Thanks for the input Ray. I have been trying to keep this project as simple as possible, but your input has led me to believe that I should consider adding another heating element. I have been concerned that bottom of the board will get much hotter than the top, and perhaps having two elements, instead of one, may be the route to go. And instead of using coiled wire, perhaps I should just use a wireform on both the top and the bottom of the board. Hmmmmmmm.....
@Tubular
I think the thing to try would be to see what your natural heat decay is from the setup you propose. Eg heat it up ( using any means ) then stop the heat and note the decay profile. Unless you have insulation, you might find that you don't need any holes at all
I am fairly certain that I will need some sort of ventilation, but I agree that I should test first, which I intended to do. Before brazing the top and bottom plates to the square tubing, I will rig something up to perform some tests.
Working tonight and into the wee hours of the morning, I will try to finish the drawer assembly, which is a key aspect to this project, and certainly the most time consuming so far.
I suppose it is needless to say that I have zero experience pertaining to the reflow process, but I must push forward, so I will have to make design rules. One of these rules pertain to the maximum allowable height of the components that can be shoved into the oven. I am under the firm belief that taller items, such as bulk capacitors should be hand solder, otherwise these items may be to close to the heating element, or I will have to enlarge the heating chamber, which I do not want to do. I also imagine that headers and such will also have to be hand soldered.
These decisions directly affect the size of the heating chamber, the size of the drawer opening, as well as the size of the drawer front, which will cover the drawer opening. My current thoughts are to allow 1/2" high components to pass through the opening, but I really don't believe that I need this large of an opening, however it is better to have more than not enough So essentially I think the drawer opening should be approximately 13/16" X 2-3/4".
Connectors are regularly reflow soldered these days. You do not want to be hand soldering HDMI, USB-C or even the lowly USB micro or mini, microSD. A 0.5" height restriction seems quite a restriction although I cannot think of a SMT connector that I use that would be higher than this. Some SMT electrolytics are likely to be 10-15mm high.
While most of my boards are less than 2-3/4" when you panelise the boards you will often see 6+" for the boards that I do. But I would not be typical as I specialise in tiny boards as does Peter.
Also, you should not have heat too close to the board or components as otherwise you are going to get hot spots.
A 0.5" height restriction seems quite a restriction although I cannot think of a SMT connector that I use that would be higher than this.
I was going to go for a 0.75" height restriction and that was only when considering the capacitors necessary for power supplies or motor drivers. Another consideration of mine was the size of the drawer front. I really did not want to machine the width of the drawer front and I want the sealing edges to be symmetrical.
Alright..... I really did not want to increase the cubic inch capacity of the heating chamber, but since I now want two heating elements, and unless I want to do a bunch of redesigning, as well as remaking parts, that is what I will need to do. So I will be increasing the size of the heating chamber by approximately another 5.7 cubic inches.
This increase in size will allow me to use 1-1/4" wide material for the drawer front. Additionally this increase in size will result in a 1" X 2-3/4" drawer opening, which will allow components having a height of 11/16" or less to pass through.
Your sizes really depends on what you’re trying to achieve. If you know your pcb size will never exceed xxx and height yyy then that’s fine.
But it seems like a lot of work when a modified toaster oven would get you there much quicker, especially if you have other pressing jobs to do. If you need the challenge, then you’ll learn a lot in the process.
2.2" X 1.65" is the target size. As for 'Z', I currently have a through hole capacitor with a height of around 0.5", which is mostly likely the maximum height that I will need.
In this thread, I discuss PCBs that have a similar size and other similar characteristics, as Parallax's Circuit Overlay Board, which will allow it to plug into various Parallax PCBs, like the Propeller Activity Board, Propeller Board of Education, and the BASIC Stamp Board of Education.
But it seems like a lot of work when a modified toaster oven would get you there much quicker, especially if you have other pressing jobs to do. If you need the challenge, then you’ll learn a lot in the process.
The cost of the materials is very low and actually, I really don't have that much time wrapped up in it, except for the time spent designing and making alterations. If I can ever get it to work properly, I should be able to produce them quickly and inexpensively.
