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[Martin (Admin)]

Hey Bunkerbarge!   

Bit off-topic but, do you follow  Keith Appleton on Utube,  I saw him assemble big end crank arms on shaft only using Loctite ...
 https://youtu.be/D_IBmkrdZn8?t=160

 Is this a real thing / good way to do this?

 Martin

[Bunkerbarge]

Martin,


There are basically three types of engineering fit, a transitional fit, an interference fit and a clearance fit.  Basically a clearance fit is where, for instance, the maximum tolerance of a shaft diameter is less then the minimum tolerance of the bore so it is guaranteed to slide in.  An interference fit is where the minimum tolerance of the shaft is actually greater than the maximum tolerance of the bore so it is guaranteed to 'interfere'.  The 'degree' of interference is determined by the range of tolerances for both components.  Some interference fits can be put together with a hammer, some my require a hydraulic press but the heaviest fits may require heating of the bore and even cooling of the shaft to change the fit to a clearance fit to put it together.  When the temperatures normalise you will then have the full interference fit.


Fabricated crankshafts on large marine diesel engines are assembled with heavy interference fits.  There is no other mechanical device holding the two parts together yet they are capable of transmitting the power of the engine to the shaft.  I don't know what kind of fit Keith has created in his shaft components but, if he has machined them correctly they should not need any assistance from a locking fluid.  If he is using one it might be just because he feels he needs a greater level of security or he may be unhappy with the fit and feels it needs a little help.  Personally I would prefer the fit to be a good interference fit that does not require help.


As an interesting aside, when you do a crankcase inspection on a large diesel engine you check the 'witness' marks.  These are small marks stamped into the end of the shaft and the web of the crank.  If there has been any undue load on the engine from say a water leak into a cylinder that wasn't cleared before starting or the propeller hits something then there is a possibility of the interference fit slipping.  The witness marks show that the fit has not moved.


Keith is actually a very competent engineering modeller and used to come down to Kirklees occasionally so I know he knows what he is doing.


I hope this helps


Best regards


Richard

[Baldrick]

You must remember that in many of his videos Keith is repairing customers engines which have problems and his methods as circumstances dictate may be to overcome problems he has been landed with and not how he would proceed with an engine he has built himself.


see >  www.mainsteam.co.uk

[Martin (Admin)]

Thanks Chaps!

Not sure if it was this video, or one of many others, the crank was a 'clearance fit' (?) as  Loctite was applied and the crank slid on to the shaft by hand and left to set.

Incidently, please could you define 'transitional' & 'clearance'  fits please? 
 
 

[Bunkerbarge]

Very basically and thinking of shafts in bores, a clearance fit is where the shaft remains free to rotate when fitted, an interference fit is where that shaft has to be forced into the bore, which then holds it, and a transitional fit would be a close fit that would allow rotation but only under a degree of force.

[Baldrick]

Very basically and thinking of shafts in bores, a clearance fit is where the shaft remains free to rotate when fitted, an interference fit is where that shaft has to be forced into the bore, which then holds it, and a transitional fit would be a close fit that would allow rotation but only under a degree of force.

  TIGHT, SLACK OR JUST RIGHT   

[Circlip]

Let's not go down the "Shy 64th" or "A proud sixteenth" route. (Early apprenticeship). Should be noted however that many early motorcycle crankshafts were friction fits on the crankpins.


   Regards  Ian.

[Bunkerbarge]

We actually went by a "midge's dick"!

[Netleyned]

RN Artificers Gnats Cock end😁
Ned

[JimG]

Was informed by an ex toolmaker friend that it was a "Ba' Hair", although it would vary depending on Imperial or Metric.

[Circlip]

And another apprentice, "How many thous are there in an inch"


  "Oh I don't know, b****y millions"


  Regards  Ian.

[ooyah/2]

Hey Bunkerbarge!   

Bit off-topic but, do you follow  Keith Appleton on Utube,  I saw him assemble big end crank arms on shaft only using Loctite ...
 https://youtu.be/D_IBmkrdZn8?t=160

 Is this a real thing / good way to do this?

 Martin






Martin,
When making  crank shafts for a model application Like the Stuart D10 , 10V and Score engines you can make the shaft by machining the Forging supplied by the kit.


I have made shafts for all of these engines by making them built up and glued with Loctite 603 and a pin thro' the web and glued into the 9/32"main shaft .


My method is as the pics.


I make the crank webs and drill and ream them 9/32" to fit the main shaft and the big end crank pin both ends 1/4" dia  machined to the same length to clear the big end of the Con Rods, they can then be slipped thro" the 1/4" dia holes but not to be glued at this point, slip them over the 9/32" dia main shaft , pull the crank webs apart and glue them back into the 1/4" dia holes with the 603 glue.
By doing this it keeps them in line for future assembly, be careful not to let any glue get on the main shaft holes.
When cured in about 15 mins they will not move and allow you to then place the webs in position to clear the bearings and set them at 90deg to each other, apply some 603 to the crank webs and leave them to cure overnight, you can when cured drill holes 1/16"dia and drill thro" the webs at the main shaft and and glue in some pins, this method ensures that the crank webs will never move, you can if you wish not the pin thro" as I have tried this method and then tried to destroy the crank web joints with no success, in fact it twisted the 9/32" da i shaft and had to be heated with a blow lamp to release the joints.

By pinning the joints it allows you to set the shaft up in the lathe for machining the webs at one side and hand filing the other end out of the lathe.

George
Please excuse the pics as I am still learning to size the pics for posting


 
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