Electric hot wire knife?

Does anybody here know of either a site or have information how to build one of those electric heated wire knives?
I was thinking about building a hot wire knife with a difference. Instead of just one tensioned wire I thought that a simple jig could be built to string a series of parallel wires like a comb. Say as many as 12-20 wires per inch and about a foot wide. This could then be used to melt a row of shallow notches into the end edge of a piece of light louvre. The notches could then be used as a guide to string a wire stator (30 guage) without the need for a jig. Further once strung ot would be easy to solder the wires together at the ends or segment as desired. This is not so unlike the idea of useing holes at the end of a panel to thread the wire through but much less work.
Any input would be most welcome. Thanks in advance. Best regards Moray James.
OK tell me what a step&repeat jig is?

Thaanks Sy I had thought about useing one of those Weller soldering guns as a power supply but I do not think that I've seen one that has a variable heat control, though some have two temperature settings on the trigger. Maybe a small variac could be used in conjuction to set a working wire temperature? Train set power supply... now who do I know that has kids with a train set? Any other ideas? Regards Moray James.
I think you can put together a reasonable jig with a board and a fine brad. The idea is to fix the hotwire, have the brad spaced by the step distance, then sequentially move the plastic bit by putting the brad into the last melted "cut". This isn't written very clearly, I'm afraid, but a bit of sketching should make it clear.

Toy train transformers are variable, cheap, and effective.

Ok I get it as far as the reference brad to line the wire up. Are you suggesting just a single wire for the tool and to move the piece for each cut? Would a string of spaced wires not work? IE dificulty in generating consistant wire temperature along the string? Given the number of cuts to be made 12 to 20 per inch I figured a long tool would be more consistant and easier to do time wise. Regards Moray James.
Alternate idea

Wonder if I just couldnt' heat up a length of threaded rod and use the thread of the rod to "score the plastic grid all at one go? the cuts don't need to be very deep to hold a piece of 30 guage wire. So how do I control the heat of a piece of 1/4 or 1/8 32 threaded rod that is a foot long? Moght be just as easy to set the thing down on a old iron set to the right temp. Any other good ideas? (I kinda like that last one myself) Regards Moray James.
Here's another method of building "light grid" stators:

Jig is made from: 2pcs 1"x12" electrical conduit, 2pcs 1/16"x3"x18" sheet metal, 2pcs 1/16x1"x18" sheet metal.

Drill four 1/8" mounting holes about 1/4" from one of the long edges of each piece of sheet metal.

Mount the 3x18 sheet metal on the end of the conduit pieces so that the edge with the holes extends 1" or so beyond the conduit. (Forming an elongated "T" about 13" tall.)

Bolt the "Ts" to 2 front-front light grids (wire will be on the outside) using the outer rows of cells in the grid. (The sandwich is sheet metal, 2 grids, sheet metal.) This gives you a big "single blade paddlewheel".

Suspend the "paddlewheel" between a couple of workbenches so that it is free to rotate but not otherwise move.

Attach the end of your wire to one of the grids.

If you get the "right" amount of tension on the wire, it will pretty much stay where you wrap it. Rotate the paddlewheel while feeding the wire and you end up with a big rectangular "coil" about 1" thick by whatever length you are making the cell.

Adjust wire spacing if required, superglue the wires to the grids, cut the wire at the end of the grids, and presto...two stators! (If you want more than 1/2" of wire at the ends, add a stick of wood or some other spacer at the ends of the paddlewheel.)

Hope that was clear enough!

Wings WTW
Moray, for a hot knife, you want nichrome wire and low voltage. A nice high current transformer (easy to find these days) of 5 - 28vac with a variac in front of it to control temp works ok...

The problem with your scenario will be controlling the "burn" - the nichrome likes to start out hot, and cool as it meets the work. Getting a consistent depth of burn will be the most difficult part. Not sure how you could do that.

Nichrome also does NOT stay tensioned when it heats up - you'd have a shot at going width wise on 8-9" wide or less cells. Not the long way at 4 ft... :whazzat:

The fumes are TOXIC!

Threaded rod will not yield parallel lines, dude! :D

I think I'd opt for a different method.

I'd set up a jig with a very fine saw blade - they are sold in precise thicknesses, btw. You could easily stack a number of these blades (typically 3-5" diameter) on the arbor of a table saw with precise spacers and cut a number of slots in one pass.

Incra sells a "step and repeat" jig for table saws - or you can make one for this sort of thing very simply, given that you only need to go the width of a louvre, (or 8-9" like Acoustat?) or less.

This will give you repeatable and accurate depth of cut and width.

If you use this, please give credit! :cool:

_-_-bear :Pawprint:
cutting slots

Thanks Bear for the input. The more that I think about the wire cutter device the more work it seems. I had long ago thought about multiple rotary cutter disks on a single mandrill but did not want to spent that much money or time.
Yesterday I did some simple tests with some machine screws and also with some wood screws. The machine screw (1/4-20) worked well enough simply heated on the stove but the thread is not deep enough to form a nice deep slot. The wood screw which has a deeper thread was almost good enough to get away with. By the way both screws formed very nice evenly spaced slots on the end edge of a piece of light louvre.
I will have to take a piece of threaded rod to a machine shop and have the thread made deeper. Then I will spot weld the rod to the edge of a piece of steel bar stock and then brase the bar stock to the bottom of an old iron. That way I will have a convienent heat source that is fully adjustable. With a little lubricant on the threaded rod and just enough heat to melt but not burn I should be able to get the job done. I have found that the end of the light louvre has to be smoothed down after cutting (melting) as the plastic that was where the slots now are pushes out. This was easy to clean up with a few strokes of a good file. Hope that this information sparks some interest and experimentation. Best regards Moray James.
Groovy ends

