From: lschuler@cellular.uscc.com Date: Wed, 07 Jan 98 17:50:31 -0600 Subject: COZY: post-cure (long) Here's an note on my first post-cure "experience" (understatement). Hope someone benefits. Just finished my canard and first post-cure. Post-cure scared the hell out of me; I had left canard attached (bondo) to the bench and PVC pipe under the tail etc. Top layup was done about a week earlier. Figuring existing jigs were a good way to ensure it's stability. At about 125 deg I started hearing loud snaps and bangs; sounded just like a laminate snapping. With three months invested, I Almost stopped, but said to heck with it; if the glass cracked already, going on wouldn't be worse and I'd still end up with junk. Turned out the PVC/Bondo coeficient of expansion is significantly different than epoxy/glass. especially over the 'length' of the PVC. DUH! Bondo was giving way. Why is it always the simple (*&^%$ that bites! Neat way to get the canard lose though; no physical effort required or possible delams from pulling on it wrong or sawing into the glass. The post-cure was done at 150 Deg for 4 hours as specified for EZ-10/84. Should get me a Tg of 196 Deg. per spec sheet. Certainly better than the room temp cure Tg of 151 degrees. Not necessary, but opens some options not otherwise available. I made the tent out of 1/2" insulation sheathing held together and sealed with box tape. Box was 2' x 2' x (canard length + about 12"). Made it big enough to be able to re-use on main spar. I used a 1500 Watt space heater. The heater has a small fan in it, but didn't seem to have much flow, so I mounted a small squirle cage fan I had (I am a pack rat) about 2 feet behind [cold side of the heater] to keep the air moving and prevent hot spots. I used two thermometers made by Poly Fiber and moved them around occasionally to make sure the heat was even; the flow from the fan sure was helpful for even heating. Interesting way to calibrate thermostat to the thermometers (had to trust something, so I trusted those): Used a cardboard box (because I hadn't bought the insulation yet), stuck the heater, fan and all in it and set the thermostat for max. And set the fire extinguisher close by. The heater has an internal thermostat, but I couldn't get the temp up beyond about 130 degrees; so I bypassed it with a diferent thermostat. The temp controller was made out of a thermostat designed for 120/250 Volt home baseboard electric heating. Bought at Menards for about $12. It had an adjustment/callibration screw; that's convienient! So I re-calibrated it for the range I needed (72 degree center, just ain't the same as post-cure needs). After getting that all wired in, I set it for Max and started again. Then adjusted the cal screw until I maintained 170 degrees. Found that the temp swung + and - 10 degrees (20 deg) from thermostat off to on. Interesting, but figured it was the best I could do and keep it cheap. Figured it was probably due to the cardboard box - turned into a heat exchanger at 170 deg(there's more... keep reading). Marked the dial at the max for 170 deg after stabalizing at 170 read on thermometers (+/-10). Then, over the next 3 or 4 hours I adjusted the dial down and stabalized (+/- 10) at ten degree intervals (read on thermometers) and marked the dial. Didn't look like it was going to be very linear at each step, but that was due to the multiple adjustments each time (I think). I'm sure scientific repeatability is a serious issue with this set-up, but what the heck; the whole set up cost 12 bucks (assuming the wife doesn't miss the heater). During the cal process the safety fuse (marked at 113 Deg C) in the little heater blew on the way up to 170 F the first time, so out it came and replaced with a wire. What's the disclaimer?: don't try this at home kids! .... I Moved the fire extinguisher a little further away so I could get to it without getting burned. After getting down to the lowest 10 degree interval near the stop on the thermostat, I ended the cal. Turned out to be 90 degrees. Perfect range for post-cure. Measured the distance on the side of the dial between 90 and 170, marked off a piece of paper the same; then divided in 5 degree evenly spaced increments. Found the 'measured' marks to be remarkably close to my original temperature marks on the dial and that the original marks came close enough to linear that I used the measured paper to mark of the dial permanently. (Damn, could have saved about 4 hours of fideling with the individual steps) Built the heat tent around the canard as described above with the heater, fan and thermostat strategically located inside. Cut a small flap in the side where the thermostat was so I could adjust it and close it back up gracefully. Wired in a 7-1/2 watt light bulb (appliance