Mounting a DRO to a manual lathe

If you’ve spent any time in a professional machine shop, you may have noticed some older equipment is often times equipped with a small display that reads off a few numbers. At a glance it’s fairly obvious what these devices do, they take the inputs controlled the machine’s handwheels and translate that to a series digital numeric characters. The DRO, or Digital ReadOut, is quite frankly a necessary piece of equipment this day and age for the professional machinist. Not only does such equipment make life easier, it allows for much quicker inputs and calculations that were formerly done on a piece of paper and counting the graduations on the handwheels. Most machinists will be multi-tasking, running a couple of machines at once. The DRO allows you to glance over and see how far you are from your Z 0 so you don’t have a crash. And to the older gentlemen who came to this trade before computers, I salute you. 

DISCLAIMER: Using heavy equipment such as lathes and milling machines can cause injury or even death if the person(s) is not properly trained. This guide from Acsis Systems is designed to help people who ARE trained on such equipment. Power off and lock out/tag out your equipment when installing the DRO system. 

The machine we have for you today is a 1970s Italian engine lathe, with a clutch and the whole shebang. Graziano is the make and Sag 20 is the model. When I started out at the company who owns this machine, after my 2nd day on the job I convinced the owner to let us upgrade the technology standards from the ’40s to the ’80s. We ended up with a DRO called the Ditron D60-V2. The reason this is such a good example for installation; this seems to be one of the most affordable units you can buy that comes in various different lengths. And I am in no way trying to sell this product or promote it as some sort of brand deal. It just works good… (and I didn’t have a choice)

We purchased a 16″ scale for the X axis and a 40” scale for the Z. You want to get scales that are longer than your maximum travel. The best way to do this is jog your carriage all the way towards the gearbox until it hits its limit. Draw a sharpie line on the ways at the left edge of the carriage (gearbox side), near the chip wiper. Now jog all the way to the right. Measure the distance from that same edge of the carriage to your sharpie line with a tape measure. This is your maximum travel. Do the same for the X axis. For a knee mill (Bridgeport style milling machine), you’ll want atleast 36” for the X axis and 16” for the Y axis and little baby 8 incher for the Z assuming you’re mounting this to the quill and not the knee. (I have used a knee-mounted DRO before, pretty useless. mount it to the quill, there are kits out there to do this.) This gives around 4” extra on each axis so you’re not slamming the sensor into the end of the scale housing. But you also don’t want the scales protruding past the ends of the table, so not too long.

I highly recommend this DRO, it’s very accurate and fairly easy to set up for the lathe. It reads in diameter, meaning it halves the input from the scale on the X axis, same goes for your handwheel graduations. One quirk about this display is it reads down to .0004” (as opposed to a nice round .0005”) so sometimes you’ll type in X value 11.0000” and it will come up as 10.9998. Still way better than using the hand dials. We will get to that part later but the instruction manual was fairly easy to figure out. If you’re looking for a top of the line DRO, go with Newall. Sony also makes a nice DRO. I have also used old SWI Trak DRO’s, the old ones at least. Those sensors worked similar to a Trav-A-Dial, as opposed to linear scales. Expensive. Note: Those are the only other modern DROs I’ve used professionally. 

You will absolutely need a basic milling machine to make the brackets. If you don’t, you’re going to have to be very well versed in working with a belt sander and drill press, and making sure certain parts are square and true to the best of your abilities. 

The parts you will need for a similar set up as I have here are as follows: 

-1x DRO Display

-1x DRO mounting arm 

-1x X axis scale

-1x Z axis scale (the longer one) 

-1x Aluminum bar 2 1/2” x 3/8” x 8’ 

-1x Hardware Baggie (included)

-8x 5/16-18 SHCS 

-4x M5 x 20 FHCS

-4x M5 x 25 SHCS (some of the M5 hardware I had received was way too short and I had to buy longer screws, you may or may not need this) 

-a Sharpie 

-A few random scraps of angle iron or angle aluminum to fashion brackets out of

The kit does come with a couple brackets but I deemed them pretty useless right from the start. The likelihood of these being able to perfect fit your weird machine application are slim to none. It’s probably designed to go on a Jet lathe or something modern and cheap. 

