@Chuck_Comito Could the shut down be a software behaviour? What control soft do you use?
@Chuck_Comito Just mesured both resistivity of all lines going from the drivers to the motors. All of them are 0.55 Ohm, I also mesured the motors coils just in case but all of them are 1.7 Ohms. So my problem clearly has nothing to do with the motors nor the cabling…
I was thinking of connecting the motor outputs of both drivers toogether to deliver the samme amount of current to both motors. i.e. A1+ to A2+, A1- to A2- etc… Do you think that would toast the drivers?
Just to make sure, you wired the EN, DIR, STP from pin on the center of the board (you have to solder those pin) and not the one labeled as M1, M2, etc… ?
Since you are using two external driver, you can’t drive the driver from the internal drivers.
Looking at cable length is not necessary at this point, you will have a very small effect on a very big cable difference !
@Sebastien_Plante , yes both myself and @Thibaut_Robin both wire them correctly using the pins and not the motor connections. Thibaut, I did a modification today. I opened the driver and removed the crappy thermal pad and tiny piece of aluminum all of it was mounted to and added a much larger piece of aluminum that is the correct thickness and the proper thermal compound. I also plan to add to 12vdc blowers. I should be done with that mod within the hour and will let you know how it performs. To answer your other question about wiring the motor phases across the 2 drivers, I don’t that would hurt but I don’t see it solving the problem. I did think that we could perhaps pull off the sense resistors and run them on a breakout board in series with both drivers. I think this is asking for trouble though.
@Chuck_Comito On my side I’ve tried to directly connect the drivers on the 3.3v control pins with very short wires. It works! I still have a slight temp difference between the motors but no more overheating. I’ll go back to open drain tomorow but will probably wire the 5v directly from the small ATX power used to power the Smoothieboard rather than from the endstops 5v; with common ground…
As for the drivers cooling, I made an aluminium box to insure maximum heat dissipation (and faraday protection, planning to use plasma cutter). I have 2 fans blowing fresh air directly on the drivers and both 24v AC and ATX sucking hot air outside the casing.
The reason I wanted to wire the motor phases across the 2 drivers was so I’d be sure they both get the same Amps… I’ll keep you informed. Cheers.
Hmm. Send me a pic when you can. But I also am wondering where you’re located. Yesterday it was in the 90’s here and I’m in my garage so it was probably hotter. Today though is 77 so it should be cooler by default.
South ouest of France near Bayonne 93 F° 34C° tooday and still 75° at 00:00 
What about you?
24c currently in Detroit Michigan
Detroit! Love it! I spent 5 years in N.J during the 80’s
@Thibaut_Robin That’s awesome. Glad you like it… I did want to mention though that with the lower ambient temperature and the new heatsink setup I also appear to be up and running. Looks like I’ll need some climate control out in my garage. The wife will love that!! LOL Anyway, I plan to give the router a workout tonight so I’ll post back how it kept up. Let me know if you modifications continue to work as well!
@Thibaut_Robin Welp, for the record the Y axis is still going strong. The X axis however dropped out… Too HOT! Looks like I’ll have to make my modifications to all the drivers and then pray we don’t have a hot day… I’m really bummed. Good drivers are really expensive!
So in case anyone else needs the help, I added a new heatsink and new thermal compound as well as 50mm blowers and now have a working machine. I plan to upgrade the drivers to 7amp versions in the near future. This should solve the problem completely.