Re: Rolling Stock for Banavie Road

[JimG]

Plastikard Coaches for Banavie Road

Just catching up on this, those sides really do look very good. As they are non commercial I wouldnt worry about the time they take to complete, anyway its only a fraction of the time it takes to draw and program the cuts. It takes me longer to draw up the parts and program the laser path than it would to cut parts by hand, the payoff is, as you say, the accuracy that cant be achieved by convention means (at least not by me!)

Cynric,

I think I can get the times faster than the processes are taking now.  The really slow one is the 3D element for bolections and I could possibly write a bit of code that would speed that up.  But if I can cut an eight compartment coach in five hours with all the bolections cut,  then that is way faster than I could ever do it by hand.

Now that I'm getting to know the CAM software better,  the preparation for cutting is getting quicker.  I find that the original basic CAD drawings of coaches to cut the sides are fairly easy to do - its basically copying a template of the compartment windows and panels along the length of the coach.

Now that I know the machine and can trust it,  I can walk away from the machine and leave it untended except for tool changes.  The machine control software has the facility to predict the times between changes so I can go and do other things and know when to return to change a cutter.  So the CNC machining time is not captive time at the machine.

The one big drawback is that I cannot do square cornered panelling. 

Jim.

 

[JimG]

Plastikard Coaches for Banavie Road

Nothing world shattering to report but just to say that I am still plugging along with the milling machine - tending to feel like a dinosaur with all these Shapeways threads on the go.

But the work over the past month has been more of the "what can I get away with" empirical work. To date I have concentrated on some sides and ends for a fellow S Scale modeller and in working out how they would all go together - i.e. sides and ends to full width and length and with internal chamfers on the joins, or sides inside ends with the width of the ends reduced to accommodate the sides. I am now starting to sympathise with etched kit designers.

Here's the work so far on one coach - a four wheel Drummond NBR Brake Third



The sides extend to the duckets and butt up against the inner ducket former. The two parts of the ducket panelling join the inner ducket former to the brake end. The main problem area was juggling with styrene thicknesses around the brake end side windows. This is a "Beta Test" to see if things will go together fairly easily, but I expect that there might be some alterations in the brake end area. The problem is the internal construction of the coach which can become obvious through these large rear windows. This is also a proving ground for my Drummond Caledonian four wheelers which are fully glazed across the end and will show even more of the guts.

Jim

 

[28ten]

Plastikard Coaches for Banavie Road

That looks very good Jim. You might feel like a dinosaur but I bet the surface finish is much better on your sides.
Your comments on fitting sides to ends are interesting as I always find it a conundrum when designing laser cut parts, the butt joint is easier and stronger but I find a 45deg mitre looks so much better for things like brickwork. As always drawing the initial parts is the easy bit, it is how you design them to fit them together that sorts the men from the boys 

 

[Phill Dyson]

Plastikard Coaches for Banavie Road

That looks very good Jim. You might feel like a dinosaur but I bet the surface finish is much better on your sides.

Yes I agree, the end results speak for themselves  8) 8) 8)

 

[Steph Dale]

Plastikard Coaches for Banavie Road

Jim,

They look fantastic!  In terms of fitting the sides/ends I think I'll stick with Jenkinson's recommendation to make the join adjacent to the beading on the end of the coach - so the sides are full length and the ends narrowed slightly.

The only major difference I've got is that I won't have his style of removable ends.  I understand why he went that route, but I think i can get away without it...

Steph

 

[JimG]

Plastikard Coaches for Banavie Road

Your comments on fitting sides to ends are interesting as I always find it a conundrum when designing laser cut parts, the butt joint is easier and stronger but I find a 45deg mitre looks so much better for things like brickwork. As always drawing the initial parts is the easy bit, it is how you design them to fit them together that sorts the men from the boys 

Cynric

In the case of these coaches, we've decided to go with the ends within the sides type of butt join,  principally because the such joins will be well disguised by the panelling on the ends of the coach.  I also have to accede to an element of cowardice when I looked at the possible problems with mitre joints on the complex curves of the ducket ends. 

Jim.

