The original British Standard 308 was first issued in 1927. Still have my BS 308A : 1964 Abridged edition 'for the use of students'. Finally replaced in 2000 by BS 8888.
Lets Talk about Engine Drawings
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The original British Standard 308 was first issued in 1927. Still have my BS 308A : 1964 Abridged edition 'for the use of students'. Finally replaced in 2000 by BS 8888.
When I design I also try to "explain it to myself" as if I am going to make it - which for models is invariably me in any case.
I also like to post my designs for others to use.
This is probably the most awkward part I have had to explain to myself - the main block of my V4 magnetically sprung wobbler :-
Note use of symmetrical dimension about centreline and numerous section and scrap views to show how the complex internally intersecting inlet and exhaust holes are positioned.
V4 Wobbler - Magnetic Springs
Once designed built and proven, I rearrange the parts such that the part number is also the sequence in which I would recommend building to give you the best chance of machining mating parts to "adapt" to any mistakes. Then I publish them on this site.
Regards, Ken I
I also like to post my designs for others to use.
This is probably the most awkward part I have had to explain to myself - the main block of my V4 magnetically sprung wobbler :-
Note use of symmetrical dimension about centreline and numerous section and scrap views to show how the complex internally intersecting inlet and exhaust holes are positioned.
V4 Wobbler - Magnetic Springs
Once designed built and proven, I rearrange the parts such that the part number is also the sequence in which I would recommend building to give you the best chance of machining mating parts to "adapt" to any mistakes. Then I publish them on this site.
Regards, Ken I
You can make patterns from the part sizes. That is why they make "pattern makers rules" as the reading of say 6" on that will be 6.060" if it's one for a pattern that is intendedto be made in iron. If finished surfaces are indicated then the pattern maker will know to add a machining allowance to those too.
I had forgotten about pattern maker's rules.
I guess back in the day, there were not really any other good options to using a pattern maker's rule.
These days, one can scan drawings, enlarge them in 2D CAD, and then reprint them at a larger size.
When making manual patterns (which I have pretty much gotten away from, since I got a 3D printer), I typically would use vernier calipers to pick dimensions off of enlarged drawings, not really caring exactly what that dimension was, and then transferring that dimension to the wood with a scriber or marker.
I would find using a pattern maker's rule very tedious, although I understand their purpose.
And remember that you can always scan a standard rule, and then plot it to a larger scale, to make your own pattern maker's rules.
I prefer to just replot the entire drawing set at a larger size (scaled up by the shrinkage factor).
For 3D models, I draw them to scale, and add the shrinkage factor when I 3D plot the pattern.
In the 3D model, I toggle on and off things like machining allowance, parting lines, etc., since you don't want those to show up in the 2D drawings.
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Picking sizes of a drawing with callipers is bad enough let alone one that has errors due to scanning and reprinting
Yes but patterns and castings are approximate, as is an assumed shrinkage factor.
One should not spend a lot of time tring to adhere to accuracy that cannot be obtained, such as with making patterns.
You basically are making castings that will fit into a pretty wide range of tolerances.
Your casting sizes may vary far more with the alloy, or molding sand, molding methods, etc. than you would ever see in vernier caliper error.
Edit: Even slight changes in ferrosilicon (iron additive) can dramatically affect shrinkage.
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One should not spend a lot of time tring to adhere to accuracy that cannot be obtained, such as with making patterns.
You basically are making castings that will fit into a pretty wide range of tolerances.
Your casting sizes may vary far more with the alloy, or molding sand, molding methods, etc. than you would ever see in vernier caliper error.
Edit: Even slight changes in ferrosilicon (iron additive) can dramatically affect shrinkage.
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Richard Hed
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That's interesting, but A.W. was an American and the Americans were slow to do this. Almost unbelievable.
