Ultrascale crankpins

[Chris Mitton]

Am I missing something here?

I've finally plucked up courage to build the chassis of my Mogul 76079 – Comet frames and valve gear, CSBs, Ultrascale wheels. The crankpins (basically 14 BA screws) are cheeseheaded, not countersunk, so stick out from the back of the wheel – by rather more than the thickness of the rear boss. This means that each wheel needs at least one washer to avoid the screw clouting the frame. Given that the frames (more precisely the outer faces of the axleboxes) are already as near as dammit 16.0 mm wide, that leaves precious little room for any sideplay on any axle – which I don't want anyway on the leading coupled axle so it doesn't argue with the crossheads, but I do want it on the other two so it stands a chance of negotiating corners!

Looking at the diagrams on Ultrascale's website suggests they're meant to be like that, which strikes me as problematic – and I can't believe I've got things hugely wrong, Ultrascales are common enough and the frames and spacers are exactly as specified for P4 in the instructions. The obvious answer is to drill a recess in the back of the wheel to accommodate the screw-head, but that will reduce the length of thread engaged with the wheel hub and so increase the risk of it going off-square. Before I start hacking away at sixty quid's worth of wheels, what do any other Ultrascale users do about this? [The other engine I'm currently working on, a Gibson E4, doesn't have this problem as the crankpins are coutersunk.]

Chris

[Mike Garwood]

Use a Rosebud burr to introduce a recess into the back of the crank pin hole, a couple of turns should do it. Screw the crank pin in, check that the crack pin is either flush or nearly flush with the back of the wheel. Then fix in place with either 501 or fill with Milliput any gaps. Wait for it all to go off and then file back anything thats sticking out proud. This has worked for me.

Mike

[grovenor-2685]

Or just replace the screw with a countersunk version.
Keith

[Alan Turner]

Or throw them away and use the Exactoscale versions. Much better job in my opinion.

regards

Alan

[Russ Elliott]

It is possible that the cheeseheads used by Ultrascale have deeper heads than of days of yore. A judicious bit of countersinking sounds in order. (Or use some countersunk screws, as suggested by Keith, but that is a little expensive!)

[Tim V]

Thin down the head of the screw!

[Horsetan]

It is possible that the cheeseheads used by Ultrascale have deeper heads than of days of yore. A judicious bit of countersinking sounds in order. (Or use some countersunk screws, as suggested by Keith, but that is a little expensive!)

..and throwing them away in favour of Exactoscale is even more expensive!

[David Thorpe]

Has anyone actually pointed out this problem to Ultrascale? As this would appear to be a minor design fault the easiest solution, at least for future users, would be for Ultrascale to provide a different design of crankpin screw.

DT

[Russ Elliott]

As this would appear to be a minor design fault the easiest solution, at least for future users, would be for Ultrascale to provide a different design of crankpin screw.

Commissioning the tooling and doing a batch of special 14BA cheeseheads will start at £5k. Ultrascale accept sponsorship cheques.

[Horsetan]

As this would appear to be a minor design fault the easiest solution, at least for future users, would be for Ultrascale to provide a different design of crankpin screw.

Commissioning the tooling and doing a batch of special 14BA cheeseheads will start at £5k. Ultrascale accept sponsorship cheques.

It does make you wonder why they didn't think of going countersunk all those years ago.....

[David Thorpe]

As this would appear to be a minor design fault the easiest solution, at least for future users, would be for Ultrascale to provide a different design of crankpin screw.

Commissioning the tooling and doing a batch of special 14BA cheeseheads will start at £5k. Ultrascale accept sponsorship cheques.

I've never used Ultrascales, and have no intention of doing so, so am not aware of the system. However, I note that Keith suggested that the OP could merely discard the cheesehead screw and replace it with a countersunk version. That doesn't seem to require £5k's worth of tooling. Someone also suggested Exactoscale screws as a suitable alternative, and as far as I'm aware they are merely M1 countersunk screws.

If there is a problem, and Ultrascale know about it, they should be doing something to remedy it. It's not as though they are at the cheap end of the market.....

DT

[Alan Turner]

[quote="DaveyTee Someone also suggested Exactoscale screws as a suitable alternative, and as far as I'm aware they are merely M1 countersunk screws.

DT[/quote]

It was the threaded crankpin bush that I was really refering to. Yes they do use M1 screws.

Alan

[Chris Mitton]

Thanks gents for your replies - evidently it's not just me!