Okay, okay.... Since altering my plans, the cost has gone up
Since deciding to have two heating elements, I have been having trouble designing a coil, which fits well with my ceramic terminal block. As a result of this decision and difficulties with the design, I have also decided to go back to a similar wireform as the original, but instead of just one heating element, there will now be two, and instead of having a maximum temperature of 800 F, each element will be able to get up to 1000 F.
Of course these decisions necessitate the need for more wattage, which my power supply is incapable of providing. I will now need a 12V, 5A power supply. Luckily this upgrade is not too expensive, and if I decide to make more, I will certainly need a distributor to supply them.
And here is a picture of the heating elements that I intend to make.
EDIT: Now I wonder if the wireform will droop at 1000 F. I doubt it, but it is certainly possible. However, just because it can provide 1000 F., doesn't mean that I will ever need to take it to that temperature.
EDIT: Additionally, I can always change the power supply, the terminal blocks, and the wireforms later, but for now, I just want to keep pushing forward.
Well Duane, I had not put any thought into that, but I suppose the top ventilation plate could be made of glass, instead of aluminum, and it could be adhered to the aluminum tubing with JB Weld ExtremeHeat, instead of brazing.
I bought some of the JB Weld ExtremeHeat for fastening the stainless steel wire mesh to the drawer, so I do have it available.
EDIT: However, it would be a real pain to clean that window
As a builder of prototypes, I am always looking at ways to speed up the manufacturing process. However, being a mechanical kind of guy, I believe in mechanical fastening, such as screws or bolts, as compared to chemical fastening, such as epoxies or adhesives. I will be the first to admit, that drilling holes and tapping threads can be very time consuming. I may have to make an exception in this case. I believe this prototype will become a project of both mechanical and chemical fastening.
Ever since Duane mentioned seeing inside the oven, I have seriously been considering it. Mechanically fastening a viewport to the oven would be time consuming, and I really don't like the idea of using an epoxy to fasten a viewport in place. So I am now considering the use of a high temperature adhesive, for fastening various pieces, such as the viewport, the viewport frame, as well as the bottom ventilation plate.
Could you use a combined approach to attach the glass panel...
Weld or bolt U channel steel to your chassis that would allow you to slide the glass panel in/out. Perhaps U channel on 3 sides. Insert a chunky silicon "gasket" between the glass and steel frame, such that it's squeezed slightly when the glass is inserted and holds itself in-place. ie. no need for adhesive. Also makes it possible to remove/clean the glass.
The silicon seal might also be that high temperature rope-like stuff often used on industrial oven doors.
or another idea... look for an small "oven" door assembly and bolts or welds that on. Feels like there's a lot of industrial equipment having mini inspection door assemblies which seal locked and include the glass element. I can't imagine they are all re-creating that sub-assembly, or if "they" are- there might be plans and ideas our there!
I was having a little trouble finding my ambition, but I finally have the PCB drawer constructed. I am providing two photos, one without wire mesh and one with the wire mesh set in place, but not yet expoxied.
I have made the decision to go for speed and easy reproduction, so I will be using adhesive or sealant to fasten the viewport, the viewport frame, as well as the bottom ventilation plate. If the adhesives do not hold up, then of course I will have to alter the design. I will still be using screws or brazing where I believe it is absolutely necessary for structural integrity.
If the viewport ever needs cleaning, then of course it will be a bit of a pain, but hopefully it will not require cleaning often.
I was having a little trouble finding my ambition, but I finally have the PCB drawer constructed. I am providing two photos, one without wire mesh and one with the wire mesh set in place, but not yet expoxied.
Since deciding to have two heating elements, I have been having trouble designing a coil, which fits well with my ceramic terminal block. As a result of this decision and difficulties with the design, I have also decided to go back to a similar wireform as the original, but instead of just one heating element, there will now be two, and instead of having a maximum temperature of 800 F, each element will be able to get up to 1000 F.
