I purchased a HiTorque Mini Mill from Little Machine Shop. I have always wanted to be able to make my own parts for Robotics and DIY projects. I ordered a DRO kit that includes measurement scales for each of the three axis, X, Y and Z, as well as a digital display. A DRO allows you to move all three axis on the milling machine down to a fraction of inch or a fraction of a millimeter.
I asked Little Machine Shop to send me instructions on how to install the DRO and they sent me a Youtube link of the following video, by Fuzz Overload.
This video gives a good look at the finished install of a DRO, but does go into any detail on what it takes to actually install a DRO on the mini mill.
So I watched the video several times and came up with a set of steps that I used to install my own DRO to my mini mill.
This post goes into actual detail on what I did to install a DRO.
Later in the post I have included three videos that I put together showing my installation of the DRO.
I will break the install down into three sections, The Y axis, the Z axis and the X axis. The Y axis is the most involved as you have to make a mounting bracket for the Y axis scale. The Z axis is the simplest axis to install. The X axis is a bit harder than the Z axis as you have to remove the vertical column and mill head for the milling machine to access the back of the table.
X Axis Install
First let us take a look at the left hand side of the mini mill, at the bottom where the table bolts to the work bench.
Refer to the below image:
When I first received the mini mill I mounted the mill to my work bench with the bolts that were holding the mini mill to the pallet. If you look at the above image there is not much clearance available at the bottom of the table where we want to mount the scale for the Y axis. So I changed out the nut and bolt and replaced it with a cap head bolt and nut. We now have more clearance for the mounting hardware.
On the right side of the Y axis we have our gib adjustment, so we do not want to mount the Y axis scale on the right hand side of the table for the Y axis. So we must mount the scale on the left hand side of the table.
If you look at the base of the table along the Y axis between to two left hand side mounting points, you will notice that the sides of the table are not 90 degrees to the work bench or to the underside of the table where we want to attach the sensor bracket.
So to provide a parallel surface to mount the scale to, we will machine a rectangular piece of bar stock that will be bolted to the side of the lower table, that runs along the Y axis.
When drilling the mounting holes in the milling base I tried to choose hole locations that would give me some what of a level surface, but the final adjustment would be done when mounting the Y axis scale to the rectangular bar, as the scale has vertical adjustment slots built into the the scale.
See below above and below images:
On this rectangular bar we will drill two mounting holes and 4 set screw holes. I used M6 socket head cap bolts to mount the rectangular bar. I had some 1/4″ set screws laying around so I used these in the set screw mounting holes.
I then used a machinist square to level the Y axis scale to the work bench and to the mounting tabs on the base of the milling table.
Once the rectangular bar was installed and leveled, I tapped the scale to the rectangular bar and moved the Y axis the entire length of the Y axis, at the same time I also moved the scale sensor along with the Y axis to try to determine the best location to drill the sensor bracket mounting holes and to make sure that the scale was positioned to move the entire length of the Y axis.
I made sure that there was a slight amount of travel left on the scale so I would not bottom out the scale at each end.
Once I had these locations determined, I marked these locations and drilled holes in the rectangular bar for scale mounting holes.
I then mounted the scale to the rectangular bar mounting holes and setup the dial indicator on the top of the table and proceeded to level the scale until I could maintain travel within .001 of an inch.
Refer to below image:
Once the Y axis was level I tightened the bolts and re-tested the Y axis for level.
Now we can mount the scale sensor to the mill table:
As you can see in the above image, the edge of the table has been moved out of the way so we can get at the base of the Y axis and X axis. When we were doing our trial movement we should have marked a location on the cast iron base where we want to drill our holes for the sensor bracket.
Be very careful, as the Y axis gibs and dove tail is right behind this cast iron base. So we have to drill our holes high enough to miss the dove tail and gibs and also not drill our holes too deep.
In order to layout a test fit for the bracket I worked with thin card stock to fabricate a bracket. This gave me an idea on the final measurements of the bracket and the actual positioning of the bracket.
I then took this template and transferred it to 22 gauge sheet metal and, using, my vice, a hard rubber hammer and a large brass punch I formed the mounting bracket.
