Small oven project

[Berryhill]

Greeting everyone! I've been lurking for a while and finally decided to jump in. I am planning on building a small oven for baking teflon and moly based firearms finishes (Gun Kote, Cerakote, etc), which require about 300 to 350 degrees for curing.

I'd like to build something similar to the one shown in this diagram:
Ten-Ring Precision, Inc., Oven
This uses a sheet metal gun locker that is 20" wide x 18" deep x 60" high as the oven body, one electric range element for heat and an oven thermostat for control. I'm not sure about insulation yet. These plans call for rigid fiberglass duct board, which is probably sufficient but I haven't found a local source yet.

My questions are about the thermostat and wiring the stove burner element:

1. The plans don't call for it but most of the ovens that I've seen here use some type of contactor or relay along with the thermostat. Is this necessary (or desirable) for a single element oven? Do most electric kitchen ovens use one?

2. Most of the range elements that I've seen at Home Depot or Lowes are designed to plug into an outlet on the top of the range or stove. Is there a simpler way of connecting wires to these elements? I was also thinking of using a small electrical box at the bottom of the oven to shield the wires and house the connection to the element.

Any comments are welcome!

Thanks,

Dave Berryhill

[Brintiff]

Hello Dave, is this the same Dave Berryhill that was/is on pistolsmiths.com? I'm pretty sure that's where I've seen you.

Anyway, whether you need a contactor depends on the amperage of the element and what the thermostat can handle, pretty sure you'll need one. I also suggest using a PID rather than using an oven type thermostat, it's a lot more accurate and flexible. Below is a pic of my oven, it was a food service heated holding cabinet, the other pic shows a Sig P220 in Foliage green and armory black cerokote.

[Berryhill]

Yes, I used to be pretty active on Pistolsmith.com but haven't been there for quite some time. I'm a regular at the 1911forum.com and M1911.org forums.

That's a pretty nice oven you've got there! I've already got an oven thermostat and thermocouple that I bought off ebay for dirt cheap so I'm going to give that a try first. I've been using a toaster oven for quite some time without problems (other than it's too small). With the gun cabinet oven, I'll have vertical room so I should be able to do several pistols at a time.

I'm also thinking of using this as a fan:
http://www.grainger.com/Grainger/items/7C727

It runs at 3000 RPM, which is probably overkill for just circulating air. I'm thinking of rigging an underdrive pulley system that will slow down the fan and also isolate the motor from the oven heat. Do you guys think that this would be sufficient for an oven this small. I'm trying to keep this simple and avoid any ducts.

[Brintiff]

You should have the duct work so you get even heat throughout the oven, then again if you are only doing pistols I don't think you'd have much of a difference from the top to the bottom of the pistol. I use ducting but I also powder coat fairly large objects so I need the even heat.

You'll need to get that fan out of the heat or it will not last, they sell fans made for the heat.

[bhought]

I used a galvanized Garbage Can, a barbeque starter and
a oven thermometer. Because there is no insulation, it
never get over 350 degrees. You must reinforce the top
if you are going to hang things under the cover. In my case
it’s intake manifolds, and Cylinder heads.
I’m pleased with the results so far.
Bruce Houghton

[Berryhill]

I've got an electrical question for the gurus about how contactors are rated:

Since 240 volts (single phase) is supplied by two 120 volt lines (L1 and L2), do I need a 2 pole, 120 volt contactor like this:
C25DND225A 2 Pole 25 Amp 120 VAC Coil

or a 2 pole, 240 volt contactor like this:
C25DND225B 2 Pole 25 Amp 208/240 Vac Coil

Thanks!

[ed_denu]

Actually either would work. If you look at the specifications, each have an inductive full load rating of 25 amps, and a resistive load rating of 35 amps. The other rating, which you reference, is for the input voltage to drive the coil, either 120 vac or 208-240 vac. Assuming you have 240 volt service, then you could use a contactor with either coil voltage. I would suggest the 120 vac coil as there were some issues with using a 240 vac coil and the use of indicator lights, which was discussed in a recent thread.

A 2 pole contactor means that it has the ability to switch 2 circuits(up to the maximum amperage specified), or in this case, both 120vac feeds which is what you would want for a single phase 240 volt element(s).

A 25 amp contactor would be sufficient to drive around 4800 watts of heating, possibly more as the resistive rating is 35A.

[Berryhill]

Thanks! Do I need a heat sink for the contactor?

[ed_denu]

Thanks! Do I need a heat sink for the contactor?

No, only if using an ssr.

[Berryhill]

That's what I thought but I wasn't sure. Thanks for the help.