High Speed Spindle - Drilling & Mild Steel

[Chaz]

On Thor I have a 4KW 24K RPM high speed spindle. The torque curve means that generally at lower RPM there is little grunt.

Ive read about some settings on the VFD where it may be possible to increase the performance, at a cost of heat and/or reliability.

For drilling, going to carbide drills, does this allow me the option to drill at 12K rpm?

For mild steel, most of the speeds and feeds are showing 3K RPM max, of course as I increase the speeds I can do more RPM but there is a point that I cant go faster and I am nowhere near the torque curve. Apart from gearing down, is there any other way to deal with mild steel and a Chinese spindle? Different end mills? Adaptive strategies?

Thanks

[magicniner]

Mild steel is a bit "gummy" unless you use a leaded variety.
You could use interpolated milling rather than drilling for holes of limited depth?
Have you tried single flute cutters? I know it sounds mad but they are easy to sharpen and I use them on some difficult stainless steel and carbon steel jobs.
Are you using flood coolant?

- Nick

[EddyCurrent]

Have you tried a spiral drilling method using a standard endmill ?

[Chaz]

Mild steel is a bit "gummy" unless you use a leaded variety.
You could use interpolated milling rather than drilling for holes of limited depth?
Have you tried single flute cutters? I know it sounds mad but they are easy to sharpen and I use them on some difficult stainless steel and carbon steel jobs.
Are you using flood coolant?

- Nick

I could do interpolation, just getting a feel for what others do. Not tried single flute mills but willing to try. No flood on this machine (not yet anyways, and trying to avoid it if I can).

[Chaz]

Have you tried a spiral drilling method using a standard endmill ?

Isnt that the same as 'interpolating'?

[EddyCurrent]

Yes I think it is (spiral drill method is CamBam speak)

[Chaz]

Yes I think it is

I think so too :-)

So certainly an option. Getting round holes round is always interesting. That said, if you need accuracy, you could ream afterwards (assuming slightly undersized hole).

[routercnc]

Hi Chaz,

This is not what you want to hear but I only spot drill on steel, then over to the drill press to finish off. Chinese spindle is way to fast to use as-is, and when slowed down the torque is too low, as you say.

Or I use the methods above and interpolate with an end mill with plenty of oil. You can certainly hear and feel that it is cutting something tougher than aluminium (on my modest router machine anyway).

For aluminium I pilot drill using a 3mm twist drill at 10,000 rpm and peck to the required depth (occasional dab of lubrication). Then over to the drill press or cordless drill to the final size.

On my new machine under construction I have allowed scope to fit an indirect drive WC spindle through a multi-V pulley gearbox to get the speed down (and torque up).

[Chaz]

Hi Chaz,

This is not what you want to hear but I only spot drill on steel, then over to the drill press to finish off. Chinese spindle is way to fast to use as-is, and when slowed down the torque is too low, as you say.

Or I use the methods above and interpolate with an end mill with plenty of oil. You can certainly hear and feel that it is cutting something tougher than aluminium (on my modest router machine anyway).

For aluminium I pilot drill using a 3mm twist drill at 10,000 rpm and peck to the required depth (occasional dab of lubrication). Then over to the drill press or cordless drill to the final size.

On my new machine under construction I have allowed scope to fit an indirect drive WC spindle through a multi-V pulley gearbox to get the speed down (and torque up).

Tell me more about the WC spindle please.

[routercnc]

Tell me more about the WC spindle please.

Might have got you excited over nothing. WC just means water cooled Chinese spindle
See my signature mk 4 build post 86 for where I was making sure design would allow for geared spindle drive