Jump to content

Don Fogg heat treat forge on a smaller scale?


Anthony Reid
 Share

Recommended Posts

I've been using my ribbon burner forge for heat treating but it's really difficult to maintain temperature low enough to be appropriate for heat treating so it has become a bit of a dance and I have been thinking about other options. Something like the Don Fogg drum kiln appeals to me but I don't have room for anything that big. I took a look in the stickies and see that someone else has done something similar to what I am thinking of but I wanted to check in with you guys before I start just trying things. 

 

The basic outline of my idea is a 5 gallon metal pail lined with 1in of kaowool. I have read that keeping a smaller volume an even heat requires baffling to creat convection currents and I wondered what material and placement would be best?  Also my plan would be to build a small burner to heat the kiln and wondered if there is a pattern of diy burner that would be suited to this project? I was just thinking to scale down a standard 3/4in pipe burner to 1/2in pipe and try that. 

Also burner placement is a question as well as I have read that having the burner enter the forge from the top of one end and the door of the forge at the bottom can help with even heating but most similar builds appear to have the burner at the bottom and the door near the top with stainless steel hangers to support blades.  Would a kiln shelf hung with ss rods be a suitable support for the knives to allow ht of shorter and odd shaped pieces that wouldn't fit well in standard hangers? I plan to buy a thermocouple and PID to monitor temperatures but want to keep it cheap and simple as far as possible so no actual temperature controll circuitry/solenoids etc for the time being. Any ideas or suggestions are welcome I know I'm far from the first person to suggest/try something like this but info online seems pretty sparse

Link to comment
Share on other sites

Keep it simple, is my best advice. The 3/4" burner kit Hightemptools sells will work fine for this. Bottom entry horizontal is key for burner placement in this application. This allows the heat to diffuse so it's even at the top.  Kiln shelf is fine, but even a bit of large tubing or angle iron will work to hold things.

Assemble and check for even heat before adding baffles, you may not need any.

Link to comment
Share on other sites

I'd strongly suggest reading John Nicholson's thread on the jizzer in the stickys. It's simple and it works.

 

I have built a few forges, including some intended specifically for HT, mainly because actually making knives seems like bloody hard work and forges for other folk to use are well within my comfort zone. It does mean that I probably spend more time on the forge than a typical smith would

 

Bottom entry works very well full-size (55-gallon drum), but I found that top-entry, bottom exhaust worked best for me, with a chamber about 8" diameter and 18" long. To be honest, I'd faffed about with the Don Fogg design to try to reduce it to a sensible size for a hobby knifemaker in the UK. I was using a burner based on an Amal Atmospheric Injector. There's a discussion at:

 

Unfortunately(?), the video of the forge in use (by my test-pilot, who made the video) is no longer available. It was pretty bloody tedious TBH: several minutes of video showing a forge running at 816 degC, with a few seconds where it hit 817 degC and a small adjustment was made to get it back to 816 degC. 

 

The forge was made from a length of 10" thinwall stainless pipe (20-24" long? it was scrap, picked up off a site I was working on), lined with 1" of Kaowool and rigidized/coated with a homebrew mix. The ends were lightly pressed-in disks of Ceramic Fibre Board, coated with the same homebrew mix.

 

The thermocouple was a Mineral-Insulated Type K, 6mm diameter and 600mm long below a handle, Type 310 Stainless Steel sheath, curly cable with miniature plug.

 

The pyrometer in this case was a TM902C bought off ebay for under 5 bucks, delvered. I had a number of these over several years and they all performed as well as any of the big-named brands at 20+ times the cost when checked against the calibrator at work. Then I bought ten of them and they were all identically inaccurate: excellent to 800 degC, then there was a progressive error from 800 degC upwards. I can't remember which way it went, but either they read 1290 degC at 1372 degC or they read 1372 degC at 1290 degC. Either way, I could no longer recommend them to anyone without a calibrator.

 

There are several others available on ebay, etc, that also read in degF. Cost is a little higher though.

 

Pics below show it during build and on test. The last pic is of the 1/2" Amal LV injector, which is the clever bit. Gas pressure is high at 40 PSI in the pic, but I would normally use 15-20 PSI (it's a very small jet). The flame temperature is adjusted by moving the knurled part to adjust the air gap between the knurled part and the 45-degree (-ish) taper on the main casting. Temperature control is very good indeed. I was aiming for 800 degC and 801 seemed close enough to me, though another couple of tiny adjustments could have got it to 800. Once adjusted, it'll hold to within a degreeC (2 degF) pretty much indefinitely.

 

If you have access to pipe and fittings with BSP threads, I would definitely recommend the Amal Injector (with the BUTANE jet, even though you'll be running on Propane: the slightly smaller jet will give a slightly higher maximum flame temperature when that's what you want). The BSP threads probably make things difficult for the USA, where NPT threads are the norm. Burlen supply carburettors and parts for old British cars and will ship pretty much anywhere.

http://amalcarb.co.uk/downloadfiles/amal/amal_gas_injectors.pdf

 

DSCF0557 (Custom).jpegDSCF0569 (Custom).jpegDSCF0572 (Custom).jpegDSCF0574 (Custom).jpegDSCF0575 (Custom).jpegDSCF0598 (Custom).jpeg

 

Link to comment
Share on other sites

thanks for the info Tim, I am familiar with the threads mentioned above from my previous research but will go over them again for sure! today I went to my local packaging supply to pick up some plastic buckets and lids for my wife as well as a metal pail for this project and ended up leaving with 2 30 gallon oil drums as well. I'm wondering now if I should stick to my original 5 gallon plan ala  the "jizzer" or try the 30 gallon drum to be closer to the original Don Fogg design? I ordered a pyrometer and type k thermocouples with ceramic insulation tubes to protect them. I ordered 6 in long thermocouples with mounting blocks and wires etc but I'm thinking now that may be too short ? there are also 16in long versions available from the place I ordered from but Im sure I can use the shorter ones in my smaller ribbon burner forge anyway if they are too short for this project. space is at a premium in my shop but if a larger drum would make a big difference in evenness of heat I would find somewhere to put it I guess. I seldom make large blades but I suppose it never hurts to have the extra capacity. I primarily make hunting and outdoors knives, kitchen knives, and the odd axe. I have built my own burners for every gas forge Ive ever owned except one that was a commercial model and ironically I sold that one on within a few months as I wasn't happy with it. my plan for the burner is to build something like the burner Alan recommended based on the sidearm burner design. I am in Canada so as far as availability of material etc its pretty much like the US only less so in terms of easy access to specialized components ready made burners etc. I still have the better part of a roll of cerablanket, rigidizer, castable refractory etc left over from my last forge build and plumbing supplies   and propane regulators/hoses etc are all available locally so the only thing I had to order from away is the pyrometer as getting one from a pottery supply locally would be about twice the price.   

to recap 2 main questions :

1) in terms of performance and even heating is a 30 gallon drum going to be far superior to a 5 gallon pail using a single 3/4in burner? 

2) how long of a thermocouple should I use and where should it be placed ? (I presume it should be as close as possible to the area the blades will be in but should it be inserted from the end or along the side/top somewhere?)

 

thanks for the help guys I really appreciate it and if anyone has any further thoughts or suggestions I would love to hear them

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...