Saturday, April 19, 2014

Cold wire...

I recently purchased a Mastech Hy30005D power supply for a Hotwire foam cutter. This unit is working well for lighter 27 gauge wire.  However, I need to use heavier 20 gauge wire for detailed shapes, and this unit seems to be under powered for the task. Could you please guide me in a selection?  Funds are by no means unlimited, but a need a reliable unit that can provide ample heat to cut at a good pace.,

Just for reference, I'm sure this is the unit you purchased? Link

This unit has a max output of 5amps, which is going to be the source of your problems. 

Let's quick reference the nichrome data chart found on my website - Link

As you'll note, for 20 gauge NiChrome wire, 5 amps will generate just shy of 600°F. But for 27 gauge wire, 5 amps will generate just shy of 1800°F!

The thing that I've found is wire temperature and cutting speed are related, but often two different things… 

Most styrofoam products will melt at around 400-600°F, so theoretically a 600°F cutting line should suffice for cutting purposes. But remember, heat has to LEAVE your wire, and enter the sytrofoam to melt and cut the substrate. So your wire has to heat BACK UP in order to cut the next section of foam. Often what people will notice is when the wire FIRST touches the styrofoam it will cut REALLY well, then it will slow down as you get more into the cut.  This is because the heat has left your wire, and the wire is having a hard time heating back up to match your cutting speed. 

The fix is that you need to send more current through your wire. You need to have a hotter over-all wire, to increase your cutting speed. The heating-cooling-heating process will find a happy medium, you just have to find out what that is…

For 20 gauge nichrome, 5 amps will work.. albeit a little slow. For some people, considering the cost, a little slower cut might be acceptable if you have a working product as a trade off.  

From a power supply, I think you would want to have the ability to increase your amperage to 7-8 amps, just so you can play around with your final cutting speed. Here are a few options
30v10a - Link - $94
30v10a - Link - $170
18v10a - Link - $140

Another option would be to select a variac, which is an AC transformer… higher voltage, so be cautious during use
130v20a - Link - $109
130v30a - Link - $134

For the money, I'd select the $94 unit from circuit specialists. It has both a higher voltage (good for small wire) and a higher amperage (good for large wire). 

Friday, April 18, 2014

Tattoo Power Supply Freak Out

I am building a hotwire table. I'm using my tattoo power supply as a source. It's output is fine (3-15-V Dc).Even the clip cord reads the same . When I connect it to the table my voltage goes crazy! So the problem has to be in my table components. Is a "stove" Bolt necessary? Or will any bolt do?

Any bolt will do fine, but I agree the problem is not necessarily with your power supply.

So… let's see if I can keep this simple. 

Any time a power supply is placed under an electrical load (your cutter) you will see a small voltage drop at any attached reader. This is a normal result of electrical resistance, current output, etc. 

But your problem is MOST likely related to the maximum output amperage/wattage of your power supply. If the numbers are going all crazy once you hook up your supply, then I'd wager a guess you're "clipping" out the power supply as an over current protection. Or, if there is no OCP, then it could just be feeding back, overloading your power supply and it's shorting out. 

Here is a document I have on OCP - Link

While you mentioned your power supply is 3-15v DC, that is not the most important part. You need to determine the maximum safe output amperage and/or the max output wattage. THAT is what tells you the capacity of your power supply. In MOST circumstances tattoo power supplies max out around 2.0 - 2.5 amps, but usually 2.0. Some are only 1.5 amps. The issue is that most hot wire foam cutters, depending on what wire gauge you use, require about 2.5-3.5 amps to heat effectively.

Relating all this back to your cutter.

Your cutter has a defined resistance, and when an electrical pressure (voltage) is placed on that circuit (cutter) it will generate a current (amperage). If your resistance is too low, and your voltage is too high, it will allow too much current to flow; and that flowing current may be higher than what your power supply can handle. 

Your solution is to use a smaller gauge nichrome wire (which has a higher resistance) or include a resistor in your circuit. I have a tutorial video on making your own resistor out of aluminum wire. 

