Ultrscale crankpin question

bjuleff
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Ultrscale crankpin question

Postby bjuleff » Tue Sep 15, 2015 3:52 pm

Perhaps some of you guys may be able to put my mind right on this one.

I am currently building an outside cylindered loco, my first in fact! I am using the Ultrascale system and have got into a pickle over the leading axle crankpin arrangement. This is the Type C (recessed behind slidebars). As I see it, the coupling rod has to be assembled to the sleeve and the sleeve/nut is tightened by screwing the crankpin through it from the rear, thus drawing it into the wheel recess. There is no way to tighten the nut from the front as it is recessed into the rod.

Now all this suggests to me the rod should be attached to the wheel before the wheel goes onto the axle. And if this is correct then once the wheels are on the axle and quartered, there seems no way in getting the rod off again. Maybe I'm wrong, but I'd like to know if I'm missing a trick here. Obviously, at some distant stage, I will need to strip the chassis down for painting once I've got it to go properly, and fortunately the wheels can come out as sets, ...but with the rods on?

Any words of wisdom will be gratefully received.
Bob

JFS
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Re: Ultrscale crankpin question

Postby JFS » Tue Sep 15, 2015 4:07 pm

Hello Bob,

I think your description of how these work sounds about right, but it is not necessary to fit rods before fitting the wheels. What I do is just to fit the screw from the back of the wheel as usual, then fit the threaded bush through the rod at the appropriate time. I tend to put a "nick" across the face of the "thin nut" part of the threaded bush using a VERY fine piercing saw (6/0), you can then make a screw driver from fret-waste to tighten it. This of course, also means you can undo the thing later if needed.

It should also be mentioned that to get the best out of the design it is necessary to counter-bore the face of the rod - if such a counter bore is not provided by the design of the rods, it is easier to drill this through the "front" layer of the etching before soldering the laminations together. If you are scratch-building then you won't need any help from me!

I will take a photo and post it shortly (well, after the camera battery has woken up again)

Best wishes,

JFS
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Re: Ultrscale crankpin question

Postby JFS » Tue Sep 15, 2015 4:14 pm

just a further thought...

Whilst you are in the early stage of assembly - ie doing the quartering and such like, and before you have fitted your outside cylinders, you can just use an ordinary crankpin bush and nut on the leading drivers. Only when satisfied that all is well, adn when you are ready for con rods / slidebars / crossheads / combination levers / union links do you need to substitute the proper bush.

Reading that list reminds me why I envy the Diesel brigade!

Best wishes,

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Tim V
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Re: Ultrscale crankpin question

Postby Tim V » Tue Sep 15, 2015 4:15 pm

I do it the same as Howard, using a file I obtained many years ago that cuts a slot for a screwdriver.
Tim V
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bjuleff
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Re: Ultrscale crankpin question

Postby bjuleff » Tue Sep 15, 2015 4:49 pm

Many thanks for your speedy replies, Howard and Tim. A good suggestion regarding using the ordinary type crankpins first, however as I've already assembled the wheel sets and filed down the head of the crankpin at the back, I'm a bit stymied now to go that route! But at least I've got a way forward now with the screwdriver slot, thank you. The rods I'm using (Dave Bradwell) do indeed allow for the nut to recess flush.

Interestingly, (or maybe not), both the S4 Digest and EMGS manual describe assembly quite fully but add a note at the bottom - if your wheels are already assembled a slightly different sequence may be found beneficial. Helpful or what?
Bob

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45609
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Re: Ultrscale crankpin question

Postby 45609 » Tue Sep 15, 2015 5:25 pm

A photo of a loco I've worked on recently shows what I believe is being described. Sorry the con-rod is partially obscuring the nut. I use a modified Romford screwdriver to tighten the nut.

image.jpg


Morgan
Last edited by 45609 on Tue Sep 15, 2015 8:31 pm, edited 1 time in total.

JFS
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Re: Ultrscale crankpin question

Postby JFS » Tue Sep 15, 2015 7:10 pm

... and mine as promised - looks like great minds think alike

Fairburn Leading crankpin.jpg
Fairburn Leading crankpin.jpg (444.5 KiB) Viewed 5393 times


This is a Bachmann LMS Fairburn 4MT 2-6-4 tank - there is absolutely zero clearance behind the crosshead. By contrast, the BR Std. 4MT from the same stable has loads of room.

Both of these pics illustrate what I meant about recessing the nuts into the con rod. This is key to getting the value out of these crankpins which I think are super products for the job.

