Machinability is one of those words that everyone uses but everyone also seems to have a different meaning.

Nudge, Nudge. Know what I mean?

Here is a look at just a few of the aspects of what that person you are talking with might have in their mind when you say “machinability.”
1) Surface feet per minute. High surface feet per minute equates to fast cycle times. Fast cycle times mean lots of finished parts per hour. Thus surface feet per minute equals machinability. (But too high surface feet per minute can mean premature tool failure and higher costs and downtime).
2) Tool life. Rapid tool wear is a sign of poor machinability. Long tool life equals better machinability. (Too long tool life can mean overpaying for tools or too slow cycle times).
3) Ability to hold surface finish and close tolerance. If you are constantly fighting the setup to keep the finish acceptable or to hold the specified tolerance, you are not experiencing “good machinability.”
4) Uptime. If the doors are open and your operators head is in the machine and his backside is pointing out, you aren’t making parts. Downtime equals not so machinable.
So what are the units of machinability? Is machinability measured in surface feet per minute? Tool Life? Surface finish or tolerance? Machine uptime?
In order to measure anything, you first have to have units with which to measure.
May I humbly suggest that the proper units of machinability are parts produced by the end of the shift, conforming to print, and requiring the least amount of operator intervention to produce at the quoted cost?
Only when we agree on this definition can we get a meaningful discussion between Purchasing, “I want the cheapest material.” Operations, “If you gave me better tools or material I could get this job running.” Engineering, “Why can’t you guys hit the cycle time, we figured that job ourself?” And Management, “Why can’t you guys hit plan? I buy you everything you want…”
The value that shop management adds is to facilitate the organization’s arrival, together, to the optimum state for the shop to produce given the resources available. To do that everybody needs to be on the same page.
When we’re talking about machinability, that page ought to read “parts produced by the end of the shift, to print, and requiring the least amount of operator intervention to produce.”
So how do you define machinability?
Have you seen the tragic results of a department maximum that cost the rest of the organization dearly?
(Not at your current employer, of course!
” Nudge. Nudge. Know what I mean?”