Ridders Coffee Cup Stirling

[a--d]

Hi,

I've started building a Ridders Coffee Cup Stirling engine here in Yorkshire, England.

After spending a year turning a lot of metal into swarf and not really getting anywhere other than fixing a few things on the lathe itself I decided a proper project would be a good start.

I appreciate these LTD stirlings are quite difficult to get running but hey, if you're going to do something why not jump in head first? There is also an almost worrying level of coffee consumption by everyone both at home and work, so what better to start with?

I only have a lathe, no mill, so I was looking in particular for something that could be achieved simply within these limitations.

First I downloaded the plans from ProjectsInMetal a few months ago and started to remake them in Autodesk Inventor. This is so I can learn the software and get my head around the parts before making chips.





The plans call for 5 mm thick end plates, but these are being made from 5mm sheets. They might be a little thinner than intended. I'm sure that'll be fine as long as the internal volume of the displacer cylinder doesn't change too much, and that's controlled by the cylinder walls, a separate part.

I don't have access to a bandsaw, so hacksaw it is all the way. I figured drilling around the edges would speed up the cutting process by removing most of the material for me. It did.






Once all the sections are cut out the jaggedy blank was super-glued to a large chunk of aluminium and very, very gently turned down to round with a bit of support from a live centre in the tail stock, a centre-drilled piece of scrap and an off-cut of some kind of anti slip matting from work.

Gently heating the metal sandwich on the gas hob and prying with the blade of a scalpel separated the two pieces nicely, with the sacrificial blank ready to use again for turning the upper plate.

I'll do this in the future with the window open from the get-go - it smells really bad.



After the upper and lower plates were turned to round the large chunk of aluminium was turned mostly into chips - it will be a rudimentary pot chuck to facilitate facing the thin displacer cylinder plates and the smaller diameter flywheel later on. It still needs a bit of de-burring in this photo.

Boring this out took an incredibly amount of time - after the lathe motor stalled a few times I took a close look at it again: only 1/4 HP! It really struggles on even medium sized cuts near the OD.



That's pretty much what I have documented so far - I hope you've found it interesting. I've got an OU exam in a week's time so I should probably be concentrating more on that...

Aidan

 

[a--d]

The upper displacer cylinder plate and I have had a falling out, so I've put it to one side for the moment so I can think about it. I accidentally faced off the punch mark for the larger of the two bore holes, then carelessly drilled a ridiculously off-centre hole for the new hole, making it really hard to dial in for a bore.

:wall:

Instead I spent a few hours this evening starting the work cylinder - it's made of brass which is nice to machine. The stock I have is only slightly larger than the largest OD so getting it running as true as possible was important. I picked up a tip somewhere on YouTube about using two chuck keys when centring a 4-jaw and it's really sped things up! Notice how clean the lathe is at the moment.



Once I'd turned down the stock to size (20 mm OD on the smaller section) I stuck a scriber in the tool post and picked up the faced end. Then, using the dial indicator stuck in another position I scribed lines avery two millimetres for the fins. They aren't critical dimensions but it would look a bit off if they were incredibly out of proportion.

I could probably do this with the compound but it's an imperial lathe and I'd rather not think too hard!





Once marked out it was a simple job to groove the fins - two millimetres wide, two millimetres deep. Brass is such a joy to work with (except for the splinters!)



A quick touch with a spongy sand paper type of thing and the layout marks are gone and the brass has a nice look. I'm definitely happy with the way this part is turning out so far, long may I not mess up.



I'm waiting for a 13 mm reamer to arrive (should come tomorrow) before I start the bore, then I'll part it, flip it around and do the lower side. Besides it's getting late here and it's not the time to have noisy machinery running in the garage.

 

[danstir]

I'm enjoying watching your build, thanks for sharing it.

 

[a--d]

Hi danstir, thanks, glad you are enjoying it.

