We wanted to share with you some of the details and inside information of the MetMo Driver, so you can get a real behind the scenes look at how each part is made and why the parts are the way they are. We will also touch on some points around what we changed on the original Driver.
If you didn't know already, the MetMo Driver is now available to buy directly from our website! You can now drive yours home in record time!
Advanced warning, this is a long one! So lets get stuck into it.
Chuck
The business end of the driver. Machined in 2 processes on a CNC machine, we start with a solid bar of a grade of stainless steel that is designed specifically to be heat treated. This technique tempers the material all the way through, unlike on some knife treatments that would just harden the surface. Not only does this part hold the bits perfectly, but structurally it holds the entire driver together when it's combined with the neodymium magnet and shaft, secured in place via a press fit dowel pin.
Inside view of the castellations and compound angles
The castellation shape has been modified from the original. We noticed that the rotation of the chuck against the ratchet pin causes some unusual twisting motion, but thanks to modern CNC machining techniques we are able to incorporate a compound angle that totally mitigates this and would never have been achievable when the original was designed.
Chuck Shaft
This part is hidden deep inside the driver and is what everything turns around as the central axis. Made from stainless steel so it can't corrode or seize, this component is permanently attached to the chuck. This is how the original was designed and has worked well for nearly 100 years, so we figured we'd let it roll!
Barrel
Barrel here with the brass bush before being pressed together
The Barrel is the second most complex part after the chuck, as it houses the ratcheting pin and holds the handle together and is also the mounting point for the brass bush. This part requires a lot of machining, first turning, then Milling and tapping as well as precision reaming to perfectly align the holes. Produced from an aerospace grade aluminium, which is no ordinary aluminium! This is 7055 T77, where the T stands for terminator, just kidding. This alloy was developed specifically to withstand the repeated stresses placed on aircraft and has a strength as good as steel, but without the weight, corrosion or possibility of cracking under repeated stress. This part evolved a lot through the design process, increasing in size to allow for a larger barrel pin (ratchet pin) to spread the load more evenly. (We are just working on some more simulations in this area to demonstrate how tough this is, so watch this space!)
Brass bush
Moving down we get to where metal meets metal and bearings are needed. There is potentially a lot of contact between the handle and the barrel, so we incorporated a custom turned brass bush that has been left exposed to add a visual flair and a much needed improvement over the original design. It also ensures the handle can have a really good engagement on the barrel, so pressure is more evenly distributed form the handle without any risk of the friction causing a less than smooth motion.
Barrel pin
We knew from the outset this was likely to be a weak point, even though on the originals this was much smaller, we increased the contact area by 4x compared to the original patent. We also decided to up this to a tool steel that is machined then through hardened. Once hardened it can no longer be easily machined making it incredibly hard wearing. This is also unique in that it's very high in chromium, so it is still corrosion resistant even after hardening.
We've left this part with its natural darkened or deep purple treated surface, unlike the chuck that is treated then we sand back the surface just enough to bring through the natural colour of the steel on the outer surface.
Pin handle
No Ratchet would be complete without a forward and reverse capability and this component makes this possible. Since it’s only function is to move the barrel pin into a new position, we opted for a knurled brass over the original steel ball ended pin. The extra thickness in our design allows for the knurling and makes it much easier to handle the pin. We also added a screw thread on this part so it could be easily replaced or maintained if needed in the future.
Handle
The humble handle, machined from a solid billet of aluminium and then hard anodised. This has been designed to be simple and really comfortable to lean on and really get all of your weight behind. The modified shape from the original patent allows the arm to close over then handle in any position and is a bit bigger so is more suitable for the larger hands of the 21st century! The handle mounts to the central chuck shaft and like the original, uses a grub screw to locate it in place. Because the force is always going down the handle towards the chuck, we do not need anything heavier duty than this here.
We ran through around 5 different handle styles, before settling on this final one.
Bent arm
The stainless arm and the part that is going to get the heaviest handling of all! We looked at a lot of the originals and observed there was not much deformation on them, considering their age and use. We knew this component would need to over perform, so switched the original mild steel in the patents for a thicker hardened stainless variety, this is machined from a solid plate before being bent on a CNC folding machine, heat treated and then hand finished.
The looped handle in this design was taken from the original and is actually very clever, as although you are pulling or pushing on the arm, it translates that and both pulls and pushes at the same time, so is always spreading the load evenly around the axis of the screws, so you are not wasting any motive effort.
Neodymium magnet
Simple but vital for modern bits, this magnet holds the various bits in the chuck during use. Neodymium magnets are some of the best, much stronger than a conventional iron magnet. Most of these now are actually recycled from old computer hard drives and then reshaped.
Spring
A classic spring, these are just fun. This is essential to the whole driver working as it allows the ratchet, to well... ratchet! And applies constant force to the barrel pin, allowing it to reciprocate when the chuck rotates. We first tested our 3d prints with a cut down spring from a MetMo pen (as we had a few of these laying around) and as luck would have it, the tension was about right! Obviously we use a spring that fits snugly into the barrel now, but that tension is still about the same.
Steel spring plunger
True to the original we have kept this feature but have upgraded it to a stainless so it doesn't rust. We found these spring plungers to offer a much more satisfying click of the handle as it locks into place, as well as being much more secure and reliable over many 10’s of thousands of repeat operations.
Grub screw
What can I say about the humble grub, it's a screw with a custom pin end that aligns perfectly with the chuck shaft and really ties the handle to the rest of the driver, but importantly still allows the handle to spin freely. Simple but effective, and based on a technique that has been used for hundreds of years.
The screws
These two screws were chosen for their particular hard-wearing nature, with a minimum tensile strength of 1040 MPa, sits locked against a collar that the handle pivots around so they can’t work themselves undone. Some of the originals have screws and some have riveted pins, we liked the option here of having something removable, again so it could be serviced and allow the arm to be replaced just in case the driver goes up against Chuck Norris.
Phew that was a long one, are you still with us?! Let me know in the comments!
Peg and the MetMo team
