Ray's 4mm Workbench, Metalsmiths Turntable (end of P.13)

[Miss Prism]

I had wondered whether 'dodgy platforms' might be involved. However, the maximum width across these cylinders was 8'11" and on the 28XX this was at 2' 6¹/₄" above rail height. Dropping that to 2' 3¹/₄" would put the curved bottom of the casing perilously close to the 8' 8" width at 2' above rail height. Then you need to add an allowance for tyre and bearing wear. Holcroft actually says "...there was insufficient clearance in the load gauge to enable the cylinders to clear it with worn tyres and axlebox crowns."

 

Ah yes, see what you mean. It does get perilously close on the smaller wheeled locos.

 

The later designs without the offset used a different cylinder casting and all had larger wheels than the 28XX.

 

I had forgotten that. Silly me.

[tender]

That's way under what it should be. Conn rods on a 5mm throw will never clear that slidebar pitch. You'll need to send Castle out on 5322 safari with his trusty tape measure to find out what it should be. ISTR Comet admitting there were compromises made in the crosshead design - the Comet 2003 mods to the 2-cylinder etch addressed only the relaxations to the valve and piston centres, and I think Jeff Ayers was reluctant to do anything more fundamental.

 

Pity this has only just come to light, I had to deepen the slide grooves in the crossheads quite a bit to get them to fit (and slide smoothly) in the slidebars. Looks like I would have been better off thinning the slidebars instead. Taking some measurements off a drawing it looks like the distance between the slidebars should be nearer 5.5mm. I think I might get another slidebar etch and 2 new crossheads and rebuild this part.

 

Still doesn't explain why it's sitting too low!

[Miss Prism]

Even at 5.5mm slidebar pitch, the clearance at wheel top centre is about 2 fag papers, and the clearance at wheel bottom centre is zero fag papers.

 

 

Btw, 2-cylinder slidebar material on a Hall is 5.5" wide, but maybe a little bit less on a Mogul.

[ozzyo]

Hello Tender,

 

you have a PM that may help.

 

I did think that the wheels had the wrong throw, first thought. Then it was about the length of the rods, in that they may be the wrong length.

Looking at them all. The cylinder C/L looks low and the gap between the slide bars looks too narrow (as pointed out by Miss. Prism)

 

So what do you do? New slide bars and cross heads (Markits). The con rods maybe a bit on the thick side? (as they do look a bit on the chunky side).

 

How does the cross-head look when at full forward?

 

OzzyO. 

[tender]

Hi OzzyO.

 

Many thanks for the PM.

 

I've made a few measurements and compared them with the drawing.

 

crank throw 15", Markitks wheel 5mm 

 

connecting rod length ~6'11", comet etch 27.5mm 

 

So they look ok.

 

Here's a picture with the cross head forward.

 

 

I'll check out the Markits catalogue an see if I can find a suitable replacement crosshead/slide.

 

Edit: Looking at the picture in the Markits cat. The base of the slide grooves are only 3.35mm apart in the drawing so i don't think that's not going to help any.

[trustytrev]

Hi OzzyO.

 

Many thanks for the PM.

 

I've made a few measurements and compared them with the drawing.

 

crank throw 15", Markitks wheel 5mm 

 

connecting rod length ~6'11", comet etch 27.5mm 

 

So they look ok.

 

Here's a picture with the cross head forward.

 

forward.JPG

 

I'll check out the Markits catalogue an see if I can find a suitable replacement crosshead/slide.

 

Edit: Looking at the picture in the Markits cat. The base of the slide grooves are only 3.35mm apart in the drawing so i don't think that's not going to help any.

Hello,

       Could you fill the hole on the connecting rod and redrill it slightly further towards the front,then taper the slides to suit?

[Rail-Online]

I think I may have the solution!

 

GWR 51xx no 5199 at Llangollan. I presume it is prototypical........

 

 

Cheers Tony

[Castle]

You'll need to send Castle out on 5322 safari with his trusty tape measure to find out what it should be.

Hi All,

 

Is someone taking my name in vain again?!?

