Adaptation to existing CNC....

Hello All,

I am new to this forum and new to RepRap as a whole. I am NOT new to CNC in fact if you look me up "coogrrr" on CNCZone.com you will see why I am posting this question.... here it goes....

I have already built a large CNC that has .0001th inch ability. I have it all running with Mach3 and its done. What it does not have is the printing head. So I am asking is there any reason I could not adapt the hot end to my CNC and use it to print? Of course I would assume the answer to be yes but as you know I am a RepRapNoob so I am starting at this question and when I am finally printing you will all be telling me to bugger off I am sure

I appreciate the coaching and help the community may assist me with even in advance of getting any. I know from the reading I have done the last couple of days your all sharp and helpful.

Thanks again!
Coogrrr
A.K.A. - James

What travel speeds does your cnc rig achieve? That may severely limit print speed.

coogrrr Wrote:
-------------------------------------------------------
> Hello All,
>
> I am new to this forum and new to RepRap as a
> whole. I am NOT new to CNC in fact if you look me
> up "coogrrr" on CNCZone.com you will see why I am
> posting this question.... here it goes....
>
> I have already built a large CNC that has .0001th
> inch ability. I have it all running with Mach3 and
> its done. What it does not have is the printing
> head. So I am asking is there any reason I could
> not adapt the hot end to my CNC and use it to
> print? Of course I would assume the answer to be
> yes but as you know I am a RepRapNoob so I am
> starting at this question and when I am finally
> printing you will all be telling me to bugger off
> I am sure
>
> I appreciate the coaching and help the community
> may assist me with even in advance of getting any.
> I know from the reading I have done the last
> couple of days your all sharp and helpful.
>
> Thanks again!
> Coogrrr
> A.K.A. - James

I am interested in doing the same thing. I am currently building a CNC milling machine myself.

Gary H. Lucas

Greg Frost Wrote:
-------------------------------------------------------
> What travel speeds does your cnc rig achieve? That
> may severely limit print speed.


My machine can achieve 200IPM if I desire it was built to do wood working on a 36x48 inch bed. The ability to slow this down drastically is easily done of course. I can change the steps the feed speed and if I want to the gears on each axis drive. I use a 2 toothed pulleys with a belt setup to change ratios on the stepper this is how I achieve the .0001 resolution.

Hope this makes sense and helps to answer the question.

Thanks
Coog

Maximum axis speed is of little importance when compared to acceleration. A typical 3d printer will run acceleration in the order of 300"/s^2 or higher (around 1g). Throwing a 150g printer nozzle around at 1g isn't a big deal. Try that with a 50KG gantry.

Just look at some youtube videos of infill printing. A typical router would walk across the floor while bending itself into a pretzel if it had enough power-to-weight for that kind of movement.

Note that poor acceleration (probably 10-30"/s^2 for a router) has impacts beyond slow printing, It is impossible to instantly change direction in a corner so they must either be rounded off, or reached with an exact stop:
[www.machsupport.com]
[www.dynomotion.com]
Even with corner rounding, at the low accelerations of a router, your machine is unlikely to reach its maximum constant velocity.

Note that this kind of issue has repercussions beyond just slowing down your prints. Plastic will be extruding at a near-constant rate (or more accurately, the plastic extrusion rate will be a trailing average of the machines velocity) so every time your machine slows down your machine will blob and then starve.

None of these factors prevent you from converting a router into a 3d printer. Its actually been done before (search repstrap).

Its just that you are not going to end up with something better, or even comparable to a typical 3d printer. A large router just isn't designed for this.

My personal opinion is that you are already going to be buying 80% of a machine (extruder, heated bed, electronics*) regardless so you might as well shovel over another couple bucks for the rest of the printer. Swapping everything back and forth is a PITA and you really don't want to run 40 hour prints through a 3x4 router.


By the way, resolution has nothing to do with accuracy. A typical 3d priner will also have resolution in the 0.0001" range or better. I suspect that a typical DIY router build is actually much less accurate than a typical 3d printer, especially where backlash is concerned.



*It is likely that you will need to completely swap over your machine to dedicated reprap electronics every time you want to print. 3d printers do not use standard g-code. If you wanted to use a computer/parallel port for control, you would need to either code substantial changes to mach3 or switch to emc2 and write a bunch of stuff as well. Both options are far more work than they are worth, especially since a reprap board will run <100$ without stepper drivers.

Edited 1 time(s). Last edit at 01/23/2013 01:46PM by 691175002.