Brimsdown-The last grand project.

[Paul Townsend]

Tony uses the contact style with eyelet designed for soldering. The back end protrudes from the housing so use of insulating sleeve is desirable.

I prefer to use the crimp style contact pins as they are shorter, do not protrude and so no sleeve is required. They are intended for use with an expensive custom crimp tool. They can be used perfectly well by lightly crimping with pliers just for mechanical stability while soldering to complete the joint.

An obscure advantage of not sleeving is that a meter probe can contact the back of a mated connector pin, great for testing.

[Paul Willis]

This is an excellent series, can I suggest that this is incorporated into the Scalefour Society Manual?

David

Isn't this a candidate for Notes?

Richard,

Quite possibly - that is why the facility was created. To enable material (whether it is short tips or a lengthy article) to be collected and easily accessible to all members.

It was also as an alternative because the Society has had very few volunteers to write new Digest sheets in recent years.

Cheers
Paul Willis
Deputy Chairman

[Tony Wilkins]

Tony uses the contact style with eyelet designed for soldering. The back end protrudes from the housing so use of insulating sleeve is desirable.

I prefer to use the crimp style contact pins as they are shorter, do not protrude and so no sleeve is required. They are intended for use with an expensive custom crimp tool. They can be used perfectly well by lightly crimping with pliers just for mechanical stability while soldering to complete the joint.

An obscure advantage of not sleeving is that a meter probe can contact the back of a mated connector pin, great for testing.

Hi Paul.
Wouldn't argue with that in the least.
In general I am not a great fan of crimped connections even though they are widely used in industry (to speed up production) as I have had several failures over the years, so where I do use them, like you, I resort to a bit of solder for added security. The PCB connectors I use are a case in point.
Regards
Tony.

[Martin Wynne]

In general I am not a great fan of crimped connections even though they are widely used in industry

Hi Tony,

I tend to disagree there. Crimp connections are widely used because they are more reliable. They are flexible and ideal for terminating flexible cables. Soldered connections are not flexible and can crack and fail. Also can be subject to dry joints and corrosion.

If soldered connections are used, they must be protected from flexing by having the outer cable firmly clamped in a connector housing.

Crimped connections don't necessarily need a housing, the shells can be used as-is. The socket shell will clip-fit into a fixing bracket if needed.

The most economic are the automotive types, such as:



They are very reliable, being intended for use in harsh environments such as vehicle engine compartments.

A 15-way plug & socket pair complete with crimp inserts can be had for around £6 if you buy a pack of 10, see for example:

https://www.autoelectricsupplies.co.uk/ ... category/7

The saving easily covers the cost of a proper crimp tool to clench the ears in correctly:

https://www.autoelectricsupplies.co.uk/ ... ategory/87

There is a wide range of accessories for these connectors, such as covers and sealing gaskets -- not really needed for a layout.

(no connection)

cheers,

Martin.

[Tony Wilkins]

Now that I have more or less reached one end of the storage sidings, I have got to backtrack for a while and update baseboards already wired to include extra functions and associated wiring, before working my way in the other direction. I have used 38 and 56 way connectors thus far but have already had to upgrade a couple to 90 way as I ran out of spare ways, in one case just for 1 extra wire. The best laid plans of mice and men and all that. Fortunately this is less onerous than it might be, as it is possible to remove the contacts from the old block with an extractor tool and move them into the replacement one by one, without the need to unsolder anything.

One disadvantage of using the daisy chain method of wiring baseboards is that although some wiring, such as the power bus, is consistently on the same tags, in my case 1 to 11, then come the rail feeds starting from the inside face of the layout dependent on the number of tracks crossing each baseboard joint, others can change from board to board so when it comes to testing each setup can be different and a degree of flexibility is called for.
I have had to make a test box with 8 switches in order to test the turnouts controlled by each relay card and in the case of the pair shown above, one relay card controls all the turnouts on both boards so they had to be tested as a pair.
Tony.

[Tony Wilkins]

In general I am not a great fan of crimped connections even though they are widely used in industry

Hi Tony,

I tend to disagree there. Crimp connections are widely used because they are more reliable. They are flexible and ideal for terminating flexible cables. Soldered connections are not flexible and can crack and fail. Also can be subject to dry joints and corrosion.

If soldered connections are used, they must be protected from flexing by having the outer cable firmly clamped in a connector housing.

Crimped connections don't necessarily need a housing, the shells can be used as-is. The socket shell will clip-fit into a fixing bracket if needed.