 

[lancer1027]

Plastikard Coaches for Banavie Road

Very impressive Jim

 

[JimG]

Plastikard Coaches for Banavie Road

Jim,

They look fantastic!  In terms of fitting the sides/ends I think I'll stick with Jenkinson's recommendation to make the join adjacent to the beading on the end of the coach - so the sides are full length and the ends narrowed slightly.

The only major difference I've got is that I won't have his style of removable ends.  I understand why he went that route, but I think i can get away without it...

I have also given up on the removable ends.  I now glaze from the top rather than one piece of glazing inserted from the end,  so I have no real need to have the ends removable.    My earlier uses of DJ's words and music had fitted,  removable ends and I think that I remember it being a fair bit of work to get really good joints,  and if the ends had any curving,  like a lot of Pre-Grouping designs,  it was a fair bit of work to get the end curves exactly right and to stay that way when you didn't have the facility of permanent attachment to the body to help.

Jim.

 

[28ten]

Plastikard Coaches for Banavie Road

I agree on the ends, more removeable bits just make construction more complicated. I may have missed it but what are you using for the roof?

 

[JimG]

Plastikard Coaches for Banavie Road

I agree on the ends, more removeable bits just make construction more complicated. I may have missed it but what are you using for the roof?

I've been dodging that. 

I'm looking at using the mill to shape a wooden armature,  then cover the top of that with thin sheet Plastikard to which I can attach rain strips and gutters.  The roofs are straightforward plain arc roofs,  so no major problems foreseen in doing that.    In previous coach ventures,  I've actually built the roofs with ribs and stretchers from Plastikard - a bit like model aircraft fuselage building - then covered them with a base wrapping of heavily grooved 20 thou sheet to let it bend easily,  then sand that smooth and finish off with a smooth 10 thou sheet cover and then paper to simulate canvas.  I've just looked at a Midland clerestory roof I did that way some fifteen years ago and it is still sound,  and hasn't warped.  There were plenty of ventilation holes in the sub-structure to avoid trapping Mekpak in the structure.

One thing I am contemplating is fixing the roof permanently to the sides and making the coach body split from the frame at floor level.  I picked up that method in an article somewhere and thought it worth a try to see if it had advantages over the removable roof style of construction.  The roof and sides might make a stronger body part than the (almost) traditional underframe and sides with lid on top.  The problem might be arranging that glazing can be inserted from the bottom. [Edit]  Just looking at the elliptical roofs on the NBR stock,  a fixed roof might be better.

Jim.

 

[28ten]

Plastikard Coaches for Banavie Road

I have always gone for fixed roofs as I think it is easier to conceal the join at floor level, the harder part to me is shaping the roof profile and I have always tended to go with a rolled metal roof and some formers, but as I have said elsewhere I am useless with plasticard.
Talking of Midland coaches here is another approach http://www.mousa.biz/info/

 

[JimG]

Plastikard Coaches for Banavie Road

Talking of Midland coaches here is another approach http://www.mousa.biz/info/

Very interesting.  I hadn't seen this work from Bill Bedford before.    I note that Bill doesn't state any prices for his coach frames.  I believe from threads on 3D printing here and in other places that the costs are proportional to the volume of a part which might render these frames quite pricey,  especially in the larger scales.  I can see a market for people who might want something to stick sides ends and roofs to - maybe even milled Plastikard ones  - but I think I might stick with the Jenkinson method for a building frame since it is quite easy to construct,  although I can see me having to re-think the method if I stick the roof on,  with the parting line at floor level.

Bill's roof frame is not unlike what I did with my clerestory roof in Plastikard.  I don't know how well his "X" shaped frames will support roof materials.  I put my formers quite close together to avoid the roof covering sagging between supports over time.  The reason I'm thinking of making a wood armature is to provide an infinite number of supports to completely avoid any sag. 

Jim.

 

[Simon Dunkley]

Plastikard Coaches for Banavie Road

In previous coach ventures,  I've actually built the roofs with ribs and stretchers from Plastikard - a bit like model aircraft fuselage building - then covered them with a base wrapping of heavily grooved 20 thou sheet to let it bend easily,  then sand that smooth and finish off with a smooth 10 thou sheet cover and then paper to simulate canvas.  I've just looked at a Midland clerestory roof I did that way some fifteen years ago and it is still sound,  and hasn't warped.  There were plenty of ventilation holes in the sub-structure to avoid trapping Mekpak in the structure.

