1/9th Halifax U/C

[kenking-King Design]

cont'd.

As a little light relief from soldering I took offcuts of the two steel tubing sizes to be used for the legs, set one into the other, then polished the smaller diameter, being the oleo leg which will protrude from the Messier casting .....

then positioned it in the sliding tube to see how it looked with the retainers and nuts ......

I thought that looked good, but decided I'd bored out the retainer plates too big, and there wasn't as much land left as I'd like to act as the downstop for the leg, catching the larger diameter tube. A second set of retainer plates was therefore made, corrected accordingly.

If any of you are thinking I was just mucking about, looking for ways to avoid the final soldering job, all I can say is 'How very perceptive of you'.

Having thought about it a bit more in the interim though, I realised I was needlessly making life very difficult by trying to solder on the INSIDE of the assembly, hence putting all previously made joints at risk. The idea had been to avoid much external cleanup, but soldering round the OUTSIDE avoided the dangers, so that's what I did. Trying to leave a proud bead resulted in some less than pretty seams ....

and I can't pretend it was all plain sailing, but eventually the job was done. The trusty belt sander was used to VERY carefully reduce the beads back to the desired surface, bearing in mind the sheet components are only 1.5mm. The first one is sanded as far as I'm willing to go ......

and there remain small surface defects and sunken areas which I intend to fill screed over using Lilliput epoxy putty, before a final sand.

Huge sigh of relief from me, and perhaps I detect some from readers who have been flogging their way through this saga, and are now look forward to more interesting aspects?

To finish the 'castings' the arches and shrouds will have balsa infills and be skinned with lining paper to give a smooth continuous surface through the tunnel, and rear clevises added for attachment of actuating arms. I'll show them when finished; I reckon we've all seen enough of these for a while. you can all have a gold star for endurance,

Cheers, Ken

[alan p]

Well done Ken excellent work.

Noting your trepidation re the final soldering it is hellish difficult to keep existing joints whilst completing subsequent one's.

In admiration

Alan

[kenking-King Design]

cont'd.

I know I said I'd not mention them again until finished, but couldn't resist a picture of the head sculpted to show the shallow ribs over the top pivots. The radiused edges help make it more casting-like and add a little more realism ...

Just one more hot process to go through before filling in the arches, and that is making and attaching the leg clevis brackets for connecting the retraction arms.

I scaled bracket dimensions from the Messier service manual cutaway, and have started machining them ....

I'll get two out of this block, then repeat for the second casting .......

Once they're on, the arches filled in, and the brass liners with stud plates are bonded in, I plan to give a spray coat of silver/grey which I hope will complete the casting illusion. Can't wait for that. Then when Ben paints them black he can simulate wear and chipping in strategic places to reveal the casting colour beneath - a standard 'weathering' practice I've admired in the work of you real scale artists.

In the meantime I've also started planning the dampers construction. I have four spring-loaded ball type non-return valves, salvaged from some hand soap dispensers, and hopefully they will play a part in changing resistance with direction. Silicon oil struck me as being a promising fluid to use, and I will initially run some simple tests, pushing and pulling a plunger in a tubeful, to get a feel for how resistance alters with different plunger clearances, using knowledge gained to fix the design. More on that later,

Ken

[kenking-King Design]

cont'd.

Having finished the clevis brackets, thanking my lucky stars I'd remembered to make L.H and R.H. versions ....

I soldered them on in what I hope is the scale position. I'm going to fit a tiny brass bush in each eye, flange facing inward, to prevent undue wear, and house a 3mm stainless dowel pivot pin for the retraction links.

That was the end of hot processing, meaning I could give my attention to block balsa infill of the arches, and a 1.5mm sheet on the rear faces. Balsa was shaped to fit the spaces, but left oversize, and was epoxied in place, a task which took a lot longer than I had anticipated. When all was hardened, the bandsaw was used to cut and nibble off most of the excess, but wanting the arches to be smooth and true prompted me to make a sanding drum of sorts, actually a bit of old fencepost .......

but it did the job, whilst adding more layers of wood debris to the lathe ....

Please overlook the yawning gaps between blocks if you will.You should have seen the amount of rubbish epoxied to my fingers after the exercise of trying to slide each into place without dislodging the previous ones.

After sanding, the arches were lined with - well - lining paper, what else ? and would have looked quite tidy but for this new adhesive also getting all over my fingers, then transferring the grime to the paper with faultless adhesion.

I really CAN'T wait for the spray primer to arrive.

A new day dawned, and a start was made on the spring/damper cartridges, the first elements of which are the soldered assemblies of 5/8" brass tubes, bottom plates and studs. I used lead-free silver bearing solder for this as it's stronger and harder than tin/lead.

