Sunday, May 18, 2008

What I am reading

Creating and Maintaining a World Class Machine Shop: A Guite to General and Titanium Machine Shop Practices, Edward Rossman, 2007.

As the title implies the book is about machining practice. It is written to the shop owner/foreman and assumes a detailed knowledge of machining practice and shop management. As the title implies a large section of the book is about speeds and feeds for titanium machining, specifically milling.

What are some of the practices leading to a world class machine shop: optimization of cutter life versus machining time, a facility allowing for flexible tool layout (multiple utility drops throughout the facility allowing easy equipment repositioning), tracking of scrap rate (less than 1%), tracking of job costs and time, well maintained equipment, (tracking of spindle runout, .001 TIR desired), tracking of pecentage on time delivery.

A check list for reviewing a shop is presented. The check list items are: initial impressions and greeting prior to going out on the shop floor, clarity of safety instructions, general cleanliness, equipment appearance and condition, in-process job-tracking with appropriate paperwork (heat numbers, operation sign-off, inspection results), operator training, fixturing and set-up. This check list is intended to aid a shop owner improve his shop.

The practices and checklist are useful for an engineer in locating or qualifying a shop to perform work. Perhaps the single most important item is the tracking of on time delivery rates. If a shop tracks on time deliver they probably will pay attention and deliver on-time. My experience has been that any shop that has been in business a while delivers parts accurately made to print. On time delivery, however, is another matter.

So what else did I learn that is useful in the book to the practicing engineer, as opposed to the machinist? The most useful item I found was a discussion relating machine accuracy to required design tolerance. A rule of thumb was presented: The resulting error in machined features is N times the machine accuracy or

error=N X machine accuracy

N is a number determined from experience. The value of N given in the book ranges from 4 to 10.

So it the machine accuracy of .0002" and N is conservatively taken to be 10 the resulting error in the machined feature will be .002"


Blogger The Scylding said...

In answer to your request some time back on my blog, I've started writing on architecture...

Tuesday, June 10, 2008  

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