Of course these decisions necessitate the need for more wattage, which my power supply is incapable of providing. I will now need a 12V, 5A power supply. Luckily this upgrade is not too expensive, and if I decide to make more, I will certainly need a distributor to supply them.
When making these grand plans, I figured that the two heating elements would be wired in series, and they should be, but wiring them in parallel, would surely be a lot easier and neater, but unrealistic
I did not stop to think how I was going to wire these two elements in series 20/20 hindsight
EDIT: I guess one connection will have to be on the upper terminal block and the other on the lower terminal block
Alrighty, my friendly forumistas, the designing is done, and this is what I intend to make!
The bottom ventilation plate has been replaced by mounting brackets and a base.
Hopefully my fan and rubber feet won't melt If they do, then I will extend them with standoffs.
EDIT: To clean the inner side of the viewport, the fan, drawer, and heating elements can be removed, providing much better access for cleaning purposes.
I just wanted to share a few of my current thoughts pertaining to this project, before I forget to mention them.
1) Considering the modifications that have taken place in the design, I will no longer be using adhesive.
2) Considering that brazing aluminum can be difficult in certain circumstances and that I currently have limited material on hand, I have decided to screw everything together for the prototype, instead of using a brazing process. If I can get it to work well, then I will begin to braze certain portions on future units.
3) The top viewport frame will always be screwed in place, so that the viewport can easily be removed for cleaning purposes. This will greatly simply the ability to clean the viewport.
Early morning yesterday, I was preparing parts, but today, I had to go back to the drawing table. Luckily, I will be finished after this post and can get back to machining parts. I just wanted to keep you all updated.
During the designing process, I always kept thinking about temperature monitoring and thermistor placement. As it pertains to this particular design, there is no perfect scenario, due to several factors, such as aesthetics, high temperature, limited space, possibility of electrical shorting, etc... In an effort to keep moving forward, I knew I had to make a final decision concerning the placement of the thermistors. One of the main factors in determining the location of the thermistors, was the designed maximum height of electrical components, which was and is 11/16". So the top thermistor had to be at least 11/16" above the PCB, otherwise there would be the possibility of unwanted contact. Considering the design restraints, I made it exactly that measurement, and I also placed the lower thermistor an equal distance from the lower layer of the PCB. This required clearance pushed the thermistors fairly close to the heating elements, but what is a guy supposed to do? I will just have to compensate in the programming stage, providing the thermistors work out at all. I suppose I could shove them off center and toward the inner edges of the square tubing..... I will put some more thought into this.
Anyhow, instead of coming through the sides of the tubing, with the thermistors (which is actually a better scenario for temperature monitoring (very tight restraints)), after considering all factors, I decided to come through the rear, along with the heating elements. So now, instead of two seperate terminal blocks, I am going to cut the back of the tubing wide open to accept one large terminal block that contains two heating elements and thermistors.
In an effort to convey these thoughts, I have attached another drawing.
When profiling we usually use a number of thermistors placed over and under the pcb(s) to verify even heating. Once profiled it’s not necessary to have so many as thise remaining are just to verify the correct profile occurs.
I suppose that I could keep my current design, providing the thermistors don't get too hot.
Let's say that I leave them as they are, but for testing purposes, they would only take readings at specific times, as dictated by other thermistors which actually determine the profile.
Does that sound about right?
I could create a special drawer, containing numerous thermistors, just for setting profiles.
When setting up i just have a number of thermistors with the leads coming out the door/drawer so i can plug/unplug to measure various temps. When live, just use the built in temp and ensure it’s as expected.
Comments
Thanks for the input Ray. I have been trying to keep this project as simple as possible, but your input has led me to believe that I should consider adding another heating element. I have been concerned that bottom of the board will get much hotter than the top, and perhaps having two elements, instead of one, may be the route to go. And instead of using coiled wire, perhaps I should just use a wireform on both the top and the bottom of the board. Hmmmmmmm.....
@Tubular
I am fairly certain that I will need some sort of ventilation, but I agree that I should test first, which I intended to do. Before brazing the top and bottom plates to the square tubing, I will rig something up to perform some tests.
