I've been designing an 80/20 based CNC flatbed. Here is a quick snapshot.

I'm planning on a Gecko G540 with 2 628in/oz on X, 1 628in/oz on Y, and a 282in/oz on Z.

Cut area is right at 48"x48" with a Z range of 5".

I should be able to work Hard Wood, Plastic, CF Plate, Aluminum, and mild steel.

I need this CNC to assist me with a project I've been working for a while now. I am working on a UAV for Cal Fire. It's a blended wing, dual EDF, with a span of 10'. The skin is a foam, CF plate, kevlar composit. The airframe is Aluminum, CF, and light ply. Attached files

 

Yah, I looked at a few on the web that I liked and made it work for what I need. I am not done yet. I still need all the hardware including the gussets and other brackets.

I'm going to an 80/20 dealer here "in town" (actually down in Powey neer my SD office) tomorrow. They have all the components there so I can get a better feel for how this will all actually fit together.

The budget for the machine is $2500

 

Great!! that's a really neat frame design....

However, from an engineering point of view, I would have a few concerns.... I hope they're helpful to you. Coming from a background of designing very large motion control rigs, my experience tells me you need to think carefully about a few more things.

First of all I would ditch your plan to use two steppers on the X axis... You won't need that much torque, particularly as you can't match it on your Y Axis unless you were to fit a second motor there as well.

The second problem is one of synchronisation. You're going to find that locking the position of the two X steppers together is very very difficult or even impossible, without some sort of mechanical locking between them. If one of them loses steps anywhere then you're going to jam the whole thing up.

It'd be far better to centrally mount a single stepper and run transmission belt or chain belt drives out to the two screw threads. That way they are always perfectly synchronised. Your bed isn't wide enough to have the need to run separate steppers over that width in any case.

If you feel you must run two steppers then you should at least look at mechanically locking them together again that could be achieved with a transmission belt design.

I also have some concerns about the robustness of the frame design when you're feeding that much torque into it. You need to be looking at a steel truss bed with that alloy frame bolted to it. maybe with spacers between the two. I'd also have concerns about the distance between your bearings on the bottom of the Y carrier frame. They need to be much further apart and the Y carrier frame in general needs much more stress support or it's going to flex a lot more than you think and throw your cuts way off.

I think you're being very optimistic to expect to work Aluminium and Mild Steel on that bed design. It's a router bed design, not a milling machine design. Wood and plastics yes, but not metals. Metals require an entirely different machine design to that.

Have you done any calculations of the rotational torque and stress loading for that frame design? It'd be interesting to see those numbers.

Other than that it sounds like a very interesting project and I hope the above pointers are helpful to you.

Best Regards,
Julian (Fozzy The Bear)

 

Hi Julian,

Thanks for your insights and yes I’ve done some calculations. The 4” wide x .25” plates you see spanning either side of the bed plus the one on the gantry are high carbon steel plate. This is the load bearing member for the trucks and are secured to the rails with hardened fasteners. The structure is extruded thick wall aluminum reinforced with steel plates and brackets at the joints as well as hardened fasteners at the butts. The bed will be 2 sheets of 1 inch thick MDF fixed to the frame. The first sheet will be milled flat and the second sheet (sacrificial) will be fastened to this board. This will provide additional stiffening.

The Gantry structure will deflect no more than .0002 inch along the Y axis on the Gantry under 200lbs of load based on the structural beam as well as the steel flat plate. The Gantry side beams will be gusseted to the gantry span beam and the external trucks and reinforced with steel plate to resist torque on the beams.

I am looking into tying the 2 steppers on the X axis at the rear of the machine via a belt to fix them mechanically. But I want to experiment without this first since this option adds complexity and cost. I don’t need the torque as much as I need even distribution of torque along the full aspect of the axis. A single central screw will tend to rack at the extents of the axis.

Cutting aluminum and mild steel should not be an issue for this design, I have seen many
similar machines used for such purposes. I will not get cut speeds of 150IPM working metal but I do expect to see 50IPM.

I have an appointment tomorrow to sit and review my plans as well as get them engineered in CAD from my Sketchup drawing. The 8020 dealer I am working with have free engineering design review on site. I know I’ve made mistakes in the design (since I am not really done……
They also have “canned” CNC flatbed designs I can use but I really want to design my own….

Matthew

 

Hi Matthew,
OK I'll buy the fact that you've done some calculations. I don't think they're close to reality, but I'll buy that you did them. I think you've missed a lot of factors. It's the only way I can explain your results.

Good luck! But I think you're going to find that you're not going to achieve the cut pressures and stress loadings that you think you will with that design. If you do, then I'll be very very impressed and asking you to sell me your design patent. If you can build a machine that is that capable for that amount of money, then I want one!!

Like I say, I'll be really impressed if you achieve these tolerances and cut pressures. Go for it! if you think you can achieve it then I really do wish you the very best of luck with your project. I'll be the first one to congratulate you if you manage that.

Best Regards,
Julian (Fozzy The Bear)

 

Thanks Julian for the response....yes I found that I need to make some changes to get close to what I want to do. I actually meant .02 not .0002.....

My IPM estimates were a little off.....I'm looking at much lower speeds when cutting aluminum and after talking with the engineer I decided to not even try the steel......I don't want to deal with coolant (I didn't think of that) nor the tool wear....he recommended a local shop that will do small one offs in any steel alloy I want....

