Hi Hanermo:
I seem to be looking at the cycle times a bit differently from you.
I don't think I can mill the thread OD, threadmill it and drill and ream it in a minute and still get a decent finish or decent size control.
I'm pretty sure I can do it quicker on the lathe since I can keep the tool cutting almost continuously and I can typically push it harder on the lathe without tearing up the tool.
You may have a different experience...I don't know, but as a rule of thumb I've typically budgeted a third the price for turning over milling with operations like these and I've not had to cry about underbidding turning work very many times.
A great example is the time difference to chamfer a round part in the lathe vs the mill.
In the lathe the cutting time to do a separate op for a chamfer is around 0.04 seconds to make 2 revolutions of the part if it's spinning at 3000 RPM and you just touch it with a chamfering tool rather than running a turning tool along a path.
On the mill, a toolchange and tool approach might be almost as fast as the lathe, but the path length is 1.5 inches (0.5" diameter part) so at 15 IPM is about 2 seconds just for the milling and if you have to do it in 3 places on the first operation it really adds up.
You'd have to run the mill tool at 600 IPM to be as fast as the lathe is for chamfering.
Also, the stock handling on 250 parts is significant if you've got to chop up the bar into 250 bitsy little blanks and debur one end of each.
It's why I love bar feeders and bar pullers and cutoff blades.
I can hit length perfectly, I can debur in the same op and I never have to touch the bar except when I load it and when I toss the remnant.
I believe just the time saved on that preparatory op avoided, is significant and more than pays for the extra cost per hour of the turning center assuming it's true they actually cost more to run. (I bill both out at the same rate in my own shop but I do not have sophisticated turning).
Another point to consider is that by turning them it's one chucking per part to drop a completed item, and it's a fast, bulletproof chucking.
On the mill it's three if you count cutting up the bar into blanks, four if you include the deburring step.
The last argument I can make for turning is that I don't have to build anything; just fire up the toy, load my tools and my bar, write a bit of code and push the big green button.
So I just can't see any scenario where I can outrace my lathe with my mill on these parts or make more money on the mill, or for that matter even make
acceptable money on the mill.
Of course 250 piddly little parts is not much of a moneymaker on the lathe either; but the OP has a good customer who's needs he'd like to serve, so it's worth it just to keep the customer sweet.
I'd still heave a sigh, tear down the lathe run the piddler job and set the lathe back up to do what it's supposed to be doing.
I might even get lucky and not have to set up very many new tools or take out anything that's already in the turret.
I'd be cursing a little bit until the cheque comes in, and then it'd all be OK again.
Cheers
Marcus
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