The most economic are the automotive types, such as:



They are very reliable, being intended for use in harsh environments such as vehicle engine compartments.

A 15-way plug & socket pair complete with crimp inserts can be had for around £6 if you buy a pack of 10, see for example:

https://www.autoelectricsupplies.co.uk/ ... category/7

The saving easily covers the cost of a proper crimp tool to clench the ears in correctly:

https://www.autoelectricsupplies.co.uk/ ... ategory/87

There is a wide range of accessories for these connectors, such as covers and sealing gaskets -- not really needed for a layout.

(no connection)

cheers,

Martin.

My 20 plus years in a repair environment left me with a rather different impression.
Granted poor quality solder joints are an issue and when using flexible wires solder tends to wick into the strands effectively causing it to act as one solid piece so yes some sort of cable clamp is desirable.
The reason for inventing crimp connectors was to eliminate the use of solder altogether. Repairs can be made in the field more conveniently too.
Cable terminations can also be made on mass by machine.
However if using them, one really should invest in the correct crimp tool for the connectors and the wire size being used.
Often there are two parts to be crimped. The first part for the metal core of the cable and the second part to clamp the insulation to relieve the strain on the joint, so it is important to strip the right amount of insulation from the cable.
Some of the better types have a ratchet so that the crimp tool cannot be released until the required force to swage the metal parts together has been attained and this can be more than one might expect. Herein lies their weakness as a poorly crimped joint can result in the crimp subsequently parting company.
Done properly they can give reliable service. You pays your money and takes your choice.
Regards
Tony.

[Tony Wilkins]

Among my collection of cable is ribbon cable, sometimes called rainbow ribbon cable due to the colours, rather than being plain grey with conductor 1 marked with a red stripe. I use this for jumper cable applications up to 10 way although I do have some 20 way where the colours repeat. My old stock is beginning to run down, so I recently purchased some new stock. Spot the difference.

DSCF0985.jpg

Tony.

[davebradwell]

Somebody doesn't know their resistor colour code!

DaveB

[Tony Wilkins]

Somebody doesn't know their resistor colour code!

DaveB

Precisely so.
For those who don't, there has been a convention in the electronics world for many years of using colours to represent the numbers 0-9 as follows:
0 Black
1 Brown
2 Red
3 Orange
4 Yellow
5 Green
6 Blue
7 Violet
8 Grey
9 White.

Hence the sample on the left follows this.
There is an argument to be made for beginning the count from 1, but this would make Black = 10.
The bigger problem comes when repairing existing electrical installations as the variation between new and old stock is apt to lead to confusion.
I have already wired up one cable the wrong way round by starting with the black lead out of habit.
The old stock was made in the UK. The new stock was made in China. Nuff said.
Regards
Tony.

[Tony Wilkins]

So what else have I been up to?
Well I have been using the 8 relay control card for the initial (I began from the middle and worked outwards) Storage yard board as a pattern for the subsequent relay cards fitted to each completed storage yard board. As mentioned earlier, I have had to retrace my steps as the initial baseboard was only partially wired before testing it as part of the initial pair. As I would need to fit this 8 relay card (the blue one to the bottom right), I decided to make all the required relay cards in one hit and get that job out of the way. I then needed to make enough jumper cables to go with them.
The small brown PCB to the right is special isolator card and uses the new 'wrong' ribbon cable.

DSCF0986.jpg

The 8 relay card has now been fitted to its baseboard and after what seems like an interminably long time, connected up the remaining wiring, which has been tested and proved. It houses a 38 way connection at one end. A 56 way connection to the control panel (yet to be build) and a 90 way connection at the other end. Only 5 more baseboards to go, then I will be half way round!
No sooner had I finished this than I retrieved the next baseboard from its storage space and began tackling that one. So far the 4 point motors are fitted and I am part way through fitting the droppers. The good news is that the amount of wiring deceases with each baseboard until I reach the end of the storage yard. The bad news? Only slowly.
Regards
Tony.

[Andrew Bluett-Duncan]

Hello Tony
Impressive planning and wiring as I would expect from you! What do the relay cards do? I’m sorry if it’s very obvious and / or you’ve already gone into great detail about it and if that’s the case tell me and I’ll go hunting....
Kind regards
Andrew

[Tony Wilkins]

Hi Andrew.
This is one of several topics that I have not explained yet, so no, you haven't missed it.
The relays control the point motors and some isolation breaks.

