I've created a section view drawing of the Z axis parts in both their current configuration as well as an alternative configuration.  If this site permits .CRV file uploads (a highly recommended feature) then it is attached.  It would need a new bottom piece of the bracket that surrounds the gantry rail.  The front part of that bracket would be replaced by the back of the Z axis bracket, and the router mount would now be attached to a plate that had the bearings mounted on it.  If you have VCarve or Aspire please have a look if you want.  Any feedback appreciated. 

 

4D

Z axis Redesign 4D.crv

Edited July 4, 20178 yr by 4DThinker

One extra advantage of my proposed re-design is one less part to make.  That might make Probotix at least consider if it would be worth their trouble. 

 

4D

I think there is something to like about both configurations.  With the modification it doesn't look like you would be able to get as low with your spindle.  I guess it makes a difference as to what project you are going to make.  They could offer them as options and let the buyer decide which one they like best.

I've added a line to represent where the top of the MDF bed would be on both versions, and it helps see how far down the router mount can get in both versions.  With minor change to the backplate of the router mount both versions go to the same elevation (roughly 1.6" above the MDF).  In the current design the bracket that holds the guide rails has bottomed out on the MDF.  On my version only the router bit would be in contact with the MDF at that lowest extension. 

Z axis Redesign 4D.crv

I went ahead and sent my re-design proposal to Len at Probotix.  I don't expect to hear back from him today or ever, but I'll let all know if I do. 

 

4D 

Good idea 4D.  If things go as I hope they will this year, I"ll probably get another machine as well.  That's my biggest concern -- the depth of the z axis when using a regular bed on the frame.

 

Good thinking!!

That makes things a little clearer and I would rather have your configuration.  Glad you pointed this out.

By adding an outline of the router in place in my drawing I see that you can better take advantage or the Z clearance under the gantry.  In my design now you can lift the bit above the bottom of the gantry when at its highest position.  You can't do that in the current configuration without lowering the rail bracket relative to the bit and reducing your potential cut depth.  So in theory you could have a 3.5" thick 4x4 under the gantry and still be able to cut roughly 2" into the top of it (depending on your bit length).  My design shifts to where you can maximize how much of the 5" of Z travel is usable.  At best the thickest chunk I could cut into the top of right now is about 2.25" thick.  Thicker than that and you'll get warnings from LinuxCNC that your cut will exceed Z clearance.

 

4D   

4D you probably should send drawings of this with router to Probotix along with this explanation so it is quickly understood how the change would improve their machine.   

Len (owner/boss at Probotix) sent me a reply:    "The reason why the design ended up the way it did had a lot to do with machinability of the parts. We designed them such that almost every part had every critical measurement machined in the same operation so that flipping them or moving them to or from fixtures didn't affect the relationship of the critical features to each other."

 

He said early prototype drawings were similar to what I'd proposed.  Through iteration for machinability and mass production it evolved to the current design. 

 

I may give it one more try to revise for simpler machining. It doesn't look like there is a new Z axis to come though. 

 

4D

Darn

Let's see .... new parts could be cut with a CNC machine and then installed.  Of course you would have to find a CNC some where.

His goal was so all the parts could be machined from the top and side without needing to flip them over.   The tall vertical part of my design would need to be flipped over to be able to countersink all the bolt heads. Where I've got it though there is enough clearance to not need to countersink on the center where it attaches to the X axis bracket. Or not need to where it attaches to the top plate.  

 

I may draw up plan views of all 5 parts needed with hole layouts.   When our university opens up again for fall classes I have access to a large Multicam CNC that will cut aluminum plate. I'll use my own Meteor to try out the new parts.  I could cut a prototype set out of 1/2" BB plywood using my own CNC just to mock it up. Might be tempted to use glue and some fancy joinery to connect it all.   I've seen whole CNCs made out of plywood so it might not be bad in use functionally.  Any holes into the edge of it need a cross dowel nut.  Threads into the edge of plywood don't last.   Reminds me of an idea I had to make drop in nuts that perfectly fit a slot you could cut with a CNC.  It surprises me that no one makes such a thing already.  

Len's reply to my latest email:   "Wouldn't it be easier to just replace the gantry uprights with taller ones? Because that is something coming down the pipeline."

 

Taller gantry uprights!

 

I replied to him with warning....  when the Z axis as currently designed gets down in the bottom of its 5" travel there is more moment/twisting force against the bearings.  Our Nebula will vibrate badly when profile cutting in the Y direction in dense hardwoods.  This is with the existing gantry height and Z axis.  

 

4D

Old post, I know.  I just thought I'd add an update that I'm now located in a new fabrication lab where I have easy access to a large CNC that can cut aluminum.  We also have a large plasma CNC. 

 

Our college budget is strapped at the moment, but I can likely convince the lab manager that my Z-axis revision is worth investing in. He is already aware of the weaknesses in the current configuration. We may be able to make parts to assemble at least one for our nebula over the Christmas break between semesters.

 

4D