Starting my new build of a MPCNC Primo and just looking to get some thoughts on this idea. The only issues I seem to see about the MPCNC is rigidity. I have not tried a MPCNC myself so can not speak towards the validity of this but had this idea.
I was thinking of getting the thinnest possible tubing off speedymetals and epoxying a carbon tube to the inside for rigidity.
1" OD, .930" ID, .035"
A 23.6mm ID so would need 23mm carbon tube
or
1" OD, .870" ID, .065"
A 22.098mm ID so would need 22mm carbon tube possibly? Roughen and sand the inside.
My first post here so take err easy. Is there something that would not work I donât see here?
Why not first try it as designed? You may find it fits your needs. Look thru the âThings Youâve Madeâ section and youâll see some pretty impressive things along with stories of the machines not being modified for added rigidity.
Welcome to the forums, and best of luck with your machine! I suggest spending a little time with DiscoBot to move up the ladder of privilege on the forums, and searching for rigidity improvement topics.
There is a long history here on the forums of folks suggesting theoretical improvements to the rigidity of the tubes on the MPCNC, often from first-time posters like yourself. There has not been nearly as much âhereâs what I did and how much better it made thingsâ data posted. There have been some interesting double-decker approaches folks have shared.
This is very much your machine to do with what you like. Feel free to experiment, but the consensus so far has been there will likely not be a lot of gain for the money and effort expended as compared to using the largest of the defined tubing sizes to get the best rigidity âout of the box.â
The lack of posts on this suggest you might be breaking new ground to use the 611. And unless you have a great source of carbon fiber tubes, CF not being inexpensive, can you buy what youâd need for less than the cost of another router?
I donât know how youâd spec CF tubes but the cloth theyâre made from comes in different weaves, Iâd think for increasing the stiffness of the metal tubes youâd want to look for something with the bulk of the fibers oriented longitudinally.
Yeah after some research it looks like pultruded cf tubes would be best in this application. The are longitudinal. In Canada looks like Composites Canada lists 20mm x 18mm x 1.2m pultruded cf tubes for $30 each. Going to see how much shipping is tomorrow.
Several people running the 611 on the mpcnc. Iâve got one on each of mine. Biggest concern for me is the loss in rigidity from it hanging out farther from the center.
Possible that whatever you gain in rigidity from the tubes, you lose on the tool holder at the z.
According to a quick google search, the modulus of elasticity is about the same between carbon fiber and steel at 200-ish GPa. So adding carbon fiber should be roughly equivalent stiffness-wise to adding the same thickness of steel, but of course it would be much lighter.
Your outcome may be better or it may be worse, but thats what the traditional theory predicts.
The comment on thickness made me do some comparisons and I found the following. I probably would not spend this much on my build but I just thought it was interesting.
According to the speedymetals website 1" .065" wall thickness 48" long tubing weighs 2.6208lbs which seems like the most popular option for the 25.4mm machine and considered the best on the forum for wall thickness vs weight.
3/4 inch Emt 48" long weighs 1.74lbs according to cooperindustries and has an ID of .824"
A solid 19mm pultrusion carbon fiber rod .750" thick weighs 1.2lbs according to acpsales and sells for $63.
So it looks like a peice of 3/4 inch emt with a 19mm thick carbon fiber rod in it would weigh only roughly 300g more than the stainless steel piping not accounting for the epoxy.
How do you get glue to spread evenly from end to end in a 48 inch long pipe with so little clearance? Or does it need to adhere to the pipe the total lenght?
If the tolerances are tight enough I donât think you would even need to glue it. You could just make the pipe and tube extend past the legs and make a end cap.
Well, if your intent is to gain knowledge of unexplored solutions, Good On Ya! I hope youâll share what you learn.
But if your main focus is a well functioning machine, given the cost of CF tube, possibly epoxy, and at this point unknown benefit, will you really be ahead going that route rather than buying another router? Donât forget, even with a stiffness increase?, youâll still be accelerating, decelerating, and pushing more mass around.