What we are getting into here begins to delve into the control philosophy of the layout, which in most respects is fairly traditional DC (analogue).
There will be switches to control things on the control panel, so far so normal.
Here we are confronted with choices and there are many possible options. I have elected for electrical control via point motors.
As I think I have already mentioned, It was originally intended to use Fulgurex point machines, but these (as far as I can tell) are no longer available, so the choice was either Tortoise or Cobalt units. I chose the latter, partly due to their more compact size.
The next decision was how to control them, which for me was an easy one as the system I used on Green Street has proved reliable.

There are several ways of wiring point motors, but the diagram below shows two main variations.

Point motor supply002.JPG

Diagram 1 utilises one 12 volt DC power supply but requires a Double Pole Double Throw cross wired reversing switch, connected to each point motor or crossover and two wires from the control panel to each point motor.

Diagram 2 utilises two 12 volt DC power supplies with the negative of one connected to the positive of the second and forming a common return rail which connects to the return side of all the point motors. Which side this turns out to be will need to be determined for each point motor dependent on its circumstances. This is known as a dual rail or split potential supply. In this case only a Single Pole Double Throw switch is required with one wire for each point motor from the control panel.
The disadvantage of these methods is that the control wires must carry the operating current all the way to each point motor and that of two with a crossover. True that the currents are not that great, but some of them will be several baseboards away from the operating switch.
I therefore prefer to switch the power as near to the point motor as I can and so the relay replaces the switch in the above diagrams.
The relay draws far less current than a point motor and so thinner wire can be used with no worries about voltage drop.
The relay in turn is controlled by a switch on the control panel and can be just a Single Pole Single Throw type.
The wire saved is then negated by a detection wire coming back from each point motor giving positive indication that the motor has indeed thrown.

[DougN]

Thanks for that Tony. I have been looking at this issue from a different perspective recently. My little layout, that is slowly coming on, will have tortoises (as I have already collected them), I went for the common return version from the Tortoise control diagram using 2 diodes and a AC supply. I have figured out what components to use and purchased these here in Australia. For some unknown reason Australia the UK and the US all use different codes which drives me batty at times. This was a cheaper solution as it has only 1 power supply ($AUD5 more expensive than a DC supply of the same size) and 2 diodes (about $AUD1.60) Below is the diagram from the instructions

circuit.jpg

I will say the layout will be no where near as big as Brimsdown so I have no concern about voltage drop. I am thinking about the option to use the LED's on a mimic panel but I have not made up my mind.

[Terry Bendall]

My preferred method is the third option shown by Doug which is essentially (to get a bit technical) half wave rectification using an 15 volt AC supply which as Doug says is one method shown in the instructions for Tortoise point motors and I have used it on all the four layouts we have built. It still requires a higher current capacity for the majority of the wiring than using a relay near to the turnout which is one of Tony's objectives but it works well. On Pulborough a system similar to that used by Tony is used with relay used to switch the motor and other contacts on the same relay switch the supply to the common crossing. On our lay,outs I have added micro switches to the Tortoise motors to avoid the unreliability, of the built in contacts.

For the LED indication, my method is a bit cruder but I can understand it. I use a DPDT switch for the point motors with one side switching the motor and the other side switching the LEDs. This reduces the wiring on the layout since the LED wiring is within the control panel. The LEDs have a separate power supply from everything else and are used to show if the turnout is switched to normal or reversed.

Terry Bendall

[Tony Wilkins]

My actual power supply is home made and uses a different circuit to those shown / described for the split rail point motor supply and can be used with a center tapped transformer winding.
The relevant section is shown diagrammatically below. This gives full wave rectification using a bridge rectifier.

Point motor supply003.jpg

The complete unit contains additional supplies for 12v Digital, 12V Relay and 4 separate 15V AC outputs for train controllers.

Power supply.jpg

I can post the complete circuit diagram if anybody is interested, though probably a little old fashioned with today's use of switched mode power supplies.
At least I can understand how it works if things go wrong.
I also much prefer to have an indicator wire coming back from each point motor and sometimes from isolator relays as well giving confirmation that they have obeyed instructions. I did this on Green Street with the Fulgurex Point motor wiring modified to suit for reassurance after one stalled and melted the plastic base.
Regards
Tony.

