Hollow threaded rod or ...

[Wobbly John]

Werl... I haven't got an M8 drill bit for the uprights and Wobbly John has already been experimenting with 5mm brass rod...

Actually, it was nearer 12mm rod - an off-cut. 

I went into the model shop today for some 5mm, as we haven't got any in the workshop, but they haven't any stock. 

Tried drilling a 40mm M5 steel bolt - the drill bit snapped at about 22mm deep - it wasn't very free-cutting. 

[Jurek]

I have a couple of unused extra- length (around 200mm if memory serves) drill-bits at home - although I cannot remember what size they are - I've a feeling they might be M8. I'll check tonight.
Would that be of any use?
I'm quite happy to put them in the post to you.

[jsabine]

I can't help wondering if the suggestion up there^^^ somewhere of repurposing presta valve stems wouldn't be sensible - certainly it seems to me less work to investigate it than to start threading tube or drilling rod. Lengths up to (at least) 75 or 80mm readily available, either using tubeless valves or by sacrificing inner tubes ...

[Wobbly John]

...except they are neither the correct inside nor outside diameter... 

[TheLurker]

I went into the model shop today for some 5mm...

Twas ever thus and evermore shall be so. 

Tried drilling a 40mm M5 steel bolt - the drill bit snapped at about 22mm deep - it wasn't very free-cutting. 

OK, so as well as the cost of several lengths of rod I owe you a drill bit as well.  I do hope you're keeping a tally.

... it wasn't very free-cutting. 

Yeah, I used rather a lot of Finish Line Wet when drilling out the coach bolts and they were (are) at the cheese end of the spectrum as regards hardness.

repurposing presta valve stems wouldn't be sensible - certainly it seems to me less work

Wot Wobbly John said plus this has become a "project" now.   Joking apart I'd like these particular components to be both robust,  large enough to not to lose easily when in the field and to be easy to manipulate with old* and or cold fingers. 

*I'm not especially ancient but I have noticed a distinct degradation in manual dexterity over the last few years.

I still don't understand how & when you assemble the components in your first picture.

There's not much assembly.  The threaded rod takes an M5 nut/wing nut either side of the frame.  Remove the nuts to reposition the bolt up or down in the frame arms for deeper / shallower fuselage.  To allow for a narrower / wider fuselage alter the position of the nut/wing nut along the length of the threaded rod.   

Most of the time the height setting is likely to remain the same so in the field it'll usually just be a case of adjusting width by backing off the nuts and moving the threaded rod in/out as necessary.

I'll go away and scribble something and / or take a few more pictures to see if I can explain things more clearly but may not make it back with a reply this evening

[andytheflyer]

.......goes off to look in box of bits for an Irvine 25........

[Jurek]

I appear to have an M8 drill bit - length 250mm (I reckon that'll drift like f*ck over that distance)
And a pair of M5 bits - length 160mm.
All unused.
Does that help at all? Wobbly? Lurker?

[Crumbling Nick]

I still don't understand how & when you assemble the components in your first picture.

There's not much assembly.  The threaded rod takes an M5 nut/wing nut either side of the frame.  Remove the nuts to reposition the bolt up or down in the frame arms for deeper / shallower fuselage.  To allow for a narrower / wider fuselage alter the position of the nut/wing nut along the length of the threaded rod.   

Most of the time the height setting is likely to remain the same so in the field it'll usually just be a case of adjusting width by backing off the nuts and moving the threaded rod in/out as necessary.

I'll go away and scribble something and / or take a few more pictures to see if I can explain things more clearly but may not make it back with a reply this evening

Thanks you for a patient & tolerant resopnse.

I've finally worked out what I didn't understand about the existing set-up, that the "lash-up" alu. tube goes through the M5 bolt section. I had read your explanation, which is fairly early in the thread, more than once & managed to misconstrue it.

Meanwhile the creative half of what little brain I have left has been fermenting (fomenting ) reduced design constraints.

First thought is that the 1.5mm hole doesn't need to be very deep. I was thinking about a depth of 2 or 3 diameters to provide support against bending. I think the strucural engineering term is pin-ended column. The rest of the hole (opposite end from aeroplane) could be bigger, up to the maximum that could safely be drilled with the M5 thread. With a root diameter just over 4mm, that might be as high as 3mm, given that the greatest bending loads are at the support plate, which is where the drilling would start & so be least eccentric. The larger drill, being stiffer, should be able to penetrate much deeper for the same eccentricity.

Second thought is one I've already suggested, viz increasing diameter. M6 looks attractive, possibly using tapped holes in the support plates.

Third thought is pushing the boundaries a long, long way. I was reflecting that in a cycling forum, the obvious source of single strand steel wire for the retaining wire is spokes. I have built with 2.0/1.5/2.0 mm double butted spokes, & the centre 1.5mm section would be more than long enough. The more common double-butted size is 2.0/1.8/2.0 mm. Would that fit through the motor peg?  1.8mm drills are not common, though I have one. The final idea is a plain gauge 2.0mm spoke. I doubt it would fit through the motor peg. I had already ruled out any modifications to the aeroplane, so I'm asking whether that is an absolute design constraint.

