Brian Daniels
Western Thunderer
I thought of your coach build today as I was stood next to a duel braked BG so I took a couple of pictures of the airbrake set-up for you.
Building an MMP RMB - a box of delights
- Thread starter Heather Kay
- Start date
Heather Kay
Western Thunderer
As the 57xx build reaches its conclusion, thoughts are inevitably returning to this coach build.
Next on the underframe is the brake gear, and I want to include a representation of the automatic brake calibrator gizmo that Bob posted information about earlier in the thread. Having a few minutes to spare between coats of paint, I sat down with Bob's info and sketched out the main dimensions.
I've marked on here average dimensions, because the drawing showed a variety of lengths for the rod on the left which is the part that moves in and out of the main body. The figures in brackets are the size of the materials I need to use. So, tube of 2.3mm OD and wire of 0.6mm.
With the 3D visualisation, I can work out where the brackets fit, where the air cylinder goes, and how it all kind of fits together in amongst the frames.
Next on the underframe is the brake gear, and I want to include a representation of the automatic brake calibrator gizmo that Bob posted information about earlier in the thread. Having a few minutes to spare between coats of paint, I sat down with Bob's info and sketched out the main dimensions.
I've marked on here average dimensions, because the drawing showed a variety of lengths for the rod on the left which is the part that moves in and out of the main body. The figures in brackets are the size of the materials I need to use. So, tube of 2.3mm OD and wire of 0.6mm.
With the 3D visualisation, I can work out where the brackets fit, where the air cylinder goes, and how it all kind of fits together in amongst the frames.
richard carr
Western Thunderer
Heather
SO thats 3/32nd OD tubing, you might be lucky and find some with an ID of 0.6 but it might need tobe a nit more than that.
A nice idea though
Richard
SO thats 3/32nd OD tubing, you might be lucky and find some with an ID of 0.6 but it might need tobe a nit more than that.
A nice idea though
Richard
Heather Kay
Western Thunderer
I have various tubes in stock, one of which will be close I'm sure. The plan is probably to either use larger wire, or just fill the end of the tube with solder.
Heather Kay
Western Thunderer
Let choirs sing and trumpets play! I've started work on the RMB again today!
The leedle grey cells 'ave been worrying away, and I set about fabricating the self-adjusting brake doodahs.
From my notes, I have an outer brass tube 2.5mm OD/1.5mm ID, 15mm long. Inside that a brass tube sleeve, 1.5mm OD/0.6mm ID, 20mm long. Through the whole thing is 0.6mm brass wire, with a pivot bracket formed at one end by hammering flat and drilling through.
Good enough, I think.
The leedle grey cells 'ave been worrying away, and I set about fabricating the self-adjusting brake doodahs.
From my notes, I have an outer brass tube 2.5mm OD/1.5mm ID, 15mm long. Inside that a brass tube sleeve, 1.5mm OD/0.6mm ID, 20mm long. Through the whole thing is 0.6mm brass wire, with a pivot bracket formed at one end by hammering flat and drilling through.
Good enough, I think.
Heather Kay
Western Thunderer
Sometime next year, after prototyping is finished.
The bracket and spring comprises part of fitting the SAB in the frames. There's a bit of jiggery-pokery to sort out, with the air brake as well as vacuum bits to fit, so I'm building myself up for that stage.
Steph Dale
Western Thunderer
Heather,
Although I'm not a great fan of Mark 1 coaches (and they were still over a year away from the timing of the layout) I do love to see these sorts of details being applied to coaching stock. I seem to have the same sort of masochistic tendencies as you in spending ages modelling bits most people won't see and even fewer really care about.
Which reminds me, I really should finish off my Maunsell 'Nondescript' and 'Thanet'.
Steph
Although I'm not a great fan of Mark 1 coaches (and they were still over a year away from the timing of the layout) I do love to see these sorts of details being applied to coaching stock. I seem to have the same sort of masochistic tendencies as you in spending ages modelling bits most people won't see and even fewer really care about.
Which reminds me, I really should finish off my Maunsell 'Nondescript' and 'Thanet'.
