CNC Surprises
September 18th, 2014No Cigar
I feel like updating the saga of my CNC progress. I have learned a great deal about CNC, but in relation to the amount that I need to know in order to be competent, I know just about nothing.
First thing: do not build a CNC lathe. Do not even waste your time. A mill will do nearly everything a lathe will do, plus a million things a lathe can’t begin to do. You can thread with a mill. You can turn parts with a mill. You don’t want a lathe. Believe me. And if you have a lathe, no one will want to help you, because only about 10% of CNC hobbyists use lathes. Even software makers ignore us.
Second thing: precision is expensive. You can fix a machine so the computer compensates for backlash. But it doesn’t actually work. Say you’re milling a round hole instead of boring. You have to make the cutter travel in a big circle, as well as rotating. Every time an axis changes direction, you’re going to get error due to backlash. The only way to get rid of it is to use ballscrews, and cheap ballscrews don’t really work, although they may make you feel good. On the web, people with cheap screws talk about backlash figures between 0.005″ and 0.010″, which is huge.
When I got ready to build my lathe, I figured the machinery itself would be simple to create. The plans I bought didn’t mention ballscrews. Then I got it running and found out I had 0.018″ of backlash on the z screw. The software compensates on simple parts, and that’s very good. It’s worth a lot. I can do a lot of stuff I could not do with a manual mill, and I can do it with good accuracy. But sooner or later I’ll want to cut a part that requires a sudden change in direction on z, and I won’t be able to do it well.
Another annoying lathe issue: you have to tell the computer about the cutters you use. When you use a tool, only a tiny part of it will touch the work. The computer has to know where that contact occurs. Tools have rounded corners, so there won’t be a sharp, defined point where the tool makes contact. It will vary as the shape of the work and the direction of tool movement change. Lathe inserts vary a lot, so you may have to have a whole bunch of tools defined. I’m not sure HSS is useful at all, because you can’t grind it precisely. If you try to tell the computer the radius on a tool made from HSS, you’ll definitely have error.
I have not used a CNC mill, but it stands to reason that it should be less complicated. Say you’re using a half-inch end mill. You know exactly where the lower surface is, at all times. You know where the sides are. Not complicated. Maybe I’m wrong, but I can’t really see myself spending days telling the computer about the small number of tools I’ll use.
I’m going to keep the lathe, because even with limited precision, it can be useful, but I would not waste my time building another one. I’m hoping to use it for threading and tapers, as well as curved parts like dial handles. Things like that will justify its existence until I get a mill going.
People are telling me I should have bought a used machine. There are a lot of old CNC machines out there that have obsolete electronics. I may be wrong about this, but I will relate what I understand to be true. Years ago, CNC required big dedicated computers and expensive controllers. In 2014, a secondhand PC can handle most of that stuff. There are old machines out there with screws and motors that still work, but they have heavy, useless built-in electronics. Commercial users want to get rid of them, so hobbyists buy them and bypass the ancient circuitry, running them with Mach3 or LinuxCNC.
I would love to have an old vertical machining center, which is just a very fancy milling machine with an enclosure that keeps chips and coolant contained. But they’re gigantic. There’s one for sale down here, and it weighs over 8000 pounds. I’m crazy, but not that crazy. Also, what if you buy one, and the screws are no good? You’re out maybe six grand, and then you have to put another two or three thousand in. Arrgh.
I am thinking I should get a new Chinese mill, like an R45 clone or a Grizzly G0704, which is a little smaller and less rigid. I would have to put decent screws on it, which would give me gastric distress, but it would do just about anything I want to do. I still have the ability to add 6 more axes to my controller, so I should be able to keep the lathe and add a mill with no problems.
I bought Dolphin CAD and CAM, which is a pretty good commercial program. They gave me a big discount. I haven’t gotten to where I can actually use it, but I’m working steadily. I have managed to get Mach3 working (most of the time), so I use it to fine-tune the machine. Yesterday I cut a #2 Morse taper in aluminum, just to see if it would work. Tapers have to be very precise, but the geometry is simple, and the tool doesn’t change directions while it’s on the work, so I figured there was some hope that my lathe would pull it off.