Check out my Electrical Calculations Videos ( link ) which should be a really good walk through from beginning to end.

Monday, April 14, 2014

Large length CNC cutter

Another email, a user in Malaysia is trying to build a CNC foam cutter. Needed help on a 10 foot cutter… This message starts out already broken up, and with my replies.

I'm in orange.


I live in Malaysia, and our current here is about 240V, i believe.

Yes, you're right, but not to split hairs :) You're Voltage is ~220-240v, the Current will be depend on your circuit. 

I am trying to make a mini hot wire cnc cutter for my small production area, to cut our 8ft x 4ft x 2ft block of 16kg per piece foam. The machine I intend to build is about 10 ft x 5 ft x 4 ft, actual cutting is about the block size. One block at a time, I will need to cut them. I went to your site and saw this, you recommend a gauge 26 straight wire from Jacobs.

Yes, in general I recommend 26 gauge for straight wire cutting. But 26 gauge isn't necessarily the best choice at lengths greater than 2-3 feet. It is a higher resistance wire, and a lot of the times you then need a higher voltage in order to power it. 

A lot of CNC and Wing cutters have recommended going with a stainless steel wire OR using 27 gauge Rene wire. Jacobs just started carrying 27 gauge Rene wire and Terminal Tackle has stainless steel leader wire. 

You may find that Rene wire or stainless steel wire allows for a higher tensile strength and allows you to keep your wire tight while cutting. The 26 gauge wire may bow during cutting and/or may snap if you place too high of a pressure while cutting at those lengths. 

, and with the calculator, I used, it seems to say, at about 5 ft across, using a gauge 26 hot wire at 600F temp, I will need a 28Volts & 2.1Amps.

However, sometimes, if I change the direction of the plane to 10 ft cuts, it will require 56Volts & 2.1Amps.

I am running two setups on one machine, in that case, do I use 2 different power supplies with variable voltages & variable amps? or do I just go with something that can cope with two of them, since I only use either one setup at any given time.

Definitely go with one power supply that can cope with both circuits. The last thing you want to do is switch between power supplies half way in. 

Your calculations are very accurate, and you did a great job. But the ONE thing that most people don't take into account is cutting speed. And that has just as much to do with wire temperature as anything else. 

Technically 600°F is enough heat to melt and cut foam, but as that heat transfers from the wire to the foam your wire is cooled. Then your wire has to heat back up. This is a continuous and ongoing process as you cut foam, and often you will find a "steady state" where heat is leaving your wire and the wire is heating back up. 

As a rough gauge, I like no less than 4 amps pulling through a LONG wire at any given time. While it is a hotter cutting temperature to start out, the total wire temperature will actually decrease once you start cutting. So if you start out calculated and start cutting at 600°F and it cools to 400°F, that is a lot slower cutting than if you start out at 1000°F and it cools to 800°F. Also, at a higher current (4-5 amps) the wire will replenish heat quicker, which means there will be less of a temperature drop than at lower currents. Of course, all theoretical temperature drops, but it illustrates the point. 

also, you said something about adding a 20% on top of this numbers, so I should getting something like 33.6Volts & 2.52Amps for the 1st setup (5ft)? and 67.2Volts & 2.52Amps for the 2nd setup (10ft)?

Yea, you never want to run a power supply at 100% capacity. You should aim for 80%. You CAN run it at 100%, but that may decrease the life span of your power supply. At 80%, it doesn't have to work as hard. 

If you're interested in building your own variable voltage power supply, Jacobs does have some transformers that would work really well. Here is the link. Scroll to the bottom, I'd recommend the XFR-3018e. It would have a wide range of voltages and currents for you to work with. 

Otherwise you  might want to consider finding an "AC Step Down Transformer" also known as a "Variac". Those are usually nice units, and good for the price. But not too many are rated for 220V input. They're out there, just have to find them. THis is one unit from Mastech (link)

I hope that answers your questions, and feel free to write back. I'd be happy to help. Also, I just put up a new link from They are from Canada and specialize in large scale CNC cutters. You can try to get a hold of them and see what help they can provide too. 


