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Post by doubletop on Sept 21, 2018 9:50:14 GMT
I supose I'd better do a bit of a catch up on where I've got to with this project as there has been a bit of progress and I've just been slack in reporting it. Let's start with welding up the frame that I posted earlier. Nothing spectacular really only that its the first welding job I'd ever done by myself. I'd done a few bits and bobs with Dave as my mentor when we were doing the steaming bays work last year. But Dave was always there to fix any problems I maye have introduced. He wasn't shy of grinding the whole thing apart and doing it again. The jig to hold together the end frame angled sections. The frame welded up. No Dave this time. I did have it in mind that if it didn't go well I'd chuck it in the van and go over to his place for a bit of re-work. I haven't gone yet. Its 50mmx25mm tube. Maybe a bit oversized for this job but it was given to me. It should be strong enough for 3 or 4 passengers and I have a way of hidding the bulk. Pete
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Post by doubletop on Sept 21, 2018 10:22:14 GMT
In parallel with the frames I was working through the bogies. These are not prototypical they are based on some components from a supplier in Oz and a variant of a local frame design. My reasoning being that I shouldn’t have any problems getting approval for passenger running and anyway once the footboards are on who is going to be on their hands and knees point out they are not authentic Collet bogies. I missed the boat on placing an order for a set of steel side plates that were being laser cut. I also thought they would be rather heavy so after getting expensive quotes for water jet cutting in aluminium decided to do them myself in 7075 tool plate aluminium. 7075 has twice the tensile strength of mild steel. They were done by hand using the DRO functions. A process I call MNC (Manual Numeric Control) using the smooth arc and line of holes functions for curves and angled cuts. Due to the complexity of the shape CAD was used to determine all the datum points for the each of the DRO functions. Other than that, once initially camped in place the workpiece was not removed, or moved, from the mill for the entire process. This has been discussed elsewhere on this forum The final result, a lot of hours now serious consideration to modify my mill for CNC. The Oz supplied parts were only the wheels and axles. Apart from the bearings and nuts and bolts, springs etc I made the rest Pete
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Post by doubletop on Sept 21, 2018 10:58:32 GMT
The wheels had taken some time to get here from Oz while I waited it was time to tackle the buffers I’d purchased from Tom at Little Western The biggest problem I had was how hold the buffer stock to get a hole through from one end or the other to exit at the right point. Apart from the footsteps on the top and bottom faces nothing else was concentric or parallel with anything else. These are 3.5” long so any slight deviation could end up with the hole exiting anywhere in the base. The solution I came up with was to us a small precision vice clamped in my milling vice to provide a set of vertical jaws. I could hold the stocks by the footsteps. Find and centre drill each end and then set them up on a centre ‘spike’ clamped to the mill table and aligned to the quill centre This allowed the stock to be drilled down close to the end. The final exit being completed later with the spike out of the way The buffer shafts were centered in the mill and then the head held in the four jaw in the lathe with the end in a centre to turn down the shaft. A height gauge was used to ensure the buffer head was held horizontal to drill and tap the thread for the cap head screw. The screw would hold the buffer in a slot in the lower face of the buffer stock to stop the head rotating Pete
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Post by doubletop on Sept 21, 2018 11:24:39 GMT
So I have a frame, bogies and buffers I need coachwork to go on top. The intention has always to make an A27 variant autocoach basically because before getting hold of the John Lewis book the only drawing I had was of an A27 which was a size that, with a bit of licence, I could recreate in a length that would fit in my van. Now I have the book the A27/A28 variants are very similar apart from the length. I’d had needed to get to grips with CAD for the bogies, that quickly extended to the frame and then to the coachwork. As things progressed tweaks were made but it encouraging when things actually fit and go together as expected. I must admit there is a point where JFDI kicks in no amount of playing with CAD can beat actually making the item to see if it does what you think you’ve drawn. Pete
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Post by doubletop on Sept 22, 2018 10:37:58 GMT
