Here is a list of all the postings Steve Crow has made in our forums. Click on a thread name to jump to the thread.
|Thread: Cosworth V8 1:12 scale|
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.
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.
|Thread: Another engineering masterclass|
The Sabre was a beast. This is from Wiki;
"Development continued and the later Sabre VII delivered 3,500 hp (2,600 kW) with a new supercharger. The final test engines delivered 5,500 hp"
This was from a 37 litre engine. To get that power ratio with aircraft reliability? Then along came the jet....
At the other end of the scale, he turns a Honda SS50 (my first bike) into a SS100 V-twin. and then he does the same with a C90 engine.
At the end of the day, all his bikes look right as well. Nothing Frankenstein's monster about them - they look like (deranged) manufactorers models.
The very definition of a shed based genius.
|Thread: Cosworth V8 1:12 scale|
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.
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.
This is the gear train for the cams. The camshafts rotate counter to the crank. The blue gears (EN1A) are driven or drive and the orange/yellow (brass/nickel silver) ones idle.
This is quite a bit simpler than the full-size engine, which has compound gears, but it does resemble it.
The gears are Mod 0.3 as I have a set of involute cutters. It would work in Mod 0.4 or 0.5 as well.
This is part of the build I'm looking forward to most.
Thank you, I've just checked them out. It seems that 14BA screws are more easily available than M1 so I'll probably go for that. A finer thread too - M1 is pretty coarse at 0.25 pitch. I can single point thread down too 0.25 pitch on my Sherline lathe but I need at least 60 screws!
14 BA taps are quite pricy though. I might have to redesign a few bits so there are no blind holes, then I can get away with a single taper tap.
All the ones I've seen seem to be around the same price, £15 each so I suspect they are all the same manufacturer. There can't be too many companies making 14 BA taps! Has anybody got any recommendations?
No typo. By 2 stroke, I meant a simple expansion engine with 2 cycles, in and out.
I suspect I am not using the right terminology.
Here is another cross-section, this time between the cylinders.
When designing this, I had a bit of a headache making sure the screws didn't clash with anything or each other. The problem is, even using the smallest economically available, the screws are grossly over scale.
I'm using M1.6 allen screws with the head turned down to 2.35mm to hold the sump, block, heads and cam carriers together.
12 BA cheesehead screws with the head turned down to 1.95mm for the con rods, exhaust and inlet manifolds and also the cam covers.
I will use either M1.0 or 14 BA cheesehead to secure the cam shaft. I want to find a good quality supply of steel screws first(non-stainless, I'll be blueing them). When I find them, I'll buy the appropriate taps. If anyone has any advice on this, I would be grateful.
Here is a drawing of a cross-section through the cylinders. It is sort of colour coded. Grey is EN3B, light blue EN1A, dark blue are screws and silver steel and orange or brown are brass except for the exhaust headers which are copper tube.
The air is fed from the two brass vessels (plenums?) in the vee.
This a hypothetical cross-section as there are 4 valves per cylinder and the banks are staggered.
Edited By Steve Crow on 02/11/2020 19:48:28
I know. I considered a central one but life's too short.
I've actually thought about making a 1:12 English wheel to form beer can aluminium for said monocoque.
Has anyone heard of this being done before?
Here is some of the crank in situ.
The flat-plane crank is assembled from EN1A webs and 3mm silver steel journals.
The assembly was a tight friction fit then drilled, countersunk, pinned and riveted. 1mm mild steel pins were peened into the countersink then filed and polished over to render invisible.
The unwanted journals were then sawn out and the gaps between webs cleaned up on the mill.
This still needs a bit of cosmetic fettling.
Edited By Steve Crow on 01/11/2020 16:23:37
Edited By Steve Crow on 01/11/2020 16:34:11
I then fly-cut some steel to size for the cylinder head blanks and drilled and counterbored to suit the block. All in all, I had to tap 30 blind holes to M1.6 in the block. A bit scary.
I also cut to size blanks for the cam carriers. They can just be seen in the background.
I made some endplates from 1/8” mild steel flat bar. These hold flanged bearings for the crankshaft, 4mm at the gearbox end and 3mm at the cam-drive end. There is raised boss on the back of both which are a snug fit into the crankshaft bore to keep thing nice and true.
The one on the left will house the flywheel and the one on the right, the cam gear train.
The sump and block were drilled and tapped 12BA to secure the endplates and everything was assembled.
The next job was to remove some metal from the inside of the sump and the block to provide clearance for the con rods.
Here is the block, ready to be milled. Note the miniature brass V-blocks – very handy things. You can see they are numbered. This is to ensure repeatability when using them with a 4-jaw.
And here they are completed. The block now weighs 60g. The initial square blank weighed 370g. That might not sound a lot of swarf to you guys with big-boy’s lathes, but it made a mess of the kitchen table with my Sherline.
A few months ago, I decided to have a go at making a 1:12 scale Cosworth V8 DFV Formula 1 engine.
It will be a 2-stroke running on air (or CO2?) with a bore of 7.2mm and a stroke of 5mm.
I want to share my progress so far as I’m sure I will need some advice.
After making the drawings, the first thing I did was make card models of the main components.
This helps me visualise things and see if any screws interfere with each other etc.
The block started life as 1” square mild steel bar.
I sawed of a piece about 3” long and this was clocked in the 4 jaw and eccentric bosses, on the crank centre line, were turned at both ends. This gave me an accurate way of holding it while boring out the cylinders and milling the block to shape. In the picture below, the milling is part done.
The block, milled to shape. The bores are a bit rough but true. They will have brass liners anyway.
The block was drilled and tapped and the sump blank bolted to it.
The whole assembly was then drilled and bored out as one piece and the bosses removed.
More to follow….
Edited By Steve Crow on 01/11/2020 14:47:22
Edited By Steve Crow on 01/11/2020 14:48:04
Edited By Steve Crow on 01/11/2020 14:52:27
|Thread: Bending small copper tube|
Thank you all for responding.
It looks like the Dubro tool is out of the question. The radius is ok but I need to make bends close together.
I really like Glyn's simple bender but I am also Intrigued by Geoff's.
I don't get MEW but would like access to the plans and article. If I subscribe to a digital edition, will I get this and previous articles as part of the digital archive?
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.