You wrote "As a rough gauge, I like no less than 4 amps pulling through a LONG wire at any given time. While it is a hotter cutting temperature to start out, the total wire temperature will actually decrease once you start cutting. So if you start out calculated and start cutting at 600°F and it cools to 400°F, that is a lot slower cutting than if you start out at 1000°F and it cools to 800°F. Also, at a higher current (4-5 amps) the wire will replenish heat quicker, which means there will be less of a temperature drop than at lower currents. Of course, all theoretical temperature drops, but it illustrates the point."

so, at 56V, 2.1A on a 10ft gauge 26 Nichrome wire. you said that it would be better to start out cutting around 1000F, which means both the V and A are now increased to 86V & 3.2A.
what I am confused is, do I just UP the Amps, or i still use the calculator for both Volts and Amps INCREASE, as you said maintained no less than 4Amps?

This is a tricky one to explain, but once you understand it, it will make sense. 

When you are controlling a power supply, typically you can only ever control "voltage" you can not directly control amperage. Your amperage is a function of the applied voltage and circuit resistance…

However, when you're heating a wire, Amperage (and/or wattage) is what correlates to heat and temperature. 

So when I say I like about 4 amps, thats just a rough gauge based on a desired temperature and cutting speed; I was also only using 1000°F as a generalization as well. In order to obtain 4 amps, the voltage will vary depending on if you're using 26 gauge or if its 16 gauge. 

You calculated correctly, to hit ~1000°F with 10 feet of NiCr 26 gauge, you'll need around 85v and 3.2 amps. 

But again, at such long lengths, you might want to consider stainless steel wire or rene wire. 

when using bent shapes, i need to go for around gauge 16 ya?

Yea, that would be about right. Shouldn't need anything thicker. 14 gauge at most.

In that case, is there any place, you recommend to get 0~20Amps, 0~100Volts variable power supply? @ 220~240V input?

MastechPowerSupply has this one - link

It is called a "variac" or step down AC transformer. Much like what is available on jacobs online, but this one is an all-in-one model. You just have to attach your supply lines to the front and then over to your cutting equipment.

The one tricky thing is that this power supply has a built in voltmeter, not an ammeter. Which.. you're going to care about amperage, not voltage… but functionally won't matter.

Regarding the cutting speed, i saw many online uses 22inches/sec cutting speed?

not sure if this is too fast, this is the first time, I'm on this subject, so it will depends if I can figure out everything and do something that speed.
but just for information, do you think 22"/sec is ok cutting speed, given that I heat it up to 1000F to begin with.

Honestly I've never heard of 22"/s cutting speed. That is damn fast… are you sure that is the speed?

the power supply you said, is XFR3018E.
and the one I saw is XFR3024E.

I am a little confused because, it said:
is for  very large wire gauges of moderate length or very long lengths of medium gauges -- up to 87 inches of 14 gauge or 125 inches of 18 gauge."


"XFR3024E is for very long medium gauge wire -- up to 102 inches of 16 gauge or 139 inches of 20 gauge."

shouldn't XFR3024E be more suitable for my applications since, we also need to bend wires of gauge 16 sometimes to make bowls or domes?

just need some explanation of what's the differences and how I should be picking my Power Supply.

Now that I take a second look, I'm not sure either will work. If you go 10 feet with your 26 gauge, you're going to need 86v which neither supply can provide. So…. I think going with the variac from mastech would be best. 

Also, only occasionally that we will use more than 1 hot wire for cutting, so, normally its fine, on a 1-to-1 circuit.
on that special occasion when we do use 1-to-2 or more, would you recommend parallel or serial circuit to use?

Well… the easiest thing you can do is run them in series. That would only then change the voltage requirement of your circuit. 

