I am slowly building my first ever engine - a Stuart 10H.
Got to the part of building up the crankshaft from (kit supplied) bar and flat stock. Followed the recipe published in the book on building the 10V. (Being a novice, this gave me a "comfort zone"). All went well until I sawed out the middle of the crankshaft, after cross pinning and silver soldering the joints. (Again - a novice at this, but all seemed to go well - using fire brick hearth and Propane torch). The crank pin and one web was not properly soldered and the joints failed as I was cleaning the crank after soldering. I suspect I had made the joints too close a fit - and the solder had not properly penetrated. (Yes, I thoroughly cleaned all the joint faces before hand and "anointed" them with flux - as per the recipe).
So I have got a new set of raw materials and will try again - my question is - how much of a sloppy fit need I allow for solder - or should I be better off using Loctite 603 (I think they say a max. "gap" of 0.1mm for Loctite)?
Can anyone offer advice/experience of Loctite as better over silver solder (it is a very small crank and will not be stressed too much)?
Thanks for reading this and apologies if it has been done before - but I really need a bit of help.
My first steam engine was a 10V. First attempt at silver soldering was on the crank, I experienced the same problems and used Loctite instead. Nice easy fit and make sure it covers the entire shaft surface before assembly. Give it a slight twist when assembling but be quick! Ran like a top! I understand that it is NOT a glue: it works by expanding in the gap in the absence of oxygen, and creating, in effect, the interference fit that was required in the first place!
Funnily enough I've been looking at this today. It depends on the type of Silver solder you are using but generally the minimum gap between parts is 0.002" (2 thou) or 0.05mm it's the maximum that varies.
Note this gap size is at brazing temp so dissimilar metals may cause issues due to unequal expansion...
Click on the links on these pages to get gap size.
Hi Klank Out of curiosity I made two crankshafts when I made my 10V, one Loctited and one silver soldered, I think in retrospect I prefer the Loctite method, it's less hassle and there is less potential for heat distortion. Ron
This experiment may be of interest you are looking at a piece of 9/32 silver steel pined in to a bit of mild steel with Loctite 438 the shaft was a sliding fit on the hole I recon on about 0.002" clear. I left it for 24 hours at ambient temp them laid on it with a 6" stilson and as you can see there was no movement.
I shall remember your tip (Staffordshire) Paul (two Pauls on one post!) - makes a lot of sense - I am still very bad at silver soldering.
I made my second crank yesterday and fitted it up with Loctite 603 equivalent (called "Delta", from Chronos) - tried to make the joints a good fit, but not too tight. Let it cure for 24 hours - all joints were rock solid - except one! One of the (unpinned) joints to the crank pin pulled out as I sawed out the middle of the shaft - too much slop this time I think.
Over all, I think I agree with Ron about Loctite - overheating could distort and the whole shebang needs a lot more cleaning up afterwards. The down side is that it takes 24 hours to cure properly (according to manufacturer).
So on to make mark 3 - and pin all 4 joints this time. Will try Loctite again.
That picture is fascinating, Paul - thanks for posting it. You gave it a fair old going over by the looks of it. Your joint is properly made - I think mine was too sloppy.
Just finished crank number three - this time success. I silver soldered it after all - having under cut the shoulders slightly and added a small bevel on each as you suggested Paul. I used very fine silver solder (wire) and cut small loops to fit around each shoulder - this time it worked fine with no need to overheat. Thanks for the help - maybe my soldering will get better now? Anyway - onwards and sideways for now - the con. rod is next, however the little-end looks a bit of a puzzle to do but here's hoping.
Well, I finished the engine at last and after making a bish of the timing at first - it ran beautifully on my compressor - ticked over like a watch at less than 10p.s.i. Reducing the throw of the crank by 0.6mm (thanks Tel) because I over-machined the cyl. length by 1.2mm doesn't seem to have hurt it at all. All painted now. Lagged the cyl. with obeche strips set in Stabilit Express (a very good epoxy resin - goo plus powder mix), sanded it all down and cleaded that with polished brass sheet in place of the Aluminium strip supplied in the kit..
Just going to make a start of the "Babcock" type boiler - for the Wenceslas engine - from Tubal Cain's book (2).
I would try to post a pic. but have not a clue how to.
Its only a 10H - nothing special compared to the many fabulous things shown on here.
Don't deride your own efforts Klank, I always feel that some modelers don't publish cos their renderings are not up to "Exhibition" standards. It's sad really cos some of the acknowledged experts work, when examined under the close up lens and displayed on the covers of the modeling mags don't stand up to close scrutiny. Old saying,- Publish and be dammed. Regards Ian
Hi, I'm new to the forum within the last week or so. I've been model engineering since 1972 but have had a long six/seven year layoff. My interest has been predominantly stationary engines and I was drawn to this thread because it happened to be topical. I have been a firm believer in Loctite for many years and used correctly in the right application it makes many tasks so much easier. It is not, most definitely not, an 'easy way out' nor a substitute for poor fits but does take away the stresses and distortion sometimes attributable to heat and the need for very tight tolerances where push or shink fits are concerned. As I read the thread I was about to start the build up of a crank for a Mc'Onie engine which is my tentative 'toe in the water' after such a long time. I took the opportunity to take a few pictures as I went along though it has taken me a while to find out how to get the pics posted - something that would not have happened without the help of Forum member 'Baggo'. Thanks John. The pics are captioned but if there are any questions please ask. I hope then that these are of use to someone, somewhere.
These are the crank webs part machined. The outer faces are finished and the inners rough milled. The 'feet' are to keep every thing square until the last minute.
Parts ready for assembly. The webs are fixed to their respective webs but left separate from the pin at this stage. The red line denotes a small flat filed on to allow escape of air
One of the benefits of using Loctite. One of the spigots was slightly undersize. Loctite does not fill gaps(!) so the spigot was turned down, and a sleeve Loctited on and re- turned to fit. With the correct Loctite - 603 or 638 this can be done within a very short time - 30 mins or so
This does not have to be done but it does give that little bit of extra strength. It was felt neccessary here because of the following turning op. The web is drilled - thru' the crankshaft spigot - thru' into the web about 2mm. A pin is then loctited in, peened over, filed and emeried as in the next image
These next two views show the final assembly.
The vee blocks are tight against a straight backstop to ensure the shafts are in line. The crankpin just rests on a parallel and the clamps are only just nipped enough to secure the shafts. It was left like this for about an hour before fitting to the bearings. It was not felt neccessary to cross drill the crank pin.
The finished item ready for the next bit. It took just over a day to make and runs very true.
No stress in the workpiece and none in the builder (well so far!!)
Hi Ramon, Just got my internet connection back and running, so a bit late in replying.
Thank you so much for the posts and excellent photos. A most useful set of pics. and info. on how to do it right. The end result looks well nigh perfect - a lovely piece of work. I have read the serialised build of this engine in ME and having seen yours I am very tempted to go for it as a next build.
Hullo Peter Thank you for your kind comments. Regarding the crank, glad to be of help. The Mc'Onie engine certainly is an attractive subject but definitely has some traps for the unwary. If you or any one else is interested perhaps a new thread might be called for on it's build. I've been working on it over he last couple of weeks and now have the cylinder finished and temporarilly installed. Good luck with your build - Ramon