32 mm Pipe Build?

Mostly Printed CNC - MPCNC Advice
1

Kia’ora from New Zealand,

We have a AS/NZ Standard of pipe in New Zealand that’s 32mm so you can find it quite cheap.

Would using a a larger steel 32 mm tube increase the rigidity of the CNC? vs a 25mm tube.

I understand there is no CAD models for 32 mm, any of those in the pipe line?

 

Cheers

 

2

I haven’t started my build yet but I did see something like this from the UK. All in all, have the printed parts changed to fit 32mm or buy the smaller size online. I think the thicker wall is where you gain rigidness from, not the larger pipe size. Large pipe can have the same thickness as smaller pipe. I was thinking a tube with cement inside. Welding a seam would cause a bend in the pipe from heat stress. I hope you can get it figured out. Printed parts change would be my choice if you can print. Otherwise, go with buying the correct pipe and save yourself a lot of stress and headaches. Mike

3

Hey Mike,

Thanks, Yeah ill keep my ear to the ground to see if I can get my hands on some smaller diameter Tube (25mm).

 

I’ll also play with the scaling of the parts to fit the 32mm tube, however i know this will cause some issues in the geometrys with the bearings and possibly other parts, oh well time will tell…

Cheers,
Pouakai

4

Kia ora! Where are you in New Zealand? I know a couple of places around Christchurch you can source tube, I ended up using just steel 1"tube and it’s been fine, pretty cheap too…

5

Haere Mai!

Thanks for the reply, that’s epic I’ll pm you to get the details, unless they have an online store you can link?

Cheers

6

Hey mate,

Couldn’t work out how to PM on this forum?

If you don’t mind shooting me a email to: contact at pouakai.co.nz

that would be cool!

Thanks

7

Stiffness is (almost exclusively) the result of tubing diameter.

By way of a somewhat ridiculous example, compare the following two pipes, both 2m long:

  • 25mm diameter tube with 6mm thick walls.
  • 100mm diameter tube with 1.15mm thick walls.
Both pipes have the same cross-sectional area and therefore the same weight per meter. Which one will be stiffer?

An online calculator estimates that with at 10kg weight suspended in the middle the first pipe would deflect nearly 70cm and the second pipe less than 3mm.

That example is a bit extreme (very thin walled tubing is prone to buckling when loaded), but it does demonstrate that diameter trumps wall thickness when it comes to structural stiffness.

 

8

You are right that stiffness of the tubes is much more strongly influenced by diameter than wall thickness, but the overall system also has belts and plastic parts.

At the recommended sizes, the tubes are not the biggest contributor to deflection. I think if you were to compare normal with large size tubes you would be disappointed with the improvement in stiffness if the system.

9

The point about tube stiffness is that while most of the other sources of flex you mention are independent of machine size or cutter position, flex in the tubes matters most in the middle of the X-axis travel and has a larger effect the longer the X-axis is made. Using stiffer tubes isn’t going to increase the machine’s stiffness along the edges of the work area, but it will make the machine more consistent across the X-axis, and raise the stiffness where it is most lacking.

In addition to which, several non-US countries have tubing standards that make 32mm SS tube readily available at the same price as, or cheaper than, 25mm. For both of these reasons I’d still welcome a 32mm Lowrider.