By continuing to use this site, you agree to our use of cookies. Find out more

Member postings for kenking-King Design

Here is a list of all the postings kenking-King Design has made in our forums. Click on a thread name to jump to the thread.

Thread: 1/9th Halifax U/C
29/08/2020 10:39:55

Hello Alan, yes it was a slitting saw job, and I forgot which way the backlash on the leadscrew went, hence nick.

Others may be wondering why the first clevis soldering went awry, given the near-perfect result illustrated. It was my own fault, so doubly annoying - I thought I'd just fill that wee step with solder, and one thing led to another, as it does. The final results, after some injudicious filing, were less pretty than desired, so moved to the back seats.

Method of activation is up in the air (boom boom) but it could be screwjack, or perhaps worm and wheel quadrant. It's not yet decided whether individual activation in each nacelle, or one central drive with sideshafts will be used. A dummy nacelle is really needed to help make these design decisions, hence the drive to complete the linkages and have something to play with. Unfortunately shed time has been limited lately so it's all taking longer than one would wish, and it's made for a very long drawn out section of blog I'm afraid, just a collection of snippets rather than an epic episode, but please continue to watch this space, it can only get better ...... can't it ?

Ken

29/08/2020 00:59:45

cont'd.

Still working on the arms, making the clevis ends, in two different ways as a learning exercise.

The first method involved milled clevis pieces, slotted at the other extremity to fit over a retraction arm.

clevis end part dsc04281.jpg

Eagle-eyed reviewers will note a wee step in the slot wall of this one due to a momentary lapse in concentration. Having clamped the two parts together in an old toolmakers' clamp reserved for this sort of duty, I played a gas torch over the faces and aluminium soldered them into one ....

Soldered clevisdsc04280.jpg

then flipped over and did the other side. That looks neat enogh doesn't it ? In truth they didn't all come out quite so well and though perfectly serviceable I've downgraded them to be the rear ends of the arms, tucked up at the back of the wheelwell. I may end up changing them once the method of transmitting torque to the back ends of the arms is established.

Tackling the promoted front ends somewhat differently, I made clevis side-pieces from 2mm sheet, with a 0.5mm rebate milled along one edge. The sheet was then drilled, and cut into strips 8mm wide, each strip having three holes. The purpose of the rebate is to contain the flange of a brass bush, a rough prototype of which can be seen.

front clevis parts dsc04285.jpg

Pegging two pieces to an arm (the original end-hole of which has been cut off) shows how the clevis will be assembled before being clamped, using that good old tool again. With pegs removed I hope to sort of plug-weld through the holes with solder, effectively forming rivets. (Yes, I know I could just have used rivets, thanks)

parts pegged to arm dsc04286.jpg

As the bush flange equals the rebate depth, the clevis internal width between flanges is the same as the arm thickness, which by a stroke of great good fortune is the same as the link end going in there,with a few thou clearance. Amazing or what ?

view of clevis fork and insertdsc04284.jpg

The next post will reveal the results of plug-welding, so fingers crossed.

BTW, I've been thinking about the damper cylinders and method of assembling endcaps to tube body. Out of consideration for the Oring seals I've decided that heat should play no part, so will consult with Loctite Technical Service to ensure using a product guaranteed to be proof against silicon oil. That shouldn't be difficult, I think, and will be a much more sensible approach. More later,

Ken

20/08/2020 00:26:54

cont'd.

Well Dennis, assembly is certainly nearer, but we're not quite there yet. I'm very pleased to tell you, however, that persuading the Oring seals into their wee pockets was no trouble at all. Two cocktail sticks, one with a square cut end, did the job in short order, 'almost as if it was meant', as a friend of mine usually acknowledges the conclusion of any meticulously planned and executed venture.

Before I can proceed further I need to provide means for introducing oil into the assembled cylinders, and for venting air at the same time. 'A glaringly obvious requirement' I hear you cry, and justifiably so, nevertheless it has the undeniable air of afterthought about it. In truth, I had expected there to be plenty of room to whack in a couple of holes, with provision for threaded plugs, and hadn't overly concerned myself with it, but now find it's a bit tight, though achievable I think. The accompanying diagram says it all, being a section through an endcap and seal assembly, with my exploratory thoughts on angled hole positions sketched in.

vent hole drawing dsc04279.jpg

When I tell you I'm hoping to use 10BA plugs you'll have a feel for the situation. With a degree of optimism I've acquired some nice plastic syringes with blunt needles, with which to inject oil through said plugholes.

