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Why not Make Two?

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Steve Withnell24/10/2011 18:32:48
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858 forum posts
215 photos
I started thinking about where the effort is going in these engines I've been making. Most of the time is thinking and designing how to machine a part, one aspect at a time. Then there is the making off all the jigs and fixtures and the "special" tooling (the things you have to make to make the thing your really wanted to make in the first place), then you have to set it all up, operation by operation. Finally, you get to cut real metal. Then I make a mistake at the "high value" end of a component and have to wind back and start all over.
 
Strikes me that making two of everything would actually add very little to the elapsed time. I guess it would be cost prohibitive for Loco's and Traction Engines and projects of that class, but for small barstock engines it seems to be a sensible way to go.
 
 
wheeltapper24/10/2011 18:43:14
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424 forum posts
98 photos
If you think you are going to get me to make TWO Nemett engines you can think again.
 
seriously, its not a bad idea if you have all the jigs and doodads already.
I'm considering making Bogstandards puddleduck engine, I suppose I could make one vertical and a horizontal, same bits practically.
 
Hmmmm, food for thought.
Roy

Edited By wheeltapper on 24/10/2011 18:43:50

Ramon Wilson24/10/2011 20:01:42
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1655 forum posts
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Hi Steve, I guess you are actually refering too all those small parts you have in front of you to make on the Whittle engine.
 
You're quite right - time spent making jigs and fixtures to achieve a certain machining op can certainly outweigh the time to make the actual part in which case it can be beneficial to make more than one. However to gain any advantage of it of course one has to make duplicates/multiples of all the parts and there by lies the paradox
 
As you've possibly seen, when I did the Racers I set out to make two cases just to ensure that if I made a boo boo that I wouldn't, as you say, have to rewind back to the start again. End result was two cases and the potential for two engines. Same for the Eta's set out to achieve two, but made three and ended up with three engines. With these small single cylinders, and no valves of course the part count is quite small and the jigs and fixture were actually quite minimal in which case it proved a viable proposition
 
The Bentley BR2 on the other hand is a different kettle of fish altogether. Lot's of jigs and fixtures have been made as well as tooling but to consider making duplicates of everything would be a major undertaking - more akin to what I did at times at work - not impossible of course but possibly rather daunting
 
The big thing to consider if you do make a duplicate engine, and you could bring yourself to part with it of course, that it could always be used to fund the purchase of some better kit - CNC naturally - to make it even easier
 
Hope you are progressing on yours well - I've had a good break but am about to get back into the fray
 
Regards - Ramon
 
 
 
 
Hugh Gilhespie24/10/2011 20:01:45
130 forum posts
45 photos

I don't make two of everything but I always buy enough materials for two to allow for the inevitable cock-ups.

And I am sure that there is a subsidiary of Murphy's or Sod's law that states:

Where a part requires multiple operations, the likelihood of a major mistake increases exponentially with the percentage sucessfully completed. Bitter experience....

Regards, Hugh

Steve Withnell24/10/2011 21:49:21
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858 forum posts
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Well I've now got two crankcase blanks to size, ready to be marked out for the camshaft. The decision point on one or two will be when I have to divert to make a second crankshaft!
 
When I thought about the possibility of ending up with two, I thought "Vickers Vimy" rather than selling one...
 
If Hugh's version of events holds true, I've two more crankcase blanks to make to get just one!
 
I've started blogging the Whittle build, as my Stuart Victoria blog seemed to go down well with over 20k page views so far.
 
Steve
Steve Withnell24/10/2011 21:49:24
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858 forum posts
215 photos
Well I've now got two crankcase blanks to size, ready to be marked out for the camshaft. The decision point on one or two will be when I have to divert to make a second crankshaft!
 
When I thought about the possibility of ending up with two, I thought "Vickers Vimy" rather than selling one...
 
If Hugh's version of events holds true, I've two more crankcase blanks to make to get just one!
 
I've started blogging the Whittle build, as my Stuart Victoria blog seemed to go down well with over 20k page views so far.
 
Steve
Hugh Gilhespie24/10/2011 21:53:37
130 forum posts
45 photos

Steve,

Nice to see that you're even going as far as making two postings as well.

