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Author Topic: Crankshaft materials and machining techniques.  (Read 5519 times)

gondolier88

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Crankshaft materials and machining techniques.
« on: December 28, 2009, 11:57:04 PM »

Hi,

I am currently building a stuart turner D10 (see www.modelboatmayhem.co.uk/forum/index.php?topic=21618.0 ).

However I have struck a small problem- the crankshaft.

I have already started construction on the silver soldered method. ST supply 9" of 9/32" dia silver steel and two 3" lengths of 3/8" x 5/32" silver steel section. Their method for silver soldering is to drill the sections with the correct (3/8") throw that become the webs, then part the shaft and crank sections and solder the whole peice together.

Sounds simple doesn't it!!!!! >>:-(

I CANNOT get it to solder accurately, on my last attempt I heated up the webs and sections in the lathe chuck while soldering with one end in the headstock and the other in the tailstock chuck I rotated the peice while the solder was still 'wet' hoping this would alleviate any 'off centre' problems, but to no avail.

I have now given up on this method as i'm just flogging a dead horse.

So my question to you guys is thus- what is the best method of crankshaft construction you know of that can be completed on a drill press and a lathe?

Also, ST specify silver steel as the shaft material, however the bearings are brass not bronze, is this really a good idea- won't it exscessively wear?

I was thinking of brass (weighted and balanced if pos') webs, with an iron shaft? Or even bronze? Your suggestions please...?

Thanks,

Greg
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HS93 (RIP)

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Re: Crankshaft materials and machining techniques.
« Reply #1 on: December 29, 2009, 12:07:52 AM »

I always thought you left it in one length  solder and then cut the section out countersinking the Webb allows silver solder to flow in the Webb's. you would do both at the same time on a D10

Peter

also doing it on a biger scale

http://madmodder.net/index.php?topic=2266.45
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gondolier88

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Re: Crankshaft materials and machining techniques.
« Reply #2 on: December 29, 2009, 12:43:22 AM »

Yes thats what I thought, but they only supply enough to do the actual shaft, not to waste any!!!!

Greg
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HS93 (RIP)

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Re: Crankshaft materials and machining techniques.
« Reply #3 on: December 29, 2009, 01:06:45 AM »

just buy a length of silver steel , how wide are the gaps in the webs ?

peter
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Bunkerbarge

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Re: Crankshaft materials and machining techniques.
« Reply #4 on: December 29, 2009, 09:20:06 AM »

Greg, I also think it's worth remembering just how the heat is going to flow while you are silver soldering.  If you are holding the job in two chucks have you insulated the job from the chucks?  If not the heat will flow into the chucks and mean you might have to pump more heat than necessary into the job to keep the temperature elevated, which could cause more deformation at the job.  If you insulate the job from the chucks the soldering might be just that bit more controllable.

Only a thought, if you already have it insulated my apologies for stating the obvious, but it may be worth thinking about.  It may even be worth setting the main length of silver steel in a hearth, resting on two blocks of insulating material to keep the heat flow under control rather than between chucks.
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Circlip

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Re: Crankshaft materials and machining techniques.
« Reply #5 on: December 29, 2009, 11:34:35 AM »

Other than the method described by HS93 with the mainshaft as a continuous peice Greg try this one. If you support and hold down both halves of the main shaft on couple of blocks of a solid material the same height, then support the crank web and heat the webs up.

  If starting from scratch, allow a couple of thou clearence for the Silver solder to flow into the joint and apply heat to the WEBS, not the shafts and clamp everything square on supports.

  Probably trying to teach you to suck eggs, but worth a mention.

  Silver Steel shafts in brass bearings are OK, if you want to go over the top, Gunmetal sleeves set into the main blocks.

  Regards  Ian.
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gondolier88

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Re: Crankshaft materials and machining techniques.
« Reply #6 on: December 29, 2009, 07:35:42 PM »

HS93,

The shaft between webs is 5/16".

BB,

No didn't insulate the shaft, I think perhaps I havn't explained exactly why I mounted them in the chuck as opposed to in the hearth- I had already soldered it up and it had gone well- I mounted it in the lathe chuck to check concentricity, and found it was running about 1/16" out of true!!!! So I chucked both ends and reheated to hopefully set the shaft centrally- however, despite spending 10mins reheating and rotating over and over i cannot get it to center, not because the work has deformed, but because I can't get the webs and shafts exactly -/+ .005" alligned.
 
So i'm starting again!

Circlip,

I think, I feel, that soldering the shaft in many loose peices is perhaps the crux of the problem, and using the method HS93 mentioned is definitely the best course of action.
I will stick with silver steel at your behest then guys, thanks for all the advice- got me down a little bit as it's the first engine i've made- enthusiasm is re-imbued!

Greg
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frazer heslop

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Re: Crankshaft materials and machining techniques.
« Reply #7 on: January 30, 2010, 09:59:09 PM »

Ive never had any luck silver soldering cranks without them distorting .The method I use is to glue them with loctite and then pin the webs with 1/16 or 1/32 silver steel and have never had any problems .Hope this helps
regards
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derekwarner

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Re: Crankshaft materials and machining techniques.
« Reply #8 on: January 31, 2010, 12:29:44 AM »

Another fabricated approach with very accurate results is to provide the form of construction as shown in Greg's post  on: December 28, 2009, 11:57:04 PM....however parallel hand ream the web holes...again if both sets of web bores could be achieved as a pair each......all the better from an accuracy point

Then add two each longitidunal light triangular gouges ...say 0.002" x 0.002" along the length of the four webs bores

1) Assemble the components dry & [machine drill & taper ream with trefolex] for four x 1/16" taper pins.......naturally the setup here is critical........if it could be achieved between centers all the better
2) When completed, disassemble the components & soak in solvent
3) Reassemble the components using Loctite 7471 Primer + Loctite Super Stud Lock between the webs & the journals
4) Gently tap the 1/16" taper pins until securely home
5) The Loctite stud lock will migrate into any void in the taper pin cavity

http://shopswarf.orconhosting.net.nz/taperpin.html







Let cure over night [at the recommended curing temperature], the remove the journal internal extension piece & trim the taper pins .......the result will be a truly square & undistorted & stress free crank shaft assembly  :-))

So where do we get this form of construction? .......literally modeled from the real world of full size crankshaft engineering  O0

The only down side is that 1/16" BS Taper pins probably come in packs of 100  >>:-( ....Derek
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