i finished up my oven, based on Frank N's plans.....i'm using a two setting, low/high, heat gun. the low setting holds around 275 and the high 450. i was going to run some experments today to achive the 350-375 range but since my shop, aka, garage doesn't have a vaulted ceiling and the rain couldn't wait, i thought i'd seek some counsel first. anyone with an idea to achive the proper temp. (without buying a multipe setting gun, which i now regret saving a few buck), i'd appriciate a good starting point....
thanks again. matt

Matt, I just used my new oven two days ago for cooking a couple of rod sections. I'll send you the results on heat maintained and cooking time, etc. in a p.m. I was quite happy with the results based on the times and temps I went with. If you have more questions on the details then p.m. me back.

Instead of PMing each other why not post it here so that others can benefit from your experiences--after all that's what this board is for.

You're right FlyDoctor and I apologize for that. But I will say that from my POV I thought it may be a little presumptious to post all the info I sent to Matt on the open forum.

And now I find that my message box doesn't record the items I have sent and so will have to ask Matt to post the pm I sent to him. ??

Or

failing that then I'll post the times and temps of my heating regime tomorrow for you.

here it is...thanks don...once the rain stops i'll put'er to work...anxious to toast some cane....

Matt, my heatgun is really a single heat gun with a knob on the side to control the airflow. By restricting the airflow it makes the air hotter. I think that maybe you could still control the heat by turning the gun off and on. Here's my record of the process:

0 mins. -gun on

5 mins. - top thermometer at 300F

10 mins. -bottom thermo at 350F

Reset to 0 mins. - start cooking
temp on top thermo drops to 320F

5 mins. - temp back up to 335F

8 mins. - back up to 350F

12 mins. - rotate two sections end for end. temp at 363F.

14 mins. - temp at 375F

17 mins. temp at 380F

22 mins. temp at 385F. Heat gun off.

25 mins. - sections out and temp at 320F

----------------------

I based my timing on Bob Milward's instructions that the optimal time and temperature is 20 mins. at 290F. But no more than 290F and no more than seeing a colour change. The colour change I saw seemed to be about appropriate and I planed three splines yesterday and found no brittleness apparent. The time and temp are of course up to you but this is at least something definitive that I believe worked well.

It's probably worth stating that I talked to Milward before I cooked and told him the temps I was achieving in the heatgun oven. He told me that if I cooked at that temp and time then I would be doing better than 3/4's of all the rods ever built. Milward, in case you haven't heard of him, is probably one of the most technically experienced people in the rodbuilding trade and I trust his opinions 100%. This is of course my first rod too and I guess I'll live and learn but for now anyway I would repeat the process about the same way.

Best of luck and let us know how you make out with your cooking.

Don



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Damn, I started reading what I sent and I found I wrote 290F is the max. It should read 390F is the max. And thanks for reposting that Matt.

Matt,

Are you binding the cane directly together, or are you using the MD Heat Treating Fixtures? If you are using the MD fixtures, you should run a test with them, as they will suck up a bunch of heat. It is a great deal of mass to heat up. I put my strips, bound in MDs, in the oven at 390. The temp will drop significantly down to the lower 300s, then slowly climb back. I use a simple 2 temperature heat gun.

Even if you are not using MDs, the best way to dial in your oven is always to just take 6 or 7 extra strips and cook them. Every oven, and I mean EVERY ONE, is different. They will not cook the same. Put the strips in (unbound) when the oven is fully hot (probably above 375), see where the temperature drops to, and see where it regulates (if it gets much above 380 just dial the gun down to low until it cools). Then, after about 7 minutes or so, pull out a strip, follow that by pulling another after another minute, then repeat until all strips are out. Once they cool, look at them and try to see at what time you started to see a very slight color change. That is the time you are looking for (see the Bamboo in the Laboratory article for an in depth discussion of this). I also test break the strips after testing too. You want them to be very firm and resilient, and break with the fibers in a long interlaced pattern. If they break like a toothpick, they are overcooked. I have run this test several times in my oven to really understand how to best treat the bamboo.

