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Browsing articles from "April, 2010"

“Pro” vs “Hobby” Servos

Apr 29, 2010   //   by Bob Warfield   //   Blog, Techniques  //  No Comments

How different are the performance specs of “Pro” vs “Hobby” servos?
I’ve heard a lot of claims, but it’s easy enough just to go look at the published specs. Here, I’ll take a Yaskawa 750W Sigma-5 AC Servo (typical axis drive for a Haas VMC) against the HomeshopCNC 850 oz-in DC servos I have installed on my IH mill. Here’s what I get from the respective (linked) spec pages:
– Power: Yaskawa = 750W / HomeshopCNC = 612W (a little smaller servo)
– Peak Torque (oz-in): Yaskawa = 1184 / HomeshopCNC = 850
– Max Speed: Yaskawa = 6000 rpm / HomeshopCNC = 4200 rpm
– Voltage: Yaskawa = 200V AC / HomeshopCNC = 72V DC
One interesting figure is to take the power consumption of the two and equalize what the torque should be from the HomeshopCNC were it to consume 750W. That value is 1042 oz-in, which is still less than the 1184 oz-in from the Yaskawa. AC servos are known to be more efficient, and that sort of quantifies it a little bit at 12-15% more efficient in producing torque for a given amount of power.
This is all just out of idle curiousity and interest.…

Why Do I Have to Know a Range of SFM’s and Chiploads?

Apr 28, 2010   //   by Bob Warfield   //   Blog, Software, Techniques  //  No Comments

Saw a great question over on CNCZone this morning. A beginner was trying to understand why so many cutter manufacturers publish ranges of surface speed (SFM) and chipload (inches per tooth) values for their cutters. I suspect his broader question was how to know what number in the range to use when calculating the feeds and speeds of his specific machining operation. He also couldn’t understand why the calculator software he was using also had to know the range. After all, it’s a computer, doesn’t it just know the right answer?
Here was my response:
The “right” SFM or chipload depends. The ranges of surface speed are quoted because there is a range of cutting conditions. The more your calculator can take those conditions into account, the less you need to look at it as a range.
Take a look at Niagara’s charts, for example:
http://www.niagaracutter.com/techinf…mat/index.html
Head into 6061 aluminum. Lots of numbers, but they’re organized based on what you can tell it about cutting conditions. The principle variables are:
– Are you peripheral machining or cutting a full slot?
– What is your axial or radial depth of cut?
– What specific endmill is in use in terms of…

More Shaper Tricks on a CNC Mill: Cutting Splines

Apr 27, 2010   //   by Bob Warfield   //   Blog, Techniques  //  1 Comment

I continue to be amazed, entertained, and intrigued when I see Simpson36’s work with his fancy 4th axis rig on his scratch-built mill. His latest is showing how to cut splines and other fairly exotic shapes using a lathe tool lashed to the side of the mill head:

Something to note: this is a very cool capability, but don’t try to attach the tool to the spindle directly. You don’t want to be bashing your spindle bearings on each stroke. Build a holder that affixes to the side of the head.…

Kluber’s Magic Spindle Bearing Grease

Apr 27, 2010   //   by Bob Warfield   //   Blog, Techniques  //  1 Comment

Since having published the details of where to obtain it in small quantity (directly off their web store), I’ve seen a number of folks over on CNCZone pick up a tube. One fellow (gd.marsh on CNCZone) is now testing the spindle on his Chinese mill to 8000 rpm–cool beans!
After seeing all this, I finally place my own order for a tube of the magic grease. I’ll be using it on my IH mill belt drive project, when I finally get to it.
You want Kluber Isoflex NBU 15. It ain’t cheap–about $30 with shipping for a 50G tube–so what makes its so magical? This diagram will serve to illustrate:

Bearing Speed Factor for 7207 AC Bearings Showing Grease vs Oil Lubrication Regimes
Those “dN” numbers are called “bearing speed factors.” They basically tell us how well the lubrication is working on the bearing, and hence how many rpm it can turn. That diagram shows the normal regime for grease versus a need to go to an oil mist system. Most recent VMC’s are using oil mist, BTW. Anyway, the magic of Kluber Isoflex NBU 15 is that it has a BSF of 850,000 dN rather than the normal 400,000…

