Stirling Engine : Laura

.

Brian,

I'm not being funny, but; earlier you wrote that it was all 5.93 diameter.

How good are your measuring instruments ?

MichaelG.

.

P.S. ... Who supplies your Silver Steel, and do they quote a specification ?

I see Michael got in before me but I have a jotted note that claims silver steel is +0 / -0.015. I think that was from the first lot I ever bought, so it might vary.

You didn't say how you measured the diameter, so it might be your tool or technique that's out. Apologies if you're an expert or are naturally good at it but taking measurements can be harder than it seems. Here's 10 successive measurements of my 0.25" rod that demonstrate that I'm a clumsy oaf when it comes to using a calliper: 6.35, 6.35, 6.38, 6.39, 6.37, 6.33, 6.36, 6.34, 6.36, 6.32

I do better with a micrometer, but only if I'm careful to keep the anvils straight.

I measured some of my stock and got these results - note the errors!

Rod Micrometer Caliper

0.25" (6.35) 6.35 6.31 (Error 0.04)

5/16" ( 7.938) 7.94 7.93 (Error 0.01)

5mm 4.99 4.96 (Error 0.03)

You did me a big favour. I thought my stock of silver steel was all metric and it isn't! My 6mm rod is actually 0.25" and my 8mm rod is 5/16".

I've also had problems like yours after reusing a small bearing. On first insertion the axle rod was a tight fit. After a couple of re-fittings the rod and bearing became too loose. Most annoying: I replaced the bearing and now see in another of Michael's posts that there's a Loctite.

Keep up the good work. I've learned lots from your threads.

Cheers,

Dave

Michael : I probably forget to zero my digital callipers before measuring ; either way it is NOT 6.0mm. Your idea of using bearing lock is a good idea but I want to see if I can avoid using it for now. I think there are things to be learnt here.

Minitech supply my silver steel and I don't think they give a specification but I will check with them tomorrow.

I might try fitting two sets of roller bearings in each bearing support. There is enough room to do that. I have no idea why that should be any better...just a hunch !

But in case nothing else works, I will buy some bearing lock tomorrow morning

NOTE : I have just tested a new 12.9mm piston and it goes like the clappers. ID of the cylinder is14.5mm. No more testing required on this point.

Edited By Brian John on 28/06/2016 14:58:47

Edited By Brian John on 28/06/2016 14:59:46

.

Here you go, Brian **LINK**

MichaelG.

I tried the engine with four roller bearings (two per side) and it was no better. It seemed like a good idea last night but I don't know why I thought that !

I purchased some bearing retaining compound (Chemtools 8609 from Coles Air Tools) . It only took a very small amount. It says fixture in 30 minutes and full cure in 24 hours but it gripped in about 10 seconds. It was a good thing I had the correct position marked and that I did not have to adjust it afterwards ; that would not have been possible. I cleaned all the surfaces of oil using methylated spirits prior to using the bearing lock so I am confident that it should hold.

I think this has solved my problem but I will run it a few more times before I declare it a success.

Could I have used Loctite (222 or 263) thread locker for this ?

.

Glad to know that you are making good progress

I don't know the Chemtools product, so can't really comment.

Of the Loctite products; I would use 'Bearing Fit' ... because it's specifically engineered for the job.

222 or 263 would 'work' but would probably be much more difficult to dismantle if/when you need to.

MichaelG.

Here is the specifications for the 8609 retaining compound. My bottle says fix time is 30 minutes but the website says 10 minutes...I would say about 30 seconds so be careful !

http://www.chemtools.com.au/product/adhesives-threadlockers/retaining-compounds/general-purpose-2/

Edited By Brian John on 29/06/2016 08:37:18

Thanks for the link, Brian

Just skimming through the Technical Data Sheet, 8609 seems more of a general purpose retaining compound [similar characteristics to Loctite 601 and 638], whereas 'Bearing Fit' is intended for relatively easy dismantling.

