Waiting for the other Gantry to drop

When cutting the first side of the gantry I used the "traditional" hold down method of clamps and the like on the edges. That works ok when you have a much larger piece of alloy than the part you are cutting. In this case there isn't much spare in the height axis (left right as shown) and as you can see very little in the x axis (up/down in the below image). My clamping allowed for more vibration on the first cutting than I like so I changed how I went about the second side of the gantry.

For the second gantry, after flipping things in the software so that I was coming in from the other side I drilled out 4 m6 holes and countersank them.

This way the bolts (m6x40) were almost flush with the work piece. These bolts go straight through the plywood and connect with t-slot nuts in the alloy bed of the cnc. So there isn't much ability to use bolts that are too long for this application. Counter sinking the bolts helps on a machine with limited Z travel as using some non stubby drill bits really locks down the amount of free play and clearance you can get. The downside of this work holding is that you are left with 4 m6 holes that don't really need to be in the final product.

In this case it doesn't matter as I can use them and a new plate to mount one or two cameras on the back gantry facing forwards. I have found that the best vantage for CNC viewing is when not in the same room and looking at the video streams.

In future jobs I might move the countersunk bolts to the edge so they are not on the final work piece.

So now all I have to do is free this piece from the waste, tap a bunch of m5 holes, drill and tap 5 holes on 3 sides of the new gantry pieces and I'm getting close to loading it on.

Non self replicating reprap 3d printer

The reprap is designed to be able to "self replicate" to a degree. If a part on a reprap 3d printer breaks then a replacement part can be printed and attached. Parts can evolve as new ideas come along. Having parts crack or weaken on a 3d printer can be undesirable though.

A part on this printer was a mix of acrylic and PLA, both of which were cracked. Not quite what one would hope for as a foot of the y-axis. It is an interesting design with the two driving rods the same length as the alloy channel at the back of the printer.

A design I thought of called for 1/2 inch alloy in order to wrap the existing alloy extrusion with a 3mm cover. The dog bone on the slot is manually added in Fusion 360 so it is larger than needed. The whole thing being a learning exercise for me as to how to create 2.5D parts. The belt tensioning is on a 6mm subassembly that is mounted on the bracket in the right of the image below.

The bracket and subassembly are shown mounted below. Yes, using four M6 bolts to tension a belt is overkill. I would imagine you can stretch the belt to breaking point quite easily with these bolts. The two rods are locked into place using M3 tapped grub screws. The end brackets are bolted to the back extrusion using two M6 bolts.

The z-axis is now supported by a second 10mm alloy custom bracket. This combination makes it much, much harder to wobble the z-axis than the original design using plastic parts.

Printer bracket fix

Similar to many 3d printer designs, many of the parts on this 3d printer are plastic. Where the Z-Axis meets the Y-Axis is held in place by two top brackets (near the gear on the stepper is a bolt to the z alloy extrusion) and the bottom bracket. One flaw here is that there are no bolts to the z-axis on the bottom bracket. It was also cracked in two places so the structural support was low and the x-axis would droop over time. Not so handy.

The plastic is about 12mm thick and smells like a 2.5D job done by a 3d printer 'just because'.  So a quick tinker in Fusion 360 and the 1/2 inch thick flatland part was born. After removing the hold down tabs and flapping the remains away 3 M6 bolt holds were hand drilled. Notice the subtle shift on the inside of the part where the extrusion and stepper motor differ in size.

It was quicker to just do that rather than try to remount and register on the cnc and it might not have even worked with the limited z range of the machine.


The below image only has two of the three bolts in place. With the addition of the new bolt heading into the z axis the rigidity of the machine went right up. The shaft that the z axis is mounted onto goes into the 12mm empty hole in the part.

This does open up the mental thoughts of how many other parts would be better served by not being made out of plastic.