Etched PCB track construction?

[Richard Hall]

I like soldered PCB construction for pointwork, it is pretty robust and check-rail positions can be tweaked slightly before the whole lot is painted.  What I don't like is the way the rail sits flat on the sleeper tops, and the horrible job of cutting hundreds of insulation gaps, then carefully filling them and having to etch-prime the whole lot before you paint it.  So I was wondering about marking the chair bases on PCB strip with etch resist pen then dropping them in etchant, leaving sleepers with small copper pads to solder the rails to.  It seems obvious but I can't find any reference to this method of construction anywhere, apart from a brief mention on the FS160 track page which suggests it as a possibility for plain track.

 

Obvious possible problems: 1. without the copper backing the PCB might not be strong enough. 2. The little copper pads might come unglued from the PCB due to the heat from soldering.  3. I don't know how thick the copper layer is, etching it away might not give a chairplate thick enough to be noticeable. Marcway sell 2.0 x 1.6 sleeper strip which should be thick enough to take care of point 1 and (if my measurements are right) give a rail height to match plastic-base plain track (Finetrax/Easitrac). So what else am I missing?

 

Richard

[2mmMark]

It's been a while since I bought any 2mm Association PCB sleepers but the plain track ones at least were pre-gapped.

 

The copper layer isn't really thick enough to represent a chair base. In 2mm this needs to be about 10thou/0.25mm.  The Association sells etched chairplates for both plain track and pointwork.

 

Soldering to a small pad of copper would indeed be tricky as it's easy to overheat the joint and affect the copper/base material bond. I prefer a bigger area of copper to act as a heat sink.  Cleanliness of the parts is essential and a temperature controlled iron is useful.

 

A quick way to gap ungapped PCB sleepers is to make 2 close cuts in the copper with a knifeblade and then overheat the copper between the cuts which just then pops off the base material.

 

1.6mm thick PCB will be too high to match Easitrac.  1mm PCB is about right as Association sleepers are 0.8mm thick, correct for scale. Unfortunately, anything other than 1.6mm resin/paper backed PCB is very hard to find these days. You can get fibreglass backed PCB in a variety of thicknesses but that's difficult to cut into sleepers as the fibreglass backing ruins most cutters and saws, you need tungsten carbide blades.

 

A couple of years ago, I found a one-off source of 0.8mm PCB suitable for sleeper production and the Association made a considerable investment to ensure a regular future supply. Our sleepers are guillotined rather than sawn so they have a very tidy finish.

[Echo]

I too prefer soldered construction for pointwork. I use Association sleepers with little bits of 0.3mm wire or metal strip under the rails to raise them above the sleepers. The solder forms the shape of the chairs. It is a little tedious, but not too bad in the great scheme of things. Filling in the gaps in the copperclad is not that difficult either.

 

Laurie Adams is producing some etched chairs that look more like Easitrak when they are soldered. I am not sure when they will be available though.

[Ian Morgan]

I would expect problems with small copper pads coming away from the PCB when being soldered. You may be lucky, so it might be worth an experiment.

 

To get the rail lifted above the sleeper, you really need brass chairplates. These will slow down your progress, but do produce the desired effect. Get a tub of solder balls off eBay (I use 0.6mm diameter) so you get uniform size solder blob chairs. You can also chop up solder from a reel to get the same effect, but solder balls are cheap and uniform size.

 

Association sleepers for plain track are pre-gapped, and benefit from filling with Milliput as you say. Point timbers are not pre-gapped. It is possible to produce a gap using a round file to create a gentle dip, which does not need filling and can look OK when painted, but that does not always work out.

 

Ian.

[Caley Jim]

I believe the issue of needing to fill the gap is overstated. I've never done it and I defy anyone to detect that from more than a foot or so away. While I agree that soldered turnouts can be tweaked as you suggest, I see no benefit in building soldered plain track. Easytrac is so much quicker and easier to lay and looks better than most soldered systems.

 

Jim

[bertiedog]

If you really want to cut fibre glass PCB sleepers at home, then the diamond cut off disks that fit Dremel will work. They are very cheap on ebay, and last quite well on the cutting edge.

 

They do take a wide cut, wasting a bit on each pass, but the cut surface is clean. On the insulation, yes you can etch the break, but a lot of work to do it. For straight and curved plain track a jig with a Dremel can be run along the track, using again the diamond wheels to cut a consistent break. It can pay to have the break to one end,leaving no obvious break in the middle.

 

My own 2mm layout uses wood sleepers with PC about every 5 sleepers, with the side cut. Chairs are punched brass strip reduced to hundreds of half chairs and glued on.

The wooden sleepers are sawn from old oak parquet floor blocks on a table top sized bandsaw from Axminster, Any hardish wood will do.

 

Or simply get the Association parts, mine was made before the track was made available.