Steph
Heather Kay
Western Thunderer
I seem to have the same sort of masochistic tendencies as you in spending ages modelling bits most people won't see and even fewer really care about.
I am taking that as a compliment.
I now recall why I have been putting off this stage of the construction. The kit provides for a standard vacuum brake system, with "over-the-top" pull rods into the bogie. I am complicating matters by adding in air braking gear.
Craving David's indulgence for reproducing part of the instructions here, but it helps to explain what I think I am trying to do.
First, take note of parts 48, 49, 50, 51, 52 and 53. This assembly lives up in between the main frames. 50/51 are connected to 45, which is on the brake cross shaft. 50/51 form the actuating lever attached to the pull rod into the bogie. Parts 52 and 53 - I am pretty certain - are not wanted on this build, along with 54, 55 and 56, because they are the hand brake linkage for brake coaches.
With me so far? Good.
Now, let's look at Bob's 3D rendering, which I have inverted so it avoids me having to flipflop things in my head all the time.
Am I right in thinking the entire sub-assembly formed of parts 48-53 is not needed? If I have it right, the cross shaft lever (parts 45) is attached to the SAB, which is attached to the pull rod. I need to repurpose some of the unused parts to give me the air brake actuating lever, and provide a crossbeam for the air brake cylinder to sit on.
Having typed all this out, it is making much more sense. I would appreciate confirmation though. Bob?
Here's all the parts for one set of brake gear, including the parts I don't think I actually need for the dual braked combo.
I was sceptical about being able to bend the castings, but they are exactly as advertised. I just took my time and bent the DA valve connection pipe slowly in stages, and it was easy!
Dog Star
Western Thunderer
The 3D illustration of a slack-adjuster in a dual-brake underframe corresponds pretty closely to a carriage which I photographed at Winchcombe in December 2012. The only difference that I can see is the bracket which surrounds the shaft of the SAB... that bracket was not present on the carriage at Winchcombe. On the other hand, Bob has given notice of a SAB having a location bracket at one end and the SAB fitted to the prototype underframe, that I photographed, had no such bracket.
My tuppence worth is to follow 99% of Bob's drawing.
My tuppence worth is to follow 99% of Bob's drawing.
Heather Kay
Western Thunderer
Graham, thank you for that. It helped clarify things in my head. It's so easy to get lost in this kind of detail, forgetting that most of it will be all but invisible under normal circumstances.
This is the mocked-up interpretation of Bob's drawing. It's all loose and held together with long lengths of wire, but it helps me to work out the best locations for the actuating levers and the extra crossbeam for the air brake cylinder.
Already it's obvious the SAB lever is too long, so I'll set about that in this evening's session.
This is the mocked-up interpretation of Bob's drawing. It's all loose and held together with long lengths of wire, but it helps me to work out the best locations for the actuating levers and the extra crossbeam for the air brake cylinder.
Already it's obvious the SAB lever is too long, so I'll set about that in this evening's session.
Dog Star
Western Thunderer
Heather,
This is looking good, do tell where you got the air brake cylinder.
"Mk.1 Coaches" (HMRS, Parkin) has an underframe drawing with sections showing the construction of the cross-girders. My reading of that drawing is that the outer / smaller cross-girder (underneath your SAB rod) comes in two forms... one form for bogies with the pull-rod under the axle and one for bogies with the pull-rod over the top if the bogie headstock - the difference is in the orientation of the lowest piece of angle. I read the photo of the kit underframe as showing a cross-girder for a bogie with the un-equalised brake so you may need to address this point to get the clearance between that piece of angle and the pull-rod.
Bob has omitted this piece of angle in his drawing... not surprising given the (impression of) limited clearance in his very useful 3D illustration.
regards, Graham
This is looking good, do tell where you got the air brake cylinder.
"Mk.1 Coaches" (HMRS, Parkin) has an underframe drawing with sections showing the construction of the cross-girders. My reading of that drawing is that the outer / smaller cross-girder (underneath your SAB rod) comes in two forms... one form for bogies with the pull-rod under the axle and one for bogies with the pull-rod over the top if the bogie headstock - the difference is in the orientation of the lowest piece of angle. I read the photo of the kit underframe as showing a cross-girder for a bogie with the un-equalised brake so you may need to address this point to get the clearance between that piece of angle and the pull-rod.
