Ohrndorf V12, new challange

[fumopuc]

Wow, and I can't even get a flame eater to work.

All the flame eaters I have seen from you are running well ?

[Niels Abildgaard]

Next challenge, to find out the right overlapping, which can be machined with my tools reliable for all press fits between pin and the to made crankshaft cheeks.
tbc

 An engine manufacturer made two stroke crankshafts from 25mm stubs pressed into 24.9mm holes 16mm deep and expected survival of 600Nm test torque

[petertha]

Very nice progress!

Regarding pictures in post 94, what is that dark red substance on the parts & in some of the holes?

Regarding masking tape + CA glue clamping fixturing in post 95, I've seen this method before & tried myself but with inconsistent results. I do a lot of modelling work with CA so quite familiar with its properties & variants. The biggest issue is even when part comes off the fixture cleanly, the CA glue residue can be very stubborn to remove. Acetone, strong thinners...even dedicated CA de-bonding solutions are very slow to remove it without extra hand work. (Favoring 5-min epoxy with heat release but that's a different story). Anyways my other issue is that cutting fluids that work well with aluminum also have a habit of acting as a solvent on the tape adhesive itself - the part is bonded to the tape well enough, but the tape adhesive releases from the fixture. First I thought maybe the CA is soaking beyond the adhesive to fixture but I tested that & the adhesive layer is quite impermeable. Just wanted to run this by you in case there was some magic trick. Maybe the type of tape?

It has been some time since I modelled the engine in CAD but can you tell me, are the connecting rods laterally free floating between the webs along the crank pin? ie. there are no spacer washers between the rods & webs? Or the bronze bushings do not extend proud of the rod to make a bit of gap?

[fumopuc]

Very nice progress!

Regarding pictures in post 94, what is that dark red substance on the parts & in some of the holes?

Grease, copper paste

[fumopuc]

Regarding masking tape + CA glue clamping fixturing in post 95, I've seen this method before & tried myself but with inconsistent results. I do a lot of modelling work with CA so quite familiar with its properties & variants. The biggest issue is even when part comes off the fixture cleanly, the CA glue residue can be very stubborn to remove. Acetone, strong thinners...even dedicated CA de-bonding solutions are very slow to remove it without extra hand work. (Favoring 5-min epoxy with heat release but that's a different story). Anyways my other issue is that cutting fluids that work well with aluminum also have a habit of acting as a solvent on the tape adhesive itself - the part is bonded to the tape well enough, but the tape adhesive releases from the fixture. First I thought maybe the CA is soaking beyond the adhesive to fixture but I tested that & the adhesive layer is quite impermeable. Just wanted to run this by you in case there was some magic trick. Maybe the type of tape?

No magic trick.
Cleaning the sacrifice plate and the part with acetone, tape on both parts and the CA glue between the tape layers.
The tape I do use https://www.3m.co.uk/3M/en_GB/p/d/b40067049/ 

[fumopuc]

It has been some time since I modelled the engine in CAD but can you tell me, are the connecting rods laterally free floating between the webs along the crank pin? ie. there are no spacer washers between the rods & webs? Or the bronze bushings do not extend proud of the rod to make a bit of gap?

The design does show very thin thrust washers made from bronze.
Already done, pictures following soon.

[fumopuc]

 An engine manufacturer made two stroke crankshafts from 25mm stubs pressed into 24.9mm holes 16mm deep and expected survival of 600Nm test torque

Hi Niels,
here we have 6 mm pins and a 7 mm depth hole.


I think the load/torque is not very much.


I have made some simple experiments to find the way.
The material for the webs I will use should be ETG100, similar to 1114 stressproof.
First I made a 5,8 mm hole with a normal drill bit.
And first supersize, the 6H7 mm reamer did not make a single chip when passing through.
So another useless tool in the scrap box.
Next attempt a brand new 5,8 mm drill bit and the 6H7 mm  reamer.
Now I have got what I expected, a slit fit, pressing the pin into the hole against the air coming out in a very thin gap, so some force is necessary.
But so impossible to get a press fit.
The pin is a hardened standard part of the shelf, so the hole has to be modified.
I have ordered a new reamer, size 5,98 mm and the hole was made than with a 5,7 mm drill bit. 
No I have got a real press fit with the earlier mentioned standard pin size 6m6.
The real pin in the web will be shorter than a standard pin.
I have shorten it with the tool grinder, that means flat surfaces at the end and new made small chamfer.
Also with this modified pin a trial fit was made successfully.
tbc

[fumopuc]

With this small new chamfer at the pin I have been unsure with the first set up, so I have made another disk with a bigger hole as guide to adjust for pressing in in straight.
Now I have felt confident with the procedure.


Next to attack, the webs making.
The designer of the engine has recommended to use round stock in the lathe with a round recess out of center to clamp the raw machined disk an fix it by a bolt.
Than to make the con-rod pin hole with the lathe.
I have been not happy with this idea, because the position will be given by the outer contour, what could create some inaccuracy for the hole already.
So my idea is to make these con-rod bearing holes always in pair of webs.
If a pair has a minor deviation, it will not have any influence of the entire crank assembly.
So a fixture was made to clamp two raw machined discs together and make the hole and reaming together.


