Newbie- Suggestions for small CNC - mobile gantry

[602CNC]

Hi All! I've been engulfed in learning about a CNC router and have been perusing the forums for months and am ready to take the plunge but I haven't seen any CNC router that would fit my requirements. So I thought I should ask before I spend another 7,000 hours reading more threads.

I need a CNC router that is pretty small (7"-12" travel Y axis) that would be a mobile gantry. It's mostly going to be used to cut intricate edge cuts (like dovetails but way more complex) on longer boards. I'll be doing other things as well but very intricate joinery will be mostly what it'll be used for. I would prefer to buy something since I need it by Christmas but DIY is what I'm thinking that I'll need since I haven't seen anything commercial that would work for my purpose. The reason why I'm thinking mobile gantry is because if I'm cutting long boards a moving stage won't work due to the weight (unless I really beef up the steppers). My budget is about $1500 but would obviously prefer to spend less.

Not sure what I should buy/build so any help from all you experienced CNC'er would really be appreciated.

[judleroy]

If you can find a machine thats inside your budget and capable of doing what you need buy it and get to work. I don't know enough about what your doing to suggest a machine for you but good luck.
judleroy

[DonFrambach]

Originally Posted by 602CNC I need a CNC router that is pretty small (7"-12" travel Y axis) that would be a mobile gantry.

Just curious as to why you don't want a fixed gantry router when you want a travel of only 7 to 12 inches. There are cost and rigidity benefits to small fixed gantry routers. The added space required of a fixed gantry is minimal when travels are so short.

[602CNC]

Originally Posted by DonFrambach Just curious as to why you don't want a fixed gantry router when you want a travel of only 7 to 12 inches. There are cost and rigidity benefits to small fixed gantry routers. The added space required of a fixed gantry is minimal when travels are so short.

It's a very good question. This requirement is something that I realized as I was starting to order a machine. If I'm cutting long boards usually between 1-6 feet of hardwoods, how heavy will the board be? More importantly, how big of a motor with I need to support the maximum? In thinking about this I thought it would be simpler if I just went with a mobile gantry system instead.

[DonFrambach]

Since you're going to work on large, heavy boards, it sounds to me that a moving gantry router will be better for your application.

[adprinter]

Originally Posted by 602CNC It's a very good question. This requirement is something that I realized as I was starting to order a machine. If I'm cutting long boards usually between 1-6 feet of hardwoods, how heavy will the board be? More importantly, how big of a motor with I need to support the maximum? In thinking about this I thought it would be simpler if I just went with a mobile gantry system instead.

If I am comprehending correctly what you are saying, I can tell you what I do with my machine, in order to handle long boards, etc.
I basically just bolt down a couple of pieces of angle steel to the table to act as guides. Then I clamp down the work piece, and make all the carving cuts that my machine can handle (up to maybe Y=32" X=32"), then I un-clamp the work piece, and slide it along the table.
(In the case of long pieces, I use roller stands which I set up at the ends of the table to support the work piece, as it slides off the table). I then Re-clamp the work piece to the table, and continue cutting in this manner. My machine is a moving gantry type, DIY which I designed and built myself. The stepper motors I am using are rated at 906 Oz. In. driving 48"x1/2" 10 TPI lead screws. The gantry with router weighs about 200 lbs. and it can cut solid oak with no problem.
I built this thing, in hopes of being able to machine metals with it. So it's a pretty sturdy construction of all steel, with aluminum slats for the table surface. To date, I have invested about $3K including the software investments I have made. Without the software, I estimate that I have probably about $2100 tyed up in the build.
I Hope this helps you in your build/buy decision. I can say that the machine I wound up with, would probably cost at least $5000 or more from a commercial supplier. Probably more, since I have now added a 4th axis to my machine (effectively building a combination Lathe/Mill Router table).

[JohnZ]

If what you will be doing is milling the ENDS of long boards, I am wondering if you may want to design a mill that has the "Z" axis flipped back 90 degrees so the axis of the router bit is parallel to your long boards. You would then have a fixed "Gantry" in the normal sense of the word, but would lift the gantry "Bridge" up and down, and the router would then move along the width of the bridge on a typical "Z" axis laying flat on its back to move the router in / out with regards to the board clamped to your stationary table. Wish I had a quick sketch to show what I have in my mind. To me, it just makes sense to do it this way if what you are intending on doing is routing the ends of the board.

[JohnZ]

I forgot to mention that many here on the zone have built machines with stepper motors in the 700 - 1000 in / oz size that are moving several hundred pounds of gantry or table, some able to cut at 300 in / min or faster. Sure servo motors would be better for a commercial operation, but for the hobby user, steppers work great.

In my case, I have ~900 oz / in Nema 34 steppers moving about 80 lbs on my x axis, and (soon to be) 300 lbs on my y axis. At 150 - 200 in / min, I cannot stop the machines motion putting all my weight into the moving table. Either the machine or my feet end up sliding across the floor. With steppers, it is not a matter of how much weight you are moving, but at what acceleration you are trying to move that weight. The more weight, the lower the acceleration needs to be to avoid missing steps. The key to high speeds / acceleration / torque is using high enough voltage and good controllers sized to your machine.

[louieatienza]

I assume you will be machining the face on the end of one board, and the corresponding end of another board, in which case a mobile gantry would be best. There are a lot of folks that have made auxiliary vertical clamping surface for such tasks. Check out the solsylva.com plans. They are very easy to make, and just as easy to add a vertical clamping surface. You would just need something to support the board on the other end, when on the flat.

I should add that my current machine uses 425 in-oz steppers, runnning 8-start leadscrews (1tpi effective), with a 24V power supply, and I can't stall them under my own power evevn at 150ipm! So you don't need mega-power or weigt to machine woods, even hardwoods!

[602CNC]

Originally Posted by JohnZ If what you will be doing is milling the ENDS of long boards, I am wondering if you may want to design a mill that has the "Z" axis flipped back 90 degrees so the axis of the router bit is parallel to your long boards. You would then have a fixed "Gantry" in the normal sense of the word, but would lift the gantry "Bridge" up and down, and the router would then move along the width of the bridge on a typical "Z" axis laying flat on its back to move the router in / out with regards to the board clamped to your stationary table. Wish I had a quick sketch to show what I have in my mind. To me, it just makes sense to do it this way if what you are intending on doing is routing the ends of the board.

Thanks for this and your other thoughts. It's an interesting idea that might just work. It would basically be a mobile ganty but turned 90 degrees. I'll try to mock something up and see what works.

Thanks for the advice and link louieatienza. I'll look into that site to see if something may work as a hold down.

[judleroy]

You could also use a mobile gantry machine thats not center drivin and stand your board up under your gantry. You would have to set the machine high enough above the ground. You would also need a plate attached to clamp the board to in that position.
judleroy

[602CNC]

Originally Posted by judleroy You could also use a mobile gantry machine thats not center drivin and stand your board up under your gantry. You would have to set the machine high enough above the ground. You would also need a plate attached to clamp the board to in that position. judleroy

I had the same idea but then I thought that having an expensive machine high and off the ground would make me nervous.