Step 1: Mounting Z axis scale

I started with the Z axis, it was a lot easier to install this one, as I really only needed to make one bracket to hold the sensor. Now huge disclaimer, there are hundreds of machine tool brands and thousands of designs. So your application may vary from mine. But at the very least we can compare notes and you can take this information and modify it to fit your needs. 

Firstly, mounting the scale is priority. This is “establishing zero” in a way, to better help you mount the sensor bracket later on. Start by measuring the length of your scale, and take your aluminum bar, and cut your bar 2” longer than the scale.  The extra 2” shouldn’t affect your set up in any way, mainly just gives you some extra real estate if you stripped out a hole or something. Make sure your aluminum bar is straight and true as to not put any unwanted flex when the scale is bolted to the plate. I then drilled and tapped the two holes to allow for the scale to be mounted flush with the bottom of the aluminum bar. These should be M5 threads, double check your hardware included that the SHCS head can fit into the pocket on the scale. You can do this with a regular pistol drill, or if you have a knee mill in the shop, that’s what I used for this. Use a sharpie or a pin punch to mark the locations. The reason the milling machine is better for this is it allows your holes to be accurate on the Y plane. Remember, we need this scale to be perfectly level with the ways of the machine. (This is fine tunable with an indicator at the end of this step). For now, bolt the sensor to the aluminum bar relatively straight. Now you can take this over to your machine and hold it up on the backside to get an idea on where you want to mount it. You probably shouldn’t mount it further than 6 inches or so from the underside of the carriage, reason being a longer distance equals a longer bracket needed, which can flex or even vibrate when the machine is in use. That could affect the performance of the DRO system. In my example, my bracket is 5” long. 

IMPORTANT: The scales must be mounted upside down. This is to prevent coolant and chips from fouling up the scale over time. This makes mounting the sensor a little more challenging but this is the only way. You can see how nasty my example is just after a few months. 

I went with 3/8-16 SHCS (Socket Head Cap Screws) for mounting the aluminum plate to the machine, but I found that this was overkill. You can use any size you want but 5/16-18 (or 8mm) is more than enough to securely fasten the scale to the machine. The trick here is having at least 3 points of contact. Ideally I would have wanted a bolt in the center of the aluminum bar however that just wasn’t possibly with the design of this lathe without adding spacers and stuff to fill in the gap. Two bolts on one end and two on the other end are plenty fine. I’m not a huge fan of 1/4-20 for this.

Once you’ve roughly figured out where to mount the bar, go ahead and accurately drill clearance holes for your 5/16” hardware. I went ahead and milled out slots to allow for better adjustment, this isn’t necessary but highly recommended. Once your holes are drilled or milled in the aluminum, center punch (or transfer punch if you have a set) again taking care to make this as level as possible to the machine. Using a level here is highly recommended, but we’re going off the level reading of the MACHINE not the floor.  Again this is adjustable later on but you want as much positive karma as you can get with this stuff. Do it once, do it right. 

Now I understand drilling and tapping holes into your equipment sounds like a major sin, but in this case it’s the only way for this to work. The parts of the machine are almost always cast iron, non hardened, which is very easy to drill and tap by hand. Be careful when starting the tap as to keep it straight with the hole. Some prior tapping experience is recommended. I believe I drilled 1” deep into the bed and tapped them 3/4” deep. 

IMPORTANT: You must understand the relationship between the overall carriage travel versus where you’ll actually be mounting the scale and sensor mount. Understanding where the sensor will be when the carriage is all the way as far left as it can go, and same with how far to the right it can travel. This is going to take some critical thinking on your part to determine where to mount the scale in order to give enough room on each end for the sensor to fully travel to and fro. If you study the images provided, the scale is mounted more towards the gearbox than the tailstock end. Also note that the sensor is mounted offset to the gearbox side. This is to minimize the amount of cable required to reach the DRO display. You don’t want to run short on slack as the cables aren’t very long. Just remember if you mess up or something isn’t mounted correctly, you can always try again by drilling new holes in your machine. It’s not the end of the world. 

