Machining Parts - What school didn't teach me?! 1

[ryandias]

I am new to the industry and working as the only Mechanical person in my location.

I have been asked to design a part (heat sink adapter) and have it prototyped (say 20 pieces).

I know how to draw/Model. But what school did not teach me is , Tooling time, ways to save money/ lower cost, other ways to improve the product while reducing time/cost.

Any suggestions? or books, or other info sources?

 

[MikeHalloran]

It doesn't happen often, but you will occasionally find a spec that brackets a surface finish, e.g. with two numbers. It is usually the result of an expensive lesson.

When Rover first built GM Hydra-Matic transmissions under licence, they didn't work right. The finish of a particular surface was too good, the mating friction material couldn't grab hard enough to stop the surface fast enough, causing rough shifts and broken transmissions.

That was not the lesson. The GM prints had a specific range for surface finish before that factory was constructed.

Some arrogant fool elected to ignore the history of the part, reflected in the print.

That is the lesson.



Mike Halloran
Pembroke Pines, FL, USA

 

[wes616]

If I specify 125, and the fabrication process achieves 16, then the work has exceeded specification, and there is no need to do anything else.

We bond a lot of machined parts into honeycomb sandwich panels. If I specify a surface finish, that is the finish I want. We reject parts when they are to fine finished - a rougher finish produces a better bond.

Wes C.
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Light travels faster than sound. That's why some people appear bright until you hear them speak.

 

[ewh]

I agree, and often have to mark up drawings that specify a finish of XX "or better" so that the intent is not open to interpretation.

 

[strokersix]

Another surface finish example where smoother may not always be desired is injection mold tooling. There are various different processes specified to create surfaces in the mold which are then impressed in the molded part.

 

[drawoh]

wes616,

If you want a rough surface, you have to specify a rough surface. A surface finish symbol with one number calls up the maximum allowable surface roughness. Anything smoother than that is acceptable.

If you have two numbers on your surface roughness symbol (see the Machinery's Handbook), then you have specified a range, and you can reject stuff for being too smooth.

In my case, I was specifying a non-reflective surface for an optical device.

JHG

 

[telecomguy]

Though it's not a machining exercise, I thought this link kind of fit the subject:

http://www.profilesmagazine.com/p32/driscoll.html

<tg>