[Andrew Bluett-Duncan]

Hello Tony
Thanks for your very comprehensive reply, electronics apart, It was clear and I fully understood it ( slightly to my surprise). I do sometimes find it quite surprising just how many different approaches there are to model train control and yours, Doug’s and Terry’s approaches illustrate it very well. My own approach with point motors being servos controlled by Megapoints boards being another.

Thanks again
Kind regards
Andrew

[Tony Wilkins]

Each baseboard poses its own particular challenges. The latest one was due to the anti-sag ribs I installed near the end of this baseboard limiting the space available to mount a point motor. The hole above the point motor shows the first attempt, but the point motor would not fit.

DSCF0998.jpg

Fortunately, because the track above board was at an angle, it was possible to use an extended tie bar and create just enough room for the point motor to fit.

DSCF1001.jpg

So that's another one down.
Picture below but by now each one looks much the same as the previous ones.

DSCF1008.jpg

It will be on with the next tomorrow. The main challenge this poses will be a pair of double slips in succession.
Tony.

[Tony Wilkins]

A bit more on electrics now. Wiring up a simple live crossing turnout.
This is actually not as simple as it may first seem. Why?
Well there are actually three possible ways a turnout can be wired.

Turnout wiring A.JPG

A) is the simplest with the Vee crossing rails extended the length of the sidings.
This works because both rails of one exit track are at the same potential, a loco stood on that road sees no volts, so is effectively isolated. it is OK for dead end sidings but for loops problems will arise when different roads are selected at either end. The fiddle yard sidings on Heckmondwike were wired this way (not by me in case you wondered) and caused no end of problems and various electrical chicanery to get round it. I thought at the time that there had to be a better way.

Turnout wiring B.JPG

B) is also relatively simple, but with the Vee crossing isolated from the exit roads. Instead the two exit roads are linked with their polarity counterparts. Common feed as well as common return. This method is therefore best suited to DCC layouts although can be used with conventional DC in some circumstances. The Nottingham Area Group's Test Track was wired throughout this way for simplicity's sake, but each of the four roads could be switched out for isolation.
Both A and B only use one changeover switch for the Crossing polarity leaving your typical point motor with one spare.

Turnout wiring C.JPG

C) uses both switches as the second is used to switch the feed between the exit roads.
This is the correct way to wire turnouts for conventional DC layouts and how both Green Street and Brimsdown are wired.
In this example the negative rail is effectively wired as a common return rail.
Both A and C isolate unswitched roads and are thus generally unsuitable for DCC operation.
The guiding principle with Brimsdown is that the supply follows the track as switched by the pointwork and signals. In the case of the storage sidings, there are no signals.
Tony.

[Tony Wilkins]

The afore mentioned double slips.

DSCF1012.jpg

An earlier version of this area used turnouts, but took up twice the length thus shortening the siding length. Operationally a pair of Barry slips would have created the desired traffic paths, as the straight through roads on tracks 2 and 3 are not really needed, but in the end I decided to go the whole hog and use double slips. These created extra problems, especially the way I make em.
It is not possible to use my cheap tie bar arrangement to operate four blades with no pivots and space between the center blades is at a premium, so a different solution is required.

Back to the future!
What I use is a variation on the original Studiolith operating units but utilising the Exactoscale Tortoise adaptor bases with Cobalt point motors. As the Cobalt motor's footprint is smaller than the Tortoise, the hollow in the adaptor plates needs to be filled in. I used layers of plasticard.

DSCF1010.jpg

Next new fixing holes need to be drilled for the Cobalt motors. I modified a Tortoise drilling template for this purpose.

DSCF1011.jpg

This should only be used to mark where the holes go as the soft plastic soon wears if drilled through each time. Guess how I know.

With this design the operating rods come up just outside the stock rails for each switch blade and therefore holes need to be drilled to accommodate them. I drilled a 2mm hole down from the top surface outside each Stock rail (approximately 24mm between centers).
Despite the best intentions at the design stage problems will arise later on. This is where the holes came out on the underside, marked with a felt tip pen for visibility.

DSCF1013.jpg

DSCF1014.jpg

Therefore sufficient wood had to be removed for the turnout operating units to be installed. Not neat but needs must. My trained rat needs to do better!

DSCF1015.jpg

DSCF1016.jpg

DSCF1017.jpg

The pilot holes are then opened out to 6mm from underneath taking great care not to break through the surface and damage the rails above. A hand drill is best for this job. As can be imagined access was difficult with some of them. I suspect that you can guess which set of blades I tackled first as this was all something of an experiment.
Anyway, after much cursing and trial and error an acceptable result was obtained.

