How Big should I go?

[fizx]

I am new to this and have been doing some reading. I am looking to build a cnc table that is 2x4 but configured so I could slide a 4x8 sheet in and do 2 feet and then slide down and do another 2 feet so on and so forth. Is this possible or should I just get this out of my head? Also I have 1000 to play around with can I build one that would do alum? I have the computer for it. Cutting speed does not matter. Recommendations on stepper size? Are gecko drivers the only way to go? Just trying to get a place to start.

[RTP_Burnsville]

Hi,

A 2x4 router is a nice size in my view and is about the size mine will be when finished. Not sure how you envision getting a 4x8 sheet into a 2x4 router unless one side is open. If that is the thought I would be concerned about getting a strong enough frame especially if you want to do aluminum as well.

You don't mention what sort of rails you plan to use. Gecko drives are nice but there are other options as well. A quick search through the forum will get you many others.

What sort of spindle are you thinking?

I would concentrate on a solid built 2x4 size with maybe a laminate router as a spindle. Step motors (example Automation Direct) are reasonable in price as are the Gecko drives. Not sure on the rails with your budget. There are several nice designs on this forum using Baltic Birch and MDF. Good luck and keep us posted.

[fizx]

Here is what is in my head. Sorry for the lame artwork. I was just hoping to do 2 ft then stop it and do 2 more ft then stop it so on. That way I could do a whole sheet. I have used a cnc plasma arc cutter that could do that with their software but what it would take to do it im not sure. I just would like the option. My table will prob look much like many I see. I am hoping to use ball screws ive been pricing them on ebay. I have a dewalt cutting tool like a roto zip and I am going to try to use that. I really need help on the size of the stepper alittle over kill is ok. I am going to make my table out of mda and alum since I can weld it and its light.

[fizx]

here

[RTP_Burnsville]

Ahhh, I see what you have in mind now. Duh, on my part! I had a mental block as all I could picture is my machine which is a reverse of what you plan and it can't hold a 4x8 sheet.

If ball-screws get to expensive there have been some recent conversations about the use of timing belts. No idea how they work but what I read sounded interesting and workable.

Your roto-zip might be a bit small, depends on what exactly you intend to route.

[Madclicker]

I built my table along the same lines as what you are talking about. I have 50" travel along the axis you labeled 4' and 34" along your 2' axis. I wish I had made it cut 50x50 now, but I didn't think I had the room. Now I realize to get 50" on the other axis I would have just had to make it 16" longer. Anyway, I can feed full sheets from the front or back. I never do, because I don't know of any way to clamp larger sheets without a vacuum table and I don't have one. When I get one and a bigger shop I expect it will be handy.

Making a gantry this big is not trivial. It has to be extremely ridgid or it just won't cut right. I built mine from 4 torsion boxes and my back-up plan if it wasn't ridgid enough was to drive it with 2 screws. It turned out really well and I never had to do that.

I have a 1390 oz/in 42 frame driving the gantry, a 640 oz/in 34 frame on the z trolley and a 450 oz/in 34 on the z. I get 120"+ rapids on the x and Y and 100" on the z.

I had no clue what I was doing when I bought the motors and got lucky. Many large motors would be wasted on a router. The ones I bought just happened to have torque curves that extend far enough to make them useful.

Good luck. It's not easy, but man when you get it running it sure feels GOOD.

[gun_maker]

You might want to check this out. http://www.solsylva.com/cnc/misc.html Its about halfway down the page. I bought his plans and was impressed on how much detail he put into it. Pictures, drawings, text I almost think a monkey could build it. You mentioned aluminum, You could use it instead of lumber. I know so far I have all the materials need to build the large table and have spent less than 200. I still need to get motors, software and the router but I should be well inside your budget.

[andy_ck87028]

Mine is designed in the same manner except that I have built it so that all the drive gear for both the X and Y axes are on the gantry. I have used timing belts on both axes. Consequently, if I want to change my 800 * 1200 into a 2400 * 1200 all I have to do is butt a 1600 * 1200 frame onto the existing frame and replace the timing belts for the X axis with longer ones.

I accept that butting the existing X rails with the additonal 1600 X rail extensions will be difficult but if necessary I can also change the rails.

I agree about the flexing issue on such a long gantry (1500 in total with useful cutting of 1200) but if that is an issue, I can reinforce through the use of torsion boxes

Andy

[fizx]

hey thanks for your input. I am alittle confused though isnt a 1309 oz way bigger then you would need? I was looking at something like 200 or 300 oz

[Madclicker]

hey thanks for your input. I am alittle confused though isnt a 1309 oz way bigger then you would need? I was looking at something like 200 or 300 oz

There are at least 2 things a router can't be. That's too ridgid or too fast.

Think about it. The gantry you are thinking about building for a 4x2 machine would be the same one you would build if you made a 4x8 machine instead. Would you try to drive that machine with copier motors? In your first post you said speed didn't matter....be careful what you wish for. I don't think anyone ever built a router and then said it was too fast

I got 3 of those 1390 oz motors for $75 delivered. There was no way I wasn't going to give them a shot for that little. Like I said I got lucky on the torque curve. They put out 700oz at 2000 rpm.

[randyf1965]

WOW... better make sure your stop limits work... or they might just keep going and you will never see them again!


I got 3 of those 1390 oz motors for $75 delivered. There was no way I wasn't going to give them a shot for that little. Like I said I got lucky on the torque curve. They put out 700oz at 2000 rpm.[/QUOTE]

[fizx]

that is awsome any chance you can get your hands on some more....... I keep looking for some deals would ebay be the best place?

[Madclicker]

that is awsome any chance you can get your hands on some more....... I keep looking for some deals would ebay be the best place?

I did get them, and all the motors I have, off ebay. Haven't seen many good deals there lately. You gotta look constantly to snag the best deals.

[Walt@SGS.Inc]

If you are going to do 2 feet then 2 feet ect etc, remember doing the first two feet lets six feet stick out the in side. When you are doing the last 2 feet, 6 feet of the four by eight board is sticking out the out side of the machine. You are going to need almost 16 feet of working space in your shop to handle the 4 by 8 foot board.
This is a large amount of overhang to be supported..
Just a thought. Regards Walt.