Milling a slot in a steel guard. RPM?

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peppen108

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Apr 14, 2012
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Ok, I've been reeding up on milling for a while now but I just cant get a handle on spindle speed. I have done some hand calculations previously but since i operate the machine manually i have no idea how valid the are.

What spindle speed would you use if you wanted to mill a 1" long 3/16" wide slot in a 3/16" tool steel bar in say 10 minutes? Using a regular endmill and using the machine really carefully whit no coolant.

Any answers will bee greatly appreciated. :)
 
peppen108 said:
Ok, I've been reading up on milling for a while now but I just cant get a handle on spindle speed.
I have done some hand calculations previously but since I operate the machine manually I have no idea how valid the are.

What spindle speed would you use if you wanted to mill a 3/16" wide slot
Using a regular endmill and using the machine really carefully with no coolant.

Any answers will be greatly appreciated. :)
Click to expand...


Some will know this off the top of their heads, but let's work through it.

You're missing some info for the calculation
You need material type to get a cutting speed

The end mill
material assuming HSS
size assuming 3/16"
number of flutes assuming 2

First you need to determine the cutting speed in SFPM from a table

http://www.whitneytool.com/assets/PDFs/35.pdf
So toolsteel with HSS endmill
say 50sfpm (middle of the range on a table) random table picked off the net with first Google hit.

Now you have to calculate that in rpm


You can use the calculator on this page the second one down
http://www.custompartnet.com/calculator/milling-speed-and-feed

(50 SFPM x 12) / tool circumference .187 x 3.14 = 1021 RPM
to get inches per minute / tool circumference in inches = revolutions per minute

Yes about 1000 RPM


Re feed, you could do a feed calc for a rough idea of how fast to turn the handles, but the tables are production oriented.
Watch your chips, a nice light brown colour is nice, blue is the max you want to push it.

You can still use a hand pump oil can or squirt bottle with oil if your machine is not flood coolant equipped.
 
Last edited:
Really super! The 1000 is from top of the head of an engineer and I have about 1200 from another calculation.

Thanks!
 
Thanks Count, this finally makes sense to me, I can't count :D the times I've read through these calc.s and posts on F&Spd.

slow learner

Thanks
Mark
 
I've never had a calculator on the same end of the shop as my mill.
I use 1/8" end mills for my guard slotting and run somewhere between too slow and too fast. ;)
Usually either 1200 or 1500 RPM - I usually just leave it on whatever the last setting was. :thumbup:
Don't over-think this stuff.
Probably 95+% of the time, if you break an end mill, you were just pushing it too hard.
Slow down.
Don't crank as fast and take smaller bites.
Save your calculator batteries.
 
Karl B. Andersen said:
I've never had a calculator on the same end of the shop as my mill.
I use 1/8" end mills for my guard slotting and run somewhere between too slow and too fast. ;)
Usually either 1200 or 1500 RPM - I usually just leave it on whatever the last setting was. :thumbup:
Don't over-think this stuff.
Probably 95+% of the time, if you break an end mill, you were just pushing it too hard.
Slow down.
Don't crank as fast and take smaller bites.
Save your calculator batteries.
Click to expand...

Very true with manual feed. More difficult with power feed :)
 
I'm with Karl- since my mill isn't variable without being a PIA, and its manual, 99% of
the milling I do is with 1200rpm's. For some special reason I may change it but not often.
Slots or milling the bulk out of a frame same speed.
Ken.
 
Karl B. Andersen said:
I've never had a calculator on the same end of the shop as my mill.
I use 1/8" end mills for my guard slotting and run somewhere between too slow and too fast. ;)
Usually either 1200 or 1500 RPM - I usually just leave it on whatever the last setting was. :thumbup:
Don't over-think this stuff.
Probably 95+% of the time, if you break an end mill, you were just pushing it too hard.
Slow down.
Don't crank as fast and take smaller bites.
Save your calculator batteries.
Click to expand...

Works for me! :D
 
Theres a tutorial somewhere if you search that Karl did, since reading it a while back, I have not broken a mill. So I would suggest searching for that....and throw out a thanks to Karl as well
 
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