Another prerequisite for assembly is to have the pistons finished and attached to their spindles because they in turn have to be threaded through the endcaps and tube before the final soldering together, at which point I'll have to have effective heat sinks in place around the seals so I don't frazzle the Orings.

You see what I mean Dennis? Definitely not there yet, and if you're wondering whether a little more forethought might have avoided some of the obstacles catalogued here, well, you are not alone, but HeyHo, sometimes one has to be the fool rushing in whilst the cautious and wary angels never get started. It's a viewpoint, OK?

Later this evening, by way of light relief, I dowel-pinned my prototype retraction arm sidemember to three more blanks, and entertained myself on the mill, cutting off excess and matching the profile ....

retraction arm side members dsc04275.jpg

As you can see, they taper to each end. Pairs will be connected by a stout plate at the front, where those dowel holes will be cut off and a clevis fork substituted, ready to mate with the tubular links made earlier. I spent some time cleaning up edges as I was marooned in the shed by three hedgehogs getting frisky on the nearby patio, and not wanting to interrupt production of hoglets, I kept busy until they'd called it a night. Lovely!

More later,

Ken

14/08/2020 23:22:39

cont'd.

The endcaps have lost some weight as promised, and the components required to complete the Oring housings therein have also been produced - just simple washers .030" thick. They are soldered into the larger recess, creating pockets behind them for the Orings to live in.

The photo shows on the left an endcap for processing, and below it a washer and solder ring, the latter formed by winding turns of fine solder around a mandrel and slicing through. On the right is a soldered item. A weighted probe held the washer firmly down in its recess during heating and subsequent cooling to maintain spacing, as otherwise such small items tend to bounce around and settle in arbitrary positions of their own choosing ......

endcap components dsc04271.jpg

Here are the eight finished endcaps, although the ugly one (that's why it is at the back of the group) may need to be reworked ....

soldered Oring housings dsc04273.jpg

My next trick will hopefully be the insertion of one of those Orings into each housing, with the aid of some lubrication and dexterous manipulation of cocktail sticks. Holes in the washers are larger than spindle diameter, covering only the outer 75% of the Oring, thereby giving me a little more room for manoeuvre. In the next posting I'll let you know how I got on,

Ken

13/08/2020 03:26:43

cont'd.

An even longer absence, for which I apologise. Let me start by tying up a couple of loose ends, or rather, by restating the situation.

Firstly springs. I had selected two concentric springs, and Alanp quite reasonably worried about the mere 0.2mm clearance between them. In the event there was no problem - with the longer inner spring compressed the outer was still free. We have moved on, however, and I have since found I can satisfy all requirements with a single 64mm long spring, saving some weight and better still, gaining the ability to adjust the setup to match final aircraft weight. This is achieved by adding to the precompression in 1mm stages via washers at the end where it presses against the damper cylinder, 1mm equating to around 1/2 kg in aircraft weight.

Speaking of dampers- therein lies the cause of my prolonged absence, or some of it. I had previously decided that the unintended generation of vacuum voids in a partly filled cylinder rendered my use of a piston valve pointless - the partial filling being due to the need to cater for introduced piston rod volume. After much thought mostly at subconscious level, the conclusion was thrust upon me that a through-rod cylinder was the way to go i.e. a cylinder in which the rod emerges at both ends.

One advantage is that the internal volume remains constant, and so the cylinder can be completely filled with oil, thus avoiding any vacuum void generation, and giving fully controlled movement at all times. A second is that this then allows piston valves to act as desired, and so I have reinstated the idea to give easier compression but slower extension of the U/C legs. I hope thereby to reduce the chances of a bouncy landing whilst still damping and softening blows from terra firma. That's my idea, but if you think otherwise please say so - I'm flying by the seat of my pants on this, and mey be barking up the wrong tree. Discuss.

