www.TK560.com

[TroyO]

I have been kind of re-habbing my machine (With dramatic results) It's an over/under 24x32 and now has an upright Vac Motor/17 CFM Vac pump dual stage vac system, improved platen and a real raising/lowering frame. (Before it took two people) Performance is MUCHHH better.

I noticed the other day that my Hardi backer oven is cracking apart, and decided as long as I was redoing everything else it was time to upgrade that too. I want the next one to be pretty permanent, so I'm going to make it from a sheet of 18GA stainless I have hanging around.

Anyway... reading up on ovens, it doesn't look like I really want to up my wattage over what it was before. I'd guesstimate that to be around 3000-3200 watts.

I'll be using 220V, since I now have an outlet available for that. (Unfortunately it's 2 hots/ground. No neutral to tap from.)

For ease of construction, I am going to make a straight sided box, 22x30x6 then mount one of the outer coils halfway down the side so it's about 3-4 inches from the plastic. I Might also add an expanded metal grid between the coils and the plastic to help with evenness.

On to the questions... I'm thinking I will use 2 segments, but I may lay them out a little different than what the oven calculator shows.

If I lay it out as below, with 2 segments "nested" within the other I should be able to run it at either 1500 or 3000 watts, right? (or 1600/3200)

I was thinking that with the thicker plastic that I should be able to pull now, I could use one element to preheat thick stuff without burning, then flick a switch to turn it up to full heat. (Blue and red are the 2 segments. Black/White are Hot1/Hot2)



I realize the spacing is a bit wider in "One segment" mode, but using a 6" deep stainless oven should even that out some?

Can I even stretch the ~11 inch coiled segment far enough to cover the ~250 inches of linear distance to lay it out this way?

Thoughts, observations advice? All are greatly appreciated... if I'm barking up the wrong tree that someone else has already tried please let me know that too.

[crashmann]

Wow, it sounds like you've done a lot of work revising your machine! I'd love to see some pictures if you don't mind sharing.

My Hardibacker has developed the Grand Canyon crack over the past year (or more), and one day I'll get around to replacing it, or building the monster 32" x 48" over under machine.



I think you'll get better performance with the stainless steel oven because it will reflect much more energy toward the plastic. Mounting the outside coil a little closer to the plastic sounds like a good idea to me, but I have no experience with that yet.

11 coiled inches stretched out to 250 inches?!? I think your not going to have very much coiling left once the wire has been stretched that far. Go back to the oven calculator and see what it says for "straight length needed." Having straight wire (versus coiled segments) shouldn't make a difference if the oven calculator says it will work.

Please post the numbers you entered in the calculator so I can double check your work.

I also like the nested coil idea, but I think it may be too hot for preheating unless you drop the plastic just a little from the oven.

You've definitely piqued my interest since I hope to do a similar project!

Charlie

[TroyO]

What I put in the oven calculator kind of depends on how you look at it, LOL.

You could look at it like (2) 1600 Watt/220V ovens, OR as (1) 2 segment 3200 Watt/220V oven.

Layout wise, it's closest to (2) 1600 watt/220V ovens... so the oven calculator is set to 1600 Watts/220V 22X30 and 4 loops. It's still got the double run around the outside, so I can drop around (30x2 + 22x2) 104 inches from the total length of 296 inches, for 192 inches stretched from a 10.083 inch coiled segment. (For practical purposes 10 inch coils, 200 inch stretched) (1500 watt works out to 10.75 inches.) The straight length listed is about 344 Inches.

Anyway, up the watts to 3200 and double the segments and you have pretty much the same values, but the layouts are different.

Hmmm.... but, if I jump to 24 Ga uncoiled nichrome, 16.6 Feet (200 inches) @ 1.671 Ohms per foot would be 27.7 Ohms and 1750 watts per segment... add in the vaguaries of layouts and the little bit of extra spent making bends and it would be just about right using 24Ga straight wire. That's mighty interesting... I'll run through some other numbers, it seems that with straight wire you could run a lot closer pattern and get more "loops" in your pattern which would help with more evenly distributed heat.

[TroyO]

Hmmm.... actually, thinking it around again...

Running it with normal wound coils but set up as a 4 segment oven may work out better. It uses a lot of wire, but the stretch factor works out better. And really... since you get it in 10 foot chunks, as long as you use less than 10 feet who cares?

Each nested loop is a 1600 Watt/2 segment setup.

40 coiled inches (Per nested segment) stretched out to 200 linear inches. (Roughly) 80 Total coiled inches are used.

It would look more like this:



Crashman... what about hooking it up a little different? Nothing saying one couldn't have one nest run at 2200 watts and the other at 1000..... if you think 1600 was too hot anyway.

Hmm.... actually, that makes a lot of sense.... that gives you 1000W/2200 Watts and 3200 watts as an option...... 3 temps, two switches.

Damn.... back to the calculator.....

[TroyO]

OK... same basic layout, but....

Red uses a 32.25 inch coil stretched to ~200 inches.
Blue uses a 54 inch coil stetched to ~200 inches.
(86.25 coiled inches used.)

Red puts out 2000 watts, blue puts out 1200.

Red OFF/Blue OFF = 0 Watts ( ;-P)
Red OFF/Blue ON = 1200 Watts
Red ON/Blue OFF = 2000 Watts
Red ON/Blue ON = 3200 Watts

Kind of nifty, huh?

(Edit... fixed some math.)

[TroyO]

OK, this is approaching my final layout, I think....

(Note... the grey lines are just jumpers of regulat copper wire, so I can get from the outside row in without overlap.)



That's a 4 segment oven, with a nested layout.