Changing to countersunk screws isn't the ideal solution - I'll still have to do some surgery on the wheel boss to provide a countersink recess, so I might just as well drill out a recess for the screws provided - it doesn't need to be too much, sinking to a depth of about .2 mm ( i.e. a couple of turns by hand in a pin vice) should be enough to get the head sticking out less than the boss. Or maybe a bit less and adopt Tim's suggestion of filing down the screw heads (but not enough to remove the slot!)

But I had thought (possibly mistakenly!) that having purchased a product with a Rolls-Royce reputation - and price to match - that it would be "ready for the road". I don't see a need for the company to change the pin design though - I know nothing about production engineering, but I would have thought that a shallow recess at the back of the crankpin hole in the wheel boss wouldn't be difficult, being as it's a plastic moulding. Is anyone from Ultrascale on this forum?

Regards
Chris

[Philip Hall]

Tim's suggestion is the obvious one, but another thought that occurs to me is 'why make the frames so wide apart?' A slightly narrower frame will give you all the sideplay you want and the ability to traverse far tighter bends than you could ever need. There will still be bags of room for the gearbox and motor.

Now I realise I might get shot down for yet again suggesting slight heresy and divergence from The One True Path, but the plain fact is that we want our models to work, and to do that we have to recognise that some compromise is necessary. If you enjoy making life a bit awkward by trying to stick as closely to prototype dimensions as possible (as is sometimes practised in ScaleSeven) that's fine of course. But I have always taken a more pragmatic viewpoint. I often don't know, very well or at all, the layouts on which my engines have to work, so I tend to err on the side of caution. And having just passed A Significant Birthday I realise that time is not as plentiful as it once was and I want to get results more quickly than I perhaps used to.

Philip

[Tim V]

I personally always cut the boss off, and use countersunk screws, into a countersunk back of the wheel. Frames 14.8mm apart using the EM society frame assembly jigs. I'm building for 3' radius curves.

Ultrascales are good wheels, but at the price we modellers are prepared to pay for them, you have to do some work with them.

[Chris Mitton]

another thought that occurs to me is 'why make the frames so wide apart?'
Philip

...because lacking your engineering background and long experience of model-making, I'd built the bloody thing before realising the problems! ...cheerfully thinking something labelled "P4 spacer" would produce frames the "correct" (whatever that means) distance apart. [Actually they're still a scale inch-and-a-half narrower than the full-size version, but I take your point.]

Now I realise I might get shot down for yet again suggesting slight heresy and divergence from The One True Path, but the plain fact is that we want our models to work, and to do that we have to recognise that some compromise is necessary. If you enjoy making life a bit awkward by trying to stick as closely to prototype dimensions as possible (as is sometimes practised in ScaleSeven) that's fine of course. But I have always taken a more pragmatic viewpoint. I often don't know, very well or at all, the layouts on which my engines have to work, so I tend to err on the side of caution. And having just passed A Significant Birthday I realise that time is not as plentiful as it once was and I want to get results more quickly than I perhaps used to.
Philip

Having also passed several Significant Birthdays, and endured a warning from the Grim Reaper (a week in cardiac and a life sentence of pills!), I couldn't agree more! I don't seek perfection because I'm nowhere near capable of it, and I tend to model extremely slowly (whoever said retirement brings time?) - but slightly less slowly than I'd manage without the help and advice on this excellent forum.

Regards
Chris

[Philip Hall]

Thanks for the compliment, Chris, but my Dad was the one who had an engineering background and I suppose I got some of it from him. I went into a bank! But that's another story.

You're quite right to assume that a spacer marked P4 will be OK for the purpose. Unfortunately, as with so many things in this fine hobby, there's a lot of choice and philosophies to go with it, and somehow you have to pick your way through. Which you seem to have done, anyway, and you've learnt a bit in the process. Your 2-6-0 isn't a particularly critical engine as regards curves, anyway, and a little sideplay at the rear and a touch more in the centre should see you through. I would thin down the head of the crankpin screw, though, rather than take it out and countersink the wheel. Once assembled, I like to leave such things alone.

Please let us see a picture of your finished engine sometime.

