Self contained buffers, the easy way.

mickoo

Western Thunderer
There are many ways to achieve this, I've not seen them all or even attempted the ones I have seen, but the few that I have tried always ended up total failures involving intricate work and tolerances well beyond my skill and more importantly enthusiasm level.

First off I apologise if this method has been done before, but it's how I've worked out how to do it and do not claim world breaking news.

The objective was to make self contained buffers with the simplest of hand tools, reliably and in as basic form possible, though I did use a lathe for a couple of the operations they are also easily achieved with a pin vice and a little more patience. I also wanted to be able to remove the buffer head later for painting or servicing, something many self contained buffer systems lack, especially if there is no access from the rear (behind front buffer beams whose rear is exposed and detailed).

Ingredients required:-

One Slaters LNER/SR Step parallel buffer.
One length of thickwall 3 mm brass tube (3.0mm OD x 2.0mm ID).
One 12 BA cheese head screw - Steel preferred, 10.0 mm long minimum.
One 12BA washer - Brass preferred.
A 3.0mm drill.
A 2.4mm drill.
A 1.0mm drill.
A 12BA tap.

There is no requirement for a oven or gas mark 4 in this mix.

This is image heavy and not a particularly short post, so a cup of coffee might be a good companion.

So to start, first an assessment of what we get in the package from Slaters.

First off the brass housing casting, salient points here are a 2.5 mm bore at the rear (approx) and a 4.0 mm bore for the buffer head shank at the front.
Second the steel buffer assembly with a 4.0 mm shank and 2.2 mm stub threaded 8BA with associated brass nut.
Finally a steel spring approximately 3.8 mm OD and 3.4 mm ID

IMG_0473.jpg

Clearly when the buffer compresses the nut on the rear outside will protrude through the buffer beam.

The conversion.

Step 1:

Open the rear hole up to 3.0 mm dia and trim the stub to roughly the thickness of your buffer beam. I used a lathe for this as it was just quicker than hand balling it.

IMG_0474.jpg

Step 2:

Take your 3.0 mm tube and bore the inside out 2.4 mm or just enough to clear the screw cheese head, 12BA is nominally 2.3 mm. I bored a depth of 5.0 mm but it's not overly critical right now and you can bore deeper by mistake and not need to panic.

IMG_0475.jpg

Next I cut it off around 5.5 mm long which is way over length but we'll be trimming it later anyway. This gives me two bores, one at 2.4 mm 5 mm long and one at 2.0 mm 0.5 mm long. I found the small bore just a touch to large for the 12BA screw, so as added insurance to stop the head pulling through, soldered the washer on the end and trimmed to the same OD as the tube. The important bit is that when you cut it off some of the original smaller bore is still at one end.

In reality you could drill right through and just add the washer, but the tube wall would be thin and the solder joint less resilient. In truth I suspect just the plain drilled bore would be fine, we're not going to be pulling on it, just compression.

IMG_0476.jpg

Screw passed through the (what I call the retention cup) showing washer soldered on.

Step 3:

Converting the buffer head, this vexed me for some considerable time, how to drill the hole in the base whilst holding the buffer by the head straight and square, in the end the eureka moment came and I simply drilled from the front right through and then tapped 12BA right through. Fret not all will become clear later.

IMG_0478.jpg

IMG_0477.jpg

Once all the parts are made it's time to assemble them

IMG_0479.jpg

The above view gives an idea of the basic assembly order. Below is what it would look like if the outer casting was removed, though the screw would be wound in more and not visible from the rear end of the tube.

IMG_0480.jpg

Step 4:

The 3.0 mm OD tube was a smidge over size for the drilled hole in the rear of the buffer casting, which is good as it will give it a nice tight interference fit when fitted, I ran it in the lathe and gently held a #4 flat file on it to give a slight taper as well.

IMG_0481.jpg

Insert the tube from the rear with the washer (narrower bore) end toward the front, the depth isn't actually that critical but for those wanting to know it's about 4.5 mm from the top lip. The excess on the rear will be trimmed later. The friction fit means you'll probably need to use a vice to push the tube in but if yours a bit loose a dab of solder once in position will secure it nicely.