If you place them in parallel, you will change both amperage and voltage. Which… sometimes can be used to your benefit if you want to play around with different types of wire… But parallel circuits just take a bit more calculations. 

If you check out my Circuit Theory page, I go in depth with series and parallel circuits, and what properties change. 

But again… series is just easier as long as your power supply has enough voltage (which that mastech will).


Nothing to be sorry about. It's all good. I learnt a lot from you and I deeply appreciate your help.
My pleasure, always glad to help!

I am considering a dual transformer to perform the required output, but it would seem too wasteful of resources, which I should instead go for the Mastech you talked about.
Yea, your goal should always be one power supply to handle all circuits. It's not ALWAYS possible, but usually is. It cuts down on supplies, and upstart cost. 

14ga. Wires might be too much for me, so I go ahead with the 16ga. Wires and that should help me with keeping voltage down a little while still keeping the contours of what I need. Normal for dome or bowl shape items only.
Other long shapes will use the Rene 27ga. Wires to run CNC with.
Remember that your electrical requirements are opposite for small and large wires. 

Large gauge (16ga) requires less voltage and more amperage.
Small gauge (26ga) requires more voltage and less amperage. 

So when you're setting your dial on your power supply, always start out at zero and then turn it up until your wire has reached a desirable temperature and cutting speed. 

Speed wise, let me check, might be wrong with 22"/sec. Yes, i am wrong indeed, it should be max 55"/min. NOT per sec. Sorry about the confusion and thanks for the reminder.
Okay that sounds better…!  22"/second is DAMN FAST, but a 55"/min max is a bit better. That is about 1" per second which is a desirable cutting speed and temperature.

So confirming the wires, I will need output of max voltage about 100V & max amp about 13A for use with 16ga. (These are with 20% safety buffer)
Um… sorry, what length of 16 gauge are you using? I lost that in the emails somewhere…

But if you're applying 100v to 16 gauge and want 13a max, then you're wire has to be 30 feet long… I doubt you'd be using a wire that long?

So with the Mastech, I no longer need to buy the dimmer, fuse holder, slow blow fuse, and on/off toggle switch?
Or I still need them, slightly confused, because this is still just a variac transformer?  What's else am I missing?
No, you won't need any of that. It is a completely contained unit. All in one. I'm not 100% sure if it has a fuse or not.. probably does… but either way you probably won't need it. 

I decided to go with the new MasTECH for this one:

input 220V
output 0~250V , 0~20Amps
USD $168

I think will be best for all my applications, if one day, I decided to do something larger, I can still work on them without over killing my power unit.

Yea that is a really nice variac. It has a high amperage, and is nice for you that it has a 220v input. 

Most variacs are strong and withstand a lot of work. I think you'll be happy with that unit for quite some time.

there's only red and black at the front of the unit, it says IN/OUT, so where do the 3rd ground wire connects to from my outlet?
still looking at your serial connections.

These units only have an in and out, they're wired differently than the jacobs-online transformers. These units are essentially fool proof. 

The IN is what comes from your wall, and the OUT is what goes to your cutter. 

On the front of the unit, there is a little brass tab with the universal symbol for "ground".

This is where you'll want to attach the ground from your wall AND the ground from your cutter. BOth can touch there. If it doesn't fit, there is a screw on the other side that you can attach a wire too as well.. Or just make a jumper with a wire nut. 

still very grateful for all the help I am receiving.

I made a little mistake about the 16ga. wires.
only need about 30V & 11.2A to make it happen, even for the 10ft contours @ 800F.

That makes more sense :)  And yea, you wouldn't need much voltage at all to achieve that amperage and temperature. I bet you'll be happy with the dial set around 30-45 volts.

for the 27ga. rene wires, it takes about 70V & 2.6A to make it work, and yes its the max 10ft straight line @ 800F.

Yup, that too looks like a good estimate :)

the MASTECH 5K will do more than enough for all my applications and at a very reasonable price.
thanks for recommending MASTECH to me, it solved all my doubts and problems.

