Building a milling machine

[870Fragmaster]

Someday, I would like to build a mid-sized, robust cnc gantry mill for machining steel and aluminum. Right now I'm collecting infor mation on the manufacturing processes/skills involved. Does anyone know of good source of information about the mechanics of building a machine from scratch? Are there any sources on the internet? I have not found much. I have ordered Gingery's book on the coal fired furnace and building a lathe. They have not come in yet so I don't know what kind of info is contained in them. I have seen web pages where a few people have made small stuff, but that is 1, small and 2, not robust enough.

Some questions for example:
1. what kind of ways should be used in different situations?
2. do you buy or make the ways?
3. if you can make the ways how?
4. how do you go about mounting the ways?
a. fastening
1. machine out of cast?
2. bolt?
c. alignment
5. what kind of bearing/sleeves whatever would you use on the spindle?

these are some of my thougths, im sure there is a large can of worms here that could be spilled . but i think it is a fun topic to think about. Does anyone have any thoughts to contribute?

[metal mite]

Frag,

That would be an impressive project.

I would put a milling head on an old planer.

Considering time and materials required, you may be better off in the used machinery market purchasing something already proved out.

Machinery designers have spent millions of
R&D dollars, designing these machines. I don't think I would be capable designing and building one first time out.

Some old jig bores (sip and others) are configured this way and go really cheap these days.

mite

[Alistair Hosie]

I gave this notion of yours some consideration however metal mite is right I dont think it would be easy to get the rigidity required,and at the same time the flexibility to cut without binding.There is a device which cuts in a similar manner for wood its called an overhead router,I contenplated making one with a standard router attached to an old photo enlarger to give the vertical movement but by the time you went out and purchased a table or made one with good x.y coordination the whole thing would probably be uneconomical but I would love to hear how you progress you could also use an old small lathe for the vertical post I'm not sure if it would work but i'm sure half the achieve,ment is the fun of overcoming problems encountered along the way so long as you are not in a hurryI also thought that it might be possible to utilize parts from an old chisel moticer.Alistair

[Rotate]

>1. what kind of ways should be used in different situations?

dovetail made out of cast iron, flame hardened and ground.
>2. do you buy or make the ways?

You can buy, but they are pretty expensive (Reid sells thems), however machining them yourself won't be that much less expensive (price out some gray cast iron stock).

>3. if you can make the ways how?

You'll need a milling machine to do this. As noted above, you'll need to machine the surface and the dovetail profile.
>4. how do you go about mounting the ways?

Use cast iron gibs for the carriage. The ways themselves can be bolted down to the table.
>a. fastening

Bolts.
>1. machine out of cast?

Yes.
>2. bolt?

Yes.
>c. alignment

Using dial indicator and precision square should yield good accuracy.
>5. what kind of bearing/sleeves whatever would you use on the spindle?

No simple answer for this one. As long as they are ABEC 5 or better and they can sustain both the axial and radial load, there are many type of bearings that will do the job. It's all a function of the load, life expectation, and rpm.

Sounds exciting. Go for it and let us know how it turns out.

Albert

[870Fragmaster]

It will be a while before I ever get around to it. Got to get out of grad school and then start piecing it together. I figured it would cost a lot to build one, but like Alistair Hosie said, the fun of it is overcoming problems and developing innovative solutions along the way. If I keep an eye out for scap there is no telling what I can find.

I heard a few people mention gibs what are these?

The best example of what I would like, but in a much larger example is an Arboga that I had the oppertunity to use to make some molds for a university design competition. Little bit of overkill, but it was available Here is the link to a picture.

http://www.me.msstate.edu/CIM/pics/arboga.jpg

Figured I would make something like this. From the picture you can see that the X axis has box shaped ways and I think the Z axis does too. I havent been able to see the Y axis because it is covered up.

If you make your own ways, do you machine it as close as possible and then lap it? And if I dont have access to a large surface plate how do i check its accuracy along its length?

For the bed, I have thought to use a large plate of steel and then weld a stiffening lattice underneath using some flat bar welded perpendicular to the plane of the plate. The supports for the Y axis would be attached to this. Something like the concrete pad in the picture.

Thanks for the replies so far!

[Thrud]

870Fragmaster:
Precison Ball Bearing Profiled Rails are used on almost all newer machines. They save so much money in machining costs that they are the best solution for one-offs.

Mannesmann/Rexroth, Thomson Industries, and INA have engineering departments that can assist in proper application in their motion control products (Rails, ball screws, servos, etc.). You can find them on www.thomasregister.com

I think Metal Mite is right in saying convert and old planer over. That may be the cheapest way to get a "cheap" gantry mill of large proportions.

[jcurrell]

I got a very nice 6600 pound verlical mill with a # 50 taper for 1500.00 off e-bay and it is 10 times the machine I could ever make.

------------------

[metal mite]

jcurrel,
You got it.
You couldn't make the patterns for $1500.
What kind of mill is it?
Green with envy.
mite

[metal mite]

Fragmaster,
Seriously, I would advise you start with a smaller less ambitious project.
You may get into some problem and become disheartned with the whole deal.
There is the Quorn Grinder (MAKES THRUDS HEART THROB) , and Westburys Vertical mill
to get your feet wet.
Just an idea!
mite

[Rotate]

Thrud,

"Precison Ball Bearing Profiled Rails", are these adjustable or are the bearing mount and the rails machined so precisley that there's no play? Surely they are not as stiff and durable as cast iron way with dovetail profile (provided they are similar in size)?

I've seen some self lubricating ceremic bearings which come in strips (no balls). I think INA and Pacific Bearings make them. Are these suitable for milling/lathe applications?


Albert

[Alistair Hosie]

FRAG AS FAR AS THE C.N.C DEVELOPEMENT IS CONCERNED WHY NOT ASK www.ShopBotTools.com they may be able to offer some advice i'm not sureAlistair

[Thrud]

Albert

The rails are high strength hardened steel alloys sized appropriately for the load in question. The bearing packs in the highest grades are essentially slop free. Everything comes at a price, of course. The very large units support hundreds of thousands of pounds and except for the high moment of inertia associated with such heavy weights the loads are far easier to move than any standard slides. They can be ordered with rail wipers to greatly enhance service life. They require less machine work to get better results - although it could be argued a hand scraped machine carefully set up might be a little more precise - but it is doubtful. They are part of the reason complete CNC machines of high quality now start at $20K (US).

Even though they are extremely expensive they still cost less to install than machining those big dovetails. When they wear out (usually from lousy maintenance) it is so much cheaper to bring the machine back to "like new".

The Silicon Nitride Balls are most likely the next step in their evolution but I do not believe they are being used in them yet - they are normally reserved for extreme duty (corrosive, high temperatures) use in turbines and pulp mill bearings and such.

Low friction strips have been around since Teflon was discovered by accident. The ceramic stuff should be more resistant to scuffing than thermoplastics.

[This message has been edited by Thrud (edited 05-22-2002).]

[870Fragmaster]

thanks for the replies guys!