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Whittle V8 - Crankshaft

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Steve Withnell20/06/2011 10:35:22
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858 forum posts
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Shadows have softened the lefthand edges, but this is the current state of play.
 
Anyone here made one of these?, the journal pins are now down to 5.9mm (finished size is 5.56mm ie 7/32) and it''s getting exceptionally difficult to avoid chatter. I''m regularly honing the tool to best effect but even with the lightest of cuts, it''s like trying to finish turn spaghetti!
 
I have a cunning plan, but be interested in your more experienced ideas on how to get some rigidity back into the workpiece. The journal pins are .33 inch wide.
 
 
Ian S C20/06/2011 13:38:26
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Sounds as though you need some sort of steady, but I'm not sure how that would work, I'v bent crankshafts bigger and simpler that that, so I understand your problem. Ian S C
Gray6220/06/2011 17:21:37
1058 forum posts
16 photos
Hi Steve,
My first crankshaft looked pretty much the same as yours
I machined up some eccentrics which clamp to the crank whilst finish machining the throws, these are then held in bearing four point fixed steady. Using this method, I was able to produce a straight finished crank.
That said, I have now abandoned the project and am embarking on a X2 scale version of the same engine for various reasons.
The other option would be to set up the crank on the ofset centres and then use a toolpost grinder to finish the journals. A good quality mini flexi shaft can be used for this, just check that there is minimal runout in the bearings.
I have used an american built Foredom flexi drive with reasonable success although, I have replaced the bearings with higher spec than original.

regards

Graeme
Ramon Wilson20/06/2011 21:00:41
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1655 forum posts
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Steve I have not made a crank as small nor as slender so cannot offer any advice based on experience.
 
However having spent a while looking at your pic and wondering how such a problem could be addressed I wonder if a sleeve, with a reasonably thick wall and turned to a light push fit over the webs, may increase the rigidity some what.
It could possibly even be split and clamped with something like pipe clips leaving enough of one journal to be done between centres then turning around, sliding the sleeve back to do the other and then the centre.
 
Just a thought - it should certainly reduce flexing though whether it would eliminate it is debatable.
 
Very nice work so far by the way
 
Regards - Ramon
 
ady20/06/2011 23:31:54
612 forum posts
50 photos
Watchmakers and instrument makers must have encountered problems like this over the last 200 years.
 
Have a dig and read about on the netty looking for articles concerning small highly skilled manual stuff and their various solutions.
 
It will probably slap you between the eyes as you read about subject A, and realise it could sort out problem B.
 
I've had quite a few eureka moments using this approach.
 
Articles on pultra micro-lathe work for example, and cowells lathes.
Your primary lathe may actually be a bit too cumbersome for this kind of work.
 
The entire micro-lathe industry was born out of a need for simplifying micro work.
All the micro lathes had solid bearings as well, they insisted on this.
 
GL

Edited By ady on 20/06/2011 23:45:22

Richard Parsons21/06/2011 15:43:24
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645 forum posts
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I have had to machine a similar item in about 1979. It was not a crankshaft. How I did it was to machine up two pipes which were a nice snug fit onto the bits you will call ’webs’. These support the parts not being machined. I made two attachments to the fixed steady well wider than the bit I was machining. These supported the pipes. And away I went very sharp tool and very fine cuts and a slow feed. Job done! By the way the tailstock end of the pipes ran in a ball race.

You might try a Jacot tool and a set off pivot files instead.


All the Best

 

Dick
mick21/06/2011 18:43:20
421 forum posts
49 photos
Hi.
I've made a scaled up version of this engine and appreciate the problems you are having. I would suggest you do all the milling before you finish turn the journals. This is for two reasons, you will reduce the weight of the eccentrics and therefore the fly wheel effect, secondly you will also reduce the over all section, again reducing the eccentric effect. Dead slow speeds, geared if possible, very shallow cuts, plenty of cutting oil, will help cut down any vibration. It may seem odd, but if you increase the feed, this will sometimes stop the vibration from starting in the first place. My crank shaft took 18 days to machine complete. There is a great sence of satisfaction and relief awaiting you at the end of it all. Best of luck.
Mick.
Steve Withnell22/06/2011 07:03:10
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858 forum posts
215 photos
Thanks all. I think the plan then is to machine a tube from one inch diameter EN1 to slip over the workpiece. If I slot it and use pipeclips as clamps then then should sort it. The advice to run really slow is helpful as I'd defaulted to running much faster.
 
I'll mill out the webs next. Using the tube clamp should ensure that the workpiece is as straight and rigid as possible for finish turning.
 
My plan had been to make some miniature jacks to set between the webs and loctite them in place, but that would have been much less efficient than using a tube.
 
