CNC spindle thoughts.

[kcmillin]

I am seriously considering building a CNC machine from scratch. I am hoping to be able to mill aluminum and possibly steel with up to a 3/8" to 1/2" and mill. I cannot find what I am looking for in ready to go machines for less than $2000 Three words "Capacity Capacity Capacity" I would like to get 12"x18"x5" of movement.

What are my options for a machine spindle? I was thinking about making an ER16 spindle from scratch, but don't know what to use for bearings or a motor. Could a variable speed router be connected via pullys to a spindle? I would like to get the rpm's from 500-1000 on the low end, and up to 10,000 or more.

Another thought was to use an X2 spindle. Are there any other ready to go options I can consider?

Kel

 

[Admiral_dk]

Almost all continental European "home build" CNC machines use a Kress "mill head" see :
http://www.kress-elektrik.com/Products.55+M52087573ab0.0.html

and go down to "Milling Tools". I'd tried to post a direct link, but it didn't work.

You can get 3, 4, 5 & 6mm. metric and 1/8", 3/16" & 1/4" (and maybe more) collects to it. Got a 1050 FME myself and it's a high quality tool + it's a standard 43mm. mount.

 

[mu38&Bg#]

Perfect timing. I'm going to start a spindle in the next couple weeks. I learned of making a milling spindle here. I've designed my own and after chasing down bearings on Ebay and ready to begin. Well, after I finish the current customer project. I decided to get real spindle bearings. I have 1 1/2 sets Barden 104HDL. I'm going to use a CTC tools 20mm shank ER16 collet holder (extension). The brushless motor will be from Neu Motors and it will be controlled by an industrial Aveox brushless motor control, but AMC or other brushless motor control would work. I've attached a sketch of my spindle. I have three different layouts, but I think I'm going to use this one. Almost forgot, Max RPM is 36k, about the max the bearings are rated for on grease. I do a lot of small milling even with 1/16" endmills and I feed at up to 20IPM in aluminum and some steel. I hope to replace my current old Precise Super 45 grinding spindle to get better performance and greater dept of cut.

I see the forum resized the image, so right click and select view image for a readable version.

Greg

 

[kcmillin]

I like that Idea Greg.

Are the bearings tapered? How are they pressed into the housing and onto the shaft? Did you have to modify the ER16 collet chuck?

Sorry for all the questions.

Kel

 

[mu38&Bg#]

Bearings are angular contact ball bearings. Forget buying new, they cost something like 150USD each. Ebay price is under 50 for a pair.

These bearings generally don't get pressed. The front pair is clamped by the ring that is screwed in and the rear bearing is spring preloaded and floats. The bearings are clamped on the shaft at the top. The tapered nose piece is a press fit onto the collet holder. No mods to the holder, it's hardened (probably).

Greg

 

[BillC]

Hey Greg and kel,

Magnito bearings (angular contact ball) work fine and are available in quite a few standard sizes. I've used them for high speed grinding spindles but I needed to spring load (bellville washers) the bearing opposite the load thrust bearing to compensate for heat. That spindle will get hot! Speed makes heat.

The Motor will be excellent until it begins to slip without some feedback to the controller, then you will make heat. Close loop feedback to the controller to compensate for load. That's a hungry motor too - probably wound Y for power...?

BillC

 

[mu38&Bg#]

I'm a bit concerned what idle current will be in the spindle. I do have a water cooling setup that should be adequate. I was thinking about working a fan in somewhere, but there is little room. The brushless DC motor is efficient and should not run hot unless the bearing preload is substantial. The motor control uses hall effect sensors for position so there is no slip. The motor is used at 3kW in some applications and my controller is only good for 500W, so I'm hoping idle current is not excessive. Another controller could be sourced if needed. If the spindle is successful, a grinder for the lathe is also in the books.

Download the Timken, NSK, or other bearing suppliers machine tool bearing catalogs and read through the engineering data for an idea of what goes in to these things.

http://www.timken.com/en-us/products/Documents/5918_09-09-29.pdf

Greg

 

[mu38&Bg#]

Ebay 280641223147 This is the kind of bearing you are after.

 

[BillC]

Yeah, it gets complex Greg, to be sure. But if you look at the specific purpose for the spindle, you do not need super precision angular contact bearings. The set-up and housing precision is the primary concern for any bearing whether it costs $1000 or $10. Either will be destroyed due to improper set-up and preload. The main concern is the heat generated and a means of lubricating the bearings without an oil feed system that will spray hot oil from the end of the quill. You will need a seal there - labyrinth works... The thermal expansion of the entire quill is a major concern as well and since angular contact bearing require a specific preload, the thermal growth of the quill will certainly become a problem. Loose bearings destroy themselves.

I have a design for both a bellville spring preloaded or a simple multiple compression spring preloaded high speed spindle. But for the milling machine that kel is after - it may not be what he will need. He needs a spindle with massive side load capacity. A milling spindle....

BillC

 

[mu38&Bg#]

It's my understanding that high speed milling spindles are built this way today. Those are the suggested applications in the engineering catalogs for the bearings. The bearings give appropriate design guidlines for the housing, thermal expansion, etc,. If limited to a 3/8" cutter by ER16 rapid material removal can only be had with high speed, in aluminum at least. In steel you'll be limited by surface speed in most cases. Super precision is required to get decent runout for tool life. I've broken a few 1/4" carbide endmills in the tiny Precise grinding spindle and the bearings are the same as they have always been.

