Plasma Cutter

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Plasma Cutter

Postby bdring » Mon May 14, 2012 11:28 pm

For my next learning experience I thought I would tackle a plasma cutter.

I am going to use hardcoated Makerslide with steel V wheels. I have a bunch of angular contact wheels left over from my original laser design. I think they will do better in a harsh environment.

I am going to start with a 24" x 48" table area so that is stays small and does not take up too much room in the shop. Once I am happy with the design I will scale it up to at least 48" x 48".

I cut a piece of hardcoated Makerslide on my chop saw. Normally the saw just slices right through. This time it was a bit harder to do and it sparked. It never sparks when cutting aluminum. I was not sure what was sparking, but now I think it was some carbide from the saw teeth. The blade is quite a bit duller now than it was. I will definately be cutting and tapping the rest of the pieces before they are hard coated. That stuff is hard!

rack_drive_01.JPG


I used JB weld to glue the rack in place. It was easy to install because it registers on the inside corner of the Makerslide V. The rack I used is a 24 pitch 14.5° pressure angle 24" long piece I had laying around for a while. I used a 15 tooth pinion gear. I found that larger diameter gears tend to ride smoother on the rack. This was the largest 1/4 shaft pinion McMaster had. 1/4" shaft fits all the other pulleys I had. I uses a 20/48 timimng pulley setup from laser parts I had. The drive head swings to adjust for rack engagement. When properly engaged I cannot feel any backlash. I am sure there is some, but it is prbably below the resolution of what a plasma can do. The design will fit NEMA17 or NEMA23.

Here is a rendering of the basic rail design. The Misumi 2080 extrusion will add strength plus shield the v rails from slag spray. This is the Y axis. I will use the same drive for the X axis, but I doubt I will use the 2080 on the X.

rack_drive_01.jpg


Plasma Cutter Choice: Coming Soon

Torch Height Control Choice: Coming soon
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Re: Plasma Cutter

Postby mattrsch » Mon May 14, 2012 11:46 pm

My brother and I have been talking about building a plasma cutter for a while now, so I will be watching this thread with great interest :D
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Re: Plasma Cutter

Postby tylerv » Tue May 15, 2012 12:02 am

Bart is coming up with interesting projects faster than I can follow.. :)
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Plasma cutter machine

Postby bdring » Tue May 15, 2012 12:27 am

While I want to be able to support a really cheap plasma as an option, I am thinking about going with the Hypertherm Powermax 45 with the machine torch option. It has a very good reputation and brings out all the controls necessary for a CNC system onto a connector. Most cheaper systems you have to do some serious hacking. I like the machine style torch too.

The torch has a built in rack, but I cannot find any decent dimensions or specs on it. It would be cool to use the rack, but a more universal Z might be a better idea.

Powermax45mechanizedtorch.jpg


HYP088012.jpg


I really don't see cutting anything thicker than 1/4", so it should be plenty powerful.

I have heard the cheap harbor freight type plasma have come a long way recently and have a decent pilot arc start and don't blow out all the electronics in the room every time they start anymore.
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Torch Height Control

Postby bdring » Tue May 15, 2012 12:51 am

The next bit of special electronics you need is a torch height control system.

As I understand it you could create a system without active torch height control, but it would not do the best job and would probably eat through the consumable parts of the torch.

Typically, the THC has a mechanical or other sensor to determine absolute height over the work piece to set the piece height. One running it goes into a voltage monitor mode. The voltage is proportional to the distance so the circuit can determine the height using the voltage and adjust as it goes.

The ones I am looking at just send a move up/move down signal to a Mach3 type program and that takes care of the actual movement.

I have a good friend who wants to make an open source design for this, but for starters I will buy one.

I like this design from Cambell

LCTHC-Detail-Text-small.png


http://www.candcnc.com/LCTHC.html

I also saw this on eBay, but could not find a lot of people using it.

ebaythc.JPG
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Re: Plasma cutter machine

Postby macona » Tue May 15, 2012 5:02 am

bdring wrote:While I want to be able to support a really cheap plasma as an option, I am thinking about going with the Hypertherm Powermax 45 with the machine torch option. It has a very good reputation and brings out all the controls necessary for a CNC system onto a connector. Most cheaper systems you have to do some serious hacking. I like the machine style torch too.

The torch has a built in rack, but I cannot find any decent dimensions or specs on it. It would be cool to use the rack, but a more universal Z might be a better idea.

Powermax45mechanizedtorch.jpg


HYP088012.jpg


I really don't see cutting anything thicker than 1/4", so it should be plenty powerful.

