2011-02-03 06:40 start target max temp seems to be around 1250C k-type thermocouple 1300C + wire $25 - 28 http://www.auberins.com/index.php?main_page=product_info&products_id=39 $21 +$8 shipping carlafloripa http://search.ebay.com/150546932163 45A 240V SSR $9 + $5 shipping http://search.ebay.com/150552748002 kiln bricks (these are in garage) dimensions: 9 x 4.5 x 2.5 inches qty: 25 (some minor transport damage to 5 or 10? need to check) part numbers: A6017 133875 ST00 IFB-2300 max temp: looks like 2300F = 1260C is the maximum for these bricks droolworthy: http://www.zircarceramics.com/ heating element calculations --------------------- 18ga wire is 0.0407 inch dia wikipedia says nichrome is 1e-6 to 1.5e-6 ohm*m units '(1.e-6ohm*m)/((0.02in)^2*pi)' ohm/ft 0.375ohm/ft also this handy page http://www.resistancewire.com/mainpage.php?page=techinfo says 0.403 ohms/ft for 18ga nichrome (dead link) double-check resistance with multimeter! target temperature is 900C in order to achieve 1000C surface temp of wire, according to http://www.resistancewire.com/Html/Technical/CurrentTemp/CurrentTemp.php we need 15A 15A*120V = 1800W (maximum household wattage, possible to do 2x coils to run on either 120V or 240V) 120V/15A = 8ohm 8ohm/(0.403ohm/ft) = 20ft "Aim for 5000+ Watts per cubic foot." (heat treatment oven design) joppaglass says no more than 3000W per cubic foot for small kilns in case of "stuck on" fault condition 10A*120V = 1200W (typical power strip cutoff current) 120V/10A = 12ohm 12ohm/(0.403ohm/ft) = 30ft 13.5 OD box has 2.5 thick walls and 8.5 ID 1200W/(8.5in*8.5in*9in) = 3200 W/ft^3 close enough these interior dimensions are for 3 bricks laid out side by side on one row, and 1 and a half laid out long ways, like so: | || || | | || || | 9 |_||_||_| _____ ___ _____|___ 4.5 9 4.5 |--13.5--| stainless incubator box can be used ID 13.5"W 14.5"D 14.5"H OD 15.25"W 16.25"D 16.25"H with feet and knobs 17.5"H may need some bending of the sheet metal around the door frame table for target temperature: https://en.wikipedia.org/wiki/Nichrome#Table_2:_Current_.28A.29_vs._temperature_characteristics.2C_straight_wire. nichrome up to 1150C operating temp (1300 melting point) kanthal a-1 up to 1400C (1500 melting point) "When deciding on wire gauge it's best to stay 10-20% below the max surface load in order to have the longest usable life of the element. Surface current load for Kanthal a-1 is between 14 and 32 watts per sq inch of wire surface area. The higher the temperature you intend to operate at the lower the current load capacity." http://resistancewire.com/uploads/page/ADT2001_12_17_KA1_ENG.pdf 18 ga kanthal is 0.5387 ohm/ft and 1.02mm diameter 8ohm/(0.5387ohm/ft) = 15ft (15A or 1800W) 12ohm/(0.5387ohm/ft) = 30ft (10A or 1200W) 1800W/(30ft*1.02mm*pi) = 40W/in^2 1200W/(30ft*1.02mm*pi) = 26W/in^2 so 16 ga kanthal or even 12 ga would be better for long life, but more expensive this handy table recommends? roughly 3 feet of stretched coiled element length: https://en.wikipedia.org/wiki/Nichrome#Table_1:_Resistance_per_inch_.28.CE.A9.29.2C_closed_helix.2C_80.2F20_alloy. 30ft of 1/2" diameter coil is 230 loops of helix or 9 inches when fully compressed winding and basic mounting technique: http://dcknives.blogspot.com/p/winding-kanthal-a1-element-for-an.html more advanced heating element mounting techniques: http://joppaglass.com/small_el_kiln_proj/Instruct_kiln_proj.html http://joppaglass.com/small_el_kiln_proj/Electricals.html http://joppaglass.com/small_el_kiln_proj/marinite_install.html http://www.joppaglass.com/elements/groovb.folder/grvbrick.html http://www.joppaglass.com/elements/ceramic_rods/ceramic.html misc glass info: http://ceedweb.org/glass/list-archive.html web based heating element calculator: (metric, in polish) http://www.artom.com.pl/Promienniki/0013.htm example build: http://youtu.be/AyJAwBQ2Iuo