Well, finally, as promised, here's my how-to.
Q. What's a heat sealer?
A. Also known as an impulse sealer, a heat sealer uses a resistive heating element to seal and/or cut thin plastic bags or sheets. Rather than using continous heat, which would turn the bag into a gooey-edged mess, it uses a timed impulse of heat - hence "impulse" sealer.
This instructable reveals to you many secrets that certain people do not want you to know! I have already received several death threats from one of the major recloseable bag companies. Please enjoy this instructable, which might be my last....
Step 1: Why Would I Want a HEAT SEALER, Anyway?
Using a proper heat sealer, you can do a much more than making toothpaste packets!
Click on the pics below to find your reason. If you do not see it, then perhaps playing with Dremel tools and electricity is reason enough.
And dare I say, you can even store your beads with it?!
Step 2: So HOW Do You MAKE THIS THING?
Some of the things you will need are:
1. Some plexiglass or wood, approx 1/4" thick and about a foot in length. I always have some plexiglass around, so that's what I used, but hardwood would probably be better.
2. Four nails
3. A Dremel tool or router, and preferably a routing table.
4. Routing bit and side-cutting bit (or perhaps a thick cutting disk would suffice).
5. A drill and drill bit the same size as your nails
6. Coarse sandpaper
7. For plexiglass: some acetone and a dropper bottle, or some epoxy.
For wood: wood glue? I dunno much about wood-working.
There are literally an infinite number of ways to skin this cat. I can't describe them all, so I'll tell you exactly how I made it, using a laptop power supply, 19.5V and 3.16 amps.
If you have the power supply and the tools/supplies to make the structural parts, and you can solder smd parts and read a schematic, I can provide you with the exact circuit components I used. The kit would include all of the following items.
1. Nichrome wire (this comes in a plethora of specs and sizes. After much experimentation and for several reasons, I have settled on Kanthal A1, 27 gauge.) 2 yards of it. More than enough for a couple of screwups.
2. A power mosfet that can handle 9amps!
3. A PIC microcontroller, custom programmed to provide the pulse and to be user-programmable on the fly so that it can be instantly adjusted for a myriad of wire length, power supply, and bag thickness combinations, using only a single button!
4. A bicolor LED, red/green.
5. A 78L05 voltage regulator to power the PIC
6. A couple of caps and a few resistors
7. Some SIP headers, male and female
8. Some protoboard
9. 30AWG kynar wire, about 3 feet.
Step 3: The Science
So, what's going on here? Well, ohm's law is a good place to start. I began by taking a look at my available power source... a 19.5v, 3.16A powerbrick for a laptop. My particular nichrome wire has a resistance of 4.4 ohms per foot. So in making a 12" heat sealer, I use just over a foot length of nichrome wire.
19.5V/4.4 ohms is... 4.4 amps! This draws too much current! Well, yes, and no. The rating on a laptop psu is the constant current rating. A peak rating is typically 2-3 times as high. Because the pulse is going to last under 1 second, it's all good. So let's get started.
Click on each pic below and read the highlighted captions.
Step 4: Ok, Now What?
Ok, so take the blade and sand the cutting edge flat as you can. Use coarse sandpaper. Take your time. This part is important.
Then you can make the base. Basically, I just used some scrap pieces of plexiglass and bonded them to the four corners of the base. The ones at the base are the hinge. The pair up front are guides, to keep the blade squared up.
Also, notice I put all the electronics right onto the blade. The base is just a base. This way, I can take the blade out and use it alone. This allows partial cuts, by using just the tip, or you can combine two cuts for a larger bag.
You might think "why not just leave off the guide rails." Don't do that. The guide rails are necessary, and I can't bother to explain why, at this time.
Step 5: Now Make the Circuit
Here's the schemmy. If you want to really DIY, you can forego the PIC and power it with a 555 timer and potentiometer setup.
Step 6: Ok, Now String Up the Wire
So you put a single nail in the front. Wrap one end of the wire around this nail and then twist it a few times. Then put the nail in. Then, holding the other end in a crescent wrench, or wrapped around a stick a few times, pull it taught across the edge of the blade and then wrap it around the other two nails in a figure eight. Make sure you don't pull towards your eye, in case the wire breaks while you are doing this!
There are two reasons I prefer 27AWG for this (whereas 26AWg or larger is typical). 1. It heats up very fast, even with a laptop supply. 2. It cools down very fast. 3. It is easier to get decent tension on the wire even using this crude method. Tension is important, because the wire stretches when heated. If there's not enough tension, the wire will "walk" during the impulse. 4. It's big enough to do the job. Mine will seal 4 mil bags. I use 2 mil for everything in the pics.
Step 7: Now Set Up the PIC for Use
Click the video link to see a demo. For my particular setup, it takes about a half second impulse for get a good seal on up to 4 mil bags.
Now here's a video of it in action. Mind you, in this vid, I am still experimenting with 26AWG KA1, so the impulse is much, much longer than it is, now, and it doesn't work quite as good.
Step 8: Now for Some Tips and Tricks
The best bags for heatsealing are polyethylene or polypropylene bags. The more they stretch when pulled, the better. The bags can make a big difference in how strong a seal you get. The bags I use are polyethylene, 2 mil thick, 9x12" bags made by Uline. They work alot better than a seemingly similar polyethylene bag I was using before!
Here is a pic of 4 different ways to use your heat sealer.
But how good can these seals hold? See on.
Step 9: Water Tight Resealable Closure With PACKING TAPE? Are You Serious?!?!
Here's how to make a recloseable seal that is OJ-tight. Click on the pics below to see the step-by-step.
Step 10: I Want One!
Well, the longest part by a long shot was to obtain the wire and to program the pic. The rest was relative child's play. I always buy in bulk, because I never know what I might want to make next, but in this case, I have way more nichrome and mosfets than I'll ever know what to do with. The minimum order from the specialty shop I found for wire was 2000 feet! So I have the parts to make several of the control circuits for this project, and will be putting together some kits for my fellow enthusiasts.
I'll be giving away kits on my favorite electronics forum, http://dutchforce.com/. Check the Trade Forum under the "Want its," section. They should be avail in the next few days. If there's any demand, I might try selling some on ebay!