type; borrowed from our refrigerator) to an old light socket I had laying around and into the thermostat/heater. Mounted this to the top of the heat tent so I could tell when the heater came on. Anyone recognize McGiver yet? I really liked that TV show! Set thermostat for 90 degrees intending to ramp from there (shop is at about 68 normally). Plugged it in and watched the thermometers go up to 125 before stopping. Ouch! Then drop rapidly to about 100 and slowly decayed from there for about 15 minutes before the heater kicked back on below 95 or so. Next 4 hours were spent chasing the thermometers and thermostat in an attempt to keep the wild swings under control while slowly increasing what I thought was the average temperature. My goal for the ramp upand down was not more than 5 degrees per half hour. Just a bit difficult given the wild swings. It was at one of these points that I heard the first rather loud cracks of Bondo give way and felt my stomach hit the floor. Finally dawned on me that the wide swings were due, in part, to the considerably larger area of the tent vs the cardboard box and the flow of air around the thermostat. The fan and thermostat were placed at one end of the tent and the heater about in the middle (lengthwise). The arangement was intended to provide the greatest circulation and to keep the fan motor at least not hotter than the surrounding air. Cut a couple of slits in the lid along the tent and stuck my hand in. Nothing wrong with airflow anywhere. But small confines of the cardboard box and proximity of the termostat to rapidly moving air were very different. Dug into another box of pack-rat stuff and came up with a 120 Volt muffin fan. Same type available at Radio Shlock if someone needs to buy one. Mounted the fan a couple inches away from the thermostat (pointed at the thermostat) and plugged it in. VIOALA! Temp held within +/- 2.5 degrees (5 degree swing) from heater on to off to on! Better than my cal box and certainly acceptable. I was happy. From there on, the ramp up at 5 degree intervals went like clock work and the calibration and measured marks I had done earlier matched the thermometers within about 2 or 3 degrees all the way up to 150 and back. Soak time at 150 was right at 4 hours followed by 5 degree per 1/2 hour back to about 100 degrees, then pulled the plug. Left the fan on (no heater) over night letting the last 30 degrees or so taper off via heat loss from the box with no attempt to maintain via the heater. McGiver lives! I'm just slower that the story writers he had. Note: Don't remember what I paid for the Poly Fiber thermometers, but saw a nifty inside/outside digital thermometer at Radio Schlock yesterday for $22.00 which goes up to 158 Degrees F and 'could' be used later in the airplane. The thermistor for outside temp is very small and on the end of a 9 foot wire. Perfect for imbeding just under the outside skin somewhere. Thing reads relative humidity too for those using leftover 2427 and has a high/low memory to see how hot the cockpit really gets in Arizona..... FYI Some fill and sanding to do, then on to the elevator. Canard took me 3 months so far. Larry Schuler plans #500 lschuler@cellular.uscc.com Date: Thu, 08 Jan 1998 10:20:39 -0500 From: David Domeier Subject: Re: COZY: post-cure (long) Larry, re " Bondo was giving way. Why is it always the simple (*&^%$ that bites! Neat way to get the canard lose though; no physical effort required or possible delams from pulling on it wrong or sawing into the glass." Thanks for sharing your experiment with home made oven cure technology. I would template and carefully sight line the canard after that heat trick to insure that it is still straight. I can visualize the structure sagging for lack of adequate support after the bondo let loose. I've used a hair dryer the change the shape of none structural parts and it is amazing how pliable any lay up becomes when heated. dd From: lschuler@cellular.uscc.com Date: Thu, 08 Jan 98 15:35:43 -0600 Subject: Re: COZY: post-cure (long) dd wrote: >Thanks for sharing your experiment with home made oven cure technology. >I would template and carefully sight line the canard after that heat >trick to insure that it is still straight. I can visualize the >structure sagging for lack of adequate support after the bondo let >loose. Done. Came out same as it went in. I also had clamped a 7" long layup of 2 plies UNI (some old scrap stuff) in the oven as well. Clamped on one end and hung 3 lbs of stuff (bolts and such) on the oposite. Came out flatter than a pancake. May not be scientific, but sure nice for confidence factor. >I've used a hair dryer the change the shape of none structural parts >and it is amazing how pliable any lay up becomes when heated. The room temp cured Tg of