Working tonight and into the wee hours of the morning, I will try to finish the drawer assembly, which is a key aspect to this project, and certainly the most time consuming so far.
These decisions directly affect the size of the heating chamber, the size of the drawer opening, as well as the size of the drawer front, which will cover the drawer opening. My current thoughts are to allow 1/2" high components to pass through the opening, but I really don't believe that I need this large of an opening, however it is better to have more than not enough
Connectors are regularly reflow soldered these days. You do not want to be hand soldering HDMI, USB-C or even the lowly USB micro or mini, microSD. A 0.5" height restriction seems quite a restriction although I cannot think of a SMT connector that I use that would be higher than this. Some SMT electrolytics are likely to be 10-15mm high.
While most of my boards are less than 2-3/4" when you panelise the boards you will often see 6+" for the boards that I do. But I would not be typical as I specialise in tiny boards as does Peter.
Also, you should not have heat too close to the board or components as otherwise you are going to get hot spots.
I was going to go for a 0.75" height restriction and that was only when considering the capacitors necessary for power supplies or motor drivers. Another consideration of mine was the size of the drawer front. I really did not want to machine the width of the drawer front and I want the sealing edges to be symmetrical.
Alright..... I really did not want to increase the cubic inch capacity of the heating chamber, but since I now want two heating elements, and unless I want to do a bunch of redesigning, as well as remaking parts, that is what I will need to do. So I will be increasing the size of the heating chamber by approximately another 5.7 cubic inches.
This increase in size will allow me to use 1-1/4" wide material for the drawer front. Additionally this increase in size will result in a 1" X 2-3/4" drawer opening, which will allow components having a height of 11/16" or less to pass through.
But it seems like a lot of work when a modified toaster oven would get you there much quicker, especially if you have other pressing jobs to do. If you need the challenge, then you’ll learn a lot in the process.
This project came by as a result of my discussion in this thread: forums.parallax.com/discussion/172053/circuit-overlay-modules
In this thread, I discuss PCBs that have a similar size and other similar characteristics, as Parallax's Circuit Overlay Board, which will allow it to plug into various Parallax PCBs, like the Propeller Activity Board, Propeller Board of Education, and the BASIC Stamp Board of Education.
The cost of the materials is very low and actually, I really don't have that much time wrapped up in it, except for the time spent designing and making alterations. If I can ever get it to work properly, I should be able to produce them quickly and inexpensively.
Since deciding to have two heating elements, I have been having trouble designing a coil, which fits well with my ceramic terminal block. As a result of this decision and difficulties with the design, I have also decided to go back to a similar wireform as the original, but instead of just one heating element, there will now be two, and instead of having a maximum temperature of 800 F, each element will be able to get up to 1000 F.
Of course these decisions necessitate the need for more wattage, which my power supply is incapable of providing. I will now need a 12V, 5A power supply. Luckily this upgrade is not too expensive, and if I decide to make more, I will certainly need a distributor to supply them.
Here is a link to the power supply that I will be using for this experiment: https://newark.com/multicomp/mc141010/adaptor-ac-dc-12v-5a/dp/02AC7188
And here is a picture of the heating elements that I intend to make.
EDIT: Now I wonder if the wireform will droop at 1000 F. I doubt it, but it is certainly possible. However, just because it can provide 1000 F., doesn't mean that I will ever need to take it to that temperature.
EDIT: Additionally, I can always change the power supply, the terminal blocks, and the wireforms later, but for now, I just want to keep pushing forward.
I suppose it's possible to trust the gauges but I always like to verify the solder paste has turned shiney by looking through the oven window.
I bought some of the JB Weld ExtremeHeat for fastening the stainless steel wire mesh to the drawer, so I do have it available.
