paul
Member
Posts: 8
|
Post by paul on Feb 23, 2007 18:48:37 GMT
|
|
simonwass
Part of the e-furniture
Cecil Pagets 2-6-2 of 1908. Engine number 2299. Would make a fascinating model....
Posts: 472
|
Post by simonwass on Feb 23, 2007 19:18:49 GMT
You could simply convert by the 25.4 factor but this would end up with lots of measurements not on a ruler! I'd go for a complete redraw, either in CAD or 2x or 4x on paper. Just round everything to the nearest 0.25mm or whatever increments they use in that funny foriegn standard ;D
|
|
John Lee
Part of the e-furniture
Posts: 375
|
Post by John Lee on Feb 23, 2007 19:32:10 GMT
Paul you risk raising an old debate. Despite being an old fart I am am all for the logical system of metrication.
But, why bother? Just learn a bit about the Imperial system and another world of designs will open up. Do both....., Imperial is not logical but it's not too complicated.
Regards,
John
|
|
Lurkio
Seasoned Member
Posts: 101
|
Post by Lurkio on Feb 23, 2007 19:44:51 GMT
Paul,
I agree with John here....try and get on with imperial measurements. It's still widely used in this hobby, so if you get familiar with it you'll be on level terms with the 'old hands'. You'll have the option to use imperial measuring tools too, which will be another string to your bow.
Surprisingly, you'll still find it in use in some corners of industry.
Lurkio.
|
|
|
Post by mmaidnz on Feb 23, 2007 19:49:54 GMT
I'm using the standard drawings to build metre maid,but since i use metric fasteners,it would seem expedient to build the whole thing in metric.But is there such a thing as metric pipe fittings?Presumably i would have to make them all. .All my threading gear is metric,with just a few bsf taps.And the ME taps/dies are quite expensive. If you do convert the whole drawing to metric,you'll find that you would need to make some parts to fit it's matching part,which might not necessarily be to the exact size. But let's face it,a drawing is really only only a guide,right? The accepted wisdom is too NOT mix sizes on a model.I think i may have to throw that rule out the window though ;D.
|
|
|
Post by havoc on Feb 23, 2007 20:29:01 GMT
I would start with something you would make from standard parts. So, suppose you need according to plan some 1/8" axle, then change this to 3mm. Next up is the hole it fits in, this becomes also 3mm. Then the fastners go from whatever they use in imperial to a near size in metric. Same for pipes, O-rings, balls etc.
Then you clean up any needed mechanical dimensions. Like the distance between pivots, stroke/bore. This is the most exacting stage since all geometric relations still need to be correct. As example, if you change the distance between pivot and axle in an oscillator, then you will need to change the place of the ports accordingly.
Then you look if you don't need a bit more metal around some holes (in case you used the next larger fastners/axles).
Last you change those dimensions that don't have any function (mechanical function I mean). It doesn't really matter if some openings is supports are a few tenths smaller or larger, or if the foundation plate is a mm larger. There you just make it yourself easy and round to available metric sizes.
If it are only 30 parts, then you could just copy the plans (or even enlarge them at a copycenter) and pencil in the new measures. Remember: "never measure on a plan".
|
|
John Lee
Part of the e-furniture
Posts: 375
|
Post by John Lee on Feb 23, 2007 20:30:07 GMT
Errr not quite, because the BA system is metric based...almost. So your fastenings can be metric, and the rest can be imperial....
Omigod, an old old engineer, if its held together strongly, just improvise, I did helicopter bits this way in the Navy and nobody died...... ;D
John
|
|
paul
Member
Posts: 8
|
Post by paul on Feb 23, 2007 21:19:27 GMT
Thanks as usual for the helpful tips!
As I've only recently caught this bug I decided to buy metric drills, taps, dies etc thinking it would make more sense (!) I don't have a problem using imperial (I remember pre-decimalisation) it's just that I have a 'wants list' that stands at about £500 already without adding imperial kit to it!
