My Denford currently has a 1.5 HP DC Motor controller with the original Sprint 1200 controller. The RPM on this is 4000 rpm which then runs via a belt at a set of gears at a 1:1 ratio and in turn runs the spindle at 4000 RPM.

Based on some calculations (FSWizard) and similar, I should be able to cut the type of speeds and feeds that I require in Aluminium with relative ease. My biggest drawback at the moment is the low RPM. On that basis, I have to feed slower.

Something that concerns me is that I have stalled the spindle before. I am using flood coolant most of the time and I tend not to be aggressive on speeds / feeds and WOC / DOC. For example, if using something like a 6mm 2 flute carbide with no coating, I will cut no more than 2mm deep when doing profiling. I am still experimenting with different options for plunging and ramping down based on all the options in Fusion 360 (which is excellent btw).

I have also blown the 10Amp fuse that feeds the board numerous times when the spindle stalls, not good but I keep the fuses in bulk for when it happens.

So, question time.

How 'strong' is this DC setup? If FSWizard indicates I only need 0.5 HP (For example), surely the DC spindle should be able to manage? Could there be a setup problem with the DC drive (ie, just not setup correctly)? The fact that it is blowing 10A fuses implies its taking full power. On Saturday I had the spindle start to act odd, I need to see why but it runs and blows the fuse now when I power my mill (even before I ask for a spindle run).

So, options ....

Do I replace the Sprint controller with a modern isolated version for £170ish excluding VAT?

Do I spend £470 on a 4KW liquid cooled Chinese spindle with suitable VFD? Are they really able to deliver 4KW? From what I can see, I can probably cut a new plate (if I can get my spindle working properly) and get a 10 tooth gear onto the motor. The current gearing is 18 / 18 tooth. So this will take me to a max speed of 13300 RPM which will be good however I dont know if the system will have enough torque.

What does the torque / speed curves look like on them?

I would also likely need to replace the bearings on the spindle, additional cost.

If I now run at 10:18 gearing, the slowest speed is probably around 3000 rpm, but can it actually cut anything at that slow speed (lack of torque)?

Thanks