[mungee]

Hello everyone!

This is my first post as well as my first build. I'm looking forward to getting this machine started and hoping that all of you can help point me in the right direction.

I'm in the planning stages of building a 4' x 8' cnc router made (almost) completely from steel. I've been reading threads here for about a month now, and I've decided on a design that borrows from several different builds I've read about. Here is a mock up of what the machine is gong to look like. I was going to include the .skp file, but I can't seem to get it to upload. I'll upload it to a file sharing site and include a link later.



All the steel is going to be 0.250 wall including the riser plates and braces. The x-axis rails are going to be 2" x 3" with a 0.250" x 3" plate as the rail; the cross pieces, legs and supports will be 2" x 2"; the y-axis will 3" x 4" with a 0.250" x 5" plate as the rail; and the z-axis with be 1530 with a 0.250" x 4" plate as the rail. The table bed and the gantry are going to be welded, and the legs and supports will bolt on.

I'm sure that most of you realize by the design that this is an R&P based router and I plan on using mostly "cncrouterparts" components. I'm going to opt for the nema 34 motors because of the weight of the gantry and this machine is going to be used a lot.

I've done deflection calculations and I think the design is good but I'm interested in anyone's opinion. As soon as I take possession (Oct 1) of my new unit, I'll be getting started on the build.

Please let me know what you think.

Thanks,

Mungee.

[RossMosh]

I'd suggest adding 15 series extrusion for your X axis. It's going to save you a ton of time and only cost you probably another $200-300.

As for the frame work, I'd add horizontal bracing to keep everything square. I also see using 8 legs as being a pain to level everything out.

[PaulRowntree]

I would agree : 8 is a lot of leg. If you go with 6 (with adjustable feet) and make the angled braces longer (still at 45 degrees), you should be able to get the X beams supported every 16" or so, which should be plenty strong.

How long are the X-bearing carriages? Longer is better for resisting twist about the three axes, especially on a big machine. Try to put the offset weight of the router+Z carriage near the middle of the X carriages for stability.

[mungee]

I'd suggest adding 15 series extrusion for your X axis. It's going to save you a ton of time and only cost you probably another $200-300.

Are you referring to attaching the 1/4" flat bar to the tubing? It's going to be welded. I plan to have the tubing machined at my brothers shop before welding up the table bed. This will allow for everything to be square and level. I want the bed as high as possible to allow for easy material handling.

As for the frame work, I'd add horizontal bracing to keep everything square. I also see using 8 legs as being a pain to level everything out.

I knew I was forgetting something in the model. There were suppose to be 4 horizontal braces in the corners the same size as the leg braces. I'm not sure leveling will be that big of a deal. Are you speaking from experience? My first model was 6 legs but the x was 2" x 4" and the bed was 2" x 3". I thought it was overkill and settled on this design.

[mungee]

I would agree : 8 is a lot of leg. If you go with 6 (with adjustable feet) and make the angled braces longer (still at 45 degrees), you should be able to get the X beams supported every 16" or so, which should be plenty strong.

If the bottom of the legs aren't secured, won't they tend move outward when the weight of the gantry is in the middle of the span? I know it wouldn't be much, but I'm not sure what tolerances I should be shooting for.

How long are the X-bearing carriages? Longer is better for resisting twist about the three axes, especially on a big machine. Try to put the offset weight of the router+Z carriage near the middle of the X carriages for stability.

The x carriages are 8.5". That's a great point about moving the gantry back on the carriages. I didn't think about the weight of the router/z carriage cantilevered over the front of the x carriages.

[PaulRowntree]

If the bottom of the legs aren't secured, won't they tend move outward when the weight of the gantry is in the middle of the span? I know it wouldn't be much, but I'm not sure what tolerances I should be shooting for.

CarveOne did a terrific build with the metal bolted down; his thread might discuss the levelling process in that case. I would say adjustable feet are required if not bolted down; I know that my floor and my construction skills are less precise than my table! I can't imagine the legs spreading from weight, but if you wanted to be certain, you could put a simple metal tube near the floor, on all sides of the frame. They may rack during use, regardless of how many legs you have. Diagonal braces would prevent that, which is why I think bringing your braces down to evenly divide the top beam would be a good idea.

For my Mk2 I am considering a 2x6 channel on the X beams, supported on the corners of the 4x4 table by 2x4 channel on feet, then bracing to divide the 4' span of the X beam into 3 equal lengths.