Two questions, Jim.
Firstly, was the 20 thou sheet grooved on the outside?
If so, then why sand it smooth and add the 10 on top? If you had left it as it was, it would have given a good impression of the planks underneath the canvas. Was there a technical reason for this?

Please do tell...

 

[JimG]

Plastikard Coaches for Banavie Road

Two questions, Jim.
Firstly, was the 20 thou sheet grooved on the outside?
If so, then why sand it smooth and add the 10 on top? If you had left it as it was, it would have given a good impression of the planks underneath the canvas. Was there a technical reason for this?

Simon,

It was grooved quite deeply on the outside (with a skrawker) to get it to bend easily into the contours of a Midland clerestory roof.  And I like my roofs smooth.   

But the grooves were at a relatively coarse pitch - probably too wide to represent the planking on a coach roof.  I would probably have had to add the smooth sheet anyway and score it lightly to represent the planks.

Jim.

 

[JimG]

Plastikard Coaches for Banavie Road

Just a word of warning to anyone who might be contemplating using the Seklema Multimat - its thickness is not all that constant. 

I've just had a fairly exasperating week working on the coach sides.  I had initially started off referencing the cutter height to the top surface of the styrene sheet and that had given me some problems with the variations in thickness that you can get with styrene.  Last week I decided to alter my methods and reference all the cutter heights from the base of the styrene.  Then I could use a thicker sheet and surface cut it to the thickness required,  then do all the milling of the panelling.  This method should have guaranteed that all the depths of cuts should be correct,  but on the various attempts and tests I had done,  they were anything but that.  I tended to start looking at the CNC setup for the problem.    The software sends data out to the mill and expects it to follow the data accurately.  There is no form of positional feedback from the machine to the software (except for limit switches) so it is possible for the mill to do something different to what is intended.  So I've spend days with a dial gauge,  a micrometer and digital calipers trying to tie down what was or wasn't happening.  I never even thought about the Multimat.  I had checked the table under the Multimat and it was about two thou out along its length.  That was as close as I could get the Contiboard to being flat and I had accepted that.

However,  I thought I might just check the Multimat.  It's not easy to measure directly because its surface is resilient,  so I laid a steel rule on it and set the dial gauge on the rule's surface,  and found that I had a 15 thou variation in six inches.  At last I had my reasons for the errors.  I had been setting tool height at the edge of the Multimat with a piece of metal of a known thickness then the tool was moving further into the centre of the material, and the Multimat,  to start the cutting.

I also checked the unused bit of Multimat with the calipers and that shows similar amounts of difference around the edges.  I have never seen a tolerance for the thickness of the Multimat.  I had assumed wrongly that it would be quite tight in tolerance since it was intended for engraving where cutting depths are quite small and variations in material thickness would become quite obvious.    I might be able to query the manufacturer via their web site to see what they say.

In the mean time,  I'm back to looking at low tack double sided tape and I've googled a few suppliers so will get a roll of that to see how it does.

Just in case anyone else was looking at purchasing Multimat (at £65 /sq.ft  :shock: ) and expecting constant thickness.

Jim.

 

[28ten]

Plastikard Coaches for Banavie Road

That is a bit of a pain. 15 thou is quite a variance, thin double sided tape on mdf sounds a cheaper alternative and, although it is horrible stuff, 18mm mdf is normally fairly consistent in depth across a board.

 

[JimG]

Plastikard Coaches for Banavie Road

That is a bit of a pain. 15 thou is quite a variance, thin double sided tape on mdf sounds a cheaper alternative and, although it is horrible stuff, 18mm mdf is normally fairly consistent in depth across a board.

I'm sort of licking my wounds at the moment.    I should have checked the product before I started using it but I assumed (dangerous : that it was flat within quite tight limits.  I still haven't had a response to my message to the maker.  I have to wait for a bit until my roll of low tack double sided arrives so plenty of time to edit the next edition of the Society magazine. 

Jim.