I have heard the cheap harbor freight type plasma have come a long way recently and have a decent pilot arc start and don't blow out all the electronics in the room every time they start anymore.


good choice on the Hypertherm. I used to be a service tech for welders and plasma equipment. Hypertherm is still made here in the US by an employee owned company. They really make the best machine out there.

A friend has a Hypertherm Max 200 for a cnc machine, though that might be too big for you! It will cut 2" steel.

The torch is made to pretty standard specs on the OD and the pitch of the rack. They are, for the most part, interchangeable with Oxy-acet torch heads for gas burning. It is mainly used for adjusting the torch when you set it to a 45 or something to cut a bevel. Also us used for gross height adjustment, say you need to cut a piece in a structural shape piece of steel.

Most lifters use a generic ball screw, nothing fancy, just the cheap black rolled screws. One other thing a lot of people forget is a collision stop. This stops the machine if the torch runs into something, which can save a lot of money in the long run. They are very easy to build. The simplest uses air. Basically two plates are sandwiched together with three steel ball in a triangle. The balls (Or cones) are attached to one plate. On the other plate there are holes with an o-ring seal on the surface where the balls or cones sit into creating valves. The holes are all paralleled together by either small hoses or the plate is drilled to create a manifold. The two plates are held together with a through bolt, spring and a nut to adjust the tension. This all comes together to create something like a touch probe for a cnc machine but pneumatic. On the line that feeds the 3 valves is a low pressure regulator and a pressure switch. The switch is just a simple on/off that opens at 1 or 2 psi and the regulator is set just above the pressure needed to close the switch.

Operation is simple. During normal operation all the valves are sealed. If the torch is hit from any direction one or more of the valves are opened and there is a pressure drop at the switch which opens and triggers a stop.

This can also be used to help set the initial height. The letter drops the torch down till it senses a touch with the collision detection and then moves it up a set distance. Some of the commercial height controllers are very, very simple. They are nothing more than a DC motor on the lifter screw. The control box after touch off just sends power to the motor for a short predetermined period lifting the torch. The actual distance is not very critical. Then the torch fires and the box just uses a comparator to control the motor up and down. There is a basic filter to smooth out the movement and some thumbwheel pots on the front to set the voltage for the comparator. Often you do need to install a voltage divider in the plasma cutter which is nothing more than a power resistor and a filter cap.
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Re: Plasma Cutter

Postby callcbm » Tue May 15, 2012 11:23 am

I'm presently building a plasma and using the tch from candcnc great service and product. I built a control console to house the pc/monitor/tch my only worry is the electrical noise produced from my aged plasma making thing go funky.
Thanks Randy
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Re: Plasma Cutter

Postby bdring » Tue May 15, 2012 12:37 pm

Thanks for all the info @macona.

I think I will not use the built in torch rack for the Z drive. It makes it more complicated and limits the usage to the expensive Hypertherm machine. I hope to use the same rack drive module for all three axes. They are simple parts that can be cut from sheet on a router or printed on a 3D printer. I hope to run around 400 ipm on the X and Y.
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Motor Testing

Postby bdring » Wed May 16, 2012 12:22 pm

I installed an old NEMA23 motor. I don't know the exact torque, but I think it was around 300 oz/in. The drive system has about 3.8:1 ratio. Is is a lot stronger than it needs to be so I may change the ratio to about 2:1 so I can get the speed I want.

The power is is quite impressive and a little scary. I have not been able to stall the motor by manually holding it back. I think if I mechanically locked it down, something would fail before that motor stalled. I think the weak link right now is the pinion on the shaft. It came without a set screw and I had to put my own in. The hub wall is not very thick. I think the best way to change the ratio would be to get a bigger pinion.

The setup has quite a bit of hold torque with the motor off. This will make my Z simpler. It will not free wheel down if power is lost.

I plan to drive the Y with two slaved motors. A friend runs the fab lab at the local museum. They have a Shopot with a similar setup. He says they square the Y by manually sliding the Y against hard stops with the motors off. That sounds like it would be fine for me.

PS: I am going to Maker Faire this weekend. I will bring my little sample of hardcoated MakerSlide with the rack installed. I will also bring my Quantum. I don't have a booth, so I will be hanging out with Inventables and ShapeOko.
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Re: Plasma Cutter

Postby te_gui » Wed May 16, 2012 2:12 pm

Don't want to hijack this thread, but have been wondering how many folks were going to be at Maker Faire this weekend, and if any OrdBots were in attendance. I'll try and introduce myself if I get a chance.

Brian
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