Bear: yes I only want the grooves at the ends. They will only be used to anchor the stator wire as it loops around to serpentine back to the opposite end. Much the same as the plastic jig that Strickland used on the Acoustat except that I dont have to glue this one onto the louvre. The wire guage is 30. Present panels use 20 wires per inch but I would like to increase this to 32 wires per inch. I look forward to reading you suggestions. Be certain that if I do use any idea of your that I will be most willing to give full credit. Thanks and best regards Moray James.

Putting the grooves only at the ends will not ensure that all wires are running perfectly parallel. Wires are never perfectly straight and/or tend to shift. So, while the positions of the wires may be perfect at the ends, it is usually not in the middle.
I have built several wire stators (both rigid wire and flexible (tensioned) wire), and I always needed some device to correct the position of the wires.
Slight twist

Bear: have played around with useing heated threaded rods and the difficulty is in the shallow depth of the pitch of the thread. I looked int having a machine shop cut the grooves deeper and it turned out to be less expensive to have a piece of angle aluminum cut to the exact width and depth necessary. This was still more than I wanted to spend though. After some thought which was stimulated by your suggestion I had the idea to use your idea with a twist. Rather than a host of parallel multiple saw blades, I plan to look into hack saw blades that have perhaps twenty or more teeth per inch. If I can find a blade with a deep enough tooth pattern then that can be used (when heated and sprayed with silicon) to melt the necessary notches into the end edge of the louvre.

MJ: you are right about keeping the tensioned wires spaced parallel along the length of the louvre. I too have built a number of these panels and have had to deal with this problem. In the past I have set up the wires as evenly as possible by hand once they have been strung on the jig. Then I spot glue at spaced distances across the width of the louvre starting in the middle. This is not really a big problem with small panels but with metre long size panels it is a concern.
Should the hack saw blade idea work out then a simple jig with a number of identical blades mounted running across the width of the panel could be used to hold the wires nicely positioned as the wires are glued into place.

Paul W: thanks for the winding jig idea. That is a very similar method to what was preposed and I think used by Janszen for his panels. The idea is very simple, clever and works. I am however building large long panels (9" X 46") and it becomes a large space consumeing piece of gear. I just don't have the room for a jig that big. I want to do the whloe stator panel on a bench not much larger than the panel itself.
For larger volume production where you did not want a high tech solution (read expensive) I think that this would be my first choice. I believe that it could be made to work very quickly with little effort. The key would be to find a fast and secure method of fixing the wires to the louvre once wound so that the next set of louver panels could be fitted into the jig for "stringing". You would want to do the bulk wire bonding off of the jig and then set on racks while the adhesive cures.
There may be some reading that could make use of a jig like this. Though most here are interested in limited diy applications I believe that such exchanges may cause some would be manufacturers to jump off of the fence and into a small business. That in the end benefits those DIY wannabe's who just never seem to "get too it" as someone has then produced an affordable product. Not to mention the influx of fresh ideas. Lots of competition in any market place breeds new products and improved manufacture/priceing of existing product. This all helps to push the envelope. Very best regards Moray James.
Saw blades a bust

Spent some time speaking with custom saw blade shops today. Cannot find a blade with deep enough teeth to do the job. So I have inquired to a number of bolt manufacturers to see if there are any specialty threaded rods (as stock items) with deep enough thread and minimal pitch. Will post back findings here when they arrive.
Had another thought that a round gear could be machined with the desired number of notches per inch. this could be heated and rolled across the end of the louvre. Might get a bit messy as it would require multiple revolutions to go any distance and this would increase the chance of plastic build up on the gear. I still like the threaded rod idea best. Regards Moray James.
I used superglue while on the jig...otherwise the wire will just spill off in 4' sections when you cut it. Superglue the ends, then middle, then 1/4 length points, 1/8 points and so on until the wire stays where you want it without adjustment. Superglue the remainder, and then cut the wire.

The panels I built were 2'x4'. The 2 piece jigs are only 12"x18" each.
To refresh one of the better ideas posted by SY

Sy did indeed post one of the easiest methods to produce accurately spaced slots. The method can be used with a hot wire as depicted or using a metal slitting saw which can be found in very thin guages. A slitting saw will require an arbor and a special setup as they are not very large in diameter. But with some ingenuity head scratching and general consternation you will probably throw in the towel and use the hot wire method. :D

This method is used all the time in wood working. The back fence can be anything handy. The pin would ideally be a hacksaw blade. Personally I would make a partial cut into the fence board and glue it in the kerf. If I was worried about it coming loose I would epoxy it in place. The wire or saw or whatever you use for cutting the slot will make the notch. The notch will fit into the knife edge that you have spaced as you wish. Each sucessive cut will be set into the knife edge. They will all be the same.

I've used a beefed up variation in cabinetmaking for years. I have made multiple finger joint jigs and dove tail jigs that fit so tight that I had to sand some sloppiness into them. The dovetail jig makes cuts that fit together and stay together without glue!
So I'm very confident in the uniformity of the process. Plus it is fast.



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