After much pondering (variations on that phrase get used a lot around here), I have decided to go with the simplest (relatively) solution for propelling the traverser, a single lead screw. It was always one of the options and after chatting with Trevor Marshall and Ryan Mendell at lunch, it was decided. Ryan deals professionally with assorted ad hoc projects and he tells me that lots of people try belt drives and fail to consider the tension required to get them to work properly. Since I have no desire to see if the traverser baseboard will bend under sustained tension, lead screws are the best alternative.
I conflate ball screw with lead screw in my thinking but I understand a lead screw is better for my applications since there is not requirement to handle heavy loads or avoid backlash of a couple of thousandths of an inch. My concern with this option was that aligning the screw, table and baseboard would be tricky and prone to binding. Ryan suggested attaching the nut (brass bit in the picture) so that it floats a bit. I thought about it and I have a plan to do that.
So, the alternatives considered:
- single lead screw
- single belt drive: two pulleys doing the same job as the lead screw but avoiding fine alignment challenges
- two sychronized steppers with two lead screws or two belts attached to each end of the table.
- one belt attached to each end of the table belts driven by pulleys mounted on a common shaft attached to a single stepper.
- one belt routed so that it was attached at each end of the table. This is a simplified version of how printers are designed.
As you can see, I have been looking at all kinds of fun approaches. I still like the single last one but, besides the tensioning challenge, it represents a substantial increase in required hardware with an estimated 5 idler pulleys in addition to the driver pulley as well as roughly 8 feet of belt. None of that is especially expensive on a per unit basis but the total adds up. At that point, I am would be investing in additional entertainment value.
I ordered an 8mm lead screw, nut, flexible coupler and bearing combo of the required length (sadly not available locally as far as I could discover) and it arrived yesterday. Actual installation work will wait on vacation and the right mood.
I spent a long weekend traveling to watch migrating birds so no active modelling happened. On the other hand, the evenings do provide some quiet time to do some reading. One of my finds at the Great British Train Show 2018 was Layouts to Inspire compiled by Mike Merritt for the Gauge O Guild. The Gauge O Guild is the UK based association of 7mm (and the other “O”‘s including 1:48) modellers so naturally the layouts featured are all of some flavour of “O” scale.
An entire book of layout features is just the sort of thing I like. The layouts in the book were selected by the members of the guild and cover everything from indoor/outdoor garden layouts to micro layouts. O Scale Magazine contributor Neville Rossiter’s Bay Ridge Harbor Rail Road makes an appearance but otherwise it was all new to me. The photography is excellent and the articles are generally in the layout creator’s words which gives insights into how they go about the hobby.
The only downside for an inveterate layout planner like myself is that not all the articles include a track plan. This is a foible of British model railway journalism as far as I can tell since I have noted the same lack in some articles in UK periodicals as well.
Inspire was published in 2016 but does not appear to be still available. I acquired mine from a vendor at GBTS 2018 so presumably one has to get lucky at a show.
My initial intent for ensuring sufficient rigidity in Comstock Road’s baseboards was to achieve the equivalent of a solid top with a combination of subroadbed and sheet foam. As time has passed, I have observed that the subroadbed does little to prevent twisting and that there isn’t that much area for the foamboard to go. I am reluctant to commit the alignment of the trackwork to wishful thinking so I decided to make the diagonal bracing overt.
An added advantage (assuming it does the job) is that my traverser won’t need a bottom. This will simplify the design and make the mechanism easier to install and access.
Here is the traverser section waiting for the glue to set. I am using some 1/4″ fir ply strips I cut up for a prototype since it will get them off the wood rack. I don’t really like the stuff since it is one big splinter dispenser but it does mean I don’t have to cut any more plywood. Note also that advantage of portable baseboard sections: the ability to tip the thing on its side for working on the bottom. Wiring without dripping solder on yourself is to be recommended.
One of the things I like to do when I am traveling (and when I am not 🙂 ) is visit public libraries. It gives a glimpse into local literary tastes and sometimes interesting public architecture. The Halifax Central Library is definitely worth the visit. The building is almost new and impressively not just a big glass box. I also enjoyed the book return conveyor/elevator/sorting system which is purposely visible at points.