 

Stephen,

[BG John]

Martin Wynne (85A Models) used to make them in 4mm scale 40 years ago. I think they were machined rather than etched. I used them on my EM layout, and they were still in one piece when I scrapped the layout about 10 years ago. No idea about how it would work in 2mm though. Maybe Martin could help.

[bertiedog]

I have used the solder balls commercially in instrument manufacture, they would be perfect for track, make sure you get leaded type. From experience with them it just needs a brush wiped in a soft flux, brushed across the joint, and the ball added. The very hot iron is applied to the work, in this case the rail top, the iron tip tinned, but all excess wiped away from the tip. This transfers the heat and capillary action on the melted solder does the business. All parts must be clean! you get total consistency in appearance.

Thanks for the note on them being on Ebay, as I have had trouble getting them since retirement. Best bargains look like Chinese supplied.

Stephen

[bertiedog]

Going from experience with the solder balls and handling them, what I did was get an old mamod type oscillating engine and ran it with a motor to make a very simple low vacuum pump. The tube, PVC, had a nozzle which just took one solder ball at a time from the hopper, and the tube had an aquarium airline switch fitted, when pressed it released the ball onto the fluxed area. Other than that it is tweezers!

Stephen

[Richard Hall]

Thanks for the feedback everyone.  At the moment it sounds 50-50 whether it will work, which is good enough odds for me.  As regards sleeper height I'm actually looking at doing this in 9mm gauge (boo, hiss) to mate up with Finetrax flexi track which I think is a bit deeper in the sleepers than Easitrac. But I haven't completely abandoned my bonkers idea for a hybrid 9.42 / NEM / NMRA standard, and if you can get track gauges for 9mm Code 40 bullhead rail I haven't seen them. I haven't found anyone yet doing soldered PCB track in 9mm so I thought I'd get more sense on here, and I was right. So I'll start with a bit of 9.42 plain track (I still have loads of 2mm Assoc sleepers, roller gauges and a track jig from my brief venture in 2mm FS) and if that works, try a plain B6 turnout, 9.42 but with wider clearances than 2mm FS, and see if I like the result.

 

Richard

[Richard Hall]

I'll call this first attempt a qualified failure.  Lots of problems:

 

1. The "etch resist" pen in my Ebay PCB etching starter kit is rubbish.

 

2. I based the etching time on stuff I read on the Internet (no instructions with the kit).  So I left the sleepers in far too long, the etch solution started munching away at the chair pads and they ended up all different sizes with holes in them.

 

3. I haven't done soldered track for 15 years and did this in a tearing hurry before dinner.  One of the sleepers slid out of position when I tried to solder it, and a couple of the solder fillets didn't "take" - not enough flux.

 

4. Yes, the copper is far too thin to make a chairplate. It's only about .03mm on the 2mm Assoc sleepers. (I think: it's hard to measure the difference between etched and unetched sections as the sleepers vary a bit in thickness anyway along their length.)

 

But some good points as well. With small copper pads it's much easier to make a neatish fillet, and soldering is a lot quicker as well.  (I included half a dozen standard sleepers for comparison).  It seems pretty strong, I have pulled and twisted it and none of the pads have fallen off. I'm wondering if the thickness of copper coating varies in line with the thickness of the board.  That would make sense, and the Marcway 1.5mm stuff might make more of a chairplate when etched. So I'm encouraged enough to buy some 2 x 1.5 point timbering and have another go.

 

[2mmMark]

 

"I'm wondering if the thickness of copper coating varies in line with the thickness of the board.  That would make sense, and the Marcway 1.5mm stuff might make more of a chairplate when etched. So I'm encouraged enough to buy some 2 x 1.5 point timbering and have another go."

 

 

I doubt it. I've been doing some work milling z gauge point bases from 1.5mm PCB and the copper is still only a few thou thick.

 

Neat results though, track looks good.

 

I get neat "chair blobs" by using a resin cored 0.5mm solder wire without any extra flux - just like soldering components onto a circuit board - which is in effect what we're doing with PCB trackwork.

 

Have you tried just a simple permanent marker as an etch resist pen?  The ink will wash off with a solvent after etching.

 

Mark

[Richard Hall]

 

"I'm wondering if the thickness of copper coating varies in line with the thickness of the board.  That would make sense, and the Marcway 1.5mm stuff might make more of a chairplate when etched. So I'm encouraged enough to buy some 2 x 1.5 point timbering and have another go."

 

 

I doubt it. I've been doing some work milling z gauge point bases from 1.5mm PCB and the copper is still only a few thou thick.

 

Neat results though, track looks good.

 

I get neat "chair blobs" by using a resin cored 0.5mm solder wire without any extra flux - just like soldering components onto a circuit board - which is in effect what we're doing with PCB trackwork.

 

Have you tried just a simple permanent marker as an etch resist pen?  The ink will wash off with a solvent after etching.

