Technical 2' x 2' CNC Plasma Table Build (in installments)

It was suggested that I do a thread showing the build of my small CNC plasma cutting table. I am happy to do so, but it requires my digging through my collection of old photos, and may take a while to show the entire project.

Let me start off by saying this wasn't my first CNC plasma table build. I used to own a company that manufactured these things (Torchmate), and while I'm now retired, I had many years (since around 1996) to play around with different designs. While we made all sizes (up to 10' x 40'), it was always the small shop or home sized machines that appealed to me most.

The CNC plasma process is a fabulous aid to metal fabrication. Many potential owners are put off by the supposed floor space requirements and the dust and debris the process produces. A small outdoor unit eliminates most of these obstacles. If you have a small outside area away from public view, and can provide 50 amp electrical service, you are in business. I have built two personal tables for home use over the years. The first table was mounted on casters, and rolled out of my garage for use. My current table, which I have had for about 4 years, sits outside my ba*****t door. The compressor, plasma cutter (Hypertherm 45xp), and laptop computer are just inside the door. I had a 60 amp sub-panel installed nearby to handle the electrical requirements.

The first photo below shows my first personal CNC table, which I built in 2002. The other photos show my current installation. Future installments will show step by step photos and explanations of how this table was put together. I will deal primarily with the physical table. Most manufacturers of low cost machines today buy their electronics and software from another company and merely fabricate the physical table. There is no reason you can't do the same thing and eliminate the middleman.

First personal table:


Current table:


Shown here with an arc voltage torch height control that proved unnecessary:

 

I'm in, eagerly awaiting the next installment. Sources of required parts would be great if possible. Do you have a plentiful supply of water should the worst happen?

Chris

 

Installment 2:

First, a short explanation of the rationale for the configuration I chose in building my table.

There are three main requirements that must be met in fabricating a CNC plasma table:
1. The gantry must be supported and guided in such a manner that there is no slop (side play) in the movement of gantry along the X axis or the torch carriage along the Y axis.
2. There must be minimal rolling resistance along both axes.
3. The motors must have a suitable mechanical speed reduction, and must be able to achieve that with virtually zero backlash. If stepper motors are used, which is generally the least expensive route, the pulses of the motors must be absorbed to smooth out the motion.

I dealt with the first two requirements by using Origa (Parker/Hoerbiger) linear rails and roller c***ettes on both axes. While the rails can be quite expensive in longer lengths, they are not so bad in the sizes required for a 2' x 2' capacity table.

Reasonably priced planetary gearboxes generally have an unsatisfactory amount of backlash, and I have always thought ballscrews to be too finicky and hard to keep adjusted properly. The third requirement was met by using spur gears and gear racks in combination with timing pulleys and belts. The spur gears are adjusted to fully engage the gear racks with no backlash. The timing pulleys and belts provide a 3.4 to 1 reduction, at the same time absorbing all the pulses from the stepper motors.

OK, now on to the table construction. I built my table using an absolute minimum of parts that could not be purchased from industrial supply houses. It is always cheaper to buy parts that are m*** produced than to make them yourself. The only parts I fabricated myself were the motor mounts and gantry support brackets. Of course these could be made in seconds with the plasma table, but they can still be made with a drill press and a bandsaw, and some elbow grease. Access to a milling machine would make it a bit easier.

The 24" x 36" support table, shown below, is a work stand purchased for about $125 from Rockler (https://www.rockler.com).



To be continued ..............

 

oop subscribed.....

 

Installment 3:

The table will use 2" square aluminum extrusions purchased from the 8020 Company (www.8020.net). They will also supply eight 8 hole right angle brackets as pictured in the photos below. Note that I will provide a more concise list of materials, including the extrusions, brackets and t-nuts/cap screws a bit later on. Also, feel free to ask any questions along the way.

 

Looking forward to more on this. Would like to have a table but don't justify the spend but like to build things. Thanks,

 

Cool.

 

I appreciate the detailed instructions. I may not follow them exactly due to variations in size and material but it is really nice to see what actually works.

 

Installment 4:

The build uses Origa linear rails and c***ettes (sometimes referred to as "Parker" or "Hoerbiger" products) to support and guide both the gantry and the torch carriage. These can sometimes be found on eBay in the correct size, but are available from a UK company (https://export.rsdelivers.com/productlist/search?query=parker origa#). I have purchased these items from that company (RS Components) and shipping is both fast and reasonable.

These linear rails and c***ettes are the most expensive part of the physical machine (about $700) and I need to make the case for using them in spite of the cost.

Most hot rod/street rod/muscle car builders think nothing of investing $50,000 or more in their car. Doesn't it make sense to be willing to spend 1/10th of that amount for the most useful and labor saving piece of equipment in the shop? Furthermore, a CNC plasma table can probably pay for itself in a year's time.

