[307startup]

Does anyone have any thoughts about designing, building and setting up a router table like a panel saw? In other words, almost vertical, with a slight angle, so that it doesn't take up as much space. Loading and unloading sheets of material would be easier and I was planning on using a ledge at the bottom edge as a register for material. Either a stop or using angle stock as a vise to hold the bottom edge...with another stop or angle-stock vice at the non-mobile end of the table...constant location of all sheets, +/- .010".

[Madclicker]

I've been pondering this for a while. The one place to start in the design is a vacuum table. While a panel saw cuts straight through and the quality of the cut is not affected much by whether the sheet goods lie truly flat or not, the opposite is true for a cnc router table. The problem is compounded by the lack of helpful gravity in a vertical design.

[307startup]

...not to mention if you need to get at any of the manifold or fittings, or even installing new vacuum "modules" it would be pretty easy to get to. I myself like the idea of a mostly vertical design because I can have a double head gantry...one side for a router, the other side for a plasma cutter...that's why I didn't suggest a vacuum table to begin with. I'm not a big fan of "uni-tasker" machine tools.

[Madclicker]

I don't consider a vacuum table an option for a machine like this. Heck, now that I have started using them, I don't consider vacuum tables optional for even smaller machines.

Funny, I just happened across an epay ad for a vertical router:

dynacnc

[Jason Marsha]

Here is a homebuilt one

http://www.otocoup.com/index_e.htm

Jason

[PowerCNC4u]

DynaCNC has been building one for a long time now. www.dynacnc.com. I want one someday, but the plasma table I own is working for me now. Hopefully soon.

[307startup]

So this obviously is not a crazy idea. Plus with the slant it allows swarf/slag to drop away from the cut area and the path of the cutting tool. My only real concern was with gravity helping the part to move out of position before the cut was finished, but by cutting bottom to top, this takes the worry out of the part falling into the tool...if it does fall, it would fall away from the router/plasma torch.

[wizard]

I would suspect that by cutting bottom to top you would loose any hope of accuracy unless there was substantial use of vacuum chucking and other holding mechanisms.

In general though I don't think the idea is bad for a router. There are issues to overcome not the least of which is getting enough stiffness in the arm to maintain squareness under stress. This is not impossible of course. But dealing with the work holding issue and this issue up front should lead to a usable design.

As to getting the machine to do double duty I don't think it is impossible but then I don't think it will be cost effective either. Beyond the work holding issue, where on a Plasma machine gravity is even more important, you have the issue of conflict of interests. That is what works well for a plasma table likely will be a negative for sheet goods that get routed. I could see two different sub tables that get rolled into place depending on the machines usage, but by the time you go to all that trouble you could have built two complete machines.

So in summation I'd certainly try for a router design. There is little doubt in my mind that it can be done. A plasma machine is another issue though. With Plasma you can't really clamp the sheet so I'm not sure how you would get the required hold down.

I don't want to discourage you as I agree with the advantages if it could be made to work. The manner of holding even modest tolerances on parts as they are being cut escapes me.

Dave

So this obviously is not a crazy idea. Plus with the slant it allows swarf/slag to drop away from the cut area and the path of the cutting tool. My only real concern was with gravity helping the part to move out of position before the cut was finished, but by cutting bottom to top, this takes the worry out of the part falling into the tool...if it does fall, it would fall away from the router/plasma torch.

[307startup]

I fail to see how accuracy would be lost by cutting bottom to top...the cutting action would be inducing any movement, not gravity, because until it is cut free, gravity is acting on it in exactly the same manner as it was prior to being cut free. My concern was with cutting top to bottom or side to side and having the cutting forces move the piece out of alignment. By cutting all inside movements first, and then cutting the exterior from bottom to top, you leave a margin of safety of the finished workpiece if gravity were to pull the piece out of position, due to shifting or cutter-induced momentum. Or rather I should say, initial cutter position for outside movements would start top center and move down, around bottom, back to top center so if/when the workpiece shifts it will fall below (in relation to floor) the spindle and cutter.

