In the second installment of my Milwaukee USA factory tour, I talked about the differences between how bi-metal Sawzall blades and carbide-toothed Sawzall blades are made.
Here, in the last post of the series, we’re leaving Sawzall blades behind and I’m going to walk you through the process of how a Milwaukee Hole Dozer hole saw is made.
Advertisement
Milwaukee Hole Dozers are bi-metal hole saws, meaning that the teeth are made from a hardened metal that’s different from what the rest of the cup is made from.
Milwaukee says that the bi-metal hole saw is “the workhorse of the industry,” and is used by many different trades, and so it needs to be able to cut holes in clean wood, nail-embedded wood, and in different types of metal.
Milwaukee has two different lines for producing hole saws: an automated line capable of producing high volumes, and a “high flex line” for quickly responding to demand. Below, we’ll follow the journey of how a hole saw is made in high volume line, because that’s what we were allowed to see.
Have you ever wondered why hole saws are described as linear edge products alongside reciprocating saw blades?
Making Hole Saw
In this factory they make hole saws from 5/8″ to 6″ in diameter. Above, you can see some of the stages of making a hole saw: from hot forming the flat stock to a round blank, to welding the seam and the cap, tempering the hole saw, and painting/pad printing the branding.
Advertisement
Forming the Flat Blank
Making a hole saw involves many of the same steps as making a Sawzall blade. The steps that are noticeably different are the hot forming and welding processes that turn a flat blade into the cup-shape that makes hole saws recognizable.
The hole saws start out as a coil of bi-metal flat stock with the “rip guard” teeth already formed. From the roll, the strip of metal goes into a straightener and then gets fed into their presses.
There are four different presses on the high volume line. One stamps the size markings onto the blank. Another cuts the slots for removing the plug. The last one cuts the strip into shorter lengths for bending into hole saws of the specified size. The fourth press isn’t used in production, it is used for prototyping — they gave us the example of testing new types of slots.
Hot Forming
The blank gets heated red hot and then is fed into the hot forming machine. The hot blank gets dropped in place between the cylindrical center die and the rear concave die.
Stuart’s Note: I could watch this all day!
First, the rear die pushes forward, to partially wrap the hot blank around the cylinder. Then, the side dies come in to wrap the blank further around the cylinder. Finally, the front die completes the wrap around the cylinder. The now round blank is removed and placed on a conveyor which moves through an air cooling tunnel.
Welding
From the cooling tunnel, the round blank gets loaded into the welding station. It uses three robotic arms that work in concert to pull the round blank off the conveyor, weld the seam on the side, and weld the cap to the bottom.
Below you can see a closeup of one of the robotic arms placing a hole saw into a fixture to weld the seam.
Painting/Printing
Next, we were taken through the room with the tempering ovens. This is where the hole saws would go after heat treating to be baked for several hours to get to their hardened state. We were not allowed to take any photos of the tempering process and were hustled to the painting/printing part of the line.
Milwaukee recently switched over their hole saw coating lines to a thermoset paint. Unlike the old paint, this new paint doesn’t gum up when the hole saw heats. This change in the type of paint results in faster cutting times and longer battery life.
You can see workers loading and unloading holes saws from the conveyor on the coating line. Once the hole saws go through the paint booth and oven, the hole saws are removed from the line and pad printed. In the background of the video you can see the carousel for the pad printer. They have two different pad sizes, one for larger hole saws and one for smaller hole saws.
Once the saws are printed they are inspected, and placed on a collection tray.
Earlier in the tour they showed us a staging area for hole saws that are ready to be packaged and shipped. They wait as long as they can to package them so they can respond to demand for the type of product they need to ship, whether it’s single cups in clamshell packaging with no arbor, packs of 2 shrink wrapped together, single cups with arbor, bulk boxes, or sets.
Milwaukee Factory Tour Wrap-up
Now we’ve covered everything Milwaukee manufactures in their Greenwood Mississippi plant. First we covered how a regular Sawzall blade is made, then we talked about how they make their carbide-toothed Sawzall blades. Finally in this article we covered how a hole saw is made.
But Milwaukee has a lot more capacity at the Greenwood plant. All of the manufacturing we saw was in a single building. There is also a second building, where most of the space is walled off with controlled access. They didn’t even hint at what we would see if we went into that part of the factory, so we’ll just have to wait and guess.
I’d like to thank Milwaukee Tools for inviting me down to Mississippi to tour their plant. Having worked with manufacturing before, I know there’s always more to building products than most people realize, but I was still surprised at how much I learned. I’ll never be able to walk by a hole saw or reciprocating saw blade again without a new appreciation for the people and processes involved in making them.
firefly
That’s so cool. I wonder what those forming die are made of.