Below is a photo of the taper. It fits fine in the center bore of my rotary table. I put Sharpie ink on it and tried to rub it off on the inside of the bore, to check for high and low spots, but I couldn’t see any problems in the result. It would definitely be sticky enough to hold a drill chuck in the lathe’s tailstock.
If I can make tapers that actually work, it will be a nice ability to have. I should cut an R8 and see what happens. My experience with lathes is that even with error in the chuck, you can get a very nice, round part as long as you don’t move it around while cutting it. If you take it out and put it back in, it won’t be in the same position. I don’t think it’s unrealistic to try to make an R8 taper, but the dial indicator or test indicator will tell me for sure.
I am enjoying the lathe. I plan to keep working on it until it can thread. But compared to a mill, it’s…handicapped. That’s just how it is.
September 19th, 2014 at 4:24 PM
I’m not very tool-savvy. Can you make soft cushions or a comfy chair with a lathe?
September 20th, 2014 at 1:13 PM
I can’t even make nice red uniforms.
September 22nd, 2014 at 8:21 PM
CNC controls are purpose built, and probably always will be. Only hobbyists use pc’s to control cnc, despite the hue and cry among the hobbyists. Fanuc is the gold standard, and again, probably always will be- the Fanuc 0 control has been in place and in use, unchanged except for processor speed, for twenty years. Several companies have attempted to use PC’s to operate commercial machines, and those companies are all bankrupt now. Those heavy useless built in electronics are still in demand and still in place making pretty much everything everywhere. Fanuc controls, Haas controls, Mitsubishi controls, and to a lesser extent Dynapath and even NUM are bulletproof and reliable, and are what everyone wants when running cnc. Many manufacturers use embedded PC’s to act as operator consoles for these controls, but the control is still a purpose built piece of equipment, and more than likely always will be.
You don’t have the power to run any but the most rudimentary real cnc controls, and the PC based ones won’t have the oomph to do anything but light work, but for most people the light work is OK. If you ever get to the point where you move to a place with a better shop with better power, you want a Makino KE55 mill, and a Harrison Alpha lathe. Both can be used as excellent manual machines with extensive and very easy to use features, and both will accept nc code to make complex parts, but neither will run on anything less than about 20 kva of 3 phase power.
The things you’re learning will lend themselves to plenty of other technologies, and that’s when the stuff gets the geeks excited. Keep experimenting, it’s rewarding and lots of fun when it works.
September 24th, 2014 at 8:25 PM
When you talk about needing power to run big machines, do you mean computing power or motor power? The board I bought will run 8 motors at once, but I think the current tops out at something like 6 amps per motor. The famous CNC hobbyist Hoss cranked a bunch of little motors like mine all at once, and I think the total current coming out of the power supply was around 3 amps. It’s on Youtube but I’m too lazy to check.
I would guess that the computing power would not be a problem, since this little board does that all by itself, once the info is in the buffer. Problems with the PC should not be able to stop it, unless it’s something heinous, like a BSOD. This is why I’m asking which type of power is the issue.
What do you think of the plan to get a small mill and CNC it? I think doing a Bridgeport would be a waste of time because it would be a huge space-hog, the screws would be very expensive, and if I ever got room for something nice (like your Makino), I would rather have the small mill plus the really nice mill instead of trying to sell a modified BP and replace it.
I’m amazed at the things people are doing with small mills. The engraving alone makes them worth the price of admission.
I was surprised that I could cut a working taper on the lathe. I know tapers are generally ground, but the finish on this thing is fine, and it does grip the bore.
September 24th, 2014 at 10:06 PM
More about actual power. CNC controls run circles around PC controls because motion control is all they have to do, they don’t have to support an operating system. Any FANUC cnc will support multiple axes, I have done robotic systems with 32 simultaneous axis of motion. I think 0 controls will handle that many.
