PDA

View Full Version : Print Reading Help



Wess
03-22-2007, 09:11 PM
I am building a stirling engine from a kit and need a little help in deciphering some of the symbols on the print. This page is a cross section of the flywheel.

http://i162.photobucket.com/albums/t270/Wess23/Flywheel.jpg

What does the triangle thing with the 1.6 represent?

Are the boxes with the "A" and the 0.05 and 0.10 tolerances? Why does one box have slashes and the other the upside down T symbol.

As you can tell I'm somewhat new to the hobby and any help would be appreciated.

Also what kind of thread is a M3-7H. I get the 3mm part but what does 7H mean?

lane
03-22-2007, 09:24 PM
Try to answer in order
1. surface finish its in metric so i`m not familarwith the1.6.

2. // parallel to datum up side down T square to 90 perpendicular to datum

3. class of thread 7H
Hope this helps

John Stevenson
03-22-2007, 09:49 PM
http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/g&t.jpg




.

Wess
03-22-2007, 09:52 PM
Thank you for your reply. If I could get some clarification on the tolerances. I'm assuming the upside down T at .05 means that the hole has to be square to the datum by the .05...ie the hole is not crooked. It's not referring to the diameter of the hole itself, correct?

Wess
03-22-2007, 09:54 PM
Thank you John, I searched google for and hour looking for a list of symbols like that.

wierdscience
03-22-2007, 10:07 PM
Thank you for your reply. If I could get some clarification on the tolerances. I'm assuming the upside down T at .05 means that the hole has to be square to the datum by the .05...ie the hole is not crooked. It's not referring to the diameter of the hole itself, correct?

The hole should be prependicular to the bore within .05mm as I see it.

IMHO from experience,people who draw things and insist on using symbols and DON'T provide a symbol legend with the drawing should be shot.

rkepler
03-22-2007, 10:14 PM
Heck, it's "just" a flywheel. You want the hole for the shaft to be in the middle and everything pretty much around it and not too much off center or balance. If you want it pretty polish it up but for the most part small engine flywheels are small engine flywheels and all follow pretty basic principles.

Bill Pace
03-22-2007, 10:16 PM
[QUOTE=
IMHO from experience,people who draw things and insist on using symbols and DON'T provide a symbol legend with the drawing should be shot.[/QUOTE]

Aint it the truth!!!

ckelloug
03-22-2007, 10:28 PM
I once passed my class that included Geometric Dimensioning and Tolerancing but have now forgotten almost 100% of it. Fortunately, I do have the reference book and am now taking the chance to relearn.

From my perusal of Geo-Metrics III describing the ANSI Y14.5-1994 Geometric Dimensioning and Tolerancing rules,I cannot find the triangle symbol like that. This print appears to use symbols that are not in the 1994 version of the ANSI/ISO standard.

Enough of this is standard I can explain some of this based on what I know:

The rectangles divided into three parts is called a feature control frame. It is basically an imperative sentence of the form "What", "How Much", "Measured with Respect to".

The FCF in the upper right of the print reads that the top of the flywheel is parallel to datum A (the bottom of the flywheel) such that two imaginary planes constructed .05 above and .05 below the top of the flywheel will not intersect the top of the flywheel.

The Octagon with an A in it describes the plane of the bottom of the flywheel as "datum A" as near as I can tell.

The FCF at the bottom left hand side of the print says that the hole drilled in the center of the flywheel will be perpendicular to datum A (the bottom of the flywheel) such that two imaginary planes drawn vertically on the print .025 to the left and .025 to the right of the correct hole location will not intersect the line drawn between the center of the hole on the top of the flywheel and the cneter of the hole on Datum A (The bottom of the flywheel).

The only other thing I can do since I can't locate a reference about triangle symbols is ask if they reference notes at the bottom of the drawing or on another sheet.

ckelloug
03-22-2007, 10:34 PM
Having seen the other replies that came in as I wrote mine, I have to say that legends are unnecessary. I have a 350 page book on my desk that describes what each symbol means, how it is supposed to be used and how you can measure that the part meets the spec. The symbols are very precisely defined and sometimes the precise definition is rather complicated.

