[zaebis]

Ok I am new to the table tops CNCs but am very curious. So my question of the day is if the part in question is bigger than the range of motion what are the techniques of CNCing it? Say my CNC X moves 14' only. I have a part that is 15' wide. I can clip the part to the table for machinning but my G code calls for longer CNC ranges than the machine is capable of. What do I do?

[SCzEngrgGroup]

Ok I am new to the table tops CNCs but am very curious. So my question of the day is if the part in question is bigger than the range of motion what are the techniques of CNCing it? Say my CNC X moves 14' only. I have a part that is 15' wide. I can clip the part to the table for machinning but my G code calls for longer CNC ranges than the machine is capable of. What do I do?

"Say my CNC X moves 14' only. I have a part that is 15' wide." - Wow! That's some big machine! Must be one helluva big table it's sitting on! :-)

You can do it, but it's a PITA. You have to generate the G-code in two sections, keeping each within the limits of the machine. Then you have to re-position the piece between the two programs, and figure out how to get it precisely aligned in both cases, so the "splice" lines up well. It's not easy, and it's not fun. Ideally, you want to make sure you provide reference holes or surfaces to use for the alignment, and how well the "splice" lines up will be almost entirely a function of how accurately you align the part to the machine (well, assuming your machine is good and square, which is often not the case on these little machines).

Regards,
Ray L.

[idtkid]

good answer /\ done it a few times, PITA is right.

I wanna know what the Z travel is!? Must of had to cut a hole in the ceiling to accomodate its travel! haha

[nlancaster]

sounds like the easy answer is get a bigger machine. I dream of someday owning a Industrial Hobbies machine....

[BobWarfield]

However large the machine may be, there will be a need to machine a part that is larger: one of many Murphy's Laws for machine work.

Look at it this way:

We often have to precisely position parts before we can start machine. This case is no different, the part just happens to be larger than the machine accomodates. But, you are still accurately positioning a part. In this case, you are doing so twice to finish it, or even more times. So you will need a strategy to get it accurately positioned.

You need precision areas on the part, and on some sort of fixture or setup, that align with each other. A key task of the very first setup, which probably won't be precisely aligned as it is raw stock, will be to create those precision areas as needed for the second setup, and so on.

The other issue to worry about is the rigidity of the setup. If the part is much bigger than the setup, it needs extra work to make the setup rigid. The part can lever against things, gravity droops things, etc., etc.

Think about a part that fits your table, but that is a lot bigger than your vise. You take steps to make the vise "bigger". You use jaws to play games:



Or you bring in some 2-4-6 blocks to lend more rigidity:



Or you support the ends of a long workpiece with machinist's jacks. Or you use two vises, sometimes with jaws that span the two vises. Fixture plates may be needed. And so on.

Do everything you can to promote rigidity. Support the part if it hands off the table very far at all so that it's weight isn't working against you setup to throw you off or tweak your machine.

CNC opens up a lot of possibilities versus manual machining too. You know where the various features on your part are. So you machine one setup, then you slide the part down. Leave a feature within reach of the spindle that you can edgefind and use that to reference your CNC DRO's after you've slid the part.

Make sure when you slide, you don't twist the part. It has to stay "in tram" relative to the machine while it is being slid. Check that with an indicator, don't assume it's true. Make your fixture facilitate that location as well.

You get the idea. It doesn't have to be too much of a PITA if you've planned ahead. Think of it has 2 different parts rather than 1 really difficult part.

Cheers,

BW

[X2cnc]

The usual solution is to use a fixture that swings or pivots, or holds the part in more than one position. You perform all the operations within the machine's work envelope, then refixture the part to get to the other bits.

Sometimes a rotary table can be used to move the part in relation to the spindle to increase the work envelope.


It took me a little bit to get out of the "CNC mindset." In a CNC machine, you clamp the part and leave it there, changing tools as needed. For production on manual machines, you had the "jig and fixture" mindset, where the parts were moved or re-oriented for multiple operations, often on multiple machines. It's not as convenient that way, but it will let you handle larger workpieces than otherwise.

[Kipper]

Rotate the part in cad to be diagonal on the table and let the machine have more on X......after generating the G-code on the skew.

[cghost]

However large the machine may be, there will be a need to machine a part that is larger: one of many Murphy's Laws for machine work.

Look at it this way:

We often have to precisely position parts before we can start machine. This case is no different, the part just happens to be larger than the machine accomodates. But, you are still accurately positioning a part. In this case, you are doing so twice to finish it, or even more times. So you will need a strategy to get it accurately positioned.

You need precision areas on the part, and on some sort of fixture or setup, that align with each other. A key task of the very first setup, which probably won't be precisely aligned as it is raw stock, will be to create those precision areas as needed for the second setup, and so on.

The other issue to worry about is the rigidity of the setup. If the part is much bigger than the setup, it needs extra work to make the setup rigid. The part can lever against things, gravity droops things, etc., etc.

Think about a part that fits your table, but that is a lot bigger than your vise. You take steps to make the vise "bigger". You use jaws to play games:



Or you bring in some 2-4-6 blocks to lend more rigidity:



Or you support the ends of a long workpiece with machinist's jacks. Or you use two vises, sometimes with jaws that span the two vises. Fixture plates may be needed. And so on.

Do everything you can to promote rigidity. Support the part if it hands off the table very far at all so that it's weight isn't working against you setup to throw you off or tweak your machine.

CNC opens up a lot of possibilities versus manual machining too. You know where the various features on your part are. So you machine one setup, then you slide the part down. Leave a feature within reach of the spindle that you can edgefind and use that to reference your CNC DRO's after you've slid the part.

Make sure when you slide, you don't twist the part. It has to stay "in tram" relative to the machine while it is being slid. Check that with an indicator, don't assume it's true. Make your fixture facilitate that location as well.

You get the idea. It doesn't have to be too much of a PITA if you've planned ahead. Think of it has 2 different parts rather than 1 really difficult part.

Cheers,

BW

iv even drilled holes in a old vice to acutely bolt the jaws on to vice its self .

but machining digagonaly would involve some very intresting clamping