Minimill spindle power?

I'm looking at getting a mini mill in the near future. I'm reading some posts that indicate the power is wildly overstated, such that the 7.5 Hp spindle can't output close to that. I asked the rep for a power curve and he just restated the numbers on the website.

Can anyone shed some light on this? Example speeds/feeds/material/displayed spindle load that you use would be great. How big a shell mill is appropriate and what sort of cuts can you take with it?

Thanks!

Keep in mind I'm basing this off of an old, old TM-1. Early 2000s vintage at best. But, toolroom mills and mini mills have similar spindles, and the same HP rating.

What maxes out our TM1 is:

2.5" 45-degree lead angle face mill, .05 DOC, .008 IPT (5 flutes)

That, if I recall, ends up about 120% load. That is in either 4140 HT or 304 stainless, can't remember exactly. It took it fine.

Where you will have issues is mainly big drills - no torque whatsoever. Going carbide can help to get the RPM range up higher, therefore more torque. Taps as well. 1/2" taps in tool steel, 1" drills, that's gonna be about the max you can do, if that.

So if I was you and I got a mini mill or toolroom mill, I would go for about a 2" face mill with a 45-degree lead angle. Kennametal Dodeka face mills are amazing. With a 2" 4 or 5 flute face mill I could see DOCs of .075 with a decent IPT, even in tool steel. 2.5" would be pushing it unless you took lighter cuts.

Plan on interpolating most drilled holes over 1" unless you crank the feed down pretty low (which is certainly doable). Don't plan on hogging with end mills over 1/2". Really, due to rigidity, I believe you'd break a cutter before you bogged the spindle. I wouldn't doubt you could cut .5xD slots with up to, say, 1/2" end mills. More than that and the mix of rigidity and lack of power would bite ya.

Enjoy! There is nothing at all wrong with these machines, you just got to know their limitations.

Job Shopper TN said:

2.5" 45-degree lead angle face mill, .05 DOC, .008 IPT (5 flutes)

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What ballpark RPM was that at?

Thanks for the info! Sounds like plenty of power to me coming from much less.

FYI Haas vf4ss only has a 7 1/2 hp motor in it ,,, I have found I do ok on steel with them but run out of power on alum. A lot of times I have to lower the RPM and raise the feed to get MRR up to were I can stand to watch it cut,,,, Does the Minimills have a tag on there motor?

Here is some data from the last job in 6061:

3 Flute 5/8" End Mill:
- HSM tool path
- DOC: 2.68"
- 4600 rpm
- 145 ipm
- Step Over: 0.024"

2" Face Mill (5 Inserts):
- 5000 rpm
- 160 ipm
- DOC: 0.06

Both tools put a spindle load around 80%.

CosmosK said:

What ballpark RPM was that at?

Thanks for the info! Sounds like plenty of power to me coming from much less.

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1000 RPM or thereabouts I believe.

Yep, if you know the limitations you can work with it. You can't make parts as fast as folks with Mazaks or SS Haas, but, you also got a machine for a sixth (of new price)! So not as fast, but you can charge less... heh.