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Pyrex Bake-Round Dimensions For 3D Printed Roast Chamber Mold
makrsnak
Does anyone have the dimensions for a pyrex bake-round? I want to create a roaster model / 3D print molds for the bottom of a roast chamber.

I would gladly share any of the CAD files created for future use. Some sort of an open source project that others could share. Here's a first crack at a negative mold (Pun Intended).

Then plan is to create the mold in three parts (PLA plastic) and bolt the parts together so they can be taken apart easily. Food safe refractory cement will be the roast chamber material. The parts will be printed in a 235mmx235mmx250mm (LxWxH) dimension 3D printer.

Thanks!
makrsnak attached the following images:
roaster_chamber_lower_top_view.png roaster_chamber_lower_mold.png
sebiiksbcs
Don't know about your process but from my experience, Complex inside shapes (e.g. the 90 degree angles) such as in your current model will be really hard to get right and removing the part from the mold will be just as hard.

Also consider making a two-halves mold (which will be much easier to remove) and try to keep an eye on complex shapes as mentioned above. With concrete molds, you may also consider starting small, maybe making a composite structure out of several smaller and easier-to-do-right parts, combine those with high-temp silicone or glue, and if one part doesn't work well you only have to redo that one instead of the whole 'concrete slab'.

Edit: I don't know the exact measurements of the bake-a-round, hopefully someone will be able to measure it for you. Also take into account that concrete may expand differently under heat than pyrex, steel, etc. so you'll have to take that into account in your design and seal the gaps with something soft
makrsnak
Thanks for the advice!

I have a bake-round headed my way. So in the next week I should have measurements.

I have a working Arduino Uno, TC4 shield, SSR, and 1800w heat gun element.

I need a fan - and speed control for the fan. I would like to keep this project as reproducible as possible.

Any suggestions on a fan/motor combination. I think it would be easiest to use a DC motor.

I don't know the thermal expansion coefficient off the top of my head for Pyrex (borosilicate glass) or refractory cement, but planned on fitting a silicone o-ring around the base of the glass for a snug fit. I assume borosilicate glass and refractory cement have very low expansion compared to metal.

The attached image is rev 1.1 for the exterior shell of the mold. I am imagining a four piece mold. Two outer shell pieces, the inner mold to shape the bowl of the roast chamber, and a centering jig that centers the bowl mold with the shell.

Of course these drawings are probably going to have several revisions before/after I get measurements.
makrsnak attached the following images:
screenshot_from_2020-12-23_22-01-19.png screenshot_from_2020-12-23_22-19-27.png
sebiiksbcs
The mold for rev 1.1 looks pretty good! I've been using PLA at first then PETG for my molds and made them as thick as yours but I realized they're hard to reuse anyway so I started making 2-perimeter thin molds which could be broken/peeled off after the concrete dried out. Especially for inside molds this worked better for me.

Remember to apply vaseline (works great for me) or special "mold release" lubricant to your molds, this will also make your life easier.

Also wait a bit longer than specs for your concrete to dry, it will harden more. Better to be patient (I wasn't too many times!) than getting a part you're not satisfied with (which I do now!) Especially wait until you heat it up. Moist concrete (even if it looks completely dry on the outside) will crack pretty easily when still moist on the inside.

Sounds like you're as far as me with your design. I live in East Asia and can't easily obtain a bake-a-round, but I've had the luck to know a guy/company(?) who custom makes quartz tubes of fairly any size and thickness for a good price, which also simplifies the design process.

I also utilize a heat gun element including the steel tube it came in.

As fan I am using a vacuum cleaner motor of a model that is fairly common and cheap (and mainly not too big. I've tried to salvage motors from 'regular' sized vacuums, the type that roll on the floor and those were built like tanks and sounded like air raid sirens. I then found that motors in 'stand-up' type vacuums seem to fit the bill. You might also get good results with motors from smaller DC or rechargeable vacuums, the type you would use to clean you car for example, but those might be a bit on the weak side.)

From what I've learned it is important to find out which type of motor you have so you'll be able to control fan speed. I'll share my results because I feel this isn't explained well for newbies like I am/was:

There are
DC brushed motors, --> control with MOSFET connected externally to your TC4. If you have TC4+ the MOSFET is included on the board.