I considered the need for larger tooling and though briefly about making a similar but reduced speed spindle using a ER32 or 40 setup. I've decided to see how this works out.

My design has a DB arrangement pair in the nose and a single spring loaded bearing in the top. The chances of exceeding the load capability of the bearings in my small mill is not likely. The rigidity isn't there. Based on my experience so far, its' going to take a solid mill to run a 1/4" tool at 30kRPM at any significant feedrate or depth of cut and have a usable part afterwards. The machine base is likely the limiting factor. I'm far more concerned about my ability to machine a housing to the required tolerances.

 

[lordedmond]

I know you are not in the UK but would these not do the job
http://www.arceurotrade.co.uk/Catalogue/High-Speed-Spindles-Motors-Inverters



Stuart

 

[LongRat]

I scratch built a medium duty CNC router for a friend of mine. I went with the Kress router head. Do not underestimate the capability of this unit, it has good power, stiffness and the one I used had only 2 microns of runout. It can cut metal pretty well. The only downside is that it doesn't do well much below 10,000 RPM. I like the look of the Arc Euro Trade spindles (and the Japanese VFD they sell with them) and would likely go with them if I did it again. More expensive, but heavier duty again and they use ER collets - much more versatile.

 

[kcmillin]

Those high speed spindles look great, perhaps they could be an add on later, but for now (like BillC stated) I am more interested in the milling aspect. I currently use a 2hp mill/drill that runs at lower speeds, and I rarely use the fastest speed.

What kind of performance can I expect from an X2 spindle and motor setup? I don't need to make monster cuts since the computer can make multiple passes in a breeze.

Perhaps just an X2 spindle with a higher wattage, or brushless motor would work.

Kel

 

[kcmillin]

Just had another thought.

I have an home audio dedicated 100watt amplifier of high quality (It can really move a pair of 10" subwoofers ) It plugs into the wall, and has a volume nob on it. Since speakers run on DC current the amplifier essentially is a DC power supply.

My thought was can I use an audio amplifier as a DC power supply? I would need some kind of smooth input signal. OOOOOOOH, if you could vary the frequency of the input signal would that make it a VFD?

Thoughts.

Kel

 

[Jakeman]

I have an home audio dedicated 100watt amplifier of high quality. Since speakers run on DC current the amplifier essentially is a DC power supply.

My thought was can I use an audio amplifier as a DC power supply? I would need some kind of smooth input signal. OOOOOOOH, if you could vary the frequency of the input signal would that make it a VFD?
Kel

Kel, this idea has actually been used a long time ago in labs, but only for weird testing setups. Not very practical, I think. Because 1 horsepower = 746 watts, your 100 watt (per channel?) amp could only deliver about 1/8 HP (100/746) to your spindle motor. Actually a lot less, because the 100 watt rating is probably some silly "music" peak power rating instead of real continuous power. There are other problems as well.
To make a VFD, you have to vary voltage as well as frequency and almost always need 3 phase output.
Sorry, but you could build a variable speed drive for less trouble than getting the audio amp to work
On trash day, check curbs for discarded treadmills. They have a DC motor with good power and a variable speed drive in them! I don't think the drive's speed regulation is great, though. Don't try this unless you know exactly what you're doing because the treadmill stuff is not isolated from the ac power line and can kill you.
Good luck!
Don

 

[steamer]

HI,

I think your going to run out of power fast with that drive. At 36000 rpm and 500W you will have about 1.2 inch pounds of torque TOTAL Then you must subtract the motor efficiency, bearing preload and any seal torque, though it looks like you went labirynth there.....What ever is left is what you can cut with.......More Power Scotty! ;D

At 3 KW, you will probably need some cooling. What is the motor efficiency? and voltage?

Dave

 

[mu38&Bg#]

I purchased, a while ago now, a minimill spindle to put on my machine, but never got around to setting it up. It all depends on what you'll be doing. I often cut foam for lost foam fiberglass parts and need high RPM. Most of my CNC metal milling is small and also needs high RPM for a reasonable feed rate. Now I have a manual mill for facing and squaring stock, so I gave up on heavier cutting for the small cnc.

The spindle I use now is a series universal motor. I don't run it off line voltage but a DC power supply. I usually set it to 40V and it never draws more than 2.5A or so under load. I think it's about 1A idle. Anything will be better than this. The planned motor is very efficient at over 80% through the expected range and can exceed 90% when loaded appropriately. More power is no problem, just a larger motor control. I could use one of my RC controllers to run as much current as I want, but I'm unsure how I would integrate it into the machine control.

 

[steamer]

hmmm I would bet that control is an analog voltage ...like maybe +/- 5v or something.....

Dave

 

[mu38&Bg#]

The RC (radio control) brushless controller uses 50-60Hz PWM for input signal. I don't use a machine board so the PC output is roughly 0-5V. Most industrial controls are 0-10V, and most of the machine boards can accommodate that.

 

[mu38&Bg#]

Well it looks like today I begin building my spindle. The one I've had for years with probably almost 1000 hours on it wore out the brushes. I replaced them with hardware store brushes which it promptly devoured in maybe 10 hours. For now I'll stick with my initial plan. New thread here.