Good plan!

Hugh

Steve Withnell24/10/2011 22:17:31
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858 forum posts
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How bizarre, not sure how I managed that!
 
Steve
 
Sam Stones24/10/2011 23:00:44
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922 forum posts
332 photos

Hi Steve,

After I retired, I met a chap who’s hobby was building model steam locomotives. If my judgement was correct, they were about three and a half inch gauge, and were about four foot long overall. He told me that he always builds two identical ones. Selling one of them covers his costs, leaving one to keep and some extra for the kitty. I saw his work by way of twin engines and tenders at one of the local weekend rallies. With identical colour and livery, both models were impeccable.

During the time when I ran my own business, it often became necessary to build small prototypes and `one-offs’ for laboratory use. As has been suggested, making two at a time was a good way to avoid blunders as each stage evolved. For anything innovative or critical, it became my normal practice. Most of the time I finished up with two good ones, and didn’t need to pick out the best.

Having mentioned this to others, it is pleasing to note that they have also taken up the idea. Most recently, and although it was a simple task, I adopted the idea for the base of my clock. I don’t mind admitting that I’m not very good at getting accurate mitred corners, and can spend ages fiddling and filing to get a good fit.

Regards to all

Sam

Andrew Johnston24/10/2011 23:09:06
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7061 forum posts
719 photos
That's why I'm making two identical (well nearly, E&OE) 4" scale traction engines. I was sold the idea on the grounds that it only takes 30% longer to make two. I suspect it's nearer 40%, and it can get a bit tedious when there are lots of long slow cuts. But, as Steve says, most of the time actually goes in thinking, designing, CAD drawing, CNC programming (am I allowed to say that?), finding/buying tools, making jigs and setting things up. The actual machining is often over in a matter of minutes.
 
I won't mention the cost though, in case anybody has a seizure.
 
Regards,
 
Andrew
Michael Horner25/10/2011 01:01:43
229 forum posts
63 photos
Hi Steve
 
Where do I find your Blog?
 
I started to build the Whittle V8 earlier in the year but after 2 bent crankshafts I got sidetracked with CNC. I don't have the patience that Eric Whittle had in abudence. I have noted your sleeve support which I will try when I get back into it. I have also done the crankcase halves and the bearing supports.
 
Mike.
Bill Pudney25/10/2011 01:14:58
622 forum posts
24 photos
When I had to work for a living, Manufacturing were often asked to make one or two of something. The expensive bit about our manufacturing was the "Non recurring" effort, drawing, planning, programming etc. Unless the required material was something exotic, material cost was pretty low as well, although the lead time for material could be weeks (remember this is Australia).
So when it seemed like a good idea I would often double or triple the engineers requirement.
The additional cost of the extra material and machine time was minimal and easily absorbed.
So when the opportunity to double or triple up arises its well worth while, and might even provide additional income via a sale!!
cheers
Bill Pudney
Steve Withnell25/10/2011 18:37:26
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858 forum posts
215 photos
Posted by Michael Horner on 25/10/2011 01:01:43:
Hi Steve
 
Where do I find your Blog?
 
Mike.

http://whittlev8.wordpress.com/

 
 
Regards
 
Steve
Steve Withnell25/10/2011 18:39:56
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858 forum posts
215 photos
It would be interesting to record the time of each machining operation, but it's hard enough remembering to photograph each one!
 
 
Steve Withnell26/10/2011 18:10:39
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858 forum posts
215 photos
Hmmm. The Whittle blog (IC topic) got 80 hits last night after I posted the links and the Victoria blog (Steam topic) got 220 hits.
 
So Dear Editor, the conclusion to this vox pop is that we need more IC articles as you are attracting the wrong clientele!
Michael Horner27/10/2011 22:29:18
229 forum posts
63 photos
Hi Steve
Viewed your blog, looks good, so does the crank .
 
Have you made 2 ? If I bend another might be a way out. ,
 
Did mine in mild steel to get the hang of things because I've never done anything like it before.
 
When you get on to the barrels check the dimentions carefully, I think the drawing dimentions are correct but the text one has an error on the length of the spigot.
 
Cheers Mike.

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