Nick Dunhill's Workbench - Pair of EM2s
- Thread starter Nick Dunhill
- Start date
mickoo
Western Thunderer
You're welcome, last test print for brake system now going in, if good then it's just a case of filling the vat with resin and leaving it overnight to churn out all the parts for two EM2's
To add further to Nicks (rather kind) words, we often chew the fat before and during a joint (loosest tense as they're Nicks builds with a few of my bits added) build, the objective is always efficiency and using the best medium to achieve that. Efficiency reduces time and thus costs and allows clients to obtain bespoke models that would normally be outside of most peoples remits.
Whilst I may produce etches and 3D parts there's still a lot of traditional scratch building going on, something often (disappointingly) missed by onlookers, the cherries on top look more appealing than the cake underneath. Even then the etched parts are often not what you'd call commercial kit viable (no instructions, no numbering, tabs only where essential) and require a level of skill to build.
A good example would be some previous tank engines, only complex parts that need cutting out are etched, bunker/cab sides, bunker ends if necessary, cab front's & rear, typically only one boiler, smokebox and firebox former; these are used as templates to hand cut the rest required.
The rest, larger flat slabs are all hand cut, boilers, smoke box and firebox wrappers, splasher tops cab roof's etc; there is little point having them etched as it increases that cost above the time taken and raw materials to hand cut them.
Despite being 'boxes' on wheels this venture has shown how complex even the simplest shapes can be to replicate, from a parts designing aspect I'd rather being doing steam engines, these two were bloody hard work
Nick Dunhill
Western Thunderer
I'd second that. The thing I have taken from this build are;
It's not just a simple box. It has taken about the same amount of time to build as would a complex 'modern' pacific steam loco.
It hasn't been a boring build. It may be a series of boxes but it has been fun to research and buld.
Parts of the job have been incredibly complex. The roof panels above the cab would have been very difficult to fabricate from brass. 3D printing has really come to our aid here. It did take a huge amount of collaboration to design and build the brass cab sections and then print a roof that would fit and be able to be blended in with the brass roof sections.
Who would have thought that scratchbuilding 4 pantographs would take around 120 hours?
There's a lot of interior to make. Corridor, partitions, representations of the visible elecrical equipment and blower units and finally it has 2 sets of cab controls and not one!
It's not just a simple box. It has taken about the same amount of time to build as would a complex 'modern' pacific steam loco.
It hasn't been a boring build. It may be a series of boxes but it has been fun to research and buld.
Parts of the job have been incredibly complex. The roof panels above the cab would have been very difficult to fabricate from brass. 3D printing has really come to our aid here. It did take a huge amount of collaboration to design and build the brass cab sections and then print a roof that would fit and be able to be blended in with the brass roof sections.
Who would have thought that scratchbuilding 4 pantographs would take around 120 hours?
There's a lot of interior to make. Corridor, partitions, representations of the visible elecrical equipment and blower units and finally it has 2 sets of cab controls and not one!
Nick Dunhill
Western Thunderer
Yep you're right Paul. Took minimum amount out to start with but will need to remove more. It's a dreadful messy job as well. my whole workshop gets covered with plastic dust.
Richard Gawler
Western Thunderer
Please Mick, your third photo on Friday shows the centre bushes free to move and set inwards from the outer ones . . . do you have a rule of thumb or even a formula for setting up side play on a middle axle or do you work it out for every new model by test running on a suitable curve? Do the bushes slide sideways with the axle? And also, is the spring a piece of phosphor bronze or piano wire or something else? I hope you don't mind me asking so much but the more I can deduce before I begin, the fewer mistakes I will be putting right later. Many thanks.
mickoo
Western Thunderer
Richard,
The questions are better aimed at Nick, he built the bogies, I just supplied the end beams and other details. Nick sent one bogie over for me to measure the prints against and make sure they fitted correctly.
I can't answer your specific questions about these bogies unfortunately, nor can I check as it's all gone back in the post today.
Personally I have a test curve with a 6 foot radius and test models on that, these bogies have quite a long fixed wheel base so I'd probably leave +- 1 mm side play but then there may be enough play in the wheels themselves on O fine track to not need that much.
