Repost: Summary of the Retrofit

In a response to Where the heck? What the he11? HUNH? on CNCZone I posted the following. I realized later that it is a good summary of my retrofit so I will repost it here.

I am in the process of doing the same thing (a Bridgeport Boss CNC Retrofit). I have the gecko drives working, a Automation Direct GS2 VFD, and a power supply built with T1 (the 240 v to 120v transformer tapped at 40v). I already had Gecko 201s but the 203s would be better because of the auto short circuit protection circuitry.

Just remember that "common" on the Gecko 201s is 5 volts to power the opto-isolator LED. Also just wire 2 windings of 4 of the stepper motors because the windings are in bifilar (which means that 2 windings are wound together). There are jumpers on the motors that show which terminals are the ends of the windings and then wire to the other side. I have 1 sigma and 2 superior and the geckos work fine so far.

I used a C11G breakout board from CNC4PC which has some extras AC relays for coolant etc and is set up for direct wiring to a Gecko drive with opto isolators.

I am using the original limit switches and wired both NC and NO contacts for a separate e-stop and enable circuits. X and Y are set up as "both limits" in EMC2 and the Z has an upper, lower and a home switch. You can actually move the deceleration switch past the upper limit if you loosen the bracket screws and use it as upper limit. Then the screw adjustable switch can be a home switch.

All this fits in the back cabinet on the mill. Mine had no side cabinet.

For software I am using EMC2. It was probably the easiest part of the project. It has a nice wizard for setting up your mill which lets you check feed rates/limits/etc. They only problem that I had was a non compatible graphics card. Otherwise it was pretty straight forward to install on a empty HDD on a Dell GX240 computer (pent 4, 512 MB RAM, NVIDIA graphics card).

I got most of this information from this forum except for explicit directions on modifying the transformer which I just figured out after reading the suggestion on this forum.

I also had an hour long talk with Mariss at Gecko tech support who has probably forgotten more about Boss retrofits than I will ever know.

Basically my costs were:
Gecko drives - Free (came with the mill)
Stepper power supply parts
transformer - Free (came with mill)
bridge rectifier - 5$ at digikey
6800 uF capacitor - Free (I had one)
VFD from Automation Direct - $260 with shipping
C11G - ~$100 from CNC4PC
EMC2 - Free
Computer (GX240 MB on ebay $40 to put in old case I got surplus)

It is really not that big of a deal to do a retrofit using the original steppers once you get your head around it.

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