Most, if not all, low cost CNC plasma tables on the market, use cam followers riding on square tubing or steel bars to both support and guide both axes. Origa linear c***ettes use four hardened needle bearing rollers set at right angles to each other, gripping hardened stainless steel rails. Replaceable felt wipers at both ends of the c***ette keep bearing surfaces clean of plasma dust. See below:



Not only does the use of these c***ettes/rails make the whole system more rigid and precise, but also greatly simplifies the build. There also is no need for constant adjustment to minimize slop which can distort cuts (circles don't end exactly where they start). There are less expensive linear rail systems on the market. Don't use them. They use little ball bearings that get clogged and fall out easily making the whole thing useless.

The Origa components come in different sizes. I used 25mm wide rails and matching c***ettes. You could save a few dollars by using 20mm wide rails/c***ettes, but why bother? The measurements provided here ***ume the use of the 25mm items.

The photo below will give you an idea of what the rails and c***ettes look like when mounted on the machine. The next installment will show you how to fabricate the brackets that bolt to the c***ettes.



To be continued ...........

 

Installment 5:

An 8" long piece of 7" x 4" x 3/8" angle iron must be purchased. Mid-West Steel and Aluminum has reasonable prices for this, but has a fairly lengthy delivery time (2-3 weeks).



Flat head 8mm machine screws will secure the above brackets to the Origa c***ettes. The holes must be countersunk to the screw heads will be flush with or slightly inset from the bracket surface. The two holes in each bracket which are shown as using studs can be drilled to 3/8" diameter and through bolted instead.

 

The motor mounts are fabricated from 3/16" steel plate. Both are identical, and are pictured below. With a CNC plasma table, they could be cut in a minute or two. By traditional methods, somewhat longer.

A 3/4" OD x 1/2" ID x 1 3/8" long flanged drill bushing is welded inside the 3/4" hole in each motor mount as shown. When the drill bushing is clamped inside the 3/4" hole with the flange flush against the plate, it will be at a perfect right angle to the plate. Weld only on the flange side of the plate. A couple of good tacks will do it.

After welding, a 1/2" OD x 5/16" ID x 3/8" long flanged oil impregnated bronze bushing will be pressed into both ends of the drill bushing. The same procedure applies to both motor mounts.

 

I'm in...

Appreciate the pics and info!!

 

Installment 6:

You will be using Nema 23 stepper motors in this build. They have a 1/4" diameter shaft. These will be fitted with 1/4" bore XL14 pulleys. Timing belts and pulleys provide the necessary speed reduction and absorb any pulses from the stepper motors. They also have zero backlash.

Each motor/mount ***embly will be fitted with a 15 tooth 20 degree pressure angle spur gear mounted onto the end of a 4" long piece of 5/16" diameter drill rod. The spur gears have two set screws to secure them. The drill rod/spur gear will be driven by an XL48 timing pulley. An XL120 timing belt will be used.

The timing belts and pulleys are available from multiple industrial supply houses such as MSC, McMaster-Carr, Motion Industries, etc. There is a great price difference a**** suppliers, and you may be able to find great deals on eBay. The spur gears and gear rack is available at reasonable cost from HubbardCNC, which has an eBay store. Just Google www.hubbardcnc.com and you will be taken there. The gear rack comes in 24 inch lengths, which can be ****ed end to end. Only one 24" gear rack per axis is needed for this build.

 

Thank you for the detailed postings, & *why* to use this instead-of that.
Subscribed, of course.
Marcus...

 

Seems modern for the HAMB but I enjoy the building. Keep posting till the Traditional police complain. When I was a kid [25yr old] I built a pantograph using an Oxy-Ac cutting torch and it followed a template that was made to emulate the part, no motors [that would have been nice], a manual follow template build up your co-ordination deal. Worked as as well as you could get the torch to cut that particular day! A few years ago I made an arm to hold my Plasma torch to the quill on my cnc machine, set up to auto turn the torch on. Worked ok but didn't have anything to make [nor time/energy] How much $$ to build?

 

Here's my first pantograph build from 1979. It used a Ford Granada wiper motor and a toy train transformer. Magnetic tracer was an iron boron magnet mounted on a rotary burr. Used a top lever O/A torch. Second photo is another I built a few years later. Third photo is a pantograph for plasma I built about 5 years ago.

 

Installment 6, continued:

As mentioned previously, the 24" gear rack sections can be purchased from HubbardCNC. You will need one length per axis. The holes that are pre-drilled in the racks are not in the correct position, so it will be necessary to drill three 5/16" diameter holes in each rack as shown below. The center hole should be near the center of the rack avoiding interference with any of the pre-drilled holes.

