Print Confusuion ??

[Tin Falcon]

I started this rather than hijacking the other metric plan thread that was already wandering a bit. And brought this quote over by John Stevenson.

What sends me ballistic is getting MACHINING drawings in fractions ? WTF ? have you ever seen a lathe or mill with fractions on the dials.
Some people may know in their head what 23/64's is but I don't.
With imperial there are always two dimensions, fractions and decimal, with metric there is only decimal, you NEVER see 6 1/2mm on a drawing, it's always 6.50mm

JS.

First of all I fully admit blueprint reading can be confusing for the newby. Print standards change from time to time and country to country.
And as john pointed out many imperial prints are in fractions. Many of the great me designers leaned this style of drawing. Rudy Kouhoupt , Elmer Versburg , Philip Duclos etc. the other thing That irritates me is when there is more than one reference point on the same part.
OK enough rant. How do we as home machinist deal with this confusion without removing the reminding hair on our heads or throwing parts across the shop because the print was read incorrectly, and we just spent a bunch of time making beautiful scrap.
1) Learn the various languages of prints. Buy a book or two on engineering drawing of various vintage,or Download old books on PDF. and read them.
2) convert dimensions to usable ones with a chart or calculator.
3) Take a file card and sketch your own print for each part made to your liking. In other words translate the print to your own language.
4) The card method will allow you to note any changes you have made as well. You may have decided to use aluminum instead of steel or the material dimensions may have changed to to material on hand vs what the print called for.
5) the card also allows for real dimensions like tap drill sizes and true ream sizes. Prints are notorious for putting a 1/4 inch shaft in a 1/4 inch hole. what is really needed is a .250 shaft in a .251 hole.
6) the card can be placed near the machine and the original print can stay clean.
Hope this helps and reduces frustrations.
Tin

 

[kf2qd]

OR - the characters that created those old fractional prints knew that most home shop machinist types were probably going to be making a ONE-OFF piece so the exactness of the part was not all that important. As long as the 2 parts were made to work together the end product would work just fine. Those nice drawings with all the tolerances just so are needed (essential) if you need to get parts made at different times by different people to work together, but for those of us working at home, we shold be able to figure out how some of those pieces need to fit to work properly, and it does give you a nice way to cover those little OOPSes.

For Instance - you don't have that nice 1/4 reamer (or it is just about wore out...) you can ream that hole to 0.249, and turn the shaft to 0.248 and continue on your way. It is just as good as perfect and only you will know.

Unless you are worried about interchangeable parts one really doesn't have to be all that anal about how the drawing is made.

 

[putputman]

The first thing I do when I get a new set of prints (especially if they are expensive) is take them to the local print or copy shop and have the laminated. This will cost a few bucks, but in the long run it is worth it. If I find mistakes or decide to change a dimension, I can use a grease pencil and not damage the original print. The original prints are clean and saleable when I am done with them. Haven't sold any yet, but maybe someday.

The second thing I do is redraw most of the print on my 2D cad program. This gets me familiar with all the details and also allows me to assemble details to check for fits and interferences.

I have DRO on my mill so many of my redraws are dimensioned from points that are more convenient for me to machine. Many times I work from a center point rather than a corner. This may not work for everyone, but it works for me.

Just another look at things.

 

[Tin Falcon]

Unless you are worried about interchangeable parts one really doesn't have to be all that anal about how the drawing is made.

kf2qd:
I think that is a bit over stated there. The point I was trying to make is there a lot of styles of prints out there. Yes there is a lot of adaptation in the home shop and everything is made to fit and "normal" tolerances can be set aside. We just need a way to make the print as easy to read and fool proof as possible when making the part. IMHO it is easier to make the need changes on paper rather than winging it and making the changes in ones head while machining.
Tin

 

[bearcar1]

Yes Arv, I do the same thing. I get all of the prints that cost a few $$$ and have them laminated and several duplicates made at Kinko's. The extra copies: 1) for shop usage 2) for upstairs reading etc, 3) optional but for a back-up. The originals then get hung up on a back wall or rolled and stored in a heavy shipping tube placed in the rafters. AFA the accuracy thing goes, there have been a number of mistakes made on several of them and I have attempted to contact the proper folks to let them know and it is strange, some of the errors re so glaring that they almost seem intentional.

 

[Mainer]

Like Arv, I frequently re-draw parts in CAD, dimensioning things the way I want them. Then I can choose my own dimension origin, add extra dimensions, etc.

As for fractions...I don't see fractions as a big deal. I've got all the fractions through most of the 16ths memorized, plus a few of the 32nds, and for the ones I don't know off the top of my head, 10 seconds with a calculator gives me the decimal equivalent.

