This project is a group effort. One of our group wants a big router and is willing to buy the materials. Others are engineers who like to build stuff.

Design and build are going on somewhat in parallel. Probably not the smartest approach, but it gets boring just looking at the computer.

We are frugal (aka cheap), so we are in many cases designing around materials that we have or can get cheap. For example, we got lucky at HGR surplus with the X rails. Two SHS35 rails 3000mm (9'10") long, plus one car on each rail, for $100. Got a couple more cars on ebay. So the X axis is going to be SHS35. Overkill for a router, but the price was right.

I hate frames that twist and flex, so I decided that a truss would be the way to go. We have lots of pipe, including some 2" and 2-1/2" schedule 40. Square tube is easier to mount things to, but very expensive. So we're using the pipe that we already have.

I used the 15-day free trial of Skyciv engineering software to analyze the base. It is going to be very rigid - deflections under 0.001" for forces of 200 lbs or more anywhere on base.

The design is happening in OnShape, which is quickly becoming my favorite 3D software. There are still a lot of loose ends, for example right now the gantry is floating in space, not connected to the X carriages yet. We're probably going to flip around the X carriage angle iron to provide a horizontal surface for the gantry to bolt to.

Attachment 479230

The base consists of a core truss and an outer truss. The core truss is the bottom frame plus the center longitudinal tube that supports the center of the table. It is sufficiently stiff that it can serve as a skeleton for assembly and alignment of the outer truss, which is made up of the tubes that carry the X rails and the diagonals running vertically and horizontally from them to the core truss.

Last weekend we completed the core truss. The base and the top center rail are 2" pipe. The rest of the truss members are 3/4". The base needs to handle mid-span loads if the machine is picked up by forklift or pallet jack, and the center rail has supports for the wooden cutting surface that are between the truss nodes, so both needed to be stiff in bending. 2" is a bit of overkill for the base; the analysis said that 1-1/2" or even 1-1/4" would work. But we had a few pieces of 2" laying around the shop. There are 3/4"-10 coupling nuts welded into the base tubes at the four corners. Currently we have some 4" long 3/4" bolts in there as leveling feet. Might wind up buying the high-class leveling feet with swiveling pads later.
Attachment 479232

Currently we are preparing the tubes (2-1/2" schedule 40 pipe) that carry the X rails. We know that a weldment like this is going to wind up all kinds of crooked. "If you can't make it precise, make it adjustable" is the mantra here. The SHS35 rails are attached to the tubes using mounts that can be tweaked. There are 10 mounts on each side, 320mm (just over 12") apart. Since the rails are so big, we can get away with supporting them at every fourth mounting hole.
Attachment 479234Attachment 479236

The light blue channels are welded to the tubes. The green part is a 5/16" thick "shim" that can be removed and either milled or surface ground thinner to precisely move the rail toward the tube. The darker blue part below the shim is called the "shelf". It too can be removed. Grinding or milling the part that bears on the light blue will raise the rail, while removing material from the outer part that touches the shim and the rail itself will lower the rail. Each shim and shelf has a number stamped on it so they can be removed, machined, and then replaced in the proper location. We're planning to use a taut wire (or kevlar string) along with a precision machinist level as a straightness reference for the first rail. The second rail will be aligned parallel to the first one using a combination of taut wire, precision levels, and a temporary "gantry" beam with a dial indicator on the far end.

This evening I welded the rail mounts to one of the tubes. I hope to have the second tube prepared by this weekend. Not sure if we'll attach the tubes to the core truss this weekend or if that will happen next week. The diagonals supporting the tubes will be 1/2" pipe, but the truss should make it very stiff at the nodes where everything comes together. The 2-1/2" pipe is stiff enough to span between the nodes and support both the linear rails and the wooden cutting surface.

Does anyone have any experience with DIY stress relief of weldments? We're thinking of heating it up evenly as much as possible with a weed burner or two and letting ti cool slowly. That would happen before we get out the taut wire and start adjusting the shims and shelves.

Questions, comments, and suggestions are much appreciated.

Still making decisions about things like the spindle. Considering the pros and cons of air- vs water-cooled.

John