EZ10 is only 151 degrees F. Bet that hair dryer gets way above that! Larry From: "John Stricker" Subject: COZY: Science Fair Experiment Date: Mon, 2 Feb 1998 19:44:04 -0600 Cozy List members, I sent this to Marc for his approval as to on-topic for the list and he gave me the OK to post it so here it is. This is topical as to composites and construction but not specifically to Cozy's. OK, I'm looking for input suggestions here. My 13 yr old son is just starting/thinking about his science fair project and he asked if we could do something with "the airplane". Seeing as how a Cozy is in the works and also as to the fact he's already done some aerodynamic stuff in the past at the fair (made a r/c aircraft wing and blew air over it to show a stall at critical aoa) we got to talking about composite construction. Here's an idea we've been kicking around. The subject is the effect of different cure temperatures on the temperature stability of the finished piece. The hypothesis is that the higher the cure temp, the greater stability of the piece in a high temperature environment. As Nigel pointed out on the R.A.Homebuilt group, this isn't much of a hypothesis as a known fact, but the degrees of deflection are not known and we will be measuring them. The outline of the experiment is as follows: Laminate 6-14" long pieces of bi cut at a 45 degree angle. Due varying temperature cures at room Temp, 100, 125, 150, 175, 200 degrees. (The plan is to do it in mom's oven, so temp control should be pretty good, not necessarily precise as to degree, but should be pretty stable.) Bolt all six pieces by one end to a fixture in a box. Weight the free ends of each piece identically and mark the deflection at room temp. Elevate the temp in the box recording the deflections of the pieces as the temperature increases. I'd like to get it up to around 225 degrees or so. OK Ladies and gentleman. What do you think?? I would appreciate suggestions in regards to the lay-up, type of glass (SGlass, etc.) Post cure process, bias of the lay-up, feasibility, potential hazards, etc. In making your suggestions, don't forget that we WANT some deflection of all the pieces, but we don't want them to be limp noodles at just above room temperature either. I'm particularly interested in SPECIFIC suggestions as I listed above. The equipment used for the experiment should be able to be shown, but the experiment does NOT have to be duplicated on the site. OK, flame away for it being off topic. But then again, it may show all of us something useful on just how composites are affected by temp and post-cure. I'm also hoping that it may uncover a "critical" temperature for lay-ups that might be informative to all of us building Cozy structures. Maybe more than we want to know. I will post whatever results he comes up with, just for the collective knowledge bank on the list. If you want to email me about this off the list if you think it's off topic, feel free John Stricker jstricke@odsys.net "I didn't spend all these years getting to the top of the food chain just to become a vegetarian" From: lschuler@cellular.uscc.com Date: Tue, 03 Feb 98 09:28:24 -0600 Subject: Re: COZY: Science Fair Experiment John Stricker wrote: >snip >Laminate 6-14" long pieces of bi cut at a 45 degree angle. >Due varying temperature cures at room Temp, 100, 125, 150, 175, 200 degrees. >(The plan is to do it in mom's oven, so temp control should be pretty good, >not necessarily precise as to degree, but should be pretty stable.) >Bolt all six pieces by one end to a fixture in a box. >Weight the free ends of each piece identically and mark the deflection at >room temp. >Elevate the temp in the box recording the deflections of the pieces as >the temperature increases. I'd like to get it up to around 225 degrees >or so. >snip Couple things to consider: *Good rule of thumb is that post cure will raise the epoxy Tg by roughly 40 to 50 degrees F. *Post cure doesn't do a thing for the glass, just the epoxy. *Following a post-cure, you should be able to raise the temp to at least 40 or 50 degrees (or more) above the highest cure temp before the epoxy begins to soften or show signs of weakening. *Remind your son that cured epoxy is a plastic and it "WILL" burn (stinks too); so don't get carried away too much with real high temps. [225-250 should be safe enough] *Tg is the resulting important parameter; however, tensile strength also goes up with most epoxyies I've read about. *Post cure is "normally" done by ramping or stepping the tempurature up to the ultimate cure temp; holding at that temp for a couple hours; then ramping or stepping back down. May be an all day job requiring baybysitting Mom's oven for each post-cure test temp. *The glass used and orientation may not be as important to the