A Robinson from rejects.

[RayW]

Finally made a start on the Robinson this week. The photos show the main casting and cylinder block loosely assembled. Both are part machined at this stage and the next big job is to figure out how best to bore out the cylinder block for the liner. I am undecided at the moment as to whether lathe or mill would be the best way to go. I suspect that it will have to be the lathe as I doubt if there is sufficient headroom on my little mill to accomodate the casting and the boring head. Either way, centering the casting and holding it securely will be crucial.
The other main job left to do on the cylinder casting is to mill out the big rectangular hole in the base as illustrated by Jason.

[Jo]

I see Graham let you have a batch of castings with his trademark protective coating too Ray.

I am pleased to say mine has worn off 

Jo

[Alyn Foundry]

I am pleased to say mine has worn off 

Jo

Waaaaay tooooo much fondling Jo! 

I must apologise to all, the forum moves so fast I'd completely missed Ian's contribution and progress, it's looking great.

I'm currently working on an unusual project at the moment....

<a href="https://www.youtube.com/watch?v=PmjGtZM21YM" target="_blank">http://www.youtube.com/watch?v=PmjGtZM21YM</a>

This may be featured in a BBC Radio 4 presentation in the near future.

Cheers Graham.

[RayW]

As Graham says Jo, definitely too much fondling has worn off all that lovely patina!
Spent today working out the set-up for boring the cylinder. As I suspected, there was just not enough headroom on the mill for the casting and a boring head and boring bar, so switched my thoughts to lathe set-up. Finally came up with the method as shown in the photos. I machined an aluminium plug to fit the cast main bore with a reduced diameter at one end to locate in the cast hole at the front end of the cylinder casting. I then bored through to accomodate a bar which was of the correct diameter to fit the bore of the lathe spindle with the other end being held in the tailstock chuck.
With the casting thus located centrally, it was just a case of bolting it to the faceplate. To attach the casting to the angle plate I drilled and tapped a hole in the base, in the area which will be milled out later. Because I could only use one bolt, two other bolts were located through the angle plate either side of the casting to prevent any possibility of the casting swivelling while being bored.

[Jasonb]

You beat me to it, I was going to post that it may be better to do the bottom recess after boring as you could tap into the metal.

I opted to drill and tap for a couple of M6 studs either side of the opening so I could mount it to an angle plate



I glued a scrap of ali to the front of the opening and punched that so I had something to locate, As the outside of the bottom of the casting had been skimmed that gave me square faces to line up to the faceplate. It's now bored out to 1.5" ready to open up for the liner



J

[Ian j]

Latest progress on my engine built from bar stock.
The hot tube chimney is a piece of thick walled stainless with a plate and burner tube mountings silver soldered on, hope it doesn't all falls apart from the gas burner heat!
 The piston is machined from cast iron bar as is the liner. I took your advice Jason regarding using loctite, I also reduced the o/s diam. of it for the length of the cut out in the cylinder casting which made it easier to apply the loctite and insert the liner. I let it cure for 24hrs and when assembled on the bed with a gasket it all seemed to be water tight. Whats the purpose of the 1/16" deep part on the bottom of the cylinder?
 When I machined the the cylinder I used a keates angle plate on a face plate, but it was just a block of ali.at that point so no awkward shapes to consider. When I do the "real" one using the castings both Ray's and Jason's methods will be a great help.

[Alyn Foundry]

Hello Ian.

Amazing progress, well done!

Ray PM'd me yesterday with the very same question, what's the idea of the step underneath? Well we thought, at the time that getting water closer to the glued joint might be advantageous. It is the hot end after all!

I'm smiling, as I used to just put the cylinder casting into the mouth of my 4 jaw and bore away. I guess having the space for a large machine has its advantages.

I had a recurring customer that worked for GEC in their massive machine shop. I once asked how he bored his cylinders, his reply, oh, I just bolt them down on the table and stick an end mill in!!

Cheers Graham.

[Jasonb]

I'm not sure that this special coating that some people keep going on about is all it's cracked up to be, seems to have worn off my casting already

Just a couple of holes left to do but they will have to wait until the liner is in place as they pass through both the liner and cylinder casting.

[RayW]

You are making good progress Jason.
I am on hold with boring the cylinder at the minute as none of my boring bars was doing a very good job so have ordered an indexable carbide tipped one as I want a really good finish where the liner has to fit.

Ray

P.S. Don't forget the vertical exhaust slot and the hot tube holes. They don't go through the liner!

[Jasonb]

You are right Ray they go into the 1.5" bit at the end, could have done them

[Jo]

I'm not sure that this special coating that some people keep going on about is all it's cracked up to be, seems to have worn off my casting already

Too much fondling 

I hope the other three engines are still moving forward.

Jo

[Alyn Foundry]

Hi Jason.

Oooh, is that a bit of shrink I can see in your photo?

This was a major problem with the earlier Rhuddlan castings, I hope it doesn't extend into an area that can't be mended?

Cheers Graham.

[Jasonb]

Yes as it was right where the remains of the riser could be seen so I had assumed that was the problem, about to go and mill it out so will report back later but I can't see it on the inside so fingers crossed.

Jo it was only a few mins of fondling that caused it to ware off, do you think I should be using silk gloves rather than a grinding bit in the Dremel?  Yes the others are moving a lot faster than some of yours This one will probably get put away now as I did not want to spend the time and effort drawing and fabricating the other parts if the cylinder was not going to be upto the job, infact had the cylinders not become available this was going to be quite a way down the list of engines to do.

J

[Jasonb]

Exhaust passage machined up OK, also did the hole for the hot tube while I was at it.

Then I thought what use is a hole without something to put in it so made the hot tube and plate that retains it.

J

[RayW]

As Graham knows, I had a bit of a traumatic time machining the exhaust valve chest due to several senior moments on my part.
I had some difficulty reading the bore dimensions on the scanned copy plans, so messaged Graham and confirmed that my readings were correct. I then, for some reason, proceeded to bore out to completely the wrong size ( 7/16" instead of 5/16")!
Fortunately, I was able to rectify the situation with a press fitted cast iron plug held in with Loctite, then re-bore to the correct dimensions.
The exhaust valve assembly is now almost complete. I just need to cut the valve seat and grind in the valve, and machine a couple of flats on the spring collet.
I have also finished boring the cylinder ready for the liner, which will be the next job.