Built up crankshaft feedback

[bobh]

Hello Graham. Never heard of"Plumbers Black". Perhaps over here on the other side of the pond it has another name? Bob

[Alyn Foundry]

Hello Graham. Never heard of"Plumbers Black". Perhaps over here on the other side of the pond it has another name? Bob

Hi Bob.
Hmmm, it seems few others have heard of Plumbers Black either. I go back around 50 years or so when, as an apprentice electrician at my local water company we were taught how to wipe Lead pipe joints. It was the companies practice to school us in all aspects of the job even if it wasn’t going to be our actual trade. Needless to say, I’ve found the recipe.

‘plumber’s black’ –
a masking fluid made of size (animal skin glue),
whiting and lamp black mixed together to a
creamy consistency

You can also use candle flame soot applied directly to the areas that don’t need soldering. It’s become popular to use correction fluid these days.

   Graham.

[bobh]

Thanks Graham. I've wiped many high voltage cable splices with lead and we used something we called tallow on the paddles and where we didn't want the lead to stick. The tallow obviously wasn't tallow, it was hard until heated but it rehardened when cooled. A yellowish color but you sure wouldn't want carbon in a 13kv splice! Bob

[petertha]

Interesting video of Millyard's assembled crank for RC374 Honda six replica. The best I can discern is - the crank elements are cold pressed into one another from middle to either outboard ends, validating axial alignment as he goes. (He starts in middle because the crank has a center sprocket to contend with). I'm not clear how he would tweak any rotation misalignment, but it would have to overcome the friction force of interference fit cold press. But looks like he keeps each segment it together (torsionally) with a dowel pin drilled axially along the crank journal / web perimeter line. Kind of like a round key.

<a href="https://www.youtube.com/watch?v=J1cQ098eqF8" target="_blank">http://www.youtube.com/watch?v=J1cQ098eqF8</a>

[gipetto]

Le Dan assembles cranks also for multicylinder engine mods. here's just one, but you can see how he does it in the last three minutes

<a href="https://www.youtube.com/watch?v=cL9ICrGbfvE" target="_blank">http://www.youtube.com/watch?v=cL9ICrGbfvE</a>

[Niels Abildgaard]

A proposed crank for a two stroke boxer.
The main part is casehardened and ground and indexes from the central bore.

[steamer]

Rugged!     I think you could.get completely acceptable performance with a simple press together design.  Remember the case is supporting the crank as well.    Lots of high power 2 strokes out there with pressed together pin style  cranks.    Take a look at Allen Milyard's v12 Kawasaki crank construction.   It gets to the point I'm making.

Or Allen's super six crank build   both on youtube

Dave

[petertha]

On the topic of torsional strength of a pressed in shaft within a hole (like a crankshaft segment interference pressed within a web element) I did some searching online & Machineries handbook. I did not land on a suitable formula. There were tables & guidelines to achieve different classes of fit including interference, but nothing I could see that related to a torsional 'breakaway' force once assembled. I would have to think the circular fit is the weak link in the chain relative to strength of solid components? I posed it as a question to Gemini AI. I've been doing this lately out of curiosity because some things it seems quite smart & useful, others... not so much. Anyways, even with a couple thou interference on a 2" nominal shaft/hole, it indicates rather anemic strength which makes me suspicious. Can anyone shed any light on this?

It seems to me the press fit is an intermediary step to getting all the elements together in a stiff & aligned assembly, but what is doing the actual torsional resistance is the axial pin along the joint line. Maybe shrink fit + pin are somewhat additive but put it this way, if the joint ever did slip for whatever reason, it would boil down to the shear strength of the pin cross section area, no?

[petertha]

I was looking into taper pins & matching drills. Where do you guys source them? The pins were relatively inexpensive on McMaster Carr USA but OMG the drills are not cheap.
I then lurked on AliExpress, lots of (seemingly standardized) 1:50 pins, but no drills unless they call them something different & I have yet to guess the password. But lots of matching reamers.

[Jasonb]

You usually drill a parallel hole to suit the small end of the pin and then use a "taper pin reamer" to cut the taper. Deep holes may benefit from using more than one drill size and doing the hole in steps.

My feeling is that in the small sizes found in models and without doing many test pieces it is hard to relate any calculated hole/pin sizes to the actual parts. Even if a reamer is used to finish the hole there can be small variables due to pilot hole size, material being cut, condition of reamer, type of reamer, etc. Most of us don't have the equipment to accurately measure these small holes to the tolerances that the calculated fit may have given so you end can end up with a joint that is not tight enough or one that jams solid part way through assembly.

I was looking at another build of the Upshur twin in relation to Brian's build and there was a good example of parts jaming on assembly and subsequently being damaged as excess force was applied trying to get them together.

[Niels Abildgaard]

It seems to me the press fit is an intermediary step to getting all the elements together in a stiff & aligned assembly, but what is doing the actual torsional resistance is the axial pin along the joint line. Maybe shrink fit + pin are somewhat additive but put it this way, if the joint ever did slip for whatever reason, it would boil down to the shear strength of the pin cross section area, no?

A multicylinder drone engine has  crankshaft with 25mm dia parts pressed into 24.9mm holes with grip length of 17mm and test minimum torque is 600 Nm.
He who  proposes conical pins or loctite will be asked to leave..

[crueby]

I was looking into taper pins & matching drills. Where do you guys source them? The pins were relatively inexpensive on McMaster Carr USA but OMG the drills are not cheap.
I then lurked on AliExpress, lots of (seemingly standardized) 1:50 pins, but no drills unless they call them something different & I have yet to guess the password. But lots of matching reamers.

I  got my pins, 4/0, from McMaster  and started with step drilling with a series of small drills and fin8shing with the reamer from there as well. A couple years ago I  sprang for one of the drills too, expensive  but work much faster. I still drill a straight pilot hole first then run 8n the taper drill. Also noted the drills were not available  much elsewhere.

[steamer]

The torsion on the joints is small.  The engine block and bearings will take most of that at the crank pins.   It's just the final drive that is a concern

[petertha]

A multicylinder drone engine has  crankshaft with 25mm dia parts pressed into 24.9mm holes with grip length of 17mm and test minimum torque is 600 Nm.
He who  proposes conical pins or loctite will be asked to leave..

Impressive torque. So that's ~0.004" annular width interference. That's why I was rather doubting the results of the calculation example I mimicked, nowhere near that. I don't have the press equipment for what I suspect would be pretty substantial press-in force. Theoretically, if the part with the hole was bored to same 24.9mm dimension & heated to the extent dropped effortlessly on the shaft (thermal shrink) would it be the same net result in the end as press? Somewhere in my travels I thought I read part of what pressing in adds is micro striations that act as friction keys, but maybe that's getting too deep in the weeds.

Any idea where a formula/calculation can be found that describes this interference/torque 9and for bonus points press in force) relationship?

[petertha]

The torsion on the joints is small.  The engine block and bearings will take most of that at the crank pins.   It's just the final drive that is a concern

That's another thing I was mulling in the back of my mind. The strength of the key in the crankshaft (to the prop washer) is easy to calculate in shear. If that somehow sheared, the wind on the whirly end stops. If the axial CS/web pin was equivalent to the key, that might be a good starting point of equal strength. But maybe how & where it fails is also important. If you had some sort of unfortunate kick back & crank arms slipped & displaced & twisted rotationally that would be a problem.