Proxxon KT 150 Digital Read Out Modification

The Proxxon KT150 is a nice cross table. Well build and well used. The only problem is the fact that you need to count the numbers of turns you make plus the issue that there is some backlash. Backlash means that you turn the x or y wheel but the table does not respond immediately. This is due to the screwthread and the guidance for this screw thread. The backlash makes it difficult to count the number of turns and in that respect the distance of travel. Backlash is not completely avoidable, but if you add a digital read-out to the table you just can read the actual travel of the cross table. Completely taking out this backlash effect.

Basically it is adding two DRO’s (digital read out) to the X and Y axe. A DRO has the same construction as a digital venier or calliper. One part moves relative to the fixed read out. Either part can be fixed or move, as long as one moves relative to the other part.

This construction contains two 150mm DRO’s with external read-out, some aluminium L extrusion 3mm wall thickness, some M3 and M4 screws. As you probably will own a cross table you probably know how to drill holes and tap screwthread.

I wanted to minimise the construction on the outside. For the Y movement you will only be able to mount it on the left side of the cross table. The read-out box is fixed on top of the housing for the wheel/screwthread with two M3 screws and a bracket. The slider is connected to the Y movement of the table and moves through the read-out unit. One aluminium L bracket is needed to fix the slider to the cross table. I covered the construction with a 25mm x 50 mm L shaped aluminium extrusion fixed to the cross table to protect the construction.

For the X-axe many of the websites create a complicated bracket construction at the front of the cross table. I did not like that construction so I decided to take the cross table apart and looked if I could build in the reader on the inside. Remarkably this is possible. The reader is fixed onto the moving X table. The slider is fixed on the static bottom plate. In order to give room for the slider you need to mill around 1mm from the bottom plate. The slider will stick out on the left and right side and you need to mill some material from the table to facilitate this. Fairly easy to determine once you have fixed the read out unit with a bracket. I mounted the slider on the left with an L bracket. This I need to change into a G shaped bracket as the read-out housing is now obstructed to move the last 15 mm to the right due to current bracket.

As these DRO’s have external read-out units I also decided to construct a box for the two units with external power supply to avoid battery changes. For this I added an existing power supply (5V / 1000mA) and with a buck pcba created an outlet voltage of 3V. Connected the DRO’s to the power supply unit: no batteries needed anymore.

I also decided that I wanted to be able to connect / disconnect the Dro from the box by creating two input mini female USB at the back of the box. For this I purchased two mini USB extension cables. Thought that was easy but encountered a problem. The cable configuration as used for the DRO’s is not following the USB protocol: used pins: 1,2,3,5. Instead the DRO units uses pins 1,2,3,4. Meaning the extension cable doesn’t work. To resolve this you can buy two female mini USB ports for PCBA’s. Cut off the female USB port and solder the wires Red to pin 1, White to pin 2, Green to pin 3, Black to pin 4. But on the male plug of your extension cable going into the display unit the Black wire is still connected to pin 5. To resolve this I opened the Dro display units and connected pin 5 (unused) to pin 4. This part is not easy as the distances between the pins is tiny. If you want to avoid this you can of course use the existing DRO mini USB and connect it directly to the read out units. It works perfectly okay. The DRo’s are very reliable and work great.

The Z-axe I used a DRO with fixed read out. I do not need to constantly move the depth during milling so this solution work well, but of course you could add another DRO unit with external read out.

Last thing I did was adding some light. I bought a set of ”angel eyes”. These round LED have Chip On Board, making it very effective and do not produce heat. The 60mm dia fits precisely under the Proxxon Mill stand BFB2000. The Angel eyes need 12V to drive and do create a blast of light. Perfect.

Attached the box with the read out units to the mill stand with 2020 all extrusion profile and two hinges. Used a mini trip head to fix the read out box to the arm.

All parts can be purchased from known websites. These DRO units are remarkably precise, reliable and you will be able to get repeatable milling results. If you want more information please contact me and I will try to answer your question ASAP.

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