed

[michael mott]

Ed, thank you, your comment means a great deal to me.

 

this evening I am having a hard time wiping the silly grin off my face.

 

Beginning cuts

 

 

Half a day later the last tooth cut

 

 

Back to the lathe for some rough shaping

 

 

I ground up a bit of a form tool to get the curved recess better.

 

 

After parting it off I slipped it onto the camshaft .

 

 

 

 

It is actually on the shaft backwards I have to set it up in a fixture on the four jaw chuck now and machine the eccentric cam for the water pump then it can be flipped to finish the front side.

 

It did mesh nicely though even without any clean up yet,

 

Michael

[Elia]

Michael,

 

Thank you very much for describing your plan and approach.

 

And that last update showing the timing gear looks sweeet. So very nice.

 

Cheers

 

Elia

[mtaylor]

You ought to be grinning from ear to ear and then some, sir.  That is a very fine bit of machining and it meshes perfectly with no fiddling..  Totally amazing to me.  I take it that you won't cut and pin the lobes until later?  I'm curious about where the timing is taken from on the cam also.

[captainbob]

Nice job.  Beautiful fit.

 

Bob

[NMBROOK]

Awe inspiring work Michael I have to admit,you blew me away when you mentioned the cam drive for the water pump   I am used to seeing marine model engines relying on a pickup for the water cooling!!!

 

Kind Regards

 

Nigel

[druxey]

Very, very sweet, Michael. Well done!

[cog]

Yesssss, that grin should be enormous, and you should hear our applause from all over the globe ...

[popeye the sailor]

amazing!!!   super work there Michael! 

[Remcohe]

That is some fine display of crafmanship 

 

Remco

[Mark Pearse]

ditto, & the photos are also a very high standard - I guess you aren't using the phone with a cracked screen….

[michael mott]

Elia, Mark, Bob, Nigel, Druxey, Carl, Denis, Remco and Mark P, Thank you all for your kind remarks. And to all who used the like button.

 

the last couple of days have been busy with some household stuff and snow removal getting water etc.

 

I have also been beavering away at the water pump.

 

Attempt one ended like this

 

 

attempt two ended like this

 

 

attempt three "this was the turning point" (apologies to the Dinsdale brothers)

 

 

I used the body of the pump to spot the position of the first hole, and because the holes in the pump body were indexed I was then able to use the same index to drill the four holes in the crank case for tapping the 00x90 threads for the mounting screws. I still might make them bolts instead of screws.

 

As each hole was drilled I tapped it straight away. used lots of lubricant and backed the tap out several times for cleaning the swarf.

 

 

using the jewelers saw to cut the slot in the screw.

 

 

assembled on the crank case I now will be able to make the linkage to the eccentric in the backside of the 60T gear the piston in the pump is 1/8th diameter.

 

 

Close up pictures can be brutally honest, I need to set up and make some adjustment on the thickness of the heads of the screws which are 1/16 in diameter, the size of the 00x90 threads are .047" max diameter, the tap drill is a number 62 Drill.

 

The inlet and outlet threads on the water pump are 6x40.

 

Michael

 

 

 

 

 

 

 

[Omega1234]

Hi Michael

 

Yes..."close ups can be brutally honest....", but in your case, it just looks brilliant to me. I can't even bang a nail in straight, let alone do one tenth of what you've achieved. I marvel and admire.

 

All the best.

 

Patrick

Edited January 17, 2015 by Omega1234

[mtaylor]

What Patrick said... goes for me too. 

[cog]

You beavered rather well I might say ...

[druxey]

Lovely, Michael. You could have used some watchmaker's screw slotting files.... (I find them useful for many things.)

[michael mott]

Wow! those files are pricey Druxey.

 

the saga of the water-pump continues.

I am not happy with the sizes of things and also the elbow is causing the crankcase to be raised off the sump.

 

 

Mass confusion and general mayhem

 

 

A number of different experiments with heavy walled tube convinced me that it is easier to bend the heavy tube than to work at drilling 90 degree holes through elbows any other way.

 

That said I have come to the conclusion that all model locomotive engineers already know and i also knew it as well and that is one cannot scale nature, a molecule of water is a molecule of water and that is the fact of life. it also became a realization that I would not be able to get enough water through the water-jacket with a scale model pump for the same reason that nature is not scale-able.

 

I was able to make the pump open and close with a .093 ball bearing similar to a clack valve but being realistic demonstrated to me that this approach would not work to deliver the volume of water needed to cool the head(heat cannot be scaled either. (Nigel you already knew this too)

 

As there are two other places wher piping enters the water jacket I have decided to continue to make a scale operating water pump from the outside appearances but the actual path of the water will be through the other piping and will use a hidden pump that will be able to deliver the needed volumes. Disappointing in one sense, but that is the way the world works sometimes.

 

experiments

 

 

Now that I am on a new track I will be able to make the pump look correct, I have already done this with regard to the operation of the pistons and cylinders insider the engine and working to keep the exterior looking like hwe real engine.

 

I have developed a couple of new tools for bending the parts of the piping.

