Gantry Aluminium thickness guidance

[dachopper]

Hi guys,

I have started acquiring components for a 1500x800x200 build area gantry style router, and still am undecided about the gantry end plate / x axis and z axis plate thickness required or recommended

I have seen some commercial hobby components as thin as 6mm aluminium for end plates, and read others recommending 15/16 minimum, or 20mm.

My Z height calls for an end piece of about 300 x 440 high. the X design has 2 x 80 x 80 T slot mounted with a 80mm gap for the X motor and ballscrew in the middle, then a 170 gap below to the mount plate on the Y axis



Can anyone give some advice on what happens if it's too thin, and what would work.

If guys use 20mm for the end plates, what do they use for the x axis and z axis plates?


All advice appreciated
Nick

60 views and no advice, someone must have an idea

[njhussey]

Hi Nick,

Welcome to the forum don't get hung up on views and no replies...it's hard to give a meaningful reply without knowing a bit more so most people will shy away from giving advice. It's a bit like saying I've a room to paint, how much paint do I need? Have you got a cad drawing of your router we can look at? What are you aiming to cut, how long is your Z axis etc. etc. etc. The strength/thickness needed will depend a lot on your design and what you're looking to cut, give us some more to go on and we'll help you out.

[Robin Hewitt]

End plates for a gantry? So what happens when you accelerate the head hard along the gantry or the tool plunges in to the side of something resilient? That is the moment you realise that a plate simply does not cut the mustard and you really needed to think in triangles.

[dachopper]

End plates for a gantry? So what happens when you accelerate the head hard along the gantry or the tool plunges in to the side of something resilient? That is the moment you realise that a plate simply does not cut the mustard and you really needed to think in triangles.

Well, the Nema 23 will probably stall if all of the end stops fail. Chances of that happening......

What happens if I'm using a tube design with thin walls and the plate rams the thin skinned tube?

Here is the basic design.

The Y extrusion is quite big, 80x160, and the others are all 80/80 profile.

This is the rough plan

This is where I'm up to



To be used for 3d Printing, Composite 3d milling, wood, and possibly aluminum

[njhussey]

Well, the Nema 23 will probably stall if all of the end stops fail. Chances of that happening......

Greater than you think....well if your home switch becomes loose from vibrations (fast trochoidal milling) so your gantry slams on a rapid home into the side beams.....luckily the AM882's have stall detect!!

What happens if I'm using a tube design with thin walls and the plate rams the thin skinned tube?

Guess it'll bend it!

Here is the basic design.

The Y extrusion is quite big, 80x160, and the others are all 80/80 profile.

This is the rough plan

This is where I'm up to



To be used for 3d Printing, Composite 3d milling, wood, and possibly aluminum

Somewhere on the forum there is a bending moment calculator which will sort this for you, however I'd say minimum of 15mm for the plates, and for the difference in cost go 20mm, and I'd strongly consider putting a plate across your two 80*80 Z axis extrusions to stiffen up the gantry.

for the Z axis I'd put thicker plates on as those don't look that thick and I'd put the rails on the front plate not back to stiffen it up. I'd also consider connecting your motors to the ballscrews via belts and pulleys rather than directly, this helps take out any resonance (from cutting) and stops it being fed back to the stepper motors.

If you're using the ballnut housing that's in picture 2 how are you going to connect it to your Y axis plates, you'll not get to the screws behind it to tighten it?

[dachopper]

Greater than you think....well if your home switch becomes loose from vibrations (fast trochoidal milling) so your gantry slams on a rapid home into the side beams.....luckily the AM882's have stall detect!!



Guess it'll bend it!



Somewhere on the forum there is a bending moment calculator which will sort this for you, however I'd say minimum of 15mm for the plates, and for the difference in cost go 20mm, and I'd strongly consider putting a plate across your two 80*80 Z axis extrusions to stiffen up the gantry.

for the Z axis I'd put thicker plates on as those don't look that thick and I'd put the rails on the front plate not back to stiffen it up. I'd also consider connecting your motors to the ballscrews via belts and pulleys rather than directly, this helps take out any resonance (from cutting) and stops it being fed back to the stepper motors.

If you're using the ballnut housing that's in picture 2 how are you going to connect it to your Y axis plates, you'll not get to the screws behind it to tighten it?

Good point - any tips?

I can do it up before installing, but that will be loaded with alignment danger

I could install a horizontal shelf over the top of it, rotate the flat face 90 so it points up, and do it up from the top instead of on the side?

[njhussey]

Good point - any tips?

I can do it up before installing, but that will be loaded with alignment danger

I could install a horizontal shelf over the top of it, rotate the flat face 90 so it points up, and do it up from the top instead of on the side?

I did the same as you, only I'd built it hence how I know!! I bought two of these style for mine and they're great.

[dachopper]

Ok guys - here is my final design

20mm thick

May put gussets over the ballscrew attachment, but Ill wait and see how rigid it is without

Nick

[dachopper]

Take 2,

I'm still not happy about having to put all this stuff on the k2 relay, but I can't seem to figure out any other easy way.

[MikeyC38]

Hi Nick

As others have said, you do need to be more specific which you have done by showing details of your build and what you intend to cut. Rigidity is your best friend for any cnc build and as others have said plates across the end of the long axis will stiffen the frame significantly. In my build here I used 80 x 40 heavy gauge extrusions ( 4kgm+) with 15mm 6082 T6 plates either end. The gantry sides are 20mm 6082 T6 water jet cut with heavy gauge 80 x 40 extrusion for the (short) y-axis. I am very pleased with the overall rigidity but will reserve judgement until I do my first cuts on metal. It might appear over engineered but I took the advice offered on the forum and I'm confident the machine will deliver the levels of accuracy I need. The use case for my machine is cutting balsa, hardwoods and aluminium at reasonable speeds, hence the robustness of the construction for the most difficult use case (cutting aluminium).

Hope this helps

Mike