Thanks
 
 
Steve
Richard Parsons22/06/2011 09:06:25
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645 forum posts
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Steve I would make several tubes. And only use two at a time. One is a very short one, one very long for the first journal. Then a longer one and cut the very long one down for the second and so on. As you have only 0.34 mm to go (0.17 mm cut -about 7 thou in real money)   I would set up a filing rest and take this off with some nice sharp pillar files. I also used the Fixed Steady on the longest part of the tube and a Travelling Steady on the other side of the journal being worked on.   Or do as I did make, two/three extra wide fingers for the steady about 20- 25 mm long to straddle the cut.   If you get vibration then add some lead bands to change the thing’s resonance and that of the tool.
 I would leave the webs alone until you have finished the journals as milling them down will leave gaps and reduce the stiffeniing effect of the tubes

Hope it helps

Dick

PS Clock makers often use files in the lathe.

Edited By Richard Parsons on 22/06/2011 09:17:10

Edited By Richard Parsons on 22/06/2011 09:23:07

Richard Parsons22/06/2011 09:33:01
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645 forum posts
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Oh bother, I have just realised that your journals are offset so you cannot use steadies in the way I did as you have over 5/16” you could rig up a single steady.


Dick

ady22/06/2011 10:55:27
612 forum posts
50 photos
By coincidence today I ran into an interesting page concerning them fiddly bits.
Dan Calkin And His ELFs
 

 
 
 
edit:
one link can be a bit weird. Just scroll up the page a bit to find the book.
 

Edited By ady on 22/06/2011 11:01:08

Steve Withnell23/06/2011 21:14:09
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858 forum posts
215 photos
Here is the crankshaft wearing it's overcoat I've taken 0.1mm off the diameter and the finish is straight off the machine (no brasso!). Cuts of 0.005mm running slowly c75rpm. Even without a pipeclip to secure, the workpiece is clearly much stiffer, chatter eliminated.
 
I made the sleeve from a one inch length of EN1A, then skimmed 1mm off the outside and then drilled 15mm/17mm/19mm which left the piece significantly oversize, so second attempt I drilled 17mm and then bored to a tight fit and ran a 1.5mm slitting saw down the length. It needs a screwdriver in the slot to open it up slightly to slide it over the crankshaft. Not sure using pipeclips is necessary. The sleeve wall is just over 2.5mm which provides plenty of support.
 
So thanks for the help!
 
Steve
 
Ramon Wilson23/06/2011 21:46:13
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1655 forum posts
617 photos
That's good news Steve,
it's very pleasing to hear that this thought proved a viable proposition.
 
How far are you into the project?
Today I finished the very last part of mine, it's a nice feeling
 
Regards - Ramon
Steve Withnell23/06/2011 22:07:04
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858 forum posts
215 photos
Hi Ramon,
 
Well, there are apparently 550 components in this engine, and when I've finished the crank, I'll have 549 to go . An old friend (who has at least 60 years machine shop experience) told me to make the crank first, because if I could do that to a decent standard, then there was nothing else in the engine to cause a problem.
 
When will you start yours up? It would be really great to see it running on YouTube.
 
Best Regards
 
Steve
 
 
 
 
Ramon Wilson23/06/2011 22:56:43
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1655 forum posts
617 photos
Hi Steve - that brought a smile to my face .
 
'First step and all journeys' spring to mind but that is certainly sound advice though.
 
Good luck with it as it's a testing project. I know two people who have built it - one very successful runner one less so. The one that ran well did so like a sewing machine.
 
I hope to have them running within a few days or so - I want to get the anodising done first and have another attempt at the nickel plating - I should think next week at the latest.
My friend who took some video of the Racers says he will do the same - trouble is I found it impossible to get it to post. Hopefully I'll have better luck this time.
 
Regards - Ramon
Steve Withnell23/06/2011 23:02:15
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858 forum posts
215 photos
I've seen a post on one of the boards that the camshaft is drawn as a mirror image, so that if made to drawing, the engine will run the wrong way. Did you come across this? A standard prop should run counter clockwise looking at it from the front of the engine.
 
Steve
Richard Parsons24/06/2011 10:38:01
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645 forum posts
33 photos
Steve have a look at the gear train which drives the cam shaft and work out the direction of rotation. using that work out the order of the valve events
regds
Dick
Steve Withnell07/07/2011 23:17:07
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858 forum posts
215 photos
Anyone know how to interpret a couple of specifics on the crank?
 

Pretty much got the hard bit done now, just need to make sure I get these final details sorted.
 
 
 
 
 
 
 
 
 

Ian S C08/07/2011 10:17:36
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7468 forum posts
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Steve, I think I would attack it with a file, I'v done that on some of my engines, some of it could come off with a Dremel tool. ian S C
mick08/07/2011 10:50:49
421 forum posts
49 photos
i left mine as is and knocked off any burrs with a suitable file, I think its only a bit of draughman's licence. Glad to hear your progressing.
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