Building Don Young's Doncaster

[Deleted]

Sept 19, 2020 9:02:09 GMT don9f said:

Wanted to add that the above is dependent on the distance between the “back edge” of each crosshead having the correct dimension to the centreline of its link pin !

Cheers Don

Thank's Don...yes all parts are accurately nade, I took great care to get the distances right. I'm assuming that Don states 'check in place' in case the other parts aren't correct? I can see no other reason to make the spindles overlength?

Pete

[don9f]

I suppose that with so many parts and other dimensions involved, an accumulation of errors might take place that could affect the rod length. What’s important here is the position of the valve bobbin relative to the ports and the link pins.

Cheers Don

[Deleted]

Yes I can see that, although I suspect it's beyond my understanding of valve gear to work out all the various parts to come to the same valve movement if something like the crosshead hole distance dimensions were wrong
The bobbins are different, I can see that the important dimension here is the distance to the outside edge of the ports either end giving the required bobbin length. Also that these can be at odds to each other as long as the length of each bobbin fits comfortably withing the valve movement which must be accurate and the same for all 3 cylinders.

At least that's my current understanding of these things...despite the 11 years experience now gained building 4472 I'm still very much new to these things.

Pete

[d304]

Great question Pete! To proceed you might need the radius rod attached in the valve cross head. The bobbin position is then set by having the expansion link in mid gear then finding top dead centre bottom dead centre by rotating the wheels. In mid gear the bobbin will move but not open the ports to steam. Looks like a bit of fiddling! Then length of the spindles at the 3 to 1 side might be the thing to watch as they will effect the middle cylinder. Hopefully everything else will fall in place. I must read again what Don Young says.

I did come across an image of the micrometer setting on a King loco spindle so I presume A3/4 would have the same. I will find the pic and send it to you.
My eyes are wide open as you lead the way!

David

[61962]

Hi Pete,

I think Don intends you check your port positions before making your valves. In the centre position the ends of the valve i.e. the exhaust edges should be exactly line on line with the exhaust edges of the ports. The steam edges of the valve should overlap the steam edges of the ports by the specified amount of lap. You need to map each port in each cylinder and make your valves accordingly. If the port positions and widths in the liners are exactly as per the drawings then you have done very well and the valves will all be the same length and the same distance apart as drawn.

Until you have made and erected your valve gear you can't locate the valve spindles accurately in relation to the valve crossheads, which is why Don has given you a bit extra length in the spindles. so you needn't worry about that at this stage.

Eddie

[d304]

Pete

A3/4 valve gear were adjusted using thin steel buttons/washer into the valve cross head moving the spindle slightly I have just read.

David

[Deleted]

Thanks guys...guess I best not touch the spindles yet even though I'm reasonably confident that the valve gear parts will be to drawing. However, I'm not expecting the bobbins to all be the same length, not considering my only way to measure the liner recess being the tail of a vernier and the angle of that not being a given. I am confident though that any differences will fit within the space available and movement required. You may recall that I made a simple toll to measure ports to make the bobbins to match.
I wasn't expecting to be able to set the bobbins until the valve gear was completed bit had hoped that the 5 19/32 measurement was sacrament so that I could mount the cylinders before finishing the valve gear....I'm not sure if I can fit the bobbins after mounting the cylinderd... it would be great if I could?

Eddie with your experience on your A4 do you think this is possible...I was thinking with the front curved running boards removed that this might be possible? If so I could fit the outside cylinders without the valves...seems possible in my head as I can't see the cylinders needing removing full size just to fit new bobbins?

Pete

[pault]

Hi Pete.
As a suggestion I would not use a pair of nuts at each end of the bobbin to locate it. It is a pain having to remove the valve and spindle to adjust the valve. A threaded top hat that screws onto the valve spindle can be locked onto it with a lock nut. The valve sits on the outside of the top hat and is locked on to it with a couple of lock nuts, or one nut against a shoulder or something similar
The valve is adjusted by unlocking the top hat and moving it on the valve rod. This would normally be done by using home made pair of ‘tools’ (box spanner type of things) which fit one inside the other.
It is well worth the extra effort as all you need to do is take off the front crosshead and cover to adjust or remove the valve, and you can see/measure exactly how much you have moved the valve. Hopefully this makes sense.
As far as holding the petticoat goes, I know plenty of engines where the petticoat is simply a push fit, they don’t tend to move as there is little other than vibration and gravity to make them move. If you were worried about it slipping, rather than a curved plate just put two small blocks, with tapped holes in them (holes in the vertical) on the petticoat at the 12 and 6 o’clock positions. Then you only need a couple of csk screws, one in front of the chimney and one behind.
As for fitting the bobbins normally just removing the part of the running board that curves down to the buffer beam should allow them to be taken in and out. Other than for reboring or similar there should be no need to remove the cylinders from the loco. Like wise I would make sure that whatever arrangements you have in the smokebox you can remove the superheaters without having to remove the smokebox from the boiler and you can replace the blower pipe ( you will have to replace it at some point) without having to remove lots of other stuff.
PS The new paint job looks spot on, very nice.