For what it is worth, in my heat gun oven, based on the same plans you used, 8 minutes is the right amount. The heat starts at 390, drops to the low 300s, then regulates at about 370-375 (a little hotter up front, a little cooler in the back). I flip after 4 minutes. Also, I have 9 foot ceilings in my garage. I run the oven in there without problems. It is wrapped with high temp insulation. I use 2 temperature probes to determine the temperature differential between the front and back of the oven.

Good luck. Taking the time to understand your oven setup empirically is the only way to achieve more consistent results from rod to rod.

Cheers,

Jay

Dumb electronics question. Would a rheostat in front of the heatgun be any good? Or would the only thing that cooks then be the heatgun ?

Karel

Rheostats are an old way of controlling speed which were applied more to D.C. motors Karel. There are other ways of controlling power to a heatgun which would work better but it's not an easy one. First, it's a high wattage appliance and so the controller needs to be high wattage rated. And second, you would be controlling the heat and also the speed of the blower motor which could cause some serious overheating problems in the gun. And btw, my gun is a model which increases the heat by cutting down the airflow with a knob on the side. Kind of the opposite of what you would accomplish with a controller.

Jay, As your post correctly points out, there are greatly varying degrees of heat obtained by different people using basically the same equipment. I find that quite understandable because just one variable I found that I had to correct was the placement of the thermometers. If the stem goes through the outer wall of the oven and is exposed to the airflow there then the reading won't be correct for the 3" inner chamber. Therefore I had to change the thermometers to the position where the two chambers are joined together so there would be no heat detection in the outer chamber which has nothing to do with the cooking chamber. Comprehende? And that's only one variable. Ambient is another big one I found and you definitely don't want to be outside where a breeze is blowing.

But along with that is the plain fact that there are widely varying opinions on the amount of heat and the time. Not to argue or disagree with your opinion but to point out the elephant in the room. This thread could be an opportunity to get to the bottom of that question. Or, on the other hand, perhaps you believe that we accomplished the same thing even though our timing was considerably different. Beginners and enquiring minds want to know.

You will never have a universal recipe that works as long as we measure the ambient rather than the bamboo itself, or have strips of varying volume and cross section. When you put a roast in the oven at 350F, you never get the meat to that temperature (at least not on purpose). You cook it for so many minutes per pound and then check its temperature with a thermometer. Sensors embedded in an MD fixture would be cool and close to the bamboo temperature, but do we need that level of complexity? Its better to characterize your oven and develop a recipe for that profile. With all the instrumentation we had in the lab, we still cooked wafers at a spread of parameters, then measured the diffusion before releasing a process.

Larry Lohkamp

I should just explain Larry that what I meant when I mentioned the ambient was that an oven would get hotter and hotter quicker in an environment where the air temp is 80F compared to where it is 50F. We had some scorching hot days here in Nanaimo this summer and I noticed a difference from now when it is about 65 or 70.

Also, using the MD fixtures would seem to me to be introducing a whole new set of variables to the heat regime. But aside from that, I should mention that I cooked my sections while they were not very far from different sizes between the tip section and the butt section. This I understand is different from what some people would do. My beginner's reasoning, right or wrong, was that the two sections would receive closer to the same amount of exposure to heat. Extra amount of planing for me as I planed the butt taper into the tip section first last night. A couple of hours at most. Now I'll do the tip to the proper taper. Stretching out the learning curve too!

Thanks for posting the data. I just built a similar oven and haven't cranked her up yet. Using the B&D 2 temp gun with it and MD fixtures. Did you insulate your ovens or are you running them without it? This might help to stabilize the temps. Also, I was wondering whether it matters how much space to leave below the bottom of the smaller tube and the bottom of the bigger one?