Next challenge the outer contour.
The designer has recommended to do it on the lathe also with a fixture as described above.
I have followed this idea first, but tried to make it more efficient.
So a fixture was designed to host 3 parts in one go.
tbc

[fumopuc]

When the design of the fixture was ready in CAD and I have locked at it, turning it around in the virtual space and suddenly I was thinking about my poor little lathe, getting knocked 3 times one turn buy the webs.
So new decision was made, it will be made by the CNC mill.
It is not much material to remove and the VHM cutter will do it nicely too.
The CAM simulation has calculated something about 7:52 minutes each web, easy going and with final cleaning, so that will be o.k.

[petertha]

Bravo. I'm watching the crankshaft construction steps with great interest. I started the post (linked below) a while back to keep the subject away from your build. The big revelation to me was how many motorcycle & sport ATV engines are entirely 'built-up' CS. I was a little bit skeptical of the Ohrndorf clamp style web, but obviously it works. The V12 is, after all, a running engine & there are other examples. Ohrndorf used a press-in (only) assembly method on more recent opposed Boxer 4-cyl but, I wonder if that's because it was shorter. Maybe pressing (entirely) just gets too unwieldly with longer length CS like this 12-cyl and when the CS has to be segmented to accommodate mid span bearings or whatever?

It kind of makes sense to me that a cross bolt could impart considerable force to the round pin element (simulating a radial interference press fit). One advantage of clamp is maybe provides a little bit of assembly alignment adjustment wiggle room rather than pressing each sub-assembly sequentially & then somehow dealing with any resultant runout if it occurs.

Anyways, what I'm really asking - do you think if you have some extra web parts available, to rig something up to test how much torsional resistance the clamp assembly can resist? I assume basically hanging a weight or applying a load on the crankpin simulating highest connecting rod force. Here I am on unchartered waters as to HOW much force is reasonable, maybe there is some simple rule of thumb? Maybe its not that simple, but wondering out loud.

https://www.modelenginemaker.com/index.php/topic,11875.0.html

[Roger B]

That's a lot of experiments and a lot of progress     

The tapered crankcase extension seemed to fit well. The initial milling should have been accurate but there was a significant chance that the long drill would wander 

[fumopuc]

Hi Peter, Roger, thanks for popping in.

Yes, a lots of experiment are necessary for me, to get more confident with this build.
I am very curious also, how it will go ahead with the crankshaft.

Next issue for me to sort out was the stack dimension of each con-rod pair.
To do this, the con-rods do need their bronze bushes.
To get an idea about what is required, I have measured all big and small eyes in the rods first.
Concerning the big eye I could sort them in 3 classes.
1 = 7,03 mm
2= 7,02 mm
3= 7,01 mm
The small eye has been over all the same 5,00 mm.
So it was time to make 32 little bronze bushes and press them into the holes.
Not my favorite job, but I had to do it.
I have tried to match all time with an overlapping by 0,02 mm for the press fit.
Testing the fit by using the akku drill, but there was finally no chance the fit them all with my 6H7 reamer.
I was mostly to tight to the pin with 6m6 mm standard dimension.
So I have ordered a 6,01 mm reamer and waited for the delivery.
tbc

[fumopuc]

So next day, when the reamer arrived, I have been happy with most of it, except 3 pieces.
There is one picture, I could not resist to ad it to family shot, with an old V10 Titanium con-rod, sleeping since years on my window board.
So what to do with 3 candidates, which have been impossible so far, to match an available standard pin.
First idea, to leave them in deep freezer for one night and try it again with the relevant reamer.
Second idea, to order some more pins, because the range of m6 class is from 6,004 to 6,012 mm and my currently remaining 3 pins are of the bigger size.
I could get 15 pieces to the conditions I have expected, by new matches and reaming the cold big eyes again.
The very last one, did me not the favor to run smooth.
Finally I have tried it by a running in process at the lathe, but it did not like that too.
O.K. 15 con-rod for finally 12 pieces needed should be fine also.

New challenge thrust washers.
Also made from bronze, 0,45 mm thickness.
tbc

[fumopuc]

I hope the pictures does explain the way I have tried to archive the right dimension of each shim.
Target was to archive a stack dimension over all, 2 con-rods and 3 thrust washer, of under 11,45 mm.
At the end I do have 7 matched pairs for 6 times needed now.


And here some motion after all these, for me, hard work.
<a href="https://www.youtube.com/watch?v=gkYG2Vwb2SM" target="_blank">http://www.youtube.com/watch?v=gkYG2Vwb2SM</a>

[petertha]

Nice Achim! We were just talking about glue fixtures. I used this kind of arrangement to make some special thin washers like yours. With a glue fixture you don't need to be so precise with the parting off width. Just sand finish the one face as you have done which then mates the lathe fixture. Here I found CA bond did a great job supporting the turning operation as long as skim cuts. I think the glue around the periphery is as important (or easily to apply) as the face itself. Machining to thickness went well, but then came the step I struggle with - part removal. I though heat would de-bond them & just require minor clean up. But CA puts up a fight & wont let go without turning into a gooey black mess. Even when it was soft I was bending the thin parts. So a rather failed experiment. But looks like your tape method is working better. I note the tape link you provided said solvent resistant.

I repeated above but this time with epoxy & allowing excess to ooze out forming the side support fillet. It worked but you have to account for the adhesive thickness. CA has thinner viscosity so is more predictable thickness than epoxy. The epoxy turns a tell tale toffee color under (heat gun) heat, softens & lets go cleanly with very little remaining residue.

I encountered this issue again with head shims which are even more finicky to remove. Here I decided to make fixtures & turn them from sheet stock of specified thickness. A bit more front end work but nice thing is you can also stack a bunch of different sheet thicknesses & turn them all down together.