Torque / Speed curves for different Spindle Types

[Chaz]

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

[JAZZCNC]

Back Charl so I'll answer here rather than email.!

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).

It's only a guide so wouldn't pay too much attention has even same grade of materials can cut different from batch to batch.
check out the controller setup and wiring first if blowing fuses. Often blowing fuses for no obvious reason is a sign somethings on it's way out.!!

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

No I wouldn't do that I'd look at alternatives.?

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.

But not this alternative.? . . . It's more of routing spindle with high speed and low -ish torque and only at the rated speed is torque any good which is too fast.
Also you have to bare in mind the Spindle bearings and there speed rating. If Max speed was 4000rpm then I very much doubt the Spindle bearings will be rated for 13000rpm.!!

I'd look to replace the DC motor with AC asyncronous Motor like this one but the correct size for your needs which is the correct tool for the job.!
http://www.alibaba.com/product-detai...57.35.1.xZ2e8p

[Chaz]

Thanks Dean.

Ironically, the top bearing is rated 11K and 13K RPM (oil / grease) but I dont know the number on the lower bearings (they are different). The top bearing is a Nachi 6007ZE (I took the spindle out to measure up a replacement plate but have not yet dropped the spindle out.

Ill take a look at that option. There is a guy on utoob that has converted his Triac to a 2,2 KW Chinese spindle and seems happy with it. Trying to get some further information from him.

At present too on the non isolated version I have, speed control is manual via a pot. Not ideal, will be nice to go 'auto'.

[JAZZCNC]

There is a guy on utoob that has converted his Triac to a 2,2 KW Chinese spindle and seems happy with it. Trying to get some further information from him.

Depends on how he's doing it I suppose. What's acceptable to him might not be for you.!! . . . I definatley wouldn't replace the main spindle with a 2.2Kw spindle has it will spoil the machine but would possible use it to drive the main spindle with a ratio to increase torque and lower 2.2kw spindle speed to match Main spindle bearings.?

If you want to try this I can lend you a 2.2Kw spindle and VFD. Thou it would be a lot work to find out it's not much good.!!

[Chaz]

Depends on how he's doing it I suppose. What's acceptable to him might not be for you.!! . . . I definatley wouldn't replace the main spindle with a 2.2Kw spindle has it will spoil the machine but would possible use it to drive the main spindle with a ratio to increase torque and lower 2.2kw spindle speed to match Main spindle bearings.?

If you want to try this I can lend you a 2.2Kw spindle and VFD. Thou it would be a lot work to find out it's not much good.!!

I was thinking to gear it 10:18. I suppose I could find a different belt / pulley setup. This is the smallest I can find (easily) to go (10) using the stock setup.

This lowers the speed to almost half and should therefore provide almost double the torque. Its a pity that the removed Servo motors are a bit small, else they would be ideal, specifically with closed loop control. They also do 8K RPM, worth a look at all?

[JAZZCNC]

Its a pity that the removed Servo motors are a bit small, else they would be ideal, specifically with closed loop control. They also do 8K RPM, worth a look at all?

Yes worth a look because it's linear torque so there rating will be higher than the 2.2Kw at lower speeds because the torque on these falls away quickly when speed is lowered unless using a more expensive Vector drive and this isn't always possible depending on the VFD make.?

Servo will offer more torque across the speed range.! . . . . You can get some largish and Cheap Servo drives from ali-express so may be worth a look and it will make a proper job of it.!