One of the book sections I am sure to go through is, of course, the model railroading and railroad history. In this case, I discovered a copy of Modelling Branchlines: A Guide for Railway Modellers by David Wright. My host agreed to sign it out for me and I read through it over a couple of days.
My initial impression was that this book was a bit of an odd duck by North American publishing standards. Rather than addressing a specific area of modelling technique, it covers a “vertical” segment of the hobby, the UK branchline. It includes a general history of branchlines in the UK, a basic overview of general layout construction methods, layout plans based on specific prototypes, some freelanced plans, some specific detailing and modelling projects and some advice on colouring with prototype reference photos.
This unexpected approach is, once one gets used to it, an interesting read. The general technique sections provided some useful ideas that I want to try. I consider the real meat of the book to be the prototype line information and associated layout plans. The section describing the construction of a stone station building from card and modelling clay covers an approach I have not seen described in detail and that I definitely want to try.
Modelling Branchlines is in print and available from the usual online behemoth. If you are interested in the prototype subject matter and some excellent trackplan treatments thereof, this book might be worth picking up.
I have the reference points of the main subroadbed (joints and end) secured. This allows me to exercise the advantage of the “cookie cutter” approach which is smooth grades. Grades, on a tiny switching layout? Yes, indeed. The end of the CNR GECO spur which serves as Comstock Road’s inspiration features a grade near its end that I estimate to be on the order of 6%, possibly more. Insane on a class one main line but not uncommon on industrial trackage where a switcher would not be expected to manage more than a couple of cars. I want to feature some small changes in grade to provide scenic interest and to capture the fact that Scarborough is not flat from a railroad point of view.
So, recent progress includes splicing the end bits of plywood on to the main piece. I used 3/4″ brass Robertson screws since those were what was on hand.
And installed supports at the main reference points using 1×2, 1×3, glue and yet more Robertson screws.
I mocked up a theoretical 8% grade for the back track. Eight feet doesn’t sound like much of a change in elevation but seen from the side it looks mighty high. I think I can ease that off to six feet or so and get the desired effect. Especially if I drop the front track a few (4?) feet to create a plausible slope.
Speaking of Robertson screws, I thought my fellow Canadians would be amused by the fact that some of what I am using are the original product passed down from others.
For non-Canadians who may not be among the enlightened, what is the big deal about Robertson screws? Besides being near impossible to strip, this:
That screw and driver are horizontal. No magnetism is involved.
I dropped a PDF file of the Comstock Road Templot plan at a local print shop yesterday only to discover that the large format printer was down. With some trepidation, I left the job in their hands (It is easier to ensure “no scaling” when you are there to remind them) and returned to pick up my printout today. The job cost me $25 CDN and I don’t have much concept of whether that is a lot or not but I do have a very good idea of how much time is saved by not having to cut and paste some 40 or so 8.5×11 sheets of paper together so I am calling it a deal.
I answered a co-worker’s enquiry about the contents of the tube by unfurling the drawing on the office floor. Many of my colleagues being of the engineering persuasion, this drew a crowd while I enthused about the project. Hopefully I did not alarm anyone with my excitement.
Here is a view of the finished product rolled out on the baseboards over top of assorted building materials. Comstock Road will probably never look this pristine again but I can call this a view from the traverser. I checked things with digital calipers and as far as I can tell the whole thing is bang on. Which is close enough.
While I was out on the weekend acquiring my table-leaf fasteners, I also picked up fasteners for the fasteners as well as assorted hardware and materials for constructing the backdrop and lighting valance. I have a rough plan in mind but I wanted to verify the height of the lower edge of the valance and the top edge of the backdrop. While I was at it, I got out the LED strip that I plan to light things with.
Here is the whole mockup in final form lit only by the LED strip. It looks reasonably bright in the photo but in person I found it a bit dim. I will have to consider a second strip although normally the room lights will also be in play.
I determined that the top edge of the backdrop is visible to anyone about 5’4″ or shorter. From what I can tell from photos of UK model railway exhibition layouts, obscuring the top edge of the backscene is not considered absolutely necessary. The backdrop as mocked up uses two foot wide material so I think this is a reasonable compromise.
Here is the mockup with the room lights on just for the curious. Note that I do not intend to have a pink coloured backdrop.