CNC the Hard Way - My Journey

Now that I have a real, working, CNC milling machine, I am learning my way into NC machining. These pages are my journal of the things I learn along the way.

2018-01-04 Re-boring the Taper inside a Crummy ER20 Collet Holder

I bought a CHEAP straight shank to ER20 collet holder so I could hold really small tools with my big honking NMTB40 holders. I leared the taper wasn't concentric with the shaft it was on. Total junk. I needed to turn the shaft down to 5/8 from 16mm, so I took off the 0.004" of diameter. I had used a pin in the collet for drive and a center in the center hole in the other end of the shaft for support. I adjusted the set-tru (buck) chuck until the pin ran true in the collet and then turned down the shank. The good news is that it appears after I cleaned my lathe chuck, I can get a long pin to be straight. The bad news is that I did not yet know that the taper for the collets was eccentric which cause the shank to end up with a slight taper. It wasn't terrible, so I ground a flat on it and put it into the qulll and spun it with the mill. The taper was about 0.010" eccentric, so I opted to bore the taper out until it became concentric on the mill. I used linear XZ moves with MDI commands to move it at the 8 degree angle with the boring bar held in a 5C collet block in the milling vise. It did a very nice job creating the taper. It appears the collets aren't all that great either. I ahve about 0.004" of TIR on the shank of the 1/16" end mill I mounted in it. The commands I used in the MDI console were:

(Increment parameter #2 which is the X offset. It is used to increase the bore of the taper by moving the table)

#2=[#2+0.002]

(Set the Z coordinate I want to move to)

#1 = 0.5

F 0.5

(Move in coordinated X and Z motion to follow the wall of the taper with the boring bar)

g1 f12 x[-tan[8]* .#1] z[#1]

(Move back to the bottom of the taper)

#1 = -0.5

g1 f12 x[-tan[8]* .#1] z[#1]

(Repeat the above as needed)

I ended up with a nice concentric bored taper in the end of the shaft.

2017-12-08 Steel Chips Galore!

Over the past week I must have spent over 20 hours in front of my CNC mill making vise press brakes. I appreciate that mill so much more than I did a week ago. It's truly a beast, and the flexibility of LinuxCNC has really shined in its ability to provide a very rich combination of soft user interface/PC features while still giving me good old fashioned hardwired buttons and knobs for things that need to be within grasp for immediate action.

Here are some things I have learned:

• • NativeCam (Thanks, Fern!) provides a really fantastic set of tools for programming the mill. I use it for 97% of all my work on the mill. It has turned the CNC mill into a tool I can walk up and use instead of committing to a programming exercise for every stupid little thing.

  • I need coolant and a way to put it on the work. It is SO boring watching the cutter go round and round with my only form of entertainment squirting the cutter with oil

    • Aluminum wants kerosene or WD-40 or cutting oil or coolant or something. I have drawn up a blower that could cast drops of oil from a dripper into the cutter. I have 3d printed it and mounted the blower, but the dripper to put drops into the air stream is not done yet.

    • For steel cutting oils produce a TON of smoke. I put a blower on the end of a long pool vacuum hose outside the shop. Then I fit the other end of the hose onto a bracket those goes up and down with the quill to suck the smoke away and blow it outside. The chips that go flying away still have smoking oil on them, so it is only partially effective.

  • Quill accessories are awesome. I have fitted a laminate trimmer to a plate that bolts to the quill so I can use it as a high speed spindle for woodwork. I also have a blue laser for engraving and cutting paper, cardboard, and tape. I also have a 3d printed arm for holding stuff that should go up and down with the quill.

  • Trying to cut a piece of metal off a chunk of stock with an end mill can get exciting. The upward force from the spiral of the cutter can fold the piece you are cutting off to swing up and into the way of the cutter. The last bite needs to be a good one or the flimsy film that is left will act as a hinge to put the piece being cut off into harms way.

  • Tool length offsets aren't for me. I don't run production, so I shouldn't use length offsets. When I run a program and it commits a tool change, it loads the new offsets, forgetting the settings for the tool I just touched off. Swearing and part gouging ensues afterwards.

2017-03-28 HSMXpress, Solidworks, Improper Homing, NativeCam, VirtualBox

In the past few days I have learned that Autodesk has a plugin for Solidworks that does 2D machining, and it is completely free. I learned that if I do not home my machine and set the work offsets the way it expects, the first and last moves it programs are part stabbing and tool breaking. I learned how to setup a linuxcnc simulator inside virtualbox on Windows 7. I also learned that NativeCam is an AWESOME addition to LinuxCNC.

I learned that I should check "in control" for tool offsets on every milling operation. Otherwise it will not use the tool table on the machine, it will use the idealized tools from the library for the paths. Not good.

I learned that I MUST home the machine as the software expects. No more homing in random positions. This is because the software EXPECTS that Z home is a safe place to go and is well above the workpiece. It rapids to it before and after many operations. If it isn't well above the workpiece; CRASH. More motivation to get my Z axis limit setup for homing.

I have learned that running all steps of an NC program on a simulator before running them on the machine is a REALLY good idea. The simulator shows rapids as actually moving fast, shows spindle RPM's, shows feedrates, offsets, coolant activation, tool changes, etc. IN REAL TIME. It is an excellent gut check. It can even be sped up with reckless abandon without wrecks.

I have learned that it is easy to install Debian in virtualbox to have a linuxcnc simulator on my windows laptop. Install went pretty much as expected. The network interfaces can get a little munged when changing their settings. In then end, a reboot had things squared away. The "secret" to getting linuxcnc installed is to go to buildbot.linuxcnc.org and modify /etc/apt/sources.list to point to the right distribution and the simulator. Virtualbox can have a shared file folder on the hard drive with the windows host. One has to open up aptitude and retrieve the VirtualBox Client tools to take advantage of the shared folder. The folder is mounted with read/write access only for root in the /media directory by default. I haven't yet gotten that changed so that it is readable by users yet.

I learned that Windows Virtual PC is the hard road, perhaps not ending in success. Even if one gets the linux image to boot and install, the resultant installation may not boot. VirtualBox has no such problems.