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This is an interesting subject.

As Mr Feathers indicated, there are many designs out there that use light bulbs, barbecue heaters and propane torches etc. There are others, however, that use off the shelf heating cartridge elements. In the case of the designs with heating cartridge elements, it seems important that there be a method to transfer the heat from the element to the bending pipe itself. It's my guess that light bulbs, barbecue heaters etc are reasonably good at radiating the heat they generate into the air around them. As a result, the heated air effectively heats the pipe. The heating cartridge elements you buy, however, are very poor at transferring the heat they generate into the air around them. As a result, if you stick a heating element inside a pipe without something other than air to transfer the heat to the pipe the pipe won't get that hot and the heating element will get really hot and probably burn out. Since you seem to be using a heating cartridge element, I believe you need aluminum in contact with the element and in contact with the pipe to transfer the heat.

It seems many people use aluminum foil to do this. They pack it tightly in the pipe, drill a hole for the heating element and it seems to work. See https://www.youtube.com/watch?v=mic5PHIzBvM for an example of this. Also, my guess is the aluminum pellets your currently using are not that effective at heat transfer vs packed aluminum foil or a solid block of aluminum. Since some of them are melting ( melting point of aluminum is about 1200 degrees F ) it suggests the heating element is getting very very hot vs the outside temp of your bending iron pipe.

Anyway.. my two cents. Hope it's helpful and good luck.

So, about a month later...rebuilt my heat pipe. 500 watt element packed in my pipe. Used quite a bit of aluminum foil and packed the element in by pounding it into place. Heats up much faster and I no longer have the large temperature drop when the wood is pressed against the pipe. Still no success.
I have tried bending air dried wood as well as my kiln dried scrap. Temperature range from 270 to 450. Tried holding the wood against the pipe with no rocking. Above 375 I do get scorching but I cannot bend with out breakage.
I tried to duplicate what John Hall does in his fox bender. Since the wood is in constant contact with the sandwich parts I thought I would just run the temp up to 275 while holding the wood against the pipe. Wood definitely gets hot but it won't bend.
Short of building a boiling trough (al la Slone) and a form or buying pre-bent sides I am at a complete loss. My Ramirez shape is "almost" a 000 Martin 12 fret but I would not be able to adjust parts as I am unable to bend.
Any ideas out there?

take a steam iron and use that with the pipe that will help soften the cells
thats how I used to bend

Sounds like you fixed your bending iron and it’s working properly but I have no idea why you are still having problems bending wood on it. Stew Mac recommends the iron be between 350 and 400 degrees for bending and I find that works well for me. I also find that I don’t need to soak the wood with water. Sometimes a wet rag between the iron and wood to keep it from scorching but that’s it.

One possible suggestion is to try something John Hall recommended to me. I tried it and it seems to work well. He suggested using a clothes iron ( I set it to the cotton setting) with a light spray of windex with ammonia D on the wood to preheat the wood and get it ready for easy bending on the bending iron. I found that when I did this you could almost fully bend the wood heated by the clothes iron by hand without the bending iron. Since experimenting with this I also found that I can also use the same technique with a clothes iron to straighten out wood sides that were improperly bent using my Fox bending machine.

Anyway, hope this helps and maybe someone else with more experience than me can provide a better solution.

After a break I saw John's comment about using a steam iron. Plug in iron, set for cotton and steam. Turn on heat pipe. Place hot iron on practice side. Nothing. After 5 minutes with the steam holes laying over my target bend area there is still no softening. I have the practice piece setting on a piece of wood to help it get hot. What kind of steam iron are folks using? What temp setting?

I have listened to John Hall's video, where he discusses wood bending temperatures, several times. I paid attention when he discussed mahogany. I found myself thinking about the 350 to 375 degree and occasional try at 400 he mentions. I have tried getting this hot but the wood scorched. Since all else has failed, I set my pipe at 375 deg. and tried one of my scrap pieces. It bent. I found that when the wood "gave" it was subtle. I was expecting it to bend easily. I practiced for two days on scraps (read two scrapped sides). This morning, finally!, I bent one side. The waist has been bent on the other and is waiting to be finished. If you see this John, Thank you.
warren barnhart