CNC Plasma Cutting When You Have No Space

[Papa Charlie]

Thank you very much for sharing all of this with us. I have compiled most everything you put in here into Excel, creating a BOM and a pictorial list of each of your posts. Not sure if or when I will get started on this. Still going back and forth between buy and build. My plan is to use it for commercial purposes. I have several busy concepts I am looking at.

I have a couple of questions:

1) If you were to build a unit that can handle a 4'x8' sheet, would you use 3"x3" 80/20 instead of the 2"x2"?

2) Why did you use the stud roller on the side opposite the stepper motor instead of the linear guide? Seems that you would have a more stable platform as the tool gets to farthest point from the stepper. But I am just guessing here.

3) What kind of torque is required by the stepper motors to drive this? I assume that all NEMA 23 motors are not equal.

4) Most of the purchased tables I see use a height motor. Is this not necessary as the design assumes very little change in material gage?

 

[Tmate]

We used to make these 4' x 8' and larger using the 8020 series 3030 (3") extrusions. We powered the gantry from both sides on some, and used a drive shaft on others. If we used linear rails on both sides it would have increased the cost substantially, with no particular advantage. Both sides of the machine would have to be parallel within a few thousandths. With the cam follower on the far side, they do not have to be precisely parallel without any effect on accuracy. Since both sides of the gantry were powered on the larger machines, extreme gantry rigidity was not needed.

Nema 23 motors will still work. Nema 23 steppers can be obtained up to 450 oz. in. or more, which is plenty with a reduction via timing pulleys or gearboxes. Steppers produce the most torque at low rpms, whereas servos produce it at much higher rpms.

Torch height controls are unnecessary on a small machine such as the one I have described above. As they get bigger, there is a greater chance for the material being cut to be warped, or to become distorted by heat. A torch height control makes automatic adjustments to compensate for that. While not essential, I recommend using a thc on anything bigger than a 4' x 4' machine.

Below is a photo of a 4' x 6' table I made using 2" x 2" and 2" x 4" extrusions, and a drive shaft powering both sides of the gantry from one stepper motor. The drive shaft can be seen in the photo. I think a 4' width would be the limit without going to the larger cross section extrusions.

 

[Papa Charlie]

@Tmate

I am curious why you went with a belt drive and rack/pinion system instead of a precision lead screw with the stepper motors directly attached to screw lead screws.

Forgive me if you have already covered this, but was just wondering. I noticed that many use the lead screws in their build on YouTube.

Also, would you use another stepper motor on the torch height control or does this require something else that is sensing the distance to the plate constantly and making adjustments?

 

[Tmate]

@Tmate

I am curious why you went with a belt drive and rack/pinion system instead of a precision lead screw with the stepper motors directly attached to screw lead screws.

Forgive me if you have already covered this, but was just wondering. I noticed that many use the lead screws in their build on YouTube.

Also, would you use another stepper motor on the torch height control or does this require something else that is sensing the distance to the plate constantly and making adjustments?

It has been done both ways, although rack & pinion drives tend to be used on the larger machines. I originally went with that approach for the following reasons:

Absence of backlash
Absorption of stepper harmonics
Easy to switch pinion gear sizes for different speed ranges
Parts availability
Ease of parts replacement

There have been several types of torch height controls on the market:

Direct contact with material with ball bearing rollers - Seldom seen these days, used to be found mostly in the manufacture of HVAC ductwork fittings. Impractical for a variety of reasons.

Proximity sensors - Rarely used with plasma arc. These are generally used in oxygen-fuel cutting when no electric arc is present.

Arc voltage torch height controls - as the plasma torch tip gets further from the material, the voltage of the arc increases to bridge the gap. The height control monitors the voltage and makes torch height adjustments to keep it within the appropriate range. Either stepper motors or servo motors can be used, although steppers are simpler and less cumbersome.

There is a long standing debate as to whether steppers or servos are better on a plasma table. Servo advocates claim that stepper motors can lose steps. Stepper advocates say that servos are too complex and rely on failure-prone encoders providing feedback to the motors to function properly. My experience has been that steppers do not lose steps in normal use. I believe steppers are best for small to medium size machines, and at some size and weight, servos become preferable. A 4' x 8' table is definitely well within the stepper range. Again, these are just my views.

