A Beginner's First Engine (Single-acting Oscillator)

[Kim]

Sorry about the mishap.  It's all a part of learning though, isn't it?  And that's what makes this hobby fun!

Kim

You can rebuild it...  make it better than it was before... faster... stronger... 
(that's my reference to the Six Million Dollar Man )

[gary.a.ayres]

Sorry about the mishap.  It's all a part of learning though, isn't it?  And that's what makes this hobby fun!

Kim

You can rebuild it...  make it better than it was before... faster... stronger... 
(that's my reference to the Six Million Dollar Man )

Gentlemen. I shall rebuild it.   

Agreed Kim - that's the way to look at it. A learning experience, and it wouldn't be fun if it was all easy.

@ Chris - sorry, I'm not sure what you mean. Any chance you could say a bit more?

@ Peter - I never gave the look of the spring much thought - just went out to local shops and bought a few different springs, tried them, and that one seemed to be the best one. Will keep my eyes open for one that looks better though.

@ Bill - yes indeed. I'm happy enough as the engine should be the better for it.

Thanks for all your feeedback guys 

[MJM460]

Hi Gary,

Most unfortunate that, but the breakage shows the weakest point.  And perhaps you will be able to work out how to make it stronger another time by looking carefully at the break line.  Looking at the photo, I think the epoxy does not appear to have taken over the whole available contact area, I wonder if there was a little oil left from when it was running.  But soldering is probably better in the long run than epoxy, however good the epoxy.  And making that section thicker on future engine will make anchoring that pin a little easier.  I  have found it the trickiest bit of each of the oscillating engines I have made.

Just another hurdle, I am sure you will overcome it.

MJM460

[gary.a.ayres]

Hi MJM -

I only epoxied it because I accidentally stripped the thread in the hole in the cylinder that the pin was to be screwed into. In this engine the design issue is that because of the flat milled on the port side of the cylinder there is not much thickness so the hole is of necessity very shallow. I think that Steve, the designer, made it that way to keep the making of the cylinder as simple as possible for beginners. I'm going to rectify that by soldering a brass plate on to allow a deeper hole, redrill the port and the pivot pin hole and tap the latter for a composite pivot of the kind proposed by Ramon on page two of this thread. I reckon that will give me a better engine than it would have been if I hadn't stripped that thread in the first place   

Cheers 

[gary.a.ayres]

 Given what's occurred it may be worth your time to take a quick run through before setting out again ? Anyway it's here if you think so https://www.modelboatmayhem.co.uk/forum/index.php/topic,53472.0.html

Regards - Tug

Very interesting and informative thread that, Ramon.

 

[Ramon Wilson]

Hi Gary

Glad that was worth a look - at least it may give you an idea or too but bear in mind there's always more than one way to skin a cat 

Tug

[gary.a.ayres]

Yes indeed!

 

[gary.a.ayres]

I'm still waiting for the arrival of the flat brass bar from which I'm going to make the plate to attach to the cylinder barrel, so I went out today and picked up some bits and pieces for soft soldering. Tinning the components then joining them was suggested to me as an appropriate way to proceed, so tonight I had a practice on some bits of scrap brass:



Not much of a photo, I know, but it was that kind of a session...

The tinning and joining procedure was trickier than I expected but I began to get the hang of it with the help of a combination of advice and reading. Wiping the tinned surfaces with a damp sponge while the solder was still liquid worked well, leaving a uniform and very thin layer of solder on the surfaces. The parts then went back in the pickle for half an hour before joining. I tried a couple of different ways of positioning the work for heating, settling finally on a G clamp (holding the parts together, but not too tightly, with the faces for soldering held level), and the clamp in turn held in the vice. Initially they didn't seem to want to solder together, which I think was the result of not enough heat. I overcame that by working in the dark so I could see what was going on, using the Sievert torch to bring the parts to a dull red glow before quenching them in the pickle.

Now, at the end of the evening, I feel *fairly* confident that I'll be able to join the plate to the cylinder by tinning, and hopefully the brass flat bar will arrive tomorrow.

Flippin' heck, I didn't know how much time and work that stripped thread in the pivot hole was going to cause! All good experience though...

I'd welcome any comments you may have about the way I approached this. If I'm doing anything silly I'd rather know about it before I ruin the cylinder!

[crueby]

Good experiment! You don't need to quench it, just letting it cool works too. On thinparts quenching could distort it slightly.

[gary.a.ayres]

Ah, ok Chris. Thanks for that.

I decided to quench the parts to try to thermally shock the flux residue etc off them.

Will heed your advice when it comes to the real thing. Don't want any distortion, especially as it's the cylinder...

[gary.a.ayres]

Antidote to photo three posts above   

[10KPete]

Something everyone needs to know about soft soldering brass/bronze is that a strong acid flux must be used for the first wetting of the brass. Unless that 'layer' is removed, follow on soldering is done with mild (rosin) fluxes to reduce coloring and ease clean-up.

I've had 'opportunities' to test that requirement over the years and will say that while one may get away without acid once in a while, defective joints will result way more often. It's not worth the pain of a re-do for me to 'risk' it.

My two coins.

 

Pete

[Jasonb]

Your G-clamp will be sucking all the heat away from the parts, if you do need to hold them in place then a thin third hand that has minimal contact is the way to go.

As soft solder flux stays soft you don't need to "shock" it off that is a method that can be used for silver solder flux which sets glass hard, should also not really need to pickle as there will be minimal discolouration (when you can heat properly) and the flux will just was off with warm soapy water and an old toothbrush. Then quick rub with a grey Scotchbrite pad.

[gary.a.ayres]

Thanks guys. Noted.

@ Pete - will check the flux I bought yesterday and buy some strong acid today if it doesn't fit the bill.

@ Jason - I bought some soft iron wire yesterday. Might try that.

[Ramon Wilson]

Hi Gary,

I've not heard what Pete suggests regarding an acid based flux but don't dispute his advice. I have used bakers fluid before which is acid based but usually use Fluxite and smear the faces to be tinned liberally with it before heating. The faces should be nice and clean preferably straight from a rub across some wet and dry paper (400-600 grit). Heat until the solder flows then wipe off across the face with a piece of folded kitchen roll paper with a smear of flux on it. Coat the faces with flux again before bringing them together for soldering

Jason is right about the clamp taking the heat away - there is also absolutely no need to get the parts to a dull red as you describe to make the joint - just heat until you see the solder flow.

I use a bent piece of piano wire to act as a clamp which keeps the heat sink effect to a minimum - might be worth a try?  Something like this.


Faces should be as flat as possible after tinning so if you have any small raised areas of solder either reheat and wipe off again or take off with a few strokes of a file. Reason for that is, that if the faces are not in flat contact as the solder melts, the piano wire clamp can induce an out of line movement as the faces close together. It might be a good idea in your case to have a small locating pin in a couple of places to prevent that.

I usually use a solvent such as acetone or cellulose thinner to clean the flux residue away.

Hope this helps some too - Tug