The Red "Nest" is 32.267 inches of coil pulled to 300 inches total for 96.8 Ohm straight resistance, 48.4 Ohn segment resistance and 24.3 Ohm total resistance. It draws 9.091 Amps @ 220V and puts out 2000 Watts.

The Blue "Nest" is 53.778 inches of coil pulled to 300 inches total for 161.333 Ohm straight resistance, 80.667 Ohm segmant resistance and 40.333 Ohm total resistance. It draws 5.455 Amps @ 220V and puts out 1200 watts.

A set of 10A 220V switches will control power to each circuit, allowing for an Off/1200W/2000W/3200W range of output.

It uses 86.045 inches of 22 Ga coil, out of 120 inches that comes in a roll. The outer "Row" of coils will have the blue (1200 Watt) mounted to around 3 inches above the plastic. The Red outer coil will be mounted on the oven ceiling directly above that. (6 Inches away from plastic.) The coils are spaced about 1.25 inches apart, so even in one "Nest" mode the spacing is 2.5 inches.

The overall box is 22x30x6 and will be insulated on the outside with 1 inch of either mineral wool (~800 degree) or Ceramic Wool (~1200 degree) insulation. I will probably make a fiberglass cloth "quilt" with it, so as to limit particles and itchiness. (At least in the finished product... I'm sure making it will suck. ;-P)

Anyone have input? Think it will work.... or not?

(Ohh, and by the way... that nice, even layout of the segment connectors just happened to calculate out that way... cool randomness!)

[TroyO]

http://www.tk560.com/phpBB2/viewtopic.php?t=452

How's that for reinventing the wheel? ;-P

Ahhh well, I kinda figured someone had to have covered this ground before... but being as it's DrCrash I'm in good company. Now off to read his thread to see if I pick up any tips, LOL.

[crashmann]

Ha-ha! You've really done a great deal of development work with your oven coil idea, and it is good to see a similar design developed by the long lost Dr. Crash.

Plugging the numbers into the calculator for two segments, I get the same values for your Red Nest and Blue Nest. I haven't tried breaking a segment in the middle and continuing it with a copper jumper. I think it would work, but I haven't seen it done (yet ) Good designs are usually aesthetically pleasing, so you must be on the right path since the symmetry of the coil connectors worked out nicely.

You probably have at least a 15 amp breaker on your 220 volt circuit in your circuit breaker box, and the load calculated above should work fine with that.

I give it a big thumbs up. Go for it!

Charlie

[TroyO]

We are gathered here today to celebrate the life of Hardi OvenOne. Hardi OvenOne was a good oven, responsible for partially melting hundreds of sheets of plastic under adverse conditions and working with the rather difficult Mr. McCrappy ShopVac.

He had a short tenure working with Mr. Happy McVacPump, which seems to have been a little overinspiring to the tired old boy, as the bang and shuffle involved with various other workplace improvements led to the untimely demise of Hardi OvenOne.

Seems rolling the workplace over an airhose created the very last disturbing vibrations that Hardi OvenOne could endure, and he passed from this earthly plane in a pile of somewhat charred rubble and clouds of dust. Although he had never met Peter Platen before that moment, I'm happy to say they did get to exchange a passing greeting during the incident.

It is rumored that Hardi's position will be taken by a somewhat more steeley eyed replacement, Mr. Multiheat McStainless.

A moment of silence please? (Psst... Mr. McVacPump, please stop hissing!)

[TroyO]

I ordered a pile of stuff from infrared heaters ($120.. ouch!) but I got everything I could think of to make it 100% right from the get go. I don't want another death on my hands....

Soo... current plan is:

Layout as above, ceramic insulators every 8 inches or so. 22.5x30.5 inch 18 Ga stainless shell, 1 inch ceramic wool sewn into a "quilt" of fiberglass cloth surrounding the perimiter. Probably mineral wool on the top, if I can find it. I would have used all ceramic wool but I did my math wrong and only ordered half what I needed. Worst case, I'll order more from infrared heaters, or see if I can score some scrap on ebay.

I also got 10 feet of the high temp power wire.... electrically I know it shouldn't be a problem "Breaking a segment" but with heat punching at it from both sides it seems like a worthwile investment. I'll also use it for power leads between the oven and switch box.

The shell will be 3 pieces, rivetted together. The long length will just be a

[jegner]

Good luck on the metal oven. Be sure to have the wires insulated, and the power tapes insulated from the metal base some way, or you run a good change of an arc, and electrical shock. Post some pics of your project if you can!

JIm

[TroyO]

Actually I'm using the 2 piece insulators to bring power in/out of the shell.

Infrared heaters site, part number PI-B-1-S

I think that is what they are actually designed for, rather than holding coils like a lot of folks have. You drill a 3/16 hole, and the square end goes through the hole and is covered by the cup part on the outside. Then you take your binding post (Stainless bolts in this case) and attach that to the coil, then go through the insulators and attach your power wires to the outside.

Anyway... I have a functional knowledge of electricity, so I think I can keep things safe. With a grounded oven shell, it actually should be safer (assuming decent implementation).

It is a bit pricey, even not having to pay for the actual stainless shell... 80 donut insulators, 9 pass through insulators and the thermal insulation... it adds up. ;-P

But.... I should only ever have to make ONE... LOL

[TroyO]

I ran into some high temp silicone sheet on Ebay, and got an 11x36 chunk of 1/16" thick stuff.

I'm thinking I can make a simple"skirt" type section to help seal the edges of the oven. It was only $15, so I figured it was worth a try. Maybe I can sew it with Kevlar thread?

[jegner]

Worth a try. Let us know how it goes.

Jim

[TroyO]

I've been taking pics as I go so I can post and write it up. So far there's lots of pics of what doesn't work.. LOL.

I think I've got the stainless steel cutting problem worked out, so I can probably get some stuff done this weekend. Yay!