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

[michael mott]

Steve interesting point regarding the polishing, I shall ponder that one.

 

Carl, I am following the same shape as that on the original, and many of the small model engines that I have looked at have the same sort of configuration and do not seem to have vibration problems, that said I shall have to see what happens, it will be easy enough to build a different one if I need to.

 

Michael

[Twister]

My goodness, if you carry on like this then I'm going to have to find some new adjectives!

 

Carl bringing up the 'balance' question got my somewhat limited grey cells working, to that end I wondered if it would be worth making the crank webs with counter balance weights. The dim and distant past prompted me to remember that the mathematics involved to calculate the precise weight were not too involved, but then like you, I've also seen plenty of minature engine builds where it wasn't done. Maybe it's because they were relatively low reving (I really can't remember) or simply that the additional forces imposed on the crank journals etc were of a magnitude that was relatively insignificant. At the end of the day while crank webs 'sans' counter weights may not adhere to good engineering practice there's no denying what actually works in practice...

 

Row

[michael mott]

Row and Carl

This is a picture looking inside the crankcase of the 3hp buffalo just like the one in Skipjack

 

 

I have modeled my crankshaft after this one.

 

Michael

Edited January 23, 2015 by michael mott

[Bedford]

In the case of the real thing I would imagine it is fairly low revving and with the cranks at 180deg from each other balance would be no problem. This engine will have to rev higher I would think but still the cranks are at 180deg and in this case because it all happens so close to the centre line any minor imbalances won't really be an issue either.

[cog]

Thanks for the preview Michael. Looks huge though ...

 

Bedford, I presume you are right about that. Considering the weight of the crankshaft ... it will not have too much of an impact as you predict

[michael mott]

Steve, Carl thanks for your thoughts , and thanks you to all who added a like.

 

Carl the real engine is actually quite a small one.

 

 

Steve, My plan is to have it as a slow running engine am thinking that I will weight the flywheel with some lead in the outer area to give it more mass.

 

My silver soldering was a great success..... not so with the clean up

 

 

look at the upper right hand con rod bearing!

 

 

Yup made the classic mistake of beginning to cut out the wrong piece

 

I went ahead and cleaned it up because after letting the universe know what a silly move it was with a little colourful language, I wanted to see how the shaft fit and can also use it as a placeholder to test fit the con-rods and pistons knowing that I do have to build a new one.

 

 

I was pleased that it did not warp and and my method of setting up the parts and pre-placing the solder by wrapping very fine strips around the shafts outside of the actual bearing surfaces worked very well. I turned up some sacrificial pins that were the same diameter as the spaces between the plates to hold things in line. after cleaning it up and placing it into the bearings the shaft spun nicely between my fingers.

 

 

 

Next on to the con rods and Pistons.

 

Michael

 

 

[Jack12477]

Superlative job of machining, Mike. Looks really good. I'm really enjoying your build.

[Twister]

'...classic mistake of beginning to cut out the wrong piece'

 

- If that had been me the realisation would have struck home after the wrong cut was completed!!

 

Great work, as usual, Michael.

 

Regards,

 

Row

[mtaylor]

Ouch on the wrong cut.  I'm surprised the air didn't turn blue down this far south.  That crank is just impressive.

 

But since you told us, you can't get away with the old hot rodder's line of "I grooved the bearing journals and crank for improved oil flow."

[Bedford]

I didn't think it was possible to make small engines like this run slowly but the leaden flywheel makes it sound very promising, if I'm not mistaken it will also help dampen any wayward vibration that may sneak in.

 

I've moved my chair up the front!

[Sven]

I bet that crank would work even with the little grooves but I know the "out of sight out of mind" line would never wash with your brand of perfectionism!

Fantastic and inspirational work Michael and it amused me to think of that sort of language from a gent like you!

 

Incidentally I was just thinking about the dim distant past when I had model aero engines. They always needed lots of mass in the prop to keep the revs at a sensible speed. I'm no engineer but suspect you will need as much crank weight as you can get. Would it be worth thinking about full circle crank webs as you are re making it anyway?

 

Matt

Edited December 3, 2014 by Sven

[popeye the sailor]

Sven isn't too much off the mark.......oil journals would increase lubrication for the rod bearings {if you plan on going that route}.  chances are your going to go with a splash type form of internal lubrication.   to incorporate an oil pump of any kind,  would need to run  from the cam shaft.

[cog]

Ah, Michael,

 

You could have fooled me Nevertheless, practice makes perfect ... It still looks awfully good to my laymans eyes

[michael mott]

Jack, Row, Mark, Steve, Matt, Denis and Carl, thanks for the encouragement.

Thanks to all for the likes.

 

I took a break from the drive train today and fabricated the Valve caps these are there to allow the valves to be removed from the head because on the full size engine the head was a single casting. because of the small size of my model I have built the head in two parts. I haven't fully resolved how I will join them yet.

 

The two outside caps which line up with the inlet ports are also set up as priming ports with a couple of little cups above the stop cocks that are threaded into them. like these on the top

 

So I had a bit of fun having a go at making a stop cock to fit into the top.

Looking down into the open valve.

