Excellent build. Thanks for keeping us updated with your trial and error.
moreil,
Looking great, just a quick question.
How are you feeling now about your design re. the two seperate parts and clamping them individually. Do you think it was a good idea and is helping you by having some flexibility in the setup, or do you think you should have built a more ridgid one piece machine with two attached moving sections? Thanks.
Excellent build. Thanks for keeping us updated with your trial and error.
By using an op amp and a bridge circuit, you can implement a driver that will keep the temperature constant (more precisely, will keep the resistance constant).Originally Posted by moreil
Success!!
Stuff deleted....
BTW: Earlier I mentioned using a constant current source. My apologies for the utter nonsense.
What we really want is a constant heat wire (I think). The wire resistance increases as the temperature goes up. Power is V*I or V*V/R or I*I*R. Ideally we want to increase the voltage slightly as the resistance goes down.
Now lets look what happens with a constant current source . When the wire touches the (cold) foam and drops in temperature, the resistance reduces and the current source drops the voltage so as to hold the current constant. The disipated power drops just when we want it to increase. Oops.
With a constant voltage source, when the wire gets cooler, the resistance drops, and the current increases, increasing the power slightly. Much better!
In an ideal world, what we'd actually want to do is measure the resistance (as a proxy for temperature) and vary the voltage/current to suit.
Either way, a voltage source is a better idea than a current source.
Not 100% sure that this makes a difference in practice!
Ken
Kenneth Lerman
55 Main Street
Newtown, CT 06470
Nice looking machine. I have built myself one and now use it in production. I use an older version of GFMC and am running 80lb stainless wire and a 9 foot bow. My table is excessively big. Anyone need IMAC wings?
I've been cutting for a couple years with my machine now.
Here's a few things I learned that you may want to experiment with.
1. To help the LE curl problem with super thin airfoils play around with the GFMC LE cut schemes. It makes a much better LE than just bringing the wire around the LE. It also gives you a small window for the wire to catch up if it has started to drag and may save the core. I've cutt 55mm long cores with less than 30mm cords with my big machine and have gotten good results. Think 30" Apogee tails. On my version of GFMC you can't change the heat in the middle of the cut.
2. On using aligator clips on the wire: I tried that but ran into the problem of the wire catching on something and messing up the core. I now clip my aligators to the wire holder and not the wire itself.
3. Cutting foam over 40psi gets progressively more annoying. The more dense the stuff is the higher temps you need to run and even then you can run into weird oscillation problems if the wire even thinks of dragging. It will make a nice wavy core with progressively bigger waves. The longer your bow is the worse the problem is.
4. I'm using Malin hard stainless 80lb test wire for cutting. I too have noticed the wire outside the foam gets much hotter. This is only a problem when you run the wire to almost red hot which I do for EPP. It causes the wire to oxidize and also stretch. I get 15 cores out of EPP if I'm lucky before the wire breaks. I try to catch this and change the wire before it breaks mid cut and ruins the core. I think if you can run lower temps this won't happen as often. I know I can cut about 10x more EPS cores before I have wire problems.
5. Always good to clean the wire between cuts. This may be the source of the little hard bits you are thinking is from the foam itself. You can clean the wire by running a scrap piece of foam over the wire when its hot. Especially important when cutting epp as the wire will build up with ash and eventually cause the wire to drag. I think the ash insulates the wire and keeps the heat from melting the foam correctly.
I also have picked up a few feet of some more exotic alloy wires but have yet to test them. Rene and Inconel are two I remember off the top of my head. I'm hoping to find something that survives better than stainless cutting EPP. I've tried Nichrome a few times and really don't like the stuff. It's too brittle, stretches with heat way too much for my big bow, and kinks easily making the wire useless for cutting.
There photos of my machine, electronics, and setup in the gallery on my website.
Next on my list is a CNC Milling machine!
Andrew
www.canuckengineering.com
Anyone tried using Mach software to cut ?
Live life like you never see another day
Hi, Can anyone post the pictures of the Hot Wire Cutter on this forum since the "http://www.homecnc.org/index.php/Cheap_Foam_Cutter" site is down.
I am interseted in making my own Hot Wire Cutter (not expensive type!) Does anybody have plans?
Thanks,
I have used my table top router for cutting small foam patterns,
Luckily my needs are simple so a solid shape is all that ?I need. I used the basic software I normally emply when cutting assorted shapes from plastic, wood or metal but found I needed to swap the Z and Y axis over. A simple drawing is produced but great care is needed to ensure the wire goes around the shap and does not take a 'short cut' across the foam and also found it best to start along the upper surface of the foam and cut the lower level last before ending up back at the starting position.
The foam is stuck to the machine with double side tape and it is interesting to watch the wire rising and falling as it passes through the foam unlike conventional routing where the cutter moves across the table. I appreciate I only make small patterns and can only accommodate foam blocks some 2 inches thick by 6 inches wide by 9 inches long but it works.
The bow is made from what in UK are called 'Junior Hacksaws' in my case from the Pound Shop, the wire is fixed one end into an insulating block with a screw that also forms one of the power lead connections and the other has a spring to keep the wire tight with the other power lead being connected to the metal saw frame. It as I said works fine for my small patterns with the power being supplied by a model railwat transformer/rectifier which is controlled by a normal lamp dimmer so as to keep the voltage down to about 2 or 3 volts.
I would however like to 'rout' the foam using a vertical 'cutter' and have modified a small soldering iron to fit the machine in place of the normal rotary spindle. The modification consisted of drilling a hole into the copper bit and inserting a brass wire 1.5 mm diameter and some 30 mm long. Great idea except for the temperature gradient along this wire prevents cutting to any depth so any thoughts on how to create a constant temperature 'tip' no more than 1.5 mm diameter would be gratefully read.
Until I solve that problem my wheel patterns will continue to be routed out of the high density foam with a small slot drill which of course limits the depth of cut to about 10 mm or so.
John (in UK)
Dont remember but I think this one is simular....as long as you are not cutting 4x8 blocks.... enjoyCan anyone post the pictures of the Hot Wire Cutter on this forum since the "http://www.homecnc.org/index.php/Cheap_Foam_Cutter" site is down.
http://www.instructables.com/id/Make...parts-availab/
Bob
So the link is not working.... Can you get it back up?
Which link isn't working???
Don
http://www.homecnc.org/index.php/Cheap_Foam_Cutter link is not working....
I would like to see the one from the first post also.The_canuck,have you got a build thread on here also?
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