As for gantry arm stiffness...take a pole and hold it straight out...now take that same pole and lean it...which takes more effort? A vertical gantry beam should be facing far less stress and abuse in a vertical arrangement than moving parallel to the horizon.

I fail to see, once again how gravity comes into play even more in plasma cutting...is there some field of physics that I am unaware of governing plasma cutting? Because this won't be a true vertical design, but rather at 10*-30* angle, gravity will still be pulling slag straight down...where there will still be floor space for it to occupy once it is clear of the material being cut. The plasma torch will still be running parallel to the plane of the material...so the cut will still be straight and not angled...and the slag would then fall towards the floor.

How different in function (not tooling) is a router and a plasma table? They aren't any different. Cutting shapes out of flat sheet material...they wouldn't be working to different goals...the goals are one and the same.

Once again...to explain how this would work...the bottom edge and the farthest edge from loading would have angle stock that would act as a register. Top edge and loading end would have angle stock on piano hinge (or something similar) that would act as a vise to hold the material square and flat. I'm not seeing how exactly the hold down would be a problem...

The tolerances for cutting parts is built into the machine tool...not in the slant of the table.

Hope this clears up my initial entry.

[ger21]

http://www.camtech.ca/products/route...ceOverview.cfm

[Madclicker]

IMO, a vertical router would be useless without a killer vacuum table. Even on a horizontal table sheet goods need a good vacuum table in addition to gravity to pull them flat and hold them in position. With a vertical table you have not only the cutting forces to contend with, but also have gravity working against you. At least with a horizontal table gravity helps hold the workpiece down.

I don't think the savings of a few sq ft of floor space is worth it.

[ger21]

One downside is that the Y axis will need much more power, because it has to lift the entire Z axis

[Madclicker]

An upside I can think of is that it could be enclosed easily to contain noise and dust.

[307startup]

Yes, enclosing it would be a lot easier...some 80/20 and some lexan or acrylic and you have a nice see through dust-catcher...or a way to prevent a curious on-looker from separating their fingers from their personage...

My philosophy would be to put a larger motor on the Y axis and mount it up top...constant tension versus compression...that and pulling something up hill with a good leverage point is easier than pushing a wet noodle with two feet on the ground...just look at how a winch works...whenever my Jeep gets stuck, it's a lot easier to tie the winch off and pull than it is to push or jerk free from behind (usually downhill)...when the motor is heading down (to the floor) it's still in tension...when you pull it up...still in tension. Mounting it below (near the ground) you are always going to have the mass of the spindle in compression and when you try to bring it back down, it'll be pushing against the ballscrew/acme screw/belt assembly...backlash problems galore. I don't think it'll take that much bigger of a Y axis motor when you consider that moving a mass is moving a mass...friction always seems lower on an incline than on a flat...I'm not saying that I'm right, but have you ever tried to push something heavy along a flat space...and getting it moving UP an incline can be a bear, but once it's moving, it likes to stay moving...you can always think of it this way...the motor will be working half as hard for half the time...only having to grunt when it's moving the head UP...and pretty much coasting on the way down.

[Madclicker]

The physics is the same whether you mount the motor above or below.

[wizard]

I fail to see how accuracy would be lost by cutting bottom to top...the cutting action would be inducing any movement, not gravity, because until it is cut free, gravity is acting on it in exactly the same manner as it was prior to being cut free.

Not exactly which in this case I think makes a big difference. The problem is that work piece will be nearly vertical, thus for the most part gravity is pulling the part down vertically with little effort keeping the part on the near vertical table. This is why I suggest that you would need excellent vacuum chucking.

There are alternatives that others have suggested in other forums. One idea is to program in small tabs to hold the work piece in place. Not totally impossible to do,you just won't get a 100% finished product off the machine.

Note that we may have differences in expectations here. I'd suggest that if you want 100% finished parts coming off the unit that are small or intricate you will have problems.

My concern was with cutting top to bottom or side to side and having the cutting forces move the piece out of alignment. By cutting all inside movements first, and then cutting the exterior from bottom to top, you leave a margin of safety of the finished workpiece if gravity were to pull the piece out of position, due to shifting or cutter-induced momentum. Or rather I should say, initial cutter position for outside movements would start top center and move down, around bottom, back to top center so if/when the workpiece shifts it will fall below (in relation to floor) the spindle and cutter.

