Author Topic: Cosworth V8 1:12 scale  (Read 8003 times)

Offline Roger B

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Re: Cosworth V8 1:12 scale
« Reply #30 on: November 26, 2020, 07:30:27 AM »
George, I think it is intended to be compressed air powered so the ratio is 1-1.

I use Volkel taps and dies via their online shop:

https://voelkel.com/en/produkt/hand-tap-set-of-3-pieces-din-352-hss-g-m-1-m-100/
Best regards

Roger

Offline Jasonb

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Re: Cosworth V8 1:12 scale
« Reply #31 on: November 26, 2020, 08:29:44 AM »
Yes it's a 2-stroke see first post, all the gears are idlers except ones on crank and cams.

I also use the Volkel ones in the smaller sizes, Rotagrip do them via website or  as "fordeight" on e-bay

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #32 on: November 26, 2020, 09:03:52 AM »
I used Volkel taps for the M1.6 holes. As soon as I got them out of the packet, they seemed superior to all my other small ones. They don't seem to do 14BA though.

Steve

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #33 on: November 26, 2020, 02:08:56 PM »
I love the fact that you're building this with a Sherline.  (I've got both a Sherline and a Unimat.)

The fact that you're mostly building it out of steel is even more impressive.  Why did you chose to use steel for the block and heads over something easier to machine like aluminum or brass?

Don

Hi Don,

Aluminium was my first choice, (after all the original is aluminium) but I just don't get on with the stuff. Swarf ends up all over my kitchen, it sticks to coated cutting tools and I thought it might be a bit soft for the more intricate parts of the cylinder heads.

I did consider brass but felt it didn't look right so I went for steel.

The block was really on the limit of what my Sherline lathe could handle. The billet I machined it from would only just swing over the table when in the 4-jaw. Even then, I had to file a few mil off one corner to give clearance. When I was turning the eccentric bosses, I had to keep the revs down real low to stop the lathe from rocking about.

If I was to make this again, I would use a different method.

Steve

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #34 on: November 26, 2020, 05:43:54 PM »
Now for the conrods.

These were cut from 2mm clockmakers brass in strips of 4.



They were then tapped 12BA.



I forgot to take photos of the clamping half but they were made the same way.

They were then separated with a jewellers saw.



I then screwed the two parts together, blended in the curves and tidied them up a bit. They were then drilled and reamed to 3mm.



These still need surface finishing.

Steve

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #35 on: November 26, 2020, 05:48:06 PM »
Before I went any further, I thought I'd test fit them on the crank.



A fiddly job attaching these but everything fits and moves nicely with minimum play. The middle one at the front looks like it isn't straight but that's the camera angle.



I then tried the whole assembly in its bearings in the block.



The conrods do foul the block in parts but this is because they are no liners or pistons in yet so the rods are rotating more than intended.



I've got to say that it doesn't look like the bottom end of a racing engine - more like some late Victorian marine engine. The thickness of the conrods is massively overscale. This is a consequence of using the smallest screws I had.

Even then, I had to turn down the heads to 1.8mm and dome them for clearance.

This is also the reason why there is only two bearings. There just wasn't space for other journals.

I'm happy to answer any questions or receive any criticism.

Anyway, will update as I make more parts.

Steve

Online crueby

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Re: Cosworth V8 1:12 scale
« Reply #36 on: November 26, 2020, 07:00:25 PM »
Very well done, watching along!

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #37 on: November 27, 2020, 03:42:14 PM »
I made this gadget (mandrel?) to hold the cylinder heads while I milled it and drilled and counterbored the inclined valve holes.



It is basically a 18mm diameter brass bar with 4mm removed on the flat. The silver steel rod is 8mm so I can hold it in various tool holders and collets.



The idea behind this is that the 16 degree inclined valves converge at a point 5mm below deck height, the bottom of the cylinder head. If I axially centre a cutting tool, I can do all the operations just by rotating 16 degs. either way.

The above photo were taken after I'd used it, hence the square pattern of shallow holes where the drill (intentionally) broke through.

Here it is set up and the flats being milled.



It took me a long time to set this up. I had to clock it axially and make sure it was centred both ends. It seemed like hours with a little rubber hammer tapping things true before I was happy. This was done before I attached the workpiece.

After that it was drilled 1.6mm through, c/bored 2mm for the valve guides and c/bored 2.7mm for the springs.



This worked a treat. My Y-axis remained locked for the whole process.

Steve

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #38 on: November 28, 2020, 01:11:16 PM »
I made 3 cylinder heads, a left, a right and a universal.

The universal is going to be used as a test-bed for cutting the valve seats and a couple of other things. After that it will go back on the mandrel and will be a sacrificial holder for the cam carrier blanks when it comes to machining them.

There are 48 inclined holes here, that's 144 separate operations.



Here is the under side of the heads. The central holes were drilled at the same time as the holding down bolt holes.



Here is a close up. The web between the two valve holes is 0.1mm thick which I was a bit worried about as even the slightest variation from this between cylinders would be visible but everything came out alright.



A close up of the underside. The central hole is not for a miniature spark plug but a guide for the tool I'm going to make for cutting a recess.



All in all, I'm quite pleased with these. I can't find any errors so all the careful clocking and indexing paid off. Saying that, I'm glad it's over. It took me a whole day of dial-counting and double checking before drilling.

Steve

Online Kim

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Re: Cosworth V8 1:12 scale
« Reply #39 on: November 28, 2020, 05:18:17 PM »
Really nice work, Steve!

I don't have a lot of experience with IC engines. So can you help me understand the difference between the Left, Right and Universal heads?  All three look the same to me.

Thanks,
Kim

Online Twizseven

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Re: Cosworth V8 1:12 scale
« Reply #40 on: November 28, 2020, 07:27:30 PM »
Looking forward to seeing the valves, cams and gearing. You must have damn good eyesight.

Colin

Offline Steve Crow

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Re: Cosworth V8 1:12 scale
« Reply #41 on: November 28, 2020, 10:05:09 PM »
Really nice work, Steve!

I don't have a lot of experience with IC engines. So can you help me understand the difference between the Left, Right and Universal heads?  All three look the same to me.

Thanks,
Kim

Hi Kim

There is no real difference between left and right - the holes are effectively symmetrical. I've just given an extra mil of metal at the front end of each to accommodate cam gears. The universal has an extra mil at both ends.

Steve

Online Kim

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Re: Cosworth V8 1:12 scale
« Reply #42 on: November 29, 2020, 05:54:43 AM »
I don't have a lot of experience with IC engines. So can you help me understand the difference between the Left, Right and Universal heads?  All three look the same to me.

There is no real difference between left and right - the holes are effectively symmetrical. I've just given an extra mil of metal at the front end of each to accommodate cam gears. The universal has an extra mil at both ends.

Yes, subtle indeed!  Thanks for the explanation :)
Kim

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Re: Cosworth V8 1:12 scale
« Reply #43 on: November 29, 2020, 03:30:41 PM »
Nice work Steve, following every step with interest.  :ThumbsUp:

Offline Admiral_dk

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Re: Cosworth V8 1:12 scale
« Reply #44 on: November 29, 2020, 08:33:29 PM »
Nice work Steve  :ThumbsUp:

Kim - as your question was a bit of two questions in one (one about this particular and one general) ->
Generally all V-engines have a mirrored parts, though the placement is usually a con-rod offset between the halves (there are exceptions, with 'Fork 'n' Knife Rods').
Inlets and Exhausts have different pressure and temperature -> bigger diameter on the Inlet ducts and valves and smaller diameter on the exhaust side -> optimum power, etc.