Stirling Engine : Laura

Why not drill & tap the baseplate, drill the bottom of the cylinder support (clamp the two bits together as you drill down the joint) and then just use cap heads from above which will match the way the bearing supports are fitted

Jason : I do not think there is enough meat to drill the bottom of the cylinder supports. I am not sure I follow ?

Whichever way you decide to finally fix the cylinder assembly to the base plate wait until you have the whole thing running and then adjust it until it runs at its fastest until tightening it down as stirlings wont tolerate much if any misalignments that cause friction , just choose a method that gives a little wiggle room to let it all run as freely as possible, the brass angle method sounds pretty good to me , leave say 0.5 mm clearance in the holes for fine adjustments before tightening down.i definitely woulnt go down the silver soldering route as it could distort the base plate then you would have problems.

I would drill the base plate, and tap the holes in the bottom of the stand, put the screws in from underneath, use a reasonable size screws, or the whole thing will rock as it runs. One of my flame lickers is mounted that way, and only has three 1/8" Whitworth screws, and it flexes a bit, but as it hasn't broken I'm not fixing it, my usual 3/16"/10 32 UNF would be what I would replace them with, 5 mm would be OK.

Ian S C

I would follow either Jason or Ian's suggestion Brian. Probably Jason's as I would use countersunk headed from underneath which would leave zero scope for adjustment.

One thing you should check on your drill - are the drills square to the table? Often they can be adjusted on one plain. Out of square can cause holes to wander about. An automatic centre punch helps or in in critical places a centre drill first - those can be pulled a little with care.

A small toolmakers square can be a useful thing to have about. They usually come with 3 blades. On straight, one angled at each end and a narrow one that can be used to measure. The blades are 100mm / 4" long.

The manic method on larger holes is to scribe a box with a height gauge and pull the drill central as the tip goes in. Done correctly the drill will break the scribed lines on all sides = positioned to better than 0.001".

John

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I have cut two glass cylinders/tubes from the supplied test tubes. I put masking tape around the test tube where it is held in the chuck. I held a diamond file on its edge to cut through the tube while the lathe was set to a low speed. The triangular file would have been better but it is not a diamond file so it would not cut very well. Once I had cut through it then I cleaned up the edge with the flat of the diamond file and then removed it from the lathe to give it a final polish with 1500 grit sandpaper.

I would have liked to make a tool holder for a dremel diamond wheel as somebody suggested above but I am still waiting for some square bar stock. For some reason I never ordered any square bar before...only round !

Next step is to make the aluminium piston to fit the glass cylinder. I am not looking forward to this at all because I have to try to round the end of the piston by hand to get a good fit in the end of the cylinder.

Edited By Brian John on 05/01/2016 06:25:23

Make a stiff card radius gauge to check against if you are going to manually make the radius. It does not need to be a perfect curve as it going to be in the bottom a test tube that is probably not a perfect hemisphere anyway. It just needs to look good in the tube.

Martin

I still think it is bad idea making things out of glass and it only complicates the issue of making a piston to fit. I know they chose glass because of it low thermal conductivity but I have seen similar Stirling engines with stainless steel cylinders. If I can get this engine to work with the glass cylinder then I will try to replace it with a stainless steel one at a later stage.

Andrew : did you get your Stirling engine to work ?

Next problem is the connecting rod for the working piston : I have to drill a 2mm hole through the 3mm steel rod. This is not going to be easy. I would hardly think I can mark the hole with a punch like I would usually do. How would you go about doing this and ensure that the hole is in the centre ? I have a bench drill and a drill press vice.

.

Edited By Brian John on 05/01/2016 11:12:15

Brian

Make a simple (reusable) jig. More pics in Cross Drilling Jig album, but I don't know how to post more pics in this reply.

Dave
The Emerald Isle

Brian, No, still not working, but in fairness I threw in the towel after a couple of hours. I will give it some more time at the weekend.

I did strip it back down, and have reasonable compression on the working cylinder, and all the linkages are free. If I give the flywheel a spin (with everything connected) it will rotate for about seven turns before stopping, so I don't think anything is binding. There are no leaks in the air path that I can tell, and the air from the displacement cylinder is reaching the working cylinder, so I haven't a clue why it wont sustain motion. Time may tell!

As for drilling the connecting rod, the end that has to be drilled has to be filed down on both sides to create two flats. Once this was done I centre dotted it and drilled it easily. If it was still round it wouldn't have gone quite so well.

Andy

Yes, of course : File the flats first !

Andrew : How much gap do you have between the pistons and the cylinders at TDC. I did read somewhere that this gap has to be as small as possible on Stirling engines. I cannot remember if they were referring to the work or displacement piston/cylinders...perhaps both.