For neatness I wanted the studs to protrude only enough to carry a nut, and show just the tip of the stud, and of course the bottom plates needed to sit square to the tubes, so a soldering jig was made from scrap aluminium bar and rod. It held the tube and plate square, whilst a turned recess allowed bolts to be threaded through the correct amount ...

After soldering the bolts were cut off behind the plate. They are steel 6BA, and the only load they carry is that of the remaining spring force when legs reach full extension i.e. aircraft aloft, or on a supporting stand. Nuts are 7BA hexagon size.

The four finished tube assemblies will be permanently bonded into the 'castings' once I've received a 5/8" reamer to dress inside the square legs. These brass tubes will push in at the moment, but are quite tight, so I reason there must be slight deformation of their thin walls and that could affect the fit of the next tubes in the sequence, removable elements which should be an easy in/out when required. The reamer will just scrape off a thou or two in strategic places. It's on its way, same as the spray primer .....

Ken

[SR 71]

Super work, but it all looks so heavy, be interesting to see the finished weight

[kenking-King Design]

Hello SR71 (fantastic looking model btw), I understand what you are saying, and frankly I share some of your concern, but I'm also mindful of the forces involved when a model weighing as much as 45 kgs smacks down at speed onto hard, bumpy terrain, and I'm intent on the undercarriage not being a weak link in the chain of force transmission into the aircraft structure. It may turn out that I've overemphasised the strength required and that too severe a weight penalty has been incurred, we shall see. Redesign is not a dirty word, and I'm always happy to receive informed opinion, and I respect the valued experience of others, so don't hold back.

I agree that the last photo looks like something from a boilermakers' convention, but in reality those brass tubes are only .015" wall thickness, the plate is about 1mm and there's not a lot of it. When you see the next photos, of the steel tube legs, then you may justifiably have conniptions.

When working out how to build something, such as these U/C units, one faces a series of compromises between material desired and what is actually available, further hampered by lack of time, facilities and funds to carry out destructive testing of alternatives, so conservative gut-feeling holds sway.

Certainly, by the time the hollow legs have been filled with springs, and damping cylinders of oil, and the hubs carry braking equipment, then these WILL be heavy units, but on the other hand fragility will not be a concern, and I hope even severe descent rates into terrain might be survived by the model as a result.

Thanks for your interest, and how about emailing me some info on that model (rather than in this blog)?

[SR 71]

Which model ? , thanks for the reply, yes the pictures can be deceptive,

[alan p]

Liked your soldering jig solution, simple and accurate Landing something the weight of 2 sacks of suds will need some thing substantial to support it. Proof of the pudding will come later but as you say gut feelings generally prevail. Projects like this show us what can be achieved with access to minimum tooling.

[Ben Arthurs 1]

Really looking good Ken . The sculpted edges around the top pivot really bring it to life.

Weight is a concern , But do not forget this is a big model, Nearly 14 feet span.. Think about the amount of metal and meat that goes into for example a 1/4 scale Seafury retract unit and leg and wheels ... I would rather robust over fragile.

Regards

Ben

[kenking-King Design]

cont'd.

Thanks Ben. A little more done over the past couple of days with the legs themselves. Each leg comprises two steel tubes, a larger one internal to the casting, and a smaller external one .......

By reaming the large bore and slightly reducing the smaller O.D. they can be persuaded to nest together, and they will be bonded with a loctite product ....

. You may remember that earlier in the blog I made up a short section to see how a polished tube would look emerging from the leg, and those pieces were bonded. I've tried knocking them apart and can't, so I'm confident in the bonding. At the end of the leg is a two-piece axle clamp, a brass upper plate, and a L.A. lower, with a 6mm transverse hole on the joint line to take the axle.The upper is brass for reasons of joining, firstly to the steel leg, and secondly to accept a torque arm from the brake drum.

Here you can see the uppers, with shallow sockets for the legs, and in the background the L.A. lower plates, yet to be seperated. Finally remembered the philately term for this (but stamps, obviously) - se tenant, holding hands I guess.

Gravity provides a most reliable clamping method.

In the lathe the plates were turned, forming a collar whilst shedding some weight ....

Those black tubes are the bits I said I would polish ! Me and my big mouth.

On another front, the grey primer arrived. It was all of five minutes before the lid came off the can, and now spraying and rubbing down is in progress. Still waiting for the reamer though, so can't fit the lining tubes yet. More soon,

Ken

[Nigel R]

Lovely work ken.

[stu knowles]

Proper works of art!

I wouldn't worry about the weight. It's a large model so wil be able to carry some and nothing will hasten its damage more than an unreliable undercarriage.

