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2014/02/15 - Recent CNC Mods

posted Jan 27, 2015, 10:46 AM by Jeff Balderson   [ updated Jan 27, 2015, 10:47 AM ]
I discuss a few of my CNC mods: Stepper Heat Sink V1, Cable Chain and Stepper Heat Sink V2. It also includes some information on how I cut some 1/8" sheet aluminum on a CNC router that's not remotely designed for it.
I work in an unconditioned garage.  When we had it built, I decided to have the walls insulated to help keep the temps to a reasonable level.  The insulation definitely helps, but it can still get pretty warm during the hotter days of the summer.  This year we had a lot of 95+ days and it was regularly 85 degrees in the shop.  The steppers on my CNC were hovering in the 150 degree range. That's still in the working range, but I'm a firm believer that unnecessary heat should be dispensed with as fast as possible.

Normally, stepper motors are supposed to be bolted to something metal to help shed the heat away.  The Fireball has an MDF frame and all of the steppers are mounted to that with nylon standoffs, so there's only the stepper motor's case to radiate the heat.  Enter the ...

Heat sink v1.0

Technically, I think it was was version 3.0, but it's the first one that made it to the cutting stage. Regardless, this was both my first attempt at making a heat sink as well as my first attempt cutting something out of aluminum.  The stepper did run 10 degrees or more below the other two and cutting the aluminum actually went smoother than expected. It may not be apparent from the picture, but it's bolted in place of the washers between the stepper and the nylon standoffs.

Heatsink V1

The Fireball line is NOT designed to cut aluminum.  Since the frame is MDF, and the guide rails are unsupported except at the end, it has entirely too much flex to cut anything that hard very effectively.  It can be done, but it requires setting the spindle to its lowest speed, keeping the CNC moving fairly fast (around 50 IPM), and very shallow cuts.  I forget what settings I used to cut out this heat sink, but there will be more about settings in a little bit.

I ran like that for a while and never got around to cutting out the other two, which turned out to be a good thing.  One thing that's always bugged me about the Fireball X90 is the cable management.  There is none.  With the way I have my system set up, the only ones that actually cause issues are the Z-axis stepper control and router power cord.  They run off the back and rub against the back of the gantry.  I imagine it's not such a big deal with the V90, but with the wider gantry on the X90, the cables can definitely get in the way.  So, to control the cables better I purchased some ...

Cable chain

The first cable chain I bought had some issues.  The links of the first one were molded as a solid piece and they were only 15mmx20mm.  The stepper control wire plug and the spindle power plug are both too big to fit through a 15mmx20mm opening. In order to use that chain, I would have had to cut off the plugs, thread the wires through the chain, and reconnect the plugs.  While searching for something else towards the end of 2013, I ran across some slightly larger chain that had a hinged piece at the top which would allow me to open up each segment to insert the cables, no cutting necessary.  Problem solved.  Well, that one at least. 

It took me a while to figure out the best way to attach it to the Z-axis carriage and to the gantry.  Then it dawned on me.  I had already worked out Heat Sink v2.0 a while back with longer tangs on two of the sides, but had never gotten the itch to cut it out.  If I left a few of the tangs unbent and sticking out the back, I could attach the cable chain to the heat sink, and screw the other end to the top of the gantry side piece.

Heatsink V2 and Cable chain

I'll eventually cut those bolts shorter.  I'll likely not bother putting a chain on the Y-axis.  They lie down fairly well next to the X90 and don't get in the way.

Heat sink v2.0 and cutting aluminum

While working on the new heat sink, I decided to take some time to really dial-in my settings for cutting aluminum.  

There are lots of different types of aluminum of varying hardness.  Based on my reading, the ones that work best are the harder ones like 6061 and that's what I think I have.  It's actually some cutoffs from someone else, so I have no idea of it's pedigree but using the descriptions from a few different vendors, it seems likely.

The design is the way it is partly because of the stock I have available.  The cutoffs I was given were 4" wide.  I'd have preferred the tangs to be the same length all the way around.

I usually work in inches.  I'd love to be able to work natively in metric, but I just don't THINK in metric and everything around me is in inches.   Since the specs/diagram I was using for the NEMA 23 stepper motors was in metric, I decided to give it a go this time.  So, the cutting settings that worked for me were:

  • Bit: 3.175mm (1/8") Spiral Upcut Endmill
  • Bit RPM: 16000 (lowest my DWP611 can go)
  • X/Y Feed Rate: 800mm/min
  • Z Feed Rate: 10mm/min
  • DOC (Depth of Cut): 0.1mm
  • Stepover: 40% (3.175mm * 0.4 = 1.27mm)

I tried using a 1/16" bit initially, but was cutting too deep and it broke.  Those thin bits are really unforgiving and break very easily.  I fell back, re-calculated everything for 1/8" an, re-started the job was still going too fast, then probably went back another two or three times to arrive at the numbers above.

Whenever I get the itch to cut the last heat sink, I'm probably going to try using a straight bit instead of a spiral.  I'm thinking the spiral causes the bit to dig into the surface, pulling the router further into the work piece since the frame wasn't designed for this and it's flexing.  It's possible I may be able to do slightly deeper cuts with a straight bit.  

Here's some pics during cutting and some more of the heat sink once it was bent into shape.

Cutting heatsink Cutting Heatsink 2

Heatsink unmounted Heatsink mounted