Bob has omitted this piece of angle in his drawing... not surprising given the (impression of) limited clearance in his very useful 3D illustration.
regards, Graham
Heather Kay
Western Thunderer
Graham, it's the JLTRT cylinder, the one they ship in the Mk2 kits. I've tittivated it by making a ram from brass wire and tube.
I will go back to my sources and look at the cylinder beam. I spotted there were variations, but hadn't twigged why. I was being lazy, and used a simple brass T-section slotted between the main frames. Fitting it between the frames, so it's higher, seemed like too much work, but I will revisit it. May as well try and get it as right as possible.
I will go back to my sources and look at the cylinder beam. I spotted there were variations, but hadn't twigged why. I was being lazy, and used a simple brass T-section slotted between the main frames. Fitting it between the frames, so it's higher, seemed like too much work, but I will revisit it. May as well try and get it as right as possible.
john lewsey
Western Thunderer
You've done a lot since I popped by this morning
Heather Kay
Western Thunderer
I have checked the drawing Graham referred to, and it would be correct to modify the cross member at the shallow end of the longitudinal trusses to match with the equalised/compensated bogies the Dia 99 would have been built with. This would effectively just be a bit of T section fixed to the underside of the crossmember. To be accurate, I should remove the web on the upper edge… lets not go there!
Pragmatically, I'm tempted to leave things as they are.
While checking the drawings, I revisited the Parkin supplement, and found a dimensioned sketch of a typical air brake cylinder bracket. It seems there were as many variations as there were workshops tasked with fitting the gear! It has also reminded me the air brake cylinder is offset away from the vac cylinder, with the SAB on the centreline, so it matches with the original brake linkages, obviously.
Pragmatically, I'm tempted to leave things as they are.
While checking the drawings, I revisited the Parkin supplement, and found a dimensioned sketch of a typical air brake cylinder bracket. It seems there were as many variations as there were workshops tasked with fitting the gear! It has also reminded me the air brake cylinder is offset away from the vac cylinder, with the SAB on the centreline, so it matches with the original brake linkages, obviously.
Bob Reid
Western Thunderer
Like you Heather, I'd be tempted to leave the angle in place. If you look at Brian's Photo's - on the SAB fitted vehicles they've removed that bottom crossmember altogether (and in some cases they just notched the top of it by cutting the original web away) - they used the crossmember above that to mount a bracket for supporting the end of the SAB where it joined the pullrod passing to the bogie needing clearance for the joint. My 3D sketch has it omitted altogether but on a lightweight underframe (missing the extra longitudinal) whereas Brian's photo's as with the frame Dave has provided it's the original 'Heavyweight' underframe.
The only comment aside from the fine job your making so far, is the lever connecting the vacuum cylinder to the brakeshaft either needs to have the end at the cylinder opened on the bottom side to form a hook - see Brian's photo's, or split into two with two additional short plates which formed an articulated joint. - both were put in (as on the Handbraked vehicles, to allow one brake's operation to not interfere with the other.
The only comment aside from the fine job your making so far, is the lever connecting the vacuum cylinder to the brakeshaft either needs to have the end at the cylinder opened on the bottom side to form a hook - see Brian's photo's, or split into two with two additional short plates which formed an articulated joint. - both were put in (as on the Handbraked vehicles, to allow one brake's operation to not interfere with the other.
Heather Kay
Western Thunderer
Thanks for the input Bob.
Now to do it all over again for the other end.
Now to do it all over again for the other end.
Heather Kay
Western Thunderer
I just realised I need to arrange a suitable fitting where the SAB meets the bogie brake rodding. Hmm, thinking cap while I work on the other end of the coach.
Heather Kay
Western Thunderer
I think I must be barking mad. All the detail, and most of it will be lost in the murk. Still, we know it's there.
Meanwhile, up the right way…
I'm off for a lie down in a darkened room, to contemplate dynamos and battery boxes.
Meanwhile, up the right way…
I'm off for a lie down in a darkened room, to contemplate dynamos and battery boxes.