[CarveOne]

I probably showed photos of the adjustable feet but didn't go into any detail about how everything was leveled. Four legs on each side wasn't much to be concerned about. The 1/4" x 4" x 12' rail mounted on edge vertically was plenty stiff but did require a little bit of tweaking between the two middle legs. The feet are just 1/2" bolts with a jam nut that are screwed into a 1/4" thick steel plate that is welded to the bottom end of the legs.

The rough procedure was to use a 48" carpenter's level sitting on the tabletop to level the table in the X and y planes using the four corner feet. During this adjustment I had the four middle feet off the floor a little. I then screwed the four middle feet to the floor with just enough pressure to support the middle of the machine from moving. All jam nuts were then tightened. One side had a small sag that was adjusted out using the two middle feet. This required an 11' long piece of 3/8" 2" aluminum bar stock that I know is straight. I flip it over to check that both edges of the bar stock show no gap. You can do this with sewing thread or fishing line, but fishing line will sag quicker than sewing thread.

When that was done I placed the level on the X rails (12' axis) one at a time and made the X rails level. The gantry rail was already very close to parallel to the table surface, so I surface planed the table top into parallelism with the gantry rail. (Y axis)

The only recommendation I have for your design is to tie the legs together 4" or so off the floor and turn it into a storage shelf for sheet materials. I have nine sheets of OSB, three sheets of MDF, and some cut-offs of MDF on my lower shelf that help add mass to the machine and the sheets stay flat until needed for projects.

CarveOne

[mungee]

The only recommendation I have for your design is to tie the legs together 4" or so off the floor and turn it into a storage shelf for sheet materials. I have nine sheets of OSB, three sheets of MDF, and some cut-offs of MDF on my lower shelf that help add mass to the machine and the sheets stay flat until needed for projects.

CarveOne

The way the shop is going to be laid out, I won't have room at the ends of the table to get a full 4' x 8' sheet out. I'm going to have a rack to store sheet stock anyways. This did get me thinking about the mass of the machine and potentially how much it will move. Since it's going to stay put and not be moved around I've decided to bolt it to the floor. I've designed a mounting bracket which will allow for the table to be leveled and still bolt to the leg and to the floor.







The legs will be drilled and tapped and the brackets bolted to them once the table is leveled with the levelers and the bottom of the bracket is flush with the floor. I'll use 'hilti' bolts to fasten the brackets to the floor.

The slots on the actual brackets will be longer than what you see here. I was too lazy to change them once I realized they weren't long enough.

I've made the recommended changes to the bracing of the table, as you can see in the last image. I've also changed the gantry. Thanks Ross and Paul.



For anyone that's interested, here are the .skp files:

floor bracket.skp.zip

gantry.skp.zip

Table with floor mounts.skp.zip

Mungee.

[CarveOne]

Those brackets should work fine. If you don't want to drill holes in the concrete, you can use epoxy leveling compound to glue the brackets to the concrete. After the machine is leveled, put the epoxy around the brackets and over the metal enough to lock just the bracket to the concrete. The epoxy compound can always be ground flush with the floor if you ever want to remove it.

Even if the suggested shelf is not full sheet size, or removable, it can still be useful for storage of other things like smaller scraps of material and "stuff" that needs a place to reside off the floor. Adding a piece of angle iron on the inside of each long side of the machine (weld or bolt-on) will let you add 2x4 lumber cross pieces and a sheet of something cheap like 7/16" OSB for the shelf over the cross pieces. If you don't do this now, you can always add it later when you need some storage space.

CarveOne

[ahren]

Cool build! The diagonal bracing you have should be really helpful at reducing vibration from rapid gantry moves. Especially with Nema 34's, a lot of mass gets moving real quickly, so stiff legs are key.

Let me know when you're looking at electronics -- we're trying to clear out some inventory of our pre-wired Nema 34 systems, so I can probably cut you a deal on one.

Best regards,

Ahren
CNCRouterParts

[mungee]

Cool build! The diagonal bracing you have should be really helpful at reducing vibration from rapid gantry moves. Especially with Nema 34's, a lot of mass gets moving real quickly, so stiff legs are key.

Let me know when you're looking at electronics -- we're trying to clear out some inventory of our pre-wired Nema 34 systems, so I can probably cut you a deal on one.

Thanks Ahren! I think I might take you up on that offer. I was going to do the wiring myself but this will get me up and running quicker. I take possession of my unit at the end of next week. I'll be putting in my order the following week.

Mungee.