[Roadsidejobshop]

Hello People,

I am in the process of designing an ISO20 spindle for a small CNC mill I'm planning on building. The idea behind the mill is to use it as a production mill for aluminium parts. I would fill up the machine clamps with stock and have the machine work independently for several hours, freeing me up to work on other stuff.

So i was looking at different threads here and on other cnc websites and decided that the ISO30 spindle is way too large for my need. My CNC mill will have a machining area of 330mm(13.1 inches) on x axis, about 300mm (12 inches) on y axis and about 125mm on the Z-axis (5 inches) - fairly small mill then. Having a spindle, whos cartridge is 130mm in diameter and weighs a ton is too much.

So I decided to design a new and smaller spindle for my mill. Currently the design weighs in about 5.5 kilograms (with toolholder(ER16), without motor) and is 160mm high, 80mm in diameter(theoretically I can go one size smaller with the spindle housing, at 70mm, but that leaves only 4mm on the side of the bearing wall). The pullstud is also custom made.
The spindle housing and spindle itself is going to be made from 1045 steel (including toolholders). The bearings are going to be NSK tapered roller bearings, 2x 30206. Upper bearing so far is still open, probably a simple deep groove.
I am planning on using 30206's since I already have them from a previous project (unused) and the 7606 angular contact bearings are too expensive for my blood (almost 100 eur where I live, per pair).

The motor right now is planned to be 3KW BLDC motor, at 48volts. Can go up to 6000RPM. Pullstud is going to be operated by a ball bearing puller. Spring is planned to be either 1500N or 2000N strength (die spring, no bellville washers). The pneumatic piston has a travel of 6mm, diameter of 70mm (piston dia 60mm, 2200N @ 8 bar of pressure).

So far thats it, If i get the spindle built before the year is out, I will be very happy . I will try to make regular updates on the design and build itself.

Thanks!

[Hezz]

The roller bearings will actually be stiffer since there is more contact area than with ball elements. They are often used in high quality large lathes. They should work well at moderate RPM's. Good luck with your future build.

Have you checked out Azalin's BT 30 project on this forum. It's pretty interesting.

http://www.cnczone.com/forums/vertic...0-spindle.html

[Roadsidejobshop]

Hey Hezz,

yeah I checked Azalins spindle thread - very well designed and made spindle . I took some design choices from there (including trying to design a stud gripper like his, but it just would not fit due to available space restrictions).

The datasheet noted that they are rated to 6000RPM with grease, but I doubt I'll go beyond 4500 almost ever.

Thanks!

[G59]

Wait.....handlewanker will more than likely want to have a say here. He is the foremost expert on all things cnc.

Anyways, ISO 20 is suitable for small tool and high rpm.

[Tkamsker]

Hi why Do you use 2 bearings maybe it is more rigid and less Finddeling to use one stronger kone bearings on Front and one on backside (in German kegelrollenlager ) ?


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[Roadsidejobshop]

G59 - yes exactly. I doubt I will ever go above 10mm endmill (and most likely 95% of time between 4 and 6mm endmills). The rpm's are not a problem, since I don't really expect to go above 1000mm/min in feed anyway, since the machine travel is so small. Theoretically, the machine should be able to do 4000mm/min, but I'd rather not slam a table into endstops at full tilt

Tkamsker - I'm using them in that way to stiffen up the spindle. Since the motor I'm planning on using is max 3KW and according to my power requirements I would need about 0.3-0.4 KW in most cutting operations - I would rather have a stronger spindle.

Thanks!

[handlewanker]

Hi....I have ISO 20 on my Skyfire SVM-0 mill......difficulty is to find tooling with that shank taper......I bought ISO 20 tool shanks with ER32 chucks with the mill.

ISO 20 tooling is available on EBAY but only with ER16 chucks.

I highly recommend you go to ISO 30 and design the mill head around that spindle cartridge like Azalin is going to as the tooling is more freely available.

BTW......convention "suggests" that 2 angular contacts at the bottom and a floating deep groove radial at the top works best.

For economy, no need to have a matched pair angular contacts if you space them apart with a spacer as the bearing retainer cap at the bottom does the preload.
Ian.