I realised there wasn't a photo of the underside of the buffer showing the retaining cap screw, which also serves to stop the buffer head rotating. The footstep isn't on the wrong side as Toms castings have them on both sides so they aren't left or right handed. You don't know the bottom one is there when they are installed. Pete
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Post by doubletop on Sept 22, 2018 11:20:22 GMT
When it comes to the coach body it was never going to be practical ‘as drawn’ as a wagon of this size is expected to take passengers. I’m also considering using it as my driving trolley as it will have plenty of space for all the bits and bobs for running my Dart, including a large primary water tank. So the approach I’m taking is an inner plywood box with an outer skin in with external details. Basically, a 12mm plywood plate covering the frame and a set of bulkheads, as shown previously in the CAD images. The bulkheads are cut at the roof line the top sections will become formers for the roof seating and allow access to the internal storage areas. The large rectangular slot at the bottom fits over the plywood baseplate and down the side of the 50mm section of the frame. This then hides the bulk of the frame leaving 1.125” visible, representing the 9” of the frames of the prototype. Then came the coach sides. I had always intended to use a friends CNC router to cut them (another reason for having to learn CAD). We discussed materials I had always considered using 3mm ply, but other options included MDF and various plastics. In the end I stuck with my original decision to use ply. A local company is a router and laser cutting operation and they offered to do the job as they could also supply the polycarbonate panels for the windows. They laser cut the side panels from ply, turning the job around pretty quickly. So here it is with the outer panels temporarily tacked in place And that’s pretty much where I am at the moment…. Pete
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Post by doubletop on Dec 2, 2018 8:54:06 GMT
Time for another update. Since the last post I've been back to the UK and managed to fit in a visit the the Burghclere track open day. They are doing a fantastic job there. A side trip to Didcot, where I managed to pick up a copy of Vol 1 of the GWR Autotrailers book to go with the Vol 2 I'd found in Australia. A a pleasnat day out at the Midlands show. Now I'm back I've made a bit of progress and the coachwork has been in the paint shop Trial Fit In addition I've modified the bogies with a far more workmanlike vacuum cylinder than the DIY job I had used before Look on Ebay or Aliexpress for VW/Audi turbo waste gate vacuum cylinder. I'm pretty close to marrying up the bogies with the frame and doing the full instal of the coach body. More later Pete
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Post by doubletop on Dec 11, 2018 9:58:25 GMT
I've been on a bit of detour. I realised that I could install the bogies in the frame and add the coachwork on top with the whole lot on my bench but how was I going to get it into my van? Moving the thing for test runs at the I had assembled the various parts on the van link rail and pushed it into the van. Doing the reverse on the return from the track. This clearly wasn’t a long-term solution, especially when the inside of the autocoach was likely to fill up over time with tools, water tanks, lunch boxes and beer coolers😊.I needed some sort of mobile stand that I could use to move the autocoach into an out of my van and be at a useful height for working on it. As I think I’ve said before, I’m no welder, but I’m getting a bit better and nothing that an angle grinder and a lick of paint can’t help fix. This stand needed to be 2.2 metres long and I realised that being able to have the autocoach at working height I could make a lower storage rail. To be useful the vertical uprights needed to be far enough apart to allow footboards to clear them, without having to remove the footboards. The upper cross member needed to be high enough to clear coach roofs and the chimney of my Dart. Lower deck being fabricated. Initial uprights and crossmember. This was a test fabrication using only 25mmx25mmx1.6mm tube I had laying around. If I wanted to use the top deck for working on the loco I really needed to use the 50mmx25mx3mm tube I’d used for the lower deck framework so a rework was in order. Wagons installed. It rolls around the garage nicely and is remarkably stable. It easily takes my 100kg weight sat on the centre upright frame with minimal deflection (there are no castors on the centre fame). . Now back to the autocoach. I really don’t like the padded seats as the roof. I may change it to a solid roof like the Toad on the lower rack. I’m not that fussed if the PAX don’t like it. Pete
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stevep
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Post by stevep on Dec 11, 2018 10:00:59 GMT
Looking great Pete.
