Should these connections get hot?

I have this extender cables installed and at the connectors they get pretty dang warm to the touch while machine is running. Not the whole cable just around the connector area. Not thinking this is normal. Can anyone shed light on this if anyone else noticed or what might be going on!


Mine do similarly. I believe it’s the greater resistance in the connection dissipating the heat. It’s pretty typical for these kinds of cheap connectors pulling as much current across them as the stepper motors do. I don’t get too concerned unless it’s very hot to touch. I used to fly a ton of electric model planes and would get much hotter connections than I’ve experienced with the extensions.
If you’re concerned you could measure the resistance across the connection to see if it’s unusually high.

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No they shouldn’t, but they do. I had 2 of mine get so hot it actually melted the connectors. I first thought my Z axis motor failed, but it turned out being the connector. Same thing happened on my X axis, started jumping. Connector again.


Hey Randall, hey Bill, hey Mike, hey all,

are any of the other connectors getting hot? Or only certain connectors, e.g. at the extensions? At the controller, at the X axis input (especially since they are subject to permanent motion and are lacking strain relief), on the front at Y axis inputs?

Randall, you show extensions which are probably 3rd party, are these the only ones that get hot?

Some background: In principle, since they are rated 8/9 A, they should not get hot, but the specification is of course only valid if they are crimped correctly (see here for instructions of how to crimp them), which means with the matching crimping tool. If you consider the fact that the correct crimping pliers cost about $300 for the Molex version, about $750–$950 for the Amphenol version, I’m not sure if the Onefinity manufacturer, but especially the 3rd party supplier for the cable extensions, really uses the correct crimping pliers. And only if you use the correct crimp pliers, you have the specified current rating valid. I have seen people soldering(!) such connectors. The cheapest way to have the correct crimping pliers I have found is to buy the Knipex 97 49 26: Crimping die for connectors in the Mini-Fit™ series from Molex LLC (16-24 AWG model) for the Knipex 97 43 200 A Crimp System Pliers for exchangeable crimping dies (version with case) (version without case) pliers (I own the pliers, but the insert for these Molex is about $200! I assume it’s because of patents, since all other dies for these pliers are at about $50.

Stepper cables are power cables.

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Where do you get they 3rd party. They were ordered with the machine. So Onefinity sends 3rd party cables?

Mike, they get pretty warm at the connectors, no signs of melting though. I happen to touch after a 3 hr carve is how i noticed them.

Hey Randall,

I think I remembered some were offered at But you are right, Onefinity offers some, I had forgot that.

I bought a set of 2’ extension cables from Onefinity when I bought my machine and cut them approx. in half to create the pigtail cables coming from my G540. The connectors you see in the pic laying on the table just behind the controller are the ones that gave me issues. Both X and Z got hot to the point that the connectors were heat-damaged and no longer provided a stable electrical connection.

Thats the same connectors that get hot on mine.

They should not get hot. Something is wrong if they do.

If you’re customizing anyway, replace connectors with bigger ones rated for higher current. If you’re going long, I’d also replace the wire with a heavier/thicker gauge. High current through small connectors/conductors and long wire runs = increased resistance = lots of heat. Lots of heat can lead to melting of plastic parts and insulation which can then lead to arcing and worst of all, fire.

Not customizing. These are the ones that came from Onefinity. I contacted support and they seem to think its fine and didn’t offer a fix or solution!


Sorry, my reply was directed at the general audience, primarily based on what happened to Bill’s connectors.

Excessive heat = connectors/conductors not appropriate for the task. If you can hold onto the cable and connector with your bare hand, the heat isn’t excessive. If you can’t because it’s too hot, then it’s excessive, even if the cable or connector doesn’t immediately show signs of damage.


I always looked at those connectors out of the corner of my eye with untrusting suspicion, and had always planned on upgrading per some that @Aiph5u posted some time ago. However, the OEM cables & connectors were the quickest way forward & I figured they would last as long as they needed to. Oddly, these were the only ones that gave me issue. The ones that plugged into the ends of the rails seemed fine.

Could be manufacturing or assembly issues, wires missing in the crimp, etc. They should be replaced (free of charge) regardless as it’s a huge safety risk and an enormous liability for whomever made and/or sold the cabling.

Given the otherwise heavy-duty and commercial-grade build of the machine, I was surprised that the cabling was not equally conforming. My thought was that it would be an easy fix, but I never did fix it (properly) before I sold the machine.

Hey Bill, hey all,

the question is what they could have used instead.

Onefinity obviously took over the connectors choice from the project (so it’s them who made that choice), by first using their pcb layout and then modifiying it only slightly, leaving those Molex/Amphenol sockets there.

I’ve shared my thoughts on a possible choice for better stepper connectors here, and if I go with reputable industry connectors, it gets very expensive very quickly. That surely was out of the question for the Onefinity designers, which obviously had to realize a low price of entry (not to say some sort of combat price)). It would have not been of any advantage to them if you can throw the direct competitor products in the trash, but deterred potential buyers with too high a price. So they designed a machine that realizes an unusual, robust and handsome concept in the mechanical components (which led to their success), but lacks a lot of components, or the sufficient quality of those: A CNC without a machine base (you have to build the table – & the QCW frame introduced later is extremely expensive for what it offers), no serious cable routing, no milling motor, no homing sensors but using stall homing instead (which the buildbotics’s internal stepper drivers already provide for free), etc.

They realized the low price they needed, and had a great success, with many owners of other hobbyist CNC machines selling their old machine to buy a Onefinity, but the hassle of failing cables and connectors, which often comes after a year of use (=of motion without connector strain relief, or with a Z stepper cable that is not made for permanent motion), or the susceptability to positioning errors or step loss caused by electromagnetic interference (EMI) because of using unshielded cables, are a heavy legacy. I wouldn’t put the machine to work like this, at least not when I’ve spent relevant amounts of money on my wood blanks (which is easily the case in professional context – think of violinmaking and luthery).

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And what a good & valid point that is Aiph5u. Being that I’m using (was using) a custom controller, the fact that the connectors needed to pair with the Buildbotics controller was completely not taken into consideration in my thought. But you’re absolutely correct. It’s up to the ‘Bills’ and other power-users to come up with something better on their own machines. Thanks for the reality check Aiph5u! :smirk:

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When I went to LinuxCNC and external stepper motor drivers I replaced all the cabling to the stepper motors with shielded cabling and soldered connections. If I ever need to replace one I’ll need to do some soldering but I figure it’s about the same as reattaching a dodgy connector the the new motor.