For the computer programmers among us, it's just like a visual version of perl :eek:

Now, for those who use non-standard symbols and worse don't define them, your torture in hell should be confined to reading the prints of one of your buddies who uses non-standard symbols different from yours.

lane
03-22-2007, 10:39 PM
Just make every thing dead nuts and you dont have to worry about those symbols

ckelloug
03-22-2007, 10:41 PM
Or, how about dead half-nuts?

Wess
03-22-2007, 10:53 PM
Thanks for all the replies. Between all of them I now understand all the symbols. It's actually kind of obvious now that I know what they mean. I realize it's only a little flywheel , but I wanted to learn what they all meant.

Tin Falcon
03-22-2007, 11:24 PM
machinery's handbook also has a few pages on the subject.
tin
I know this only helps if you have a fairly recent copy

wierdscience
03-22-2007, 11:27 PM
Having seen the other replies that came in as I wrote mine, I have to say that legends are unnecessary. I have a 350 page book on my desk that describes what each symbol means, how it is supposed to be used and how you can measure that the part meets the spec. The symbols are very precisely defined and sometimes the precise definition is rather complicated.

Now, for those who use non-standard symbols and worse don't define them, your torture in hell should be confined to reading the prints of one of your buddies who uses non-standard symbols different from yours.

You must work for Nasa:DThey without a doubt are the single greatest offender of non-standard symbols use.

The afore mentioned symbol is a surface finish symbol in ISO,but it notes a micro-inch finish spec of 1.6 .That would equate to .0016"/rev lathe finish,or in laymans terms "machined so you can your ugly teeth in it"

For insight in the surface finish symbol mess look here,it's truly pathetic-

http://www.qualitydigest.com/june01/html/surface.html

Furthermore CAD programs have only increased the number of glaring and not so glaring mistakes being made in drawings.I typically find mistakes in 60% or better of the CAD drawings I recieve at work.It costs me time and money and I have begun charging for editing.

I was working with a EE the otherday who said it was a shame CAD programs didn't have a symbol for smoke when someone draws a dead short:D

ckelloug
03-22-2007, 11:35 PM
Thank you for teaching us all about the surface finish symbols, Lane! Having looked it up, the symbol in question means machined surface.

Here's the link:

http://www.roymech.co.uk/Useful_Tables/Surface_Texture/draw_surfin.html

ckelloug
03-22-2007, 11:38 PM
Wierdscience, is it still 1.6 microinches on a Metric part WTF!? That's just broken.

wierdscience
03-23-2007, 12:14 AM
Wierdscience, is it still 1.6 microinches on a Metric part WTF!? That's just broken.

Yup,like Evan says,you gotta love standards,there are so many of them:D

The 1.6 would throw you if you took it to mean 1.6mm.That finish would look like a thread pitch.

What I also don't see on the drawing is a spec for the bore diameter tolerances.3mm is what I get,but is that machined to what?Press fit,light driving fit,install by tossing from across the shop fit?

I see some useful basic information there,but the drawing is needlessly cluttered,especially for a part who's image will easily fit on a 8.5x11 sheet with acres of room for notations in plain english.

I love CAD,I really love CAD when one guy dimensions from top to bottom right to left and the other guy from bottom to top and from left to right.Both working at the same company,on the same part with both arriving at different dimensions.

Oh,wait I have confused Love with aggrevation again,say where does that extra .250" you guys came up with go anyway?:D

That was last weeks "Mistake-o-the week".Person drawing didn't check his work with a calculator. 2.250+1.1875+3.5625 do not 7.250" make.Hince my question to them about where they wanted the extra .250" to be:D

Evan
03-23-2007, 12:33 AM
I'm glad I don't build stuff to other people's prints. I have enough trouble reading my own. My copy of 'How to Read and Draw Blueprints' is getting long in the tooth, as is my high school drafting training.