Having wasted a lot of time and effort in trying to make dismountable Oring housings, for easy seal changes, I realised the issue was becoming far too complicated, so opted for a simple soldered housing with the hope that leakage will be negligible. Cylinder endcaps are shown in early stage of manufacture. Two different O.D.'s serve to centralise the cylinder as it spans the change from upper leg to lower. One cap has its Oring fitted whilst another is pressed into the end of the 3/8" tube for cylinder bodies ......

damper caps and tube dsc04269.jpg

The Oring seen more clearly here, is 2.29mm ID and 1.1mm section, Viton rubber. There's a lot of spare brass still to be removed btw, so caps will not be so chunky when finished .....

cap and O ring dsc04270.jpg

Two-part piston valves are also being made, comprising aluminium piston and valve ring. Pistons have just a couple of thous. clearance in the bore, whilst the valve ring has a few more. Oil must flow either around the piston for slow extension, or via a ring of feed holes (not yet drilled) to flow around the ring for easier compression. In the photo below one pair is in the closed position whilst the pair nearest the camera is spaced apart. The difference in diameters of piston and ring are barely detectable. but have a marked influence on flowrate (see earlier trials on 19/05)

piston pairs dsc04267.jpg

Hopefully manufacture and assembly of all the above will be completed in a few days for your perusal, and attention will return to retraction linkages. Until then,

Ken

.

19/07/2020 01:30:36

Hello Alan, thanks for congrats. In the background is actually the 3mm reamer in the drill chuck. Brass tube is in the foreground, laid on the vise jaw,

Ken

18/07/2020 01:29:03

A celebratory lunch today (wedding anniversary) required an extended siesta afterwards, restricting shed time. There was sufficient, however, to conclude manufacture of the four retraction links using the method established a few days ago i.e. aluminium tube flattened and drilled at both ends.

Four pieces were cut and faced to 68mm long and were marked up. The first ends, in turn, were entered into the machine vice on the mill, as far as the scribed line. Processed as described earlier, but with a second stage squeeze using a second, thinner blade formed a nice flat end, avoiding the usual dumbell section of a squashed tube ......

link sectiondsc04260.jpg

As it was important for the second end to occupy the same plane (no pun intended) a small toolmakers vise was propped on parallels to hold the first end vertical whilst the othe end was similarly dealt with ......

links second enddsc04259.jpg

The two brass blades can be seen here, as can a rusty block of steel used to give a horizontal sighting line - simple things work best, don't they ? The pressed blanks were drilled in another simple setup, unfortunately appearing on its side, sorry, forgot that would result from rotating the camera ........

link drillingdsc04262.jpg

To get the flat truly horizontal I balanced that brass tube on it and visually aligned the tube with the machine column - simplicity again you see. Both ends were drilled and reamed, pitched at 60mm centres via machine leadscrew, then all that remained was to radius them. For this a filing guide was used, comprising two short pieces of rod, 8mm diameter, centrally drilled, and bolted either side of each flat. Filing down to the rod was done in the hand, and finished off with a rub of wet and dry paper .....

finished linksdsc04263.jpg

I think they'll look alright between the arms and castings, and should be stiff enought to withstand compression loads from the bumpiest of landings. More later,

Ken

13/07/2020 13:31:59

Hi Alan, digits normal but I had to go down one size of clip in order to get strong retention on the 3/32" spindle, hence groove is .025" rather than .028" quoted previously, and yes, a bench magnifier played an important role.

Ken

13/07/2020 01:32:20

cont'd.

Only got a little work donr today, so just a short update. Found and reground a tiny lathe tool to suit the .025" thick 'E' clips, then established the required depth of cut to get a good snapon, and proceeded to groove four spindles. When I have to lick my finger in order to pick up a component it signals that I'm operating at the lower limit of feasiblity ........

dsc04257.jpg

.... and quite often outside the accepted bounds of good hygiene, but eventually managed to get all four on.

I then turned recesses in the caps to contain each clip and its short spindle protrusion, giving a flush fit ....

dsc04258.jpg

...... and was very pleased with how solidly they retain the caps, despite their diminutive size. The overlong spindles now await me figuring out what is needed at the other ends for damper pistons etc.

Regards,

Ken

11/07/2020 02:08:10

cont'd.

