Pitch Circle

Hello Howard

Measure twice cut once is quite amusing because I was once a cabinet maker and that was always said and used and is a good rule to follow, Firstly though many thanks to all of you who took valuable time to help someone who made mistakes by rushing in, other than the measure of 7/32 pitch circle which in hindsight I knew was wrong but did not think to challenge the mistake, I did look online first for the answer but google does hit you with so many results that you end up more confused and to be honest I did not want to ask these forums for help as compared to what a lot of you guys build this is quite small and insignificant and I thought I may not get a reply. One thing that I can take from all of this is that I watched a you tube loco build where the maker photocopied parts of drawings and took them to the workshop to make individual parts, this he said meant he stayed more focused, I thought great idea, approach the project in small pieces. All of the errors in my build only came to light yesterday once I looked at the full drawing as it was clear other than the misprint I was just building parts without any thought of how they go together, so now I use the full drawings until experience takes over. I very much like the idea of cad, I have Fusion 360 and sketchup but as always a lack of help to get going.

I have a Virginia 440,Maisie,B2 and Rob Roy all purchased as part builds which I now realise is another bad choice on my part as I have not been involved in the construction so far and that part of the learning process has already gone, I want to start the continuation of the Virginia so I would like to ask for help again as this forum has been much better than anywhere else, so has anyone built this Loco?

Hi Roy!

We all learn something, often every day.

Mistakes are not unusual (We are all human and fallible ) the gag is to spot and correct them before too much is lost.

Don't be like me and rush! things

You will always find help and advice on the Forum.

VAST amounts of experience of Engineers and Model Makers on here, no matter what the specialisation.

You will find it helpful. also to find and join a local Model Engineering Club, for face to face help / mentoring / demonstration.

Keep up the good work

Howard

Roy, probably better to start a new thread with Virginia in the title as that will get the attention of the Loco boys who may have passed this thread by after an initial look.

Roy,

A lot of us do not have a machining background, me included.

Finishing the Rob Roy might make more sense, it's much simpler than Virginia, but still a proper engine + far more people have built one.

Hello Howard

Actually going to a local club was where it all started, I knew the director at Myford and he had a part built Maisie just arrived that he let me have, I was his Tailor, I went along to the local club, I live near Cambridge and 1 person bought in for me to photo his build of Maisie, but that was it, no one else was interested in really talking to me as it seemed a boys club just for a select few boys, I did go to the Saffron Walden club at Audley End and they were great but they now seemed to have vanished. So after the visit I just shelved the projects much to my regret and sadness. It is during this lockdown and no business to open and run in London that I kept looking at my Myford Tri-Leva and Boxford VSL500 that I thought I have to build something as I have a well equipped workshop just idle and lets be honest some of you guys build the exceptional from very little.

Hello Dave

One thing is clear though, everyone on here has a lot more common sense than me, I did start with the Rob Roy before getting Maisie but the then editor of Model Engineer who was Mike Crisp I believe told me I should start with an engine I liked as I had far more chance of finishing that loco, so I had two in mind, Virginia and Gresley A4, as you can see from these choices I aimed low using my bounds of common sense until a visit to the model engineers exhibition had 1 stand laughing at the thought of a first timer with no complete loco on his list building an A4.

I think it might have been a couple of weeks ago someone on here had written a prog/code to calculate PCD's using XY co-ordinates. I seemed to remember that the co-ordinates could be calculated from a point outside of the circle and that is what interests me in a jig boring sort of way. I have looked back at previous posts but cannot seem to find this one.

Apologies to the chap who was responsible but I cannot remember his name. If you can prod me in the right direction I would be grateful.

Rik

Hi Roy,

I envy the folk who have the skill and patience to produce working and highly detailed models.

My stuff just gets made from whatever is lying around! Which explains changes of course, mid voyage!

You are not too far away from me, in Peterborough. (Waiting for Club meetings to resume and see friends again )

Have never visited, but have met a couple of members of the Cambridge Club. Sounds a good place to join./ visit.

With a lathe, ALL manner of things are possible.

Howard.

A very useful addition to any workshop would be a Zeus book of engineering formula. There is a page showing how to produce pcd's using X and Y coordinates on mills and jig borers if you don't have the luxury of a rotary table.

