Need Help!- A CNC machine able to cut unlimited sized material??

[metalworkz]

Hello,
I have an idea for a CNC build and wanted to get some input to the feasibility of this idea. I have just recently completed my first small CNC router build and am now thinking about the next machine. I had thought a bigger machine with larger travels would be the logical step until I had a wild thought about a mid sized machine with unlimited material size cutting capabilities. Has anyone presented a similar idea before and is this a possible feat? The idea would not really appeal to everyone as a larger machine can do parts within its travels in a single toolpath, whereas what I am proposing would be a method by which the smaller machine would be able to reposition on the material and do any sized part. Naturally it will still be able to do anything within its travels in a single toolpath but it would also have the capability to do any sized part. If this sounds feasible or just plain crazy I would appreciate your feedback so I can decide if it is worth pursuing. If there is some favorable feedback I will need to work out all the details and the method for accurate positioning on the material, but I want to thank you all in advance for any feedback I might receive.
Regards,

[Pplug]

Sounds like you want a compucarve. $1899 at sears? It uses rollers to feed the wood into your machine it can go 14" by as long as you need. Unfortunately, last time I checked, it is all proprietary hardware and software. I think the hardware is of a consumer grade as well but I've only seen pictures.

[rowbare]

This isn't quite unlimited but goes in the same direction as what you are thinking. See the section where they talk about the PowerStick (there is a video also).

http://www.shopbottools.com/shopbot_buddy.htm

Note that with conventional gantry designs you will always be limited by what you can fit through the gantry. There are some designs where you put the router on top of the material (http://solsylva.com/cnc/17x20x4.shtml) but these have their own issues:

Cutting force is limited by the weight of the machine as is maneuverability (and the are inversely proportional). You can take care of the cutting force issue by clamping the machine down but that has its own issues.

Indexing, registration and alignment from one segment to the next.

On all but the first segment, at least one leg is sitting on cut material. Not an insurmountable issue if you are cutting small relief features but a major issue if you are carving 3D.

It is an interesting problem though for all intents you can limit your max envelope to commonly available material sizes and achieve the same effect by tiling the cut. So rather than figure out some fancy machine to cut a 16 x 16 ft design and end up with some unmanageable chunk of work, cut 8 4x8 sheets and assemble afterwards.

bob

[Riceburner98]

Interesting... I've actually been thinking of something like this for years. The use I personally saw in my head was something like doing inlay in floors. You'd park the machine over "x" spot in the floor, and carve away. I'm 99% sure something similar exists - last time I was walking around downtown (Boston) I noticed a huge piece of "artwork" engraved into the granite blocks on the ground. At first I thought they could have been done off-site and placed after being engraved, but then I noticed the concrete "grout" between the blocks was engraved also. Wish I'd seen them doing that...

I'd imagine it was some sort of portable water-jet.. Hell, you could get real fancy and CNC stuff into walls with a machine like you're thinking. Just screw it in place and let it rip then fill the screw holes afterwards. That's how the giant concrete saw worked that cut through our basement wall.

[metalworkz]

Hello Pplug,
Thanks for the information on the compucarve from Sears. I am really more interested in building my own machine, but did not know of this availability. I will use all the posted information to decide which way to go with my next build, so thanks for providing some input for me.

H Bob,
Wow, you offered a lot of information and it helps a lot with thinking my idea through. I have already given the problems or indexing, registration, and alignment/mounting some thought and realize they will need to be overcome but feel those are a minor challenge in the overall idea. I have ideas for this part of the machine that seem to keep everything indexed and would eliminate the problem of registration on the surface of the material. Most indexing if done correctly and without error will produce results much the same as parts cut in a single toolpath, although some of my 3D indexing and repositioning work done on the small SX3 mill leave a minor mismatch. This is a result of inadequate clamping for the most part on the small machine table. For most wood work this is not a problem as long as there is enough material to do some finish blending at those points, although it does present more work to clean things up.
I think your final statement is true about the dividing things up to fit within available sheet sizes, but I thought what if I had a mid sized machine say 24" x 24" that I could actually use on a larger material to accomplish the work. Not being so large as to be unmanageable and yet plenty sturdy to serve as a small CNC machine for wood and metals while mounted to it's normal base? The Shopbot buddy with powerbar does seem to be a good alternative, but it only unlimits the travel in one direction, whereas what I am thinking of would do a whole sheet or even bigger. Perhaps the problems involved out weigh the advantages, and maybe the faster better way would be to have the larger machine, but then when you don't have the needed space to house and use the larger machine perhaps the smaller one with large options would be favorable over just not being able to do the larger work? I have a small CNC router I just finished and it is about 24"X x 18"Y x 4"Z and perhaps it would be better to make an attachment for this small machine to enable doing larger work rather than making a complete machine for this idea? Thanks for all the information, it really does help me think this idea through!
Regards,

[trevorc]

Originally Posted by Riceburner98 Interesting... I've actually been thinking of something like this for years. The use I personally saw in my head was something like doing inlay in floors. You'd park the machine over "x" spot in the floor, and carve away....

