Author Topic: Ouside Cranks and how to secure the on the axles  (Read 439 times)

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Offline Jon Nazareth

I'm building a model of Lion and she has outside cranks.  I was going to secure them with cone end grub screws bur couldn't find any small and short enough.  The wall thickness of the cranks is .o66 and I didn't want them poking out.  Another suggestion is to Loctite and pin but, and I haven't tried it yet, it may not be possible to get close enough because the drill chuck would foul on the wheels.  Does anyone have any ideas?  These may sound like the words of a drowning man but, what about Loctite on it's own?

Jon

Offline John Candy

Re: Ouside Cranks and how to secure the on the axles
« Reply #1 on: Aug 13 2019 09:10 »
Jon,

For "Calcutta", Walsall supplied outside (GWR-style) cranks with small grub screws which are housed deep inside the crank. I didn't measure the length but they are not very long.

I marked the axle (after quartering the cranks and lightly attaching with CA glue) and removed crank and drilled a shallow (c. 3/64") dimple to accommodate the nose of the grub screw.
Finally, I fitted the crank using a thread locker (ZAP42) to secure the grub screws and fill the void around the screw nose where it locates in the axle.

Whether that will work on "Lion" depends on how much "meat" there is to work with on crank and axle.

Mike ("753") may have an alternative suggestion since he is building "City of Truro".

Regards,
John.
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline IanT

Re: Ouside Cranks and how to secure the on the axles
« Reply #2 on: Aug 13 2019 09:25 »
Hi Jon,

I've 'joined' quite a few things (both tooling & modelling) with Loctite 638 and it gives a tremendously strong grip if applied correctly to a well made joint (see the data sheet). I've never used activators but I do use a solvent cleaner before applying the Loctite - clean surfaces really help here. The only way I have a managed to break a Loctite'd joint is by heating it - I've never managed to break one using just force.

https://www.henkel-adhesives.com/uk/en/product/retaining-compounds/loctite_638.html

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline Jon Nazareth

Re: Ouside Cranks and how to secure the on the axles
« Reply #3 on: Aug 13 2019 09:36 »
John
The wall thickness of my cranks will be .066".  What is the wall thickness of your cranks?

Ian
because of their size, I may finish up by using Loctite.

Jon

Offline 753

Re: Ouside Cranks and how to secure the on the axles
« Reply #4 on: Aug 13 2019 09:49 »
John

I used countersunk hex headed screws, but my axles have square ends for auto quartering.
I would use the countersunk screws on plain axles, set the cranks so all wheels turn well, then cross drill and pin with brass pins interference fit, that way if you ever needed to remove the cranks you loosen the countersunk screw and turn the crank to break the pin.

Mike

Offline John Candy

Re: Ouside Cranks and how to secure the on the axles
« Reply #5 on: Aug 13 2019 09:55 »
John,
Approx 0.168" but the tops of screws are seated about 0.100 below surface.
Could be worth speaking to Les or Roger at WMI and asking about the screws fitted on the cranks of their Armstrong locos.
Regards,
John.
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline IanT

Re: Ouside Cranks and how to secure the on the axles
« Reply #6 on: Aug 13 2019 10:26 »
Jon,

I've just noticed some advice/links on WT referencing Model Engineer posts on this subject. There was a discussion some time ago about the need to machine 'grooves' in shafts to let the Loctite work - and keep the axle/wheels a very close fit. The need for additional 'pinning' was also recommended. I don't think this need worry you.

Firstly, the need to groove Loctite'd joints has been disputed, with a ME reader contacting Henkel for guidance. They stated that provided the data sheet advice was observed, no further precautions were necessary. With regards pinning, this was somewhat belts & braces on the driven wheels of larger (3.5/5") engines. Personally, I don't think it's a problem in 2.5" but opinions do vary.

If you do decide to Loctite - then you will need to have some quartering method ready to go - you will only have a minute or two before it sets. With regards 'fits' the data sheet calls out <0.25mm (<10 thou) but in practice a smooth sliding fit (but with no wobble between parts) is about right. Wipe off any surplus Loctite immediately after fitting - it's unsightly if squeezed out liquid is left to dry and it's hard to remove.