In order to raise the bracket high enough to clear the dove tails and gibs, as well as to prevent the bracket from rubbing on the scale I placed two pennies on each side and used this position to mark the locations for the drill holes in the bracket.
I drilled slightly over size holes in the bracket where I wanted to mount the bracket to the mill table. I then used a transfer punch to mark those holes on to the case iron base and center drilled and drilled the tap holes. Cast Iron is soft and taps easier than aluminum. Do not drill too deep.
I used a transfer punch to mark the holes to drill into the cast iron base of the mill table.
In order to mark proper location of the scale sensor holes into the bracket, I took some M5 bolts and ground the heads off of the bolts and ground points onto the bolts. I then screwed these into the sensor mounting holes and mounting the bracket to the cast iron mounting holes and positioning the scale in the correct position, I tapped the bracket onto the sharpened bolts to mark the sensor holes. I then did a test fitting and moved the table to verify the Y axis travel.
One last thing has to be done to the Y axis scale. When you received your scales, you should notice that there is a thin orange plastic slide mounted under the scale sensor. In order to move the sensor along the scale you have to remove two of the four screws.
Leave the plastic slide mounted and do not remove the other two screws until you finish mounting the bracket to the mill and scale. Then you can remove the plastic slide. This allows the scale sensor to move freely and affords some extra freedom of play in the sensor. If you take out the orange slide before you properly align the sensor you could create a situation where the scale sensor will bind and you could break the glass slide or interfere with the proper movement of the sensor.
Z Axis Installation
The Z Axis is the simplest axis to mount. First we must remove the measuring scale from the vertical column. We then can tape the Z Scale to the vertical column. I raised the Z axis to the very top, to give me enough room to position the scale. We also want to remove the small Z axis pointer from the milling head.
Again we want to take our time and position the Z axis scale so we can move the Z axis the entire length while still having complete travel of the Z axis scale sensor. We also need to take note of where we mount the scale sensor to the milling head.
We do not want to drill into the dove tails on the Z axis or drill too far into the the milling head. I called Little Machine Shop and made sure that I was not going to hit anything critical in the mill head. Also as always watch how deep you drill, no more than 1/4″ – 1/2″ on the hole length.
Once the scale and sensor mounting points are set, Transfer punch the scale holes and drill the holes. Mount the scale and align the scale using the dial indicator. We can now make and mount the scale sensor bracket.
Using the transfer punch and M5 screw punches that I made, I drilled the holes in the bracket and then drilled and mounted the scale sensor bracket to the milling head. Perform a travel check on the Z axis. Remember to remove the orange slide from the scale sensor. We can move on the the X axis.
X Axis Installation
The X axis is the next most time consuming axis to install. We have to remove the vertical column and mill head to get access to the rear of the X axis. We have to mount the X axis to the rear of the table and drill and mount the scale sensor in a fixed position on the base of the X axis.
At this stage, you can use all of the above procedures to align and mount the X axis. Drilling the scale mounting holes are not as critical as there are no gibs or dove tails that high up on the table. But you still do not want to drill through the table. I again first tapped the scale to the table and perform a travel check to make sure I will have enough travel on the scale to match the travel of the table. There is a metal bracket that holds the rubber boot that covers the travel of the Y axis. I removed that bracket and used the bolts and washers to mount the boot back.
There is not a lot of room to mount the scale sensor to the base of the X axis, so you must be very careful where you drill you bracket mounting holes. You want to make sure you have enough clearance to miss drilling through the bottom of the X axis cast iron base.
Drill and mount your scale. Use the dial indicator to level the scale. Mark and drill your sensor bracket holes and holes for the base mounting location. Test install the bracket and then transfer punch the holes in the bracket to the case iron base. Drill and tap your cast iron tap holes.
Mount the bracket and perform a travel check.
Reinstall the vertical column and milling head. Once you are done you will have to tram the mill again.
Mounting the Display
My installation kit came with a display bracket, a display arm and of course the display.
I marked and drilled display bracket locations as close to eye level as I could. I mounted the display and zip tied the cables.
I then turned on the display and performed travel tests on all axes.
I put together some YouTube videos of the installation that goes over the procedures documented here.