I have seen this machine (in photos) used to do things like you describe, it just was not mounted to a board/table.

[metalhead781]

Lets say you made a 48" gantry for the y and z axis with a support structure like shop bot however use simple shop rollers to support a sled with an underside rack and pinion setup. Under the sled the rack along with aluminum track could be attached for bearings. The pinion gears would be on a spring loaded arm and on each side of the sled a clamp mechanism to hold the sled down in place on both sides of the gantry. You could have a few different standard sized sleds for different lengths of material. When the machine is not in use the sleds can be stored and the machine rolled out of the way. This could also increase productivity even on a gantry half that size. Having two sleds. While one sled is cutting the other is being reset. To handle the x zero issue, a flip out tab could be fixed. Load the sled up to the tab, lock it down with the pinion gears engaged and away you go.

A compucarve was mentioned in earlier posts. CarveWright makes the CompuCarve machine for Sears. I own a CarveWright and i do not recommend it for any serious millwork. If you want to invest $2000 into a proprietary machine with over priced bits and will not produce a good cut in material over 1/4" thick then go ahead. If by chance you're looking to do a lot of v carved text within it's constraints then by all means. To take a 1x8x8ft piece of material and make an 8ft long sign or subsequent smaller signs loading the machine just once. It will hold up for a good while.

[metalworkz]

Hello metalhead781,
I appreciate your reply about the sled used basically as I had implied in this thread. I guess I had a wild thought that I could make a small machine with greater cutting area capabilities than a machine with specific table travels and perhaps limited access on 2 sides. I'm feeling less like this is a viable method since seeing some of the posts to the thread, but maybe it does have some merit and perhaps there is some pros to the idea. It is just a question of if the cons outweigh the pros, and also can I find a way to make something like this work well when it seems there have been others that have failed? Maybe I should put this idea on the backburner and stick to my plan to make a machine wide enough for 48" material and include a 5th axis of my own design.
I will wait and see if there are any more posts to the thread to decide. Thanks again for replying with the information!
Regards,

[metalhead781]

It certainly is a viable design. My carvewright machine uses traction belts(sandpaper) and two rubber rollers. It also has a board sensor and tracking wheel to make sure the x is on track. A 1/8" fixed fence on one side and another adjustable fence on the other keep the board tracking straight. The only thing this machine really does well is V carvings in text. Other then that it's pretty much grandpa making the kids gifts. Not to let the cat out of the bag but i'm going to be taking an old ryobi drum sander and using it's drive system and belt to create my own version to get rid of the machine and still be able to do v carved moldings up to 8ft, hopefully. I'll still be restricted to around 12" width but all i'm doing for the moldings is vcarving text with dingbat fonts the length of dimensional lumber. Good luck and i'll try and remember to update you on what i come up with. Don't know when but i will be working on it.

Good Luck
MH

[brihoo2k]

How about making a setup where your y and z were limited but you x axis wasn't. What I'm talking about here it is whats used every day in the computing world in the form of printers. All you would need to do is replace the x axis with a set of rollers. This would allow you to have an infinite length you could cut with the x axis while having a relatively small footprint.

[metalhead781]

Originally Posted by brihoo2k How about making a setup where your y and z were limited but you x axis wasn't. What I'm talking about here it is whats used every day in the computing world in the form of printers. All you would need to do is replace the x axis with a set of rollers. This would allow you to have an infinite length you could cut with the x axis while having a relatively small footprint.

That's exactly what the carvewright does and what i'm planning. Read Above.

Thanks
MH

[vger]

Wes,

I also have somewhat limited space (garage) and would like to be able to work with larger material sizes but still get the car in when not in use. I had thought of using a smaller machine, say 25" X 25" for the CNC'd part and have it mountable and indexable on a much larger set of rails. I thought of using some heavy wall aluminum tubing, 2" diameter or so, or even aluminum extrusions for the long rails and just have index holes spaced 24" apart that pins (tapered pins perhaps) could drop into for positioning. Perhaps use sand bags on the ends of the first pair of rails to hold them in position.

Still toying with the idea but thought I would share it with you.

Steve