Undercarriage making on a lathe

[Andy Bladen 1Participant @andybladen1]

[Andy Bladen 1Participant @andybladen1]

Hi all

I'm building a 1/4 scale rc spitfire I need some advice on maching the undercarriage

Would it be possible to mount a solid piece of alu into a 4 jaw chuck carve out the outer detail and bore the inside to correct diameter to allow an oleo tube to fit inside and machine the rest with a milling machine I know it's a big job can you also suggest a suitable lathe which for the job ?

Thanks

[JasonBModerator @jasonb]

Possible but certainly not an easy task for someone new to turning.

The angled part at the top will dictate the size of lathe needed as you need to allow that to swing while turning the main leg so that puts it a 5" swing and over but for comfort I'd be looking to allow quite a bit over that size.

An easier method may be to make it drom 3 bits of steel tube silver soldered together and then add the detail, depends how much weight you can afford to add

[Andy Bladen 1Participant @andybladen1]

That would certainly be easier but as its a a flying model I need it to be as light as possible so aluminium would be ideal

[Paul LousickParticipant @paullousick59116]

You could fabricate it with aluminium tube and glue it together with permanent Loctite (type 271 or similar).

Paul.

[Ady1Participant @ady1]

I'm building a 1/4 scale rc spitfire

Are you going to knock up a V12 Merlin engine for this model??

[Andy Bladen 1Participant @andybladen1]

Your joking I could not build a V12 ! Would be nice I've seen people build them but my engineering skills are not that good!

So alu tubes could they be soldered or brazed rather than glued it needs to be capable of bearing some weight

[Gray62Participant @gray62]

Andy,

Aluminium an be joined using something like Alutight or Durafix, I personally use durafix and have had excellent results with ally fabricattions. Some care needed with small parts or thin section as the heat required can cause distortion (or total destruction if not careful DAMHIK!)

Takes a bit of practice and preparation and cleanliness is key to success.

Edited By CoalBurner on 23/01/2015 11:02:43

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andy Bladen 1 on 23/01/2015 10:50:11:

So alu tubes could they be soldered or brazed rather than glued it needs to be capable of bearing some weight

.

Andy,

Properly executed, a joint made with Loctite Retainer should be entirely adequate.

MichaelG.

.

Edit: … or, of course, a PermaBond equivalent !!

… see here for avery useful Design Guide from PermaBond

 

 

Edited By Michael Gilligan on 23/01/2015 11:22:42

[JasonBModerator @jasonb]

Would there actually be enough of a surface for loctite to work on? The three main parts I was suggesting be joined would be the outer cylinder and angled top piece which would join a tube that forms the circular bit at the top so really only an end on scribed butt joint. All the little fancy bits could be stuck on though.

Think coalburners suggestion of one of the low temp ali "welding" rods would be stronger, I bought some at Sandown but have yet to try it. Probably do most of the machining but leave things over size and do a final machine incase anything moves during teh "welding"

J

[Bob Brown 1Participant @bobbrown1]

I think you will need a gap bed lathe if I read the dimension of the upper section correctly at 9.25" and not easy to hold. I would be inclined to cast the upper and lower sections with a tube for the middle. I would screw the sections together Loctite to seal and hold the position.

Bob

[Neil WyattModerator @neilwyatt]

I think you could do some judicious spigoting of the joints without compromising the working of the mechanism.

Thin nylon bushes work very well with aluminium tubes sliding within each other, that's how some mountain bike forks are/were made.

Neil

[JasonBModerator @jasonb]

Bob I took it that these were the full size dimensions and the part would be 1/4 of that.

3.92" sounds about right for the OD of a full size strut

Edited By JasonB on 23/01/2015 13:11:44

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 23/01/2015 11:59:22:

Would there actually be enough of a surface for loctite to work on?

.

It would be a simple matter to make a test piece, to check.

… As Neil says, some spigots could probably be added.

It might be worth looking at some of he bonded bicycle frames, for inspiration.

MichaelG.

[Nick HughesParticipant @nickhughes97026]

Here you go:- **LINK**

But you'll need to build the airframe to 1/5 scale as well.

I seem to remember the construction was serialised in Model Engineer (During my youth).

As for the Oleos, I think you need to go down the Lost Wax Casting route

Nick.

[Speedy Builder5Participant @speedybuilder5]

I wouldn't worry about the strength of epoxy glue – They glue aeroplanes together with it !!

BobH

[Danny M2ZParticipant @dannym2z]

I agree with Nick, . lost wax casting for the axle fittings maybe with the master 3D printed in wax.

Here's a suitable engine, made here in Oz. **LINK**

* Danny M *

[John OlsenParticipant @johnolsen79199]

Having built both model planes and having a lathe etc…If I wanted an undercarriage like this, to good scale, I would do a 3D model and then have it cast by lost wax, as suggested by others above. There would still be some machining to do, but you could have a good quality job. As I see it there would be two castings, the lower piece with a steel stub axle pressed in and the upper piece. There would be a steel tube leg, with a spring inside. This would make the job quite similar to making the full size one, and if you paid someone to do it no doubt the cost would be similar. Still, the necessary machinery to do it yourself would not be cheap either.

It doesn't strike me as being the ideal first job for a newcomer to machine tools.

Having seen what can happen to model undercarriages, I'm not at all enthusiastic about gluing one together with epoxy, or any other sort of glue. When they use glue on airframes it is for large areas of sheet metal with good contact areas, not for highly stressed local loads.

Finally, remember the old rule…don't put it in the air unless you can afford to lose it!

John

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Olsen on 24/01/2015 05:15:19:

Having seen what can happen to model undercarriages, I'm not at all enthusiastic about gluing one together with epoxy, or any other sort of glue. When they use glue on airframes it is for large areas of sheet metal with good contact areas, not for highly stressed local loads.

.

John,

I bow to your wisdom, but [for the avoidance of doubt]; when I suggested using Loctite Retainer, it was specifically in the context of appropriately designed joints … it is not suitable for butt-joints.

MichaelG.

[Andy Bladen 1Participant @andybladen1]

Thanks for all your advice most helpful

Does anybody have a good tutorial on lost wax casting it's something I've never done before

[Michael GilliganParticipant @michaelgilligan61133]

M.A.P. published a good little booklet on Lost Wax Casting, but that was about 1972 , I think.

… So far as I am aware, it is not available from MTM or MyHobbyStore.

This may be a good time for the Publishers to consider an updated edition [to fit with the 3D printing boom].

MichaelG.

Edited By Michael Gilligan on 24/01/2015 09:00:39

[Paul LousickParticipant @paullousick59116]

I don't think that lost wax casting would be suitable for making thin walled tube. the wax pattern would require a core to cast a hollow tube. It would however be suitable for casting the ends of the struts.

The suggestion of using glue (Loctite) is not intended for butt joining parts but for joining the tube to a spigot which goes into the ends of the tube. The end pieces would have to be machined from solid, cast or fabricated and welding.

Added strength could be achieved by threading the spigot and tube. Loctite 271 is extremely strong and is used for permanently fixing nuts and bolts. It needs to be heated to 250 deg C if you want you want to remove a nut.

If the tubes were threaded and secured with Loctited to the ends pieces, the tube would probably buckle before the connection failed.

Paul.

Edited By Paul Lousick on 24/01/2015 09:14:10

Edited By Paul Lousick on 24/01/2015 09:15:20

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