ML Midge Diesel

[Ramon Wilson]

Steve - that's some nice clean work you are doing there, the Midge is a nice little engine 

Re getting your clearance on the liner for milling - have you considered mounting it on a mandrel?

Either a straight one with an end cap (washer) and screw or an expanding one (easily made) Just make sure you relieve it where the milling breaks through so that as you remove the liner it doesn't burr and possibly gall on the mandrel.

Good luck with the rest of the build - nothing quite like a diesel 

Regards - Ramon

[steve-de24]

Ramon, thanks for your kind words. Can I also thank you for so readily sharing your expertise on this and other sites with the build logs for your ED Racer, Super Tigre and ETA engines.

Regarding my Midge, I did think about a mandrel but it was fear of jamming the cylinder on the mandrel with burrs on the ID from drilling the ports that put me off. Would an expanding mandrel that was only 12mm long ie. half the length of the cylinder, hold the cylinder well enough?
Then I'd be drilling into free space and burrs wouldn't prevent removal of the cylinder.

This evening I've thinned down (from 2 to 1.4mm) a parting tool that came on the end of a 6mm square HSS tool bit; I will need it to cut the fins in the cylinder head. I can't make up my mind whether it is better to cut the fins before or after drilling the holes for the hold-down bolts. One way gives me lots of burrs in lots of holes to tidy up, the other gives me an interrupted cut with a parting tool.... 

Steve

[sco]

I'd  take the interrupted cut route as the holes are more likely to stay in line. I also think I'd go  for a full length expanding mandrel with axial relief to avoid the problem with the burr.

Simon.

[Ramon Wilson]

Hello Steve - Thank you too.

I have done both but deburring the holes is a real pain. Holes first are definitely the better way to go  - as Simon says  (oops) there is far less chance of drill wander. The interrupted cuts are nothing to be that wary of, as long as the tool is sharp and the cut is gently applied you will soon be past the holes. Deburring the holes then is a doddle - just run a drill through on 'finger power'.

You should get away with using an expanding mandrel as you suggest. As long as its length in the bore is longer than the diameter it should easily resist the cutting forces. If you can arrange tailstock support (if doing it in the lathe) so much the better or possibly a temporary jack using a bolt and nut underneath if on the mill. It's quite amazing just how much holding power there is with such little amount of torque on the expanding screw on these mandrels. BTW it's definitely worth turning a cap-head head to 60 degrees to match a centre drilled hole than using a countersunk head to force it.

I have also relieved the mandrel to give clearance but this does mean cutting away some of the clamping force and can spoil the mandrel for further use.

You could also make a plain, stepped, mandrel and a stepped cap and just use a cap-head to hold it in place.

Hope that helps some - anything else I can assist with do say.

Merry Xmas to you and to you too Simon - any news on the L&B ?

Regards - Ramon

[sco]

Hi Ramon - still dreaming about the Lane and Bodley but also wondering about a Hoglet.

Merry Christmas to one and all,

Simon

[steve-de24]

Thanks for the advice guys - drilling the holes first seems to be the way to go, but that will have to wait until the cylinder is finished. I'm hoping to get some workshop time over Xmas but not sure I will achieve it.

Simon, is that a Corliss valve Lane and Bodley you are referring to? that would be nice.

A picture of my favourite piece of L&B 19th century engineering is attached, I just love their concern for health and safety. It even seems to come with its own vulture to clean up the blood and bits.

Best wishes to all for Xmas and the New Year.

Steve

[sco]

Simon, is that a Corliss valve Lane and Bodley you are referring to? that would be nice.
Steve

Yes it is a Corliss valve engine and is nice but the castings are chuffing expensive and only available from the States so postage is astronomical :-(

Simon.