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Post by doubletop on Dec 11, 2018 20:09:02 GMT
Thanks Steve For now I'm taking a bit of a time out on this project. There are aspects of it I'm not happy with and until I've reconciled them I'm not planning to do anything new. There's also Christmas to deal with and starting anything new and not being able to see it through to a conclusion is always a recipe for a cock up. Then again it is summer here so not doing anything is unlikely.... Pete
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Gary L
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Post by Gary L on Dec 13, 2018 0:55:28 GMT
[Snip] In addition I've modified the bogies with a far more workmanlike vacuum cylinder than the DIY job I had used before Look on Ebay or Aliexpress for VW/Audi turbo waste gate vacuum cylinder. Pete, that looks like a superb idea for a vacuum actuator! Over here we can get proprietary vacuum actuators from a specialist miniature railway supplier, but in our club we haven't found them completely satisfactory. By contrast anything made for the automotive industry these days has to be highly reliable. I have no idea what a 'turbo waste gate vacuum cylinder' is or does, but they are readily available over here and relatively cheap. I can only see one possible snag, which is that it is normal for there to be a pass-through valve in the diaphragm, so the train pipe exhausts the reservoirs via the actuators to pull the brakes off. I'd be very surprised if these auto parts were so fitted. Have you come up with a solution for this as well? Gary
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Post by doubletop on Dec 13, 2018 5:53:29 GMT
.................. I can only see one possible snag, which is that it is normal for there to be a pass-through valve in the diaphragm, so the train pipe exhausts the reservoirs via the actuators to pull the brakes off. I'd be very surprised if these auto parts were so fitted. Have you come up with a solution for this as well? Gary Gary I didn't quite follow you I'm afraid. These cylinders are good for systems requiring brakes on with vacuum applied, brakes off when the train pipe is open to atmosphere. The cylinders don't have any bypass vents. It just requires and simple two way port brake valve. All the cylinders I've come across don't have any bypass arrangement. I believe there is a way to use the type of cylinder with the vacuum holding the brakes off but I'm afraid I've not had any experience of them. Pete
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stevep
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Post by stevep on Dec 13, 2018 10:23:50 GMT
Pete,
Most of the vacuum brake systems fitted here work like this. The vacuum is applied to one side of the piston, and pulls it toward one end of the cylinder. When the piston get near the end it physically opens a valve which then connects that side of the cylinder to the other - which also has a large vacuum reservoir (oxymoron) attached to it. So the piston remains at that end, with vacuum applied both sides.
When the train pipe is then opened to atmosphere, the vacuum on the other side of the piston (with the reservoir) pulls the piston, applying the brakes.
The reservoir means that the reduction in volume of the evacuated space when the piston moves is significantly less than without it, meaning that the level of vacuum is maintained, with the associated force.
Re-applying the ejector (or vacuum pump) to the train pipe then pulls the brake off again, returning everything to its previous situation.
Hope that's clear.
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Post by Deleted on Dec 13, 2018 10:28:37 GMT
.................. I can only see one possible snag, which is that it is normal for there to be a pass-through valve in the diaphragm, so the train pipe exhausts the reservoirs via the actuators to pull the brakes off. I'd be very surprised if these auto parts were so fitted. Have you come up with a solution for this as well? Gary Gary I didn't quite follow you I'm afraid. These cylinders are good for systems requiring brakes on with vacuum applied, brakes off when the train pipe is open to atmosphere. The cylinders don't have any bypass vents. It just requires and simple two way port brake valve. All the cylinders I've come across don't have any bypass arrangement. I believe there is a way to use the type of cylinder with the vacuum holding the brakes off but I'm afraid I've not had any experience of them. Pete Hi Pete/Gary I've just read your comments and in particular Pete's comment re vacuum holding brakes off. I believe the term is auto-braking, if so I can say that 'Doncaster' uses this form of vacuum braking which is how the prototype themselves work. Loosing vacuum in say a loco becoming disconnected from it's train will apply full brake to both the runaway engine and it's disconnected train. Pete
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Gary L
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Post by Gary L on Dec 13, 2018 16:57:55 GMT
Gary I didn't quite follow you I'm afraid. These cylinders are good for systems requiring brakes on with vacuum applied, brakes off when the train pipe is open to atmosphere. The cylinders don't have any bypass vents. It just requires and simple two way port brake valve. All the cylinders I've come across don't have any bypass arrangement. I believe there is a way to use the type of cylinder with the vacuum holding the brakes off but I'm afraid I've not had any experience of them. Pete Hi Pete/Gary I've just read your comments and in particular Pete's comment re vacuum holding brakes off. I believe the term is auto-braking, if so I can say that 'Doncaster' uses this form of vacuum braking which is how the prototype themselves work. Loosing vacuum in say a loco becoming disconnected from it's train will apply full brake to both the runaway engine and it's disconnected train. Pete SteveP and Pete Greenglade - thanks, that is a much clearer explanation than I could manage! Yes, over here we tend to think "Automatic Vacuum Brakes" (erm) automatically. It sounds like Pete Doubletop is using "Simple" vacuum brakes, which become inoperative in the event of the train parting. Nonetheless this is too good an idea to lose. I think we can probably exclude dismantling these automotive units, they don't look to be dismantleable, so any extra valve would have to be external. Would a one-way valve adjacent to the vac reservoir do the same job I wonder? And is there a convenient source of such a thing that would be reliable and leak-tight with the small pressure differences we are talking about? Gary
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stevep
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Post by stevep on Dec 13, 2018 19:53:38 GMT
The valve is normally built into the vacuum cylinder so that the piston physically touches it. The main reason being that the force on the piston is quite substantial compared to that needed to open the valve.
