# Where to get Metric plans?



## DiegoVV (Jun 19, 2015)

Hello dear machinists!

I am planning to build a new engine. My decission is biased towards radial type engine. The problem I have is regarding metric / imperial units. 

Having grown in Spain I am used to metric units, being really difficult for me thinking and working in inches. 

Since the 90% of our hobby in developed in UK and USA, all the plans I find are in inches. I know that translating a complete set of plans to metric has inherent problems as lack of precission, redesign of certain parts and a bunch of weird things I don´t want to face.

Can someone tell me where can I find/buy a good  set of plans for a radial engine in metric units? 9 cyl. Hodgson one is a real beauty and something similar would be perfect!

PD: I have almost completed in Autodesk Inventor the rebuild of an Whittle V8 but in metric units. If someone wants the files, feel free to send me a PM! Since the Whittle design is free, I will share my work for free also.

Thank you very much in advance!!!


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## Jasonb (Jun 19, 2015)

There is quite a nice 9cyl radial on the first page available from this German supplier in metric and another 9cyl further on.

http://shop.vth.de/bauplane-frasteile.html?cat=14


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## DiegoVV (Jun 19, 2015)

Thank you Jasonb!

The engine you mention looks very good, but I am afraid not to find building information about this engine. Anyway, it seems promising to me.

Best regards!


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## deboom_j (Jun 19, 2015)

The P+W R985, and R1830 plans drawn by Bob Roach of Australia are all in metric.  Not sure of their availability anymore tho.  His contact info is on this webpage:


http://modelenginenews.org/~modeng74/vernal/index.html


  Bruce Satra used to offer castings for both engines, but this new website says he's handing the business over someone else, and it makes no mention of the the WASP castings, only the Morton castings  (I can't comment on whether the Morton drawings are inch or metric).


http://www.vernalengineering.com/



  Maybe some one on here has more info,  or perhaps you need to send some emails to Bob and Bruce.


  I don't want to get into a fight about inch versus metric here, I had plenty of those in watchmaking school.  The parts I've made for my radials were made on  manual machines with inch dials, inspected with inch based measuring tools, and even my CNC programs I wrote used inch units that were converted/calculated from the metric units on the blueprints.  25.4 is your friend here!  

  I guess that's the advantage/disadvantage to growing up in the US during this time period, everyday I deal with something that is Inch, Metric, or half and half.  So I have to use both.  I think of it like being bi-lingual!  Although some days I wish there was only one system.

John


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## petertha (Jun 19, 2015)

DiegoVV said:


> Can someone tell me where can I find/buy a good set of plans for a radial engine in metric units? 9 cyl. Hodgson one is a real beauty and something similar would be perfect!


 
Jung as 5, 7 & 9 cyl radials
http://www.cad-jung-shop.de/epages/...729/Categories/Baupläne/Bauplane_Modellmotore

build of Jung 7-cyl here
http://philsradial.blogspot.ca/

Ohrndorf has 5, 9, 14 (double row)
http://www.engineman.de/

All of these are metric + methanol/glow ignition + 2D plans from 3D original CAD models.


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## barnesrickw (Jun 19, 2015)

24.5 should do it.


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## Cogsy (Jun 19, 2015)

barnesrickw said:


> 24.5 should do it.


 
Ummm, that's not quite close enough for me , I use 25.4


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## barnesrickw (Jun 19, 2015)

Well, look at the egg on my face.


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## DiegoVV (Jun 20, 2015)

No Barnesrickw, 25.4 will not do anything if you want to make things with the precission I like to achieve in my works.

For some things conversion is possible, but in this case it is not an option.


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## Cogsy (Jun 20, 2015)

DiegoVV said:


> No Barnesrickw, 25.4 will not do anything if you want to make things with the precission I like to achieve in my works.


 
Not only would converting everything by 25.4 be extremely precise, but absolutely accurate as well. 1 inch is equal to exactly 25.4mm.

BTW, just to clear up any confusion of terms, precision is hitting a number/dimension almost spot on. Accuracy is hitting the exact number/dimension called for. You can measure parts very precisely with an improperly calibrated micrometer, but to measure them accurately your micrometer must be calibrated.


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## Swifty (Jun 20, 2015)

DiegoVV, I'm confused by your mention that converting from imperial to metric is not accurate enough for you, why not, it's how it is always done. If you want to work in microns, you would have to have a temperature controlled workshop and equipment to handle the precision.

