Quench plates are a fantastic tool for the heat treating of knife blades. If you’ve read my posts on How to plate quench or the various heat treatment guides for popular knife steels, this is essentially an extension of those. Plate Quenching uses “quench plates” where the knife is placed between two aluminium plates and the heat is drawn out of the blade through conduction. Quench plates also have the advantage of helping to achieve good flatness without warping.
As I offer heat treatment services to knife makers and have been doing more regular heat treatment, it’s shown me that a more repeatable solution was needed.
Problem:
If you’re heat treating one or two blades from time to time, Aluminium quench plates are an amazing tool to have in your toolbox. Previously I had them loose and I would place the blade in between the plates, and then clamp them all together in a vice. For all intents and purposes, this works perfectly fine and I would cool the plates in between each blade by dropping them into a cooler box of water.
But I always wanted to mount the plates in a vice (which I had lying around) and this raised an issue when doing more than one blade. If they are mounted, I can’t take them off and cool them when doing longer runs. As a result, the plates would warm up with each use and I fear would not allow me to achieve repetitive results. The first blade would be perfect, but the 3-5th etc blade could be a little softer / introduce bainite / have a higher % of retained austenite like a quasi “austempering” deal which wasn’t ideal. Those fears are thankfully negligible or a non-issue [1], but they raised the question and provided the motivation to finally get started.
Solution:
If you have ever come across John Grimsmo’s youtube channel (really cool) you may have seen his videos on the water-cooled quench plates he made. I’ve watched this multiple times and I finally bit the bullet and decided to convert my plates to water-cooled versions.
My father and I went through a few different designs for the channels and orientation of the plates before we settled on a final design. John has access to high-quality CNC machining and I did not (sad face), so the final design takes into account that everything would be done on my manual milling machine.
Unlike John Grimsmo’s approach, the piece that would be in contact with the knives would be the thicker (25mm) aluminium plate, which would not be replaceable. I’ve used my plates for a few years already and they’ve held up fairly well to the “abuse”, so I’m not sure if they will ever need replacing but hey, you never know. It also made sense to maximise the surface area in contact with the water and therefore to increase the thermal transfer efficiency. The larger plate would have 3 sides in contact with the water (better), rather than the thinner plate (12mm) which would be insulated from the channel by the liquid gasket, leaving only one (1) surface to transfer the heat.
The water-cooled quench plates would need to be mounted in a vice. I had an old Record W90 woodworker’s vice with quick release that was perfect for the role but it too needed to be mounted vertically to something. So we designed and built a new mobile quench station. This would hold the vice (vertically) with the plates and water container plus my oil quench tank in one neat unit.
If you’ve been to my shop you’ll know that I’ve been on a consolidation/space-saving drive over the last few months and this project fell into that as well.
Machining the plates was not as straightforward as I thought. They were far too big to fit in my machine vice and I didn’t have any work holding accessories that would allow me to machine the top surface of the plates without obstructing the cutter. But when you have a milling machine and lathe at your disposal, you can make the tools you need. So I made a set of low profile clamps [2] and an X-axis stop for the bed (both were oil blued). The stops allowed me to have repeatable stop points for when I machined the channels, which was very important. If you have Y and Z stops on your mill then they will also help you with this project (especially the Z).
The milling of the water channels took me longer than I thought it would (about a day each) with a 2 flute 12mm end mill. The depth of cut was 3-5mm per pass for a total depth of 18mm. There was a lot of back and forth.
Below is a series of pictures showing the process. I do highly recommend making sure the plate is squared up to your mill, to begin with. I had previously milled the back edge with the face-mill to ensure a smooth surface and used a dial indicator to square it all up.
Now matching the two plates (top and bottom) up and drilling the holes was a challenge mainly because you needed to drill holes blind and not hit a channel. There are a few different ways of doing this… but I settled on using transfer screws to transfer hole locations from the thick plate with threaded holes over to the thin backing plate (blind holes). I started with the two mounting holes for the vice (M10), and then added transfer screws and worked my way from there. Each set of additional screws acts like an index pin for the next set of holes. If you don’t have a set of transfer screws just take your existing screws (M6 in my case) and grind a point onto them. [3]
Once you have your spot marks, I recommend using a centre drill to start each hole as a normal drill bit can wander a surprising amount. When dealing with 13+ screw locations, you need to be incredibly accurate to ensure everything lines up. If you are slightly off, you can over-drill the hole in the 12mm plate by a millimetre or two.
The liquid gasket liner worked quite well. I recommend spreading it on one or both surfaces and lightly tightening (finger tight) the screws. Allow the gasket to cure and then fully tighten the screws and compress the gasket. The advantage of this is that the gasket doesn’t squeeze out and become papery thin.
Parts List:
- 1/4″ NPT 12mm hose fitting x 4
- 1/4″ NPT Tap
- Pond Pump 5kw
- 12mm Tubing x 5 meters
- Aluminium plates 25mm / 1 inch thick x 2
- Aluminium plates 12mm / 1/2 inch thick x 2
- 12mm 2F End Mill
- Fly cutter or 50mm face mill
- Liquid Gasket x 1 tube
- M6 Counter sunk screws (Hex) x 30-50
- M6 Bottom Tap
- M10 bolts (mount plates in vice) x 4
- M10 Bottom Tap
Conclusion:
Is this a cheap upgrade? No, not at all. The aluminium, machining (4 days), vice (free) but otherwise R4000, pond pump R500 and fittings and extras all add up.
But it is a great addition and upgrade to the workshop. I’ve used it a handful of times already and I’ve been impressed with how well it’s functioned. In the past, I had to cool the blades further after being removed from the loose plates but now they reach room temperature in the vice/plates. The main goal of not having to cool the plates in between blades has also been achieved.
I aim to do some tests on the setup to see what type of performance increase has been achieved (cooling rate) but I would assume that blades will cool faster, reach a lower temperature than you would with a non-cooled setup and more importantly, its repeatable.
Thank you for reading this far and I would love to see/hear if you tackle this project yourself.
References:
