Here is a list of all the postings Phil H1 has made in our forums. Click on a thread name to jump to the thread.
|Thread: Rob Roy Build/ Rally|
I need to beg forgiveness from the late Martin Evans. I hadn't read the section on coupling rod clearance properly.
He says the driving bush should be a good fit to give smooth running but the leading and trailing bushes should be opened out with a letter F drill. Letter F is 0.257".
|Thread: Rob Roy advice needed|
I was going to machine mine from solid but I thought I would give the laser cut versions a try. They arrived and consist of 4 flat profiles with 2 additional rounded ends for each rod (a rounded end is silver soldered either side of the flat profile of each rod). A photo will probably help I suspect.
I plan to silver solder all the additional ends to the flat profiles, bend the reverse rods as carefully as possible then set all 4 onto the same fixture to machine the expansion link slot with a slitting saw.
|Thread: Rob Roy Build/ Rally|
Yes - a good plan. It wont freely roll without coupling rods yet i.e., the wheel bearings are slightly tight. It will roll freely if I put weight onto it though. The coupling rods without bearings are tight but tight all the way round the rotation.
I think I was lucky with the wheel centres which probably helps. With the wheels and axleboxes fitted, I measured across the axles with a big micrometer (M&W - lovely thing), there was no difference from one side to the other - not even a fraction of 0.001"
I like the house brick idea.
I've got about 0.005" extra length on the intermediate pin/ nut. but the tongue and slot is quite snug. I was going to allow about 0.005" on the coupling rods but I will now go for 0.010" as you suggest and about 0.010" extra at the back of the coupling rod to prevent rubbing the rods to the wheel hub. I might also double check the wheel hub run-out again to make sure.
Mr Evans did mention a snug fit on the driver crankpin and mentions the need for movement on the leading and trailing pins but doesn't suggest an actual clearance.
I did a few geometry sums and as you say, they must need at least 0.003" before metal to metal contact is made between the pins and bearings and that assumes that the quartering is perfect - so I think you might well be right at 0.005".
I will wait a while before cutting metal just in case somebody comes with a 'yeah but'.
Believe it or not I have just taken delivery of some laser cut parts that include the David Machin, stainless steel ashpan. I haven't studied the ashpan but do you have any idea how it is an improvement. Does it get the fire working better or prevent the spread of ash - or maybe both?
Some might suggest that laser parts are cheating. Everything so far is traditional build but if I carried on using the traditional methods, I reckon I would be complete by about the year 2100.
Baz, thanks - nice tip regarding the slightly long bush - I will do that.
What about the other end - the nut end. How much clearance between the round nut and the coupling rod. The wheels can 'float' side to side. Do the coupling rods need to float also and if so about how much?
Thanks for the tips. I have found some online information from Don Ashton. I will definitely study it before diving into the valve gear.
Next issue....As you can see, I am ready to make the bearings and intermediate coupling rod pin. The intermediate pin is turned from rod with a 45 degree (90 degree included angle) head to fit a countersink in the back of the rear section of the coupling rod. I will add a short section of 4BA thread at the front of the pin for a brass washer and 4BA nut. I am assuming that I need to machine the pin so that the washer and nut tighten up to a shoulder on the pin rather than 'pinching' the coupling rod. The same will happen on the trailing crankpin and driving pins. Is that the right approach and if it is - how much clearance - a couple of thou or should it be more?
Also, I was planning to fit plain hexagon nuts. Would round nuts with flats be closer to the real thing? I don't have any 2BA and 4BA nuts anyway, so turning a few round ones would not be an issue.
How long is the model? I have articles for a plant capable of driving a 4 foot long model and the engine for a 6 foot version is still available from Reeves.
|Thread: Rob Roy Rally - Cancelled|
Thanks. I will keep plodding along (slowly) during the autumn and winter and see where I get to by next year.
The rescheduled Rob Roy rally was supposed to be today (I believe) so I thought I would show where I am up to. Unfortunately, not much progress but I have managed to get a few of the tricky parts out of the way i.e., machining the steel parts for the coupling and connecting rods.
I just need to add the bearings and I am going to fit brass oil cups to all the 'ears' on the top of the coupling rods but the good news is that the wheels still rotate with the coupling rods fitted. The rotation is tight but smooth.
|Thread: Flycutting on the speed 10|
Also, my current draw bar for my Myford Super 7 consists of a simple length of M10 screwed rod. As you suggest yourself, that can be fed through from the headstock end with the washers and nuts fitted at the changewheel end.
Another option.... for my Myford ML10 (when I had it), I drilled a hole in the end of the drive peg used on a standard drive plate, fitted a grub screw through the side and inserted a short length of round HSS for the tool bit. It worked really well for all sorts of jobs like cylinders and aluminium blocks etc.
|Thread: Copper boiler plate flanging, or not?|
I think Jason answered it earlier. He said that the external butt strap would interfere with the design of that particular traction engine.
Edited By Phil H1 on 22/08/2020 15:22:33
It is possible that I have misunderstood but I was under the impression that this kind of 'swaged' extension joint for the firebox sides is acceptable. Is this now frowned upon? Forgive the rough sketch - I hope it makes sense. I would agree that without lagging and cladding - it isn't pretty.
Can I ask a question about Minnie please? It has a remarkably small boiler (page 3) - hence the name I guess but what can it realistically do? e.g., on a really nice flat surface, can it pull the driver or do you run it like the little Mamod traction engines using a long control rod?
|Thread: Silver steel axles|
I am in your position i.e., not finished a build yet (I'm building Rob Roy at 31/2" gauge). I am beginning to ignore calls for gauge plate for this and silver steel for that. Maybe you and others will take a different view but I will honestly take great pleasure in renewing axleboxes and various pins because it will mean that I actually finished the bloody thing and had it running.
Loads of engines before yours have run for a long time with BMS axles and plain gunmetal axleboxes or even BMS and cast iron.
I bought some EN8 (Im sure it was) from Kennions for my Rob Roy axles and it appears to be nice round material and tougher than my ordinary BMS to machine.
Designers get carried away sometimes.
|Thread: Silver soldering a Minnie traction engine boiler|
I think we are also in danger of wandering off trail a bit aren't we. The point is Mark is doing a great job so far - looks nice.
All you have done is agree with what I have written.
In Bobs defence for a moment.... I have seen about 3 or 4 model locomotive boiler designs e.g., Rob Roy, Simplex, Betty and Jubilee all by Martin Evans or LBSC. Every single one of them have newer recommendations and or required modifications. So to simply say that you need to follow a published design is complete nonsense.
What I think is meant - surely - is that you should start with a published design, speak to your inspector and incorporate a few of the more up to date modifications/ recommended changes and you then stand a chance of success.
|Thread: Rob Roy Rally - Cancelled|
Thanks for that. It has made me feel slightly better. I started mine in 1977 (when I was 16) but any parts that I made then have been scrapped. I restarted and took the build seriously late last year. However, there are about 10 chapters in the book and I am now coming to the end of chapter 2. So is that about 20%ish done?
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.