 

In all seriousness though, Miss P is right about the tollerances. If you get the opportunity with a static GWR loco, try and look at the gap between the cross head and the coupling rod end on the front wheelsets. It is freakishly small even in 12":1' scale. The gaps, arrangements and so on are so tight that on the Castle, there is a special nut with a special box spanner with semicircular cross section lobes on it to fix the coupling rod to the pin unlike the centre and rear that have a large nut and taper pin to fix it in place. You can see it on Tony's picture of No. 5199. The special nuts are secured by a long bolt that goes though the nut and the pin on the driving wheel that in turn has a nut and split pin to prevent it coming undone. The thing is though that the bolt can only be put through the wheel from the back, when the weight of the whole locomotive is on the springs as only then will the springs compress enough to put the rear of the pin in the right position to get the bolt in... The things you learn!

 

All the best,

 

Castle

[John_Hughes]

Lumme! I knew that the prototype clearances were tight, but it's fascinating to have the exact details!

 

And I've heard some of the dafter P4 fanatics claim that all prototype dimensions and clearances should be scaled down!

[Mike G]

And I've heard some of the dafter P4 fanatics claim that all prototype dimensions and clearances should be scaled down!

 

Really?...Where exactly did you 'hear' this? In the 20 years I've been modeling P4 I have never found any of them daft or fanatical, so perhaps you'd like to point out these people you've 'heard' from...

 

Mike

[PenrithBeacon]

...It is freakishly small even in 12":1' scale.

...

I would doubt if any tolerances or clearances on any steam engine are 'freakishly small'. I would say that they're just normal, working, practical, limits and fits.

[tender]

Been trying to get hold of some Markits cross heads today but nobody wants to answer the phone.

May have to go back to Comet and have another go with them increasing the gap between the slides this time.

This ones on the back burner until after the weekend now.

[Captain Kernow]

And I've heard some of the dafter P4 fanatics claim that all prototype dimensions and clearances should be scaled down!

That assumes, of course, that there are some daft ones to begin with......! 

 

 

 

 

 

 

 

 

Only joking - of course there are! 

[Castle]

Hi David,

 

The gaps FEEL freakishly small when actually work on these things! When you consider the amount of meal thrashing round in such a small space at 75mph+, if you haven't seen it close up, it is somewhat counter intuitive to think that there are such tight tolerances on these bits. I like to bring my work and experience at 81E to life in such away that it easily understood and enjoyable for those reading it, hence the 'rich' turn of phrase rather than relying on more specific engineering exactitudes. I know the machinists we have working on No. 4079 to have got these fine tolerances spot on - they looked pretty good when we moved her frames a short distance to reposition the wheels at the weekend! When pushing the loco along with pinch bars, you can really SEE it all going round without all the regular noise and other distractions. It is quite majestic really. Especially if you are on look out and not straining to move the engine.

 

When discussing these tolerances prior to machining we specified to the guys that they should be between freakishly small and scarily tight. You wouldn't believe what the set of vernier gauges we have for measuring in these units looks like...

 

Yours cheekily,

 

Castle

[ozzyo]

Hi David,

When discussing these tolerances prior to machining we specified to the guys that they should be between freakishly small and scarily tight. You wouldn't believe what the set of vernier gauges we have for measuring in these units looks like...

 

Yours cheekily,

 

Castle

 

I would, I had a set years ago and it said to b00dy big on one side, to bl00dy small on the other, and in the middle it said just right.

 

TIC

 

OzzyO.

[John_Hughes]

Really?...Where exactly did you 'hear' this? In the 20 years I've been modeling P4 I have never found any of them daft or fanatical, so perhaps you'd like to point out these people you've 'heard' from...

 

Mike

I had quite a session with Adrian Tester over exactly this issue some years back, before he got into 7mm. Will he do?

[Castle]

Hi All,

 

I have had a chat with the project manager of the Saint project (who has had a set of cylinders made!) with regard to the 2 1/2" offset and he has come up with the following data which may be of interest.

 

The first Saints (2901-10 Ladies / 2911-30 Saints, 2971 Scotts (ex 4-4-2) and 2998) all had the cylinder centre line 2 1/2" above the wheel centreline.

 

Courts built in 1912, have cylinder centreline and wheel centreline coincidental (Nos. 2931-55)

 

All subsequent 2cyl 4-6-0s were coincidental (Halls, Granges, Manors and Counties).

 

Locos at Didcot apart from Nos. 2999 that have the 2 1/2" off set are Nos. 3822 / 4144 / 5322 / 5572 / 6106 / 7202.

