DIY heat treat oven - front loading vs top loading?

L

l0tek

Joined
Nov 27, 2008
Messages
3
Hello everyone,

I've read a lot of great heat treating information on this forum, and I have all the parts required to build my own heat treat oven.

the following tutorials have been great help:

http://www.viddler.com/explore/rashid11/videos/3/
http://www.britishblades.com/home/articles.php?action=show&showarticle=31
http://www.weaponeer.net/forum/forum_posts.asp?TID=2854&KW=Auber

however, I' really having a hard time finding information on which oven type would be best for heat treating knives.

I can build either type in the machine shop myself, I was hoping to gather some feedback from the experts, with respect to the advantages/disadvantages of both types.

The internal area would be small 4x4x18" max, and I'll be winding my own coils, therefore I can go with either design.. I'm just not sure which is best and why.

__
Andy
 
I am in the process of building my HT oven also. I am going with the side door. I would not feel comfortable opening a top loader while hot. I would perceive the notion of getting your face melted off when trying to reach in there fast to grab a blade for the quench. Although I am sure there are some folks that might cook their blades with a top loader, I will not be one of them. Just my uneducated opinion there...:thumbup:

Hey, welcome to the forums!!
 
To forge I use regular side door forge but I'll build a top loading forge for damascus projects, I plan to open a side door to it just like that:
Fogg-forge-Norris-built5.jpg
 
Gixxer:

yes, eheh, I agree, the top loader did worry me from a "melt your face off" perspective. The one detail the top loader seems to have working for it is the fact it has a coil running around the entire inside of the oven, which could provide a more even heat distribution. (some commercial models with a front door actually have an element built into the door). I'm not sure how much of an issue this is, in such a small oven.

Munky88:

Glad to help! I'm pretty sure I originally found all those links through this very forum, but it can sometimes be daunting to go and dig those links up again.

Galadduin:

Nice forge! Once I get my own shop space, I'll be building a gas forge. My current knife making setup is limited to what can be done in my basement space, using elbow grease and some electric tools.

I have access to a machine shop on weekends, so starting off with stock removal methods seemed to be the the way to go.

I am really just starting out in this hobby, and I don't mind starting from the bottom, a trusty set of Nicholson files, vice, and abrasives should keep me busy for awhile.

I also plan on using the HT oven to build other small tools, and learn as much as I can about annealing, hardening and tempering them.

__
Andy
 
i figure there's a reason that every "knife maker's kiln" available from the commercial world is a front loader....

Personally, I would REALLY not want to reach over a hot kiln and then down into it to get something out. Not to mention, if something slips while you load/unload a front-opening kiln, you just drop something on the floor of the kiln. With a top loader it'd be really easy to drop a blade and damage your elements beyond repair...

Just my $.02.

-d
 
Front door. I'd hate to reach into a 2000 degree space, or over a 2000 degree space for that matter. Front door and long reach pliers/tongs is the way to go.

On a side note, make sure your connections to your kanthal wire are tight, and check them periodically. Heating cycles can loosen things up a bit, and my kanthal shorted at one of the power posts, burning through the wire last night. Thankfully it's an easy fix right next to the post and not in the middle of the wire coil.

--nathan
 
l0tek said:
Gixxer:

yes, eheh, I agree, the top loader did worry me from a "melt your face off" perspective. The one detail the top loader seems to have working for it is the fact it has a coil running around the entire inside of the oven, which could provide a more even heat distribution. (some commercial models with a front door actually have an element built into the door). I'm not sure how much of an issue this is, in such a small oven.

Andy
Click to expand...

When I decided to build my own oven I did a lot of thread reading. The only thing that came up that I noticed was some folks were concerned about the tips of their knives getting too hot from being too close to an element, cause the idea is that the elements get hotter than the ambient temperature in the oven to maintain the temperature. They were experimenting with a barrier of sorts. Not a firebrck per se, but something with mass so the heat can pass through in an even manner, and the tip gets protected from the "overheated" condition. And I believe this was only discussed in one, maybe two threads out of the hundreds I browsed through. You would be surprised how many threads you can read when you have hours of downtime every day and a computer. But then again, a lot of folks do not have that problem and cook blades all the time.
 
Allowing the entire oven to soak at temperature for 20 minutes or more will allow the entire mass of the chamber walls and oven to be temp-soaked, so to speak. This provides a more stable temperature condition with less required from your elements to keep you there. My inside chamber is maybe 8" across and about 14" deep. The coils are evenly spaced on the left and right side of the chamber and they enter from the back wall. I place my knives on spine in a refractory holder I fashioned from some soft brick that only serves to suspend the knife above the oven floor in the middle of the chamber while blocking as little area of the knife as possible. I've heat treated O-1, 440C, and now CPM154 with long soaks with no problems noted at the tip, although, a buffer to block extreme element heat would be a nice safe guard. BTW, my thermocouple tip is positioned at the same height that my blade is within the middle of the chamber to try and squeak a little bit more accuracy out of the oven.

--nathan
 
Front Loading it is!

Deker,
thanks for your feedback, it now seems "obvious" once I got feedback from everyone, for both the ease of unloading, and of course the security issue of working above a blast of 2,000 degrees!

Gixxer, Silver_Pilate,
I hadn't run into any threads about the problem with the proximity of the elements and the tip overheating. Which brings up another question with respect to the design:

If you had to build a new oven, would you make it wider? I was planning on using 4" width (as opposed to Silver Pilate's 8" wide oven area) however now with the "overcooked" issue, I am wondering if I wouldn't be better served by a slightly wider design.

I'm going to do more digging through the forums to read more about "burnt tips" and overheating problems, I'm curious to see what sorts of "barriers" have been tried.

I will also be sure to position my k-type thermocouple at the same height I plan to put the blades at.

I appreciate all the help, thanks,

__
Andy
 
Something to consider is the proximity of your coils to the blade. I don't know if your knife will experience problems due to overheating, but kanthal is typically rated up to 2300 degrees, and I'm sure it momentarily can get hotter than that as it cycles on and off. Maybe overheating could be a problem.

Another thing to consider is that when the oven is on, the coils are live at 220 as they are unshielded. At 4" width, that's not a lot of wiggle room, so to speak. Thusly, be sure to rig up some sort of safety switch that you either kill prior to opening the oven or a contact switch that automatically kills power to the coils when you open the door. Imagine grabbing on to a red hot blade with long reach pliers. If the blade slips or you're careless in removing the blade, 220 isn't much fun, especially if your other hand is grounded: it can ruin your whole day.

Also, during use, the coils expand quite a bit. With a typical home built setup, there is the risk of the coil "jumping" out of its groove, even if pinned to the soft fire brick. If the blade is very close to the coil, you could short your coil if there is contact.

Just things to consider. Research the overheating problem a bit, and if you build it 4", build it stoutly and safely to avoid coil shorts or zaps to yourself. Most makers will tell you that you'll eventually want it bigger.

--nathan
 
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