DSCF1018.jpg

A blow up from the above picture shows a bit more detail

DSCF1018a.jpg

and here is the underneath when the board was "completed" a week ago.

DSCF1019.jpg

So that is the last of the straight storage yard baseboards, 8 down 16 to go.
Next time I shall expand on the TOU arrangements.
Regards
Tony.

[Tony Wilkins]

So that is the last of the straight storage yard baseboards, 8 down 16 to go.
Next time I shall expand on the TOU arrangements.

So ended the previous post, but before I do a quick update on progress.
The 9th baseboard.

DSCF1032.jpg

DSCF1038.jpg

Done. But it may not be quite so easy from here on in, he says mysteriously.



Variations on a theme.

DSCF1037.jpg

On the left the original Studiolth / Protofour Turnout Operating Unit (TOU).
In the middle my design as used on Green Street. ABS plastruct L & Square sections glued together with a 6mm square paxolin bar.
I would probably have stayed with this design but for two factors. I was running short of the hypodermic tube i used and the plastruct sections are no longer available in ABS only polystyrene and the wall thicknesses are much thinner.
On the right my Exactoscale variant. The reappearance of these mounts at Scaleforum last year made this option rather attractive if I could source some more stainless steel hypodermic tubing.
My first attempt proved a non starter when the firm I found offered me an expensive minimum order quote. They were in the USA.
My second attempt proved successful however and I have more than enough tube for several lifetimes layouts now.
Hypodermic tubing is available in many different sizes and with varying wall thicknesses.

standard-gauge-304316.pdf

I chose 21gauge, the same as the original Studiolith version.
For the operating wires I chose Phosphor Bronze as I thought this would be tougher than Nickel Silver as there was going to be a lot of bending required to form them.

DSCF0677.jpg

The weakness with the Studiolth design was always the small area of the soldered joint between the operating wire and the point blade. As I leave the foot on the inside of the rail, this only makes the situation worse. The crank handle shape allowed the throw to be adjusted by pivoting the cranked end in the tube. I obviously wished to increase the bond area considerably for greater strength and reliability.
Mike Norris's article on stretcher bars for Preston in Scalefour news 181 looked promising, so how to combine the two approaches?
In short, what I required was a horizontal length of wire that could be soldered against the inside face of the switch blade whilst the vertical part fitted into the tubing of the TOU. Clearly some careful thought was going to be needed both to calculate the necessary dimensions and how to form them as there would be little scope for adjustment.

[Tony Wilkins]

The original Studiolith units were designed for 1/2" thick baseboards plus a 1/8" layer of cork. My baseboard tops are only 3/8" or 9mm thick plus 1/8" cork so 12.5mm nominal. I would thus need shorter tubes. The spacing would also need to be reduced from 24mm centers to allow for the fold back built into my operating wires. I made a prototype.

DSCF0675.jpg

This showed how tricky it was going to be to make them consistently. I therefore devised a simple bending jig.
I needed right angle bends at 4mm and 8mm from the top end. I therefore cut two lengths of tube to these dimensions from an off cut of tube and drilled holes for these in a block of wood, so.

DSCF0663.jpg

The 8mm piece marked 1 and the 4mm piece marked 2.
Making sure the tubes are fully inserted, insert a 23mm length of wire into 1 until it bottoms

DSCF0664.jpg

and bend to form an almost right angle bend.

DSCF0665.jpg

DSCF0666.jpg

Next insert the bent over end fully into 2

DSCF0667.jpg

and bend over sideways.

DSCF0668.jpg

Resulting in this.

DSCF0669.jpg

Repeat the process, but the second needs to bent sideways the opposite way.

DSCF0670.jpg

Now comes the tricky bit, forming the reverse kink to go around the rail foot.
My first attempts met with limited success as nothing I tried gripped the wire firmly enough. Then I tried using some surgical seizers I bought many moons ago and these proved to be the solution. They have a vice like grip and enabled me to achieve what I was beginning to think was nigh on impossible.

DSCF0673.jpg

The object of the exercise is to bend the wire over the side of the top jaw of the clamp.

DSCF0674.jpg

Bending such a short length is difficult and I found the best way was to place the jaws against a flat surface and gently but firmly apply pressure to roll the wire round the jaws. Some further bending may be required to remove any distortion from the desired shape, but after several practice attempts some degree of consistency was achieved.