If you have 100 amp service in your home you have about enough power to run one lathe or one mill. But don’t turn on any lights. Three phase at the wall is best, and you want 200 amps of it if you can get it.
We have cheap little industrial units here, like a two car garage with a small office and a bathroom and three phase power. They’re giving great deals on them locally because there isn’t much demand. Maybe you can find something like that, or maybe you’ll move someplace with more power.
Coolants can be smelly and difficult, and you will eventually about have to use them, and that would be nice if it wasn’t attached to your house, too.
September 26th, 2014 at 8:49 PM
I would be totally happy with x, y, z, rotation, and spindle. To be totally crazy, maybe a thing that swaps tools. I can’t even guess what I would do with 32 axes.
I think you’re talking about machines I will never know what to do with. I looked at the specs on some of these things, and they’re pretty crazy. I saw one that had a table rated at 6500 pounds. I would be amazed if I ever cut anything weighing even a hundred pounds. If I could mill things a foot wide by a couple of feet long, I would be thrilled to death.
Right now someone is listing a vertical machining center with a 15 HP motor. I am too lazy to look it up, but I think that’s about 50 amps all by itself. The Makino you mentioned has 7.5 HP on the spindle. That’s as much as my lathe, which was way overkill.
One impression I get from looking at this stuff is that the professional tools provide speed a hobbyist would never need. Maybe I’m wrong, but it seems like they run them very fast, to make them more profitable. Because my machining time is worthless, I don’t care if a part takes ten minutes instead of fifteen seconds.
September 26th, 2014 at 9:02 PM
Another thing about the speed: I do not understand hobbyists who make the machines fly through jobs. I want to be have time to hit the big red button if the machine is about to crash. I realize it’s cool to make something in five seconds, but carbide isn’t free.
Here’s a link to the kind of machine that gets me excited. A clean knee mill from a reputable manufacturer, with low hours and a cushy work enviroment.
http://www.ebay.com/itm/EXCELLENT-LOW-HOUR-2001-LAGUN-CNC-MILLING-MACHINE-ANILAM-3300MK-bridgeport-Mill-/361040697307?pt=LH_DefaultDomain_0&hash=item540fb3d7db#shpCntId
September 27th, 2014 at 10:10 AM
I only mentioned the multiple axis because you mentioned processing power.
The Lagun machine is an excellent one, and the very best places to find that sort of thing are in trade schools. More than one very nice lathe and mill has been purchased in like new condition when a trade school closed it’s doors or upgraded it’s equipment.
Support is an issue. Anilam controls, a lot of them, have been discontinued. Parts are unavailable. Your support team is you, and a soldering iron. Fanuc, Mitsubishi, Mazak, Haas, all have good support networks and you can continue to get parts for most anything. Fanuc parts are the most expensive but least likely to fail. Haas parts are the least expensive and only moderately likely to fail
The Fanuc Robodrill is probably the most useful piece of equipment you can buy for the money. Very difficult to kill, good toolchanger, simple to operate. Common as dirt and easy to repair. Not anywhere near as nice or useful as a Makino KE66, but easy to find cheap. From a stability and reliability standpoint much nicer than a knee mil of any kind.
Horsepower is not necessarily about speed. If you’re cutting stainless, it work hardens as you cut. You cannot take small cuts, it destroys tools. You have to take big cuts at very carefully calculated speeds to get anything done. if all you will ever cut is aluminum or brass, one of those little cnc routers will do all you need. if you want to do steels of any kind, you need horsepower. A knee mill will give it to you, and a cnc knee mill is very versatile, but a true cnc or a machine like a KE55 is the last word in versatility and convenience, and you will most likely never outgrow it.
let’s say you decide you want to make very nice guitar pickups. You probably want to make them out of stainless or some similar material, or something nonferrous like titanium. You will need coolant, and you will need horsepower, and rigidity.
I know a lot of people who began as hobbyists and now have full machine shops, people who can machine are scarce and in high demand. Most of them have gone through the DIY stage, and it’s a good learning experience, but you’ll be a lot less frustrated with good tools.