We changed to metric dimensions perhaps 10 years after I started work, so I am very familiar with both systems.

Paul.


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## barnesrickw (Jun 21, 2015)

When I worked in a lab, and a machine shop I converted frequently.  Seemed to work well.  Not having to deal with significant figures because this is not school helps even more.


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## barnesrickw (Jun 21, 2015)

And now that I think of it, 0.001 inches would equal .0254 mm. That puts that last digit in microns.  I can't measure in microns.  I would round .0254 mm up to 0.03 mm, or at most 0.025 mm.


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## Jasonb (Jun 21, 2015)

Its not just the straight conversion that is the issue, In mainland Europe its not easy for a hobbiest to obtain imperial materials, fixings, bearings and tools. Even when thay can be obtained its quite an investment on something like a 9cyl radial to tool yourself up with reamers, taps & dies and buying in lengths of stock that you may only use a small piece of.

Simple example, do you turn a piece of 5mm drill rod down to 4.7625mm which is into microns or buy 3/16 drill rod if available. I'll leave you to make your own reamers.


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## bazmak (Jun 21, 2015)

Most people of similar age to myself are familiar with both systems
I prefer metric for larger untoleranced dims but prefer thous for tight tolerances.Converting imperial to metric with the use of 25.4 is very accurate
I think the point being made is that a direct conversion for all dims is 
not feasable,availability of matls and tooling play a big part in partial
conversion.Which is made difficult but not impossible.Conversion and rounding
up or down should be strictly checked to avoid mishaps.Having a combined metric/imperial engine is not a problem


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## Cogsy (Jun 21, 2015)

bazmak said:


> I prefer metric for larger untoleranced dims but prefer thous for tight tolerances.


 
Interesting, I work the opposite way. One thou is 0.0254mm and while I can only measure to 1/100th of a mm I do aim to hit within that hundreth. I can only measure to 1/1000th of an inch so if I was working to the same tolerance I would be +/- 0.0254mm rather than +/- 0.01mm. 

If I'm working with vernier calipers I prefer to use the inch scale for ease of readability.


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## Cogsy (Jun 21, 2015)

Jasonb said:


> Simple example, do you turn a piece of 5mm drill rod down to 4.7625mm which is into microns or buy 3/16 drill rod if available. I'll leave you to make your own reamers.


 
I get what you're saying (I'm having similar issues staying with imperial dimensions for my V4 build in Australia, more for bearings, seals and fasteners though) but realistically the 3/16 drill rod is not accurately 3/16 into the microns anyway. If it was required to be 3/16 and 5mm wouldn't do then I'd turn it down to 4.76mm and (if I hit my number exactly) it'd only be 0.0001" off 3/16. I believe a commercial reamer would work at that size and if there was doubt a "d bit" reamer could be made from the same piece of stock.


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## Swifty (Jun 21, 2015)

The main problem that I see in converting imperial drawings to metric, is smaller shaft sizes. I'm not talking about short pieces that can be turned to size, but longer, small diameter pieces. Some allowance would have to be made to change the drawing to suit shaft sizes available. If engine builders are not confident in making changes to the drawings, I can see where this could be a bit of a problem. On my current Howell V4 build, the wrist / gudgeon pins are called up as 7/32" dia, not having any drill rod, or reamers this size, I just changed to 6mm dia. I have made a few other changes to suit sizes that I have available, no one will be any the wiser after its all finished.

Paul.


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## bazmak (Jun 21, 2015)

Thats the point i was making.Many years ago in the apprentice school,a major project for all the apprentices combined was to built a half size metric
version of one of the company products.A bread wrapping machine.Full sized mc was nom 3ft wide x 4ft high x 6 ft long.Concept spent many weeks in the apprentice DO,doing what we have been discussing on a grand scale.Sizing shafts up or down,chains sprockets Brgs etc.Then the pattern shop and foundry for castings
18 mths later we had a working model wrapping hovis sized sliced loaves of bread.My involvement was on the fitting and turning and finally sheetmetal guards.A no of different models of varios wrapping machines was made over the years. Very interesting.Logistically very difficult at the drawing stage


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## DiegoVV (Jun 21, 2015)

Swifty said:


> DiegoVV, I'm confused by your mention that converting from imperial to metric is not accurate enough for you, why not, it's how it is always done. If you want to work in microns, you would have to have a temperature controlled workshop and equipment to handle the precision.
> 
> We changed to metric dimensions perhaps 10 years after I started work, so I am very familiar with both systems.
> 
> Paul.