Best wishes,

bjuleff
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Re: Ultrscale crankpin question

Postby bjuleff » Wed Sep 16, 2015 8:10 am

Thanks for the pictures, Morgan and Howard. Which now prompts me to ask, how do you make sure it stays tight - there's not any evidence of soldering? Not that I'd want to in such a confined space.
Bob

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45609
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Re: Ultrscale crankpin question

Postby 45609 » Wed Sep 16, 2015 8:38 am

As I said in my previous post I use a modified Romford screwdriver (available from Markits). The photo below shows an unmodified one as it is the best picture I could find with a quick google search. The modification is quite simple. The outer edges of the two prongs are chamfered with a file so that the screwdriver does not foul the coupling rod boss when you tighten up the nut. I considered this the primary means of keeping the screw tight. If it loosens and falls off the crankpin when test running then I'd say that there is something wrong with the mechanism causing the nut to come loose. It is usually a clearance, or more correctly, an interference problem. Excessive rubbing of crankpin nut shank or face with the coupling rod being a prime culprit for self loosening of the nut. Once I'm happy that all is running well and there is no further reason to remove the coupling rods I will loosen each one slightly, add a tiny drop of thread locking compound (Loctite 290, Shellac or Enamel varnish are suitable), and re-tighten them. This is a secondary locking method just to be sure as dropping a crankpin nut at speed can be quite catastrophic, even in models.

Cheers....Morgan

Romford Screwdriver.jpg

bjuleff
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Re: Ultrscale crankpin question

Postby bjuleff » Wed Sep 16, 2015 8:48 am

Hi Morgan,

Yes, I was thinking varnish might be good if it doesn't have to cope with much torque. As you say, the test running should reveal any snagging. Interested to hear you suggest Loctite 290. I am not sure what the various Loctite compounds are all about, but have it in the back of my mind that Loctite only works if one of the surfaces is ferrous. Maybe 290 gets around this?
Bob

Philip Hall
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Re: Ultrscale crankpin question

Postby Philip Hall » Wed Sep 16, 2015 9:08 am

I use 278 Threadlocker. (I used to use 242 Nutlock until it ran out) 278 is very much stronger and I only use it because for some reason lost in the mists of time Loctite sent it to me as a free sample years ago. Beware, though, it is very strong, and I have had much grief sometimes in trying to unlock a nut locked with it, so I only use the tiniest drop. I just unscrew the nut slightly to leave a recess, put the drop in and retighten.

I think Loctite cyano is supposed to work on brass in the presence of steel (which is maybe why we all sometimes have grief using it on plastic wheels) but I have had no problems with this stuff on brass crankpins. On one occasion I even used it to lock a sloppy return crank on, and I usually solder them. I know I should do it properly, but this works for me...

Philip
Last edited by Philip Hall on Wed Sep 16, 2015 10:31 am, edited 2 times in total.

bjuleff
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Re: Ultrscale crankpin question

Postby bjuleff » Wed Sep 16, 2015 9:34 am

Sounds a bit high risk to me! But thanks for the tip Philip.
Bob

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45609
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Re: Ultrscale crankpin question

Postby 45609 » Wed Sep 16, 2015 9:43 am

Bob,

As far as I know Loctite 290 is a general purpose thread locker and not just for use on ferrous metals.

http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802623848449

There is a huge range of Loctite compounds for all sorts of applications so there may be one that is optimised for this. I seem to vaguely recall some discussion about using Loctite on the wheel to axle interface (i.e. plastic to steel) and that perhaps Loctite was not going to provide an ideal bond. The Loctite litereature tends to back this up with the lowest bond strength factors being quoted for metal to plastic. I tend to not trust it and you'll notice that the wheel in the photo I posted has a wire keyway inserted between axle and wheel boss to lock the quartering. I've been doing this for quite a while now and is based on the article Mark Humphrys wrote for MRJ229. I do still use a little Loctite 648 when inserting this pin into the keyway hole but again only as a method of secondary retention. I've also done one or two locos with the Chris Pendlenton method of wheel axle retention MRJ219 & 221. Brass bushed wheel centres machining to an interference fit of the axle. This is a lot more time consuming than the keyway method. Apologies for digressing from the subject of crank pins.

cheers....Morgan
Last edited by 45609 on Wed Sep 16, 2015 9:57 pm, edited 1 time in total.

bjuleff
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Re: Ultrscale crankpin question

Postby bjuleff » Wed Sep 16, 2015 4:45 pm

Thanks for the info about Loctite, Morgan.

