New Machine Build- Building a 10' by 7' plasma

[bleker]

Hi all,

This is my log on my new cnc plasma build. I originally planed a cnc router, but struggling to find someone with a cnc plasma to cut parts for the router, I decided to build my own cnc plasma first.

I sourced most of my parts from China directly due toe the huge cost of buying the components locally. So far I am more than happy with the quality of the parts and service I received from China.

The machine:

Mach 3 and Sheetcam

The X axis:

3 meter long travel with double lead screw, one either side. The lead screws are 20mm diameter with a 10mm lead. The stepper motors are 2 x Nema 34 583 oz.in again one either side. The linear guides are custom build, cnc water jet ,3 meter long 100mm wide, 8mm thick mild steel rails. The carriages will be build into the gantry.

The Y axis:

2 meter travel, single lead screw, 20mm diameter with 10mm lead. The stepper is a Nema 34 249 oz.in. The linear guide is a 6mm thick, 150mm wide, cnc water jet, mild steel rail. The 2 carriages is from CnC Router Parts (USA), the extended ones.

The Z axis:

200mm travel, single lead screw, 12mm diameter with 5mm lead. The stepper motor is a Nema 23 180 oz.in. The linear guides are proper ABBA linear guides with bearing blocks, 15mm wide rails. Still contemplating on which THC to use, but it will have the auto height sensing on the limit switch. I will also fit an air scribe next to the machine torch for marking and scribing.

The main frame is build from mild steel square tube, 100mm x 100mm x 2mm for the legs, rectangular tube 100mm x 50mm x 2mm for the top sections and 50mm x 25mm x 2mm for the bottom sections. The frame will be extended with 200mm high x 5mm thick plate sides on witch the linear guides for the X axis will be mounted. It will have a 4 inch deep water table all welded in to the main frame.

Here is some pics off of the components from China and the main frame I started welding together. I have received all my ball screws, end blocks, motor couplings and the linear guides for the Z axis. The plasma cutter, stepper motors with controllers, power supply and break out board are on their way. They will be here hopefully early next week, I will post some pics when I have received them.

Please feel free to comment I will appreciate the input.

Thanks for reading.

[bleker]

Hi All,

This is just a quick update on the build. I didn’t have a lot of time to work on the machine this past week, but got some work done.

The frame has all its supports in and the welding is done. I still need to smooth of some welds on the front, sides and bottom parts of the legs before the bottom section is completely finished.

I started with the adjustable levelling feet and will finish them tomorrow. They are build with a 16mm bolt, 100mm diameter pole cap and a 100mm diameter, 5mm thick plate. I am going to round off the bolt head slightly before welding it together, this is just to make it turn better during adjustment if it stands a an angle.

I had some good news from DHL today, my last shipment from China has arrived. Unfortunately tomorrow is a public holiday, so it will only be delivered on Wednesday. I will post some pics on Wednesday.

[hawkmoon77]

bleker,

Good info so far. I was wondering what prices you were seeing for the steel tubes. Also, who is your supplier for the ballscrews?

In looking at the feet, I am wondering if they won't introduce wobble into the machine. Do you find that they are stable enough?

[Phife]

Looks good so far, Like the steel frame. You may have some screw whipping issues with those long screws. Can you calculated the max speed for the screws yet?

[bleker]

Hi All,

Thanks for the replies..

Hawkmoon:

The steel tubes are costly same as the steel plate that I would need to finish the build. I calculated the steel for the machine at roughly $800, this is just the big stuff, some of the plate sections I will have to get bent, the $800 is excluding fabrication cost.

I will PM you the ball screw supplier, they were very helpful and friendly. I will forward you Lisa’s email she is the one that helped me.

The feet are big, 100mm diameter and they screw in to 2 nuts welded together on top of each other in the base of the leg. The hole in the pole cap is a snug fit with an extra washer welded to the under side just to give it more strength. I think the weight of the machine with the water tray and all will be quite heavy and would put enough force on the feet to keep them stable. The other option, if I do get wobble or vibration is to weld the pole cap to the bolt.