The final part for this step is to simply indicate your scale by means of the 5mm SHCS we tapped earlier. The scales have slots to allow for quite a liberal amount of adjustment. Keep one side tight and just crack the other side loose so it’s adjustable but still snug. Run your carriage back and forth with a magnetic indicator mounted to the carriage. You might need to hire someone to crank the handle for you while you are on the other side observing the indicator. On mine I had to shim one end with a .010” shim that was included in the kit, to get the mounting plane straight. Try and get it dead nuts straight, both height wise and the mounting plane. Take your time and be patient. All these steps are to set you up for success later on. A lot of people most likely have less than ideal accuracy because the scales weren’t mounted good enough. The sensor can’t be dragging on the frame of the scale in any way. It must run free to prevent premature wear and aforementioned inaccuracies. 

Hooray! Your Z axis scale is now mounted. 

Step 2: Z axis sensor bracket mounting

At first it seems like an impossible task. You will be working in two axis here, height  of the bracket and depth to reach the sensor. But don’t worry! It’s quite simple to do this. A good technique although archaic, is to take a piece of cardboard and fold it to get the rough shape of bracket you need. You might be lucky enough to get away with mounting a straight piece of that 2 1/2” aluminum, but more than likely you’ll have to fashion an angle bracket like mine. The cast aluminum brackets included in the kit are a good source of inspiration, and yours may even fit. At least try them out. Mine were way too short on length. 

Here I used a 1/4” thick piece of angle aluminum, and wide enough to be able to mount the sensor too. There is also a spacer I had to make to shim the distance accurately. Two 5/16” tapped holes were drilled into the bottom of the carriage, 3” apart. Again, I just went about 1” deep with the holes, and 3/4” deep with the tap. Refer to the diagram in the previous step, it’s hard for me to articulate exactly how to do this, but if you can mount stuff with C clamps prior to drilling, you can travel the bracket back and forth on the carriage to confirm that it isn’t going past the ends of the sensor. You will also have to add the 5/16 clearance holes, and I had to mill out some of the radius with a long endmill to allow for the socket heads to mount nice and flat.

Now that you have your holes set for the bracket, it’s time to start working on mounting the actual sensor. These are also 5mm threads, and this is why I recommend possibly needing longer hardware than the stuff they provided. You won’t find these at Home Depot. I ordered mine from McMaster Carr. (Great company)

The spacer I mentioned previously is my control point to set the distance between the sensor and the bracket. I started with finding the distance of the holes on the sensor (about 60mm, or 2.362”) and simply used another small section of our 2.5” aluminum bar, squared it up on the mill to about 3.160” long (the length of the sensor) and maybe .500” in width. The thickness was still the virgin 3/8” to start. I drilled the clearance holes on the milling machine as well. (A 13/64 drill bit at ø .203” gives you about .010” of clearance)

In this case, the spacer was way too thick. I kept milling it down until I reached a thickness that kept the sensor completely in the middle of the scale housing, and keeping it relatively vertical. (In this pic, it’s probably about .290″ thk for reference) These scales do allow for *some* play or flex, but not much is really recommended. The sensor should rest roughly in its natural spot. Take your time with this part so you don’t have to go and add a bunch of washers and shims later on. The washer method I don’t like because, while the hardware pack comes with a bunch of washers that don’t even fit the 5mm that may suggest doing washers, you risk not having the sensor perfectly flat and true. But if you feel you must do it this way, go for it. You might need to buy more washers. 