I'm looking forward to watching it develop.

[kenking-King Design]

cont'd.

Another week of lockdown, and some more done, though not as much as I'd hoped. Still waiting for the reamer which I need before I can assemble the liner tubes into the 'castings'; ten days in transit, 2nd class post from down South, and still no sign, most frustrating, In the meantime the castings just hang there in their grey primer, waiting, waiting ..

Transferring my attentions to the legs, I bonded upper and lower segments using a lathe setup to ensure alignment, then gave thought to axle location. You may recall the planned arrangement of a split foot for axle clamping between a brass upper plate and LA lower, with half diameter troughs - actually .005" less in each, giving .010" clamp gap. I want the axles to play an active part in maintaining rigid leg parallelism and uniform movement, in other words to hold the leg spacing at the design centre distance at all times in a foolproof manner. A groove machined into 6mm (simulated axle) rod was supposed to locate on a ridge left in the half-bore of the brass part, but achieving a satisfactory ridge proved too difficult, so the half-bores went straight through, using a slot drill. Ridges was added later by parting off rings from a brass tube, and soldering them into the bores at the outer end. The rings are .070" wide for no reason other than to match the groove width from my parting tool. Holding them in location whilst soldering required lateral thinking in the jig department, but a solution was found - two down, two to go .....

Two rings are visible on the left, adjacent to an axle groove. The first one done was fiddly and did not behave itself at all well, the reworking reintroduced heat stain to the lower leg, so that's got to be cleaned up, again, and water spray urgently needed further along to prevent the bonded joint from degrading. Steep learning curve, and the second was much simpler.

It was pleasing to assemble the first clamp and feel the rigidity achieved. That little brass collar will carry no real load, it just positively locates each axle end in legs at the correct centres, until the four clamp bolts are tightened ...

Perhaps my reamer will arrive tomorrow??

If not, its hydraulic damper time, and I've had an idea for a very simple valve to change damping rate according to direction, much better than my original vague notion of spring loaded ball valves from soap bottles. The aim is to have but slight hydraulic resistance as the U/C compresses on a hard landing, but significantly more resistance to the U/C expanding again, making it slower to recover full length and hopefully limiting or even eliminating bouncing. Of course, I have no control over how the tyre reacts, but springs I hope to control with a firm hand. Anyone care to comment on this approach ? I'd love to hear of your experiences with damping mechanisms,

Ken

[SR 71]

Dont think we can comment, your way above us mere mortals

[Ace]

Like SR71 way, way above my skill level : "Comment" - brilliant, more please

[kenking-King Design]

cont'd.

Thanks for the kind comments chaps, but you flatter me undeservedly, as you will see later on.

My reamer did in fact turn up the next day, so I was able to forge ahead, getting square tubes ready to accept liners freely, and proceeding to dry run assembly of the parts, at which point some problems arose. Leg/axle assemblies would not slide consistently, and parallelism was an issue. It turned out that the 'collar in a groove' idea gave more trouble than benefit, although it took me ages to finally work out what was going on. A tiny bit of excess solder, collar positioning and fit in the groove, as well as some clamp issues, were all combining to induce very slight cant in the legs as the clamps were tightened, so I took the decision to scrap the idea. To restore accuracy I put each leg into the lathe in turn and faced the brass foot, making it absolutely square to the sliding axis. I then put two feet together face to face, and bored right through, giving me a true semicircular trough in each. The aluminium clamps were modified too, the 6mm diameter groove being opened up to an 8mm curve but retaining the same depth.

This new arrangement gave true axle bedding in the feet, with no possible interference to alignment from the clamps.

Sorry, that's perhaps too blurred to see the effect. At any rate, it solved the problems and I was able to put things together and repeatedly achieve very free leg movement.

Great ! A lot of time and head scratching but I was finally at the point where I could permanently affix the liners, ...

and THAT, dear readers, is where it all went wrong, horribly, HORRIBLY wrong.

[kenking-King Design]

cont'd.

I had a Loctite product to bond them in, and at the same time I would apply a little bead of epoxy to the top of each foot to fill the slight irregular gap where it abutted the endface of the 'casting'. I mixed some epoxy and applied it, ran some Loctite the full length of the first liner surface, and proceeded to insert it, taking care to align it rotationally. Unfortunately I hadn''t appreciated just how quicky the bonding would take effect, and before fully home it was stuck - really stuck. In trying to turn the liner with grips the stud flange bent and finally broke off, and there I was, up to my neck in poo. Talk about snatching defeat from the jaws of victory !

