1/8" Aluminum Side Plates - STRENGTH! (?)

Hi All-

In an effort to stamp out flex and subsequently reduced accuracy and strength, I’m looking at what might be enabling it. I think a decent source of flex are the plate steel side plates at the end of the gantry. I’m putting a longer X extrusion on right now, and I can definitely flex the whole assembly a bit.

For a while I’ve been batting around the idea of having new ones made out of thick plate aluminum - aluminum 6061 in 1/8 inch. Next week my favorite shop to do waterjet cutting online is running a sale where you get the same price for a couple of pieces as you would for a lot. Makes them pretty reasonable…even for low taper cutting.

Wondering if anyone else has tried this, or has any thoughts on this idea. I don’t think it’ll HURT…but I want to make sure it’s worth it. As I reassemble my machine with the new X extrusion, I’m looking for any way I can make it all rock solid.


Aluminum is weaker than steel but thickness will add strength. E modulus is the number against bending, Steel 210 and Aluminum 70.

Thickness adds a lot resistance to bending to the cube so a 4,5mm aluminum plate is as strong as steel.

Thicker gantry plates will help but anything above 1/4 will be stronger than the side flex of the Y rails and the wheels.

An earlier post with some interesting ideas is:
shapeoko forum post

Thanks @ErikJanssen. Food for thought.

If I’m reading this right, 1/8" aluminum wouldn’t be much stronger than the stock plate steel, correct?

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That s correct, it is a lot less

3mm steel = 3^3 * 210 = 5670
3mm aluminum = 3^3 * 70 = 1890 (only a third)
4,5mm aluminum = 4.5^3 * 70 = 6379
6 mm aluminum = 6^3 * 70 = 15120 (three times the steel strength)
12,7 mm aluminum (1/2") = 12.7^3 * 70 = 143387 (overkill)

Thickness adds the most, that is why the new Makerslide profile with the 4mm side walls is so strong. If you are really concerned with the side flex replacing the Y rails adds more strength than thicker gantry plates.

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That’s good to know. I’m making some new gantry plates and Y plates out of 15mm aluminium tooling plate, and hoped it would be ott

That will probably be the stiffest piece of your system :wink:
15mm (5/8") will be firm…!

…and heavy, anything above 6mm is overkill. The more weight on the gantry the higher the forces on the belts due to the accelleration.

I’m actually in the process of swapping from belts to leadscrews, and increasing the gantry height considerably so I wanted as much strength as possible.

I’ve been in the process of doing this redesign for a couple of months now but I’ve been busy, although I have everything ready to go when I get some time.

I think when I’m finished the only “xcarve” bits left will be the Y rails, X carriage, and some of the frame under the wasteboard.

After replacing the motors (at some point) I think it’s time to build a new machine from scratch lol

All my plates are .25". And stiffness is definitely improved.
However I have 2 spare custom plates. If you would like pm me and I can send pictures and what not.

You have two of the .25" plates? I’d be interested.

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@PhilJohnson @ErikJanssen or anyone who would be able to help.
I would like to pick your brains. I have a Z Slider that I bought fro China and in order to cut down weight, I would like to change the backplate from approximately 11mm to 6 or 5 mm. 6 mm is what is available from a local seller and the 5mm, although I have not seen it yet will be given to me for free. My question is would, 5 or 6 mm, be strong enough for this application?

The strength of a plate depends on the size.

For a flat piece of material you can calculate this number with the formula (width * height^3)/12
This shows a 5mm plate is 8 times weaker than a 10mm plate.

Reducing the plate thickness and adding side skirts of the same amount of material you saved would help in strengt but not in weight.

So there is no point in using thinner the plate then. Thanks for the information.
I am already cutting down around 500gr by using hollow 16mm shafts and I had hoped to save around the same weight using a thinner plate than the stock one.

What is it you intend to achieve by reducing weight?

A 6mm plate isnt uniformly 6mm in thickness, it will vary. I would facemill one side, flip it over and facemill the other side, this will ensure a fairly uniform plate. I would keep the thicker plate but would mill out pockets to reduce the weight.

Thickness is what provide stiffness.

There are many alloys of aluminum and their properties vary greatly. 7075 is a great alloy. More expensive than 6061T6. The strength of a mid grade steel.

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Just elaborating on my logic :slight_smile:

If I wanted 6mm thickness I would mill that down from thicker stock. I have done this myself and it work very well with smaller pieces (14x4" for instance) and thickness is much more uniform than in stock form.

I personally prefer more weight as well, heck my current Z-axis, without router, is 7lbs. (DIY’d one)
More weight = less chatter, increased resistance against vibration etc.

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I have mine resting on speaker cabinet spikes on top of hockey pucks :slight_smile:
Regarding weight, I stiffened my gantry by adding roughly 9lbs of EpoxyAggregate (yes, no X-carve for me)
That helped tremendously.


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Well, it is because right now my z axis + stepper motor weights about 11.25 lbs

Actually, I would like to modify the slider to save money and not end up using the thing as a paperweight. I bought the slider for about 90$ and did not pay attention to the weight. From what I read mine is about double the weight of the cnc4newbie.