Movable Bed CNC machine 14

The milling spindle and the end mill router bits that I ordered had arrived by post recently.

It was one of the reasons I did not do anything during this time – because I was waiting for them to arrive. With the spindle at hand, I was able to fabricate a holder for it.

I had wanted to use a set of 2″ pipe clamps, but when the spindle arrived, the latter could not fit in. So I decided to fabricate a holder out of a piece of soft wood, using my hole saw, drill press and hand files.

According to the plan, the dimensions of the spindle holder were somewhat restrictive. It must be small enough so as not to take up precious space. It must also be strong and able to withstand dynamic and static forces on the tool and the machine supporting structures. I added the side and end walls for the Z-axis plate in order to make it into a box-shaped structure, which ultimately would result in a strong structure. As usual, working with hand tools only, I needed to saw and file as best as I could. In this case, I screwed and glued the pieces together. I needed to countersink some of the holes because they protruded out, otherwise they would disturb the free movement of the Z-axis.

I found that one particular area in the clamping piece for the milling spindle was far too  small, and could possibly break off if I applied too much pressure when tightening the clamping bolts on the spindle. My solution was to reinforce it by winding a couple of sewing threads around the clamping piece and then embedding them in epoxy resin as a substrate, making it a composite. Although it looked somewhat odd at this time, I could dress it up later for appearances. But for the time being, I left it as it was. Once the resin had set, I simply cut off those threads that were in the way.

My next challenge was to figure out how to clamp the work piece in place. Using T-slotted bed with bolt clamps as in most industrial machines was out of the question as this was way beyond my means. I needed some easier solutions.

My movable Y-axis bed would need to travel across the edges of the motor/lead screw support ends. This meant that it would be almost impossible to have any bolts protruding out at the bottom of the movable bed. So nuts fixed on the table with bolts driving through the bed would be out of the question because the work pieces would not always be of the same thickness all the time. Changing different bolts lengths for different thicknesses of work pieces would be simply crazy. So this idea was ruled out.

Carriage bolts protruding out at the top of the movable bed could be a solution if the former were placed out of the way of the moving milling tool. The limitation was also in the spaces available for the carriage bolts and their clamps, as there were not much space to place the bolts. My first reaction was not to go with this idea, as the thought of having steel bolts sticking out from a moving bed with a high speed rotating cutting tool moving above gave me the shivers.

I saw a seemingly feasible solution on the internet of someone using a pair of wedges to hold the work piece in place, by clamping from the sides. There were also a few commercially available side clamping solutions using eccentric sleeves/bolts. I suppose they would work if the bolts could be secured in place by T-slots already in the bed.

It was worth trying out the idea. Using a piece of hardboard, I drilled a network of holes, fitted in metal shelf pins, cut a set of wedges from the same hardboard and tried clamping the work piece in place. However, the hardboard wedges were too thin – they could not hold the work piece in place. So I made another set of wedges out of thicker wood, and it did work. The work piece stayed in place quite firmly. Yet I was not fully confident that it would stay in place when I run an actual high speed rotating milling tool over it.

Then it dawned on me that this type of clamping arrangement would only work if the work piece was quite thick. It would not work at all if I had a thin piece of material to machine. So I decided that this was not going to be how I would be clamping my work pieces. I would have to find another solution.

Well, since the work piece had already been clamped in place, I took the opportunity to work out how to instruct the machine to go to that exact spot where I wanted the milling tool to run. To stay on the safe side, I substituted a ball-point pen refill of the correct shaft diameter (1/8″ or 3.175 mm) and length and fixed it to the spindle chuck arbor and programmed the software to move accordingly – to touch off the surface of the work piece as the cutting depth –  and ran the program as a plotter.

The plotter worked.

In between the testing, I had to change some settings of the configuration and installed hardware to make the whole assembly work better, like interchanging between X and Y axes, inputting more accurate numbers for the lead screw pitches, velocity, and acceleration of the stepper motors. I also replaced the 9VDC 1A power supply with a 24VDC 13A unit as I needed it to drive the spindle too.

After this, I went back to the drawing board to worked out how to install the carriage bolts on the movable bed with clamping bars.

The lengths of the carriage bolts were cut so that any movement of the Z-axis holder and tool would not be able to touch it. Likewise with the position of the carriage bolts.

The lengths of the clamping arms had to be determined once the position of the carriage bolts were established, so as to give clamping coverage for any work pieces.

With all the above done, I was ready for my first cut.

The result of my first cut was quite satisfactory. I cut it using a 1/8″ straight milling bit. Because of the inherent weakness of the softwood, there were some imperfection in the cut due to tearing at weak points in the grain and joints. (These kind of tearing were also observed when I hand sawed the material) The results were noted as a finding for future tests.