A Chuck Hauler

Apr 24, 2010   //   by Bob Warfield   //   Blog, CNC Projects  //  No Comments

One of my readers (thanks, Pablo), sent me a link to this great idea over on the Candlepower forums. Lots of interesting stuff over on Candlepower, BTW. Folks over there are making custom high-tech flashlights, and a lot of the work is really cool.
This idea is designed to make it easier to mount medium-sized chucks on your lathe. Take a look at what I’m calling a “Chuck Hauler”:

The chuck goes on the hauler like this. You can grab the bar on either side of the chuck to use both hands…

Place the hauler onto your lathe’s ways. The hardwood base protects the ways from harm…

Line up the bar with the spindle bore and slide the chuck into position. Pretty slick!
For really heavy chucks you’re going to want some sort of overhead hoist system. In fact, the hoist will even come in handy for loading large workpieces. Here is a nice shot of Ray Behner’s setup from PM:

Cradle for round stock, and a little piston unit on the hook for fine positioning. Just open the value to gently lower the workpiece. Note the disc brake and indexing by the chuck!…

Another Use for a Dual Indicator Rig (aka Traminator)

Apr 22, 2010   //   by Bob Warfield   //   Blog, CNC Projects, Techniques  //  No Comments

I love my “Traminator” (what I call the dual indicator tramming tool I received as a gift), but had thought of it as a very special purpose tool only useful for tramming the mill until I saw this picture on a Practical Machinist thread:

Ray Behner created this tool, and what a cool idea it is! It’s shown here tramming a vise, but I can imagine it would be handy to align almost anything into tram on the mill table. It’s going to be faster to tap it in this way too I would think since you don’t have to wait to sweep the indicator (although I’m pretty fast at it these days, so it won’t save much).
Now I need a precision rig that will hold my Traminator at right angles so I can use it for jobs like this. I’ll have to think about it a touch, but doesn’t seem it ought to be too hard to make. BTW, if you don’t recall the Traminator, you’ll recognize it from the picture:

My tramming and preventative maintenance gear……

Kurt Vises for Sheet Metal Bending (aka Way Covers)

Apr 13, 2010   //   by Bob Warfield   //   Blog, CNC Projects, Techniques  //  No Comments

Kurt-style vises have 1001 uses, I am sure. Maybe this is 1002. Having my nice set of Vise Jaws of Doom sitting on the table from an engraving project gave me an idea. Could they be used as a sheet metal brake? You betcha!
Here are the jaws:

Here they are being used to bend with the aid of some clamps and a handy piece of cast iron that was waiting idly for another project:

And here is the finished way cover (bottom Y cover):

Not quite as nice as it would have been with a real brake, but it’s very functional. It would be so easy to make a simple attachment so I could use those jaws as a real brake too. Hmmm……

4th Axis Disk Brake

Apr 12, 2010   //   by Bob Warfield   //   Blog, CNC Projects  //  1 Comment

Nice video of a disk brake to lock a 4th axis for machining:

The caliper works by screw action. The cylinder rotates a screw that snugs the brake pad on the rotor. This is a very high performance shopmade 4th axis. The servo will spin it fast enough he can use it as a lathe. This is an earlier version making an air fitting:

 His project log is over on the Mach forum.…

Machine Tuning as Preventative Maintenance

Apr 11, 2010   //   by Bob Warfield   //   Blog, Techniques  //  No Comments

I like to fiddle a bit with my machines every now and again to make sure they’re adjusted to tip top condition. The CNC mill seems to benefit from this the most. For example, the gibbs and sometimes the Mach3 motor tuning parameters benefit from periodic adjustment. Perhaps surprisingly, the tuning varies depending on conditions.
When its cold (like it is right now in my area), the mill is stiffer and seems to require lighter settings. When I load the table with two 6″ Kurt vises there is enough weight to slow it down too. Right now I have the combination of both, so things are kind of “worst case”, at least until I decide to throw a cylinder block up on the table and try to machine on that!
In addition, Z is the most sensitive (being the heaviest), followed by X, followed by Y.
So my current settings, which I regard as a worst case, are as follows:
X 110 IPM, 10 acceleration
Y 120 IPM, 15 acceleration
Z 110 IPM, 10 acceleration
I generally just leave Z right where it is. However, if the weather is warm and the table is lightly loaded, I may bump X…

Interpolated Holes Not Round!

