A Loft In Denver

I’ve been doing some more work on the table recently and decided to try out some video with the camera.  As they say a picture may be worth a thousand words but sometimes a picture might prompt a ton of questions as well.  When I say I’m milling something, what does that mean anyway?  Have a look!

A brief CNC mill background

First of all, this is using a Bridgeport CNC vertical knee mill. CNC stands for Computer Numeric Controlled which means that instead of controlling the mill manually by turning a bunch of big knobs it’s all controlled by computer. You can use a number of “canned cycles” built into the mill which are programmed to do certain things such as milling the inside/outside of a rectangle or circle, drilling hole patterns, etc. However in the video you can see the very top of a computer monitor at the back of the mill – it’s much easier to write a little program to do what you want and send it to the mill from the computer. This allows you to save something for later and also opens up much more advanced options such as CAD/CAM, etc.

I said “program” but it really isn’t as complicated as you might think. In fact the one line which does all this work is this:

G170X1.5Y1.5Z.05X2.79Y2.79R.3Z2.8Z.15P.2F12.;

What this is saying is: use canned cycle 170 to do an “outside frame mill”, center it at the coordinate (1.5″,1.5″) with a clearance plane (distance above the the piece we’re milling), mill the outside of the “frame” to a width and length of 2.79″, put a radius of .3″ on the corners, go down to a total depth of 2.8″, step down .15″ each time, with an entry clearance of .2″ (when it goes in and out of each step), all using a mill feed of 12″ per minute.

If you were paying attention this does 19 “steps” of 12″ (around all four sides of the 3″ tube) – at a feed rate of 12″ per minute that’s 19 minutes plus a bit of time for the entry clearance to do each piece.

Hope that all sort of of makes sense? Now let’s see it in action!

Some video to make sense of all that:

Here’s a close-up of milling using a CNC mill.  First it turns on the mist – this is used for both cooling and lubricating during the cutting process.  Then it moves to the beginning point of the cutting process.  It moves to the depth of the cut and then gradually cuts in and continues all the way around the piece.  Then it comes off the piece, moves down again, and then continues the process.  This video shows a bit of the beginning, middle, and end and really helps you to visualize what’s happening when I say I’m milling something.

This video shows the bigger picture of what’s happening  – hopefully it will clear up a little from the video above.  What you can see here is the controls for the mill; at the very top and out of the frame is the motor which turns the spindle, the bottom of which is protruding and has the milling tool attached to it.  The only part of this that moves is the spindle telelecopes out (up and down) to get vertical motion (Z axis).  In order to get the horizontal motion the table (which the part you’re milling is clamped to) moves forward and backward (Y axis) and side to side (X axis) – you can see this sped up at the end of the video.

Finally, you can see a problem which I caught on video.  At the end of creating the second piece I had it doing a finishing pass which was going over the entire area but going in another .002″ to see how much smoother it got.  When the finishing pass was over the mill is supposed to retract the tool up and stop at the left front corner.  I happened to be taking some video and you can see that the tool didn’t quite clear the piece and I ended up breaking the tool – luckily the mill was fine but it’s amazing how the 3/4″ tool just snapped so easily.  To this day I’m not sure exactly what happened – I think it had something to do with resetting the Z axis as this piece of tube was a tiny bit longer – but that doesn’t make sense because it cleared the top at the beginning of the program.

Where in Denver am I doing this?

If you’ve just joined us, this is all being done at Club Workshop in Denver, Colorado.  They have a series of 5 “How to use a CNC Mill” classes which give you a thorough introduction to using the mill manually, using canned cycles, and an intro to programming it for CAD/CAM. These classes will prepare you to come in on your own time and use the mill for your project. You can see my other Club Workshop blog posts and have a look at the rest of the blog to see what I’ve done there.  If you end up going to Club Workshop be sure to tell them you heard about them from A Loft In Denver and you’ll get a special deal!