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"

1 Comments:

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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