[G59]

Here is my take on the use of 30206 bearings. They're just fine for what you want to do. Two bearings opposed each other, with preload adjusted and set by a lock nut, and you won't even need a radial bearing to worry about the minimal amount of belt tension.
Your bearings are good for 8500 rpm on grease.
Think how much pressure your cars spindle bearing are under continuously. Your belt tension won't even come close to comparison.

However if you decide to go that route, you'll have to remember to include a warm up cycle before you actually start cutting as roller bearings generate more heat and well, you know, thermal expansion.....

[mactec54]

Hi why Do you use 2 bearings maybe it is more rigid and less Finddeling to use one stronger kone bearings on Front and one on backside (in German kegelrollenlager ) ?


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Because that's a bad Idea, for a spindle like this

[handlewanker]

LOL.........car's spindle bearings???........I'd like to see a car's wheel bearings rotate at 4-5 thousand RPM without heating up........that's take off speed.

As spindles are known to run warm if not hot on occasion, proper planning for a bearing configuration to offset the effects of spindle elongation due to heat build up at the design stage leads to less tears at the running stage......too late to remake a spindle bearing set-up when, for lack of foresight, you skimp on the design requirements.

I expect in the end the means at one's disposal are the prime reasons for a design application, but swimming against the stream is not a recommendation when common practice says otherwise.

BTW.......the belt tension at the top DOES put a wear factor loading on only one side of a deep groove radial bearing, and this can lead to premature wear (looseness) unless the bearing outer race is rotated 180 deg sometime in it's life, but that's being super pedantic when we're just talking about a hobby mill application not heavy industry.

To make sure the bearing set-up is capable of having a reasonable life span and be maintenance free, I would put a double row deep groove sealed bearing or two single radials at the top and forget it/they existed.

A single deep groove radial bearing under belt tension loading.......the belts are going to be timing belts if ATC is in the picture and they are run tighter than Vee belts........ will develop looseness even when ruin in a radial mode that it's designed for and that will be displayed at the cutter.

One way to overcome this is to use another single angular contact bearing at the top in place of the single radial bearing, with spring tension to maintain a tight spindle tracking as it's self adjusting for belt tension forces........but as lubrication and sealing are another problem, that's probably a bit of overkill.
Ian.

[handlewanker]

Oh yeah, I forgot to mention.....design the spindle to eliminate the effects of drawbar impact loading on the bearings.

If I remember correctly, this design requirement was mentioned on the Azalin ISO 30 spindle build with pics, by Mactek54, to illustrate it too I think
Ian.

[G59]

LOL.........car's spindle bearings???........I'd like to see a car's wheel bearings rotate at 4-5 thousand RPM without heating up........that's take off speed.

As spindles are known to run warm if not hot on occasion, proper planning for a bearing configuration to offset the effects of spindle elongation due to heat build up at the design stage leads to less tears at the running stage......too late to remake a spindle bearing set-up when, for lack of foresight, you skimp on the design requirements.

I expect in the end the means at one's disposal are the prime reasons for a design application, but swimming against the stream is not a recommendation when common practice says otherwise.

BTW.......the belt tension at the top DOES put a wear factor loading on only one side of a deep groove radial bearing, and this can lead to premature wear (looseness) unless the bearing outer race is rotated 180 deg sometime in it's life, but that's being super pedantic when we're just talking about a hobby mill application not heavy industry.

To make sure the bearing set-up is capable of having a reasonable life span and be maintenance free, I would put a double row deep groove sealed bearing or two single radials at the top and forget it/they existed.

A single deep groove radial bearing under belt tension loading.......the belts are going to be timing belts if ATC is in the picture and they are run tighter than Vee belts........ will develop looseness even when ruin in a radial mode that it's designed for and that will be displayed at the cutter.

One way to overcome this is to use another single angular contact bearing at the top in place of the single radial bearing, with spring tension to maintain a tight spindle tracking as it's self adjusting for belt tension forces........but as lubrication and sealing are another problem, that's probably a bit of overkill.
Ian.

Again???
You are WRONG on so many fronts.

[ynneb]

Ha ha, its been years since I have posted in this forum and many months since I have visited it, yet the very first post I have looked at, this one, seems to need moderation. (Despair )
I see that it is a project log and hijacked by others disagreeing. Please remove your unwanted bickering and give this man back his thread. I will also remove this post once you have removed yours.