 

[David Morrow]

I created an Excel spreadsheet - one column for fractions and another for decimals - and hang it by my mill. Great quick reference.

I also make a copy of the plans and just write dimensions on that as / if needed.

I suspect the practice of using fractions made it easier for some home machinists more used to woodworking as fractions are the common sizing method for wood.

 

[joe d]

Hi

Some years ago Lee Valley Tools included a chart in one of their catalogues, number, letter and fractional drill sizes, with equivalent in metric to 2 decimal places, and decimal inch to 4 decimal places, from number 97 up to 1". I got it plastic coated and it hangs on the back of the door right next to the workbench. Sure makes life easy!

Joe

 

[twineman]

Hi
I have found plastic charts with conversions from fractions, metric, number & letter drill sizes to decimals given out free at most industrial supply houses.
I have 8 or 9 of these laying around the shop on every machine and bench so are always close at hand.
Al

 

[bearcar1]

Yep, same here. I was given a couple of plastic cards from Starrett that contained all of the info for fractions to decimals s well as drill and tap sizes. I took them to work and enlarged them to 11"x14" and they have been very handy many, many times. I could have gotten them laminated in plastic but if they get too grunged up, I can always print off more as I did scan them and saved the file.

BC1

 

[mu38&Bg#]

One issue with prints is whether the print was drawn for inspection of manufacturing. An inspection print will have functional dimensions, which could be totally useless for manufacturing. Having worked as a mechanical drafter and designer and having done both type of drawings, it's important to know who will be reading your prints. Fractions on prints is not something I've seen other than carpentry and large hand made sheetmetal products.

I design the parts I make in metric. Of course my lathes are inches. My little CNC mill fortunately has metric ball screws and EMC is set up in mm. Milled parts go straight from Solidworks to VisualMill to the mill. Drawings for the lathe are dual dimensioned.

Greg

 

[Noitoen]

Metric, Imperial, meters, feet, left or right hand driving ??? .........I don't know why in the 21th century the world still can make up their mind. It's even said that NASA's mishap with the $165m Mars Polar Lander in 1999 was due to a meter/feet confusion due to software design in both sides of the Atlantic. When will this end? :hDe:

 

[bearcar1]

End? Most likely when an extremely large number of fatalities is recorded due to that sort of problem, but then again, this has only been talked about for like the past 50 years that I know of, if not more so who really knows. ??? ??? ??? ??? ???

 

[David Morrow]

Metric, Imperial, meters, feet, left or right hand driving ??? .........I don't know why in the 21th century the world still can make up their mind. It's even said that NASA's mishap with the $165m Mars Polar Lander in 1999 was due to a meter/feet confusion due to software design in both sides of the Atlantic. When will this end? :hDe:

I don't think it so much a sorting out process as bring the remaining Imperial holdouts (USA, Liberia, and Burma) into a metric world. Unfortunately we here in Canada are still very functionally Imperial as are a few other places.

 

[Tin Falcon]

Guys lets NOT turn this into a metric imperial DEBATE !!!
This is about how to make prints work for YOU?US in the shop. Not who is right or wrong as to how a print should be authored. Let not beat deceased Equines.Back on topic please!!
Tin

 

[mu38&Bg#]

I also like to model my stuff in Solidworks. I have the drawings for the Barr and Stroud Sleeve valve engine from SIC. I modeled it and found that the sleeve will allow the ring in the junk head to fall out at the bottom of it's travel. I did go over everything more than once, but it still might be my error. There seem to be a couple that were built, nobody mentioned any problems. Modeling allows me to find errors and make drawing in a way I can understand. It's usually several days of drawing, but I do it every day so it goes rather quickly.

 

[wespe]

1) Learn the various languages of prints. Buy a book or two on engineering drawing of various vintage,or Download old books on PDF. and read them.

For this I would highly recommend this book: http://books.google.ca/books?id=SqgJAAAACAAJ&dq=engineering+drawing+and+design. This is the book that my college uses for a textbook in our CAD classes. It takes you from basic hand drafting and sketching skills to an overview of CAD systems, auxiliary views, basic and geometric dimensioning, sectioning, and working drawings. It also has chapters devoted to specialized drawings (welding, CNC, electronics....), fasteners and processes, and machine parts and design concepts. Need the dimensions of a retaining ring? V-belt? roller chain? Got it. O-ring tolerances? Fits and clearances? Got it. Need to draw a cam? Gear? Easy. Each chapter includes reviews and assignments, so you have plenty of drawings to work on at your level. I cannot count the number of times I used this book during my internship. A bit pricey, but since it is a book you can use forever, well worth the price. I would highly recommend for anyone who want to learn Engineering Drawing the proper way.

-Tom