 

[28ten]

Plastikard Coaches for Banavie Road

If the email is from identitag.co.uk then it will be dead as they have been taken over. I have found them a pain to contact and I want to order £200 of Rowmark, I guess it is better to call there

 

[JimG]

Plastikard Coaches for Banavie Road

If the email is from identitag.co.uk then it will be dead as they have been taken over. I have found them a pain to contact and I want to order £200 of Rowmark, I guess it is better to call there

I sent a message to the actual maker in Germany via their web page.

When I visited Identity (now Trotec) in Bristol,  they were in the process of changing over to a new accountancy system and there seemed to a sort of gentle chaos in the office  - but otherwise I was well treated.  They certainly had what looked to be a well stocked warehouse across the road from the main office and I suspect that the person who looks after that is the person who really knows what they have got and where it is,  and he doesn't get to look at emails. 

Jim.

 

[JimG]

Plastikard Coaches for Banavie Road

There has been some progress.

After the problems with the Multimat, I did a search around to see if there was anything else which might be suitable and eventually came upon Letraset Low Tack double sided tape. I find this tape to be really good and almost as good in operation as the Multimat. It is reckoned to be re-usable but on a milling machine table with all the swarf around, it's easier to use a new bit than try and clean of a previously used bit.

I've also changed my modus operandi. Previously I had referenced all my cut depths to the top surface of the Plastikard and, with the variations in styrene sheet thickness, this was giving me problems with depths of cuts. I discovered that my CAM program would also work by referencing the bottom of the material, so I now use that method and I now start off with a sheet that is slightly too thick and surface cut to the maximum thickness required then cut to all my other thicknesses. This has now brought an element of predictability to the process, and piles of white swarf.

I've now cut all the sides I need for two rakes of five coaches and I thought it about time to actually start putting some together. Because my quarterlight glazing will be at a different plane to the droplight glazing I had to give a bit of thought on how I could hold the glazing in place. I like my glazing removable to make painting a bit easier so I had to work out some way of doing that with the David Jenkinson construction method. Eventually I decided on milling a thick inner coach side with the levels to suit the coach side shape and with slots to hold the glazing material - in my case 10 thou Plastiglaze. Here's a pic of two inner sides of the four compartment first followed by a closer shot of the slots for one compartment.





These are cut from 80 thou Plastikard and the small square holes in the lower sides are for ventilation. The quarterlight slots are 12 thou deep to give a bit of clearance for the 10 thou glazing and the droplight slots ate 22 thou deep to give clearance for the glazing plus the 10 thou droplight frame.

Before sticking the outer sides to these parts I formed the curved lower tumblehome sections of the outer sides in the oven. I had machined a male mould in alloy some time ago and I fitted a couple of clamps to hold the sides in shape. The next pic shows the mould with the clamps released and the following one shows the mould with a side clamped in it before being put in the oven. The sides are "cooked" for about ten minutes at 100C but at that temperature I've left a side in the oven for a bit more than ten minutes and it survived with no apparent over-cooking damage.





Putting the two parts together wasn't too difficult. The inner sides were machined shorter to allow for 20 thou thick ends and the main concern was to line the sides laterally so that there was an equal 20 thou difference at each end. Holding the sides vertically with the toolmakers' clamps meant that the bottoms of both sides could be lined up easily.



I used the minimum amounts of Mekpak to join the sides - basically along the top and bottom seams and a small dab in the bottom of each droplight slot. I don't like getting too much Mekpak around Plastikard - too much can have longer term knock-ons.
I had cut out a pile of droplight frames from 10 thou Plastikard



and one of these was stuck to the glazing material to make up the droplight, and the glazing for the two quarterlights was cut, then the lot inserted in one compartment to see how it looked.



I've only half inserted the left hand droplight glazing. Apologies for the rather dirty glazing material - since it was only a trial I wasn't taking too much care in how I handled it. I'm happy with the end result and, of course, I can have droplights in open positions as well if I want.

On a parallel course, I've done the artwork for a nickel silver etch of sprung "W" irons for the coaches and I might see the results back from PPD in the coming week.

I've also just been milling the ends for the coaches as I write this, so I will form a couple of them and see if I can get a body together fairly soon.

Jim.