Tubing Recommendations

I’ve done a lot of searching and just want to get clarification.

 

I’ve seen some posts where they recommend 1" Outer diameter with a 0.65" ID for stainless, I’ve also seen others recommend something with a thinner inner diameter, and conversely others stating a thicker wall would be even better, indicating a larger ID would be best.

 

I guess I’m just asking what the latest recommendations are for:

Most affordable?

Most rigid / long lasting?

To start, it’s not 0.65" inside diameter, it’s 0.065" wall thickness. With a fixed outside diameter, a larger inside diameter has thinner walls, which is cheaper and lighter but also weaker.

Thicker will be stiffer but it’s diminishing returns. It’s just one of several parts that can deflect, and beyond a point there is no benefit in stiffer rails but there are downsides. Stiffer tubes are heavier, which can make the machine slower because the maximum acceleration without missing steps is lower. Lower feedrates can in some cases also shorten tool life and perform generally worse.

By the time the whole thing is built, the price of increased wall thickness is not that much higher. To me it seems the 0.065" recommendation is not simply a tradeoff between price and stiffness. It’s where stiffness is not really improving and the additional weight (and cost) are not buying anything.

This balance can also be influenced by the build size. Larger machines incur a stiffness penalty that’s larger than the weight penalty, so thicker tubes could make a difference. Smaller machines are stiffer to start with and thicker tubes might offer nothing but downside in weight and cost.

For the most affordable I wouldn’t go below 0.065" but you could get mild steel (non-stainless) and keep it dry. For extra stiffness you could get stainless with 0.12" wall thickness, and while you might never see the difference, you can sleep well knowing that the rails are not the limiting factor in the overall system stiffness.

 

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What sort of trade off’s would their be with Stianless vs Mild in terms of longevity?

I’m trying to source stainless locally but every place I’ve contacted has an MOQ which I don’t come near meeting. If I need to order online Mild steel seems to be much less.

 

Also thank you for the information on dimensions regarding the tube.

Jamie that was very well said, thank you. I might need to link that somewhere (linked on the parts page, thanks!).

 

The bearings have a crazy high point load on the rails. Stainless is a bit harder and rust resistant, for those reasons I chose Stainless. Usually it is not all that much more, if you want to try it the other way It will work, but stainless is a bit better. That might seem like a bit of a half answer but we have no idea how big your build will be, what you plan on using it for, or your expectations.

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I don’t really have expectations in mind. It will be my first cnc used. That being said the stainless quote I got was around $190 for a 4x5 work area. Trying to keep it cost effective for the wife lol

Try these guys. https://ecommerce.metalsupermarkets.com/Material.aspx?ProductId=STRO304/1065

Yikes. To give you an example, my local metal supplier has 1" 0.65"wall, Stainless-Seamless in 20ft length for around $50. More than enough to do a machine that size. Will Call MOQ of 1 piece (e.g. you must buy the entire 20ft).

 

I think MetalsDepot.com might have some decent pricing last I checked.