However, an external valve would work just as well - it just needs to be set up so that when the piston moves to one end of its travel (brakes off), something (maybe the operating lever) touches the valve to open it. The only drawback I see is that you will need two holes in that end of the cylinder - one for the train pipe, and the other to connect to the valve.
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Post by Deleted on Dec 13, 2018 20:34:58 GMT
Hi Gary
You can find the drawing for 'Doncaster's) vacuum cylinder on page 23..alas I'm not sure if I posted a drawing of the relief valve or not. Looking at the drawing you can see where the valve fits, the fine spindle sits just below the metal collar below the diaphagm. The diaphagm only has to move the smallest of amount to brake the vacuum and apply full brake. I may be able to post the drawing once I'm feeling better..currently diagnosed with pneumonia..again...lol
Pete
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Gary L
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Post by Gary L on Dec 14, 2018 1:22:59 GMT
Hi Gary You can find the drawing for 'Doncaster's) vacuum cylinder on page 23..alas I'm not sure if I posted a drawing of the relief valve or not. Looking at the drawing you can see where the valve fits, the fine spindle sits just below the metal collar below the diaphagm. The diaphagm only has to move the smallest of amount to brake the vacuum and apply full brake. I may be able to post the drawing once I'm feeling better..currently diagnosed with pneumonia..again...lol Pete Pete Sorry to hear you are ill. Hope you will make a swift recovery (sounds like you've had some practice!) Your info is helpful, though no, I don't think you did post the drawing of the valve. Wouldn't it be great if somebody found a proprietary item that would do the job, just like Pete's vac actuator! Maybe a big ask, but who knows? -I'd never of dreamed of finding a suitably sized vacuum actuator on a car! I have a feeling that the ideal valve would be a flap valve: simple, compact, and should seal readily with a very small pressure differential. I fully agree with SteveP's point that in our scales they are usually actuated by the piston or diaphragm movement, but I am not sure that this is essential. I found a couple of our proprietary plastic valves had lost the 'stem' that opens the valve on contact, but the units didn't seem to function noticeably worse. As far as I can see in full size, practice varies. Sometimes the valve is outside the 'cylinder,' sometimes inside, but I haven't come across an example with a prodder stem incorporated. Full size is not necessarily a reliable guide though, because in miniature we tend to separate the reservoir from the actuator, whereas in full size the two are typically combined. Also, full size generally uses a higher vacuum than we do. I wonder if we ought to take this discussion to a separate thread? Gary
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Post by Deleted on Dec 14, 2018 1:36:16 GMT
Gary when I recover I'll try to post the valve drawing. I would say that the valves I made are a prodder stem type. They sit outside on the lower section as shown on the drawing on page 23. IIRC they have the prodder(spindle), a stainless ball and spring which when assembled sit in a horizontal position. I think that I covered them in detail in my build...it can't be to many pages after 23. I'll try to take a look tomorrow. Thanks for your well wishes...I'm back to see the doc tomorrow...here's hoping the blood results didn't turn up anything nasty.
Kind regards
Pete
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Post by Deleted on Dec 14, 2018 1:41:22 GMT
I just had a quick look, god knows why I didn't before..christ the details are on the same page...lol
Hope they are of interest...
Pete
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