As Todd said in the other thread rough castings are not acceptable these days, I've made my fair share of engines where holes don't come in the middle of cast bosses or where two castings mate mate together the profile is way off and needs a lot of work. So anything that can be done to get them closer to the design is good be that accurate scaling or making of patterns so 3D printed or CNC cut patterns should go a long way towards that and if for production then not so hard to tweak things to get the shrinkage factor right if the first test casting is not quite right..
ajoeiam
Well-Known Member
Did a look through your drawings for the engine.
The only think I could see that wasn't laid out with dimensions was the flywheel.
There was no information on how to develop the spokes - - - - as they're likely ellipsoidal and then with the curves into the hub and the rim.
Wouldn't be a problem 3-D printing but not a lot of information if anyone wanted to be doing this some other way.
(Would be very difficult to dimension as well..)
Me - - - I would suggest keeping on keeping on.
The usual convention at least with model engines is that the "cast" surfaces are not dimensioned as it is assumed these are used as cast. The dimensions really only detail machined surfaces, holes, etc.
Fine when building from a set of castings but does require more work for anyone wanting to replicate an old design, change size of an existing or simply make by fabrication and cutting from solid.
Eliptical parts often had the eliptical section shown on the elevation of the part.
Fine when building from a set of castings but does require more work for anyone wanting to replicate an old design, change size of an existing or simply make by fabrication and cutting from solid.
Eliptical parts often had the eliptical section shown on the elevation of the part.
Attachments
I noticed in your post #3 of your drawing that a number of dimensions are within (over) the outline of the part - whilst sometimes unavoidable or because it simply makes more sense to do so - is best avoided and all dimensioning should be outside the part being dimensioned.
It is also quite common practice to make the outline "bold" to define the realm of the "part" vs the realm of the dimensions.
I am not claiming this to be correct or "THE" way to do it (in fact there are a few errors in it).
FYI
Regards, Ken I
It is also quite common practice to make the outline "bold" to define the realm of the "part" vs the realm of the dimensions.
I am not claiming this to be correct or "THE" way to do it (in fact there are a few errors in it).
FYI
Regards, Ken I
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I got so deep into the fog of the green twin design that I pretty much lost track of some things, such as putting a lot of dimesion on the flywheel, especially at the spokes (the diameter, rim, hub and such are dimensioned).
At first it was going to be a barstock build, but I really had little experience with that other than some practice pieces.
Then we decided to make castings, but really had no concept of how to do that either.
I really just learned as I went, and I must say I learned a lot.
The flywheel along with the entire green twin engine design was developed from three oblique photos, and so everything was extrapolated from photos that were not straight-on.
The entire green twin build is an approximation of the real engine, but I am pleased with how close I got, and I never expected to get very close to the original design, and never really expected to be able to make the engine at all, since I had never made an engine before.
It was all part of a challenge from my Canadian buddy, who showed me three photos, and sort of dared me to make a 3D model.
It was a very whimsical thing, starting as just an exercise to improve my 3D modeling skills.
I never really expected it to turn into two real engines, much less get published.
It was sort of like climbing a mountain.
I kept reaching plateaus, and could see the next plateau ahead, and so I just kept climbing, not really knowing how high I could make it, or whether I would ever make it to the destination.
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Conventions are good, but..........
If you were trained in the conventions for one reason or another, then by all means use them.
If you are planning on sharing your drawings or using them to order some work to be done on your behalf you need to make sure that everyone will understand them, so use standards where possible.
If you are making a plan for only your own use then the whole world changes and you can create your own standards.
If you are using CAD for only your own use, you can let the software help you. I use layers to create dimensions and notes that can be turned on or off to determine the final look of what I want to view or print. If things go to a version I want to share or etc. I combine, collapse, edit, etc. to get a more "standardized" output.
BTW, I turn off autosave and periodically manually save a new version (the number of which is the last part of the filename in my file-naming convention). That way, autosave does not save the major mistake I just made and allows me to go back to a "known" step in the process if I've led myself astray. (Also BTW: I run a text file while working for notes that are independent of the drawing file, as I also may run a spreadsheet that is not linked to the drawing for details I want to count, like fasteners or cutters required.)
--ShopShoe
If you were trained in the conventions for one reason or another, then by all means use them.