Havoc: yeah I'd figured that I'd need to pay close attention to the distances involved - this engine is slide-valve controlled so the port positions & eccentric bits will need careful thought. I suppose I could stick to making the non-critical bits first and see how it goes with the conversion process.
Useful tip and something that could easily have slipped by!
If I can convert it to metric satisfactorily I'll publish it on my website so others have access to a 'metric engine' - something that seems difficult to find except for the smallest/simplest oscillators.
John: lol they probably just disappeared off the radar so were counted as MIA rather than dead!
|
|
|
Post by Laurie_B on Feb 23, 2007 22:12:51 GMT
I would start with something you would make from standard parts. So, suppose you need according to plan some 1/8" axle, then change this to 3mm. Next up is the hole it fits in, this becomes also 3mm. And you would presumably need to have metric sized reamers for the main and big end bearings,etc.,as 1/8" (.125") is slightly greater than 3mm (0.118").Good luck with the project.
|
|
S.D.L.
Seasoned Member
Posts: 107
|
Post by S.D.L. on Feb 24, 2007 0:12:52 GMT
Does anyone have any tips on converting plans from imperial to metric? I'm looking at building a simple stationary engine (only about 30 main parts) but the plans are in old money. The engine concerned is 'Theseus' (rather like Perseus here www.modelsteamenginesuk.com/model_steam_engines_persues_and_isis.aspSome of these desigms come with metric plans, this one does. www.modelsteamenginesuk.com/model_engineers_kit_bottle.aspSome of the designs are by Anthony Mount and have dual metic and imperial dimensions in the magazine series. Dont know for your engine but woth seeing if done with both in a construction series. I have got the drawings for a 1/3rd scale Foster in metric and it uses metric special pitches for the pipe fittings. I have gradually bought most of the taps and dies at various dealers where they get ignored and go cheap. Steve Larner
|
|
|
Post by jgb7573 on Feb 24, 2007 7:54:34 GMT
A close relative of Theseus and Perseus but in Metric dimensions is Vulcan. In fact it's a doubled up version with cylinder 38mm bore by 50mm stroke, with the flywheel 215mm dia. The drawings show castings for the cylinder and flywheel, but these could be relatively easily fabricated. I found the drawings on a second hand book website last year. Let me know if you'd like any more information.
|
|
|
Post by steammadman on Feb 24, 2007 20:17:33 GMT
Only 30 parts?, sit down at the kitchen table, arm yourself with a digital caliper,a pencil ,and of coarse your drawings, start at a convenient place, set your digi caliper to "imp", then adjust to the required measurement, press the "mm" button and hey presto you have a accurate conversion, mark it on the drawing ,with your pencil,and move on to the next part, and do the same again, it will not be too long before you have converted your drawings
|
|
paul
Member
Posts: 8
|
Post by paul on Feb 24, 2007 22:06:52 GMT
JohnB: 38mm bore sounds massive to me but if you could point me n the right direction that'd be great Steammadman: Yeah, but 14.28mm (for 9/16") is a bit tricky to mark out - I have enough trouble seeing 0.5mm markings on a ruler! I've made a start anyway, let's see what happens...
|
|
paul
Member
Posts: 8
|
Post by paul on Feb 24, 2007 22:32:15 GMT
This is the baseplate. I used 150x75mm (6"x3") and worked from the shaft position (I don't know what the distance from the leftmost cylinder support to the left edge of the base is but it doesn't matter!). I propose using 3mm holes as the original shows 1/8" (3.175mm) and 6BA (2.8mm) (I don't really understand why they aren't all the same on the original!). Anyone see any bloopers?
|
|
Myford Matt
Statesman
There are two ways to run a railway, the Great Western way, and the wrong way.
Posts: 621
|
Post by Myford Matt on Feb 24, 2007 23:21:23 GMT
If you are working to the nearest quarter mm then wouldn't 1/8" be more like 3.25mm? Though the nearest drill would be 3.2mm, in my set anyway!