I could see where that might work in relation to vacuum chucking if your parts are of rather simple design. I do see this as a significant additional programming effort. In any event I still believe that without some sort of vacuum chucking it will be troublesome. Part of the problem here is that it really depends on what your expectations are.

As for gantry arm stiffness...take a pole and hold it straight out...now take that same pole and lean it...which takes more effort? A vertical gantry beam should be facing far less stress and abuse in a vertical arrangement than moving parallel to the horizon.

That wasn't the stress I was concerned about but rather the reaction forces due to the tool. This is something to consider if the basic arrangement of the axis is the same as a panel saw. Even here it is a matter of expectations. If the machine is used to rough out sheet goods for home building it might not matter. If you are trying to hold dimensions to a few thousands it will likely be an issue if some design effort is not put into the arm.

I fail to see, once again how gravity comes into play even more in plasma cutting...is there some field of physics that I am unaware of governing plasma cutting?

Plasma cutting will be a bigger issue because the process introduces heat into the work and combined with the almost 90 degree change in the gravity vector will result in distortion of your part to a greater extent than if they where laying flat on a level surface.

The operation of the plasma torch will not be impacted at all. What will happen is that you will have both gravity and heat distortion working against you. With the part laying flat you only have to worry about heat distortion.

Again if you are just slicing up plate into simple smaller chunks it might not matter. Attempting radical work will be much more trying in my opinion.

Because this won't be a true vertical design, but rather at 10*-30* angle, gravity will still be pulling slag straight down...where there will still be floor space for it to occupy once it is clear of the material being cut. The plasma torch will still be running parallel to the plane of the material...so the cut will still be straight and not angled...and the slag would then fall towards the floor.

Slag really isn't an issue in my opinion. It all boils down to being able to cut the product you want with the tolerances you need. There are a lot of variables here for sure. One thing you could try to do is to cut some parts from a sheet, mounted approximately as you would in a real machine, manually. Take notes on how the sheet distorts and supports its self as you take chunks out of it.

How different in function (not tooling) is a router and a plasma table? They aren't any different. Cutting shapes out of flat sheet material...they wouldn't be working to different goals...the goals are one and the same.

The only thing they have in common is that they work with sheet goods. To sum up some of the differences:

1. Router often have vacuum tables to hold the sheet goods down. A Plasma system on the other hand has the work supported by an iron grid to allow the plasma to blow through.
2. The router generates significant reaction forces that the mechanics have to deal with. Plasma systems have almost zip in the way of reaction forces.
3. Routers produce flammable dust. Plasma systems produce extremely hot metal streams.
4. The control of tool height is different from one tool to the next. A router has to control depth of cut based on commands from the NC control. Plasma needs to control tool hieght based on the behavior of the arc.
5. Because of the plunging alluded to above router gantry can't ignore the vertical component of the reaction forces. Plasma has far less of a problem here.

In any event people normally think of these machines as having two entirely different working tables. This is why I think you will need to have swappable tables to make this work.

Once again...to explain how this would work...the bottom edge and the farthest edge from loading would have angle stock that would act as a register. Top edge and loading end would have angle stock on piano hinge (or something similar) that would act as a vise to hold the material square and flat. I'm not seeing how exactly the hold down would be a problem...

Again it is a question of expectations. But imagine that you are cutting a bunch of small parts out of the machine. The registers are fine but what about the rest of the sheet.

The tolerances for cutting parts is built into the machine tool...not in the slant of the table.

You can have a machine that holds tolerances perfectly as far as a plasma torch is concerned but that mean little if the sheet goods is moving below the torch independent of the CNC system.

Hope this clears up my initial entry.

I think I understand what you want to accomplish. For a router, with some limitations on what you can do, I do not see a huge problem. The plasma torch is another thing though.

Like I alluded to above the problem with the plasma approach is highly variable. You might get acceptable results out of thick stock as opposed to say 16 gage steel. This being highly dependent on the parts being cut.

In any event don't let me hold you up. Give it a go and report back the results.

Dave