Decreasing flex

[Hamzter]

I've recently finished building a CNC router, flex in the machine makes it difficult to make accurate small parts however (like gear teeth), are there any techniques to reduce the effects of flexing?

A few things I've thought of but yet to test include

• Increase the router speed
• Decrease the cut depth
• 'Rough out' the profile of a shape before doing a final pass
• Alternate between clockwise and anticlockwise on each pass

Any thoughts?

[margni74]

Its tough to get a really rigid machine out of mdf.

Can you post some closeups of your machine? perhaps you can toughen it up by fastening some metal rail to the flexing parts.

[Hamzter]

My machine is sat in the conservatory which is a bit gloomy to be taking pics at the moment, here's an older pic tho. I've since added various metal supports to try and reduce flexing, flex at the cutter is about 2-3mm with a reasonable force applied now. I don't think it's possible to make a completely rigid machine out of MDF, it's just a matter of reducing it to an acceptable level, I think with the right tool paths, feed and cutter speeds I can get some pretty accurate parts.

[sonicwonder2000]

I am a newbie myself, but can you identify where the flex is originating? If you can narrow it down to a certain joint or part, you could selectively beef up those parts.

[Hamzter]

There's a little bit from the axis bearings (barely detectable), a bit of flex in the sides of the gantry, plus little bits of flex all over. Total flex is about +/-0.5mm when cutting, so it's pretty minor, maybe I'm just expecting too much from an MDF machine!

[margni74]

Have you thought about 'boxing in' the z axis ?

[sonicwonder2000]

You could try this procedure:

1) With the spindle off but the steppers powered, hold the collet of the machine and try to exert some lateral forces.
2) Take note of what flexes first.
3) Beef-up the flexing part if poss.
4) Goto 1 and repeat

I don't have first hand experience with mdf machines, as mine is all steel and aluminum. But even with all metal, I can induce .5mm flex with hand pressure so i'd say you might be at the limits of your material choice?