Evenheat problem

[Precision Edge Sharpening]

So I just received a brand new evenheat LB18 with the tap 2 controller today. I’ve only made two test fires at 538 Celsius with a hold time of 5 minutes. Ramping as fast as possible. (That’s evenheat test file) I was seeing temps from 544 to 528. Is this something that will resolve itself or do I have some settings wrong? I was under the impression that it would be more precise then that.

 

[DevinT]

Try slowing the rate of heating, not as fast as possible.

Hoss

 

[Precision Edge Sharpening]

Ok, I wondered about that, I just used what was on evenheats test fire

 

[DevinT]

The lower the target temperature, the slower it needs to heat up.

Hoss

 

[Taz]

Does the controller need to auto tune as well? When I built my oven, I had to auto tune my PID for 1500 when I used it for carbon steels, but when I went to 2150 for Magnacut, it had huge swings and I had to auto tune it again for the higher temps. If it's auto tuned for a higher temp, it may not be as accurate holding wise at a lower temp.

Like Devin said, ramping as fast as possible can lead to temp swings. The bricks need to soak in the heat so they can radiate, but ramping as fast as possible is running the coils at 100% all the time, which can easily lead to over shoots depending on the cycle time of the controller. Once I auto tuned my PID, it usually holds within 1 degree, maybe 2.

 

[JV Knives]

T Taz Precision Edge Sharpening The control is simply an on/off switch. The ramp rate essentially sets the temp of the coils. In essence, it takes a while for the heat, once the coils are off, to evenly move through the system. So, the quicker you ramp up, the more the differential between the coils and the surrounding material temps. There is an entire science behind thermal transfer (thermodynamics) that focuses on all the variables to really achieve "even heat" but you are on to the gist of it! This works in reverse when you are cooling down to temper (if you temper in this oven), so remember that in reverse. Just because it drops down to 350F on the controller with the door open doesn't mean it won't jump back up again when you close the door and the system normalizes. Takes a while to get used to the rates and such but I sincerely doubt there is anything "wrong" with your new oven. Evenheat has always treated me well and can be a great free resource for technical questions.

Best,
John

 

[Precision Edge Sharpening]

Thanks. I lowered the rate to 1000/hr and it really helped, I still had about 5 degrees Celsius of swing but I reckon if I slowed it down a bit more it would help with that too. And I’ve about decided I won’t be tempering on it. Because to drop it down so low so fast is one thing, but then the bricks and everything are still way hotter so it seems like it would take a long time to get it cooled

 

[Taz]

What you could do is a snap temper in the kitchen over at like 300 and let the ht oven cool down, or do an hour in cryo and then temper in the ht oven. But cooling the bricks quickly can lead to cracking. I am going to convert my oven to a 110v tempering oven once I build up a new oven with the correct bricks this time! I have most of the supplies I need already, including element, wiring, SSR, PID, etc. I find my oven is around 100 degrees the next morning still after using it the previous afternoon!

 

[Precision Edge Sharpening]

I might have to do this, because even if I get the air cooled down, once you shut the door, the bricks would heat it right back up. Just not sure my mom wants me using her oven
I will say though, the results were so much better then what I’d been trying to do in a charcoal forge.

 

[Seedy Lot]

In my oven I lowered ramp down to I think 200°F when I was using it for tempering but then realized that the kitchen oven is superior to holding consistent temperature for low tempers.

 

[Keith Nix]

A 30-45 minute soak at temp will help even out fluctuations in temperature. A thrift store toaster oven will suffice for tempering with some light modifications.