Cheap D.I.Y. Vacuum oven for less than 250

[overbudjet]

Du to the high price of vac oven and the fact that i only need to process small batch ,i choose to built one to accomodate myself and some friends.My goal is accuracy and stability of the temp inside the oven.
Shopping List
1. Silicon heating mat 40.00
2. Variac 40.00
3. Temp. controller 16.00
4. Chamber and lid 125.00
5. Piece of granit ????


1.I take a cutout from a old granit contertop and rond it up the best i can(i use dimond blade on my bench saw)
2.I drill a small hole in center to accomodate the temp sensor and glue it there.
3.Apply silicon heating pad on back of rock.
4.Drill a little hole through your chamber put your heating shelf inside your chamber pass wire and seal hole.
5.Use variac to step voltage down(help avoiding heat spike)and use controller to ajust temp of the shelf.
And voila!You have your own vac oven for less than 250 box.

 

[exploziv]

Nice project. Looks clean too. Congrats!
How about the other equipment you use to create vacuum, costs more or is it included in the 125 usd for the chamber?

 

[flatslabs]

May I ask why you are using an sth temperature controller AND a variac and not just a simple PID controller?

 

[overbudjet]

For me variac combined to a temp controller allow better control over temp,if i use the full power of this mat even combined with a good PID it will overheat the shelf and cause big temp swing (over 10 deg.last time i have check).With the variac no temp swing at all,set the temp you want and VOILÀ.
I.m.h.o. the temp stability is due to 2 main factor
1. Mass of the shelf
2. Control the heating power(variac)

 

[soysoz]

Very cool, been thinking about a design similar to that one. How does the vacuum hold with your sealant?

 

[overbudjet]

Very well hold vacuum for day's

 

[overbudjet]

Nice project. Looks clean too. Congrats!
How about the other equipment you use to create vacuum, costs more or is it included in the 125 usd for the chamber?

I use a small 3cfm single stage vacuum pump from ebay around 70.00

 

[SkyHighLer]

My aluminum stock pot vacuum chamber has a concave outside bottom surface, so I push the mat up into the slight depression with plenty of padding/insolation.

Mats I've tried and how I set them up,
https://www.icmag.com/ic/showpost.php?p=5915060&postcount=4

The sensor must be in firm, full contact with the bottom of the mat.

DIY PID controller with solid state relay/heat sink,
https://www.icmag.com/ic/showpost.php?p=5935324&postcount=152

 

[overbudjet]

Nice chamber SkyHighler !Does the temp inside the chamber is stable?when i have try this way(heating pad under chamber)i see some good temp swing. I choose Kenovo after reading your's tread by the way the heat sensor is embedded in the granit slab just below rock surface .

 

[flatslabs]

SkyHighLer: May I ask what PID values you are using?

Also, does your mat have a built in thermocouple (K / J?) or simple thermistor... or are you using an external temperature probe?

 

[SkyHighLer]

Nice chamber SkyHighler !Does the temp inside the chamber is stable?when i have try this way(heating pad under chamber)i see some good temp swing. I choose Kenovo after reading your's tread by the way the heat sensor is embedded in the granit slab just below rock surface .

To make it work there must be insulation under the mat, I've found four layers of 100% cotton terrycloth washcloths works well. The mat itself must be pushed up against the bottom of the pot to make up for any irregularities, and the sensor must be firmly, and fully in contact with the mat. The temperature of my oil sitting on parchment remains stable, maybe rising/falling a degree for a short while when vacuuming down or letting the air back in. Do you have insulation under the granite slab?

SkyHighLer: May I ask what PID values you are using?

Also, does your mat have a built in thermocouple (K / J?) or simple thermistor... or are you using an external temperature probe?

JLD612 PID controller
http://www.amazon.com/gp/product/B002PIM3R8/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

Manual for the controller
http://deadeyestudio.com/JLD612_Manual.pdf

Solid state relay and heat sink
http://www.amazon.com/gp/product/B005K2IXHU/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

PT100 thermocouple
http://www.amazon.com/gp/product/B008MU0VFY/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

It was Auto Tuned

Menu code 0036:

P 1.1
I 117
D 029
SouF 0.2
Ot 002
FILt 0
END ---

Menu code 0089:

Inty P10.0
outy 2
Hy 000.3
PSb 13.0 (this is my Set Point versus actual oil temp differential at 115F)
rd 0
CorF1
END ---

Don't leave your oil sitting in the stock pot with the lid on and no vacuum for long, the hot trapped air will cause the oil temp to rise.

 

[Sirdabsalot46n2]

I know I've posted it many times, but here she be again....

Consider the price of some sand and a cheap deep dish griddle...
Very consistent temp, with very little spike or drop.

My setup...
https://www.icmag.com/ic/showpost.php?p=6246460&postcount=9