Likewise 3/16" to 4.75mm.
MM
|
|
paul
Member
Posts: 8
|
Post by paul on Feb 25, 2007 7:15:15 GMT
Cheers Matt; I though it might be easier to manipulate some dimensions because if I round everything to the nearest 0.25 I'll get compound errors (probably somewhere nasty).
The baseplate holes I made 3mm because - beginner's workshop zone - my drills are in 0.50 steps. I put the 4 corner holes at 5mm rather than 4.75mm 'cos it's easier to measure and puts them fractionally more inboard but they won't foul anything.
|
|
|
Post by alanstepney on Feb 25, 2007 10:09:37 GMT
Here is where the ideas of simplicity start to fall down. Whilst it is a nice idea to go metric, and, one hopes, have all thise simple measurements and nice whole numbers, but then.... The original 1/8" holes you have made 3mm. Fair enough as a 3mm bolt will fit a 3mm whole. The 6BA clear holes you havent marked. I assume that you plan to use metric threads throughout. (Yes, I know BA is metric based.) To clear 6ba one would use a 2.9mm drill. The closest metric thread to 6ba is 3mm, so again a 3mm drill will suffice. Should you need a tapped hole, the tapping drill for that is 2.65mm.Not one that is in the 0.5mm steps that many of the metric drill sets work to. So at that point you need to start buying extra drills. When converting to metric, there are recomended metric sizes for model engineering, (see www.alanstepney.info/page77.html ) The limitations of metric (threads) are that there isnt just one standard, but several. Additionally, there isnt the option of "size smaller" and hence more accurate to scale, heads and nuts. I can see what you are trying to do and sympathise with you and everyone else who has been bought up with metric, but if you take the trouble to learn Imperial measures and threads, and can then use either (or both) and it will open up a far wider range of choices for models and materials.
|
|
|
Post by havoc on Feb 25, 2007 11:24:34 GMT
Of course. But I don't think that anyone would convert from imperial to metric if he had all tools in imperial. The only reason I see for conversion is to use the tooling you have.
Very likely you'll get errors like that if you don't take precautions and double check your results. One of the reasons I would not round to 0.25 but to the next 0.1. So I would change the holes for the cilinder support from 22.25 and 39.75 to 22 and 40. It is only a support. On the other hand if you can drill a hole that precise, go ahead.
You say you don't have drills in steps finer than 0.5. Anyway, you'll have to buy the drills for tapping M2, M2.5, M3 etc. When drilling a hole that need to be tapped Mx, drill it with a diameter of (x-pitch). So for M2 you drill 1.6 = (2 - 0.4).
|
|
|
Post by merlin on Feb 25, 2007 13:09:14 GMT
Keep to imperial as you may end up with accumulative errors i.e. if one dimension is taken from a former dimension you will be bringing errors forward into your next dimension.
It will only work out if all dimensioning is taken from one common datum and even then beware if any angles are involved.
I changed a number of old hand drawn engineering drawings from imperial to metric on cad for my Students at College last year, this was to suit standard metric bar stock and upgrade the drawings to current 3rd Angle Projection Standards. A lot of errors became apparent so I just kept the original concept of the drawings and totally re-drew in metric (a 2 minute job became a big job)
|
|
|
Post by alanstepney on Feb 25, 2007 16:20:56 GMT
One advantage of Imperial is that there are vast amounts of tooling around, and much can be had for a pittance. The numbers of drills, threading tackle, reamers etc that I have found at, for example car boot sales, is amazing. OK, you can pay out a lot of money if, (a) you have it and (b) dont have better uses for it, but there are bargains to be had, more often with what isnt popular as it isnt used in industry.
My advice is, dont decry using any measurement system, and dont restrict yourself to one because you dont have the right.... whatever... at this stage. Meanwhile, gather and collect all you can, and you will soon have a wide selection of odds and s*** (or need a bigger workshop!).
|
|