Hello Swifty, 

You are absolutely right, but here is an example of what I am saying:

In the Whittle plans the distance between some bolts is 0.416 in.

Ok, go to mm....0.416 x 25.4 = 10.5664 mm. 

I am happy working with ine hundred of an milimiter, but this would require working in tenths of thusands of milimiters....this is going too far for me.

This is not for speaking about drilling and / or reaming holes in inches. I dont have easy access to drills and reamers in inches.´

At last but not least I don´t know how telling me how bad machinist I am for prefer working with milimiters is going to help. No, 25.4 does not solve my question, as everyone here knows how to operate a calculator.


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## Cogsy (Jun 21, 2015)

The thing is, if we go back the other way, 10.57mm / 25.4 = 0.41614". So either way we are at the limits of our measurement capabilities. At that scale 1 10,000th of an inch or 6 1000th's of a millimeter is irrelevant. If we can't measure that small a difference then we can't know if our 10.57mm is actually off by 6 thousandths.

I can understand issues getting materials and tooling but the argument about lack of precision is lost on me.


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## barnesrickw (Jun 21, 2015)

I googled "convert standard to metric for machining" and found a few videos.  Too many to watch and evaluate and send links for, but they are out there.


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## bazmak (Jun 22, 2015)

Why not round it to 10.5mm ctres and same with any matching parts


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## barnesrickw (Jun 22, 2015)

Page 39 of volume 2, Sterling and Steam engines you can Build.  He converts one inch to 32mm. "This makes the model 20% larger, but .125in becomes 4mm.  .375 becomes 12, and so on".


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## Swifty (Jun 22, 2015)

DiegoVV said:


> Hello Swifty,
> 
> You are absolutely right, but here is an example of what I am saying:
> 
> ...



DiegoVV, you are worried about things that you will find are easily conquered. As you know, there are 25.4 microns in a thousandth of an inch, if you drop 6 of them on a dimension, it won't make any difference to the job. If you measure some fasteners you will see that they are under nominal size, this straight away gives you extra clearance on hole alignment. When I'm trying to hit a dimension using my digital readout, if I'm .01mm either way, that's close enough. I might finish machining something on a day when the outside temperature is 40C, but start again the next morning when it's only 15C, the workpiece would have changed all by itself overnight.

I work most of the time in mm, all my drills, except for one 3/4" one, are metric, I have actually had to order a couple of imperial reamers for my current build, they come from Hong Kong, and I'm sure that they will post to most European destinations, just use eBay.

I don't believe that anyone has called you a bad machinist, that's not how this site works, everyone is always willing to offer advice, it's left up to you to accept which advice you want to consider.

Paul.


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## oasanti (Aug 28, 2015)

Hello, I want to coment about two convertion methods from inch to metric. 
One is to use a conversor. Its simple, fast and realiable. The other is very simple, faster and very intuitive, it is a very gross simplification, but is uselfull for this hobby, and is to set 1" = 32 mm. This scale up the model about 20% (or scale down if use in the other way) but you get round dimensions. Say: 1/32" = 1mm (real dimension: 0,79375), 1/16" = 2mm (Real dimensio: 1,5875). This idea come from "Steam And Striling Engines You can Build".
I hope it can be helpfull.
Sorry about my english but I refuse to use the language converter and dont know a simplification method !


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## barnesrickw (Sep 2, 2015)

oasanti said:


> Hello, I want to coment about two convertion methods from inch to metric.
> 
> One is to use a conversor. Its simple, fast and realiable. The other is very simple, faster and very intuitive, it is a very gross simplification, but is uselfull for this hobby, and is to set 1" = 32 mm. This scale up the model about 20% (or scale down if use in the other way) but you get round dimensions. Say: 1/32" = 1mm (real dimension: 0,79375), 1/16" = 2mm (Real dimensio: 1,5875). This idea come from "Steam And Striling Engines You can Build".
> 
> ...




You make a very good point.


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## barnesrickw (Sep 2, 2015)

Oasanti, you make a good point.


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