I actually have both but it was not until this morning that I realised the zeus book had this in, that said due to the help from others here I wont face the problem again hopefully.

This is a common problem with clubs because most ordinary folk are nervous of newcomers. They are more afraid of you than you are of them. Stranger danger! It's well known that the only two Englishmen within 5000 miles who find themselves sat next together for a week in a train crossing the Gobi Desert won't speak unless they've been introduced.

Some clubs arrange a special greeter to make sure newbies aren't put off by their initial cool reception, most I've attended leave folk to get on with it.

The secret is to persist. Quietly find out what each member is into, who is approachable, and who the gits are. Mutual acceptance grows each time you turn up. Smile and nod a lot, and ask appreciative questions. Amazing, how did you do that?

After 3 or 4 visits, you will be Chairman...

Dave

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I dropped in on the Cambridge club two years ago as I happened to be in the city on a Sunday and found them extremely friendly. After tea and biccies I got a ride round the track on a loco that happened to be needing a test run, then a guided tour of works in progress. Seems likea great club if you can afford to live in the county.
A lot of men seem like grumpy sods so at a club those ones are the ones not deep in conversation with others, So the newcomer seems to be drawn to them with inevitable bad results. Don't expect club members to recognise that you are on your first visit and welcome you appropriately. I can't remember half the members of either of the clubs for which I'm membership sec. Twenty years ago I could greet them all by name, but now the names sort of come to me a couple of hours later. When you arrive just say "I'm new here" so they know and can go into welcoming mode.

Rob Roy - the build was probably stopped when it was found the valve rods didn't line up. Common fault in the design - search the forum for mentions of this and other problems.

Miranda engine - are you going to build the boat? It is an interesting display engine but looks crap in the launch as it is too big by far and forget the boiler. There is however a great wheeze published on Paddleducks forum. If you turn it upside down by exchanging the base and top plates it makes a very nice paddle boat engine.

I am in no way trying to run Cambridge MES down, there were some seriously clever people there, I also got to do a couple of laps on a 7 1/4 gauge loco, in many respects I looked at what they were doing and the Locos that had been built and felt completely out of my depth, I should now really go back and make a better effort, to be fair though I have learnt more in two days on this forum from a simple post than I have in 20 years.

Rob Roy was discontinued due to some errors but the thing I am learning here is that a lot of drawings have errors and with a bit of experience you learn to spot them. One thing I did as a cabinet maker when presented with drawings was to take the finished size and then subtract all of the components to hopefully end up at zero, any differences were spotted long before the mistake was made, if I had used the same thinking here I would have seen that some things just did not work, I knew 7/32 pitch circle was wrong but I did not know how, so I assumed that measure was taken from somewhere else, I just followed the error with out questioning it.

With regard to using the Zeus data book, I took a look at it last night and I realised that it did not have a 4 hole patten and I did not know if you could use some math to change a 8 hole patten. In any case the reference asks you for the pitch circle which I was still believing it was 7/32 so I would probably of still ended up here, this experience on here has now made me feel that I can just get on and if I get stuck just ask, I have also decided to stop reinventing the wheel and just use the full set of drawings where I can see the whole layout rather than A4 sheets of components.

Bazyle many thanks for the link to Paddleducks, that looks interesting and I might give it a go.

For a 4 hole pattern where the holes are at 45deg to each axis like your drawing a simple method is to multipy half the PCD x 0.707

So 0.5 x 27/32 x 0.707 = 0.298" so you can mark off that dimension in both directions ( also shown bottom left of the sketch I posted)

If the holes are at right angles then they are simply placed on the radiu eg half of teh PCD so 0.5 x 27/32 = 27/64" or 0.422"

Many Thanks, So simple when you know how.

Those handy coordinates have been omitted from my last-bought Zeus and I can't find the old ones!

I'm surprised that the jig boring coordinates are missing from a Zeus book as the metric revision has been out for a number of years. I have recently bought some copys marked issue 11/19 and the hole spacing page is about 3 pages after the UNF threads.

PM sent to the OP.

Andrew

Many thanks for that. I have just checked and the coordinates are indeed there on one of the middle pages.

I think I must have had in mind the omission of the "BA std threads" data from later editions; the BA tapping drill sizes are still present in the 1995 metric revision and the newcomers are, of course, the NC pages and the drawing symbols and abbreviations.