Designing a Metal milling bushless Spindle

Hi all,
im new to Diy CNC'ing in general & finally bit the bullet & started ordering parts for my own 3-axis router. i started ordering the parts looking at the Target'ed work envelope & pretty soon i realized that it would be better if i start building the machine around the Spindle. therein lies my problem as i would like to mill metal & i would appreciate some help from you guys collective experiences.

at the moment im researching brushless motor choices against:

1. power requirements(W)
2. Suitable Kv(RPM/V)
3. power source (coupling matched pairs in series &/or parrellel to reach the target motor operating range- not necessarily motor max)
4. shaft diameter & coupling method(ie:- replacing the motor shaft with the collet shank / end-to-end-lovejoy type / threading the motor shaft & screwing it into the collet shank) ect.

as a compromise for spindle stability vs bearing RPM Max vs target RPM for metal, i figure a 12mm shank dia was a good starting point so i went ahead & bought a "C12 ER16 100mm collet chuck shank" along with 2 matching single row a/c bearings & a radial bearing(good for 20k on oil).

im hoping i'm on the right track so far,

im really hoping you guys can point me in the right direction on the points listed, and any others i need to be aware of. how would you go about tackling this build?
hopefully this will turn out into a dedicated build log.
Thanks,
Kevin

http://www.mycncuk.com/forums/showthread.php?t=3793

That thread may interest you!

Many of the larger motors are around 500kv, these motors allow you to replace the motor shaft with the collet system.

You can use higher kv spindles but their diameter reduces and the vibration obviously becomes worse and needs balancing.

Another good spindle totally re made to test your engineering skills,

http://www.dieselrc.com/projects/cncspindle/

I have my 450kv motor running on a 24v power souce using a 100a speed controller, i rarely go over the limit of the power supply and trip it, but when i do its usualy an error!

There will be more experience people along soon to help with the bits i cant :) and of course welcome!

thanks totts,
i read both of them, the dieselRc build is impressive, but lacking in detail as to how & why regarding motor choice vs power requiements to cut metal. ie, typical spindle rpm/feed rate/depth of cut ect...
yours is approx 10k rpm, what kind of feed rates & depths is it comfortable with? im assuming you have an ER collet series?

Hi, yes it is a bit vage! My cnc isnt highly robust so roughing cuts are usually a 6mm slot drill 0.5 deep at around 6000rpm, usually at 200mm/m. I do a lot of engraving so its usually running flat out, but finding i need higher rpm, so currently finding other solutions. There are calculations that can be used to find the apropriate speeds and feeds, but machine stability limits these.
I currently have a er20 set up as this will cope upto 13mm shanks which is ideal for 1/2" shanks.

Hope this helps.

finally recieved all the parts to start designing the spindle, pretty much whats been seen on the forum. Attachment 8129. the motor is a NTM Prodrive 35-42 1000kv unit from HK. Im targeting 12k RPM as its my bearings upper limit, on a yet to be converted ATX PSU.
.

Im guessing it should be 1000kv? On a 12v atx power supply?

Have you got a link for that motor?

What size shaft has it got?

I may have to make another spindle for the higher rpm ..... Look what you have done haha.

my mistake, it is 1000kv, on a 12v atx PSU. NTM Prop Drive 35-42 Series 1000KV / 700W shaft is 4mm, but im using a coupler bolted to the motor housing & clamped at the ER shaft end.

Attachment 8140

Ahhh i seee now! Hopefully you wont get any vibration / miss alignment from the joint, keep us posted!

well, i got the spindle done!.. Attachment 8756

a shot of the coupler, i had to redesign it to clamp the shaft using grub-screws. the entire construction is using EN19.

Attachment 8760