It doesn't make the slightest bit of sense to spec something such as surface finish on that drawing unless it was stolen from a set of production prints somewhere.

ckelloug
03-23-2007, 01:03 AM
Good point about specifying 1.6 micron surface finish on a drawing for a model engine.

Also wierd science, I remember how a company I worked for needed that smoke symbol. They were working on a 24 layer board in a piece of test equipment that was late. They found a catastrophic problem with a chip on the board so they spend 5 or 6 figure money getting the board spun overnight to continue debugging other portions. Unfortunately, nobody did a design rules check to notice that one of the last minute mods to the board had shorted power and ground together. This particular board that had more multi-hundred amp power supplies going into it than I could count.

The giant power supplies cleared the short in the first board of this prototype run when they were energized. They noted the location of the short after the ensuing bzzzzzzzzzzt not knowing of a symbol for smoke ;) Then the next week was spent with engineers using a dremel to try to drill out the shorted section of the remainder of the lot of proto boards to get on with testing. This of course smeared the layers of copper together and created more shorts. Eventually, they managed to get one drilled with no short though I don't know how.

On a different day, the engineer that accomplished the drilling managed to probe a pin on a pingrid array 6 rows and 6 columns back from the edge to prove a vendor was lying about the signals put out by the chip. After a day of practice, he was able to hook a 30 guage wire on the pin by sliding it under the chip blind and then supergluing the wire down making a contact. He proved that the vendor had sold us 200K worth of impure silicon packaged in ballgrid arrays that had no relation to what the spec said the chip was supposed to do.

--Cameron

Evan
03-23-2007, 01:28 AM
Here is a short excerpt from "Surely You're Joking Mr. Feynman", by Richard Feynman. It's about when he had just arrived at Oak Ridge to help with the design and construction of the uranium 235 separation facility.



They started to re-design plants, and the designers of the plants were there, the construction designers, and engineers, and chemical engineers for the new plant that was going to handle the separated material.

They told me to come back in a few months, so I came back when the engineers had finished the design of the plant. Now it was for me to look at the plant. OK?

How do you look at a plant that ain't built yet? I don't know. Well, Lieutenant Zumwalt, who was always coming around with me because I had to have an escort everywhere, takes me into this room where there are these two engineers and a loooooong table cover, a stack of large, long blueprints representing the various floors of the proposed plant.

I took mechanical drawing when I was in school, but I am not good at reading blueprints. So they start to explain it to me, because they think I am a genius. Now, one of the things they had to avoid in the plant was accumulation. So they had problems like when there's an evaporator working, which is trying to accumulate the stuff, if the valve gets stuck or something like that and too much stuff accumulates, it'll explode. So they explained to me that this plant is designed so that if any one valve gets stuck nothing will happen. It needs at least two valves everywhere.

Then they explain how it works. The carbon tetrachloride comes in here, the uranium nitrate from here comes in here, it goes up and down, it goes up through the floor, comes up through the pipes, coming up from the second floor, bluuuuurp - going through the stack of blueprints, down-up-down-up, talking very fast, explaining the very, very complicated chemical plant.

I'm completely dazed. Worse, I don't know what the symbols on the blueprint mean! There is some kind of a thing that at first I think is a window. It's a square with a little cross in the middle, all over the damn place. I think it's a window, but no, it can't be a window, because it isn't always at the edge. I want to ask them what it is.

You must have been in a situation like this when you didn't ask them right away. Right away it would have been OK. But now they've been talking a little bit too long. You hesitated too long. If you ask them now they'll say, "What are you wasting my time all this time for?"

I don't know what to do. (You are not going to believe this story, but I swear it's absolutely true - it's such sensational luck.) I thought, what am I going to do? I got an idea. Maybe it's a valve? So, in order to find out whether it's a valve or not, I take my finger and I put it down on one of the mysterious little crosses in the middle of one of the blueprints on page number 3, and I say, "What happens if this valve gets stuck?" figuring they're going to say, "That's not a valve, sir, that's a window."

