Open source group project, anybody interested?

[Tom]

Irving, that's a most useful post - I'm going to bookmark those calculations for future use..., thankyou.

I recon Irving's hit the nail on the head with

The question I suppose is...

The meaning of mid-level could be very different depending on who you're talking to. Although both of these chaps has built/converted a machine to run with EMC2, you'd probably get a different answer about "mid-level" from each... :)

[ame="http://www.youtube.com/watch?v=LA5qCIB0j6k"]YouTube- Fresa CNC MDF[/ame]
[ame="http://www.youtube.com/watch?v=mxxdq6y8z8M"]YouTube- EMC2 5 axis cinci at MPM[/ame]

So how about a list of variables, so that we can discuss pros and cons?

(low-spec -> high-spec):
* Working size (min A4 -> max 4ft x 8ft flat sheet)(Z depth?)
* Linear bearings (unsupported rails -> skate bearings -> v bearings -> supported round rails -> recirculating ball carriages)
* Drive method (chain/allthread -> belt/trap screw -> ballscrew)
* Target cutting speed vs. target resolution (trade-off)
* Rigidity & strength (just cut alu, or rip through it in a breeze?)
* Spindle type and power (dremel -> 43mm router -> handheld router -> VFD spindle)

Probably loads i've missed, so copy paste and add/change bits...

On my wishlist would be the ability to add a 4th axis (parallel with x) at some future time, without hacking the machine to bits. Designed in expansion capability if you will...

[Wotsit]

So how about a list of variables, so that we can discuss pros and cons?

(low-spec -> high-spec):
* Working size (min A4 -> max 4ft x 8ft flat sheet)(Z depth?)

For me 2 x 4 is sutable

* Linear bearings (unsupported rails -> skate bearings -> v bearings -> supported round rails -> recirculating ball carriages)

Supported round rails or carriages

* Drive method (chain/allthread -> belt/trap screw -> ballscrew))

Ball screw

* Target cutting speed vs. target resolution (trade-off)
* Rigidity & strength (just cut alu, or rip through it in a breeze?)
* Spindle type and power (dremel -> 43mm router -> handheld router -> VFD spindle)))

Cut alu at a resonable feed rate, spindle down to end user but designed for VFD

Probably loads i've missed, so copy paste and add/change bits...)))

How about bed construction?

On my wishlist would be the ability to add a 4th axis (parallel with x) at some future time, without hacking the machine to bits. Designed in expansion capability if you will......)))

This is important to me

[Ross77]

Plenty of interest then.

Defining mid range could be a problem. linear rails, ballscrews and vfd spindle seems quite high spec to me....

theres enough flexibility for people to use what ever they need to suit their requirements. Although I dont think it wouldnt be very economical to mount a dremel on a machine designed to take a heavy vfd spindle?

Thanks Irving. thats perfect, knew I'd seen that somewhere. Is that the rotational force of the motor or the force required to push the axis?

If high speed is needed then would it be better to use belt drive? or would that cause problems with higher powered motors?

For the drivers has any one else seen the "CPLD tutorial" on cnc zone? from memory :whistling:

80V @ 7A with 5 micro steps and works out at £10 to 15 an axis. The only drawback is the chip is a tiny SMD so not very diy friendly. It was proposed to mount a preprogramed chip on a separate daugther board that could plug in to a 40 pin wide DIL and be sold cheaply so people could then build their own but it was never realised. any takers?

[irving2008]

Plenty of interest then.

....

Thanks Irving. thats perfect, knew I'd seen that somewhere. Is that the rotational force of the motor or the force required to push the axis?

No thats the effective linear force pushing back on the cutter. For deflection calculation purposes assume its both perpendicular and parallel to the direction of cut . For leadscrew/stepper torque calcs assume it adds to the load opposing the motion...

Also note in the previous calcs, a screw rpm of 360 means a minmum of a 12mm dia leadscrew for a 1m screw supported drive end only, or 16mm for a 1.5m screw assuming supported both ends (class B support). For bigger 2m screws you're into 20mm+ ballscrew class C support territory and big bucks.

[Ross77]

Thanks Irving thats what I meant but I pharsed the question wrong. I seem to have a problem getting the thoughts in my head to paper lol

is that 20N a worst case or would it be better to up it a little? Have you got any info for other materials or a table maybe?

I'm starting to see what you mean, this aint going to easy........efficient design isnt easy to build and requires good machining, sounds like the chicken and egg situation I'm in at the moment :heehee:

With regard to the design is space an Issue? ie. overall size. Because I cant help but think that this needs to be a fixed gantry design. The frame could then be as heavy as required and just move the table underneath. This would mean its twice as long tho.

Kip always said "router for routing and a Mill for Milling" or something along those lines.

[Ross77]

Ok I been having thinking about this and was wondering if Aliminium U channel is the answer? The only problem is that it would need welding. Steel would be easier but is quite a bit heavier and seems to cost more at the mo.

The idea is use 2 u channels vertical and the fix one top and bottom. This would provide a channel for the ball screw and should be plenty strong enough for dremel, trim router. but if more strength is required then the top and bottom cavity could be filled with concrete and rebar(could be threaded bar that then bolts the uprights to the beam)

Done a few rough shetches to get an idea, I know theres a few mistakes and will probably need some bracing in the webs of the channel (more welding) and the x axis is probably overkill........

Any imediate or obvious problems before I go any further? 100x 50 ali is about £10 a meter so with the 4 bars on an 800mm y axis it would be £30 ish

[ptjw7uk]

At first glance the design seems to ba all wrong, there is no lateral support for the x-axis and when the head moves it will move in the direction of the movement.
I think some form of twin track stacked one above the other would be better to control lateral movement.
Thats my 2p.

peter