results as consistency and repeatability. Just make sure all test coupons are exactly identical in glass orientation, glass content, epoxy type, and epoxy content. *If he really wants to see the results of epoxy cures; just test neat epoxy (no glass). Controlling the thickness of samples can be difficult; and may be a lesson in science all by itself (ie. gravity). Good luck. Larry Schuler Cozy-IV plans #500 lschuler@cellular.uscc.com Date: Tue, 03 Feb 1998 13:11:25 -0800 From: hrogers@SLAC.Stanford.edu (Howard Rogers) Subject: Re: COZY: Science Fair Experiment John, I had to jump in, here, as well, as I have done some tests very similar to what you have described, though for a different purpose, here at the Stanford Linear Accelerator Center (SLAC). We made some test samples for four different epoxys, a couple of room-temp cure, and a couple of heat-cure. I cast the "neat" epoxy into rods, hung weights on the ends, and set up dial indicators to measure deflection. Though the deflection was of some interest to us, we were primarily interested in the creep, over time. We also made some layups, in the form of boxes, filled with simulated cesium iodide crystals (very dense), and did essentially the same experiment, using dial indicators. I took data from these samples for over a year, and we learned a lot. My point here, is that initial deflection is going to be hard to measure, because it won't "stay put". If you measure it accurately for a week or two, you will see the steepest part of the deflection curve, and the dynamic nature of the stuff can frustrate you (voice of experience). Still, this sounds like a VERY worthwile endeavor, and my hat is off to you and your son for such a good idea for a science fair project. Let us know how it turns out. --Howard Rogers, A&P 2005148 hrogers@slac.stanford.edu (Howard Rogers: pilot, aircraft mechanic, saddle maker, high energy physics R+D handyman) _____________________________________________________________________ Do your part: Help stamp out the mindless, indiscriminate use of impersonal, cutesy "rubber-stamp" E-mail signatures. _____________________________________________________________________ Opinions are strictly mine, and are usually not those of my employer. From: "Ian Martin" Subject: Re: COZY: Science Fair Experiment Date: Tue, 3 Feb 1998 13:35:59 -0800 Hello John, First, nice way to involve the family in the project and further the "education" part of our hobby! Some suggestions: Use about 5 layers of UNI, this so you can re-create if necessary with some degree of repeatability. Use really good quality control in squeeze'ing out to ensure uniform thickness. A band saw cuts the pieces nicely. You can build a test machine (very simple) along the lines of that shown in Andrew Marshall's book. And test the samples for strength before and after. The math is easy. If you don't have the book I can help you with the formulas and press design. To test the heat you may want to try something like this side view |o___ glass________ use wood blocks to hold the glass in place, bolt weight on ends independantly |o | |___________ I did alot of testing similar to this prior to building. I used various types of glass and resins. The results let me know what I was capable of creating in my enviroment. Good luck, Date: Wed, 19 Aug 1998 22:41:50 -0500 From: "Joseph H. Hart IV" Subject: COZY: Simple Homebuilt Post-Cure Oven? I am considering using the German L285 epoxy and am interested in post-curing. No, I don't want to paint my Cozy black, but maybe silver. Has anyone built any sort of of post-curing apparatus? What would it take in terms of insulation, thermastatic device, energy requirements to make an oven of sufficient size to maintain 170 degrees for sixteen hour stretches? Thanks in advance for any information. Jody Hart jodyhart@communique.net From: cdenk@ix.netcom.com Date: Thu, 20 Aug 1998 07:26:19 -0500 (CDT) Subject: Re: COZY: Simple Homebuilt Post-Cure Oven? There are numerous items, and I'm just going to write aloud as I think: 1: Safety a: All materials must be well below the extreme possible temperatures b: Temperature must be uniformly distributed (a fan(s)) and monitored at numerous points. c: Don't set house on fire! 2; Doing: a: 2 choices or somewhere in between: Lots of heat or lots of insulation. b: Insulation probably fiberglass batt house insulation c: Heater: Kerosene (heating fuel oil) torpedo shaped portable type constuction heater, here in the states they are readily rented. Caution fumes indoor. From: "Nat Puffer" Subject: Re: COZY: Re: [canard-aviators] Simple Homebuilt Post-Cure Oven? Date: Thu, 20 Aug 1998 11:04:40 -0500 Joseph, Why not paint it silver and put it out in the sun on a hot day. Should get to 50 deg over ambient. Nat ---------- > From: John Rippengal > To: Joseph H. Hart IV ; cozy_builders@canard.com; canard-aviators@canard.com > Subject: COZY: Re: [canard-aviators] Simple Homebuilt Post-Cure Oven? > Date: Wednesday, August 19, 1998 8:30 AM > > Burt recommended putting the part out in the sun at the primer stage. If > it's a darkish colour the temperature can easily get up to say 150F or > more, but not sure if you can get 170. Very simple though. > John > > ---------- > > From: Joseph H. Hart IV > > To: cozy_builders@canard.com; canard-aviators@canard.com > > Subject: [canard-aviators] Simple Homebuilt Post-Cure Oven? > > Date: 20 August 1998 16:12 > > > > [The Canard Aviators's Mailing list] > > I am considering using the German L285 epoxy and am interested in > > post-curing. No, I don't want to paint my Cozy black, but maybe > > silver. Date: Thu, 20 Aug 1998 21:23:47 -0400 From: charles wilhite Subject: COZY: Re: [canard-aviators] Simple Homebuilt Post-Cure Oven? Joseph H. Hart IV wrote: > Has anyone built any sort of of post-curing apparatus? What > would it take in terms of insulation, thermastatic device, energy > requirements to make an oven of sufficient size to maintain 170 degrees > for sixteen hour stretches? > > The best method I can think of is to take your parts to an auto body shop and rent the spray booth for a weekend. The better shops have spray booths with heat and can easily maintain 150 F for hours. Several booths can get to 170 F. This is my plan. Charles From: "Bob Berg" Subject: Re: COZY: Simple Homebuilt Post-Cure Oven? Date: Thu, 20 Aug 1998 19:57:04 -0700 Jody, I'm sure some folks who are far more knowledgable will comment, but I've done post-curing using nothing but a sheet, a simple frame, an electric space heater, and a thermometer (mercury, from a Stits fabric kit). I ramped up the temperature about 10 degrees per hour until I reached my target (150 F in this case), let it sit at that temp for a while, and then ramped it back down at the same rate. Doing individual parts this way, I don't expect to ever need an enormous oven. The tub will probably be the greatest challenge. BTW, I'm planning to use L335 for the bulk of my construction, although I may use 285 for certain parts where I want a high post-cure temp (maybe near the powerplant?). I've heard horror stories about folks placing composite aircraft to cure in the sun with flat black paint, and having the foam melt out of the core. I think I want more control of the process. I read somewhere that the surface temperature of vehicles with metallic silver paint is much higher than for white ones, although I'm sure black paint is **much** higher. Bob Berg Mk IV #684 -----Original Message----- From: Joseph H. Hart IV To: cozy_builders@canard.com ; canard-aviators@canard.com Date: Wednesday, August 19, 1998 9:10 PM Subject: COZY: Simple Homebuilt Post-Cure Oven? > I am considering using the German L285 epoxy and am interested in >post-curing. No, I don't want to paint my Cozy black, but maybe >silver. Has anyone built any sort of of post-curing apparatus? What >would it take in terms of insulation, thermastatic device, energy >requirements to make an oven of sufficient size to maintain 170 degrees >for sixteen hour stretches? > > Thanks in advance for any information. > >Jody Hart >jodyhart@communique.net > > From: lschuler@cellular.uscc.com Date: Fri, 21 Aug 98 09:42:19 -0600 Subject: Re: COZY: Simple Homebuilt Post-Cure Oven? Jody Hart wrote: >I am considering using the German L285 epoxy and am interested in >post-curing. No, I don't want to paint my Cozy black, but maybe >silver. Has anyone built any sort of of post-curing apparatus? What >would it take in terms of insulation, thermastatic device, energy >requirements to make an oven of sufficient size to maintain 170 >degrees for sixteen hour stretches? I wrote up a description of my post-cure setup when I made my canard, not fancy at all, but functional. Should be in the Cozy archives. Larry Schuler MK-IV plans #500 From: cdenk@ix.netcom.com Date: Wed, 28 Oct 1998 06:02:44 -0600 (CST) Subject: Re: COZY: Post cure: good heat source? On 10/27/98 22:12:57 you wrote: > >Hi Cozy group, > The electric fan heater unit I bought is not cooperating in my >effort to raise the temperature within a small (4'x6'x1') plastic >enclosed area to at least 125-130 degrees. The thermostat kicks it off >whenever it gets up to about 90 degrees. I tried to fix this by >bypassing the thermostat control, but alas to no effect. Would anyone >have a good suggestion for a forced hot air electrical heater that I >could purchase that can be easily utilized for this purpose? I'm looking >for a name brand and model and a unit that has a thermostat that can be >easily bypassed, for say $50 or so. >_________________________ >Thanks, >Dana Hill >CZ IV, #676 > > > >___________________________________________________________________ >You don't need to buy Internet access to use free Internet e-mail. >Get completely free e-mail from Juno at http://www.juno.com/getjuno.html >or call Juno at (800) 654-JUNO [654-5866] > > A likely problem is, the heater needs air moving through it to prevent oveheating. They are usually operating in free air. When the air is ducted into a closed space, either enough friction is generated to slow the air movement causing overheating, or for every bit of air going into the enclosure, the same air (slightly smaller volume due to thermal shrinkage) must exit the enclosure. There must be an exit air opening. You might try adding another fan before, in series with the heater, or adjusting the exit opening. Its a balancing act, too slow air movement results in overheating, and too much air movement results in too much heat leaving the exit opening. Other heat sources include old electric duct furnaces from houses or commercial installations. Heating elements from an old electric oven. CAUTION: Any of this is potential fire hazard. A concern also is Fire Insurance is usually VOID if the assembly is not UL or CSA (Canada) laboratory labeled! Date: Wed, 28 Oct 1998 07:19:05 -0500 (EST) From: "C. W. Wright" Subject: Re: COZY: Post cure: good heat source? (fwd) >could purchase that can be easily utilized for this purpose? I'm looking >for a name brand and model and a unit that has a thermostat that can be >easily bypassed, for say $50 or so. I'm using a 1500 watt hairdryer and an electric strip heat thermostat. I bought a "J-box", wall socket, and the thermostat for abt $20 at Lowes. I put the thermostat in the are to be heated and either put the hair dryer in there too, or put it outside depending on the application. A piece of scat tubing fits nicely over the end of the hairdryer if you want it out of the box. This method is less eff. cuz the air is not re-circulated. C. W. Wright From: lschuler@cellular.uscc.com Date: Wed, 28 Oct 1998 09:37:46 -0600 Subject: Re: COZY: Post cure: good heat source? Dana Hill wrote: >I'm looking for a name brand and model and a unit that has a thermostat >that can be easily bypassed, for say $50 or so. First, check the archives. I wrote up how I post cured my canard. Second, most home-style electric heaters (and hair blowers) have a secondary safety thermostat usually mounted internally somewhere near the front of the element(s). Look for a small bullet shaped (about a quarter the size of a .22 shell) glass or metal wired in series with the heating element. May be covered with a protective sleeve. This little gem will cut off current to the element if the airflow gets blocked and overheats. Great for home safety, but won't let the device get hot enough for our homemade ovens. I cut mine out and bypassed it. Will never use it in the hose again! Can't recall the make/model, but is a 1500 watt unit. Plenty big if the oven is insulated well enough. I also bypassed the internal adjustable thermostat because it was made for people-comfort levels, not for post-cure ovens (couldn't be adjusted or 're-calibrated'). Made my own using a Menards (Home Depot etc) $$cheap electric floorboard thermostat and modified and calibrated it for the range I needed. See the archive. Don't remember if I mentioned this in the archive, but the thermostat is slow reacting (causes wide deviations in oven temp between on/off cycles). I solved this 'adequately' (+/- 2 deg rather than 15 or 20 deg) by using a pc-style muffin fan in the oven pointed directly at the thermostat. I also used a small squirrel cage fan to keep air circulating in the oven for even heating all over (keep bearings oiled, it gets hot in there). This fan was placed behind and the air directed at the back side of the heating unit. If I had placed the thermostat close to the air intake side of the squirrel cage, I probably wouldn't have needed the muffin fan. Next time... Thermostat was mounted in the oven just above the squirrel cage fan with a flap door in the insulation to adjust it. I manually 'stepped' the temp up using my pre-calibrated marks on the thermostat. Also had two glass thermometers stuck through the insulation (moved them around occasionally) to compare and verify my homemade oven progress. Those thermometers were purchased from Alexander (now ASS). Worked like a charm. And cheap! I was darn sure part was very well supported in original jigs, and didn't ramp/step the heat up too fast. Used same ramp schedule (degrees per hour) to cool it down to about 95, then shut it off. Whole process took all weekend. Ramp up Saturday, hold time over night (about 12 hours), then ramp down Sunday. Hope this helps. Larry Schuler MK-IV plans #500