I've parted and turned the rest of the work cylinder to size - parting was quite friendly and with a sharp tool I could do it at quite a high spindle speed which made a change! I didn't want to extend the tool and reset the height so instead I cut off this last bit with a hacksaw.



The cylinder bore was drilled, bored and reamed to 13 mm. The bolt holes and an odd "bite" from the side needs to happen still. The bite needs a bit of thought behind it, not quite sure how it's going to work out.

The bore I'm not quite sure about - it has a reasonable finish as is after a quick touch up with some fine paper, but should it be shinier? Does anyone have any suggestions for that?

 

[Swifty]

The bore looks fine to me, shiney does not always mean it's smooth, a lot of bores are lapped finished which produces a dull finish.

Paul.

 

[Hopper]

Well, I am glad to know I am not the only one still using a drill and hacksaw instead of a mill!
Looking forward to following your progress.

 

[a--d]

The bore looks fine to me, shiney does not always mean it's smooth, a lot of bores are lapped finished which produces a dull finish

Thanks Paul, I'll bear that in mind.

Well, I am glad to know I am not the only one still using a drill and hacksaw instead of a mill!
Looking forward to following your progress.

I have to admit it's starting to get a little old!

 

[Hopper]

How's progress coming along?

1/4 hp yikes! You might want to try back gear on the larger diameter stuff.

 

[robcas631]

Looks great! I am going to build the J Ridder 20 Euro.

 

[a--d]

How's progress coming along?

Slow! I recently had an exam, then disappeared to Barcelona for a few days with the girlfriend - even as I type this I'm about to head out the door to help paint the spare room. On holiday I came across a huge mechanical sculpture, but after a brief search I can't find any more information about it. For a sense of scale I think the large gears are maybe 3 m diameter or so.



I've picked up a pair of ear defenders which makes working on the lathe much easier (especially when running the leadscrew for power feed). I'd definitely recommend them to anyone. Also, I've spray painted important spanners so I can find them quickly: yellow for carriage lock, grey for compound swivel, black for QCTP nut etc. This has really sped things up!



I'm making the bearing holder at the moment - it has a flat milled out of it in the drawing, but instead I'm going to just turn it flat by mounting the undrilled blank in the lathe chuck sideways. I've done this already with an almost finished part and the bores for the bearings weren't conducive for a flat, square finish. The turned flat was so wonky I had to scrap it.





Now it's just time to re-mount and re-centre it, then bore the bearing seats.

Looks great! I am going to build the J Ridder 20 Euro.

Thanks Rob, I've got a few euro coins knocking about here; looks like yours will be quite small when it's done!

 

[a--d]

So after a, err, brief, hiatus I've picked this up again. I had to move house after my landlord sold it (!) which meant the lathe was dismantled for moving and put into storage. I miss the quick change gearbox!

I'm a member of a local community workshop though so after uhm-ing and ah-ing for a while I searched out the pieces and got going using their lathe.



First of all, collets. Goodness me, they certainly make like easier don't they? All I will say is this - if you don't have one and are considering it, just do it already.

I spot drilled then drilled to 2 mm for this small washer. The end result is 6 mm in diameter and 1.0 mm thick. I parted off a bit thick (+.25mm) and subsequently spent a lot of time with sandpaper on glass to shave it down, little by little. I got started on a number of different parts, but then got held up by quite a minor snag.





I find that turning brass with a sharp CCGT/Aluminium insert leaves a great finish, but you have to pay attention when facing and hogging off large amounts. The brass really wants to suck the tool in which ends up with taking a bit more than intended off the face sometimes.



So that's the total of tonight's work. I remade the bearing block because I lost the last one in the move. Not only is this one much more precise fit on the bearings, it was also quicker to make!

Unfortunately all of these parts are half done, mostly because I am waiting for a 3 mm ER32 collet. It appears that this one had an accident at some point in its life...

 

[vederstein]

Thanks for doing this thread. I've always wanted to see an LTD Stirling build.