Coles C-611

[Laurentic]

Can you not just chuck him another Snickers ice cream to keep him quiet Jo, to pacify him a bit, after all, anything for a quiet life? 

[crueby]

Can you not just chuck him another Snickers ice cream to keep him quiet Jo, to pacify him a bit, after all, anything for a quiet life?

Hmmm, mold some chocolate ice cream in the shape of a flywheel or cylinder to make him think its a bronze casting? Though he will scream when it melts!

[Jo]

I have found a way to keep him quiet so lets get on with the engine. I mentioned doing some measuring this is it:



What I am doing is measuring the height to the top of the piston rod. If I subtract half the diameter of the piston rod from this dimension I will get to the ideal height for the centre of the crankshaft. Having mentioned that the odd mm up and down on a model is not a concern but on full size it would cause additional bearing wear  Measuring the height to the top of the soleplate where the bearings are going to mount and found there was about 3mm to come off but only 1mm to come off the surface under the cross head guide bars.

Moving over to the mill and making sure we centre on the piston rod to provide the centre for later machining:



I also checked the measurements to the bearing surfaces and there is a slight bias to one side but it is less than 0.5mm not a problem 

Time to mill the top surfaces:



I then drilled and tapped for the crankshaft. First I tested the alignment through the bearings with a straight rod:



I then mounted up the crankshaft in the same position and found it was a little sticky as it went round:



This tells me that the crankshaft has "moved" i.e. bent slightly. This is probably because during the machining the crankshaft warmed up and then cooled slightly bent (the crank webs would have acted as a bigger cooling surface on one side and hence it cooled faster on that side  ) I will sort that later.

In the meantime I am tackling the cross head design - you may note that I have not yet drilled the mounting holes for the slide bars as this is all part of the design problem that needs solving.

I have two cross head castings (so I have a second chance if I go wrong) and one piston rod and as you know no drawings 



and using my 3D CAD package I have started looking at the problem. The photo implies one slide bar but that means that the small end pivot will be very short and cannot be removed without unbolting the slide bars so I am first looking at two bars:



As you can see the pair of slide bars at 8mm wide does not leave much in the middle.... This is work in progress in the mean time I have a Qigong Class 

Jo

[Bluechip]

I have found a way to keep him quiet
Jo

https://michaeljerkin.artstation.com/projects/8mwzR

??

[Jo]

I still think the original design had a single bar on the side so this is what I am going to attempt for the first try:



Either way the slide bars would be more appropriate at 6.35mm wide so I can now go ahead and drill/tap for the two bars on the soleplate 

Jo

[Jasonb]

Looks like a single square bar to me too when you blow the photo up and quite substantial too. Would it be possible to thin the small end of the rod a little so you have a bit more pin in each side of the crosshead if you feel it's a bit short on housing length?

Single bar is probably a bit easier to set up too as you only need 4 supports and no spacers and the captive pin saves having to do something to stop it coming out

[Jo]

I started with a "practise" crosshead 

The casting was mounted in a collet to be faced and drilled 4,1mm:



From the tailstock I could then tap for the piston rod knowing this would mean the cross head would also be correct:



Compare with the sketch I had made At this point I missed the obvious  I had put two measurements on the cross head and of course I chose the wrong one 



but there is no point worrying about doing things wrong as it is all good practise (I keep telling myself) Mounted on the piston rod screwed into that thread:



 I could turn the other side:



Then off to the mill to mill the four sides of the cross head square and to dimension:



The cross head can now be mounted square in the vice, the centre found:



Then using a nice sharp undersized cutter a slot for the slide bars cut along the centre line to depth (yes I took the wrong depth from the drawing )



The having repeated with a milling cutter the correct size the slot was checked with a piece of bar stock the same width as the guide bars:



And as you can see it is too tight, so moving the Y axis over a Tad:



The slot was again cut on both sides taking off a total of an additional 0.1mm.  I also drilled and reamed for the small end pivot:



Before turning it over to mill the slot for the connecting rod itself. However  putting it on the engine I did not like it  This was going in the sin bin... So the other casting was retrieved... Mounted up in a collet for turning:



Again in the Square 5C holder to have the sides squared off:



However this time I have made the connecting rod slot 8mm wide and 9mm deep. To make that work I also moved the hole for the pin back .75mm nearer the back of the cross head.



I also reduced the slots for the slide bars to 4.76mm deep. This time I was happier with the finished cross head shape and bearing surface areas.