NOTE : I will make the M3 thread on the end of the connecting rod 12mm long and not 6mm long as per the instructions. I want to install two locknuts there so as to make the length adjustable. All my steam engines have been constructed this way.

Edited By Brian John on 05/01/2016 12:45:04

Brian, that's a good point about the pistons at TDC. The displacement cylinder is virtually touching the end of the glass cylinder (perhaps 0.5mm clearance). I haven't checked the work cylinder, but will have a look tonight. If the gap is too big I can always make a connecting rod to your suggestion.

I'll let you know what I find!

Andy

Glass makes it easier to get the piston to fit, you can slip the glass over the piston and SEE what it fits like

Have you given any thought as to how you might make a deep flat bottomed hole in stainless?

Brian, don't worry too much about the power piston, just don't get too close too the end of the cylinder, allow a couple of mm.

I usually make my con rods from flat material, usually aluminium 1/4" thick. The width is chosen to take in the width of the big end bearing, plus a little, I mark a centre line, then mark the position of one of the bearing holes, then set the distance on a pair of dividers and mark of the other bearing and centre pop that one, it's then a case of drilling the holes. I use a little bronze bush in the little end bearing, and a ball bearing in the big end, except when the crankshaft design won't allow this, in these cases a split bronze bearing is held in place with a cap held in place by bolts. Here's one of each.

I do ramble on a bit.

Ian S C

Jason : with my small boring bar...maybe   I did have to open up a tailstock die holder today that was a bit too small to take my dies. The boring bar handled that okay.

Or perhaps make the cylinder as best I can with the boring bar and then drop an already machined 2 to 3mm thick disc down the cylinder and Loctite it in position : we now have a flat bottom cylinder.

Edited By Brian John on 05/01/2016 13:53:12

Or a tube with an interference fit disc tapped in? Or not worry abut it being flat bottomed.. just drill it and bore to the drill taper and make the piston tip to the same angle with the top side? Od not even bore it, just drill since the displacer is a loose fit.

The one I'm slowly building (butchering) uses glass cyinders and pistons. I like the idea of seeing the movement.

I made the connecting rod (13) today. I actually made four of them, two of which have been discarded. I decided not to drill the hole out to 2mm on the flat of the rod ; I have left it at 1.8mm. It will not now accept the 2mm rivet as per the instructions when fitting to the piston joint (14) but I will use a 10BA screw and nut with Loctite to hold it together instead. I thought drilling a 2mm hole was really pushing it too close to the edge of the rod. I have put 12mm of M3 thread on the other end so I can fit two lock nuts. This will allow me to make adjustments to the length of the connecting rod.

Edited By Brian John on 06/01/2016 07:02:40

I had a go at making the displacement cylinder today. I am getting there but the process has raised a number of questions. I made the bullet shape by producing a 30 degree taper and then rounding it off by hand using a large file. Jason : you are right. Turning the taper using the top slide wheel is much easier than I thought it would be...no handle required.

1. Why is it the piston made of aluminium ? I hate this stuff and my lathe does not like it either. It gums up my drill bits and my reamers and I find it almost impossible to tap. I have to drill and tap for an M3 grub screw that will hold the piston rod in position but I doubt it will be successful. I have had problems in the past tapping aluminium. If the piston HAS to be aluminium then I may have to make a brass sleeve and tap that and Loctite it in position in the piston.

2. My lathe chuck always gets very hot when working with aluminium. I noticed this a few weeks ago when I was making the aluminium columns (part 30). Why should this be ? Brass does not cause the same problems.

3. The ID of the glass cylinder is 13.2mm. The instructions say to make the piston 12.5mm but this seems like a very sloppy fit. You can see in the photo that I attempted to make one to this size (actually 12.45mm) but then stopped and made another one to 13mm diameter. This seems a much better fit and still plenty of room for free movement ie. it does not touch the sides of the glass tube. Any thoughts on this ?

Edited By Brian John on 07/01/2016 06:28:15

Brian there has to be room between the displacer piston and the cylinder ID for the air being displaces from one end to the other to flow unimpeded. Also, there has to be room for the piston to move up and down without touching the cylinder at any point -- sometimes a bit tricky if the alignment of the piston rod and bushing are not quite spot on, or as the bushing wears a bit. Half a millimeter clearance all round is not unusual, so a total of 1mm difference in diamter.

Brian, what type of aluminium alloy are you using? Something like 2024-T3 is nice to machine, the cheesy soft stuff from the usual suspects (B**nings etc) is crapola.

* Danny M *