One ring to rule them all?

[kingcreaky]

Wow!! you sound like a man with a plan.

I have nothing positive to contribute, and can only recommend you start sketching up some plans, which will start the feedback coming..

I made a servo, (of sorts) once, using an arduino... this wasnt for cnc use though (it was used for power steering on my lads toylander)

intrigued as to how you intend to tackle some of the design challenges you have suggested (ie, milling steel and titanium), no doubt you have a plan

look forward to your responses... keep the ideas coming. Sometimes new threads dont attract many replies until you start posting pictures :D

[toomast]

You are really planning a beast!
2000mm long gantry with a dual 200x100x8 steel box section.... I cant really imagine it inside Transit van.
It will be really heavy and hard to build at least in conventional home garage. But it is doable, no questions there...
Dont start buing stuff until 100% finished design!!!
Anyways take a look at http://www.mycncuk.com/threads/6619-...an-Unusual-one
Mister Silyavski is into beasts as well :D
Good luck!

[Rufe0]

Thanks guys,

I've been going over some of the numbers, I'm thinking the torsional load on the gantry is the weak point.

Using this calculator
http://www.kennametal.com/en/resourc...and-power.html a 16mm 4 flute endmill in steel with recommended chip load feeds speeds I get a tangential load of 1000n / 100kg.

Assuming a Z travel of 1m, 1000nm torque on gantry.

Using HIWIN HG25 linear rails http://cnc4you.co.uk/resources/Hiwin%20General.pdf
basic dynamic load rating (lowest rating)
26kn / 2600kg. At a separation distance of 300mm and 1m Z that would be 780kg or 7800nm (but there is 2 of them so this times two really). Clearly the linear guides are adequate.

So then there is the torsional deflection of the gantry beam.
θ = TL/GJ
θ radians deflected
T torque = 1000nm
L length = 1m
G Shear modulus = 80 steel
T Torsional Constant = 180 m4
200x100x8 box
section http://www.roymech.co.uk/Useful_Tabl...ns/RHS_cf.html

= 0.006944444 radians / or 0.12114 mm at 1m Z travel

This is the calculation of a 1m gantry supported at only one end, not sure of the calculation for a torque at the mid-point. I assume it would be less. I assume it would be at least halved with 2 box sections welded together.

So I'm assuming it would be in the range of 0.05 which is acceptable I feel. It most likely wouldn't be enough to matter in most cases and even if it did you could work around it.

What do you think? Have I made a math error?

Thanks Rufe0

[Rufe0]

Ha just realized I made 2 maths errors, actually it's
0.0694 radians or 3.978874 degrees which is 69.4mm deflection at 1m. This is a serious problem.

[Jonathan]

Using HIWIN HG25 linear rails http://cnc4you.co.uk/resources/Hiwin%20General.pdf
basic dynamic load rating (lowest rating)
26kn / 2600kg. At a separation distance of 300mm and 1m Z that would be 780kg or 7800nm (but there is 2 of them so this times two really). Clearly the linear guides are adequate.

Adequate in terms of load rating, yes, but adequate in terms of stiffness ... you need to work that one out. There is stiffness data available from THK if you dig around.

[JAZZCNC]

Completely do-able but just beware if you dream Big then be prepared to Fail Big.!! . . . . The Chances of failure are very high.

I also Agree plane vanilla 5mm box section without any special treatment will be Big fat Fail.!! . . . . It's not just deflection you need to think about. Think about resonance and quality of cut etc. Box section without being filled will ring and large section box with only 5mm walls at over 2mtr will chime like Holy Trinity bells.
I've got a large router with gantry 2mtr wide with 10mm thick walls and that rings like a bell, doesn't deflect much and for router the resonance from it is more than acceptable but for milling Steels, even mild steels then forget it. It would sing like an. .

The point being you'll seriously need to Re-think your material choice and look hard at design methods if this is to come close to working at an accepatable level. Milling steels takes you another level of building compared to routers and cutting exotic steels takes you several levels higher.!!!

But like I say still do-able but with massive chance of failure.!! . . . . Good luck thou.

Edit: I'll revise that to Massive chance of dissapointment.!! . . . . Not to try would be a massive failure...

[routercnc]

There are some vertical machining centre ideas here on this commercial machine that might be useful . . . these are purpose built cnc machines, not the converted manual machines that you are used to.

http://www.mycncuk.com/threads/9022-...ght=commercial

And best of luck with the project !

[Tenson]

Z travel 1meter on a moving gantry? I can't imagine it milling steel let alone titanium.

Get some drawings down then post them up for better advice.

[komatias]

Z travel 1meter on a moving gantry? I can't imagine it milling steel let alone titanium.

Get some drawings down then post them up for better advice.

Why not? you just need to design well:

[dodgygeeza]

Z travel 1 meter on a moving gantry? I can't imagine it milling steel let alone titanium.

Get some drawings down then post them up for better advice.

Totally agree with your statement, especially if it needs to also be transportable in a back of a transit.
To machine titanium, steel or stainless, the machine needs to be extremely rigid and 5mm box section is not even close to getting to a point where it could accurately cut.
1M of Z would make the machine flex like a rubber dildo if you tried to cut steel, let alone titanium.