To correctly space the slide bars up from the sole plate I slide a slip gauge under the crosshead with it mounted on the piston rod and measured the required thickness. You could also use any piece of steel and a set of feeler gauges to do the same 



So the good one and the rejected one:



Time to make another piece 

Jo

[Jo]

The piston rod is another of those gunmetal castings that is soft and easily damaged. We need to start by identifying the centre of the two ends:



I have increased the dimple in the small end with a centre punch. If you look you can just about see where the big end centre goes. But we are going to make that easier to see:



And I have also marked a line to show where the split will be. Having done a quick skim on either side of the big end to square it up we can now look to mount the connecting rod vertically (it fits in my vice but you could also clamp it to a angle plate) and find the centre using a suitable tool... like a wobbler:



If you put a tapping drill in the chuck and line it up where the bolt needs to go you can see the casting is rough underneath - this will cause the drill to wander...



So we use a milling cutter to provide a nice flat land for the bolt heads:



And then first drill with the tapping drill and then only to the parting line with the clearance drill (note the high tech drill depth gauge )



Now we can line up a slitting saw - from the bottom as that is the bit we want to keep 



Take a light cut to check we like the cutting line:



Finish cutting through, letting the piece that has been cut off fall behind:



Tap for the big end bolts:



Put the bolts in nice and securely:



Then prepare to mount it on a suitable jig ready for the main machining task:



Lunch time 

Jo

[Roger B]

Still enjoying      Still not sure castings are my thing 

[Jo]

Thank you Roger,

Still enjoying      Still not sure castings are my thing 

Castings are not for everyone: some like them  some do not and some prefer to watch a computer make their bits for them     Its a bit like many years ago knitting machines were the fad, these days those machines are very rare and people have gone back to hand knitting and even spinning their own wool 

Jo

[Allen Smithee]

Some buy their bar-stock ready-to-use while others spin the swarf to make their own...

AS

[crueby]

I tried spinning my own wool, but it just made the sheep dizzy and throw up.... 


Seriously, a great thread and descriptions of methods!

[propforward]

I find I can destroy bar stock just as easily as I can wreck castings. I'm ambidextrous in that regard.

[bent]

Catching up during a rare slack day here at work...nice machining, Jo.  I've not seen crank sliders done that way (travelling along a bar), have only seen them trapped between the sole plate and cap plates.  And the bronze for the crankshaft bearings has no lead in it, apparently, which seems odd?  Maybe it's more readily cast that way, and the health and safety people don't pitch fits.   


As far as cross stitching goes, I'm not into that, but did spend a couple hours on the wife's old sewing machine - I need some lifting straps made to a certain spec, so ordered some hooks the right size from McMaster, and stitched them into some nylon webbing I had laying around at home.  The straps are a way to pull a panel, with a lot of heavy hydraulic components mounted on it, out of a box so I can replace a defective component buried down inside.  Will have to travel to Las Vegas to do the repair, woe is me.  Here at work I have a lifting jig and overhead/jib cranes, none of which pack very well for air travel, thus the straps.  Oh, and curses to the vendor that built the device without captive fasteners on the panel, so that you can't extract parts without having access to both sides of the panel...grr.

[Jo]

Lunch took a little longer than expected  Lets get back on this connecting rod: The first job is to line it up on the jig. With a pointer in the milling machine chuck the small end is centred on:



Winding to the other end and moving the larger end so that it is parallel:



Then time to drill for a 2BA tapping drill 4.1mm through the rod and the jig then drill to the depth of the connecting rod:




and ream:




Now to tap the jig:



Into this I have put a 2BA Allen screw which is securing that end of the rod. Now to do the other end:




Having drilled the centre and slowly opened the hole out, with the hole 1mm undersized it was time to bring out a boring head to finish the hole to size. The hole is checked for size using a "standard" in this case the other end of my mounting arbor:



To bring the connecting rod to width the connecting rod has been mounted on (yes the same) 9.53mm arbor and turned:




It can be quiet exciting having the connecting rod flying around while turning it 



The little end is even more exciting to turn, this time held by supergluing it on a piece of bar:



With the main machining completed it was time to find some filing buttons and to round things off:




I was not happy with the finish along the length of the rod so it was cleaned up using the mill:




There was still a few casting marks so I have smoothed the inside of the slot and it will be painted. But we have a connecting rod:




  I have a few more bits to get on with if this is going to be ready for the Guildford show

Jo