 

Mark

 

Thanks for that. I used 0.5mm solder but with flux as well.  You're right about PCB copper thickness, I did some research and the copper is ridiculously thin - .03 - .05mm.  I'm amazed it conducts electricity at all. The "etch resist pen" in my starter kit was indeed a permanent marker but not a very good one.  I'll try the faithful Sharpie, normally used for blackening bright plated wheel rims.

 

I was rummaging through boxes last night and found my half-built 2mm chassis.  Oooh, isn't it pretty.  If I can find all the bits (only five wheels at the moment) I might have another go at it.  I think I'm a better modeller than 15 years ago, or at least a more patient one.  The only fly in the ointment is that I have had enough of terminus-fiddle yard layouts and want a continuous run.  I've got 4 x 3 max to play with. That means a 2' continuous curve in the scenic section and toy train set 9" behind the backscene.  It'll work in N, but 2mm FS? 

[Rabs]

 

"I'm wondering if the thickness of copper coating varies in line with the thickness of the board.  That would make sense, and the Marcway 1.5mm stuff might make more of a chairplate when etched. So I'm encouraged enough to buy some 2 x 1.5 point timbering and have another go."

 

 

I doubt it. I've been doing some work milling z gauge point bases from 1.5mm PCB and the copper is still only a few thou thick.

 

 

 

Standard PCBs are most commonly coated with '1oz' copper.  That's 1oz per sq ft or 35um (0.035mm) thick, so your measurement was pretty much spot on.  You can get 1/2oz and 2oz copper board but it's much less common.  The thickness of the copper isn't related to the overall thickness and for electronic designs you choose the combination of thicknesses you want to achieve a particular set of electrical properties.  0.8mm and 1.6mm substrates are the most common and hence the cheapest.

 

I did a very similar arrangement for board joints on my layout (http://www.rmweb.co.uk/community/index.php?/topic/72424-bath-spa-high-tech-modelling-bringing-1947-into-the-21st-century-3d-printed-scenery-cnc-milled-track-laser-cut-baseboards-and-computer-control/page-6).  I milled off the top surface of the copper everywhere except where the chairplates would be.  As you say, the copper isn't a match in thickness for etched chairplates, so I had to remove a bit of the substrate as well to get the tops of the sleepers to match the finetrax plain line I am using (I think easitrack is the same thickness).  Like you, I found that the bond to the substrate, even with just those little patches of copper remaining, seemed fine.  This was with 1.6mm/1oz, single sided FR4 material.

[StuartM]

For what its worth my view on the subject having tried most of the various methods of track making is that I now solder the rail directly to the sleeper and be dammed.

I tried using the assoc brass chairs from the etched sheets, which work well but it takes sooooooo long and as Jim mentioned earlier from 2ft away you'd never know the difference between track with or without the brass chair.

The other method is to use easitrak chairs and slide them on the rail and then glue them into place, the trick here I found is to use the odd brass chair ( the lost wax variety not the etched version) which can be soldered to the sleeper, this not only adds strength and allows for fettling, it also acts as an electrical contact between the rail and sleeper, which is useful for track continuity around the frog section.

 

I've attached some photos which show all the techniques described above starting off with rail soldered directly to the sleeper and then the other options with plastic and brass chairs. Hopefully this will give you an idea of what works and doesn't 

 

[Richard Hall]

Sexy track! That scissor crossover is gorgeous.

[Crosland]

The other method is to use easitrak chairs and slide them on the rail and then glue them into place, the trick here I found is to use the odd brass chair ( the lost wax variety not the etched version) which can be soldered to the sleeper, this not only adds strength and allows for fettling, it also acts as an electrical contact between the rail and sleeper, which is useful for track continuity around the frog section.

 

Looks really nice. Are there any pitfalls with this method? What glue did you use?

 

I also like the 4th picture where you switch to easitrack bases as soon as possible.

 

Andrew

[StuartM]

Looks really nice. Are there any pitfalls with this method? What glue did you use?

 

I also like the 4th picture where you switch to easitrack bases as soon as possible.

 

Andrew

Hi Andrew,

Thanks, I use plain old cryno or super glue. I squeeze a small blob onto a piece of scrap card and then use a cocktail stick to add a smidgin of glue to the sleeper before sliding the chair into place.

 

The forth photo was an experiment with wooden sleepers which I included just for reference. The Easitrack sleepers were used as a gauge, if you add a sprue of sleepers at each exit, they hold your rails in place and in gauge which makes the turnout easier to make.

 

But as I said, I now just solder the rail directly to the pcb as I find it so much easier and it looks just as good from 12" away

As an example in the photo attached we have from left to right. 

Rail soldered to pcb sleepers

Rail using easitrack sleepers

Rail soldered to pcb painted and ballasted

Can you spot the difference?

 

Obviously close up you can, but for me the solder to pcb approach looks good enough for my needs

The second photo shows a close up of rail soldered directly to the sleeper that has been pained and embedded into a layer of textured paint, but no ballast