That's all a bit of a brain dump, not properly reviewed, & doubtless not clearly expressed, but I need sleep after last night .

[TheLurker]

...goes off to look in box of bits for an Irvine 25........

You are a bad, bad man.  Go away and sort your nacelles out.

I appear to have an M8 drill bit...

Thanks for the offer, but I think we may have this sorted.

I've finally worked out what I didn't understand about the existing set-up, that the "lash-up" alu. tube

Phew. Good 'cos I was struggling to work out an alternative description.

First thought is that the 1.5mm hole doesn't need to be very deep. I was thinking about a depth of 2 or 3 diameters to provide support against bending. I think the strucural engineering term is pin-ended column.  The rest of the hole (opposite end from aeroplane) could be bigger, up to the maximum that could safely be drilled with the M5 thread.

You are Baldrick AICMFP.   This style of thing....


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    +------------------+                  |
                       +------------------
                       +------------------
    +------------------+                  |
    +-------------------------------------+


What do you reckon Wobbly John?  Say 0.5 to 0.75" of 1.5mm bore opening into a 2 or 3mm bore?

...the retaining wire...

Oh that's the easy bit and sorted already.  Piano wire.



These two pics to show how the height of the motor peg anchor is varied.  Spot the 5mm holes at various heights.



LurkOnnaBike on flickr

[Wobbly John]

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    +------------------+                  |
    +-------------------------------------+


What do you reckon Wobbly John?  Say 0.5 to 0.75" of 1.5mm bore opening into a 2 or 3mm bore?

That would make life easier.

I have some brass M5 studding on order. 

[TheLurker]

Excellent news.  I really do owe you one for this.

[Crumbling Nick]

You are Baldrick AICMFP.   This style of thing....


    +-------------------------------------+
    +------------------+                  |
                       +------------------
                       +------------------
    +------------------+                  |
    +-------------------------------------+

That's the idea, though this, as it woiuld be drilled

    +-------------------------------------+
    +------------------\                  |
                        \------------------
                        /------------------
    +------------------/                  |
    +-------------------------------------+

seems necessary in order to insert the retaining wire easily. I did wonder whether serious eccentricity of the larger hole would produce something like:-

    +-------------------------------------+
    +------------_______                  |
                        \------------------
                        \------------------
    +------------_______/                  |
    +-------------------------------------+

but that looks unlikely.

Have lathe but I don't have 2.5mm drill bits that will drill that deep.

I have a 3.0mm drill bit that's 100mm long - flutes extend  65mm from tip. However it's not straight; the tip is about 2mm out from the axis of the shank . It would need a concentric pilot hole to be usable. I can put it in the post if it's of any use.

[Blade]

It's been three years since I worked as a toolmaker, but when I needed to drill a smallish diameter hole of depths that required a long series drill, I'd first drill down using a shorter drill to almost the end of the flute and then use the long series drill to the required depth.

Using the shorter drill first helps with avoiding drill wandering and also guides the longer drill when it's used.

[TheLurker]

Wobbly John, with a little help from Crumbling Nick, turns up trumps.  Thanks Gents, especially WJ. You've turned what was a bit of a bodge into a proper bit of kit. Gorgeous bit of work innit?



Anyone live near Wobbly John and prepared to escort him to an hostelry on my behalf and buy him (and yourself) a couple of beers*?  He's been extraordinarly generous having spent both his own money and, I suspect, quite a lot of, time supplying these bits, but I have been unable to persuade him to accept even a small token of thanks. 

*Send me a PM if you can / want to do this.  I don't even know if WJ likes beer so any suggestions for alternatives welcomed.  A bottle of his preferred brand of bike oil perhaps? I dunno.

One of the wing-nuts I bought is a dud hence the temporary use of a hex. nut, but you should get the general idea now.  Loosen the wing-nuts and retighten at the appropriate width.  Remove completely and replace in another hole to change height. FWIW the next Hurri will have the fuselage just aft of the dog kennel infilled (like the nose) to avoid that tent effect.


A general view

[TheLurker]

And here it is in action yesterday with the Sopwith Camel I built last year.  Poor old K5083, for which the stooge was built, is still sitting at dispersal waiting for her maiden flight.

Wobbly John and Crumbling Nick might be pleased to know that their joint effort on the threaded tube is highly esteemed in the aero-modelling community.

[andytheflyer]

Blimey, they are even smaller than I thought they were!  We have a master model maker in our midst!

[TheLurker]

Blimey, they are even smaller than I thought they were!  We have a master model maker in our midst!

Hah! Flatterer.  It's a laser-cut kit build, VMC, and a very great deal, i.e. most, of the credit for it goes to the designer Andrew Darby and the production team at VMC for being careful about the wood selection.  I reckon any chump could put one of VMC's kits together well.

[andytheflyer]

Blimey, they are even smaller than I thought they were!  We have a master model maker in our midst!

Hah! Flatterer.  It's a laser-cut kit build, VMC, and a very great deal, i.e. most, of the credit for it goes to the designer Andrew Darby and the production team at VMC for being careful about the wood selection.  I reckon any chump could put one of VMC's kits together well.

Now there's a challenge!  (Goes off to find the SE5A kit....)