This is my first BUILD please help.

[DigiSoft]

Its always better to have the y-rails as far apart as you can and as low down to the bed as you can to improve torsional stiffness...

I think you could reduce the thickness to 12 or 15mm without undue effect...

What is the box section between the rails? material and dimensions?

This is my newest version. I found that I must put the ballscrew in the sandwich so I can use the maximum length.
The box section of the two pieces that hold the rails is 50mm x 60mm at 4mm thickness?. I am thinking of using stainless still. What do you think. Will they bend?

[D.C.]

I don't think the backplate on the rear of your z-axis adds a great deal to the performance of the machine, if you get rid of it you can bolt a plate to the back of you gantry to improve stiffness. If that still doesn't provide enough stiffness for what you are using the machine for you can always pour concrete into the box section.

Concrete is obviously heavy but weight can be reduced by adding things like vermiculite/perlite/polystyrene beads etc into the mix to displace the sand and and some fibre glass or fine steel fibres to add reinforcement.

[DigiSoft]

hmm so you say the backplate won't do much think?hmmmm
I am thinking to use 5mm for backplate.

[irving2008]

Assuming a typical spindle/z-assembly the 50 x 60 x 4 isnt strong enough for that 1140mm length if its aluminium, the deflection in the middle will be around 0.1 - 0.2mm and torsionally the deflection under cutting loads at the tool tip will be similar, so needs to be steel. You'll still need to join the two box sections with a plate, or a series of plates at the ends and in the middle to transmit torsional forces from one to the other and to maintain the rail seperation accurately else you'll get binding. The other issue is that box section isnt flat enough to mount those rails on unless its ground flat after assembly, you'll not be able to maintain the rail spacing accurately enough to prevent binding. Aluminium extrusion is better but again needs to be bigger, e.g. 100 x 50 for tortional stiffness. 5mm plate is probably too thin, the deflection at full Z extension under cutting load could be ~0.2mm. 15mm plate seems to be the norm, and will limit the deflection to <0.1mm. These calcs are very rough.

[DigiSoft]

Tomorrow I will be cutting the aluminum pieces for the Z gantry.

For now I have two questions.

1. What type of bolts should I use? What is preferred size for bolting 20mm aluminum?
2. There are two screws on the Linear ball sliders. One is on the top in the center and one on the side of it. Why are those used for? I heard for tightening the bearings but why two?

[DigiSoft]

Here is some progress i made so far. Everything is made of steel except the font panel of the Z axis, that is 20mm alu.
Please comment.

[kingcreaky]

wow! -- excellent work.

keep the pictures coming

[DigiSoft]

Thank you, I'll make new more quality pictures. These were taken with my phone :)

[EddyCurrent]

Looks good, how did you join the side plates to the ends of the big box section ? I can see there are 6 bolts used somehow.

[DigiSoft]

Looks good, how did you join the side plates to the ends of the big box section ? I can see there are 6 bolts used somehow.

The big box section (140mm x 60mm x 5mm) has welded 12mm steel plates on the both ends. Then the ends are machined to get 90 degree. I used 6 bolts M8 to bolt the sides.