Here are four LA spring caps plus a spare, lightly counterbored to locate the top end of the 8mm OD inner spring, and drilled for a 2.3mm stainless spindle. In the foreground is one of the 'E' clip retainers. I've yet to try turning a .028" wide groove in the spindle material to take a clip. The plan is to also counterbore the other side, to the OD of the clip, so that once engaged and bedded in there it can't get off.

spring capsdsc04256.jpg

Also today experimented with making the short links from LA tube, as simply as possible. The end was flattened n two stages, the first to expand the bore width sufficiently to insert a brass blade, then the second to flatten onto the blade, thus achieving the desired end thickness to fit within the casting lugs. After removing the blade,the end was rounded and drilled, and a 3mm hardened steel dowel fitted through. The open slot accepted a drop of Loctite, and after a decent interval the grip was tested - it was very strong - perfect.

Link end test piecedsc04252.jpg

In practice the link will be fitted in the lugs, then the dowel will be fed through and bonded. All being well, dowel will rotate freely in lug bushes, and link will swing happily. A similar arrangemnet at the other end will connect link to operating arm.

It was nice to be back in the shed after quite a break, more soon,

Ken

10/07/2020 12:25:21

Alan, you are right, there is little clearance between the two springs, 0.2mm in fact, but I'm hoping that is sufficient to ensure snag-free operatiion and I'll be looking at that very carefully as soon as the springs arrive. I'll let you know !

Regards,

Ken

09/07/2020 23:48:34

cont'd.

Hello again Dear Readers. Did you think I'd deserted you? Never, though I admit to having been absent for a while, due mainly to this and that, but nothing earth-shaking, and now here we are, off adventuring once again.

Martyn K asked if I'd seen any pneumatic damping, and I have now. The leg/wheel assembly moves under gravity like one of those slow drawer closers, which is gratifying as long as I can preserve that freedom and fit.

And alan p, note that a few pragraphs ago I was using a paper cutout and pin, the more elegant drawing followed on from that vital first exercise, so we share a common approach.

So, what's been happening ? Well, for a start, I've ordered the springs for a target weight of 25 kg. Each leg will contain two springs mounted concentrically. The inner is 8mm OD, 51mm long (the full housing length) whilst the outer is 11mm OD but only 38mm long. Both have about the same solid length i.e. when fully compressed, at which point the inner exerts a force of 3.2 kg, and the outer a heavier 9kg. In practice, from full extension only the inner is acting upon the leg for the first 13mm of travel, with force climbing from 0 to 1.2 kg, so very gentle. At that point the outer spring also comes into play, and over the next 7 mm travel to the 'Aircraft at Rest' position the combined spring force climbs to 5.5 kg, which nicely supports a 25 kg aircraft. (Remember there are four legs, each of which supports 22% of the weight. The remaining 12% rests on the tailwheel).

The aircraft would have to experience a 2.2 'g' vertical deceleration in order to exercise the further 11 mm compression available, when the leg force will have climbed steeply to 12 kg. One fervently hopes this situation will not arise, and indeed it should not, because interposed twixt U/C and terra firma will be a 7" diameter pneumatic tyre and its shock absorbency, plus the gentle deceleration occasioned by the early stage leg compression, should have slowed things down a bit.

I've some aluminium in the lathe as I write, being turned into the first of four upper spring caps, and to retain them on the central spindle I've received some dinky little 'C' clips to click into a groove. The'll carry almost no load so can afford to be dinky.

The other thing I've done is cut the first 3mm thick actuating arm, measuring 237mm centre to centre, from some large extruded aluminium angle which has lingered in my metal rack for yonks. I like extruded aluminium sections because the material seems to be inherently stiffer than cut sheet, and I'm sure there is a good reason for that, buried within the extrusion process conditions. Anyway, these arms are solidly linked in pairs, hingeing at the rear of the nacelles, and at the fore ends connecting via 60mm links to the lugs on the rear of the castings. As the arms swing upward the links pull the castings back and up into the nacelle, as per the drawing of June 19th.

Ben and I share a desire to have the motion imparted via worm and wheel from electric motors. Still quite a lot of work required in that department, and a reproduction of Ben's nacelle construction will be needed to house a sample U/C assembly and allow measurements of torque required, followed by games with gears, motors and microswitches. I look forward to that, but it's some way off.

That has brought you up to date; not very exciting perhaps, and no pictures to look at, but there will be more soon. Thanks for revisiting,

Regards,

Ken

19/06/2020 16:22:12

cont'd.