Looking inside you can see that the new retention cup comes up above the internal 4.0 mm ID base and creates a rim to locate the spring.

IMG_0482.jpg

IMG_0483.jpg

The 3.0 mm OD tube fitting inside the ID of the spring.

Step 5:

Pass the steel screw in though the base and simply screw the head on.

IMG_0486.jpg

IMG_0487.jpg

The 12BA steel screw will pass right through the head and protrude from the front....perfect.

Adjust the screw so that at full compression the head sits flush or just below the mounting spigot on the rear.

IMG_0488.jpg

Finally flip the assembly over and add a dab of solder on the exposed screw thread and buffer head and then trim flush, being steel the joint will be near invisible.

IMG_0490.jpg

I've not soldered this solid or trimmed this as in part two (only 15 images per post) I want to be able to remove the head later so soldering this in will simply lock the unit as one. But if your happy to not worry about removing the head later or masking for painting then this is as far as you'll need to go.

Total time to this point was about 15 minutes work, to photography and write up, 45 mins.

That concludes the sealed unit.

MD
 

mickoo

Western Thunderer
Part two, the removable head unit.

The approach here does depend on application, for coaches and wagons or tenders, there's generally enough room inside to squeak a screw driver in and tighten up the screw from the rear, though there may not be enough room for a standard retaining nut or the screw head to enter that area behind the buffer beam.

IMG_0496.jpg

However there are applications where there is no access at all from the rear.

IMG_0497.jpg

So we need some sort of 'internal fixed screw driver blade' to tighten the screw up, here's how we achieve that.

First off we will not be soldering the screw at the buffer head and making it a fixed unit to so we need to plug that, there are two options, open the hole out for a few mm to say 1.4 mm and then insert some nickel silver rod, solder and trim, however you'll probably end up with a brighter dot in the middle.

The other way is to screw a 12BA screw in from the front a few turns, solder and trim flush, steel screw in a steel head.

IMG_0493.jpg

From here on in it is important that your screw pokes out though the top of the retaining cup when the head is compressed as far back as it will go. Otherwise the faux screw driver blade will not work. I made sure mine was about 2.0 mm clear of the retainer cup, or about 1 - 2.0 mm below the buffer casing lip.

Next flip over the casting and make two slots in the locating spigot and also open out the slot in the screw head a touch so that a piece of 0.7 mm nickel silver rod is a good fit in the two slots.

IMG_0492.jpg

Drop the screw in and solder a short length of 0.7 mm wire in the casing slots, this will be your fixed invisible screw driver blade.

IMG_0491.jpg

To fit the head simply push the head down onto the screw which will fall back to the rod, gently turn until the rod catches in the screw head and whilst gently pushing on the head screw it on. A small dab of loctite on the thread will lock the head in place.

To remove push the head down and rotate until the rod engages the screw head slot and un-tighten, clearly less is more with the loctite. I probably wouldn't use loctite, some thing like diluted PVE glue would suffice, you just need something to stop it vibrating loose.

For the next ones I'll fine tune it and add square rod in the slot to give a better grip on the screw head, whilst the rod works it is rounded and not quite 'just so'.

There is a third unit I'm going to try and trial over the weekend, rather than the rod being across the back of the casting it'll run parallel with the screw inside the retaining cup, a slot on the rim of the screw head will fit around the tube and whilst tightening and unscrewing the head will also stop it rotating, handy for oval buffer applications. Mind that unit moves from the simple and easy to the more complex in fabrication category.

Hope this'll help some folk, it's ticked every box for me, quick, easy and allows the head to be removed for painting or servicing.

MD
 

adrian

Flying Squad
Converting the buffer head, this vexed me for some considerable time, how to drill the hole in the base whilst holding the buffer by the head straight and square, in the end the eureka moment came and I simply drilled from the front right through and then tapped 12BA right through. Fret not all will become clear later.
Thanks for posting - my solution was very similar, although I think I'll tweak it in light of your modifications.
Self contained sprung buffers - Cherry Clan
I think the main difference is that I was making them from scratch and so I made the shank of the buffer head longer and drilled the rear of the shank out so that it would fit over the central core tube. I think I was worried that having a short shank on the buffer would leave it with nothing to hold it straight and level when fully extended and cause problems compressing. Probably worrying needlessly so I would be interested to see how your solution works out.
 

mickoo

Western Thunderer
Adrian, as I noted in the beginning, there's probably nothing new here and I had forgotten your approach :( The only new thing might be the hidden rod to act as a screwdriver blade to allow removal of the head in units fitted with no rear access.

