Seeking lathework help

[Timothy HuffParticipant @timothyhuff30628]

I'm making two models of wartime FN5 turrets. I need to find someone able to turn up 4 small brass components for the electric "hydraulic" rams which cause the gun-cradle to elevate and depress. The latest film in the project can be found here:

**LINK**

and the link to all available films is here:

**LINK**

The parts I need made are the two larger brass parts on this image. The smallest red "plain bearing" may be disregarded.

**LINK**

I'd be hugely grateful for assistance in this as I lack both the skills to make it, or indeed a suitable lathe. I can provide all necessary metric pilot drills, taps.

[Timothy HuffParticipant @timothyhuff30628]

Scale model of FN5 RAF turret

[David George 1Participant @davidgeorge1]

Hi Timothy Welcome to the forum There are a few people who could make them but it would help if you could give us a rough idea where you are.

David

[Anonymous]

Ideally the design needs to be simplified to make it easier to manufacture. For instance flat bottomed holes are a PITA unless absolutely necessary. And most of the radii/chamfers are undimensioned. Some indication of tolerances would be helpful too.

Andrew

[Timothy HuffParticipant @timothyhuff30628]

Apologies, I have a more up-to-date .pdf with the radii for fillets/chamfers on, but I had problems figuring out how to attach it to the post. Basically the chamfer radii are non-critical, 0.5mm R would be fine. The 1mm blind flat-bottomed hole could be made with a regularly tapered normal drill. It's simply to bring the C of G back in towards the centre, when the grub-screw is installed, and is again an approximation at 1mm depth.

Tolerances overall need to be +/0 0.05mm. Areas that need particular accuracy is the centring of the M2 thread within both components, the 4.64mm diameter on the lead-screw (+0/-0.05) and the 1.34mm dimension for the centre of the M1.6mm threaded blind hole on the smaller collar.

I'm based in Oxfordshire, between Banbury and Oxford. Many thanks for the welcome!

I'm self-taught on CAD, and dimensioning plans is all a bit new to me, so please sing out if I can do more to make the dimensions/tolerances clearer?

Many thanks again,

Regards, Tim

[Timothy HuffParticipant @timothyhuff30628]

Posted by Timothy Huff on 25/10/2018 19:50:35:

Tolerances overall need to be +/0 0.05mm. Areas that need particular accuracy is the centring of the M2 thread within both components, the 4.64mm diameter on the lead-screw (+0/-0.05) and the 1.34mm dimension for the centre of the M1.6mm threaded blind hole on the smaller collar.

This should read (edits in bold):

Tolerances overall need to be +/- 0.05mm. Areas that need particular accuracy is the centring of the M2 thread within both components, the 4.64mm diameter on the lead-screw (+0/-0.05mm) and the 1.34mm dimension for the centre of the M1.6mm threaded blind hole on the smaller collar.

[Anonymous]

Posted by Timothy Huff on 25/10/2018 19:50:35:

I'm self-taught on CAD, and dimensioning plans is all a bit new to me, so please sing out if I can do more to make the dimensions/tolerances clearer.

Fair enough. Here are some more comments on the dimensioning:

On the middle left drawing all the diameters are very confusing. Best to only have the OD and the rest on the drawing above. Conversely the drawing above can lose the OD dimension

On the right hand part there appears to be no depth given for the M2 thread and the small through hole isnt' dimensioned.

The axial position of the 1.5mm x 1mm blind hole isn't given – presumably it lines up with the M1.6 thread?

On the right hand middle drawing I assume the 4.75mm dimension is the depth of the M1.6 thread? I assume you're aware that you can't thread to the bottom of a blind hole, unless you thread mill. And you would need to sit down and have a stiff whisky before enquiring about the cost of thread mills for a M1.6 thread. Otherwise the best you can do, with a spiral flute tap, is a one or so pitches from the bottom.

Hope that helps.

Sadly you can't display PDFs within a post, only JPG files; it's a limitation of the forum software.

Andrew

[John HaineParticipant @johnhaine32865]

Do you really need 50 micron tolerances?

[Timothy HuffParticipant @timothyhuff30628]

John, in places, yes. The ram is hydraulic on the real turret, but mine is an electrically driven lead-nut propelling the tube you see in the film. In order to get the required "throw" of the tube and end-fitting, in the space available, I had to put some components much closer together than I'd have otherwise have wished, I've already stretched the dimensions of some cosmetic components to gain the depth in the ram necessary to conceal the motor and reduction gearbox, and still allow for the throw required. As I usually work to 0.1mm in 3d-printed plastics, I hadn't realised 0.05mm was potentially tricky on the lathe – as I say I'm completely new to lathe work.