DC brushless motors, --> same control like above but expensive and might have less torque/power to create enough pressure

Universal motors --> usually brushed? Can run both on DC and AC, these are used in most high-power home appliances like vacuum cleaners. Bonus of vacuum motors is they have the fan thing ("impeller") and some sort of air duct included. And as they are built for creating good suction, they create good pressure on the other side. To control this via your TC4 you'll need a "random-fire" or "instantaneous" SSR (Crydom D2425-10 is often recommended)
Edited by sebiiksbcs on 12/24/2020 11:13 PM
makrsnak
sebiiksbcs,

I have programmed the TC4 - not sure if it is a + model or not and gotten it to fire the SSR for a heat element (also from a heat gun). I also got it to fire under manual control from Artisan.

Agreed, definitely this.

DC brushed motors, --> control with MOSFET connected externally to your TC4. If you have TC4+ the MOSFET is included on the board.

Does anyone have a any recommendations for which make/model of vacuum to search for?
sebiiksbcs
I can't help you with DC motors as I am using an universal 110V AC motor controlled with a random-fire SSR. You'd have to look at car or handheld vacuums that run on DC but give you enough watts/cfm/pressure to actually lift your beans. Right now there doesn't seem to be a 'standard' as to how you can find out how strong your airflow will be. Keep in mind that for DC you'll need a strong DC power supply of several (10-30?) amps, too.
makrsnak
I found this DC motor on Amazon. It looks like its a good bet. The data sheet for the serial number indicates peak power of 644.74 W. This should be way more than enough. Torque - Speed Curve attached. Finding a power supply may be tough.

I am designing my own fan. Revision 1 picture attached. Bottom piece of fan wheel assembly - reversed inclined type.

The first revision of the chamber mold is done.

I am going to print a mold for a custom high temp silicone gasket for where the lower roast chamber connects to the glass tube.

Quote

Right now there doesn't seem to be a 'standard' as to how you can find out how strong your airflow will be. Keep in mind that for DC you'll need a strong DC power supply of several (10-30?) amps, too.


You're right about this. Manufacturers do not post their fan curve data. If you could determine all of the pressure drops in your system - you could use that to select a fan based on the fan curve. The stall current for the motor is 138A. This is the rating that should be used.

It is desirable to have a fan that produces low air volume and high static pressure rating. It gets more complicated to select a fan when you have variable size roasting weights - min/max roast sizes. Your system pressure drops change substantially. Need a fan with a "flat" curve.

1. Low air volume reduces the heating element size requirement
2. Total static pressure is made of (2) components - velocity pressure and static pressure
a. Velocity pressure is what lifts the beans in a fluid bed chamber

Thanks for the reply.
makrsnak attached the following images:
screenshot_from_2020-12-29_23-59-38.png screenshot_from_2020-12-29_23-57-08.png screenshot_from_2020-12-29_23-51-34.png screenshot_from_2020-12-29_23-49-23.png screenshot_from_2020-12-30_00-52-08.png

Edited by makrsnak on 12/30/2020 1:55 AM
sebiiksbcs
Are you really going to require 600+ Watts of DC 12V power? That's really a lot of energy. What batch sizes are you aiming for?

You can probably go with one of these power supplies:

https://www.aliex...web201603_

I have a similar one for my 3D printer and it also has bonus 5V output for the Arduino

Are you going to 3D print the impeller too? What's the funnel-shaped print in the last picture for?
Edited by JackH on 12/30/2020 8:45 AM
renatoa
I doubt RS-775/785 is able to deliver that power, I know it from one of my other hobbies, used to power bite boats, powered from 12V 6-15 Ah lead bricks, and it barely delivers 250 Watts.
makrsnak

Quote

sebiiksbcs wrote:

Are you really going to require 600+ Watts of DC 12V power? That's really a lot of energy. What batch sizes are you aiming for?

You can probably go with one of these power supplies:
https://www.aliex...web201603_
I have a similar one for my 3D printer and it also has bonus 5V output for the Arduino

Are you going to 3D print the impeller too? What's the funnel-shaped print in the last picture for?


No, I probably don't need 600w of motor shaft power, but if I ever want to increase roasting batch size, this makes the transition easier. This motor is the equivalent of about 1/2 brake horse power. That's big for a DC motor!

I am going to print the impeller and cage.

The funnel shape is part of the mold. Assembly attached.
makrsnak attached the following image:
screenshot_from_2020-12-30_07-44-45_1.png
makrsnak

Quote

renatoa wrote:

I doubt RS-775/785 is able to deliver that power, I know it from one of my other hobbies, used to power bite boats, powered from 12V 6-15 Ah lead bricks, and it barely delivers 250 Watts.