 

 

The elbow is first turned to include some flanged areas at each end, then annealed and slipped into the brass bending tools

 

 

I marked the center of the elbow with a felt pen and closed the two parts.

 

 

did the bend

 

 

after a few tries I am pleased that this method will work

 

 

 

michael

 

 

 

[hexnut]

I was going to say that I've had good success  bending thin-wall tubing with a styrene rod as a mandril, but it looks like you have the situation more than well in hand...

[michael mott]

Bob

Thanks for that tidbit of information. I shall also do some experiment with that because I will need to move water through some small pipes

 

And thanks to all for the likes .

 

Michael

[druxey]

If you can find those files, lightly used and in decent condition, on eBay, they are a lot less expensive! Nice bending work there.

[mikegerber]

Ouch Michael!

 

I look at the second image from the top and think to myself: The small decomposition of a swiss watch today looks less complicated - am I happy, that I have just an old pot on the workbench!   

 

You really are doing a great job with this build!

 

will continue to follow ...

Mike

Edited January 20, 2015 by mikegerber

[cog]

Michael,

 

As there are two other places wher piping enters the water jacket I have decided to continue to make a scale operating water pump from the outside appearances but the actual path of the water will be through the other piping and will use a hidden pump that will be able to deliver the needed volumes. Disappointing in one sense, but that is the way the world works sometimes.

 

 

A question comes to mind: Are your engine's cooling passages wide enough to let pass the required quantity of coolant?

 

When I look at the scale of the engine and its visible coolant passages and the now 'discarded' coolant piping it does make me wonder if your new setup will work. Making pipes biger won't solve the issue when it slows down due to a funnel caused by the entry in the engine/cylinderhead

[SJSoane]

 

Michael, your work continues to show the art at a level of sophistication and skill that I would not have believed possible until I see it before our very eyes...

 

Mark

[Bedford]

Nice pipe bender, another one to file away!

 

It is a pity you have to go to an electric water pump but sometimes you just can't help these things and I am sure only you and I will ever know !!

[Mirabell61]

beautiful work Michael,

you are very knowledgable in function and fabrication with those facinatiing "Oldtimer" machine parts, a delight to watch you move along

 

Nils

[michael mott]

 

Making pipes biger won't solve the issue when it slows down due to a funnel caused by the entry in the engine/cylinderhead

Hi Carl, I agree with your thoughts, I think that if I keep things consistent and have a good general flow then I should be OK.

I can push a fair bit of water through the .093 holes with a good pump and since I am not going to be running this engine for long stretches I am confident that I will be able to get enough cooling.

 

 

Nice bending work there.

Thanks Druxey, I do have the small set of coils spring pipe bender that I purchased some time ago but they only work for gentle curves, I have done some more experiments with the styrene rod as a filler as suggested By Bob. The combination of the heavy walled brass tube benders that are bored to the pipe size plus filling the tubes with the styrene have greatly improved the quality of tight elbows. The styrene gets trapped and a quick play of the propane torch over the elbow pops most of the styrene out then after removing the blobs at each end of the bent tube a little more heat and the residue flames off, leaving a good bend and flow through.

 

Thank you Mike, Mark, Steve , and Nils for your very complimentary comments. A sincere thanks to all who have shown their appreciation by pressing the like button.

 

I am continuing with the experiments with the various shapes and components for the piping and valves. I am gathering a fair collection of bits for the spare bits box. The parts to the extreme bottom left hand corner are the present iteration, that i am working with. the hex sections have been filed instead of adding in some sections of hex stock this eliminated the need for threads etc and is quick enough to do with a few strokes of the fine file.

 

 

I filled the four mounting holes with some 00x90 threaded rod and soft soldered them in place because they won't work with the new configuration that is not quite there yet but is getting close.

 

 

I have been sorting out the stack of elements and seeing how to create the look of a number of parts screwed together but really being a solid fancy tube. here there ore the vertical part of the pump the valve to bleed off any air then the anti hammer bulb. it is bored out to accept some 1/8th inch copper pipe for the bottom elbow, and a .093 hole for the tee off to the upper union that connects the piping to the water jacket as in the one on the real engine. I am using the 1/4 inch brass rod that I purchased at home depot, this rod is nice to machine and not very expensive. By using the collet chuck instead of the three jaw I can shift the brass out as I complete each element. the collet has 6 slotted sections as part of its design which makes it easy to line up to file the hex sections.

 

 

I silver soldered the tee to the bulb section, not as good as some soldering I have seen but acceptable, in this instance.

 

 

Michael

 

 

 

[cog]

Michael,

 

RIght. Pressure should probably solve the issue (blessed ignorance on my side) You keep expanding my head's storrage - hope the internal fixed disk size will suffice ...

 

Marvelous work again, with unexpected details

[popeye the sailor]

I was sorry to hear of the shortcoming.......with what I've seen you do up to now.......you WILL find a way     you plan an open coolant circuit,  siphoning water from outside the boat,  and expelling it at the other end..........but have you given any thought to a closed system?

     the only problem with this,  is you would need a radiator to cool the fluid you will use.   there are other fluids that have a higher cooling rate than water.