Apr 10, 2010   //   by Bob Warfield   //   Blog, Software, Techniques  //  No Comments

Interpolated holes are a great test of a CNC milling machine because so many things have to work right for one to come out round and on dimension. The first reaction when an interpolated hole is not round is often that it is a machine problem. Backlash on one or more axes, improper number of steps per inch, and a host of other problems can be the cause. But there are other possibilities too.
For example, suppose you’re machining a ring-shaped part clamped in a vise. You interpolate the center hole and it isn’t right. Maybe the vise is distorting your ring too much by applying pressure to top and bottom but not the sides. Another is the CAM program. From that same link comes a fellow who says he changed his Mastercam post to output circles as 4 quadrants instead of a complete circle (e.g. make 4 moves, each corresponding to a quadrant) which radically improved his accuracy to 0.0002″. I’ve seen this 4 quadrant move in posts from other CAM programs, so there must be something to it. Can anyone tell me why?
I know I will be adding a function to G-Wizard Editor so that it can…

Clever Thread Cutting Gadget

Apr 10, 2010   //   by Bob Warfield   //   Blog, Products  //  No Comments

Microprocessors and computers enable great simplification of mechanisms and the addition of lots of functionality that would have been impractical or expensive. Consider how much more your handheld iPod MP-3 player can do versus an Old School Jukebox.
The same is true in the machining world. A CNC mill or lathe offers endless flexibility compared to the manual equivalent, and often requires less tooling to boot. Consider, for example, that no rotary table is needed to cut curves with a CNC mill. No taper attachment is needed to cut tapers on a CNC lathe.
Along comes a clever device for threading:

As you can see from the video, its basically a purpose-built thread milling machine. He spins the round workpiece in the 3-jaw chuck, the thread mill has its own simple right angle spindle (just an ordinary die grinder modified), and a micro-controller of some kind allows arbitrary threads to be entered so that steppers will advance the thread mill at the appropriate feedrate to cut any desired thread pitch.
Cool beans!
Now the question for this poster is how best to monetize their invention. I wonder what sort of applications would find the machine particularly suitable? Certainly plumbers and…

Dave DeCaussin is Still At It

Apr 4, 2010   //   by Bob Warfield   //   Blog, Cool  //  No Comments

Dave is the “D” in “Fadal”, so he knows a thing or two about CNC. Lately he has been building tool changers and enclosures for Asian mills:

Don’t they look great? Nice powder coated sheet metal will do wonders for the aesthetics and is very functional.

A little more about the tool changer…
 
And here is his little CNC slant lathe……

The Little Things Can Sure Slow You Down

Apr 3, 2010   //   by Bob Warfield   //   Blog  //  No Comments

You know how it is when you’re doing some job for the first time: the little things really slow you down. I’m trying to get the home switches working on my mill. I’m tired of having to edge find every time the mill faults or I hit the E-Stop, not to mention how the position mysterious seems to get lost in a whole host of other odd circumstances. You’d think it would be easy, but the little things really slowed me down. Here they are, just for your enjoyment:
– Did a trial run, but chatter was terrible trying to hold a thin aluminum plate 11″ long by 4″ wide in a 6″ vise. So, I took time out to make my Jaws of Doom so I could use two vises and support the workpiece along its entire length. That was a whole project with its own set of little things I won’t go into. I am glad I did it though, those Jaws are bound to come in handy more than once.
– Lost my hard disk. Man, that was no little thing! That created a major detour I ought not to charge against this project, but it still…

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