Phife:

I have calculated the critical speed for the longer x-axis screws and went through some tables of other ball screw manufacturers on the net. I used 2 different formulas for the calculations with to different answers.

Formula 1 = 451rpm (80%)
Formula 2 = 341rpm (80%)

If I work with the lower one of 341rpm and my lead is 10mm then my max travel speed will be 3410 mm per min = 134 inches per min.

This is at my max distance of 2800mm apart, my base plate of my gantry is 400mm long with the nut in the middle, I might move the nut to the front to reduce the max distance even more.

If I need to cut at higher speeds I will move more to the centre of the table, depends of the size and material being cut.


I will finish the feet today and fit them to the frame, will post some pics later.

Thanks for reading and thanks for the replies.

[Phife]

Thats still pretty slow, Pretty much as fast as I can get my machine and Im not too happy with it.

You really should shoot for a 300-400IPM max speed, it really helps with rapids. I have no idea how critical the speed is for a plasma, have you looked into this?

I know with wood and metals you want a fast enough feed rate to keep the bit from heating up too much, how does it work with plasmas?

[bleker]

Hello,

The 134 in/min is not that fast, I would like it to be more round the 300 in/min mark.

My other value I got from the calculations is 177 in/min and if I look at the charts on some websites they show even more. I will only really know how fast the machine will go once its build, if the speed is not enough I can always fit some fold away supports under the x-axis ball screws.

From my research I have done I found that the average cutting speed of an entry level cnc plasma cutter is round 100 to 120 in/min. If you have a really good plasma cutter like a Hypertherm you can increase the speed more to the 200 in/min mark.
From what I have read, some sites say their industrial machines can run at 700 to 800 in/min. I don’t know if this is cutting speed or just traverse speed.

I have some working experience on a cnc router, its was a Comac machine from Italy with a 3m by 2m vacuum table and auto changer spindle. The max speed of the machine was 550 in/min, but we would normally only cut at 200 to 300 in/min with a spindle speed of 18000 rpm. This was when cutting 16mm MDF and 16mm melamine boards making a 5mm deep cut with each pass.

[johngalt47]

plasama is pretty fast at least for the plate under 1/2" you might get screw whip with axises that long.
light look at rotating nut design to fix that

[bleker]

Hi all,

John:

Thanks for the input. I have thought off the rotating nut design, the Comac machine I spoke off earlier worked on this design. It’s a really good solution but complicated design. If I do get problems and the simpler fold away support under the ball screw doesn’t work, this will be my next step.

Got the feet all welded up today and finished. I’m happy with the result. I made them stiffer than I first planed, not much movement/pivot for the plate round the bolt, but they work well.

I levelled the frame using my PLS 2 laser and I’m very happy with the result. As the pics will show, only the one centre leg is slightly out, it’s higher by 2mm than the other five with the foot hanging in the air. Pic2 shows a level leg and pic3 shows the centre leg that is higher.

I will weigh the frame down with some sand bags on all the legs to make sure the feet are all 100% on the floor and then re-level it before I weld on the top sections.

Hopefully I can get them made up this week and install them this weekend.

[bleker]

Hi all,

I received some more bits from China today, my stepper motors, controllers, power supply, breakout board and plasma cutter. Everything looks good and I’m happy with my purchases.

Not much luck today in finding an engineering shop that can bend me my 3.2 meter long side sections. Hopefully I will find one tomorrow, in time for the week end.

After receiving my steppers I just want to make the machine move.

[Eastzero1]

Hello,Rudolph
Glad to see our packing of plasma cutter and stepper motors looks in good condition.
If any help we can provide when you using our cutter,please feel free contact us.
Regards
Nikki

[Jason Marsha]

Bleker,

I see your quality control specialist has carefully inspected the power supply. I am assuming it was approved for assembly.

Looking good so far, welcome to the addictive world of building CNC machines.

Jason