I did look at your design at the time I attempted it before and decided it was a touch too elegant and home machinist for my clumsy dock worker skills ;) hence my quest for a more tiny tots club approach :cool:

If your going to Telford then pop by as I'll have a couple for folks to look at if they're interested.

Ironically with this set up you get more travel than the stock set up, about 3 mm nearer 4 if you loosen the screw a bit, at that point as you note the shank is nearly dropping out of the casing, but the screw head way back in the tube and the hole for the threaded part to travel through keeps it all in shape.

I think you're overly worrying about sag, I can't see any on these, granted they're not space race tolerances but then that's more to do with the Slaters brass casting than the bodging at the rear end.

Full extension, about as far out as you can get before the shank drops out of the casing.

IMG_0498.jpg

Full compression, you'll have to trust me that there's no projection behind the buffer beam ;)

IMG_0499.jpg

MD
 

simond

Western Thunderer
Mick,

Thanks for that, neat solution and eminently do-able with or without a lathe.

Being picky, your statement in the first post "In reality you could drill right through and just add the washer, but the tube wall would be thin and the solder joint less resilient. In truth I suspect just the plain drilled bore would be fine, we're not going to be pulling on it, just compression.", isn't quite true.

The screw head is pulling on the solder joint, when the buffer isn't buffing. That said, the spring is largely extended and the force is at its lowest. As an alternative, those with a lathe could turn the "tube plus washer" from a bit of 3mm rod.

Best
Simon
 

mickoo

Western Thunderer
Simon,

Sort off, by boring the 3.0 mm tube with a 2.4 mm drill you are in fact doing as Adrian did. However the 3.0 mm OD tube has an ID of 2.0 mm so you only end up with a internal flange of 0.2 mm around the edge.

So far on three buffers that has been sufficient to hold it all in place.

As an added security (and test) on one of the buffers I soldered a washer with a 1.5 mm hole in it, this means you now have a retention flange of 0.45 mm around the edge.

As a quick test I did a suspended pull load on the buffer head of 1 Kg and it didn't pull through either the simple bored sample or washer sample.

As you say, to emulate Adrian you would need 3.0 mm rod, bore all the way through with 1.5 mm then part way through with 2.4 mm.

Centring a 1.5 mm drill in 3.0 mm rod and boring centrally moves it to the next skill level (where upon a lathe is nigh mandatory), as opposed to opening an existing bore which is more easily done with basic hand tools.

There are many ways to achieve the same result, nearly all will be better than this. I wanted one folks could do on the kitchen table or tea tray on their lap, rather than those with workshops and more complex tool sets.
 

unklian

Western Thunderer
Thank you Mickoo, very interesting and very useful. The diagram was very helpful and I am looking forward to the results of your non turning oval buffer idea.
 

mickoo

Western Thunderer
That is one way to do it and I have tired that way, the biggest issue I had was cutting a reliable straight slot in the shank whilst trying to hold the part by the head and then cutting it wide enough to accept the wire pin. In addition the retainer washer soldered onto the steel base never really took well.

The final death knell for me was that once the pin was in, soldered and made flush you can never get the head out again. I think masking buffers is a chore at best avoided if possible.

MD
 

unklian

Western Thunderer
Nice way of doing it Steph, and probably appropriate for small scales. What I like about Mickoo's technique is it is bolt together and dismantalable . I was thinking of this for Gauge 3 where soldering the buffer bodies to the buffer beam would be a major soldering job .
 

mickoo

Western Thunderer
Nice way of doing it Steph, and probably appropriate for small scales. What I like about Mickoo's technique is it is bolt together and dismantalable . I was thinking of this for Gauge 3 where soldering the buffer bodies to the buffer beam would be a major soldering job .
In Gauge 3 would it not be easier to bolt the buffers to the beam like the real thing, soldering would take quite a lot of heat I think.