The only drawback is obviously the inability to dis-assemble without using heat - not a problem with some parts but a problem with anything near painted surfaces.

Regards,

IanT   
Nothing's ever Easy - At least the first time around.

Offline Peaky 556

Re: Ouside Cranks and how to secure the on the axles
« Reply #7 on: Nov 20 2019 23:40 »
Hi Jon,

I've 'joined' quite a few things (both tooling & modelling) with Loctite 638 and it gives a tremendously strong grip if applied correctly to a well made joint (see the data sheet). I've never used activators but I do use a solvent cleaner before applying the Loctite - clean surfaces really help here. The only way I have a managed to break a Loctite'd joint is by heating it - I've never managed to break one using just force.

https://www.henkel-adhesives.com/uk/en/product/retaining-compounds/loctite_638.html

Regards,

IanT

I’m heartened to re-read this post promoting the use of Loctite 638, as I have a difficult task involving the pinning together of two gears.  After trying a thread-locking grade (222) with very mixed results I did some research last night and independently concluded that 638 would be my best bet.  It’s in the post now, but it is with great pleasure that I have your recommendation too Ian, saving me the trouble of asking the specific question 👍
Best regards, Tim

Offline IanT

Re: Ouside Cranks and how to secure the on the axles
« Reply #8 on: Nov 21 2019 16:38 »
Well, sometimes you can actually "pin" gears together Tim

If they are spur gears (with flat faces) then you can simply drill through the bodies and insert a pin into the holes (aligning them on the axle before drilling). This is a simple way to 'pair' gears and how it's done on my EW's screw-cutting gears (much simpler than the keyways used on Myford gears). This is also a useful method for any small gearbox where you need paired gears on an idler shaft.

However, if you can only Loctite them to the shaft - then solvent cleaning (degreasing) and a nice fit will certainly help keep them in place.   

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline Peaky 556

Re: Ouside Cranks and how to secure the on the axles
« Reply #9 on: Nov 21 2019 18:54 »
Ian,
Pinning with two-off 1mm HSS pins, parallel to the shaft is exactly what I am doing, to locate a pair of gears face to face.  Trouble is a drilled 1mm hole for the pins gives a slightly sloppy fit, so the Loctite is intended to support the pins within the slightly oversize holes, such that they can resist the torque in pure shear.  The pins will also be held captive by the Loctite.  As a bonus the bonding effect of Loctite between the gear faces, and onto the shaft, will help too, but I’d never rely on that alone.  I don’t have that much faith in bonding technology!  As said, the threadlock gave mixed (read unreliable) results, so I’m expecting better things with this bearing-fit grade.

I’m away for a long weekend, so playtime will be next week.

Tim

Offline IanT

Re: Ouside Cranks and how to secure the on the axles
« Reply #10 on: Nov 21 2019 19:51 »
I hope they are not too loose Tim.

Depends how particular you are about these things but another approach might be to drill the hole(s) and then taper ream them and fit a taper pin (which will fit snuggly).  You can get TP reamers down to 1.5mm or 1/16" depending on your preference. The taper varies sometimes but is generally about 1 in 50.

So this might be a thought if you ever need a backup plan...    ;)

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline Peaky 556

Re: Ouside Cranks and how to secure the on the axles
« Reply #11 on: Nov 23 2019 17:27 »
I hope they are not too loose Tim.

....another approach might be to drill the hole(s) and then taper ream them and fit a taper pin (which will fit snuggly)....

Regards,

IanT

Definitely NOT you idealistic engineer!

To cite the Loctite literature, two of the benefits are to “Reduce or eliminate expensive machining operations”, and to “Fill gaps so machining tolerances can be widened”

I’m very happy to adopt such labour-saving methods!

Rgds, Tim


Offline IanT

Re: Ouside Cranks and how to secure the on the axles
« Reply #12 on: Nov 23 2019 17:58 »
 ;D
Nothing's ever Easy - At least the first time around.