Andrew, you're correct, the M1.5 blind hole is on the same axis as that if the M1.6 threaded hole. Regarding the 4.75mm dimension, this is essentially the depth of the hole, it only needs to be threaded to, or fractionally beyond, the centre point of the plan view of the collar, ie, not less than 4mm and not more than 4.75mm. As you've probably twigged, this drawing was prepared to talk over with someone who offered to help locally, with whom I could clarify things. I'll do my best to remove any ambiguities shortly.

Tomorrow I'll look to re-do the drawings with the amendments suggested and resubmit.

[Anonymous]

Posted by Timothy Huff on 26/10/2018 03:41:46:

As I usually work to 0.1mm in 3d-printed plastics, I hadn't realised 0.05mm was potentially tricky on the lathe – as I say I'm completely new to lathe work.

It isn't a problem; I would expect to be around that tolerance on the OD in general turning without having to think about it.

Andrew

[EmgeeParticipant @emgee]

Tim

Message sent to your INBOX, appears at the top of this page and will be flashing to catch your attention.

Emgee

[Timothy HuffParticipant @timothyhuff30628]

Many thanks Emgee, I've responded via email as requested.

[Timothy HuffParticipant @timothyhuff30628]

Hi all,

Many thanks to Emgee for his help making components for my home-made (concealed) servos to drive the elevation of a 1/4.5 scale RAF FN5 gun turret. If anyone is interested, there's a film at:

Emgees turned collar and leadscrew for FN5 turret models

and of course other films of the build.

[Brian HParticipant @brianh50089]

Awesome project!

Are most of the pieces 3D printed? It looks like you are using Fusion 360, What is your opinion of it?

Brian

[Timothy HuffParticipant @timothyhuff30628]

Hi Brian,

Thanks! I really like Fusion 360, mainly as it had (has?) a free usage for hobby purposes, and was the first free program that was worth a damn – and I tried a lot! The tutorials are good, the community support excellent, the program effective, quick and intuitive. The only area I found difficult was constructing compound curves, although one I'd got the hang of it, I wondered why that had been such a problem..

I think you may still be able to download if free on a "start-up license" and then select hobby usage.

There's quite a mix of materials now in the turrets, some sheet brass to stiffen cupola parts, an alloy base-plate (bearing surface), much SLS nylon, and some ABS printing (for dimensional accuracy). There's virtually no glue on it anywhere, ir's entirely held together with M1 and M1.6 machine-screws, as SLS nylon can be tapped.

Edited By Timothy Huff on 24/02/2019 10:59:56

Edited By Timothy Huff on 24/02/2019 11:00:24

[not done it yetParticipant @notdoneityet]

Tim,

Are these turrets destined for a model plane. Looks to be on a good scale! How large would a Lancaster be on this scale?

[not done it yetParticipant @notdoneityet]

deleted double post.  i likely double clicked on this laptop!

Edited By not done it yet on 24/02/2019 13:03:26

[not done it yetParticipant @notdoneityet]

deleted for same reason

Edited By not done it yet on 24/02/2019 13:04:59

[Brian HParticipant @brianh50089]

Thanks for the reply Timothy, and for the explanations.

I just learning to use Fusion 360 (yes, it's still free to hobbyists) and I've made a lot of progress since discovering videos by Lars Christiansen.

Brian

[Timothy HuffParticipant @timothyhuff30628]

Brian H, no problem, glad to pass on my experience of it.

"Not done it yet" – how I resemble that! – My FN5 turrets are for a Mk IC Vickers Wellington. The Lancaster has different and additional turrets: from front to back: FN5a (a widened and truncated FN5), FN50 iirc as mid-upper, and FN20 at rear. Some briefly carried FN64 ventral turrets.

To answer your question, I'm building at 1:4.5 scale, which is driven by the availability of 9 cylinder radials, as close as I can get to the sleeve-valve Bristol Pegasus. A Lancaster at the same scale would be 4.69m long and have a wingspan of 6.91m, so quite big. Mine is an unsual model in the sense that I'm building it primarily to copy as closely as possible, the orginal geodetic structure, rather than as a flying model. So if it turns out to be inappropriate to fly that's ok. otherwise I'd just make a balsa one!

There's a whole thread with dozens of stills on the LMA website under "New projects". Not sure if you have to be a member to view those though, Periodically I come across something I just don't have the expertise or tools to do, which is why I'm so grateful for the help here.

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