Larry

well i finally took the cracked out tin man, my oven, for a couple test drives...i think the we got'er down....it is insulated with regular r-13 pink insulation, nothing fancy....thanks for all the input..it really is all about just firing it up and doing some cooking...i two pipes are both six footers (6 and 3 inch dia.). The 3 inch pipe extends about 10-12 inched from the top...so by my math, thats about 10-12 inches from the bottom. my crude recipe: the bottom therometer reaches around 390-400 and top therometer reads around 275-300 on high...drop in the crash test boo and turn off for one min...when the bottom reads 350, turn on the low setting for 2 minutes, then kick on high until i hit the 390-400 range for about another minute. then took out the strips and fliped then end to end and repeated (total time approx 8 min). i mainly noted the bottom temp, as that was the highest temp. i let the strits cool and took pleasure in breaking them. nice firm bending and when they broke, splinters flew.....looked and felt done. on to the planing form...well virtual forms...but that will be a new post

matt

My heatgun is a Milwaukee gun with a single temp but which can be increased by the use of a knob on the side which cuts down airflow for higher heat. As to the wattage, I assume they're getting all that can be got out of a 120v, 15 amp wall plug. For those interested that is Volts x amps = watts. Theoretically 1800 watts but in practice much less due to loss. Any maker who claims more for their heatgun is pulling your leg. My oven is about 62" and the space is 3" at the bottom. The two pipes are the same length. I tried it first without insulation and found that it was taking too long to reach temperature so I decided to insulate it. The insulation I had on hand was some fibreglass backed t-bar ceiling tiles which were left over from a job. They are backed with about 1" of fibreglass and covered with a plastic of some kind. I was unsure of the plastic standing the temps but it turned out that they were fine. Fireproofed probably but I wouldn't want to leave the thing unattended. Fire extinguisher is standing by.

I insulated the whole thing and ran the oven and found that the top was getting a little too hot in relation to the bottom so I took off the top 12" of insulation and that's how I cooked in it. One thing worth mentioning again though is that you have to be careful where you place your thermomters. If the stems run through the outer chamber and into the inner chamber and are exposed to heat in the outer chamber then you won't be getting a true reading of the inner chamber. I made that mistake and had to change the locations to where the two chambers are joined. (tangential) And the rest is all recorded in my post. Let us know what your results are because any improvements will be good info for all.

Don.

The only thing I might add is that restricting the outflow of air will help stabilize the temp (bottom to top) inside the oven. That made a big difference in my oven.

Didn't think of that one but it's good to know! And another question for you and others using a heatgun oven. Some get higher heats at the top and some get higher heats at the bottom. Any idea why that happens in the reverse for some people?

And in fact Neunemann writes in his instructions that he would get higher temps at the bottom to begin with and then the heat would even out a bit better after a few minutes. Just the opposite of what happens in my oven? Makes me think somebody is not getting true readings and it's probably not Neunemann!

ref. http://www.fneunemann.com/fpwot/index.php?id=45

i doubt anyone is getting inacurate readings..as everyone probably has checked, rechecked, and then checked again....somepeople might get higher readings on top due to the possioning of the heat gun. if its blowing directly on the inner tube...that section will heat quicker and hotter. my gun is pointing down and away from the inner tube..thats why i have higher temps in the bottom...mybe if i angle it more towards the inner tube i'll get the top part up to temp quicker

I built my oven with the same type of design but found more consistant heat by running the unit horizontally. Put a screen in the exhaust tube for the strips to rest on and to avoid touching sides(inches from the heat source). I found that the temps stayed within 10-15* from end to end. Still flipped half way through. Very pleased with the results.

Just a quick question on Franks heat oven...I assume you are using 5' length on the outer tube, not 4.8 or whatever that comes out to be in metric lol. Having a helluva time trying to find a 6' tube to John M's heat tube.

not sure what lenght my oven is, and i'm not home right now to measure it.......i know it isn't 6'....5 ft sounds about right for the main pipe and that inner pipe extends about 6-8 inches past that.

matt