On the matter of 'fix time' ... These products are anærobics and, to an extent, they will cure more rapidly in thin films than thick layers. Also [but not relevant to your shaft-to-bearing assembly] curing is accelerated in the presence of Copper.

MichaelG.

.

Edit: Here is the TDS for Loctite 641 Bearing Fit

Edited By Michael Gilligan on 29/06/2016 08:58:41

Are you using roller bearings, or ball bearings, you should be using the latter, roller bearings have a bit much friction, and if you use four instead of two, you double the friction. Ian S C

I am using these :

**LINK**

I call them roller bearings but they often get called ball bearings on ebay. I have no idea what type of bearings they actually are. They are used in roller skates and in-line skates.

Roller bearings are wider and use little cylinders instead of balls.

Neil

They are ball bearing races. Most of my bearings are salvaged from old VHS video recorders, if you get enough machines, you can get a range of sizes from 3 mm, to 6 mm bore, along with little shafts, and bits and pieces. Ian S C

.

I suppose that's logical, in itself, Brian; but I think it advisable to stick with the standard engineering terminology.

MichaelG.

Ian's being correct but ball races will do, ball bearings are just the balls. Roller bearings come in two main forms plain ones with rollers and shells that do not have an internal a taper and taper roller bearings. Then there are angular contact types which are a little like ball races but only take end thrust from one side. Magneto bearings are very similar.

John

-

The only roller bearing that I have used is the needle roller bearing that I fitted in the bell crank/yoke in my Ross Yoke ALPHA motor because I thought that it needed the extra width for sability, and the low profile was also helpful. The other two bearings at the end of the con rods are 4 mm bearings from a video machine. Ian S C

All is going well and the bearing lock seems to be holding up. I have experimented with different D piston diameters and found that 12.7mm was very good. As luck would have it, that stainless steel D piston I made up some weeks ago is exacly that diameter so I decided to give it a go. It ran very slowly at about half the speed of the aluminium piston ; I think it is too heavy.

I noticed that the thread is badly rusted out. It has only been sitting in a cardboard box and I have never seen silver steel rust so quickly. Is this something to do with silver steel being in contact with brass which is in contact with stainless steel ?

Edited By Brian John on 30/06/2016 12:11:29

Edited By Brian John on 30/06/2016 12:12:37

Silver Steel/high carbon steel in a place like Cairns with it's high humidity, will if left un protected with oil rust quite quickly, a wipe with an oily rag before it rusts is the way to keep things shiney. Yes the displacer should be as light as possible, The relative weight of displacers decreases as they get bigger.

I had enough bits and pieces left over to build a third Stirling engine but using a brass flywheel from PM Research rather than the supplied cast iron flywheel that comes with the kit. This engine has been running well for over three weeks now but this afternoon I decided to remove the flywheel to give it a proper polish with 1500 and 2000 grit. When I initially machined this flywheel I did not give it a final polish with the wet and dry.

In the back of my mind was the thought : ''Leave it alone...it is running nicely now'' ....but no, I ignored the warning and went ahead and polished the flywheel. Upon reassembly I found an unexpected problem. The whole axle/flywheel assembly keeps pulling to the right and this pulls the work piston crank (on the LH side of the engine) in contact with the LH bearing support hence stopping the engine. I have spent all afternoon making adjustments to try and fix this but nothing has worked. I am now out of ideas.

Any suggestions ?

Edited By Brian John on 27/08/2016 10:08:04

A tiny little spacer washer in there so that when the crank moves over it contacts the washer which tranfers the load to the inner race of the bearing which rotates?

Okay, that should do it. I will have a go at making a small spacer washer tomorrow.

I do wonder why it is giving problems now whereas before it was flawless in its performance ? This is why I am going back to steam engines : I will leave the flame eaters and Stirling engines to more patient people

Edited By Brian John on 27/08/2016 12:16:53