Great. I'm heading to the shop tomorrow. If I get organised early enough, I can even have it sewn up by tomorrow night. I'll post pics of the finished product.

After doing a bit of research, I can now answer my own question.

The ideal bag shape - shaped like a truncated cone - is known as a frustum. When it's flattened it looks like a wedge cut out of a doughnut.

Apparently this is a rather easy shape for a seamstress to sew, as most dresses are based on the concept.

The tricky bit is using the formulas to map it out. I haven't tried it yet. But I found a spreadsheet that will do the calulations.

Thanks!

I haven't made a bag yet, but I am going to have access to a professional serger (overlocking stitch) sewing machine in the near future so I am designing the bag now. Suggestions appreciated.

I am definitely planning on elastic and thick, nylon tabs (6-8) for hoisting.

Michael

Pat wrote:Hi there Josh and datamichael.

The frustrum you are using is the same as the advanced BIABrewer bag design that we briefly mention at the beginning of this post. I use two of these bags of this shape and they work very well BUT I intend to make the simple tapered pillow slip design and compare the bags as I suspect there is actually little advantage in the frustrum. They are surprisingly hard to make and my local 'seamstress' actually refused to make them after doing the first two. This is due to attaching the bottom circle. As you are seeing now, they are also very hard to describe to a thrid party. (Nice work on your spreadsheet btw.)

What certainly is great are the following...

1. Elastic: This is stitched into the bag inside the top seam and is used to hold the bag on the outside of the pot. It is much easier than a drawstring.

2. Thick Tabs: I have six, well-stitched tabs on my bags. (As hashie mentioned above, a few thin tabs will cause you nothing but trouble.) They are very strong and allow for easy 'clipping' to a caliper for lifting. Having the tabs means you can have the mash paddle inside the bag during mashout which helps distrubute the heat etc. So tabs are great but only if well-made.

I think you won't have any problems using the tapered pillow slip and will find it far easier to make than the frustrum but the latter certainly won't let you down.

with the project,
Pat

Good tip!

Thanks!
Michael

stux wrote:Go with 8 tabs

6 tends to cause larger lobes to form when you gather them

My lifting tabs are made out of polyester grosgrain, about 12mm wide and are very strong

I want to make sure I get the right thing. I visited another LHBS that happens to be next to a Hancocks Fabrics store. I took a moment to go to the curtain sheers section. I saw several things that said "Voile" on the end of the bolt or a "sale" tag pinned to the remnant. I didn't see the word "Swiss" on it. An employee wasn't at all helpful when I inquired saying, "well, if we have any, it'll be over there."

Natept & BobBrews mentioned finding the fabric at Joann's, and there happens to be a Joann's very near me. I realize that it's been a year since your messages, but do you happen to remember a product # or code for the fabric?

I need to brew the two remaining extract (with steeping grains) kits before I get started on BIAB. I don't know if I'll have time to brew a BIAB before Christmas or not. I work in a busy clinic, I am playing the organ at a wedding in mid November as well as December, so I'll be practicing a lot. Gee, I wonder if my practice would be more productive after having a homebrew?!? or, at least, "seem" to be more productive.

Keith

Thanks for the links for the voile. I haven't seen anything mentioned about the cotton/polyester voile. Is there a particular advantage of one over the other? Does the cotton in the combination fabric add strength?

Question about the seams in y'all's bags: If I were making a pillowcase, I would join the pieces with seams while making inside-out, so to speak. Then I would turn it so that the seams are on the inside with the pillow. For a grain bag, would you leave it "inside out" so that there are fewer places for bits of grain to hide so that cleaning it out would be easier? Does it really matter?

Thanks,
Keith

stux wrote:I believe ikea also has a curtain sheer which is very similar

And yes, seems on the outside

A better shape is the baked bean can shape with a cylinder and circular base, but that is harder to sew, but will form a nice teardrop shape when you pull it

Thanks, Stux, I'm leaning towards the bean can shape. Correct me if I'm wrong, but I believe that's the straight cylinder with one end closed by a circle - made with 2 pieces of cloth. If so, I understand the geometry and equations to arrive at the sizes of the pieces. The material is cheap enough that I might even make a few bags. I'd like to try the bag fashioned as the "elongated D" to see how it works; it's much simpler to make. I also like the idea of the "fulstrum", but I'm having a little difficulty understanding the online calculator. The schematics make it look like too sharp of a taper - literally like a funnel with the tip cut off - instead of a gentle one, but that might just be shown that way in order to try to make it clearer.

My mother has sewn for as long as I remember - sewing clothes, uniforms, even earned upholstering, so she can certainly help me. She has a surger (Bernina) which is supposed to do wonderful things with seams.

Not meaning to change the direction of this thread, but I'm leaning towards a system in which the bag is supported inside a steamer basket or such, and this basket containing the bag is placed into, and moved out, of the kettle. There's already a thread in which this is described using a Bayou Classic turkey cooker with the included basket.

It is likely that I will be using Mini-BIAB to make 2.5 gallon batches for most beers since I'm not a big beer drinker. The smaller scale of everything might make the process easier - the most difficult part being entering the numbers into the calculator to get the proportions correct. I observed in the Mini-BIAB thread that a 2.5 gallon recipe is not simply the 5-gallon one cut in half.

Thanks,
Keith

Here are some characteristics concerning synthetic textiles.
You may find them usefull when you want to fabricate your next BIAB bag.


No in parentheses
is instant resist.
material | max temperature | Behavior in acids | Behavior in alkalines
_____________________________________________________________________________________

Polypropylene | 90°C (110°) | **** | ****
_____________________________________________________________________________________


Polyacrylnitrile copolymer | 110°C(115°C)| *** | ***
______________________________________________________________________________________

Polyacrylnitrile homopolymer|125°C(140°C)| *** | ***
_____________________________________________________________________________________

Polyester | 150°C(150°C) | *** | *
_____________________________________________________________________________________

m-Aramide | 200°C(220°C) | *** | ***
_____________________________________________________________________________________

Polyphenylene sulfuide | 190°C(200°C) | **** | ****
_____________________________________________________________________________________

Polyimide | 240°C(260°C) | *** | ***
_____________________________________________________________________________________

Polytetrafluorethylene|250°C(280°C) | **** | ****
_____________________________________________________________________________________

After some delays due to finances I am finally getting to my bag. I wanted to share my bag design, I'm sure is has been done a million times but here it goes. I am using a keggle so I based my measurements off a standard 1/2 keg. The layout of the pattern on the voile looks like a bow-tie. The center of the bow-tie will be folded to create the bottom of the bag which will be sewed on the 2 sides. The bag will look like a trapezoid when finished.

These are the measurements I am using
29 inches or 73.7 cm width at the ends of the bow-tie or top of the bag
56 inches or 142.2 cm - this is the total length of the bow-tie
14 inches or 35.6 cm with at the center of the bow-tie or bottom of the bag

This should be a tapered pillowcase bag if I did my math right. Please let me know what you think.

Brian

Thanks guys, My keggle is a 1/2 keg, I wasn't sure if there are different size kegs around the world. I did read that post and used that formula on coming up with the measurements.

B-

I went to Spotlight in Brisbane (Mt Gravatt). They had voile for curtains but it was nylon, not polyester.

I didn't get any because I wasn't sure whether this is ok.

Now that I've browsed a few other threads it seems that some people use nylon and it's ok. Is there any reason why polyester is preferable or are they about the same?

Also, does anyone from Brisbane know where I should look for polyester swiss voile?