Newbie questions on size/units and extrusion

[Btox]

Hello everyone,

In my attempt to render a motorcycle cylinder head in SolidWorks 2000
i've sketched in the part and attempted to extrude the main features
of the head however i've run into a couple problems i was hoping
someone could help me with...

1. The part when extruded appears distorted.. millimeters stated in
the drawing do not correspond with actual size. Do i have standards
or some "units" setting off somewhere or a view setting perhaps?. I
*traced* the part in actual size using a transparency taped to my
monitor, yet the image in SW is way off.

2. What is the best way to render the cooling fins on the top of the
cylinder? (see pics here for reference of what is is i am drawing:

Top surface: (right side of page)

http://beautyofspeed.com/workshop/cylinders.htm

Bottom surface:

http://beautyofspeed.com/workshop/cylinders.htm)

Should i use the "Rib feature"? ..or some other method?. I need to
be able trace each fin profile and extrude each to a uniform
thickness.

3. On the bottom surface of the head i need to render in the varying
depth of the chamber (see inverted heart shaped depression in top
surface of "Bottom Surface" pic noted above) ..should i use a
Extrude/cut feature and fillet it somehow?..

..I'm trying the tutorials in the help, but some of it is lost on
me..thanks in advance for any help or advice you can provide.

Brent

 

[MadMango]

SW2000... a bit outdated, and I'm not sure how much help I will be, since it's been so long since I used SW2000. I forget what it was capable of and what are newer features, so bear with me.

1) The units you use in modeling may not be the same units in drawings or assembles. Check them all to see if they are the same. Tools>Options>Document Properties>Units. If the parts don't look the way they should, you should be able to go into the sketch dimensions of your features and make corrections.

2) Cooling Fins, I think in SW2000 you will be stuck with having to create individual Planes for each fin, and extrude accordingly. Maybe someone can offer a better method. I don't think Radiate Surface was an option in SW2000.

3) Yes, though you might have to create some additional cutting planes.

General comments
I am hoping that this is only for eye-candy modeling, and not for anything production/manufacturing driven. Taping tracing paper to your monitor isn't very accurate to say the least.

MadMango
"Probable impossibilities are to be preferred to improbable possibilities."
Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[TheTick]

As far as the model appearing distorted, consider the following:

1.) If you are creating a model from a paper print, the dimensions on the print may not match the drawn dimensions. Also, your print revison may be outdated.

2.) Don't trust your screen. Even "flat" screens are subject to distortion dependent upon your monitor settings.
-a.) check your screen by drawing a square in SW and measuring. You may need to adjust your monitor.
-b.) examine your model in different orientations and scree positions.
-c.) The part may not have manufactured to the print.


All this machinery making modern music can still be open-hearted.

 

[Btox]

Thanks for the info, however i used the transparency on my monitor to simply sketch in the profile.. the measurements i've taken from the real cylinder head itself which i have in my posession. When i type in to extrude 10mm for example it appears much thinner... when i measure sketched lines using the measure tool in SW it also comes up short. Besides the Document Properties page "units" setting, is there any other setting which would cause such distortion?

Thanks again,
Brent

 

[TheTick]

Is this a thin extrusion? If so, make sure you are not confusing the extrude length with the wall thickness.

Sorry if I'm being too simplistic. Just trying to help.

 

[RawheadRex]

"Is this a thin extrusion? If so, make sure you are not confusing the extrude length with the wall thickness.

Sorry if I'm being too simplistic. Just trying to help."

I was just thinking along similar lines to "TheTick." It sounds like you're looking/typing the 10mm extrusion in the wrong place (i.e. editing the "thickness" value rather than the "extrusion depth" value). Look carefully when you go to do this the next time and be certain that you're updating the correct field.

I still do this quite often when I use the "Simple Hole" feature. I enter my diameter into the "depth" field. This is not very difficult to correct though as your extrusion depth is editable after the fact. Try double-clicking on the "incorrect looking" feature and see if the dimension values are what and where you want them all to be (i.e. length, width, and depth values correspond with what you thought you defined orginally). Double-click on any dimension and enter a new value to change it to and rebuild the part.

Good Luck,
Chris Gervais
Sr. Mechanical Designer
Lytron Corp.

 

[JNR]

First, I assume "render" is not being used to describe a photorealistic shaded picture ie: PhotoWorks. Just a small comment, I know, but in the SW world (and most other solid modelling software) we use that terminology for purely graphical pretty pictures. So it will be easier next time to understand eachother quickly.

I'm not sure I understand what you are really doing (nothing to do with the first comment above).

Next I'm guessing that you are kind-of on the right track by getting the shape of the sketch in first (by your tape on the screen technique) then adding real dimensions to the sketch to get it correctly proportioned?

I suggest that you forget taping stuff to the screen or any other "digitizing" method. It is incredible inaccurate. You screen is so variable it isn't even funny. It is a real pain to even ATTEMPT to scale your screen accurately when modelling and depends on MUCH stuff including your hardware and graphics drivers.

I strongly suggest you just construct the sketch from scratch using the dimensions.

It sounds like maybe you don't have the sketch dimensioned correctly. Did you edit the sketch and add the correct dimensions?

If your sketch is all blue when you edit you don't have the dimensions completed and it is not fully constrained.

Are you using the same units for the sketch dimensions and the extrude feature dimension? You aren't using inches in the sketch and mm in the extrude feature?

You do not have to reset your options for units in SolidWorks - specially if you are only using certain units
a few times. Anywhere you can enter a value, you can add the (non-default) units after it and SW will automatically convert. Example: You are set up default in inches. You want to input a value in mm - just enter 105.66mm or whatever the value you need. You can do feet, meters, fractions, etc. (Take a look at the help on units.)

BTW: You can also calculate in-line. Eg: 2*(52.83)mm would give the same result (4.15984252 inches exactly - to 8 places precision).

Note also that SW 3D MODELS are absolute size. Ie. the actual geomtery is mathmatically full size no matter what units you input it as. Most modern 3D CAD systems are this way. There is no scaling involved. That is a DRAFTING issue, not a modelling issue. If you are in a Part or Assembly file you are modelling, not drafting. SKETCHES in modelling are not the same a drafting views.

Cruise through these comments and see if anything makes sense to your problem. Then ask away again if necessary - we'll get you there in the end.





3/4 of all the Spam produced goes to Hawaii - shame that's not true of SPAM also.......

 

[Btox]

Thanks to everyone who replied!. Thanks for all the comments,tips, and info. It turns out a majority of my problem was that i was relying to much on the sketch from my "transparency taped to the screen", which i had used as a basis for my part. I started over last night by simply plotting in points and measuring out the main features then using the transparency at the end to draw the curves on the perimeter of the outside surface...much less distortion.

Also- JNR: thanks for the clarification on terminology. That is helpful for me as a layman going forward so that i can explain more accurately what my issue/problem is when i post a question to the forum,etc.