Yet more hot air

Quote from: Sanjay FLooking very tidy

Came out better than expected, which makes a nice change and is a sure sign something else is about to go wrong 

And so it proved. I made the square cylinder flange from a piece of 1" angle as I didn't have any flat bar and bored out the centre for the cylinder itself. The cylinder was supposed to be made from 1/2" round brass but I had two tries at turning down a length and both were too loose a fit so I went off to do something else for a bit. When I came back I decided it would make more sense to use 5/8" bar anyway and turn up to a shoulder and this time the fit was just right for soldering. I turned down some of the outside to about 14mm then drilled the holes for the screws and threaded the matching holes in the steel part. Next will be soldering the cylinder/flange, maybe taking a skim off the bottom then doing a bit of lapping.

As the piston will only be 8mm diameter and I don't have the gear for making very small parts, I think I'll stick to the original idea of a slotted piston with threaded wrist pin this time. The difference in weight between that and one with an internal assembly to connect the rod would be tiny. I'm just mulling over whether to use cast iron, brass or even aluminium for the piston...

Quote from: PaulR I'm just mulling over whether to use cast iron, brass or even aluminium for the piston...

Is one of those materials better suited for stirling engines in terms of thermal properties?

Quote from: Sanjay F

Quote from: PaulR I'm just mulling over whether to use cast iron, brass or even aluminium for the piston...

Is one of those materials better suited for stirling engines in terms of thermal properties?

I don't think it'll matter in that respect and there wouldn't be any galling from brass on brass. I might give ali a blast for a change, it's a pretty simple part so I could always replace it.

I spent some time smoothing the cylinder bore yesterday, it looks and feels pretty smooth but there are still a couple of tool marks just visible. However, I think it'll be good enough.

I decided to make the piston with a screwed-in fork to hold a captive pin after all. It will be 'a pretty simple part' I said... I had three attempts at making it yesterday and they were either a poor fit, the wrong length or the hole was off centre(!)  It's all the more annoying because I don't have any round bar of the right size so have to turn down some rectangular section stuff.

Anyway,  I thought I'd have one last go at it today, if that didn't work I'd go for a simpler design. I turned it down to about 0.5mm over size then drilled and threaded the centre hole, then plunged a slot cutter in to create a flat bottomed hole then finally turned down the OD about 0.0005 at a time until the fit was just right. Finally sawed if off (didn't want to risk parting!) then held it in some aluminium shim to face off the bottom end to length. I'm pretty happy with the final result, here's a blurry photo 

The fork will be a 4mm dia rod with a slot in the end, screwed and Loctite'd into place.

Looking very tidy, 0.0005" at a time, now that's patience! 

Quote from: Sanjay FLooking very tidy, 0.0005" at a time, now that's patience! 

Cheers, yep but I didn't want to have to make it yet again  Just spent half an hour making the central bit and that didn't work out either so that's it for today!

Tried again to make the screw-in fork for the piston and yet again it didn't come out right. I'm trying to mill a slot in the end of a 4mm round bar in the vertical slide but just can't seem to get it centred properly. In the end I decided to revert to the same style as the last engine so I plugged the end of the piston and cross-drilled a 2mm hole for the wrist pin (think the one on the photo is a bit too long?  ), the ends of which I'll round over to reduce the risk of scoring the cylinder.

Yesterday's session was spent making the steel bearing block (turning it to size as it didn't conform to stock sizes in any dimension  ) then the two 'top hat' bearings from brass. There's a gap between these in the middle of the block so oil can be fed onto the shaft from the hole above while keeping friction due to the bearings to a minimum. I also sawed off a chunk of 2" steel ready to make the flywheel.

This morning I turned the flywheel to size and made the shaft which will be Loctite'd into it, timing adjustment being made on the displacer side. Also threaded a hole for the pin as the power piston will be attached to the flywheel directly which cuts out weight of a crank/disk and more opportunities for friction to arise.

Still experimenting with the previous engine while making this one, I tried it with some GT85 spray clean/lube instead of oil and it was noticeably better - probably because I was using cutting oil before ( ) since someone appears to have stolen my can of 3-in-1 light engine oil. Also found that if I loosened off the crank pin on the con rod it was better still and runs along at a fair lick. I've yet to try the tip from Julian on the Stirling engine stand at the show: use a little meths to lightly lubricate or at least form a seal on the displacer rod.

Anyway, here's the progress, sorry it's not terribly exciting 

Today's session, making a little (5x6x14mm) crank, led to this even less exciting photograph. 

Sawing and filing the baseplate was the order of the day followed by drilling/tapping to fit the bearing block. It seems to spin ok without any lubrication and the alignment looks about right.

https://youtu.be/E66BOKX_tEs

Hi Paul,

it looks like it moves very smoothly 👍.

Michael

Cheers Michael.

Today I drilled and tapped to fit the frame to the baseplate, made the displacer rod fork (still one final bit to do), rounded over the end of the crank because why not and started recycling more garden furniture for the simple connecting rods. Here's my entry for this month's most boring photo, one of the rods being filed to width with another piece of the square grey furniture tube behind - don't click the thumbnail, it's not worth it honestly

Yesterday I completed the simple connecting rods and the crank pins and fixed the flywheel to the shaft. This morning I had to shorten a bunch of cap screws when I found that there wasn't enough clearance to tighten the hex headed ones  I just need to make a couple of brass spacers then I can think about running it in although it'll also need a wooden base and the cooling fins will need fixing.