6 Gauge Crimper From Bolt Cutters

My team was trying to get some crimpers, but only found a $170 one online. In previous years, we have used screwdrivers and a vice to crimp the battery terminals, but this year we decided to grind a $20 Home Depot bolt cutter down to make some crimpers. It only took half an hour, rather than days.

The attached photo is of the grinded bolt cutters.

That’s a pretty good idea,

We use one of these in our arbor press, it makes a really solid crimp.


Until we spent that $170 on a real crimper (which, I need to say, is really worth it), we used to use these pliers from Harbor Freight. Not the jaws, but the crimping die on the handle-side of the hinge. Most kids do not have the hand strength to do a proper crimp with these, so we would clamp the jaws into a vise for crimping and tighten as much as possible.

Our team puts the crimp connection and wire in a vice. It takes us less than a minute and the connection is strong!

We’ve tried the KoP battery connectors in a vice before, but we had trouble getting a pinch instead of a big squish. Soldering the connector seems to work pretty well for us.

Why crimp it??? Solder it!!!
Put the connector in a vice just the very tip so as not to transfer heat to the vice. Coat the inside lightly with flux (soldering paste) heat the connector and fill it about half way with solder and while the solder is still molten insert the end of the wire. Let cool and heat shrink done!

Forgot to mention use a butane/propane torch.

Once we get the KOP my team just calls up the electrician who is contracted with our school and he shows up with his nice $300 crimpers and we’re good to go for the year. We are looking into getting our own crimpers in case we need them while at an event or if the electrician is unavailable. That Forney 57637 Lug Crimping Tool could be a good option for us.

Why not solder? Because soldering is time-consuming and dangerous with these connectors. Dangerous because the metal gets very hot while soldering and it’s easy to touch it and get burned.

Crimped terminals are wonderful; we just didn’t have the right tool available for a reasonable price.

We bought this $53 hydraulic crimper on a suggestion from Triple Helix, Team 2363. It is the single best purchase we have made all year.

Here are some considerations and links to the style of heavy-gauge crimpers I like. (Measure the dies to make sure it works with your crimp terminals.) But grinding custom crimpers out of bolt cutters is a good idea. I’d make a few test crimps before using it on a robot.

(http://www.chiefdelphi.com/forums/showthread.php?p=1292736#post1292736); either one, properly, is sufficient. But crimping is generally a whole lot easier to do properly.

Okay… amongst all the reasons to NOT solder, “dangerous because it gets hot” has to be about the lamest one out there. I guess I shouldn’t pre-suppose the experience on your team, but most of my students knew what “Hot!” meant. ::safety::

The trick to getting a good solder joint on thick wire is to use a butane torch or other high-powered heater. Most soldering irons don’t stand a chance because the copper wire can wick the heat away as quickly as they can put it in.

And while I agree with most of the arguments on why one should not crimp AND solder, I’ll suggest that those considerations primarily come into play over an extended period of time. The primary risk to an FRC robot, from my point of view, was that an improperly crimped connection would come loose, not that a crimped and soldered connection would fatigue.

So in lieu of an excellent crimp, I suggest there is little wrong with adding some solder in an FRC application.


Consider the battery connections. They typically get used for multiple seasons, and they get a lot of flexing. I have seen at least a dozen cases where the wires broke at the entrance to the crimp, and the vast majority of them were obviously due to having been soldered and destroying the wires’ flexibility. (The others were apparently from someone having intentionally bent the wires hard to make things fit, instead of putting the battery in the proper orientation or assembling the lugs to point in the desired direction in the first place.)

While a good crimp should not come loose, soldering removes all doubt. However, a soldered connection must be a good mechanical connection first. We use the corner of a vise to make the crimp. (See one of my many posts on the subject) We follow up with solder but our students are taught how to add just enough solder to make the connection reliable but not so much that solder wicks outside of the terminal. Yes, this is a belt and suspenders operation but we lost a Championship to Beatty because a crimp pulled out. While I see hundreds of poor crimps every year, I rarely see a poor solder job.

I don’t usually notice badly soldered battery terminals when inspecting robots either. They’re usually well hidden by heat shrink or electrical tape. It’s only after a robot fails on the field and I get called in to help troubleshoot that I find them, and typically after looking for them specifically.

OP: how have you verified that your home-made crimpers do, in fact, make a good crimp connection?

We bought one of these tools: http://www.mcmaster.com/#7061k12/=qj71xs

Seems to work pretty darn well. Can be used with a hammer, and probably a press (though we haven’t tried). Easily fits in our electronics toolbox and doesn’t break the bank.

We have been using the same crimp tool from Mcmaster and it has been working fantastically. We crimp it with that tool and then test the connection to make sure it is mechanically sound. Afterwards we hold it in a vice and flow soldering into the connection with a butane torch. Then some heat shrink to keep it clean and protected.

We have used this crimper for quite awhile. It has dies for several crimps

It has worked quite well for us once we figured out what die to use.
It is around $55

Mr Forbes grabbed the other end of the wire while I grabbed a screwdriver, put it through the terminal, and pulled really hard. My full body weight was not enough to break it.

We could set up a pull test to make sure that the terminals are really staying on. We have a couple hundreds of pounds of weights that we use in our trebuchet.

Unless you were hanging entirely from the crimp (feet off of the ground) your full body weight was not applied to it.

Good idea. A 6AWG crimp should be able to support up to 300lbs.

I know I sound like a bit of a nit, but 6AWG crimps literally power your entire robot, any small flaws in the termination will have a negative effect on every mechanism and system in your robot. Test properly to make sure you’re doing it well!

In the preseason I tested small gauge wire crimps, with good success. We just got our 6awg crimper on Saturday… so some testing should be in order before the final 6awg wiring is done on the robot. Perhaps tonight.