Question for jimcolt

[jdh239]

Just wondering what CNC machines you have used (on the cheaper end, such as plasmacam) that you like? I noticed on a forum you chatting with the BTA guys (they have cheaper kits with stepper motors) and stuff. Made me wonder if you have tried multiple systems. I thought I saw a pic on one of your postings somewhere and it looked like you own a plasmacam?

[jimcolt]

Actually I have spend the last 30 years working with industrial cnc machines all over the world, sometimes working with the manufacturers to make sure that the Hypertherm plasma cuts better, cuts faster, and with the best possible quality and lowest operating cost, and at other times working with older machines in large manufacturing plants (Deere, Caterpiller and hundreds of others) to help them get the best cuts at the highest speeds and at the lowest cost per foot of cut. To achieve these objectives requires making all of the systems work together in harmony....the cutting machines motion capability, the torch height control, the CAD drawing and the CAM post processing all have to work together to achieve the best performance with plasma. The definition of an industrial machine in my mind...is a machine that was designed to operate for many years (typically 10 or more), 3 shifts a day at very high production rates, under harsh conditions with only minimal maintenance and operator input.

Machines that are designed to be low cost for small shops, or for hobbyist/homeowner type use are relatively new technology.....maybe in the last 10 years or so their numbers in the field have risen dramatically. The reasons for the popularity are 1. Low cost (as compared to their industrial cousins), 2. Easy to use drawing and operating software packages, 3. Lower cost, higher performing plasma systems that use non-high frequency start. All of these features were brought on by major improvements in technology in motion control, software and plasma system developments....that made great technolgy available at lower cost.

With my experiences with high end industrial plasma systems.....I know what is necessary to squeeze the best performance in a plasma.....and it is essentially many of the same features that are necessary on high end machines costing in excess of $100,000, but minus the heavy duty design and construction and large sizes that make the industrial machines do their jobs under harsh conditions for many years.

A low cost entry level machine (in my mind) needs the following:
1. Easy to learn and use CAD drawing capability.
2. Easy to learn and use CAM (Computer assisted manufacturing) software the converst your CAD drawing into a cut path, automatically generating the right code that offsetts for plasma kerf width, inserts leadins and leadouts for the cut, adjusts speed and plasma on off timing, as well as many more features.
3. Smooth, fluidic motion, good acceleration/deacceleration (critical for smooth cuts and minimal dross), and fairly good positioning accuracy (plus or minus .005" to .010" is adequate for an air plasma system)
4. A full function torch height control. The height control needs the ability to find the surface of the plate before every cut cycle is started, retract to the plasma manufacturers recomended pierce height. As soon as the pierce is complete the height control then needs to index rapidly to the plasma manufacturers recommended cut height while still in the lead in area of the cut program, and should freeze at this height until the x and y motion gets to at least 80% of the plasma manufacturers recomended cut speed (this is why acceleration is important), then the THC needs to activate arc voltage control (avc) to monitot and maintain the proper cut height throughout the cut cycle.
5. The entry level machine needs to fit your needs for the size of plates / parts you want to cut, or needs to fit in your available shop space!
6. Often overlooked....there needs to be a method of controlling the billowing plumes of smoke that plasma cutting produces.

Almost all of the entry level machines have the ability to cover most of the desired plasma cutting parameters that I have listed above, but some manuafcturers offer very attractive pricing....and in order to control the parameters you need to add a bunch of options...that will bring the price up. Some of the entry level manufacturers provide all of the components of the cnc machine in a few boxes, kind of in kit form, these machines are good because you learn about all of the components of the machine and how they interface together during the assembly process. There are some manufacturers and models that have the majority of the above listed parameters covered as their standard offering as well. There are a lot of entry level machines and sizes avaialble today.

I do own a PlasmaCam machine....the important things to me were to have a complete package (CAD/CAM software, Good motion, good full featured torch height control, easy to assemble and interface to the plasma, easy to use, good factory backup and support), and most important, I only had shop space for a 4 x 4 machine! The PlasmaCam was a good choice, however today you can get all of these features on a variety of different machines.

I have seen many different entry level machines, however I have not operated all of them. It is my goal over the next couple of years to get much more familiar with machines other than the PlasmaCam entry level machines.....so that I can help more people on these sites fine tune their plasma cutting applications much better. Putting the best plasma cutter on a machine does not automatically fix all of your cut problems, as I stated above, all of the features and systems on the machine have to work together seamlessly in order to give the best performance.

Sorry for the long winded reply, since I work for Hypertherm, and Hypertherm supplies plasma systems for virtually every brand of cutting machine, industrial and entry level, I have to remain neutral in regards to alliances with these different companies! I have the PlasmaCam because it fit my needs quite well when I bought it, and I am verry happy with its ease of use and cut quality, as well as with its reliability. I'm sure there are a half dozen or so other brand machines that would suit me just as well!

Jim Colt

[jdh239]

Thank you for your reply. I find it quite interesting.

Regarding servo and stepper motors, I understand the basic differences; however, I was wondering if you think servo motors necessary on the lower end machines? The only real drawback I can think of is that if the rails are bumped, then the controller wont know where the cutter is to the table and will continue to try and cut the piece (which may now be off). Is this correct?

Given the choices, I assume you will still go for something with servos rather than steppers?

[jimcolt]

I do like servos for the simple reason that they use encoder feedback.....and they will get to the position they are programmed to go to. They often are more expensive as compared to steppers.

Steppers have good power, are low cost, but if the torch hits something (relatively common) during the cutting process...positioning can be lost, meaning all of the rest of the parts on a multi part nest could be out of position. You can overcome this with larger, more powerful steppers, but then the cost becomes similar to a servo drive system.

I am sure that those that like steppers will respond in defense of the technology. If you look at high end industrial precision cutting machines.....there are no stepper drives. In fact, many of the companies that produce low cost machines with steppers.....defend the steppers vigorously, but offer (for a price) upgrades to servo drives.

Bottom line, my opinion of course...if the cost of procuring a cnc is your biggest limitation....then go with stepper drives. If performance, accuracy and long term reliability are more important than price, then I would choose servos.

In reality...it is a bit more complicated. There are different types of steppers and different types of servos. The best machines have servo drives with zero backlash gearboxes, helical rack gears and inertia matched drives which produce the best performance and cut quality. Don't expect to find those features on entry level priced machines!

Jim

[daddy]

Jim, I have a buddy who is looking at the plasma cam table, and a 1250.

Are there any reasons why he might choose another model? The 1250 was probably recommended for thicker cutting.

We have one at work, and love it, just not sure if it is the best choice for the table.

[jimcolt]

The 1250 has been used on hundreds of PlasmaCam installations.....it interfaces exactly the same as the Powermax45, Powermax1000 and Powermax1650. I'd be happy to talk with your friend concerning his cut requirements in terms of duty cycle, thickness (max and average cutting thickness) to help determine which Hypertherm plasma would best fit the needs.

Jim jim.colt@hypertherm.com

[daddy]

I'll give him your e-mail. Thanks.