Philip

[Chris Mitton]

I would thin down the head of the crankpin screw, though, rather than take it out and countersink the wheel. Once assembled, I like to leave such things alone.
Philip

Wise words. I started by following other advice in this thread and removed one crankpin (not straightforward with the wheels on the axles), and made a small countersink. Bad Idea. It seems that if you remove a hard brass screw from a threaded hole in hard brass then put it back, it will find its way in. If you take a hard brass screw out of (relatively) soft plastic and put it back, it will simply cut a new thread and shred the original one - do it again and you'll have a nice clearance hole! Fortunately the design is such that the pin stays rigid because the wheel boss is in effect clamped between the screw head and crankpin bush by the retaining nut. For the opposite wheel I did what I should have done and followed your advice, filing a bit off the head - carefully so as not to create excessive side pressure and putting the pin out of square. Mercifully it didn't need that much to do the trick. Equally mercifully, I only had to do this on the rear axle, the driving axle and front axle have enough washers to keep the back of the screw clear of the frames. Once I'd managed this, I put the wheelsets in the hornguides, threaded the spring wire into place, then put the coupling rods on one part at a time, and found to my surprise and delight everything went round (and up and down) without too much tweaking / swearing!

So to the next few problems.....I've found that on one of the front wheels the crankpin nut keeps on trying to unscrew itself (the opposite wheel doesn't). These nuts are round so I'm struggling to get them properly done up - the driving and rear axles have hex nuts and are no problem. [My Gibson E4, which also has round nuts, shows the same symptom, but only on one wheel!] A friend suggested securing it with a touch of nail varnish (somewhat less permanent than Loctite) - is this sensible advice? - If so I'll have to get some funny looks in Boots - Senior Management says she doesn't use the stuff.

Today I plucked up courage to secure the connecting rods to the crossheads and install them - the resulting clearances are measured in fag papers. A bit of tweaking is still needed to get everything going round consistently without the front crankpin occasionally fouling the crosshead and connecting rods colliding with slide bars, but I think I can manage that - then on to assembling the various Walschaerts sub-assemblies. Which brings me to today's last question - what is the best way to secure the return crank? So far as I can see, the options are solder it to the crankpin, solder it to the crankpin bush, or clamp it against the crankpin bush by means of the retaining nut. The first two fill me with dread at the thought of waving an iron anywhere near expensive plastic mouldings, the last seems to risk it slipping out of position. What does everyone else do?

Seriously though, Philip is dead right. When I reflect on where I've got to it seems slow, but since I joined the Society and this forum I'm attempting skills I never dreamed I could manage a few years ago - so thanks everyone! In particular, thanks to all the CSB freaks (and to Chris at High Level) - both 76079 and E4 are fully CSBed and while I initially thought the whole idea resembled watch-making, I've not actually found it especially difficult, and it works! The only secret I don't think anyone has mentioned is oodles of patience, do everything one step at a time and don't take any step until you know the last one works. But I'm still glad the other engines intended for Stowe Fen all have inside cylinders!

Please let us see a picture of your finished engine sometime.
Philip

Finished? That's an interesting concept! Maybe when I've got the chassis actually working (the body is mostly built but unpainted etc), I'll get my son to bring his decent camera round - hopefully this side of Christmas but don't hold your breath.... Just the Walschaerts to fix, re-attach the dummy springs, fix up some current collectors, add a few more details such as pipework, finish the body detailing and unite chassis and body, paint and line it then sit back and enjoy!

Regards
Chris

[Philip Hall]

I usually secure crankpin nuts with a little Loctite 242 Nutlock once testing is complete. I unscrew the nut a couple of turns, drop a spot of 242 into the recess and then screw the nut down again. It's not a permanent fixing, and can be undone with a pair of pliers. Nail varnish is another workable idea, but probably not superglue as it might be difficult to undo should the need arise and the glue work properly. I am currently using Loctite 278 Threadlocker, for no other reason than it came as a free sample some time ago and I've run out of 242. It's a lot stronger and a bit thicker, though, as it's intended to be more permanent - so more difficult to undo again but not impossible.

For securing return cranks there is the proper way, outlined by Chris Pendlenton in MRJ 175 and 200, which means screwing the crank down tight so it won't come undone; the correct angle of the crank is taken care of by using shims so when the crank is tightened down fully it's in the right place. Usually I have gone down the Guy Williams route, which involves soldering the crank to the crankpin. In this case I always use a brass crankpin, as per Ultrascale, as it solders more easily than steel. I also chemically blacken everywhere I don't want solder to go, like the back of the return crank, the rods etc. and use a hot iron, acid flux and a trace of 145 solder. It is possible to unsolder it if you get it wrong without melting anything, as the solder is only there to stop the crank from unscrewing. Yes it's a bit hairy but I haven't had a disaster yet (what am I saying?!)

However, I have been much impressed with the strength of the 278 as outlined above, so much so that I've used it for one set of return cranks and will do so again this week for a BR 82XXX 2-6-2T.

Philip

[Andy W]

"do everything one step at a time and don't take any step until you know the last one works" - that's probably the biggest lesson I learned building locos.