Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.
Yes, I have a Cress, about 18" cube inside, top lid. It's expensive to run, about $5 to get to 1800 degrees f. And it takes a long time, couple three hours (IIRC). Both to warm up; and cool down for tempering. It's fine for larger parts. One thing to know; the temperature gradient in a large kiln is very noticible.
I also have a small 115V dental style kiln. Much nicer for parts under 3" sq x 6". Heats quick, cools, and only cost $0.50 to get to temperature.
I put electronic controls on both of them.
Dave J.
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.
TomB wrote: Don't they make an affordable infrared temperature sensor?
I have one that is intended for use in melting. It was not what I consider affordable.
Effective range runs from 600° C through 3,000° C, and shifts readily between C and F. It is an Ultimax Model UX-20. It would be useful for hardening, but does not go low enough for drawing. There may be lesser expensive models, made by others, for lower temperature use.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
A handy oldtime trick for annealing - NOT tempering, which requires a clear "endpoint" - is to heat the metal past the transition temperature and then bury it in a tub of limestone. Get it a few inches deep, and it will take several hours to cool.
For decent control a front loading electric furnace with a good controller is what you want. Depending on what you plan to heat treat, it should go to 2000 or 2200+ F.
I picked up a Thermolyne furnace that was surplus to a semiconductor fab lab with about a cubic foot capacity for around $300. Be sure to check the elements are still good. Given your location, there might also be similar deals from resellers of surplus semiconductor fab machinery??
Continuously there are gov't auctions. The trend is less mech to esoteric. A "lot" named lab equip may include many good items. The Thermolyne 1400 i acquired in a pallet of other stuff was ex-FDA.
Keep in mind a heat treat oven is only going to heat up so many times before a heating element burns up
I bought this old unit ten years ago on Ebay. Fortunately it came with spare heating elements. When the heating elements are gone I'll probably scrap the oven for lack of replacement elements.
I also have a Netcraft oven as a backup. Both are in the basement of my home. I open a basement window and use a fan to vent out the smoke from oil quenching. I don't seem to get complaints from the wife when I heat treat.
However, heattreating is interesting and fun to do. Also keep in mind commercial heat treaters do a much better job than I can do at home and it is not expensive to have done.
I have friends that bring me small parts to heat treat because they know I can do it overnight and have the part finished by 8:00 AM. Every time I power up my furnace I charge a flat
rate of $60.
I certainly agree with Jim's comments about commercial heat treaters. Oxidation is a big problem, especially for long soak cycles, but the commercial guys generally use controlled atmosphere furnaces. The items change color, but are generally free of scaling.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
JimGlass wrote:Keep in mind a heat treat oven is only going to heat up so many times before a heating element burns up...<snip>....When the heating elements are gone I'll probably scrap the oven for lack of replacement elements.
While I realize that this is a hypothetical, it is possible to get replacement elements. I refurbished a ceramic kiln by ordering new coiled elements from these guys:
All you need is the wire diameter, coil diameter, and resistance of the coil, and they can make replacements. They have Kanthal, Nichrome, etc. in several types and sizes. As it turned out, they could furnish the wound coils for less than it was going to cost me to buy the wire.
Need a heat treat furnace? Build it. I've done two so far and have made and installed elements in two others.
For the box, I use 2-1/2 or 3" insulating tiles available from Green refractories or any other local industrial supply that carries firebrick. The spec on it is 25# per cubic foot insulating tile. It cuts well with a hacksaw blade and you can easily route slots for elements with a 1/2" straight carbide router bit in a die grinder.
I use Harbor Freight .041" stainless steel lock wire for the elements. For 120VAC, 10 amps, you use 32 feet of wire wound around a 1/4" diameter rod and then stretched for about 3/32" or 1/8" spacing between the winds. Where the ends of the winding go through the caase, you double over the ends of the elements and twist them together. The element connects at the end by taking a piece of copper, drilling a 1/8" hole with a set screw intersecting it. You put the power cord end and the twisted element end through the hole in the copper and tighten the set screw to clamp the cord to the element end.
I canned my furnace in /030 aluminum sheet and hung the door on a ushaped bar that flips up to open and down to close.
jpfalt,
Nice work! Been kicking around doing one myself. So far the torch set works.
You could probably draw up a good set of drawing/instructions and sell them. I'll be your first customer.
