Author Topic: 20 cc Horizontal 2 Stroke Diesel  (Read 47576 times)

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #30 on: February 28, 2016, 08:36:32 PM »
It's 80mm. This engine is on the limit for my lathe  ::)
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #31 on: March 13, 2016, 04:51:30 PM »
I got a new belt for the mill and had a go at milling the ports in a piece of scrap aluminium. The exhaust ports are at 45° to the bore and are machined from a flat area where the exhaust pipe flange will sit. The top of the ports need to be on  a curve the same radius as the cylinder so that they will be level. I centre drilled and then drilled 3mm hole in each port to start. The end mill was fed in using the quill and due to the angles I was having to lower the quill and move the X axis together  ::)

I'm fairly happy with the results and can see how to improve the real thing.
Best regards

Roger

Offline Brian Rupnow

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #32 on: March 13, 2016, 05:27:35 PM »
Roger--very nice work.---Brian

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #33 on: March 13, 2016, 06:46:36 PM »
Thank you Brian, the geometry of angled ports takes a little thought  :headscratch: The originals would have been cored in the casting as below.

I then had a go at the transfer ports. These are angled at 60° which made clearances more of a problem. The centre port was not flat so I need to go and recheck my calculations (something to do in the evenings in China next week  ::) ) Access with the full length cylinder will be harder. I may need to get a longer milling cutter but then the deflections will also be greater  :headscratch: plenty to think about and there is still enough of this trial piece for another couple of goes before I wreck the real thing  :toilet_claw:
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #34 on: March 25, 2016, 06:30:13 PM »
Back from my travels and in the workshop again  :) I've got a lot of catching up to do on the forum, I could get the words in China but the pictures took for ever  :(

I sorted out my geometry problem, rather than reducing the circles radius by the Tan of the port angle I needed to make it an ellipse with the longer axis extended by the Tan of the port angle  :insane:

To aid the clearance problem I found a 3mm straight shank end mill, not very stiff but reaches the parts other end mills cannot. I tried cutting the two outer ports but the left hand one ended up much to high. I wasn't sure if I had made a mistake or the cutter had deflected so I milled another transfer passage and tried again (one more go left  ::) ).

When I am cutting these ports I initially plunge the end mill straight in and then widen the port keeping to the line of the ellipse. Looking at the results it suggests that the initial plunge is relatively true (as the forces are balanced) but when I widen the port there is significant deflection. The centre port was started in the middle and the two side ports were started closest to the centre port. I need to think about this some more  :headscratch:
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #35 on: March 26, 2016, 04:32:47 PM »
I had another, more successful attempt an the transfer ports. To reduce the deflection problems I started by plunging on the right hand side of the ports (looking from outside from the crankshaft end) and then reduced the depth of the following cuts to around 0.5mm instead of 1.2 - 1.5mm. This was significantly better than before  :) Now I have to consider if I will get more cutter deflection in cast iron  :headscratch:
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #36 on: March 29, 2016, 04:42:34 PM »
I decided to start on the real cylinder. First I needed an angular reference so I decided to drill and ream the fixing screw hole to 3mm to give me a 90° reference series. I only have a four jaw independent chuck that fits on my RT so I mounted it on a MT2 adaptor in the lathe to centre the cylinder.

I didn't have enough Y travel for the exhaust port initially and had to move the setup. I am using the angle block from my quick set Keats as it is the largest I have.
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #37 on: March 29, 2016, 04:47:34 PM »
With the exhaust port cut I had to turn the cylinder 180° to do the transfer passage. I checked the angle against the mounting holes and the exhaust port. To get enough clearance I had to clamp onto the reduced diameter for the water jacket which gave a significant overhang. Luckily this didn't cause any problems  :)
Best regards

Roger

Offline fumopuc

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #38 on: March 29, 2016, 07:41:42 PM »
Hi Roger, some interesting set ups on your machine.
Kind Regards
Achim

Offline Kim

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #39 on: March 30, 2016, 05:51:43 AM »
Yes, certainly some inventive setups you used to fit in your limited Z-height.
Well done!
Kim

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #40 on: March 30, 2016, 07:34:08 AM »
Thank you both  :ThumbsUp: Holding the complete cylinder at 45° and 60° for milling the ports is the next challenge. It is too long to fit my tilting vice (used for the trial piece). I think that I can clamp the Keats V block to an angle plate.
Best regards

Roger

Offline Admiral_dk

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #41 on: March 30, 2016, 09:34:02 PM »
Hi Roger

Quote
Holding the complete cylinder at 45° and 60° for milling the ports is the next challenge.

Why those angles - the optimum angle for the transfer to enter the cylinder is very close to 15 degrees and zero will work just fine - admittedly with a Schnürle porting (and that requires at least two transfer ports) .... hmm - perhaps I should just  :-X

Best wishes

Per

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #42 on: March 31, 2016, 05:54:32 PM »
Hi Per, a valid question. This engine is based on two prototypes, the Field Marshall diesel tractor and the Petter Atomic diesel. These were developed before Schnürle porting and had simple opposed transfer and exhaust ports with reed valve induction. The high compression ratios and requirement for a compact combustion chamber meant that a deflector piston was not practical. Both engines used slightly coned pistons with a steeply angled transfer port and in the case of the Field Marshall an angled exhaust port (there is a picture of this further up this page).
I have attached a section of the Petter engine taken from my father's 1947 copy of 'Heat Engines' by A.C. Walshaw.
« Last Edit: March 31, 2016, 07:31:30 PM by Roger B »
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #43 on: April 02, 2016, 06:20:39 PM »
On with the ports. When I went to mark out the exhaust ports I found that I had not cut the flat wide enough so back onto the mill  ::)
I was able to mount the V block from the Keats on my angle plate with enough clearance under the mill.
The milling went quite well. I started each port with a centre drill followed by a 3 mm drill and then opened up with a 3mm end mill. The flat sides were cut with a combination of X travel and quill movement due to the angle. The curves were cut with a series of plunges.
I am glad I made the test piece first rather than starting on the 'real thing'   :)
Best regards

Roger

Offline Roger B

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Re: 20 cc Horizontal 2 Stroke Diesel
« Reply #44 on: April 02, 2016, 06:36:00 PM »
The transfer ports were not so easy  :( The long 3mm endmill wouldn't cut the CI and just deflected. In the end I used a combination of a short centre cutting 2 flute end mill (the centre drill was not happy with the compound angles), a 3mm drill and a 3mm endmill. As the ports go right to the side of the transfer passage the wider part of the endmill limited the depth I could cut to.
Unfortunately one of the transfer ports had a bit too much deflection and ended up a bit to high  :( I was already expecting an amount of hand fettling and had bought a cheap set of diamond rifler files (10 Francs (or Dollars or Pounds or Euros they're all much the same)) It looks like I will be able to fix it, but both ports will be around 0.5mm higher than planned so I can make the piston slightly longer and recess the cylinder head to compensate  :headscratch:
Best regards

Roger