If you are planning on sharing your drawings or using them to order some work to be done on your behalf you need to make sure that everyone will understand them, so use standards where possible.
If you are making a plan for only your own use then the whole world changes and you can create your own standards.
If you are using CAD for only your own use, you can let the software help you. I use layers to create dimensions and notes that can be turned on or off to determine the final look of what I want to view or print. If things go to a version I want to share or etc. I combine, collapse, edit, etc. to get a more "standardized" output.
BTW, I turn off autosave and periodically manually save a new version (the number of which is the last part of the filename in my file-naming convention). That way, autosave does not save the major mistake I just made and allows me to go back to a "known" step in the process if I've led myself astray. (Also BTW: I run a text file while working for notes that are independent of the drawing file, as I also may run a spreadsheet that is not linked to the drawing for details I want to count, like fasteners or cutters required.)
--ShopShoe
ajoeiam
Well-Known Member
Please - - - - comment wasn't supposed to be read as a criticism - - - - actually great drawings - - - that's what made the spokes stick out - - - - it was the only thing that didn't have some kind of measurements associated with them - - - lol.
When I see a drawing were everything is real easy to understand (also don't give two raps for 'standards' as they most often are used to cover a host of ills) well - - - I want to cheer - - - - - - - - your's are such. Dimensioning those spokes will likely be somewhat of a nightmare. That's the only part that isn't completely dimensioned.
Thank you ever so much for taking us along for a ride when you've been doing your pieces - - - - tossing a heap humongous big bouquet your way!!!!
Nope, I did not see it as a criticism at all, but rather an interesting comment.
I like all comments and criticism, good or bad, and feedback of all sorts.
The only way to learn is to listen to others, and so I greatly prize feedback of all types.
Pat J
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I like all comments and criticism, good or bad, and feedback of all sorts.
The only way to learn is to listen to others, and so I greatly prize feedback of all types.
Pat J
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A couple of things which I have noticed: Since the advent of CAD drawings folks seem to have a lot of really weird dimensions. When I see a dimension like. 1.336 I immediately assume that the dimension is critical. Usually it just means that something was placed in approximately the correct position and the designer just decided to leave it there instead of moving to some standard dimension. If 1.336 could easily work just as well as 1.375 or even 1.5 move it to a standard position so that folks are not trying to figure out if the dimension is critical. I hate weird dimensions and was taught to try for reasonable dimensions. In the past the same thing was true when a lot of designers just started building something without any drawings and designed as they went along. When they were done they gave the final product to some draftsman who just measured the finished product and made the drawing without actually understanding the final product or understanding what was critical and what could be about here. There again when I see a dimension like 47/64 I assume that there is some reason why it had to be that dimension when it could have been somewhere between 5/8 and 3/4. I have seen things like a vent hole dimensioned like that.
I think that's completely fine. I don't see it here, but there's always someone who's going to dislike something. Rules are fine to break for better clarity. If you are happy with your project and the way the drawings look, more power to you. You've put a ton of work to validate the design.
I recently drafted and plotted a 30 foot production drawing and the comments rolled in with (usually) constructive feedback. There's always somethin' someone don't like or shoulda-coulda done better. You give it your best and roll the next rev.
Gordon, guilty as charged but I fully agree with you - so elsewhere on my drawing there are usually notes about tollerances dependent on the number of decimal places - with the caveat that untolleranced 2 decimals (metric) when given for co-ordinate data does not imply tollerance (unless stated otherwise).
Another thing that technology has done in my business is now that I use so much waterjet and laser cut parts (and other CAD/CAM processes), I only dimension the bits that need machining as per example below.
The different colours are different layers - simplifies extracting the data for any CAD/CAM process - no need to even put the dimensions into the drawing.
In this example the lower drawing is the waterjet cut "blank" and is oversize where needed for machining - as indicated.
I don't do this in my model drawings where obviously more information is needed not everyone can extract the necessary CAD/CAM data from a file.
Regards, Ken I
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ulfw
Member
If making them better you should use mm
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