Once you have established your spacer thickness, now it’s time to set the height. This is fairly easy, since the angle bracket we made is mounted securely, and our spacer is finished, you can slide the spacer freely around in there since no 5mm bolts are attached yet. We are going to be milling slots that are also .203” wide, and to allow us to fine tune the height, also to level the sensor. Again, 60mm apart. Take the angle bracket off the lathe and head back over to the mill. Mill two slots approximately in the location of the height of the sensor. (Another Sharpie moment). The slots don’t need to be any longer than 1/2” or so. I also spot faced the bracket where the slots are to ensure the bolts are mating directly to a perpendicular surface. I should have put washers in there to prevent the slots from getting mushroomed, but oh well. Like I said, my washers didn’t fit (they were like 3mm really tiny). 

Alas! You should be able to put all this stuff together for real now! See the picture below to see how the sensor is about 1/32” from the scale housing, so it’s not rubbing but it’s also not stretching the magnetic scale out of its housing. I pretty much just eyeballed it until both ends of the sensor were evenly spaced. 

Step 3: Mounting the X axis scale

We are going to be repeating the fundamentals we learned in steps 1 and 2. We can gloss over a lot of details here, as all the same principles apply. Let’s first discuss the mounting position of the scale and sensor. It is mounted on the right side of the carriage, specifically joining the cross slide and the saddle together. The scale being mounted to the saddle, and the sensor to the cross slide. It is mounted on the right side, or the tailstock side, simply because this keeps the system out of the way of the chuck and the workpiece. If the sensor is mounted to the left side of the carriage, you risk destroying the whole scale and sensor if you were to ever crash the machine. Also it would get very dirty, very quickly. The scale mounted on the side of the tailstock does have one big con, that being you’re going to lose about an inch and a half of tailstock travel when drilling holes on the lathe workpiece. You risk slamming the tailstock into the sensor too, but this can be resolved by installing a bolt in the saddle to act as a stop. (pictured below)

Same deal as before, mounting the scale upside down. I had to make quite the ridiculous bracket to get this to work the way I wanted it to. FHCS (flat head cap screws) were utilized here to allow the tailstock to get as close as it can to the bracket, and also used on the top to not reduce the swing capacity of the lathe. 

First, I cut my remaining aluminum stock to 17” in length, matching the scale length. I did not add an extra inch to each end this time like before. (mainly because I had this down to a science at this point, and wanted it to look clean as this part is visible from the front of the machine) The machine again included nice surfaces to mount to. I mounted the scale really close to the top of the aluminum in an effort to reduce the length and floppiness of my future bracket. All the pieces were made up before I tapped holes in the machine, as I wasn’t sure where it was going to end up. I wanted the top of the bracket to sit a little bit below the cross slide, so in the event a heavy part lands on the carriage, the sensor and everything would be spared (in theory). Every lathe is different, and this lathe is specifically kind of bizarre. It’s got a huge swing for how short it is so the tool post sits really high up and honestly provided ample room for the install. 

The Newall DROs use a really simple scale system, it’s not protected at all, and you don’t have to do this crazy wrap-around like we see here. Their sensors are superbly well made so chips and grime don’t affect the seals at all. This entire bracket is just so we can clear the scale housing without rubbing, while also firmly holding the sensor. (I am not a Newall salesman btw…) 

Once you have your 5mm holes tapped in the aluminum, you can then mount the scale to the aluminum temporarily like before. Now you can loosely figure out the position to mount the scale, giving about 1/2” height clearance from the top of the scale to the top of the saddle. I pushed the scale to the rear as far as I could, and keeping in mind where to mount the bracket. Grab your sharpie and draw a couple of ticks approximately containing the location of the bracket. You should be able to travel the cross slide all the way in and out to its limits within the constraints of the scale. In this case, it was fairly smack dab in the middle of the saddle. You may use the pictures as a baseline, however like I said before, all machine models are different and I can’t guarantee this will be 100% correct for your equipment. 