 

 

Now closed

 

 

From the side

 

 

 

The valve cap is threaded 8x36 into the head these were made from some 3/16th rod from Home Depot (nice hard brass)

The valve body is machined up from some 1/8 hex stock, I have a fair bit of it left over from a commercial job 20 years ago (it was a special order locally and I had to buy 16 feet of it) it is also a nice free machining hard brass.

 

The steel insert is a mystery steel (salvaged rods from a library card catalogue system filing cabinet) it seem to machine freely and is 1/8th in diameter.

 

The threads on the valve body is 1x72 with a # 59 drill hole through the length. The cross hole was 1/16 then tapered with the largest clock making tapered broach. the steel was tapered to match on the lathe and threaded 0x80 for the retaining spring and nut. the handle end was shaped with needle files while still on the lathe then heated in a pin vice and bent with some flat pliers.

 

Once the steel was shaped I set it into the brass body put it back into the lathe and drilled through the steel with the handle in the open position using the same #59 drill from the opposite end. It looks a bit crude and now that I know I can make one this small I will set up and make a pair that are a bit closer looking to the ones on the 1:1 engines

 

Michael

[michael mott]

Built another priming cup and stopcock, it is getting closer still needs some refining.

 

 

 

michael

[EdT]

Magnificent.  Simply magnificent.

 

Ed

[TBlack]

This is fun to watch. I think it takes several disciplines to pull this off: First, you have to know how to do it; second, you have to know how to explain it; third, you have to know how to photograph it. I think there are several left brain/right brain things going on here. Most inspiring.

Tom

[cog]

Michael,

 

It looks very good. I have the feeling the second stopcock is the better choice

[captainbob]

It's looking better and better all the time.  Stick your thumb in the next picture to give us a scale reminder.

 

Bob

[Twister]

I agree whole heartedly with Bob - it's easy to forget precisely how small this incredible feat of engineering is, it's only when scrolling through the thread and catching a glimpse of your drawings that reality strikes.

 

Inspiring work Michael,

 

 

Regards,

 

Row

[michael mott]

Thank you Ed, Tom, Carl, Bob and Row for your kind comments and to all those who liked the last few entries.

 

I think I could make one of these small stop cocks now in my sleep. I have gone through a number of failures with silver soldering handles mainly because I was using the wrong approach to setting them up to solder.

 

The following sequence shows most of the steps and elements in the stop cocks.

`

First picture shows some 1 inch tapered clock pins cut to length prepared for soldering

 

 

This  one shows the box of tapered steel clock and watchmaking pins that that match the tapered broaches, I decided to use them instead of threading the rotating part and using springs and nuts. 

 

 

The hole through the centre was bored after the threading was done, with a number 59 drill, I used paint thinner as a lubricant, normally I do not use lubricant when machining brass but with these small diameters and threading it helps.

 

 

A finger tip as requested behind the main body of the valve

 

 

Drilling through the body for the steel tapered part. I found it helped to make up a couple of holding jigs with some hex brass rods.

 

 

Using a full pin to test the depth of cut with the taper broach of the valve body

 

 

In the palm of my hand for scale

 

 

The new stopcock on the left with the old one on the right. I Like the shape of the longer handle better and it is also easier to turn, as I am sure they are in full size as well

 

 

Another couple of overall comparison shots for scale

 

 

 

I have all the parts now to make a pair of stop cocks like the new one, plus all of the steps figured out for soldering and final assembly. I think it is also time to finish shaping the top part of the head.

 

Michael

 

 

[Bedford]

Beautiful work as always, the pins are tapered so you only need the put a locking pin through the other end and the taper keeps them in place, is that it?

Also how big is the hole through the pin that forms the valve, ie what size hole does the fuel drip through, or are these just for appearances?

[shipmodel]

Seriously terrific work, Michael - 

 

I see you found Andre the Giant to help you out.  That can't possibly be your fingertip in the photo.  If it is, I tip my cap to a true master.

 

Be well

 

Dan

[Jim Lad]

I've somehow missed your updates here, Michael.

 

What brilliant work you're doing!

 

John

[mtaylor]

After seeing this in your hand...   As Dan said.. you are a true master.

[michael mott]

Steve the hole through the steel rotating part of the valve is .041 in diameter it is a number 59 drill the locating pin with the washer is also a taper pin and keeps the main part in place. they will work as real priming cups.

 

Dan , yes it is me, and thanks for the compliment

 

John, Thanks for the kind remark The handles on these valve are really no smaller than a large belay pin at .25" long they would be a foot at 1/48 scale and 18 inches at 1/64

 

 

I like the one on the right better than the one on the left so will replace the handle on the left one tomorrow.

 

 

Some of the metalwork that I see being done on many of the ship build logs is much smaller that this engine.

 

 

And thanks for the likes

Michael

 

 

[michael mott]

Mark, thanks I still keep thinking about the tiny stuff that gets put into so many of the ship builds.

 

Michael

[cog]

Michael,

 

I would say you belong those who make real fine, precise, and (very) tiny work (besides the lage scaleyou do splendidly to). It looks magnificent, and I for one would love to hold it in the palm of my hand, just to relish in the workmanship!

[captainbob]

Michael, thanks for the pictures and information.  You are right there are a lot of modelers making very small parts.  They all amaze me.  And you are right there with the best of them.

 

Bob

[popeye the sailor]

I second that Bob..........might even go as far to add that what your doing requires a lot more milling.   your goal is also much higher

 

splendid work Michael!