So one looks at the other and says, "Well, if that valve gets stuck -- " and he goes up and down on the blueprint, up and down, the other guy up and down, back and forth, back and forth, and they both look at each other and they tchk, tchk, tchk, and they turn around to me and they open their mouths like astonished fish and say, "You're absolutely right, sir."

So they rolled up the blueprints and away they went and we walked out. And Mr. Zumwalt, who had been following me all the way through, said, "You're a genius. I got the idea you were a genius when you went through the plant once and you could tell them about evaporator C-21 in building 90-207 the next morning," he says, "but what you have just done is so fantastic I want to know how, how do you do that?"

I told him you try to find out whether it's a valve or not.

Wess
03-23-2007, 01:33 AM
To give it some perspective here is what I am attempting to build.

http://i162.photobucket.com/albums/t270/Wess23/image0.jpg

http://i162.photobucket.com/albums/t270/Wess23/image3.jpg

It looked a lot simpler in the catalog, but we all have to start somewhere.

Mcgyver
03-23-2007, 07:46 AM
As you can tell I'm somewhat new to the hobby and any help would be appreciated.
?

heck I'm 12 years into hobby and would have had to look some of that up. it may be the correct way to prepare a drawing, but overkill for a homeshop project - in a commercial environment the maker might never see or know what it attach's to, we don't have that problem and figuring out what is critical/what's not is more intuitive. That plus I'd guess most of those doing drawings aren't trained draftsmen, they're just guys trying to contribute something.

The area where model engineering drawings could be improved is clearly state clearances f& tolerances for pistons and bores. drawings that give a 1.000 piston into a 1.000 bore are a disservice, the builders supposes to guess at clearances?

Lew Hartswick
03-23-2007, 10:33 AM
I still think perpendicularity measured in a linear dimension is STUPID.
It's an ANGLE for gosh sakes.
...lew... (cotton pickin new fangled drawing dimensioning)

Orrin
03-23-2007, 10:50 AM
It looked a lot simpler in the catalog

What catalog did you find that in? I've been on the lookout for plans to built a Hog look-a-like, but have not yet found them.

TIA

Orrin

Evan
03-23-2007, 11:54 AM
I still think perpendicularity measured in a linear dimension is STUPID.
It isn't just stupid, it's meaningless. Without a slope ratio nothing can be inferred from the specification. I suspect the .05 was intended to be a tolerance for the diameter, not the perpendicularity.

ckelloug
03-23-2007, 12:53 PM
The perpendicularity specification does in fact specify a slope ratio. It is just that it is complicated what it means. This is an ANSI Y.14M compliant drawing with the added bonus of ISO surface finish which wierd science has already told us is intrinically wierd. I don't know if my description of the meaning of perpendicularity in my post yesterday was tractible or not but it's my go at explaining the definition from the book. That's why the book that explains what these drawing symbols mean is 350 pages!

Basically, it means that the slope of a line drawn through the center of the hole cannot be sloped more than the tolerance called out divided by the depth of the hole.

Rusty Marlin
03-23-2007, 01:03 PM
perendicular to -A- within 0.05 for the 3mm hole makes absolutly perfect sence. BUT there are better ways. Such as True Position, but I digress.

To measure this callout on this part:
set the part on datum -A- on three adjustable points (jack screws) on a tool room grade granite plate.
Using a set of Deltronic 0.002micron step pins, pin the bore to the closest possable fit.

Using an indictor on a HEAVY height gage, level datum -A- to within 10% of the tolerance or 0.005 (.0002").
With a steady hand lay the indicator tip against the vertical surface of the pin as close to the top surface as you are comfortable and zero it, slide the indicator up the pin a distance equal to the thickness of the part.

Rotate 90 degrees around the part and repeat.If the indicator moves less than 0.05 the part is good.

So how many guys here are outfitted to inspect that part? It would take some pretty expensive equipment.

As a gage and fixture designer I could rip this print apart, but what's the use?

BTW: 1.6mico meter finish = 63 micro inch finish. Just a pain, decent, turned finish, nothing fancy.

