Milling Question Concerning RPM

D

Dennis Paish

Joined
Jan 3, 2007
Messages
302
Greetings,
There are two identical 500 pd, bench top, square column, 1.5 hp, Milling machines that I have been researching. They are both identical mills except for different spindles.

1st Mill.
Has a R8 spindle taper with a RPM of 100 to 5000.

2nd Mill
Has a special Speed Master water cooled 8000 to 20 000 RPM spindle. The Spindle taper is one which can not accept any larger jcutter then a 1/4" balanced tool.

Both machines are CNC. I would like to use it not only for guards, but also for doing the initial cutout and rough profile for blanks in SS. (Plus, I can make the finial parts for my 2'x2' cnc router and 4'x4' cnc plasma table)

Which spindle is more useful? All feedback is welcome.

Regards, Dennis
 
The 100 to 5000 is more useful.

Almost slow enough for anything, and plenty fast for everything.

You sure the other one only goes down to 8k?

That's hauling ass.
 
Brian Fellhoelter Knives said:
You sure the other one only goes down to 8k?

That's hauling ass.
Click to expand...

You ain't a kiddin that's hauling ass !! :eek:

If that's as slow as she goes I would think it's made specifically for machining materials other than steel.

I agree with Brian completely. Not only that but finding tooling for your R8 spindle machine will be a breeze :thumbup: It's everywhere !! Anything you'll need. And most R8 tooling can be had at very reasonable cost.

If I had all kinds of $cheese$ I would love to have a big heavy 3 or 4 axis vertical (or horizontal ) ;) machining center with Cat 40 holders and through the spindle coolant.
Since I don't ................. I've settled for a Bridgeport style mill with an R8 spindle. Been real happy with it so far :thumbup: ;)
I also have a Column type Jet Mill/Drill with an R8 spindle that has been a good machine too.


:cool:
 
The high RPM mill would be good for machining wood handles - if the block per second throughput is fast enough for it to reliably feed 50 IPM or better. If not it truly isn't good for much except making circuit boards and similar. You won't be cutting much steel with it.

5000 RPM is plenty for anything you're going to be doing, and R8 is a very versatile taper that is cheaper to tool than any other.
 
Thanks everyone for your comments. Yes I am sure the RPM is from 8k to 20k as I witnessed the demonstration yesterday. That spindle is hauling ass, and it gets there in a hurry. I watched them cut Titanium jewelry (it cuts 8 hours a day 5 days a week like butter). With SS, they slowed down the feed rate.
Other then the awful noise it seemed to cut SS ok.

I made an error on the original post. The other machine RPM is 200 to 3000, not 5000. They have another 1400pd model with double the work envelope with a RPM of 200 to 5000, but it is also double the money.

Thanks
Dennis
 
RPM isn't the entire story. It is all about surface feet per minute. So, for a 1/8" cutter, 8000 RPM is great, it gives you 260 SFM which is right on the money for coated carbide tooling in steel. But it is three times too fast if you're wanting to just use regular HSS tooling. And if you want to use a 1/2" cutter the SFM is over 1000. That is fine for wood, and you can get away with it in aluminum if you have a very rigid setup - but it won't work for steel. HSS in stainless really should be 50-80 SFM, though you can get away with more if you're taking a light DOC and flood coolant.

3000 RPM is still okay for what you'll be doing and it is all that 90% of home shops have. It will only be a problem with smaller cutters. It gets back to the SFM thing. And even then, you just have to slow your feed to match the RPM. It is the chip load that is important there. A good rule of thumb for feed is .002-.004" per tooth in a 1/2" cutter in mild steel. Go up or down depending on cutter size and material and finish desired. This is why I don't like 2 flute cutters. I use a lot of three flute (if I can get away with it) where other shops would use two - it gives me a 50% feed rate advantage (and tool life).
 
The lower RPM machine with the R8 Receiver would be better for what you want to do.

Have you ever run a mill before?

Like someone else said, that high rpm machine would be great if you are doing surfacing work on very soft material like plastic or aluminum using very small diameter tools. With a small tool, you need the spindle speed for tool life.

Are either of these machines three axis or just two axis with a manual Z?
 
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