 

All the best,

 

Castle

[John_Hughes]

Hi All,

 

I have had a chat with the project manager of the Saint project (who has had a set of cylinders made!) with regard to the 2 1/2" offset and he has come up with the following data which may be of interest.

 

The first Saints (2901-10 Ladies / 2911-30 Saints, 2971 Scotts (ex 4-4-2) and 2998) all had the cylinder centre line 2 1/2" above the wheel centreline.

 

Courts built in 1912, have cylinder centreline and wheel centreline coincidental (Nos. 2931-55)

 

All subsequent 2cyl 4-6-0s were coincidental (Halls, Granges, Manors and Counties).

 

Locos at Didcot apart from Nos. 2999 that have the 2 1/2" off set are Nos. 3822 / 4144 / 5322 / 5572 / 6106 / 7202.

 

All the best,

 

Castle

 

Thanks for that - interesting!

[tender]

Hi All,

 

I have had a chat with the project manager of the Saint project (who has had a set of cylinders made!) with regard to the 2 1/2" offset and he has come up with the following data which may be of interest.

 

The first Saints (2901-10 Ladies / 2911-30 Saints, 2971 Scotts (ex 4-4-2) and 2998) all had the cylinder centre line 2 1/2" above the wheel centreline.

 

Courts built in 1912, have cylinder centreline and wheel centreline coincidental (Nos. 2931-55)

 

All subsequent 2cyl 4-6-0s were coincidental (Halls, Granges, Manors and Counties).

 

Locos at Didcot apart from Nos. 2999 that have the 2 1/2" off set are Nos. 3822 / 4144 / 5322 / 5572 / 6106 / 7202.

 

All the best,

 

Castle

Thanks for that Castle.

I had a chat with Geoff from Comet as Scalefour North at the weekend and now hopefully have a solution for the low mounted cylinders. Apparently they were made this way to accommodate different bodies. All I need to do is to pack up the cylinder block  so the cylinders fit snugly under the footplate with the body fitted. Looking at it, this should bring the slides up to somewhere much nearer their correct position.

[B15nac]

Hi

 

Did you ever get over the problem with the 43xx? Got any pictures of her finished?

 

Regards Neil

[tender]

Hi Neil.

Thanks for your interest. In post 312 i did say this was on the back burner until after the weekend. Well that was back in April so its been a long weekend.

I was never happy with the crossheads/slides that came with the Comet bits as i had to file an awful lot off both bits to get them to fit (slide) Even then the cranks still fouled the slide bars so i made a decision to get hold of some Markits crossheads. Well its taken me this long to get them, I picked them up from ScaleForum the other week. So i'll be tackling this again shortly once I've cleared my work bench of a few other projects that I've been playing with over the summer. I think I will have to make some new slidebars as well so with this in mind I picked up a few bits of brass square section rod as well. Watch this space.

 

Ray.

[sean hpw]

Just read this through end to end and find that it was amazing to see you have come from total novice, to someone who is competent and paying so much attention to detail, I wait with baited breath for the result of the Mogul...

 

 

Sean

[Simond]

I had wondered whether 'dodgy platforms' might be involved. However, the maximum width across these cylinders was 8'11" and on the 28XX this was at 2' 6¹/₄" above rail height. Dropping that to 2' 3¹/₄" would put the curved bottom of the casing perilously close to the 8' 8" width at 2' above rail height. Then you need to add an allowance for tyre and bearing wear. Holcroft actually says "...there was insufficient clearance in the load gauge to enable the cylinders to clear it with worn tyres and axlebox crowns."

 

The later designs without the offset used a different cylinder casting and all had larger wheels than the 28XX.

 

Nick

 

Funny how discussions seem to occur simultaneously

 

 

Please see discussion on same topic in my Porth Dinllaen thread (link below) post 27 et seq

 

Best

SD

[tender]

Haven't posted here for ages as we've been too busy working on and exhibiting our exhibition layout. But with a new year comes a new layout and lots of things to build so expect to see some posts here soon.

[tender]

First off is a Midland Railway Centre (Metalsmiths) 60ft Cowan & Sheldon Turntable.

 

This arrived last week in two packages, one containing the Bridge Deck kit and the other the Turntable Well Installation kit.

 

Progress so far. The two bottom sections of the Well base are bolted together with 4mm spacers (after easing the holes slightly to get the bolts in) and the sectional ply floor glued in place to the rebate in the top section and then the centre weighted down and glued to the bottom.