Just for the nitpickers among us, you'd never ever, be able to level that part to with in 0.005mm because the specified surface finish is way too ratty and the indicator tip would be showing the finish marks. This part with that tolerance needs a ground finish down around 0.2micro meters (8Ra).

TIP OF THE DAY:
To convert micro meter to micro inch finish: multiply the micro m X 4 and move the decimal one place to the right. 1.6x4 = 6.4 move the decimal = 64


Wess, do yourself a favor, spend $75 dollars and buy the lastest version of the Machiney's Handbook (27th edition). Get the one with the thumb index.
Just trust me on this, it'll be the best 75 bucks you spend in the entire time you do this hobby. ;)

ckelloug
03-23-2007, 01:21 PM
Rusty,

Cool Description of how to guage this. I've never seen any of this kind of guaging done or heard it described. Stick a caliper on it and you're done was the approach in college but we were only trying to meet thousandths to teach us not to torture machinists :D

Question however, do you mean 1.6 micrometres or 1.6 mico-millimetres for the surface finish tolerance. I believe that the former interpretation gets the 63 microns you're talking about.

Tin Falcon
03-23-2007, 01:42 PM
Hmm as far as symbols
http://www.mechanicalmodels.com/tips/symbols.htm
where to buy
http://littlemachineshop.com/products/product_view.php?ProductID=2202

It apears that Mechanical Models and littlemachineshop.com are owned by the same folks. Mechanical models is owned by siechert & Woods, Chris Woods is one of the owners of LMS. LMS apears to be the only retailer of MM products. These are china imports and the prints are chinese.

I have a simple stirling kit I won as a door prize ar Cabin Fever. One of my to do projects.
Wes :
IMHO use the print as a guide and make it to your liking. In most cases there are only a few places on a model where things fit together that dimensions are important. And even then it is the fit that is important not actual dimentions.
The symbols you ask about are for manufacturing when parts are made in seperate shops 100s of miles apart and must fit together. Make it so YOU are happy and it runs nice.
Tin

Rusty Marlin
03-23-2007, 01:43 PM
I ment micro meter, I work in mm all day so I get used to saying micros and mentally its all in relation to mm. Sorry for the confusion.

1.6mico=.0016mm=.0000016m

Rusty Marlin
03-23-2007, 01:56 PM
[QUOTE=ckelloug] Stick a caliper on it and you're done was the approach in college but we were only trying to meet thousandths to teach us not to torture machinists :D
QUOTE]

That's what machinists are for, they like it. :D But God help you if you foul up a blueprint and create something physically impossible to create.
The big thing to remeber is COST, its nice to have parts made to a gnats wisker with nice shiney surfaces, but every decimal place costs more money, and its exponential, not linear, and most of it is the guaging to verifiy the machining of the part. We use 0.001micron indicators that cost $500 just to have them reconditioned.

So if you don't need the accuracy, don't put it on the drawing. A good designer can save a ton of money on a gage by specifiing ground finishes only where they are needed and allowing milled finishes with generous tolerances on eveything else. The gage won't be as pretty as one that has "ground all over" for the finish note, but that's what wrinkle paint is for. :)

ckelloug
03-23-2007, 02:42 PM
I went to school at Harvey Mudd College and got a general engineering degree. All of the engineers were required to make a hammer, a screwdriver and a sheet metal tool tray to .001 inch for all dimensions including the wood parts.

It may not have been true but the general concensus amoung the engineers was that the profs made the prints we worked to so that everything that could either go wrong or be misinterpreted would be. We had to harden pieces of the tools and it seemed that professors were not overly concenred that 50% of the time that the pieces cracked and had to be scrapped. We always thought it was a conspiracy to teach us to be careful about processes. Especially the types that were never going to design anything mechanical. It also took some asking around to discover that the only way you could meet the surface finish criteria and not lose points was to hand lap all of the surfaces with toothpaste. . . My screwdriver was the first tool at the school to be graded by the shiny new (at the time) B&S ruby probed CMM and I got a 99/100 on it.

Making their own stuff to thousandths tolerance was enough to teach a class of engineers of whom about 1/3 had the math skills already (but had not acquired the tool skills yet) that just because something is called out on a print doesn't mean it's a good idea.