Not helpful I know, but generally leave as much side play as you need and a touch more.
Richard Gawler
Western Thunderer
Mick, I think your answer is fine. What I think you are saying is, the provision of sideplay is an empirical thing. We don't have a formula whare we plug in wheelbase, wheel diameter and ruling curve radius and get an answer telling us whether we need sideplay and if so how much.
Years ago I had a 4mm RTR loco, a BR class 14 (0-6-0) with about 2mm of sideplay on all three axles. The poor thing could barely work out how to run along a straight track. Running improved by shimmimg out the outer axles. If I am building a 6-wheeled tender (as I am just starting at the moment) I think a sensible approach is to provide minimal sideplay on the two outer axles and pack the inner one with washers. If the chassis derails, start taking out washers until it runs ok. If I am really keen I can solder the bushes in the correct locations so I don't need washers at all.
I am happy enough to do this, there was a little part of me which said, you (and Nick) have done this before, and you know how to make it work first time without experimentation. As you say, leave as much side play as you need, and a little more.
Years ago I had a 4mm RTR loco, a BR class 14 (0-6-0) with about 2mm of sideplay on all three axles. The poor thing could barely work out how to run along a straight track. Running improved by shimmimg out the outer axles. If I am building a 6-wheeled tender (as I am just starting at the moment) I think a sensible approach is to provide minimal sideplay on the two outer axles and pack the inner one with washers. If the chassis derails, start taking out washers until it runs ok. If I am really keen I can solder the bushes in the correct locations so I don't need washers at all.
I am happy enough to do this, there was a little part of me which said, you (and Nick) have done this before, and you know how to make it work first time without experimentation. As you say, leave as much side play as you need, and a little more.
simond
Western Thunderer
the basic formula is simple - T= R-(R^2 - (W/2)^2)^0.5
R is the curve Radius
W is the rigid Wheelbase
T = the Throw at the mid-length of the rigid wheelbase.
(halve the wheelbase and square it, subtract that from the square of the curve radius, and then take the square root. Subtract that from the curve radius to get the throw)
This will get you close enough. The wheel diameter does make a difference, but not much. If I'm worried, I simply cut a section of the wheels at rail top level, and see whether the flanges and rails are intersecting. I'm pretty sure it's not worth the CAD time.
If the radius is around 1800mm, the throws are typically quite small - less than a millimetre, and the clearance in 0F is quite large so it'll probably not be an issue. Tighter radius, more throw, of course. The Peco Settrack point I put in at John's earlier in the year is 1028mm rad, and that gives 2.5mm of throw on a 14' wheelbase loco - which doesn't work!
If you're running on 0MF (31.5) then the clearances will be tighter and you might need some side play on a middle axle. S7, more so again.
Obviously, gauge widening is also an option (and one the real thing used)
R is the curve Radius
W is the rigid Wheelbase
T = the Throw at the mid-length of the rigid wheelbase.
(halve the wheelbase and square it, subtract that from the square of the curve radius, and then take the square root. Subtract that from the curve radius to get the throw)
This will get you close enough. The wheel diameter does make a difference, but not much. If I'm worried, I simply cut a section of the wheels at rail top level, and see whether the flanges and rails are intersecting. I'm pretty sure it's not worth the CAD time.
If the radius is around 1800mm, the throws are typically quite small - less than a millimetre, and the clearance in 0F is quite large so it'll probably not be an issue. Tighter radius, more throw, of course. The Peco Settrack point I put in at John's earlier in the year is 1028mm rad, and that gives 2.5mm of throw on a 14' wheelbase loco - which doesn't work!
If you're running on 0MF (31.5) then the clearances will be tighter and you might need some side play on a middle axle. S7, more so again.
Obviously, gauge widening is also an option (and one the real thing used)
Richard Gawler
Western Thunderer
I have made a spreadsheet and the results tally with what I have found so far and expect to find.
Here is Simon's formula to paste into Excel:
=B3-SQRT( (B3^2) - (B4/2)^2 )
supposing B3 holds the radius and B4 holds the wheelbase.
I am thinking, the throw (T) is the lateral movement needed in one direction or the other. So the total free play needed on the middle axle is 2 x T?
