Sneak Peak 2
Version two of the CNC controller I have been helping develop is now in my workshop. I have had a chance to do some testing and it is performing very well. There is a “Sneak Preview Two” over in The Hobbyist Machine Store Blog.
This is my recommendation for the Taig CNC Micro-mill. Of course it can be used for many other CNC machines. Taig has a somewhat unique issue against running at high speeds. The 20 TPI screws provide excellent torque but require 2,000 rpm to achieve 100 IPM (Inches per Minute) travel. Most steppers max out about 1500 rpm and run most comfortably at 500-750 rpm. The original Taig CNC Micro-mill still brags about 30 IPM rapids.
The stepper motors are picked for low impedance and high speed and using a digital driver that can punch out the torque using the 36 volts, the result is solid 100 IPM on the Taig Micro-mill. It will lift the heavy Taig motor and spindle all day at that speed without stalling.
I don’t intend to do any machining at 100 IPM as the bits I use won’t take the force. It is an impressive “rapid” speed when desired. However, I also have some concern about potential increased wear with constant operation that speed. More later…
Here is a sneak peek at a brand new Taig CNC ready mill running some 185 oz/in steppers with a new control I am testing and evaluating. There will be a few updates before I can discuss the new features. Here it is running a 3D carving program at 50 IPM. Short micro moves on the Z axis are creating the crunching sound. Sweet music to a CNCer.
Here is the complete test layout.
4″ Mayan in Wax
I use the Mayan calendar as my CNC test program. It is highly detailed and makes the stepper motors really earn their keep. In these photos I show where I have reduced the circle diameter to just under four inches. This is about as small as I can go with this design. I got it off center a skosh. That’s OK, it’s not a keeper. The test is not of the Taig mill but rather the tiny wax profile bit I bought from Bits & Bits.
The bit is 1/8″ in diameter half round with a 15 degree included angle. The end of the tip is 0.005″ It looks and feel like a very sharp needle. The RPM was 10600 (max for the stock CNC Taig) and the feed I had set for 30 IPM. With ramp up it seldom got to 30 IPM except for long paths.
The total run was just over four hours. The Taig and CNC controller took this run without a blink.
I use plain air to clear the wax chips but you can see they still liked to stick around. The problem could be the slow feeds because of the intricate details. I am going to try a faster more aggressive feed on the next Item. I am thinking of trying a small lithophane carved in wax.
I ran some Lithophanes this evening. I realized I had my iPhone in my pocket so I grabed a short segment of the HB2 in operation.
What you need to note is the quiet operation with the Taig spindle running at 10.600 RPM and the bit cutting at 50 IPM (Inches Per Minute). Most of the noise is the cutter in the Corian solid surface material making the 0.10 to 0.20 depth cut. If you listen carefully you can also hear the higher pitch “chirping” of the z axis stepper motor. I am “eighth stepping” the motors so it takes 1600 steps to make one shaft rotation. You are hearing those steps.
Most folks are running very loud (screaming actually) routers or high speed rotary tools to do this work. It’s hard to even think over the noise level. I have to wear ear protection with those spindles, but not with the Taig spindle. It’s nice…
Still a Drag?
I had a great weekend. I had to mow the grass but that is expected and still makes for a great weekend. For this Blog it was great because I got to put a lot of run time on the HB2. About six hours in total.
I even ran the Mayan calendar in a 7.75″ diameter on some Corian. I’ll post some pictures soon. The detail was excellent.
I think I may still have a little drag on the axis screws. It didn’t bother the CNC work this weekend. I have some spray bearing grease I will inject behind the Thrust bearings and see if the intermittent slight rubbing noise goes away.
If the grease doesn’t help, I already have a plan to put a “step” at each end of the screws and just remove the thrust bearings. That way the only thing the screw end can contact is the center race of the bearings.
That’s what I should have done in the first place. I did find out how easy it is (when you have a lathe) to modify the ends of the axis screws.
How I noticed what may be the rub is I changed my micro-stepping from quarter to eighth. I now run 8,000 steps per inch rather than 4000. That’s 0.000125 inches per step, way too fine than really useful . This was done not to increase accuracy but make the steppers run a lot more quite (but also a lot hotter).
Quarter stepping was still more accuracy (0.00025″) than I needed and it is supposed to provide more torque. The motors run cool. The noise however is more than 3 db higher and the twin Y’s were driving me crazy with their loud sound. Now I hear a sweet soft… Continue reading