Your welcome. I have really taken a liking to the step down transformers and variacs. They're great for MANY applications and very reasonably priced. When you switch over to the DC world, there is more expense in all the internal components. Functionally, there is no difference between AC and DC circuits when cutting foam.. so go cheap and strong. 

as for you saying measuring the temperature, I saw that you use a Volt and Ampere meter to measure the desired output from the transformer.
But how do you actually measure the temperature?

WELLLL often you can't measure temperature. 

I usually only ever measure output amperage, and then reference the nichrome data chart (link) to see where my wire is. It's not the most effective means.. but it is one solution. I've tried an infrared gun before, but I'm not sure it's entirely accurate with such a fine wire. 

As far as I understand that these transformers are we can only adjust the VOLTage on it?
so if voltage increases what happens to the amperage?

Voltage directly correlates to amperage, as a function of your circuit's resistance. (Larger gauge, less resistance; smaller gauge, more resistance.)

Think of the voltage dial as a kitchen sink faucet handle. If you open the water faucet, it lets out more water because it is allowing more water pressure to escape your pipes.  If you turn up the voltage, it lets out more current flow because more electrical pressure is escaping the power supply. Voltage is your pressure, amperage is your flow.  Does that make sense?

So, in a sense, when you turn up the voltage it too will turn up the amperage. It's just that different amounts of amperage/current will flow depending on your circuits resistance. 

That's why with large gauge wire, there is less resistance, so it is easier for current to flow. Meaning, it requires less electrical pressure (less voltage) to allow the current to flow.

Where as with a small gauge wire, there is more resistance, so it is harder for current to flow. Meaning, it requires more electrical pressure (more voltage) to allow the current to flow. 

It IS the flowing of electricity that generates your wire heat. And that generation of heat is also in part related to wire resistance. If a wire has more resistance, it is easier to generate heat. Meaning it requires less current flow. If there is less wire resistance, it is harder to generate heat. Meaning it requires more current to flow. 

So they're all related….!

what i am saying is, for the 16ga. wires, we need higher AMP and lower VOLT, so, obviously I can't just go with the lower VOLT on the MASTECH as this will also correspond to the lower AMP?

I believe I answered this above… but here's my personal theory…

When you are doing calculations manually, it is only to ever help estimate your electrical requirements. Your calculations are supposed to show you which is the BEST power supply to purchase for your application. 

BUT… When you get the cutters assembled, and the power supply hooked up. There is always a difference in circuit resistance than what you calculated… THe connectors, the additional wires, the other metal, everything adds to the resistance of your circuit.. even if it's just a little bit. 

So, now that you've selected a very good power supply, my recommendation is this.

Hook everything up, with your power supply turned off and starting at "zero". Your calculations will get you to the ballpark of where you need your voltage setting. But essentially you're starting off at zero, and slowly turning up the dial until your wire is cutting at the speed you desire….

When you are actually cutting in real life, just start at zero… turn up till its cutting.. and away you go. The theoretical calculations become much less important when it comes time to test the whole thing out.. :)

there's another question I kept forgetting, but I don't see any serial or parallel wiring that you have in your transformer page?

Yea, with the mastech there aren't going to be any serial or parallel wirings. There is an input (from the wall) and an output (to your cutter). Basically, the input is your primary windings, and the output is your secondary windings.

The difference is, you're buying a complete package with the Mastech. Everything is all in one, and it's all wired appropriately.

When you buy a naked transformer (like on jacobs online), you have to be accountable for wiring in series or parallel, and adding dimmer switches, and mounting brackets… etc etc…

So with that Mastech, it is a complete solution. All you'll need for quite some time… 

I am buying that MASTECH 5K as we speak, will hope to see a good manual on how I can properly use it.
There should be a manual, lol… I can't imagine there won't be. But again, input(wall) and output(cutter). You will need to make sure you wire the input appropriately (positive and negative terminals), but the output doesn't matter. 

I hope that all makes sense!!