A change of plan, quite literally, and for the better. Following the previous exchange with Ben I re-examined the photo evidence on which my efforts to date were based, because I couldn't understand why things were not a better fit within the nacelle. I'll cut a VERY long story short by saying that the plan depiction of the U/C door was a little inaccurate and hence adversely affecting positioning of the casting pivot. A lot more eyeballing, measuring and scaling led to significant revisions and a clearerer understanding on my part of how things should be arranged.

Suffice it to say that a revised scheme now has the existing casting and leg sitting where it should, and retraction linkage is free to operate without conflict anywhere - no changes to U/C parts, wing tube position - nothing !

final U/C scheme dsc04247.jpg

Relief doesn't begin to describe my feeling, nor that of Ben I suspect, although he maintained his cool throughout.

Best of all, there is now remarkably good agreement with scaled photo evidence. You may just be able to pickout the labelled points where the casting emerges from the lower edge of the door, and the extent of the exposed tyre when retracted.

On that happy note, making the linkage can now proceed with confidence, and I'll simply HAVE to make a dummy nacelle well so that I can play uppy-doony ( as well as experiment with actuators).

Ken

13/06/2020 01:59:39

cont'd.

Three weeks have passed since the last entry, so you may have been wondering what was or was not happening.

Firstly, both 'castings' have been brought up to similar condition i.e. linered, and painted silver. Then, following Ben's revision of weight range, I revisited my spring tables and eventually came up with a series of combinations, each of which gave the required 'at rest' compression at an increment within that range. You'd think, wouldn't you, that a spring is about the simplest mechanism to deal with, but sums can get suprisingly complicated and time consuming ....... or maybe it's just me.

After that I turned my attention to the retraction linkage with a view to finalising lengths and establishing how all this gubbins was going to be fixed into the nacelles in suitably robust manner. Obviously that was going to require close collaboration between Ben and I, so I fired off a requests for detailed nacelle views and dimensions, which he promised to send in a day or two. Days passed and I realised Ben had gone awfully quiet, in fact he'd dropped off the radar completely and remained out of touch for quite a while. I feared the worst, but thankfully he eventually 'returned to the land of the living' as he put it. Quite how far he'd travelled in the opposite direction I don't know, and he isn't saying.

At any rate, a drawing did then arrive, also showing the original sprung wire U/C arrangement. I copied the side view and I plotted my best estimate of the scale casting pivot point (quite different to the wire one) and the rear pivot of the main retraction link.

linkage dwgdsc04244.jpg

A few twirls of my compasses later I realised there was a major problem. The slightly shorter scale legs, coupled with repositioned pivot, meant that the retracted wheel sat further forward in the nacelle and conflicted heavily with Ben's planned position for the 2" diameter wing joining tube (seen below, faintly coloured green, as I then was). The paper cutout over Ben's plan drives the point home.

Retracteddsc04242.jpg

Knowing Ben already had the laser-cut parts I gloomily feared I might have to remake and lengthen the steel tube legs, thereby also sacrificing the scale veracity we'd sought. Ben, however, was much more relaxed about the news than I expected, and has pretty much undertaken to reposition the tube, lifting my black cloud.

As a result I'm now back planning the linkage parts and mounts, based on my estimated scale dimensions, so watch this space.

Ken.

20/05/2020 14:32:00

No typos Ian, we've been talking kgs throughout, but you're right about the likely model weight of course. Ben was testing me I think, perhaps ensuring a good built-in safety factor. He has since revised his estimate to between 20 and 30 kgs, so you are both in the same ballpark. Maybe he is planning a full bomb load.

Ken

19/05/2020 12:04:40

I know what you mean alan p, Let's hope we don't also see even the high estimate being grossly exceeded, in the usual manner of such things.

In fairness to Ben, he deliberately gave a very wide range, within which the weight was pretty certain to be contained, in order to ensure the design of the U/C would not be a restriction, and I'm pleased to say it's not.

BTW, if anyone disagrees with my analysis and predictions about the way the damper will work, do please speak up. I'm very aware that I'm shooting from the hip here, and a different viewpoint will be interesting. For instance, I haven't really taken into account the effect of displaced oil above the piston being in a confined space. The internal cylinder volume, and initial fill, must leave sufficient top space to keep ALL oil contained within the cylinder despite the intrusion of the extra volume of the piston rod during compression. Will air be expelled or inhaled through the 'O'ring under such circumstances ? What do you think ?

Ken

19/05/2020 00:27:41

cont'd.

