So I read that there is a couple options here.
I see 23.5mm conduit, and 24.5mm steel.
Is there 23.5mm steel?
Does the inside dimension matter?
Where can I buy piping like this?
The ID doesn’t matter, but the thickness does.
23.5 OD piping. is steel, but cheap steel, and it is the dimension of common electrical conduit in north america sold as a 3/4" size, because it is spec’ed by the ID. It is available at home depot or lowes, in NA.
25.4" OD tubing is spec’ed by the thickness and the width. Because it is usually used to build something. Something like a go kart chassis. It is a common material for metal workers. The SS stuff is more expensive, and DOM is cheaper (apparently) and it is just as strong, maybe stronger. But it is close. You can find it in a local store that supplies metal workers. Not usually at home depot, but Menards apparently has some. This is totally different than 1" Conduit, which is spec’ed by the ID, and is really more like 29mm wide.
so 23.5 Conduit and 23.5 OD are both the same size and will both work for the same 23.5 3D printed parts, but the 23.5 OD is stronger than the 23.5 conduit because it is steel while conduit isnt?
Conduit is steel. I haven’t ever heard of 23.5mm tubing. Just the conduit.
As Jeffe stated, the 3/4" conduit (23.5 OD) is a low grade steel, and will flex more than stainless steel tubing. However, it is much less expensive, easier to cut with a hacksaw or common tubing cutter, and is rigid enough for the suggested size Ryan has designed the Primo for.
I have no personal experience with the 1" OD DOM steel tubing, but others here do. Mild surface rust is a concern depending on your climate, but can be controlled with a thin coat of auto or Johnson’s paste wax.
25.4mm/1" OD Stainless is a great all-around choice, but, based on comments here, is likely to be the most expensive choice. It can be ordered, but shipping seems to vary from $10-$20 or more depending on vendor. If you don’t have a way to cut it, it may be worthwhile to have it custom cut to length by the vendor, and hope they do it right.
In my case (for my still incomplete Primo), I had some 0.049" wall thickness stainless on hand, but needed a few new pieces for the rails. I found DOM at Tractor Supply for $14 for a 3-foot stick. The local Metals Supermarket had 0.065" stainless for $13 for 3 feet, so I went that route. I also bought a Ridgid 35S tubing cutter, specifically made for stainless tubing, but that was another ~$40 (Home Depot or Amazon).
Just paid $83 USD for dom tubing 1" OD .120" thick cut to length to fit a 24"x24"x3.25" MPCNC. However, the length was as much as 1/8" to long on some pieces so I need to figure out how to get it to spec.
Jason,
You have been given some erroneous information in some of the replies.
Let’s talk about some terms people throw around without fully understanding what they mean. When people mention one material is stiffer than another, that’s not the whole story. ALL steel whether it’s high carbon heat treated tool steel, stainless steel or cheap conduit has the same stiffness. In engineering terms this is called the modulus of elasticity or Young’s modulus. This is the slope of the stress/strain curve.
What we, as CNC makers, care about is how much a pipe or tube flexes when a given load is applied. This is a solely a function of the shape of the object and the modulus of elasticity of the material. With that said, as tubing outside diameter increases, the amount of flex for a given applied load decreases. Same thing is true for wall thickness. A CNC will perform best with thicker and larger tubing regardless of what kind of steel is used.
To expand on this discussion, every type of steel has a yield strength and tensile or ultimate strength. These numbers vary wildly for different types of steel. The yield strength is the maximum load a material can withstand before it becomes permanently deformed. Think about a 1/16" thick bar in a vise. If you push it lightly and let go, it springs back to it’s original shape. If you pull on it hard enough you can bend it. This is yielding. If you load the bar even more to where it breaks, this is ultimate strength.
There are other mechanical properties that are important too but they are beyond what I’m going to get into here.
Thanks for the info. I will be cutting plastic of 1/8 inch thickness, so the load shouldnt be insane. I plan to make a 1’x1’ cutting area. I know that means the actual size of the machine needs to be larger. How long do you think I should go on the rails, and do you think I should go with something thicker than 23.5?
The conduit will be fine at that size cutting thin plastic.
I agree that any conduit will be fine for cutting thin plastic. Who knows, maybe after you build the machine, you will start building other stuff with other more difficult materials. It’s easy and relatively cheap to make your final tube selection now instead of 200 hours of printing later.
This is true, or close enough for practical purposes. The “low grade” steel of conduit is not what makes a difference, it’s the smaller diameter and possibly reduced thickness.
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I used a Ridgid brand tubing cutter from my plumbing tools and tightened it gradually to cut stainless tubing easily and precisely. The cut end has a slight flare i removed with a belt sander