CNC Milling Station Basics

[rcullan]

Hello,
I am in the planning stages of building my own CNC Mill. For the sole purpose of milling primarily 6061-T6 aluminum and A36 carbon steel, for experimental rocketry engine parts. I have a few generic questions. I am a manufacturing engineer with minimal engineering experience, but an extremely well versed in both Pro/Engineer and Solidworks.

I have 2 ideas:

1. Buy a cheap drill press, a standard x-y table.
The benefits of this are obvious all the hard work is done just need to replace the spindle with some more accurate housing, and devise a way of moving the drill housing along the z-axis. The downside, its rather heavy requiring a robust z-axis and will only top out below 3500 RPM.


2. Buy a ton of aluminum t-stock and a router of some sort as my motor/spindle. This is the more expensive route, but probably a bit more reliable. However, router's have too high RPMs and I dont believe i would be able to use normal 1/4 or 3/8 flat end mills with them. They require special router bits i guess which is annoying.

(I am leaning toward #1)

My questions:
1. Opinions on what direction I should go with?

2. What kind of torque should i look for in stepper motors?

3. Where should I get my stepper motors? Anything I could rip them out of?
(I am getting an ancient plotter from work which must have some stepper motors in it, but i doubt its a very high torque)

4. Seeing as I am extremely versed at work with both Solidworks and Pro/E. What softwate should I use to make G-Code from?

5. Anything I might be over looking?

Thanks in advance!

[RICHARD ZASTROW]

Might be helpfull to describe the workpieces you intend to mill. A36 isn't as bad as some materials but it is a bit nasty. Accuracy requirements? If you intend to mill steel, I don't think plotter motors are going to have the "juice" to do but miniscule cuts.

Good Luck.

Dick Z

[rcullan]

Primarily I intend to machine small nozzles for my rockets. Small. Maybe 2" in diameter at the max.

In terms of accuracy. If I could be within .010 that would be great but I suppose I could live with .020 to .030

[ironDigit]

If your planning on producing roundshapes a lathe may be worth considering.

0.02"isn't that bad so most lathes with enough room for a 6/7" claw should cut if operated properly.CNC would be great when dealing with serieproduction and sometimes can save time with one-off's.

lathe ,mill or drill a conversion takes time so in a commercial environment i would buy ready-to-run and consider the learning-curve that comes with a new territory.

Maybe a grizz or horrible&freightening manual lathe and some tooling would form a nice introduction to using these machines and determine what you actually need the machine to do.

meanwhile scoop around for some more info on building ,converting and operating a cnc metalcutter.

Good luck

[rcullan]

Yes I have considered a lathe. However, a mill would be MUCH more helpful.
I could machine a permanent engine test stand, and details into engine housings. A thousand things more.

Also, I plan on eventually adding a 4th axis and using that as a lathe.

I really am looking for advice on both main drive/spindle motor selection as well as sizing torque for a stepper motor to provide enough force to move my axis.

I know there is a way... what is the correlation between torque and liner force provided to a bearing nut on an axis?

[cam1]

Hi:
Please tell me that you are not going to try to use a drill press as a mill.

regards

[LeeWay]

I suggest you take some time and read through some of these build logs.
http://www.cnczone.com/forums/vertical_mill_lathe_project_log/
You will see what some people have been able to do.
A router ain't going to cut steel but just a few times. A drill press is really too weak to do the job, but has been done using parts of it. A round column is generally not desirable but can be used. It is fussy about alignment.
You typical XY table is going to have some backlash that will need to be dealt with, but still possible to do. Some of those build logs will fill in some blanks for you.

[RICHARD ZASTROW]

rcullan, you might find a fourth axis a bit slow to function as a lathe for small part turning. Small parts require fairly high speed to reach cutting speeds for steel much less aluminum. I suggest planning on a lathe in the future.

Even though I don't like them myself, there are mill / lathe combo's available that are more suitable than drill presses converted to mills with a fourth axis functioning as a lathe.

Dick Z

[rcullan]

Thanks Leeway,
I am aware a drill press is too weak for milling purposes. I was planning on using the housing and replacing the spindle with a more robust one and a drawbar for a set of collets. As well as some more accurate bearings.

[RICHARD ZASTROW]

rcullan, You might find what you want for sale here on the 'ZONE

[ironDigit]

i'ld say:
do alot of reading round here.
And if your are determined to produce the parts you are mentioning in any cost effective way in you need a mill a lathe and the approperiate tooling if you start out manually maybe someone could point out some machinery thats "easily" retrofitted in the future.


If you start out cnc rightaway a 4 -axis Horizontal Machining Center would surely cut what you need and in long terms might be just as costly as the home built route ,But when combined with a dedicated training on operating your machine it will save you a crapload a time.

The manual route sure is entertaining and educative but never fast or cheap when it comes to cutting steel rocket parts.

Don't underestimate the importance of reliable and quality measurements when manual but especially when cnc cutting if you want toend up with usable parts.

Don't stop reading round here and try to find a techschool in your area where they might be able/willing to demonstrate or atleast let you snoop around they're machinepark for a couple of mins.

For steppers and steel i would guess to start from 2nm for a x3 or bf-20 size mill and rapidly rising with the size and wight of the mill.For a spindle motor 1kw and no less if you intend to use larger then 1/4" end mills on steel unless you're into encraving

If space is a consideration and only 1 machine can be fitted try golmatic they offer a very reliable design of a mill-lathe combo and conversions can be found on the net though mostly in german.

do you have a budget and time-scale in mind to be in business?

Good luck,

[tmarks11]

Get the right tool for the job.

A drill press is NOT the right tool, and by the time you get done with all your conversion, it will cost more then a mill and will be a pile of cr$%... and to do those conversion right, you will need a mill and a lathe to start with.

A lathe is the right tool, and you will be very frustrated trying to duplicate "lathe work" (ie, boring out nozzles and shaping exhaust cones) with a manual mill (and will find it impossible with a drill press).

If you can't afford an expensive mill and lathe, then buy a mcro mill and a micro lathe. Yes, limited in envelope, but it sounds like the parts you are making are small to begin with. A Sieg x2 mill and 7x12 lathe will run you $900 together (from wttool). Or you can step up one notch, and get the Grizzly G0516 for $1200 (+S&H), which is a decent Sieg C6 10x20 lathe with a Sieg X2 milling head attached. Eventually you will probably ebay or throw away the milling head and get a separate mill, and keep the lathe.

CNC is expensive any way you look at it, and trying to cnc a drill press is like gilding a pig. It is still a pig. You won't get 0.01" accuracy with it even if you cnc it.

If you want to make a router based mill, then take a look at what widgetmaster is offering. He has aluminum frames to hook stepper motors on in the mini-router and mid-router sizes. These might be okay for some small aluminum parts. You can find some interesting stuff here:

http://www.cnczone.com/forums/showthread.php?t=21872
http://www.cnczone.com/forums/showthread.php?t=37739
http://www.widgitmaster.com/

For stepper motors and controllers, try here:
http://www.kelinginc.net/CNCPackage.html

You need CAM software to convert your solidworks files into g-code. Take a look at the Manufacturing/CAM partners list on the Solidworks website to find some of the CAM software: SolidCAM, SprutCAM, SurfCAM, Bob Cad-CAM, EdgeCAM, ON CNC/CAM. Most of these cost thousands of dollars unless you qualify for an educational version.

http://www.solidworks.com/pages/partners/partners.html

Take a look at the separate forums on this website for discussions of these CAM programs.

Buy a mill and lathe, you will be happier. The more they weigh, the happier you will be.