Several hours yesterday were spent poring over my spring tables and doing sums to determine which springs could be used to cover the range of finished model weights given by Ben, the builder, anything from 25 to 45 kgs.

I'd earlier calculated wheel loadings and hence individual leg loads, so knew each leg needs springs to give from 5.5 to 9.5 kgs in the 'at rest' position. Selections worked out alright and I was pleased to find no dimensional changes were necessary within the assembly. That allowed me to start on the hydraulic dampers, which are to be located within the lower leg sections. Each damper comprises a thin-walled brass cylinder, incorporating a piston on a rod which passes through the cylinder cap, with 'O' ring seal, and extends through the springs to the top of the leg housing and a disc cap. Springs are trapped between the two caps, so we end up with almost a 'coil-over-shock' arrangement.

A very simple test cylinder was made by soldering a length of tube to a brass block, robust enough to be clamped in my vise .....

experimental damper cylinderdsc04238.jpg

An equally simple piston was turned on the end of some LA rod, initially to just comfortably slide in the tube, a bore of .375" with maybe a thou or so clearance .......

cy;inder with LA pistondsc04239.jpg

The silicone oil purchased some time ago for this very purpose was eventually tracked down, and a good fill-up added. Just to get a feel for things I inserted the piston and pressed down against fairly solid resistance, but the piston did very slowly sink . The BIG surprise came when I went to pull it back up, expecting similar resistance, but NO ! Up it came quite readily, though it felt as if I was pulling against a spring. - most intriguing.

I eventually worked out what was happening, confirmed by calculation. The piston area is so small that a pull of only .74 kgs is sufficient to overcome atmospheric pressure and create a vacuum zone below it, which acts like a constant-force tension spring. I admit that this is an aspect which had not occurred to me, at all.

The effect lasts until the oil above the piston has seeped back through the clearance gap to fill the void, something it does even more slowly because a pressure differential of only 1 bar is now motivating it.

To get some measure of performance I used a fixed weight of 2kgs acting on the piston rod, steadied by hand ...

2 kg weight on pistondsc04240.jpg

and timed the piston fall over a distance of 25mm, taking 10 seconds. Next, having reduced to piston diameter to give .005" clearance, I repeated the test, this time logging only 2 seconds.

Pulling the piston up was also quite different because the oil return flow was a lot quicker and the vacuum effect short-lived. What a difference those few thou made !

Thinking about the impact all this has upon the great scheme of things I came to the conclusion that my idea of having a clever piston valve is now quite redundant, and so my secret design will remain just that - a secret.

I reckon in practice this performance may prove to be about right. In a hard landing the tyre takes the initial blow and transmits force to the legs. They compress as fast as the damper will allow, further softening shock to the airframe. If the aircraft bounces upward the legs will begin to quickly expand again, creating the vacuum space as described. If they have not reached full extension before the next impact they will immediately shorten, the vacuum space will disappear, and at that point normal damping will resume. In the VERY unlikely event of a series of reducing, damped bounces the legs will go through repeats of the above cycle, to return in stages to their original length, ergo, no valve needed !

Making up the dampers just became much simpler, and with them, the spring enclosures. I have some springs to hand for trying things out, but the REAL ones needn't be ordered until we have the model weight firmed up. Sighs of relief all round,

Ken

16/05/2020 00:41:07

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 ......

leg tube plugdsc04233.jpg

plug trial fitdsc04234.jpg

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 ....

plug boreddsc04235.jpg

finished plugdsc04236.jpg

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 .......

leg bracket bushesdsc04237.jpg

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

.

13/05/2020 11:19:20

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

13/05/2020 03:14:26

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

liner and sliding tubesdsc04228.jpg

THE COMPONENTS AFTER

wrecked, after extractiondsc04229 (1).jpg

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

second assy, extendeddsc04225.jpg

'AT REST' COMPRESSION

at rest compressiondsc04226.jpg

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

Support Our Partners
Slec
CML
Sussex Model Centre
electricwingman 2017
Sarik
Advertise With Us
Latest "For Sale" Ads
NEW POLL - has the pandemic altered your event safety perceptions?
Q: Has the covid pandemic deterred you from attending shows and events in 2021?

 No, I'll be attending just as many as I usually do
 No, but I'll choose my event with greater care
 Yes, I'll attend fewer events going forward
 Yes, I wont attend any where previously I have

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E!