I'll start the third option this afternoon, the idea is sound, the practice may not keep up though :cool:

MD
 

unklian

Western Thunderer
In Gauge 3 would it not be easier to bolt the buffers to the beam like the real thing, soldering would take quite a lot of heat I think.

I'll start the third option this afternoon, the idea is sound, the practice may not keep up though :cool:

MD
Exactly, and looking forward to it, no pressure :D
 

oldravendale

Western Thunderer
The process described by Steph is the one I use and which I've previously discussed with Mickoo. It does, of course, have the disadvantage which Mick mentions. However, I've found nothing better to prevent an oval buffer from turning whilst being self contained at the same time. Nevertheless, for a round buffer Mick's process will take some beating for simplicity.

Shame I've already started down the path of the pinned buffers for the GNR tender, Mick!:(

B
 

mickoo

Western Thunderer
Brian,

The Mk III solves the buffer rotation issue and is fully encapsulated thus requires no access from the rear, in fact I like it better than the Mk II which requires constant pressure to engage the screw into the hidden screwdriver blade at the base, the Mk III requires none of that.

Regarding the GNR, you can have what's left of your buffers but the model now has a complete new set of Mk II buffers fitted :thumbs:

Which is doubly good as that means all the castings can now be fitted and a coat of protective etch primer added.

MD
 

mickoo

Western Thunderer
Ok the MK III

First off this is a rough and ready proof of concept build so it's a bit....a lot....rough around the edges and can be improved depending on your whim. However, even this rough and ready approach worked remarkably well.

First off the screw, we need to make a new slot on the edge for the longitudinal blade to lock into.

IMG_0500.jpg

I was a little exuberant with the saw and it's not quite in line with the machined slot, but a slot in the edge of the head we now have.

The second step is to add the internal longitudinal blade, initially I figured a piece of 0.5 mm rod soldered inside the tube would suffice, it would if I wasn't such a clumsy clutz. Mind cleaning the excess solder would of been akin to key hole surgery; so I decided to work from the outside in.

The retention cup is made the same as before, however this time I've made a longitudinal cut down the bored out section. I figured on just making one guide so using a #6/0 blade made a sort of V cut in the end.

Image2.jpg
The area in the cross being removed, the V cut reduces the size of the opposing slot and is easier to fill with solder and dress smooth later, that was the theory.

Next a largish piece of 0.45 thick brass etch waste was cleaned up, the only critical bit is the edge of the longitudinal blade which needs to be nice and flat with crisp corners.

Using the screw head as a depth guide the strip was soldered into the slot.

IMG_0502.jpg

IMG_0505.jpg

Note pi55 poor saw slot on the reverse side, I never could and probably new will, be able to cut a straight line :D

The next step was to simply remove the excess material on the outside and dress smooth and then insert the retention cup into the casting as seen in the previous examples; finally, dress the rear and simply assemble.

To assemble, just push the screw in this base as before but this time lining up the slot in the edge with the longitudinal blade, add the head and simply screw on, no screw driver needed or any need to compress the assembly to engage the screw head in the rod in the base as per the MK II.

The 'blade' runs the full length of the increased bore or in simpler terms, the full length of the buffer stroke.

A small dab of Loctite or adhesive of your choice will lock the head in the required position, the longitudinal blade will prevent it turning in service.

Fully compressed.

IMG_0513.jpg

Fully extended.

IMG_0516.jpg

For improvements you could add two blades and make the shape shown below from etch waste, the 3.0mm section will centre the front end as it's the same dimension as the tube OD, the rear end would have to be eyeballed to make sure it was all square, once fitted remove all of the external excess and you'll be left with two blades inside.

Image3.jpg

Frankly the single blade works well enough and mine is a bit loose but still works just fine.

Overall I prefer the MK III for fully retained buffers with no rear access. But next time take a little more care with the slot cutting in the tube and screw head will be the order of the day.

As has been said before, there are many ways to achieve this so no ground breaking claims made here.

Enjoy

MD
 
Top