Tiny CNC mill project

[chuckknigh]

OK, the recent activity has re-inspired me to do my CNC mill project. As I understand it, a CNC mill differs from a router primarily in precision and rigidity...it's a machining setup, more than a woodworking setup. I still have no aspirations beyond brass and aluminum, but a smaller and more rigid machine would be nice for light metalworking and extra-hard woods.

JCK's Hawk project is a good example of what I'm calling a mill.

Well, a while back I bought a small cross slide vice for just this purpose. It should provide a reasonably precise X-Y setup, and as it's made from cast iron with dovetailed ways, it should be very stiff and very good. Roughly 4x6" of travel.

It's a cheap Chinese unit, but the price was right ($20), and with some work it should make a good and cheap unit. Primarily new lead screws (I'm upgrading to hardware store allthread!) mounted in BEARINGS, and some adjusting/tightening of a few parts. It's a pretty well designed little unit, but with a few minor problems...like poorly designed bushings.

Here's a picture...



Now...the Z axis. I'd prefer not reinventing the wheel, so to say. The X-Y unit was almost predesigned...is there is single axis sliding vise? Some elegant way to make a bolt on Z axis? I could do another X-Y vise, mounted vertically, and just not use one of the axes...but that seems silly.

Anyone have a simple, elegant, and reasonably easy to build Z axis design? I'm wondering if a $5 machinist's vise from Harbor Freight would be sufficiently precise...bolt a router mount to the movable jaw, and just bolt it onto a vertical support.



Obvoiusly the leadscrew would have to be replaced for decent function, but this might work, if there's no lateral play. Surely there's a better, though still cheaply priced alternative to this approach.

I'm trying to do this on the ultra-cheap...basically, to see if it can be done...with off the shelf parts. I could do the window channel routine, and I even have some of it, but I'm not sure that would provide as much rigidity as even a cheap cast iron vise...proably better precision, though. I'm trying to stay away from the "buy some 5 inch long THK rails on eBay" routine, though, since it's not repeatable.

Comments? Suggestions? All are welcome! Help me make this project a success...

-- Chuck Knight

[chuckknigh]

Well, I've got all my supplies to make the mechanical portion of my mill. I've got the cross slide vise, some nylon insert sleeves (to act as nuts for the leadscrews), some old rollerblades, and 3 feet of hardware store allthread.

I'm ready to build a precision machine. :-) I know...it still sounds weird to me, and I've done it before!

OK...time for a request.

Does anyone have an elegant way to build a Z axis? I could just recycle my drill press, but its bearings aren't designed for side loading. Surely someone has a simple way to make a Z axis, without all the hoopla involved with rollerblades on black pipe and MDF sleds. I could do the aluminum channel trick, but I prefer it be easily repeatable for others, as well.

-- Chuck Knight

[rippersoft]

I am building my first machine and have studied everything I can get my hands on. For the Z-axis, I have settled on 3/4 drawer slides mounted to plywood. As long as the slides are straight and square, it will work. I also use drawer slides for the Y-axis that carries the spindle assembly with the Z-axis back and forth.

[RotarySMP]

Buy a cheap angle plate from ebay. That way you can get a good right angl neck. Make the dove tail parts out of CRS by filing, like I did for my cross slide.

[chuckknigh]

Thanks, Ripper. I'm trying for something with more precision than drawer glides, since this one is intended to be a mill...but it's a good suggestion. I've heard of people who get EXCELLENT results with ball bearing drawer slides on their routers.

Of course, the only drawer slides I have on-hand are 18" long, and are bizarre for my application! I don't want to go spend *money!* ;-) Heck, a decent drawer glide is in the neighborhood of $20 at Home Depot...not horrible, but definitely out of my self-imposed budget...this project is getting done on the cheap!



OK, take a look at my cross slide vise. It is a pair of sliding axes at right angles to one another. Once I upgrade the screws to something less bad than the Chinese ACME thread, it should work quite effectively for a small machine...and being solid cast iron with dovetail ways it should deliver some serious results despite its somewhat diminuitive size.

What I want for my Z axis is something equally beefy and precise, but still ridiculously cheap! Hey, I only paid $20 for the vise...and that's 2/3 of my machine, right there! :-) I intend to make clock parts from hardwoods, brass, and aluminum...definitely on the softer end for milling, but still tough stuff for the average router to handle. That's why I'm using a cast iron vise for the main "body" of the mill.

RotarySMP -- OK, I'm with you on the angle plate. An excellent idea...I've never built a mill before, so I was wondering about coming up with a mount that was perfectly orthogonal to my X and Y axes. But, what is CRS? You've piqued my curiosity...

-- Chuck Knight

[RotarySMP]

CRS is cold rolled steel. It is just steel the has a pretty good surface finish and is reasonably square when you buy it.

If you want to do things cheap but with reasonable rigidity, then get stuck into some steel with a file. Make nice dovetails, lap and scrape, bolt and bond the bits to a big angle plate. Realise though that you will never be happy with this set up! At best you will get something which then frustrates you due to the severely limited travel. The big killer is tooling. You need a fair bit of Z travel to allow tool changing.

[chuckknigh]

OK...I was thinking CRS = Composite something or another. With all the talk of Moglice, et al, it's easy to go off on that tangent.

Thank you for such good ideas.

Could you define "fair amount of Z travel" for me? I've not built a mill, before...and my router only requires a few inches.

-- Chuck Knight

[RotarySMP]

What will you use as a cutter spindle?

[chuckknigh]

The honest truth is, I don't yet know.

To start with, I'll probably use something cheap out of my woodworking shop, like a RotoZip. This isn't intended to make 1" deep cuts through tungsten...just, at most, brass and aluminum, and probably more like stable and extremely hard woods.

Nevertheless, I will be keeping my eyes open for a proper spindle on the used market.

-- Chuck Knight

[RotarySMP]

Don't know the rotozip, but you need to take into account the depth needed to remove the tool holder from the spindle.

On a MT3 taper milling machine, you have the tool length range from a 1/4" end mill in an MT collet (say 1" protrusion from the spindle to nose) through to a 1/2" twist drill held in a chuck on an MT arbor (might have 6" protrusion fro the spindle nose).

Using a router as a spindle limits the size holes you can drill to quite small ones, because of the high minimum spindle speed. Holes are suposed to be over 50% of all engineering features.

I choose Sherline industrials ER16 collet spindle for my mill. The ER16 collets are good to 10mm tool holding, are quite short, and are reported to friction drive with about 200# draw bar pull if you want to make tool holders and not use collets.

Haven't finished it yet.
http://www.wrathall.com/Interests/CN...nkenDeckel.htm

[JavaDog]

Originally Posted by RotarySMP Using a router as a spindle limits the size holes you can drill to quite small ones, because of the high minimum spindle speed. Holes are suposed to be over 50% of all engineering features.

I may be wrong (and correct me if I am) but with a high-speed router - when you are drilling holes, don't you just use a slower feed rate on the Z-Axis to compensate?

[RotarySMP]

Trying to drive a 10mm drill through metal at 10 000rpm slowly, with a low rigidity mill will give you some scary chatter. Larger drills need quite hi feed rates.