I've never actually worked as an ME but I was one of the types that would sit around in the shop and check tailstock alignments on the lathes just because it irked me that they were out. I'm at an experience level at this point (in mechanical stuff anyway) where seeing my name on a print would probably make a machinist cringe. I do mostly software and a bit of electrical generally but I'll probably be out making swarf in a few weeks when I get my shop finished after a year of too much real work.

Evan
03-23-2007, 03:20 PM
Cameron,

I see you did describe a slope criterion in your original description. I must have either skimmed over it or failed to interpret it correctly.

Wess
03-23-2007, 08:09 PM
Yep, That is the same model kit at Little Machine Shop. I bought the one I have from Grizzly. According to the LMS site theirs have the cylinders already made, the Grizzly kit does not. Thats OK with me though, it's all just aluminum and brass bar stock, material will be easy to get if I need a do over.

And you are right the prints are written in Chinglish and they are dimensioned metric. On a good note they are nice and clear, not the usual 3rd generation copy of a fax.

I bought the thing on a whim when ordering some other stuff, and so far so good. I'm having some fun and learning a thing or two.

ckelloug
03-23-2007, 09:01 PM
Evan,

The damn thing is bloody confusing. I'm not sure whether my paraphrase of the book made any sense. I must say from having worked on an ISO standard for geographic coordinate transformation that they've often written in the mathematical equivalent of legalese. There were sections where I couldn't completely follow the offical version of the standard due to it's yards above the normal intellect presentation and I wrote the reference implementation of the software it was standardizing!

lane
03-23-2007, 09:33 PM
Just make every thing fit evert thing else that it is suppose to Keep all bores concentric with out side diamenter and no wobble on edges all running fits a slip with no shake or wobble. and all surfaces square to each other. Do all this as close as you can and it will work. Plus you wont smooth polished finishes on all exposed parts In other words it should look like a jewel when you are done.Simple as that its only a model. Just do the very best you can. Thats all any one can ask for.

bronson
03-24-2007, 07:41 AM
I would like the graph that you put in the thread to print do you have a link?

TECHSHOP
03-24-2007, 07:14 PM
I few months (years?) back, I asked about Geo Tol, when I foolishly thought I could get a "job" after being out of the "professional shop" for more than 15 years. Then I thought "screw this" and retired back to my "home shop comfort zone", with the "tap, tap, damn" latern post and the "three wire thread checking". So, all I can add is: I think I saw my 20+ year old first edition "text" book today, it is still tilting the rain barrel behind the graden shed.

DR
03-24-2007, 08:45 PM
IMHO from experience,people who draw things and insist on using symbols and DON'T provide a symbol legend with the drawing should be shot.


I don't recall ever seeing a drawing with a symbol reference on it.

I believe the proper name for this is geometric tolerancing. (The drawing here being a metric version.)

It's expected the machinist knows how to interpret the tolerancing system. The main problem I see with geometric tolerancing is the designers frequently don't understand how to do it correctly.

wierdscience
03-24-2007, 09:27 PM
I don't recall ever seeing a drawing with a symbol reference on it.

I believe the proper name for this is geometric tolerancing. (The drawing here being a metric version.)

It's expected the machinist knows how to interpret the tolerancing system. The main problem I see with geometric tolerancing is the designers frequently don't understand how to do it correctly.

Exactly my point,few people do and it leads to mass confusion,lost time, lost material and occasionally death.

I have one company I work for who provides a legend on a seperate sheet.They're drawings have always been correct and I have never had to get a clarification on anything,they are the exception not the norm.

The usual drawing sees at least one error,the worst offender is a plastics company who's drawings have at times required more time on the phone than on the machines to make.

lane
03-24-2007, 09:55 PM
So far I have been working from Engineering drawings most of my life and 99 % of the time there is something wrong with the deminsons or something left off . For years I bitched and moned about but to no avail.The Engineers at ATT use to say Just make the part look like the print to Heck with the deminsons just make it work.. So we did.