[Deleted]

Thanks Paul

Any chance of a small sketch of when you describe for the bobbin...no need for any dimensions.
Thanks for the confirmation re other locos with just a push fit petticoat pipe. I'm trying to avoid any hidden screws under the cimney as that would cause damage to the paint if I need to remove the pipe for any maintenance to the superheater for example. I've been giving thought to the spindle and I'm a little hesitant in leaving the spindles over length till later...I might find myself chasing my own tail without this set to drawing as a datum, if that makes sense?

Pete

[mbrown]

Hi Pete,

I used Paul's method on my fabricated cylinders for 99 3462. There are some pictures on Page 2 of the thread for the cylinders which may be useful.

Good luck.

Malcolm

[pault]

Hi Pete,
Have a looks at
modeleng.proboards.com/thread/13406/fabricated-cylinders-99-3462?page=2
Towards the bottom there is a picture which shows Malcolm’s valves. The bit that loos like a long bolt has a tapped hole through it which screws onto the valve rod. The valve sits on the bolt with a couple of locknuts to retain it. Tradition dictates that the nuts retaining the valve do not pinch it, allowing it to float.

[Deleted]

Thanks Paul..
I did try to find it earlier but was looking at the wrong thread..I'll study it in detail once I'm sitting at the computer instead of on my phone I also have the info that Jim sent me to digest..
Many thanks chaps, hopefully I'll have something to show by end of the week.

[simon6200]

[Deleted]

Thanks for the photo, Simon... I'm currently getting my head around Malcolm's photos and Paul's description, once I'm clear in my head about this I'll make a start on my own...

Kind regards

Pete

[simon6200]

My valves have a carrier through the bore with a turned head at the rear end and threaded internally for the valve rod for part of the front end. The carrier is threaded externally 3/8 x 40 from memory, and the big nut is fixed on with high temperature Loctite. The small lock nut I'd threaded to the valve rod. I made a tube spanner from 3/4 copper annealed and bashed around a bit of steel hex. A socket for the locknut is inserted up inside the tube spanner. Very easy to adjust valve position from the front cover.

[Deleted]

Sept 21, 2020 9:09:37 GMT simon6200 said:

My valves have a carrier through the bore with a turned head at the rear end and threaded internally for the valve rod for part of the front end. The carrier is threaded externally 3/8 x 40 from memory, and the big nut is fixed on with high temperature Loctite. The small lock nut I'd threaded to the valve rod. I made a tube spanner from 3/4 copper annealed and bashed around a bit of steel hex. A socket for the locknut is inserted up inside the tube spanner. Very easy to adjust valve position from the front cover.

Any chance of a simple drawing and photo of the components broken down... as your spindle is the same as mine it could help with me grasping the full picture.

Pete

[John Baguley]

Hi Pete,

Here's a couple of photos of some I made for the 5" Brit that I sorted out:

Jim Ewins described this method in his articles about his experimental 9F back in 1981 so it may well have been his original idea. I first used it on my Helen Long back in 2006. Makes valve setting a doddle

John

[Deleted]

Thank's John, I think that I'm beginning to get a grasp of the design now, Malcolm informing me that the bolt has an internal thread to match the spindle was a eureka moment for me. I can now see how it's possible to do what Paul described and only need to remove the front cover to adjust the bobbin. The only thing that I'm not clear on yet is how well the bobbin's position is locked to the spindle, your last photo has confused me a little. I can not see an internal thread in the bolt and the external thread sits proud of the securing nut? In my mind, I was thinking that the nut would be flush with the end of the bolt and a further nut on the spindle tightened up against the bobbin assembly to lock in place?
I also note your use of 'O' rings, I don't think that I'll need those when using Flourosint? Also, what are the holes in the face of the front top hat for, are these for some form of 'C' spanner to grip?

Kind regards

Pete

[John Baguley]

Hi Pete,

Yes, the 'Bolt' does have an internal thread to match the valve spindle but I don't thread it all the way through, just say 1/2" at one end. The rest is just clearance on the thread of the valve spindle. Once the valve is adjusted, it is held firmly by a locknut on the valve spindle bearing against the other end of the 'Bolt' that has the Hex head on it. The hex head and the locknut are at the front end of the valve and are adjusted by concentric box spanners. You may need to make a couple of 'Specials' just for the job. With care you can actually adjust the valves whilst the loco is running on air.

The holes in the end caps are indeed for a pin spanner to tighten them up. I used threadlock on the threads as well to be on the safe side.

The O rings were just to make sure that the PTFE heads sealed to the valve bobbin although they probably weren't needed as the PTFE will expand once hot and seal onto the bobbin. As I only ran the chassis on air I thought that the heads may leak a little when cold.

John

[Deleted]

Whilst sitting here looking at some hex bar for the bolt and wondering how the hell I was going to cut an internal thread over 3 inches it just dawned on me, I don't need to cut an internal thread along the whole length of the bolt, just a section at the hex end, the rest can be a clearance hole for the spindle. Unless I am forgetting something a plan is beginning to form. Looking again at John's second photo, if I made mine to a similar design at the front would a nut on the spindle tightened against the protruding thread seen in John's photo be enough to lock the bobbin in place? remembering that the tail end of the bolt will be threaded to match the spindle, I can probably thread approx 1 inch at the tail.

Am I reading this right guy's, sorry for all the double-checking, some days my head struggles and also apologies to those for me not remembering that I have touched on this subject before, I found some reference to past discussions which I had clearly forgotten about... that's worrying...

Pete