(this assuming the wheelbase has three axles equally spaced)
Nick I think your locos are marvellous and I hope the diversion with sideplay I have created is short-lived and/or bearable.
Nick Dunhill
Western Thunderer
Hi All, sorry I missed a lot of this discussion. The brass bushes came with the Peartree wheels (excellent by the way) and they need to move up and down and not rotate and not really move with the end float of the axle. I love a bit of maths, but this was all done in a trail and error way. The end axles are fixed for the Delrin drive (not sure whether you can compensate a Delrin driven axle, no reason why not I suppose.) Anyway the spring wire is 0.5 mm phosphour-bronze, and located as an interference fit into the inner chassis. the other end passes through a short length of brass tube soldered to the top of the bush to stop it rotating. The phosphour-bronze wire is bent such that the weight of the bogie is sufficient to allow all 6 wheels to land on the track. The length of the phosphour-bronze wire stops the bush moving very far from side to side. I sort out the end float when it's sat on 6ft radius rail. I've used some shims to limit it a bit, the centre wheel hardly needs any end float, maybe +- 0.5 mm?
Hope this helps. it runs ok BTW
Hope this helps. it runs ok BTW
Bill Campbell
Western Thunderer
Delrin chain works fine with a compensated axle. The photo shows the chassis for a 7mm scale Judith Edge kit for a Ruston 48DS. The right hand axle rocks on a central pivot and the wheel bearings are on swing arms. The chain to the other (fixed) axle is on the far side of the gearbox.
Regards.
Regards.
AJC
Western Thunderer
Very nice, Bill - dad's done a couple of CO-COs in 4mm with compensated Delrin chain drive bogies - I keep meaning to upturn one and take some pictures to show how it was done (no real need to repeat this now with the advances in 4mm RTR mechanisms and aftermarket parts). There's sufficient play in the sprockets to accommodate that - it's quite forgiving.
Adam
Richard Gawler
Western Thunderer
Nick, it has helped me a lot. I couldn't comprehend how the bushes for the middle axle didn't just spin in the frames - the short length of brass tube explains. I might try this for a loco tender, to add springing to the centre axle.
mickoo
Western Thunderer
I file a flat on the top hat flange and then add a scrap of strip metal to the frames to stop the bearing rotating.
Nick Dunhill
Western Thunderer
Hi Tony
The sound project is by Bryan Robertson and it is loaded onto an ECU Loksound V5 decoder with a fairly big speaker. The sound project is a custom item and I got it via Rob at Modelyard in (dirty) Leeds. I have a model of Tommy in 7 mm and it originally had an Olivia's trains' sound project which I thought was a bit poor. I had the decoder reblown for a Legomanbiffo one which was also a bit weird, although it was claimed that that project was recorded from a NSR 1500 loco. This project is more how I remember EM1s sounding (I never heard an EM2.) They were pretty quiet. all you really heard was the blowers cooling the traction motors, the air compressor kicking in from time to time, clicking from switch gear and a hum from the traction motors. Oh and the mechanical clanking of a knackered loco.
The sound project is by Bryan Robertson and it is loaded onto an ECU Loksound V5 decoder with a fairly big speaker. The sound project is a custom item and I got it via Rob at Modelyard in (dirty) Leeds. I have a model of Tommy in 7 mm and it originally had an Olivia's trains' sound project which I thought was a bit poor. I had the decoder reblown for a Legomanbiffo one which was also a bit weird, although it was claimed that that project was recorded from a NSR 1500 loco. This project is more how I remember EM1s sounding (I never heard an EM2.) They were pretty quiet. all you really heard was the blowers cooling the traction motors, the air compressor kicking in from time to time, clicking from switch gear and a hum from the traction motors. Oh and the mechanical clanking of a knackered loco.
Richard Gawler
Western Thunderer
I agree . . . but Mick's technique is still useful to me. I bought a 0-4-0 loco secondhand, where the unpowered axle rocks and the bushes slide up and down in the frames. Adding the flat and the strip of metal would let me stop the bushes rotating, so I would have only one rotating bearing surface and not two. The important thing for me is, of course, to remember these things for when I get round to doing them. Otherwise life is just one diversion after another
