HY VFD and spindle at low speed

[Jonathan]

Fossilised somewhere on this forum (4-5 yrs ago) there's a thread/post where I've discussed how to get more torque from the common 2.2kW spindle and HY VFD combination at low speed. Essentially you use the voltage vs frequency mapping settings to boost the voltage applied to the spindle at low speed. This will put more current through the stator windings, so in my case I had something like 2-3 amps read by the VFD at just 4800rpm, but it did give me enough extra torque to drill aluminium with a 4.2mm HSS drill at that speed.

Adding extra heat in the stator is not too big a deal - in theory you could go all the way to the current rating of the winding, and a bit more as the iron losses should stay fairly small at low speed. However this will induce extra current in the rotor, which is much harder to get the heat out as it's not directly water cooled. I did once characterise the 2.2kW spindle to find the equivalent circuit, so you can work out how much current is permissible in the stator to have the same rotor losses as it was designed for. How much torque you actually get out of this is harder to say though, as we don't know the saturation characteristic of the stator. Not sure where that spreadsheet is now though.... so I suggest you increase the voltage until you see a few amps with no load and see if it's enough.

Another approach is to use a cutter with the right coating to enable raising the spindle speed. These have worked well for me:
https://www.shop-apt.co.uk/carbide-e...ted-65hrc.html

[Neale]

Thanks, Jonathan. I'll have a search back through forum history - I hadn't remembered this one being discussed before. My own background is electronics rather than electrics so while I understand the basics, I'm a bit hazy as to exactly what happens inside these motors. However, my thinking had also been to tweak the VF curve at the bottom end - thanks for the suggestion of using motor current to get a bit of insight.

This is the first time I have ever seriously used carbide milling cutters. I've generally used HSS on the mill and carbide for routing wood but I've been driven to carbide cutters because of this minimum spindle speed issue. I bought the ones I am using after a quick bit of web browsing but along with the cutters I was sent an enormous catalogue and looking at that, I see that there are indeed cutters that might be more suitable - at a slightly higher price... My concern about those is breaking them, either due to running them into a clamp (it happens!) or vibration/resonance due to a less than optimally-rigid structure. Ok, my machine is all welded steel with profile rails and ballscrews, but I'm still surprised-but-pleased that I can cut steel at all.

Those APT cutters look like a good deal so I'll do a bit more research down that line as well.