DSCF0683.jpg

DSCF0685.jpg

DSCF0686.jpg

[Tony Wilkins]

The next stage is to make the other half with the tubes.

DSCF0693.jpg

This was an early experimental one, before I managed to source some tube, using recovered Studiolith tubes, which are longer than I need.

The first job was to cut some tubes to the desired length, in my case 16mm.
This was done with a pin vice and a slitting file.

DSCF0676.jpg

The object next to the wood block is a slitting file. They are used in the watch making trade for cutting hardened steel shafts and are thus extremely hard themselves. A good Swiss one is worth its weight with a price to match unfortunately these days.

The desired amount of tube to be cut off, plus a cutting allowance (0.5mm), is exposed beyond the jaws of the pin vice and clamped.

DSCF0678.jpg

The slitting file is then held gently against the face of the jaws and pressing down, sawed back and forth against the tube whilst rotating the pin vice. It is not necessary to cut right through as a point will be reached where if gentle pressure is applied to the tube, it will break off cleanly. I then stone the ends to remove any burrs.
The tube is 0.82mm OD and so I drilled two No 67 size holes through an Exactoscale plastic bar at 23mm centers. It is important to drill through the operating bar as near to vertical as possible. When I made the ones for Green Street, I used a larger diameter tube that I had available and managed to find a drill that produced a good force fit. Not so here as this tube was more a sliding fit and the next size drill down was too small.

DSCF0679.jpg

I therefore adopted the Studiolth solution of squashing the extreme end the tube to flatten it.

DSCF0681.jpg

When pushed back into the underside of the plastic bar, I used the point of a scriber, it grips firmly.
I had the chance to try my prototype out on the EMAG layout at the last all day workshop before lock down in February as we were installing them under the replacement pointwork. This showed that 23mm spacing for the tubes was too great and I subsequently reduced it to 22mm. This meant enlarging the baseboard holes slightly toward the center of the track to give sufficient movement for the blades.
Armed with such knowledge, I recalculated the center spacing's for the double slip operating units I would need here and set about making them.

DSCF0679.jpg

DSCF0680.jpg

DSCF0682.jpg

Note: the Exactoscale operating bar has several small pips on its top surface, these are part of the moulding process. I have found they can increase the thickness of the bar just enough to cause sticking and now file them off flush with a smooth file as a matter of course.

DSCF0684.jpg

A Cobalt motor installed on an Exactoscale adaptor unit. The motor comes with the throw pre-centered but it is worth checking.

DSCF1027.jpg

DSCF1028.jpg

Installing them (with tubes but minus wires) underneath is not the easiest of tasks as their alignment can be problematic as you can't see both side of the baseboard at the same time, so things can move before one gets the fixing screws in.

DSCF0692.jpg

Once in place the operating wires are inserted from the top. This involves flexing the tubes to be able to see enough of the end to do so. When all four were in, the point was thrown fully one way and the wires soldered to one set of blades using a tiny amount of Orange label flux and an even smaller amount of solder. A smallish bit helps too. You don't want any solder where the flanges will run. The point motor is then thrown fully the other way and the opposite set of blades soldered. Check there is full throw of both set of blades both ways. There is limited scope for adjustment, so it is now when one discovers if ones calculations were correct. Some adjustment can be made by bending the tubes where they emerge from the top of the operating bar, but this needs to be done with great care to avoid damage.

DSCF0689.jpg

DSCF0690.jpg

There isn't much room to play with here, especially with metal slide chairs, so correct adjustment is critical to avoid potential shorts.

DSCF0691.jpg

Using these units is a lot more work, which is why I have tried them out on the hidden sidings first, but they will be standard on all the scenic pointwork. When one considers that several of these will be Flatbottom track then variation of dimensions is inevitable. I can hardly wait
Regards
Tony.

[DougN]

Seriously impressive Tony.

[davebradwell]

Can I point out that your blades are still not opening far enough - only about 1mm. The prototype opening was 4 1/4" or thereabouts so you need almost half as much again for safety.

DaveB

[JFS]

Can I point out that your blades are still not opening far enough - only about 1mm. The prototype opening was 4 1/4" or thereabouts so you need almost half as much again for safety.

DaveB

... but any more Dave, and he will have a short on the opposing slide chairs. Anyone who says double slips are easy is being economical with the truth!

Edit:- just to mention that Tony is S4 not P4 so he has that on his side

Excellent thread!