Anyway.....I've changed some of the beams to 3x3 in order to get better gusseting. He said that with the design and changes he recommended I will be able to cut aluminum (he recommended a spay bottle with WD-40 to keep the heat down) but I'll have to make multiple passes to do so.....which I figured anyway.

I'm working on my cut list now to get the quote for the materials. He also offered to cut and deburr the material for me and drill, tap, and countersink where neccessary. He is also translating the SKP file to ACAD for me to have. He also recommended different types of hardware and plates to distribute the loads better....couldn't have asked for better service!

Can you recommend some end mills for the aluminum, CF, Plastic, and Plywood? Can it be the same end mill?

Matthew

 

Yeah! no problem Matthew,
For most of those materials you can use exactly the same bits we're using on the phlatprinter... At the moment I'm using some rather nice Tungsten Carbide CNC bits which give a very clean cut. Either diamond pattern or chip breaker spiral bits seem to work best.

For the alloy cuts then you really need to use proper metal cutting endmills.... Although I'd strongly recommend that you try and buy what are called "slot Drils" they're like an endmill but only have two flutes on them. They clear the chips a bit faster and give you a slightly lower cut pressure.

The other thing to look at with this (and I don't know what sort of cutting head or power you're using) would be if possible, to use a proper milling chuck that will take screw in endmills in a collet. They're not cheap, but they provide very positive location of the bit and really help keep it in position on a heavy cut.

You also want to use some propper cutting oil rather than WD40 with that it's a bit thin and you run the risk of it catching fire. You really should use something like Cutmax or Smoothcut not sure if those brands are available in the USA but you should be able to get something similar. and if you're not pumping it to the bit then you can just apply it with a small paintbrush every so often during the cut, as long as you're careful.

Hope that helps...

Best Regards,
Julian (Fozzy The Bear)

 

Thanks Julian. I'll take a look at those bits.

For now I'm going to try and use the WD40 for now but will look for some "real" cutting oil. I don't plan to use a mist or flood system so I'll just use the spritz from a bottle methode.

 

Hello Thewz

New here but came across your topic and it caught my eye. I was going to build a gantry system much like yours but changed directions.

Looks like you are going to use Ahren’s carriages, they are nice, I have some of his parts in a box under the desk. Looks like most people that use them are happy. He makes great parts and still might be able to use what I have on a project that I have on the back burner.

I have a small desktop gantry router,( http://romaxxcnc.com/ )it has two steppers on the Y, it’s the only way I would go on a gantry router if I were to build one.. The X and Y is belt driven. Great system. I have had no trouble cutting all kinds of wood, corian and cast acrylic. Really like working with cast acrylic cuts like butter. I even proved it can make a .1 cut with a 1 inch fly cutter in aluminum, long story but now I have a very ugly 2 inch long cut in my table top. I do not cut any type of metal (intentionally) as the electronics are under the table.

I highly suggest you check out precisebits for a collets and nut that are a big improvement from what comes with a router and buy a router that he provides collets for if you do not already have one. http://www.precisebits.com/gateways/ColletsNutsHome.htm

George

 

Thanks George! Let me know if you wan't to sell those carriages....

 

Getting a cut list completed to send to the 8020 dealer. He offered to cut, deburr, tap, and countersink as neccessary. I'll get photo's when all the parts are ready. I've also got to start ordereing the custom components and linear motion stuff.

 

I've ordered some components from MSC (Couplings, clamps, thrust bearings and such). Got 25% off....cool!

Completing the 8020 order now. Total for all 8020 parts including cut, deburr, tab, countersink, bolts, hold downs, brackets, and T-Nuts is $900.

Next on the list is my order from CNCRouterparts. Total of this order will be $590.

Then order the Gecko 540 and 620in/oz steppers Total order will be $485.

I've already got the router....just need some bits.

Total estimate now is around $2200.....cool.....a little under budget. Let's see what the actuals are. Luckily the 8020 stuff is local so I can pick it up and save freight costs there.

 

Shoot....forgot one important part....my Order with McMaster-Carr.....

3 6' 1/2"-10 5 start lead screws and 1 3' 1/2"-10 5 start screw for $287....

 

I hope to have a working machine in less than 3 weeks. Pics to come as parts arrive.

 

Just got 2 boxes from MSC ! ....it's happening..... :ugeek:

Going down Thursday for the 8020 parts. I am looking at a local vendor for the screws as well since they are long and cost a great deal to ship.

 

Here is my updated design I created the cut file from.

Attached files

 

Woot! My 8020 parts will be complete next week. Once I take delivery I'll get photo's of it. I'm getting the steel flatbar ordered today as well. I'll do the drilling in the plates since the steel supplier wants $85 per hour plus setup fees..... It's just a bunch of holes but it would cost an extra $200....frick....

 

My components from Ahren are on their way. I am picking up the 8020 components on Wednesday. I've got the cold rolled steel bars ordered and will pick them up on Wednesday (I have to drill 150 holes.... ), the final parts will be the Gecko 540 and the 628 OZ steppers. Should have everything up and running by next week Wednesday.

Pics will follow as soon as I have the 8020 in hand.

 

The parts are starting to come in!

Attached files

 

1.5 hours later....

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