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  #1  
Old Wed 20 June 2018, 16:35
ayetti
Just call me: Alex
 
SLO california
United States of America
Alternative idea for the machine base

Hello, new to the forum, super excited about mechmates, just beginning to plan a build in California. I had an alternative idea for the machine base and wanted to try and get some feedback. I am thinking of building 2 parallel walls out of masonry block and setting the rails on top of that.

I am also considering the idea of skipping the steel rails altogether since the masonry wall will run continuously for the length of the machine. I thought maybe I could come up with some kind of anchoring solution as well as bedding them in epoxy.

For my particular application (dirt floor in a pole barn) this is an attractive solution. No matter what I would have had to pour a slab to set the machine on.

Thanks in advance for any advice, excited about the forum, and the machines.
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  #2  
Old Fri 22 June 2018, 08:58
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
So, I think you can check off the "heavy" and "level" checkboxes. That leaves a few more concerns in my mind.

The base doesn't just have to support the rails and the table; it has to provide stiffness between them for lateral cutting forces, and that involves a lot of vibration.

So your masonry solution needs to provide that stiffness. If you keep the steel beams ( rail isn't the issue here ), you have to prevent them from tipping or racking under the cutting forces - that's what the cross bracing in the original base does. If you don't keep them, you have to find a substitute that tightly couples the table and whatever you use for linear motion - V rails and wheels, linear bearing, etc.

If you conceptualize the machine from the end, there is a box made up of the table, the beams, and the gantry rolling on top. That box needs to be stiff in all directions.

I'm not in any form a masonry specialist, but I would expect you would need a lot of reinforcement in your upper blocks - fully filled, deep epoxy mountings for both table and rails. If you use beams, I'd be inclined to weld vertical legs that got fully encased in filled blocks beneath the beams in 3 or more places. Somebody that's better than me will have to address whether vibration can be handled without destroying the walls over time.

Finally, I'll note that you should think hard about how you're going to access the middle of the table. Due to limited space in my shop I load / unload over the rail, have limited access at the ends and none on the far side. I routinely stand on the frame, which would not be possible with a block wall.

It's an interesting idea.
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  #3  
Old Fri 22 June 2018, 15:43
ayetti
Just call me: Alex
 
SLO california
United States of America
Quote:
Originally Posted by bradm View Post
So, I think you can check off the "heavy" and "level" checkboxes. That leaves a few more concerns in my mind.

The base doesn't just have to support the rails and the table; it has to provide stiffness between them for lateral cutting forces, and that involves a lot of vibration.

So your masonry solution needs to provide that stiffness. If you keep the steel beams ( rail isn't the issue here ), you have to prevent them from tipping or racking under the cutting forces - that's what the cross bracing in the original base does. If you don't keep them, you have to find a substitute that tightly couples the table and whatever you use for linear motion - V rails and wheels, linear bearing, etc.

If you conceptualize the machine from the end, there is a box made up of the table, the beams, and the gantry rolling on top. That box needs to be stiff in all directions.

I'm not in any form a masonry specialist, but I would expect you would need a lot of reinforcement in your upper blocks - fully filled, deep epoxy mountings for both table and rails. If you use beams, I'd be inclined to weld vertical legs that got fully encased in filled blocks beneath the beams in 3 or more places. Somebody that's better than me will have to address whether vibration can be handled without destroying the walls over time.

Finally, I'll note that you should think hard about how you're going to access the middle of the table. Due to limited space in my shop I load / unload over the rail, have limited access at the ends and none on the far side. I routinely stand on the frame, which would not be possible with a block wall.

It's an interesting idea.
Thank you for the thoughtful response! I very much appreciate you taking the time. I will definitely start thinking about ways to correct the racking forces. Coming from a housing/construction background i find myself drawn to some less traditional materials.

I think on a lot of levels the masonry is a good way to go for me. I could also build walls on all 4 sides and leave window type openings in the walls. That should allow me access inside if the need should arise. I can definitely use #5 bar and grout every cell. The rebar reinforcement could turn the corners and I assume eliminate some of the racking stress.

As far as reaching the machine goes, Im a pretty big fella (6'5'') so I can probably live with reaching. Both of my partners are little guys so i might want to leave some strategic windows in the walls for them to get through or stand on should they have problems accessing anything.

This first machine im hoping to use like a traditional cnc router, but my real plan is to try and use it as a proof of concept for bringing CNC into my contracting day jobs. My ultimate goal is to try and design a house in 3d including all mechanical systems, pull the design apart and laser etch onto every board, cut marks, layout marks, penetrations for plumbing, electrical heating, plus detailed written information for the trades. I see a lot of waste and a lot of confusion everyday and it seems to me that there is room for this in my area.

In a perfect world I would LOVE to have the spindle perform the tooling on the boards, I would have no problem building multiple machines if it worked for me.
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