My Paddleduck engine build

[Dalee]

Hi,

I got started on the Paddleduck this weekend. I didn't have a whole lot of time due to youngest Grandson being here and being on call. But I did manage to square a block to size and get the bores drilled and reamed.

I also made my first ever D-bit. I was going to ream the cylinders to ,375", but evidently I don't own such a reamer. And the boring bars I own that will work that small are way too short. So, instead of buying and waiting a week, I grabbed some 1/2" drill rod/silver steel and had at making a 10mm D-bit.

I was impressed by how easy the D-bit was to make. I wasn't expecting the good finish I got either. A little bit of honing and the bores should be good to go.

I don't own a real digital camera, I used my phone for this photo.

Dale

 

[Blogwitch]

Good on you Dale for having a go and succeeding.

D-bits can really get you out of trouble when you don't have the real thing, which sometimes aren't available anyway.

Put the ones you make in a box, and in a few years, you should find you will have a nice collection, These are a few of mine.

.

I sometimes rework old ones, but because they are so hard, I use my toolpost grinder to reshape/resize them.


John

 

[Dalee]

Hi,

I do intend to keep it, I think it needs to be re-heat treated though. I don't think I got it up to snuff, it seems a bit softer than it should be. But it worked OK on cast iron.

You have D-bits like I got shop made face mills. Always seems like I need one more.

Dale

 

[Blogwitch]

Dale,

I hold the heat (bright red) for about 4 or 5 minutes then quench in cold water. I don't temper and have never had problems.

BTW, the two proto's I built during development.

Full bling.

Good luck on the rest of your build, and if you have any queries or questions I will do my best to help.

John

 

[Dalee]

Hi,

I got a bit further this weekend. I made the top caps and the packing glands. The first gland went quite well. Single pointed the little screw in parts to 1/4-28, (close enough to 6mmx1.0). Haven't hand cut threads for a very long time. But I did need to make the second bottom cap three times. Junk tap kept pulling the threads out.:wall::wall::wall: I finally ground one of my good Besly taps into a proper bottoming tap. Then things went fine.



Dale

 

[Dalee]

Hi,

I'm resurrecting this thread again ,since I've started working on the engine again. Well, between Doctor's appointments anyway.

So I have a question about the pistons and the o-ring groove. How deep do I want the groove? How much do I want the o-ring to be proud of the piston? Is there kind of a rule of thumb to go by? Too much and friction prevents movement and too little is a waste of an o-ring.

Thank you!
Dale

 

[kvom]

I didn't use an o-ring myself.

 

[Dalee]

Hi,

Ok, I will at least shoot for that fit.

Dale

 

[Blogwitch]

Dale,

Most people go for a wider ring groove than the ring itself when fitting 0-rings, to me that is counter productive as it allows the ring to roll up and down in the groove, which will soon cause it to fail to do it's job.

What you need is something supported by the groove and so wear away on just the outer edge.

I always, and always will, cut the piston groove the same width as the ring but about 0.002" to 0.003"(0.05mm to 0.06mm) shallower than the ring width. That way, over time it will just wear away on that one edge. Put a small chamfer on the leading edge of the cylinder to help get it down into the bore.
When making and running engines in my steam boats, sometimes every weekend for a year, then I would just swap out and put a new ring in even though most times it didn't need one.
The ring actually becomes slightly square shaped in cross section as it is pushed down slightly into the groove.

If you are just going to run on air, then just fit a standard Nitrile ring, or else a Viton one if eventually you are going to run on steam. No way should you fit it with silicone rings as they are affected by certain cleaners and lubricants, and will just swell up and disintegrate into uselessness.

John