Motore Glow da 5cc

[Jasonb]

I blame Ramon for this project as his posts on scratch building model aero engines are what inspired me to have a go myself, thanks Ramon.

I was lucky enough to be able to look through an Italian book that contained plans for many engines and this particular design by Gianilo Passuello for a 3cc engine caught my eye. It was Glow rather than Diesel, it did not look too hard to replicate the cast parts by cutting from solid and I liked the look of it. So I drew it up with a scale factor of 1.2 which took the capacity from 3cc to 5cc and gave parts that were still a resonable decimal size without going to many decimal places.



So I made a start by cutting a couple of slices off some 2" and 2.5" square HE30 (6082) which cost about £6.00GBP which is far less than most of us would have to pay for a set of aero engine castings and I would get a lot more shop time for my money not to mention no risk of blow holes or gummy alloy



With a CCGT tip and a little paraffin the block soon faced up nicely in the 4-jaw.



With some 3mm PVC sheet packers to protect the previously machined surfaces the remainders were soon done to leave me the main two components.





I made a start with the nose piece as this seemed the easier of the two. After marking out the bore it was clocked true in the 4-jaw chuck



Then the front end taken down to a little over finished size but something that would fit a collet.



It was then over to the mill to hog out most of the waste, One of ARC's new Premium HSS-Al milling cutters making short work of the task.



Back to the lathe and holding in a collet I turned the spigot to locate the nose into the crankcase then bored and counterbored for the bronze bearing.



Then using a parting tool I undercut to form the mounting flange



J

[Admiral_dk]

Very nice old style look  - looking forward to this build.

I'm curious - where did you buy the aluminium ?

I'm asking, because buying small amounts of new metal here in Denmark is almost impossible and if you do find any who will sell it in those size - the price will be almost as high as if I bought enough for a rather big production.

[NickG]

Looking forward to this Jason. Having tried to machine a kit for a 0.8cc Diesel engine from Woking precision models as my first
Project (of course completely unsuccessfully!) I can't understand any advantages of castings for an engine this sort of size really.

[Jasonb]

Admiral, I can't be specific about the supplier as the material was bought at one of the model engineering shows, either Sandown or Ally Pally so could have come from one of several.  Most likely College Engineering but could have been Noggin End, RNR Aluminium or someone else. I find you usually get a better deal at the shows, these were both 4-6" long pieces as like Ramon I made a spare set as a backup while the machines were set up  - more of that later

J

[Jasonb]

It was then back over to the mill to bore out the hole to take the venturi sleeve to 12mm, this hole stops just short of breaking right through into the bearing bore.



At the same time I also drilled for the four mounting holes. These are shown on the original 3cc drawings as M3 and the 1.2x scaling factor would have worked out quite well for M3.5 but they looked a bit large headed so I kept to the M3 of the original.



Back to the lathe once more and with a bit of tailstock support the nose was taken to the finished dia of 18mm while holding by the locating spigot. The venturi socket was also faced back to leave the final 1.8mm wall thickness.





With the milling vice mounted ontop of the rotary table I was able to start rounding the venturi socket



Now with the R/T mounted the other way around the last few "square" bits could be milled away, the blue marker is to highlight the areas I don't want to touch with the cutter.



It was then just a case of sitting patiently at the vice with a few needle files followed by emery, scotchbrite pads and Garryflex blocks. There is still some work to do but that can wait until all the other parts have been made as the surface is bound to get marked.



As I wanted to drill through the nose and venturi sleeve in one go the sleeve needed making first. This was turned down to a nice fit into the hole and then drilled through 7.8mm. Rather than faff about making tapered D bits or reamers I just used a very small boring bar to taper the inside from the 7.8 where the spray bar goes out to 11.5mm before parting off.



The other side had a steeper taper cut as the spray bar is nearer to that end and then the edge was rounded by hand turning.





With the venturi sleeve held in place by a toolmakers clamp the hole for the spray bar could be drilled and reamed through them both.



Followed by spot facing for the nuts to bear against. The original casting had raised bosses here but the spotface was an easier option



And thats the nose piece completed





J

[Roger B]

Very nice old style look  - looking forward to this build.

I'm curious - where did you buy the aluminium ?

I'm asking, because buying small amounts of new metal here in Denmark is almost impossible and if you do find any who will sell it in those size - the price will be almost as high as if I bought enough for a rather big production.

Here in Switzerland we have http://www.metallladen.ch/ who will sell cut lengths at retail prices and offcuts by weight for a variety of metals. (can you read enough of the German?)

[Kim]

That's a lot of work!  But for excellent results an complex piece!  I like seeing how you made that part out of a block.  Very interesting.  Thanks for showing all the steps.
Kim

[Dave Otto]

Enjoying your latest project Jason.

Dave

[Admiral_dk]

Jason - very beautiful work so far  - I like it 

Roger B - Aber klar und vielem danke 

[Jasonb]

Next up is the main crankcase, this was set to run true in the 4-jaw and the internal cavity opened up by drilling in stages followed by boring, the face for the nose piece is set back from the exhausts so that was machined with the same boring bar from middle outwards.



Test fitting the nose, its a fine line to get the right fit, not too loose that it drops out not too tight that it won't come out. I do this by testing as it gets close rather than measuring.



It was then reversed in the chuck and the back recess formed in the same way, this is just recessed to reduce weight. Towards the end of the boring I swiched from a CCGT tip to a CCMT one with a large 0.8mm radius as the internal corner needs a fillet as if it were a casting, there is also a radius on the outer edge that was just chamfered and then hand finished.



