Materials used in CNC build projects

[Ross77]

OK,I'm going to attempt it...only because I am eventually going to build the CNC in Allum but that will be sometime as I'm aquiring the gear to make my

Good on you. I wasn't trying to discourage you, just offering some options. If the usage and design can be matched then I don't see why It wont work. I just hope you arnt expecting this to mill the Ali castings you will produce

Start a build log stating exactly what size cutting area, type of spindle, motors and material to be cut and the materials you have already got.

I'm thinking something like A4, A3 max with a high speed dremmel running on metric studding for cutting foam blanks,pcbs etc......

Exactly, the sturdiness is not there if the machine is vibrating :). With perspex you will have them both: lack of sturdiness (this means vibrations), and cracking on vibrations - perfect match :).

I would tend to disagree with that :naughty:(not like me I know) it is a stiff machine that will vibrate, less sturdy machines will move and damp the vibration. The vibrations are caused by the machine in motion or the spindle and cutting tool, so if gentle accel , decel and a smooth spindle are used then it should be OK no?

[florins]

...it is a stiff machine that will vibrate, less sturdy machines will move and damp the vibration. The vibrations are caused by the machine in motion or the spindle and cutting tool, so if gentle accel , decel and a smooth spindle are used then it should be OK no?

Hi Ross77,

My understanding is like this: the lower the stiffness (I mean more elastic), the lower is the resonance frequency for a given assembly. Rising the resonance frequency over the mechanical frequencies generated by the movements and the spindle makes the assembly less prone to vibrations - that's why everybody is trying to make the machines sturdier for a given mass.

It's true, you can absorb the vibrations with an absorbent material - like rubber, or, in this case, perspex :). It's true, as well, that you can reduce the accelerations (accel & decel) and the feed rate until a given structure will not vibrate - if you are lucky enough to not obtain resonance... but, is this practical?

Now, I am sure that George's machine will work somehow, but in my opinion, the pieces or perspex he has would work much better as material for some nice products after the machine is ready :).

Just my 2p.

Florin

P.S. Absorbing the vibrations in perspex I believe is exactly what's cracking it, and it starts where the micro-fracture points are induced by mechanical processing. It happened to me before...