If this information is right; It should. I thought RS-775 was just a motor frame/dimension size?
makrsnak attached the following images:
screenshot_from_2020-12-30_07-49-21.png screenshot_from_2020-12-30_07-47-45_2.png screenshot_from_2020-12-30_07-48-06_2.png
renatoa
On the motor in the picture I read printed HC785, while item title say RS-775, pardon my confusion...

Yes, 775 is a dimension code, referencing more to the mounting screws and shaft size, but voltage/RPM/power could be different from a model to other.
The typical 775 I know are 12V, 7-9000 RPM, and $10-15.

Please make sure that this 18V version is for continuous usage, because HC785 target seems to be power tools, drills, so short time usage, then allow cooling.
makrsnak

Quote

renatoa wrote:

On the motor in the picture I read printed HC785, while item title say RS-775, pardon my confusion...

Yes, 775 is a dimension code, referencing more to the mounting screws and shaft size, but voltage/RPM/power could be different from a model to other.
The typical 775 I know are 12V, 7-9000 RPM, and $10-15.

Please make sure that this 18V version is for continuous usage, because HC785 target seems to be power tools, drills, so short time usage, then allow cooling.


Thanks Renota,

I agree. I doubt the motor is for continuous usage, but I plan to put the motor inside the fan wheel. It should receive a tiny bit of extra cooling from that.

The asking price for motor is $53, which seems inline for the product specifications.

I have not modeled the fan yet. Got side tracked on real life projects.

Here is the assembly for the mold of the roast chamber. The last piece is printing right now.
makrsnak attached the following image:
screenshot_from_2021-01-02_07-45-30.png

Edited by makrsnak on 01/02/2021 9:09 AM
sebiiksbcs

Quote

Here is the assembly for the mold of the roast chamber. The last piece is printing right now.


Nice. A bit hard to see the proportions: your heating element would sit in the narrow cylinder? How thin is the thinnest wall on your concrete part? Did you pay any attention to heat insulation so far? (Asking because I tried but didn't get any useful results haha)

I'm currently thinking up a way to recycle the hot air because no matter what I do, my heating element won't heat up properly with reasonable fan levels. It's rated 2200W but it doesn't seem to consume even half that because I tested a 10A fuse (at 110VAC) and it didn't blow. That or I'll need to make a concrete housing for two heating elements...
makrsnak

Quote

sebiiksbcs wrote:

Quote

Here is the assembly for the mold of the roast chamber. The last piece is printing right now.


Nice. A bit hard to see the proportions: your heating element would sit in the narrow cylinder? How thin is the thinnest wall on your concrete part? Did you pay any attention to heat insulation so far? (Asking because I tried but didn't get any useful results haha)

I'm currently thinking up a way to recycle the hot air because no matter what I do, my heating element won't heat up properly with reasonable fan levels. It's rated 2200W but it doesn't seem to consume even half that because I tested a 10A fuse (at 110VAC) and it didn't blow. That or I'll need to make a concrete housing for two heating elements...




Back from a long reprieve! Had to take a test for work: I passed.

Here is a better picture:

The heating element sits in the grey cylinder. It is your typical 1600W element from a Chinese heat gun. I probably won't need to pay attention to insulation since the grey part is 2.5 in thick refractory cement (Diameter is about 6in).

It sounds like you are using less than 1200W with that setup. How much air does your fan move? You should be using 20 amps with that heating element at 110V. Is your circuit rated for 20 + amps (When you add the fan in)?

Two things:

1. Make sure your element is not broken
2. Pick your fan so that it provides a lot of static pressure and very little air volume (cfm)

Point 2 should reduce your heating power requirement. It will make your roast chamber get much hotter.
Q = 1.08 * CFM * delta T
makrsnak attached the following image:
screenshot_from_2021-01-16_22-42-31.png
makrsnak
First roast finally happened...

The roaster isn't quite finished.

This was a about a 200g load. Could probably do 250g.

I need to tune the electric heater response.

The fan is a $35 Nidec brushless 24VDC 400W fan assembly.
makrsnak attached the following images:
unfinished_roaster.png first_roast_screenshot.png

Edited by makrsnak on 07/05/2021 8:16 PM
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