Resetting in the 4-jaw once more with packing to bridge over the previous holes a small spigot was formed on the top edge then three different dia holes bored - clearance around the exhaust ports, tapping size for the cylinder and finally a hole to break into the crank cavity.



I then brought up the tailstock for support while I used a parting tool to cut the waist between crankcase and exhausts followed by cleaning up the edged with a more pointed tipped tool. This holder has a pocket for the tip both top & bottom which allows it to be used as both a left and right handed tool which is quite economic.



I cut the M25.6 x 1.0 thread at this stage but don't seem to have a photo, its beginning to look like an engine.



The 4 M3 holes to mount the nose were drilled and tapped



I then used a 5.5mm stub length drill to rough out the exhausts



Followed by a 6mm 3-flute milling cutter.



Next was to use a long series 4mm cutter to round over the outer edge of the exhausts which then needed another session with the needle files to blend them into the curve of the crankcase



I used a 10mm cutter that was on trial from ARC to take away the material below the mounting lugs, full depth of 9.6mm and 0.050" feed in per cut.



The other three sides of the lugs were done with a 3-flute cutter that I had hand ground the ends of to leave me a fillet in the corners, I much prefer this to using a ball nose cutter as you can remove metal a lot quicker.



Finally the 4 mounting holes were drilled, think its time to clean up some swarf!!

[Jasonb]

The cylinder was fairly straight forward turning from free machining mild steel (EN1A), I tweaked the size of the fins slightly to suit my cheap far eastern parting tool which made a good job of doing all the grooves in one hit.





Next the 1.0mm pitch thread was cut, as there was not a lot of runout room I decided to use the internal indexable tool at the rear of the work and running the lathe backwards, that way it would move left to right and I could stop the lathe at my leasure and run at a decent speed for the carbide tip. Straight in method rather than bothering to angle the topslide.





It was the first time I had used these indexable tools and they seemed to work well giving a nice clean cut.



The cylinder was screwed into the crankcase nice and tight and then the 4 holes to retain the head drilled and tapped M3



The four passages for the air/fuel mixture were plunge cut into the cylinder using a 7.0mm endmill, the actual scaled size was 7.2 but its easier to get hold of 7mm cutters.



I made a jig so I could hold the cylinder and clock it true to the bolt hole pattern to make sure the exhaust ports lined up with the openings in each side of the crankcase, also made a plug for the bottom so I could use some tailstock support.



When I bored the cylinder I was getting a good finish with the indexable boring bar so carried on and did the final cuts to size with that too. Now I usually switch to a HSS bit in a thick bar for the last couple of fine passes as I find there is less tool deflection and should have stuck with that. The bore had a slight taper which I thought I could lap out but that did not work too well, the passages inside the cylinder took metal off the lap rather than the other way round.

This is the expanding lap I used which has worked in the past. Also some members have said that holding a finned cylinder hurts/dirties their hand and they use gloves with the associated safety issues. This is a good alternative, take a MTB innertube cut a slice off and then stretch it over the fins, makes it painless to hold and won't get caught on anything.



Quite a nice finish just a shame its slightly tapered - more on that later.



J

[Jo]

Next the 1.0mm pitch thread was cut, as there was not a lot of runout room I decided to use the internal indexable tool at the rear of the work and running the lathe backwards, that way it would move left to right and I could stop the lathe at my leasure and run at a decent speed for the carbide tip. Straight in method rather than bothering to angle the topslide.

I find those tools like threading at about 600rpm   

The set over angle is great for using the top slide as the retract, wind it in all the way, use the cross slide to add the depth, first cut, use the top slide to width draw the tool, use the finger tip reversing lever to reverse the lathe leaving the screw engaged, top slide back in all the way and add depth, back you go in forward. Easy Peasy

Delapena do a special tool for holding cylinders for honing that uses a bit of webbing wrapped round the cylinder. I will see if I can get a picture of it 

Jo

[Jasonb]

The special tool is not much good without the machine 

Is there something you need to confess to the congregation

[Jo]

The special tool is nothing fancy, it looks similar to a hand vice but has jaws ...  hang on Uncle Eric lent me one, so I can make one for myself 

Jo

[Jasonb]

A piece of 5/8" bronze was drilled, bored and then reamed 10mm for the crankshaft bearing.



The outside was then turned and tested to be a press fit into the nose piece, after parting off and turning the flange to length it was pressed into the ali with the use of a machine vice as I don't have a press.



Next up was the crankshaft from a piece of 30mm EN8, roughed out using a tool that gets use out of the other two corners of a CCMT type insert.



Then machined to finished size with a reduced dia section for the propdriver and the end threaded M6



While still in the chuck the shaft was lapped into the  bearing with 1000g powder and a drip or two of oil





It was then reversed in the chuck and the web turned back to finished thickness and the hole drilled up the middle



I then transfered to the mill and used the DRO to accurately position a spotting drill hole where the crankpin will go.



I then used my usual block of aluminium with a pair of protected grub screws to clamp the crankshaft, its then an easy job to use the 4-jaw and clock in the centre mark. The hole was then drilled and reamed making sure not to go all the way with the hand reamer so its slight taper would help with the press fit of the pin.



A small round nosed tool was then used to remove some metal around the pin hole which reduces the amount of counter balance weight needed.



The drill rod crankpin was then pressed into the hole after it had been drilled through 3mm.



Then over to the rotary table to mill the sides of the web to shape



While the rotary table was set up the port was rough drilled at the correct angle to the pin



Then milled out to final size



Then rotated round a bit and the flat to stop the propdriver rotating was cut.



And thats another part less to do



J