 

The gantry will be maintained at a perfect right angle to the rails by the X axis linear rail & c***ette. Therefore, its far end need only be supported by a single cam follower riding on a 1/4" x 2" piece of cold roll steel bar 36" long. The end of the gantry's aluminum extrusion is tapped for four 1/4 x 20 ****on head cap screws. The bracket shown below bolts to the end of the extrusion and holds the 1" diameter cam follower. The cam follower has a 7/16 x 20 threaded stud 1" long. Right hand photo below shows cam follower riding on 1/4" x 2" cold roll steel bar. Bar is bolted down to aluminum extrusion with 1/2" long 1/4 x 20 ****on head cap screws and t-nuts from 8020.net.

 

Here are more images to help you visualize the motor mounts and the timing belt/pulley set-up.

 

The linear rails are fastened to the 2" x 2" aluminum extrusions with standard (non-flanged) 1/4 x 20 x 1" long ****on head cap screws and t-nuts. The mounting holes in the linear rails are countersunk, and the recess will perfectly accommodate the heads of the cap screws as shown in the first photo below.

The second photo below shows a cross section of one of the extrusions with a screw and t-nut inserted in one of the slots.

 

Some final thoughts:

I avoided the need for limit switches on both axes by making the gear racks short enough for the spur gear to run off the end and disengage before a c***ette reaches the end of its rail.

I strongly recommend figuring out a way to do your cutting outdoors. The 40" x 38" x 18" cover in the following link works great for me, but my set-up is under a deck which helps to an extent. A recommend using a vertical machine torch with a rack and pinion torch holder. Hand held torches are cheaper, but are less convenient in this kind of application. They usually require complex "Rube Goldberg" bracketry of some sort, and are difficult to keep oriented at a perfect right angle to the work.

Rockler can supply adjustable feet for their work stand, and I recommend these over locking casters for stability. I placed four concrete pavers under the feet on mine, which keeps it level at all times, and prevents the feet from sinking into the gravel underneath.

It's best to keep the operation out of the sight of neighbors if possible. While the cutting process does require sensible precautions, it isn't the hazard that it might appear to be to the uninitiated. Obviously, you should follow the recommendations of your plasma cutter manufacturer in using your machine.

In my view, you should not scrimp on the plasma cutter or compressor. You are going to need a 240Volt air compressor that can maintain 8 to 10 cfm at 90 psi for a Hypertherm 45XP, which is what I have. Hypertherm says 6 cfm, but that's stretching it a bit. The compressor I use is shown below. It's a Speedaire with the following specs. It runs about $875.00.
Portable Air Compressor: Oil Lubricated, 20 gal, Horizontal, 3 hp, 10.2 cfm @ 90 psi


The project described above is going to add up to from $1,000 to $1,200 depending on the pricing you get at various supply houses. Whatever kind of electronics and software you decide to use, it must have NEMA 23 motors to work with this design. NEMA (National Electrical Manufacturers ***ociation) has set standards for the physical configuration of motors to ensure universality of fit.

While I used high end electronics and software for my system (FlashcutCNC) , if you shop around, you can probably come up with a workable combination for a few hundred dollars. Remember, you are doing the same thing as most low cost CNC plasma table manufacturers do - making the table yourself, and outsourcing the electronics and software.

Your CNC plasma table will be able to do things not possible with any other process (CNC laser and waterjet excepted). Your friends will bug you to make various items for them. However, they provide great word of mouth advertising, if you are inclined to use your machine for profit.

Some shapes done with my little machine:

 

Plasmaman, how much did it cost to build ? Mike

 

Some of these prices vary considerably depending on vendor. You can save by using aluminum timing pulleys, which would probably be ok. Don't buy this stuff from MSC or McMaster-Carr, as you can probably find it a lot cheaper on eBay or elsewhere. Try Automation Directhttps://www.automationdirect.com/ad...iming Pulley"&Number_of_Teeth_ms=( "14" "48"))
Shop around!

Here's a rough breakdown not counting shipping cost:

Linear rails & c***ettes $650
Aluminum extrusions & brackets $225
Rockler work stand $140
Timing pulleys, belts, gear rack, & spur gears $175
misc. hardware $50

Of course, the compressor, plasma cutter, and computer are the big ticket items, and are needed regardless of whether you build yourself or buy a ready-made $1,500 job. Bear in mind that you If you use electronics and software equivalent to such systems, the total cash outlay will probably be in the same ball park. Take a good, close-up look at table construction, and you be the judge.

 

I have had good luck with automation direct. They seem to have what I am looking for and their prices are realistic.