 

[Papa Charlie]

@Tmate
Thank you for the explanation. I am taking what I have learned here to help me design my machine. Spent several evenings looking at YouTube videos of other machine concepts and demonstrations of some factory built units. Most small and home built units I saw had lead screws, but found several that discussed whip being an issue although many use the Ball Lead Screw for the height adjustment (Z Axis) as the short travel distance doesn't present a whip issue. The ball config lead screw provides adjustment for backlash which I think would be advantagous for the minor height adjustments of the Z axis.

Saw one design where they had one gantry but two Z axis (Plasma torch and Router Spindle) and had divided the table into two segments. Although you could remove the table covering for either and use the entire 8 feet for either operation. While I like the concept, I can see issues, fire doesn't do will with wood or saw dust and routers and wood table coverings don't appreciate water. Sort of like Motorsailers, they don't sail worth a darn and they don't motor any better.

Although, the ability to be able to reconfigure the table from torch to router does sound interesting as having two machines would be a huge space issue and of course there is the cost. The router since it is operating in 3D and the forces, does require a more rigid gantry and I believe I would have to go to a NEMA 34 as they have significantly more torque than the 23.

Still learning and thinking things out. Thanks again for sharing all of this knowledge. Love this forum and the people on it.

 

[Tim9]

I totally missed this thread. That’s an awesome build Tmate. The size is perfect for 90% of what I would ever need for the rest of my years. Very cool. It’s on my long list. In fact, I just hit the Follow Thread button just to make sure I don’t forget this one.

 

[Tmate]

Incidentally, virtually all torch height controls do use screws, either acme or ball screws. The weight of the THC takes up any backlash. Absent a THC, a rack and pinion machine torch holder is generally used. While there are many types of rigs that will hold a manual torch supplied with low cost plasma tables, a 180 degree machine torch is vastly superior. It's easier to ensure that it is perpendicular to the table. It is easier to raise and lower. It comes with "plug and play" cables, etc.

 

[Papa Charlie]

My plan is to buy the Hypertherm 45XP plasma cutter With Machine Torch, which is the one you recommended.

 

[Tim9]

I'm not sure how my neighbors would react to me doing plasma cutting in my driveway so I have to plan on it being in my garage.
There's a good chance it's just not feasible at this location and the dream of CNC plasma will need to wait until I get a proper shop again.

Just a side not for all DIY types. If you ever plan on buying or renting a house.... double and triple check with the realtor and even the city to make sure that they don’t have a Homeowners Association ruling said neighborhood.
Homeowners Associations are the new norm....especially in newer neighborhood developments. Pure BS in my opinion. I’d run, not walk away.
My son can’t even work on his car in the house they own in San Antonio. Check those Homeowners association’s rules. Just way too restrictive these days with a bunch of Jackasses who have way too much time on their hands with nothing better to do than to be the New Hitler Youths. These people are power junkies. They just want to show that they control the show. And they think that just because they are anal idiots who don’t want the neighbors leaves blowing on their perfectly manicured lawns....then everyone else should be just the same.
It used to be....a man’s home was his castle. I get some rules. But heck, if someone decided to run an auto repair in my neighborhood, I can call the city and city codes would shut him down. But not being allowed to work on your own car in your driveway. Pure Bull Pooh Pooh.

 

[OCD Solutions]

We have an HOA but I still like to tread lightly, not for the HOA's sake, but for our neighbors and just basic good relations. I don'tneed covenants to tell me not to be an A-hole.

We just started taking over the HOA from the developer so it will be interesting to see which way our current neighborhoods goes. It's been decent so far and with all the construction of a new development, a few people have been getting away with quite a bit up till now and I think that's about to change.

Our last HOA actually had a ruling that stated what was allowed to be in our garages. I stood up in a meeting after being cited and explained that my garage door left a mark on the floor and that anything past that line was none of their concern and good luck enforcing it. I got a unanimous roar from the crowd on that point, the citation was withdrawn and it was never an issue ever again.