Of course, I'd inadvertently left the sliding tube inside and had started bending stuff before I realised it, by which time it was impossible to simply slide it out. I now had a double thickness tube to deal with.

I shall draw a veil over the activities of the following hours, the overiding concern being the potential destruction of the 'casting', but eventually, after much hammering of shaped probes and ordeal by fire, surgery was resorted to, and the sorry wreckage removed.

THE COMPONENTS BEFORE

THE COMPONENTS AFTER

I now have no reservations about the strength of my built 'castings', and the greatest possible respect for the strength of the Loctite bond - phenomenal. No irreparable damage was done to the 'casting', thank goodness, though restoration will take some thought and time, and parts have to be remade.

They say if you fall off a horse you should immediately remount, and so, applying the same principle plus the hard-earned lessons of the above debacle, I took the second 'casting' and, by using a much shorter bond length and not hanging about, successfully incorporated both liners in short order.

Rejoicing was tempered by thoughts of behind-the-scenes restoration work to come, but nevertheles I celebrated by adding the wheel on its axle, which really puts the whole U/C assembly into pleasing perspective.

FULLY EXTENDED

'AT REST' COMPRESSION

Scale hubs will be a major improvement and will appear in due course.

There you have it for the time being - I did promise this would be 'warts and all' didn't I ? Thanks for laughing in such a sympathetic manner. More later, much later,

Ken

[Nigel R]

No laughing here Ken. Rapid setting adhesive is a blessing and a curse.

The second unit looks brilliant.

[Bucksboy]

Marvellous, thanks for the really clear explanation too, it all takes time.

[Martyn K]

Fantastic work Ken. I am loving this.

Is there any pneumatic damping due to the good fit?

 

What stops the legs from sliding out when gravity takes over?

 

Martyn

Edited By Martyn K on 13/05/2020 09:31:49

[alan p]

Many commiserations Ken. Loctite as many engineers have found is not so benign as many think the clue being in the name Loctite. I was wondering how you would reconcile alignment issues. This is a engrossing thread congratulations.

[kenking-King Design]

Morning All. I've just surfaced after a VERY late blog session last night, and I see there are a couple of questions to answer.

Firstly, Martyn K; There are split keeper plates at the leg ends, retained on the four studs. You'll find details earlier in the blog on 2/4 and 9/4. I've not noticed any pneumatic damping during dry operation, but I guess a thin lubricant film might change that.

Secondly, Alan P., I was beginning to have serious qualms on this issue too, but since revising the foot/clamp arrangement there are no problems whatsoever. (Why do I feel vaguely uncomfortable as I write that ? Tempting Providence, perhaps ?) In truth there shouldn't be problems because the feet/clamps are pretty accurately squared to the sliding diameter of their legs, and the housings in the 'castings' came out parallel to within a couple of thou, measured across legs at full extension, thanks to the solidly made build jig mkII. Axle units now slide in and out under the action of gravity alone, (even without the wheel weight), which is as it should be, and is why I spent so much frustrating time chasing down the friction problems I was seeing.

Thanks to all for your continued interest,

Ken

[kenking-King Design]

cont'd.

Repair of the 'casting' took priority today, after having thought hard for a while, and a method being settled upon. The leg tube needs a really stout lid as it takes all the spring thrust, that's why 2mm plate spans the area, and so the repair needs to be equally solid.

First step was to mill a flanged plug for the hole at the leg top ......

A little doctoring of the flange ensured it would sit flush, then it had to be bored out to accept the replacement liner tube. As the bore equalled the square size, a cunning plan was needed. A short section of leg tube material was fitted around it whilst most of the interior was taken away, then a hacksaw cut allowed removal of the tube support, leaving a four-legged insert ....

The insert is now bonded in place with THAT Loctite, and I reckon there's more than enough contact area for the strength required. I'll also try to have the liner tube bonded into it so it will be held from both ends, so to speak.

There followed more surface restoration work and epoxy filling, and the unit is supended fro the shed roof to cure nicely overnight, to be followed by sanding and primer painting. I can't yet make the replacement liner or sliding tube as I haven't any spare material to hand; it's on order though, so with luck a few more days will see this unit back where it was a week ago. That's progress ??

There was enough time to make eight small steel bushes for the retract linkage brackets on the back of the castings .......

These will be bonded in place with the flanges to the inside, giving wear resistant facings for the link within. I ordered twenty dowels, 3mm x 10mm long, but instead received 10 dowels, 3mm x 20 long, a very minor irritation at this stage.

Ken

.

[SR 71]

The man who never made a mistake Ken never made anything, superb thread

[alan p]

I do admire the lateral thinking regarding the jigging, reminds me of the many small toolrooms that produced much with very little in years gone.