# Monday, March 21, 2011

After I re-read my last post, I realized I kind of cheesed out on the drill bit part, so I figured I would more fully flesh that part out, plus detail the opto-isolated limit switches I purchased.

Drill and Router Bits

For hole drilling, I looked at buying a kit like this one from Drill Bit City, but ultimately decided that I would just get a 10 pack of each of a few different sizes. I ended up getting #71, #70, #66 and #60 drill bits from Drill Bit City.

For milling (cutting out), I got a 10 pack of .0625 down-cut carbide bits, also from Drill Bit City.

For trace isolation, I picked up a 10 pack of 60 degree carbide “V” bits off of eBay.

Limit Switches

The purpose of the limit switch is to keep the controller software from driving any of the axis's to their physical limit and causing damage.

You can certainly run your CNC machine without limit switches, but honestly, if your going to spend a minimum of $1500 on your setup, why not spend a few more dollars (and a few input pins on your break out board) and prevent costly damage to your machine?

When I was doing research on limit switches, I was originally considering using a standard lever actuated micro-switch. But I had some questions and concerns regarding their accuracy. Over time, as a axis slams into the switch, it will deform the lever.

When a microswitch is used on say an arcade button, any imperfection or deformation of the lever will go unnoticed by the user. But in the world of CNC, accuracy and repeatability are everything.

After doing a lot of research, I stumbled upon Colin Mackenzie’s Opto-Isolated Limit Switches. Colin had the same concerns I had regarding using physical limit switches and came up with an opto-isolated switch which can be wired in an “OR” configuration.

While the opto-isolated limit switches are a little bit more expensive than a typical micro-switch (at around $2 - $2.50), at $8.50, I didn’t find the cost difference to be to great.

Next time, I’ll go into the software setup.

CNC | Hobbies
Monday, March 21, 2011 9:22:21 PM (Alaskan Standard Time, UTC-09:00)
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