EDIT: However, it would be a real pain to clean that window
I agree that it would be nice to watch the process
It appears that McMaster-Carr sells precut 3" X 3" Borosilicate Glass Sheet (Pyrex)
https://mcmaster.com/8476K13/
Of course such a luxury would drive the price of the prototype upward
Ever since Duane mentioned seeing inside the oven, I have seriously been considering it. Mechanically fastening a viewport to the oven would be time consuming, and I really don't like the idea of using an epoxy to fasten a viewport in place. So I am now considering the use of a high temperature adhesive, for fastening various pieces, such as the viewport, the viewport frame, as well as the bottom ventilation plate.
Here are some adhesives that I am considering:
Weld or bolt U channel steel to your chassis that would allow you to slide the glass panel in/out. Perhaps U channel on 3 sides. Insert a chunky silicon "gasket" between the glass and steel frame, such that it's squeezed slightly when the glass is inserted and holds itself in-place. ie. no need for adhesive. Also makes it possible to remove/clean the glass.
The silicon seal might also be that high temperature rope-like stuff often used on industrial oven doors.
I have made the decision to go for speed and easy reproduction, so I will be using adhesive or sealant to fasten the viewport, the viewport frame, as well as the bottom ventilation plate. If the adhesives do not hold up, then of course I will have to alter the design. I will still be using screws or brazing where I believe it is absolutely necessary for structural integrity.
If the viewport ever needs cleaning, then of course it will be a bit of a pain, but hopefully it will not require cleaning often.
Gloriously Golden! Really impressive work Bruce.
I just wanted to thank you for the viewport idea. Thank you.
When making these grand plans, I figured that the two heating elements would be wired in series, and they should be, but wiring them in parallel, would surely be a lot easier and neater, but unrealistic
I did not stop to think how I was going to wire these two elements in series
EDIT: I guess one connection will have to be on the upper terminal block and the other on the lower terminal block
Can't help but think you're going to want an insulating knob for pulling the drawer out, though.
You made me laugh
The bottom ventilation plate has been replaced by mounting brackets and a base.
Hopefully my fan and rubber feet won't melt
EDIT: To clean the inner side of the viewport, the fan, drawer, and heating elements can be removed, providing much better access for cleaning purposes.
You are welcome.
I agree with VonSzarvas and Tubular, it is looking great.
Thanks again for sharing our progress with us.
1) Considering the modifications that have taken place in the design, I will no longer be using adhesive.
2) Considering that brazing aluminum can be difficult in certain circumstances and that I currently have limited material on hand, I have decided to screw everything together for the prototype, instead of using a brazing process. If I can get it to work well, then I will begin to braze certain portions on future units.
3) The top viewport frame will always be screwed in place, so that the viewport can easily be removed for cleaning purposes. This will greatly simply the ability to clean the viewport.
During the designing process, I always kept thinking about temperature monitoring and thermistor placement. As it pertains to this particular design, there is no perfect scenario, due to several factors, such as aesthetics, high temperature, limited space, possibility of electrical shorting, etc... In an effort to keep moving forward, I knew I had to make a final decision concerning the placement of the thermistors. One of the main factors in determining the location of the thermistors, was the designed maximum height of electrical components, which was and is 11/16". So the top thermistor had to be at least 11/16" above the PCB, otherwise there would be the possibility of unwanted contact. Considering the design restraints, I made it exactly that measurement, and I also placed the lower thermistor an equal distance from the lower layer of the PCB. This required clearance pushed the thermistors fairly close to the heating elements, but what is a guy supposed to do?
Anyhow, instead of coming through the sides of the tubing, with the thermistors (which is actually a better scenario for temperature monitoring (very tight restraints)), after considering all factors, I decided to come through the rear, along with the heating elements. So now, instead of two seperate terminal blocks, I am going to cut the back of the tubing wide open to accept one large terminal block that contains two heating elements and thermistors.
In an effort to convey these thoughts, I have attached another drawing.
Okay, that makes sense.
I suppose that I could keep my current design, providing the thermistors don't get too hot.
Let's say that I leave them as they are, but for testing purposes, they would only take readings at specific times, as dictated by other thermistors which actually determine the profile.
Does that sound about right?
I could create a special drawer, containing numerous thermistors, just for setting profiles.