Clausing 8520 DRO Install



I have been wanting to add a DRO to my Clausing for a while. As the bearings in the cross feed table needed to be replaced, I thought it would be a good time to install the DRO while I had it taken down. Bearings were ordered from Enco, and had been sitting in the shop for about a month or so waiting to be installed.

After doing some research on selecting a DRO I finally decided on the mTech TDS 3i from I measured the mill and choose the standard JCXE scales This is what was ordered for the mill.

  • TDS 3 / TECH-3I / MEA-3 (3 Axis LCD DRO)
  • Scale Travel length -JCXE5:170mm, 6.7inch (Physical length:312mm, 12.3inch)
  • Scale Travel length -JCXE5:320mm, 12.6inch (Physical length:462mm, 18.2inch)
  • Scale Travel length -JCXE5:420mm, 16.5inch (Physical length:562mm, 22.1inch)

Total with Fedex international shipping was $510.00

An interesting note, 3 moths after receiving my DRO I received a bill from FedEx for $17.50 which was the customs/import fee’s for the package. After talking with FedEx they apparently pay these fees to clear the package and not hold it up and then bill you for them at a later date.

My order was placed on June 10th 2011, The following day I received a conformation e-mail from Scott confirming my delivery address and the scale lengths that I chose. I sent payment via paypal and received my tracking number the following day.

My order arrived on Friday June 17th at my office. As my luck would go I was not at the office that day. I had a co-worker who I would be seeing later that night pick up my package for me so I could look at it for the weekend. It came in two well packaged boxes one containing the display, and another containing the DRO.

I assembled the DRO on the work bench and tried everything out. The scale encoders are mounted to the scales with two small plastic holders to secure them during shipping and installation. I temporarily removed them to test the scales. Everything seemed to be in working order. I took some measurements and started planing the install on the mill. Included with the DRO are mounting brackets of different sizes and shapes. It turns out I did not use them on my install, as I chose to mill my own mounting brackets.

The shaft to raise and lower the knee on my mill has been bent sense I have owned it. I thought that I would straighten it out while I had the mill apart. That did not work out too well. It was deformed around the bearings, and my attempts to straighten it while in the knee were not very successful. I would have to cut it in two to remove it. First order of business was to make a new shaft. Here is a tip if you ever run into a situation like this. Make two marks on the shaft on each side of your cut at a known distance apart. I had to guess at the shaft length when I made the replacement as I did not know how long the shaft was and the cut was not clean. If I would have made those marks I could determine the length of the shaft much more accurately, and would not have been measuring all the distance of the bearing surfaces. The Bronze bushing that goes in the knee was also in bad shape, so it was replaced with one I turned up on the lathe. Some how I have misplaced the photos of all of this work, when I find them I will upload them here.

The next order of business was to drill some mounting holes in the knee to mount the DRO to. I did this on the drill press. There were already two taped holes on the knee that I could have used, but I chose to drill 4 more towards the bottom for my installation.

I also drilled some extra holes on the opposite side of the knee for the later addition of a power feed to raise and lower the knee.

This is the only photo that I have of this operation. The knee was mounted to the drill press, and all holes were taped 10-32. This is the power feed holes being drilled.

Note: Something you need to think about before starting something like this. How are you going to get the work done with out your mill. I happen to have a large floor mounted drill press, and a Mini-Mill in the shop, but if you only have 1 mill, you will need to plan carefully so that you can mill as many of the pieces as you can before disassembling the mill to install the DRO. I was planning on selling the mini-mill but after using it so much while this mill was tore down I have decided to keep it.


Machining the small T-Nuts

To mount the X scale on the front of the table I decided to use the existing t-slots. The only other option would be to mount the scale on the rear, but I would have lost almost an inch of movement in the X direction. This was not a good option for me. The T-Slot is used mostly for mechanical stops which I figure I can live with out once the DRO is installed, as I can use the display for my repeatability. I made some small T-Nuts to fit the front of the table. They are taped 10-32 this allows the bolt to clear the mounting holes in the scales.


Here I am test fitting the t-nuts I made for the front table slots.


Finished t-nuts and the spacers to bring the scale out away from the table.


On the front of the table there is a oiler port built into the original table stop. I made a replacement and used an oiler port that I had on hand from There is also a small L bracket that goes under the oiler the covers up part of the metal shield that keeps chips off the feed screw which I reused. I did not duplicate the roll pins that are in the original. They are not needed as it is no longer used as a table stop.


There were two 1/2-2 holes on the front of the knee already. I fabricated a small mount for the scale encoder to fit using those two holes. I chose to mount the encoder to the side of the table instead of the center. This allows access to the oil port, but as a result I loose about 2 inches of my X axis. I need to install a mechanical stop to keep from running the table too far and hitting the encoder. I plan on adding a power feed to the mill shortly and will be installing auto electrical stops so I did not install them at this time.  I have enough room to move the encoder to the right about 1 inch or so if I build a longer bracket which I will probably do at a later date.


While I had the table off I drilled two holes on the bottom of the Y slide. These 10-32 taped holes just clear the gib adjustment screws on the slide. I made an aluminum bracket to mount to the bottom of the slide that just clears the knee. Here you can see the small raised surface on the knee that had two holes already taped. But using it for the Z axis would interfere with the Y access scales. That is why I chose to drill the four holes for the Z axis lower on the knee.


I drilled the two holes in the knee to mount the scale after dry fitting the scale to the mount on the lower side. Small spacers were machined to hold the scales out the correct distance to align the encoder. A short cover will go over this to keep the gib locking lever from hitting the scale, as well as to help keep chips clear.


Here you can see the cover that I added. It does not cover the full length of the scale, as it is attached to the slide and moves with the table. It does keep the gib lever off the scale, and covers the encoder. The open end of the scale is pointed down so there is little possibility of chips getting in the scale. Also you can see the completed Z scale. I mounted a 1 inch thick piece of aluminum to the knee in the four holes that I drilled, then a 3/8 inch thick plate is bolted onto that to reach back along the column that the scale encoder is mounted to. I had a little clearance problem with the Clausing name plate so I chose to remove it. I was using materials I had on hand for all the brackets.


Here you can see all the scales mounted on the mill.



I mounted the bracket to the mill at an angle so that it was a little higher and at a comfortable angle when standing in front of the mill. I need to do something with the excess length of the cables. I have not decided yet if I can just going to coil them up or shorten them. If I shorten them I will have to remove the connectors cut the cables and solder replacement connectors on.


Here is another view that shows the cover installed over the front scale. I had to add a small spacer to the cover to clear the scale. It is a 1/4 x 1/2 inch length of aluminum. The cover is attached to the table and is an exact fit for the table length. Sometime things just work out, but not too often. I need to make a replacement table lock for the front. The Clausing one is not ideal. I need to build one that has a ratcheting handle as there is very little room left.

Here it is from the front. I have not used it much yet, but it does seem to be accurate from the tests that I have done. I will play with this more during the next few weeks. I will update the blog with more info.

The manual is horrible The english translation is very bad. I do not know why companies put all their efforts into nice web pages, marketing and such, and can not spend a day or so and re-write the manual into understandable english. As I figure things out I will take notes and make up a cheat-sheet and will post it here.

One thing I noticed right away is that the calculator function forces you to enter decimal numbers as 0.001 if you do not prefix it with the 0 before hitting the “.” it will interpret the number as 1 inch.

The 4th decimal place on the display when in inch mode is also very distracting. I covered it with the piece of electrical tape.




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