Koko the Talking Ape
Fascinating.
I imagine those holes in the saw are meant to allow the metal to expand with heat, but I can’t imagine why they are shaped and configured the way they are (why are there two holes? Why do they have the shape they do? etc.) The design isn’t snazzy, so I guess it is functional. Anybody have any ideas?
Benjamen
Actually if you are talking about the large rectangular holes in on either side of the cup, they are for removing the plug from the cup after you’ve drilled the hole. You stick a screwdriver in there and lever it out.
fred
Exactly – other manufacturers have different designs – some come with claims of easier plug ejection. I think Lenox once advertised their slanted holes this way. Shallow hole saws for use cutting sheet metal, electrical panel boxes etc. often come with lug ejector springs.
There are also a plethora of plug ejector ideas shown on the internet. Some would have drive screws into the plug and use the exposed screw heads as a place to grip and pull the plug out. Another idea is use the 2 drive holes at the bottom of the hole saw cup to drive the plug out. We had a shop made jig that worked with a mallet to do this. If I remember the details right, our jigs were made from a 2.5 or 3 inch round piece of 1/4 (or 3/8) steel plate – with 2 tapped holes spaced on center the same as a hole saw arbor drive pins. Two 2.5 or 3 inch long machine screws through the tapped served as the drive pins to engage the back of the plug and drive it out. It worked better than prying because it applied force more symmetrically. You might be able to make a similar one substituting a piece of hardwood to the steel plate and holding the screws in place with t-nuts.
Koko the Talking Ape
Thanks! But why are there two sets of holes, of different sizes?
fred
The only logic that I can see is that holes furthest from the teeth are for use with the narrow edge of the screwdriver bit to pry thicker plugs up and out. While to holes closer to the teeth are for use with the flat side of the screwdriver blade to finish the prying or to use with thinner plugs. Maybe Benjamin knows a Milwaukee designer who can say for sure.
Benjamen
If you look at some of Milwaukee Hole Dozers, they have a feature called Plug Jack: https://www.milwaukeetool.com/accessories/drilling/49-56-0249
Plug Jack is a stair stepped hole. What this allows you to do is get the best leverage for removing a plug. If the plug fills the cup, you start at the base and lever it up as far as you can, move up the stair which gives you a higher fulcrum point, lever it up, repeat.
I’m not positive, but I think the two holes are a different version of this. For plugs deep in the cup you can lever it from the bottom hole until the plug is far enough out so you can lever it out with the higher hole.
red92s
Correct. Same concept as the Lenox “Speed Slot” which debuted a couple years earlier.
Koko the Talking Ape
Brilliant. That makes total sense.
Jonathan
Additionally, at times when removing a plug from a deep cup, say 1″ plywood in the deep cup, sometimes the plug doesn’t leave straight, but can wedge itself at a slight angle against the hole saw wall when attempting to drive it out of the cup. Having holes on both sides give greater access since the pilot bit prevents you from entering one side and exiting on the other side.
The angle slots give you access to almost > 270° of the saw cup while still allowing the hole saw to be rigid
Thom
I must admit my Milwaukee ice hardened hole saws seem to last longer than the other brands.
John Hooper
It’s always interesting to see how things are made. Thanks
fred
I recently came across this Lenox arbor – that supposedly speeds plug ejection:
https://www.amazon.com/Lenox-Tools-1779806-Arbor-4-Inch/dp/B004CEOS8A/
Alex Caldwell
The hole saw thermoset coating line do you know who makes that machine
Stuart
Sorry, we do not.
Alex Caldwell
looking for a manufacturer of a hole saw thermoset coating line like the one in the video
Philip Joseph Donovan
Very curious, the circular saws on the hole dozers are very apparently non-circular and you can see this immediately when visually inspecting them, looking down into the opening and drill bit. Is this done on purpose? I thought at first I had a damaged one, or that I had damaged it from opening the package but then went back to the store and looked at many of the hole dozer circular saws. They all seemed to have this feature of varying radius from the drill bit. Can you comment on that?
Thank you,
Phil Donovan
Stuart
When you look at straight blades, cutting teeth are often offset or angled outwards a little, to prevent binding or for cutting performance. I always assumed that hole saws have offset teeth for the same reason – for chip clearance and to prevent binding.
Bryan
Are these tours open to the public?
Stuart
No.
Benjamen
This was an invite only tour for a small number of media people. I do not believe they have any tours that are open to the public.