As I remarked to Philip, it looks to be a trifle risky. Not so much with wheels but the thought of capillarity taking it back past the washer and into contact with the coupling rod leaves me a little suspicious of it. The old Loctite I used to use on my motorbike (misspent youth 40+ years ago) used to set only hard enough to stop the thread unscrewing but easy enough to undo with a spanner. The one you've given the link for (290) says it is disassembled with heat applied. Have you experienced any problems in this regard?
Bob

Philip Hall
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Re: Ultrscale crankpin question

Postby Philip Hall » Wed Sep 16, 2015 6:32 pm

Bob,

I should have mentioned that 278 is extremely thick compared to ordinary cyano, so I don't think there is much chance of capillary action taking it where you would not want it to be. I only use it because with care, it works very well and I had a large bottle given to me FOC. Should I need to replace it I would probably use 290.

Philip

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Will L
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Re: Ultrscale crankpin question

Postby Will L » Wed Sep 16, 2015 8:02 pm

Philip Hall wrote:I should have mentioned that 278 is extremely thick compared to ordinary cyano,


Don't think many (any?) of the Loctite thread lockers and retainers are cayano's, 278 is an acrylic. I've been a user of Loctite thread lockers on crank pin nuts for a long while, and I've never had it get were it isn't wanted (but see * below). You do have to remember that the rod should be free to pivot on the crank pin when the nut is screwed down tight against the bush below, which ought to keep it done up even without thread locker. If the nut grips the rod at all, thread locker, or anything else, won't help.

* Retaining wheels on axles with Loctite 603 (also an acrylic) is a very different story see here

bjuleff
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Re: Ultrscale crankpin question

Postby bjuleff » Thu Sep 17, 2015 8:49 am

Ok Fellas - another sceptic converted!

I'll look out for a bottle of Loctite 290 and give it a go. Comparing the datasheets Loctite 278 seems to be sold as a high strength compound giving breakaway torque figures of 42Nm !! Maybe a bit OTT for our use. By comparison 290 is rated at 10Nm. These figures assume application to steel. Brass apparently give a bond approximated 15% that of steel.

But anyway, many thanks to all who have offered their advice to me.
Bob

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45609
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Re: Ultrscale crankpin question

Postby 45609 » Thu Sep 17, 2015 9:29 am

Bob,

Glad to hear that we have convinced you. You also asked the following question.

bjuleff wrote:The one you've given the link for (290) says it is disassembled with heat applied. Have you experienced any problems in this regard?


I've never had a problem using heat to get a joint undone (that goes for both threadlock and retainer) but the problem you'll encounter in the context of loco wheels is the risk of melting/distorting the plastic centre. It very close to being a certainty. Using the low breakout torque thread locking compounds should enable mechanical breaking of the joint (unscrewing). Having said that I can't recall having to undo a crank pin nut on a loco since final locking in place. I guess I've never had a serious breakdown of one of my models that has required this course of action. A bit more browsing of the Loctite website shows that there is a compound with even lower breakout torque than 290. Loctite 222. I'm tempted to give this one a try.

cheers....Morgan
Last edited by 45609 on Thu Sep 17, 2015 10:49 am, edited 1 time in total.

John Fitton

Re: Ultrscale crankpin question

Postby John Fitton » Thu Sep 17, 2015 10:05 am

Very nice examples and discussion of 4mm scale model engineering IMHO. I am one of the diesel brigade; when I get around to converting my steam models I shall be referring to material such as this. Thanks everyone.

JF

chris58
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Re: Ultrscale crankpin question

Postby chris58 » Mon Dec 14, 2015 9:33 pm

Hi Philip
What size nut do ultra scale use on their Bachmann 08 crank pins as iv,e lost one.
Kind Regards
Chris Dales

Philip Hall
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Re: Ultrscale crankpin question

Postby Philip Hall » Mon Dec 14, 2015 9:48 pm

Ultrascale use a 14BA screw for crankpins. I'm sure Ultrascale would help with a spare proper crankpin nut, alternatively an Alan Gibson one can be used as although the thread is metric, for the few threads needed in this application it would screw tight. If you're really stuck PM me and I probably have a spare.

Philip
Last edited by Philip Hall on Mon Dec 14, 2015 11:52 pm, edited 1 time in total.

chris58
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Re: Ultrscale crankpin question

Postby chris58 » Mon Dec 14, 2015 10:00 pm

Hi Philip
what a life saver.
Relieved
Chris Dales

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Horsetan
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Re: Ultrscale crankpin question

Postby Horsetan » Sat Dec 19, 2015 8:50 pm

Sorry, Philip, but Ultrascale's current crankpin production is based on a M1 screw, same as AGW. This is because Ultrascale couldn't get their usual 14BA screws in the (small) quantities that they wanted.
That would be an ecumenical matter.

Philip Hall
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Re: Ultrscale crankpin question

Postby Philip Hall » Sun Dec 20, 2015 6:56 pm

Ivan, I think I had heard this but had forgotten. Although as it's new production that will be like this, an older set such as Chris has may still be 14BA.

Philip


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