CNC Router Build For A Friend

[mactec54]

iknowyoudo

The Xaxes rails are 20mm the Y & Z are 15mm, Y & Z linear rails are in machined pockets

As for the spindle this will be one of mine that I build, ER25 size with a tool changer

[iknowyoudo]

Mactec54,

Thanks. Can't wait to see the tool changer.

Eric

[Mp001]

Amazing work, Look forward to seeing some more.

[fastpcuser]

Any updates yet ??

[fastpcuser]

I guess no more pictures

[mactec54]

fastpcuser

Thanks for your interest, more will come, but this will take some time as I have been building other machines as well

[kevincnc]

Very nice work, please post more pictures when you can. I'm curious as to why you decided to move the rails on the z instead of bearings. Do you have any solid models of the final assembly that you could post?

[mactec54]

kevincnc
Thanks for your interest
I'm curious as to why you decided to move the rails on the z instead of bearings

This is not always easy to implement, but the benefit of extra rigidity is worth it, with having the Bearing at a fixed point, there is no change with the Z axes rigidity over its whole travel, Plus you get the added support of the rails on the moving Z axes spindle mounting plate

[notimeforwork]

Very nice workmanship! I'm anxious to see how you attach the carriage to the gantry sides...

[jsheerin]

Actually with this Z setup the stiffness of the machine does change as the Z goes up and down. A constant force applied to the tool will apply a varying load to the bearing blocks as the Z changes its position (and thus moment arm length) leading to different amounts of deflection of the tool tip given a constant stiffness of the linear bearing blocks. This leads to a varying machine stiffness with Z height. However I think in most cases it should be stiffer with this setup than with the bearing blocks moving. With moving bearings, you have a constant overhang of the plate carrying the spindle. With the moving rails, you have that same overhang at max Z extension, but at all other Z extensions the overhang is less, leading to a stiffer assembly.

[mactec54]

jsheerin

Thanks for posting

Actually with this Z setup the stiffness of the machine does change as the Z goes up and down

Yes it does, but if the force measurments that you make are when it is down,( Load/Force= Deflection) & you use those numbers as your max,Before deflection, then it does not change over it's whole travel, you have the same constant load, as it goes up it will be more rigid,as it moves up, but the load/force is unchanged,With testing the moving rails can be up to 60% more rigid,( Built & Tested ) than a Plate & moving bearing type Z axes, the one that is in the photos is 43% stiffer than the normal Zaxes moving bearing type, I have 5 different designs for Gantry type Z axes, A 4 rail Zaxes design I have is by far the best most rigid design, but costs twice as much to build as well

With the moving rails, you have that same overhang at max Z extension

Yes you do, but the assembly in the posts is 43% stiffer,at max extension than the normal Moving bearing Zaxes, enough to make it more than worth while to build

The materials I use for these stressed parts, is also much stronger than the regular 6061 that most use, so are able to get higher loading before there is any deflection

[kevincnc]

I think it depends completely on how stiff your plate with the rails mounted to it is. and how far it hangs down below the bearings. If it's weak (and I'm sure yours will not be) then this setup could be weaker than one with moving bearings. You obviously are doing it right as your testing has shown, but it's possuble that the one you compared it to could have been stiffer also even with moving bearings, right? Do you have a picture of what you compared it to? Sorry to beat this to death but my moving bearing setup is very rigid, and most rigid at the bottom of the travel (picture attached.) I was also trying the keep the spindle as close to the Y-Asis bearings as possible.

Sorry not trying to hijack your thread, I just think it's an important topic. If you want me to delete my picture I'll do that.

Now lets see the rest of it finished!