New Machine Build- wooden z axis

[galoz]

hello,
i start building a cnc router table starting from the z axis.
almost finnish the z axis, still need to mount the limit switches.
i have a backlash of 0.02mm , i guess is it due to the wooden plates.
here is the video, be glad for any tip.

YouTube- home made cnc router z axis 0.02mm Accuracy

[louieatienza]

Is that Yngwie in the background?

Looks cool, though I'm not sure where the backlash could be. Is your locknut on your ballscrew, ballnut, and coupler secured well?

[CarbonKevin]

Some of your fasteners COULD be causing the wood to compress under load, giving very small inaccuracies. You might get around this by using fender washers to spread the load, or else t-nuts or another similar insertion fastener for wood.

You could also treat the area immediately around the washer with epoxy to increase compressive strength.

Really, though, .02mm of variance is not a lot...less than .001 inches.

You should disassemble and seal that wood at some point, though! You don`t want the wood to be humidity sensitive.

[galoz]

i guess i should handle the wood and seal it.. anyway i know this is not alot (0.02mm),
but under load it will increase becoz the wooden part. there is coast for cheap materials
is it better to use MDF ?
aluminium is very expensive here ..
(BTW i dont know if it is Yngwie but it is so cool player )

[CarbonKevin]

Until you know the source of the variance, you cannot assume it will get worse under load. You may get other variance under load, but what sort of variance and how much load will be required to create that variance is unknown to you at this point.

MDF is not a better material for your project. Avoid it!

You could experiment with laminating composites onto wood to increase panel stiffness. I'm playing with carbon fiber on baltic birch ply at the moment. Neat stuff!

[galoz]

Originally Posted by CarbonKevin Until you know the source of the variance, you cannot assume it will get worse under load. You may get other variance under load, but what sort of variance and how much load will be required to create that variance is unknown to you at this point. MDF is not a better material for your project. Avoid it! You could experiment with laminating composites onto wood to increase panel stiffness. I'm playing with carbon fiber on baltic birch ply at the moment. Neat stuff!

ok, i take your advise, i will stay with wood.
i wonder why peaple use MDF, i though it is more stiff..

[CarbonKevin]

Originally Posted by galoz ok, i take your advise, i will stay with wood. i wonder why peaple use MDF, i though it is more stiff..

I wonder why people use it, too. It's not more stiff than most woods. It's more susceptible to moisture.

The only things it's got going for it is cheapness, easy to get it, and easy to work with it.

[louieatienza]

A cool material would be phenolic-coated birch plywood or PSF. They use it commonly for concrete forms (HDO is another material). Super-strong...

I guess MDF is popular due to it's easy machineability, availability, and weight. I like MDF. but special considerations need to be taken for edge-attaching fasteners, since it is prone to split. But many successful and accurate builds are made of it...

[CarbonKevin]

Originally Posted by louieatienza A cool material would be phenolic-coated birch plywood or PSF. They use it commonly for concrete forms (HDO is another material). Super-strong... I guess MDF is popular due to it's easy machineability, availability, and weight. I like MDF. but special considerations need to be taken for edge-attaching fasteners, since it is prone to split. But many successful and accurate builds are made of it...

PSF? Poly Styrene Foam?

What's HDO?

I might have overstated my opinion of MDF. But it's weakness is certainly joining pieces.

[louieatienza]

Sorry... PSF - [P]henolic [S]urface [F]ilm - exactly waht it states: Baltic Birch with pheniloc skin

HDO - [H]igh [D]ensity [O]verlay - Baltic birch with an exterior skin similar to MDF, but denser and harder...

[galoz]

Originally Posted by louieatienza Sorry... PSF - [P]henolic [S]urface [F]ilm - exactly waht it states: Baltic Birch with pheniloc skin HDO - [H]igh [D]ensity [O]verlay - Baltic birch with an exterior skin similar to MDF, but denser and harder...

thanx, i understand thay are all wood (birch is a hard and Quality wood) with Coating..