[steve-de24]

I decided to go with an expanding mandrel to complete my cylinder machining. I made it just short of the finished cylinder length and will use partial engagement when milling the transfer ports. The mandrel can then be used to complete the remaining turning by reversing the  cylinder.
I took a photo to show my set-up for tapping the 4mm thread, a 4mm long grub screw will be used to do the expanding. I used my 3 inch tap wrench and this feels like a comfortable set-up down to about 3mm taps but below that feels clumsy. I got some good ideas for tapping smaller sizes from gbritnell's hay baler thread.
Next photo is my very clumsy set-up for using a slitting saw in the mill, its only saving grace is that it gets the job done. I will have to have a go at machining my own arbors for the milling machine  - I can see quite a few applications if I can manage it.
After finishing the mandrel, and out of interest, I attached the cylinder as it would be in the mill and checked the run-out on the turned section. Only 0.5 thou inch total - so I'm going to bed a happy man.
Steve

[steve-de24]

This is just a quick post to replace the photos that went missing when the site went down.

The first 4 show the machining of the cylinder, drilling the ports and milling the transfer passages.

The next 4 are of machining the cylinder head. The last pic shows my temporary minimal cross-slide handle that's needed on the Cowells lathe to allow the top-slide to swing around to 95 degree to the lathe axis.

Steve

[steve-de24]

The last catch-up post to show the machining of the fins. I followed SCO and Ramon's advice and drilled the hold down bolt holes first which was good advice - thanks guys. An unexpected benefit was the indication this gave to stop cutting when the groove depth had passed the holes - the wall thickness is only ~1mm.

Steve

[steve-de24]

For the first time in ages I got some 'shop time' yesterday. The result of my 3 hours efforts was a banana shaped con-rod    I think it must be due to residual stresses in the bit of HE15  (UK equivalent of 2014) aluminium I used. I machined it from a piece of 3/8"  dia rod and the mistake I think I made was to machine one side fully (including holes) before flipping it over to do the second side. The result is the crank pin hole is not parallel with the wrist pin hole!  Time for a rethink about the sequence of ops.
Steve

[Admiral_dk]

Dam - but at least you are learning something and can put it down as experience in the end 

Looking forward to the next chapter in the series 

[90LX_Notch]

Sorry to hear that Steve.

-Bob

[zeeprogrammer]

There's always a plus side. 

[steve-de24]

Thanks for the kind words guys; they say you learn more from your mistakes than when everything goes ok - I just wish I wasn't learning so much at times....

But upward and onward. Today I decided to rough out the crankshaft from a piece of 3/4 inch bar and I needed to reduce 45mm of this from 19mm to 7mm dia.

I'm only using leaded EN1a (UK equivalent to 12L14) but I'm hoping it will be ok for an occasionally used engine - and I'm making this engine mainly as an exercise to get familiar with the different procedures involved.

On another current thread someone is asking for information on the Cowells ability to machine steel so this looks like a good opportunity to give a practical example. I will put more details than usual in this post - apologies if I bore anyone.

I use HSS tools and keep them as sharp as possible to keep the cutting forces down.
The roughing cuts were carried out using the back gear at 180 RPM.
I used the auto traverse which gives a feed rate of 0.055mm per rev.
This would be extremely boring to watch but the Cowells has a cut-out to automatically disengage the lead screw so you can set it going and get on with something else.

My rule of thumb for machining like this is :   Depth of cut(mm) = 16 / Dia(mm)    but I round down to make it easy to keep track of how much I've removed. I also don't take cuts greater than 1mm (ie 2mm off diameter). One of the advantages of machining like this is the tool chip breaker works and the swarf is in easily managed small curls.

So I reduced the 19mm diameter to 7mm with the following passes.

(a)  One pass with 0.5mm depth of cut - diameter reduced from 19 to 18mm
(b) Two passes with 0.75mm depth of cut - reduces diameter to 15mm
(c) Two passes with 1mm depth of cut - diameter reduced to 11mm

At this point work stopped for a cup of tea and Jaffa cakes (hey I am English).

When I got back I put on another 1mm depth of cut and set it going. I got two surprises; firstly, by mistake I had put the depth of cut on twice (before and after tea break!), so it was now 2mm; secondly, the Cowells didn't miss a beat - so I left it alone.  This reduced the 11mm diameter bar to 7mm in one pass. I am impressed with what the little Cowells can do - but I think I'll stick to a 1mm maximum depth of cut in future knowing that it is well within the lathe's capabilities.

The photo shows the resultant swarf - that on the left is from my 'normal' roughing cuts, nice small curls which are easily vacuumed - on the right are the big curls from the 2mm depth of cut pass.

Steve