Step 4: Making the bracket for the X axis and finishing up

Next, it’s time to make the primary angle bracket. I used a piece of 3/8” thick angle aluminum, leaving the radius in the corner to retain rigidity of the bracket. If you simply do not have the clearance you may have to machine this radius off. I drilled two 5/16 clearance holes for the SHCS. These holes, like our spacer before, are drilled 60mm apart (2.362”). There’s really no reason to change this dimension, you can make it whatever you want. I chose to keep the same spacing on all the parts just to make things more standardized (or perhaps it’s just my OCD). On the top plane, we want to drill two 5mm clearance holes with the 13/64 drill bit again. Two 5mm FHCS will be installed here, the goal being that they sit flush with the top of the bracket. To achieve this, I used a 90° countersink. All metric hardware takes a 90 degree countersink, whereas SAE (Standard American English) uses 82 degree. It’s quite tricky to calculate how far out this piece needs to stick to clear the whole sensor and have enough space for the vertical piece. I went exactly 3/8 inch extended, which I should have made it .050” longer. When in doubt, make this section way longer than you think. You can always mill it down to length later. As you can see in the vertical piece, I had to mill out a channel so the bracket could clear the scale housing. But with your scale assembly loosely mounted by holding it up to the side of the machine, you should be able to measure approximately the distance needed.

Now that you have this bracket established, you can go ahead and drill and tap the two 5/16 holes that the bracket will be mounted with. Keep in mind to make sure this piece is a little bit below flush to the top plane of the cross slide. I would not recommend drilling more than 1” into the side of the cross slide, double check to make sure this location is not going to interfere with the ways, or any gibs. You may need to make a totally different bracket design if that is the case.

IMPORTANT: Be very cautious when drilling into the side of the cross slide as to not drill too deep and end up accidentally drilling into the X axis ways. Some machines are also equipped with an internal oil reservoir in this location. You have been warned. 

Almost done! Next, we can go drill and tap the four 5/16-18 holes in the side of the saddle. Same deal as the Z axis, try and do the best job you can keeping it level with the [X axis] ways. Once this is complete, now would be a good time to set the indicator back up and once again indicate the outside of the sensor housing to get it running true the long way and also on the mounting plane with those 5mm SHCS. (shim if necessary). 

The final part for this build is the vertical piece attaching the angle bracket to the actual sensor. Woohoo! Home stretch. This part requires two M5 tapped holes to match the previous holes on the angle bracket. Drill and tap them as deep as you’d like, so your flat heads can rest flush when tightened. As for figuring out how long to make this piece, take the part over to your lathe and hold it up as if it were mounted. One final swipe of the Sharpie, mark the length so it ends up flush with the bottom of the sensor. If it’s a little longer, this won’t hurt it any. You just obviously want enough room to add the final two 5mm clearance holes. These holes are also going to be countersunk at 90 degrees, to also achieve a flush finish when the FHSC are fastened into the sensor. I definitely recommend slotting these because you want to be able to fine tune the sensor again, same as the bracket we made for the Z axis. If you just have a drill press and basic shop tools, you can try and wallow out the hole with the drill to make it a little more oblong. You gotta do what you gotta do. In my example, I had to add one washer per screw to get the spacing correct. 

IMPORTANT: Do not try and *brute force* bend the bracket system to take out any angle error causing the sensor to be crooked. This could weaken the integrity of the parts or strip the threads out, as those little 5mm threads are going to be the weak point, versus 3/8 thick aluminum. 

Finally. You did it! If you followed along or atleast adhered to some of the cautionary parts in yellow, you hopefully avoided some of the mistakes I thought would be common. The rest is easy. Mount the DRO arm somewhere secure, somewhere on the top of the machine. My personal preference is above the gearbox, but you may also mount it directly to the carriage if you so desire. This is quite handy on machines that are longer than 80 inches. Be sure your machine can travel to its limits in X and Z before you secure down the DRO in its place. You always want a decent amount of slack for the cables. In the pictures you can kind of see how it looks on my lathe. You will need to configure the X axis to read in diameter. Right out of the box the sensors will straight up report the full distance. I can’t remember exactly how to do it but it was very easy. The instructions are translated quite well as this company is based in China. I was really impressed.

A word of caution when typing inputs on the DRO while the machine is running, loose clothing can get caught in your chuck or spindle. Make a mental effort to be sure your body is nowhere near any moving parts. The front of your shirt or sweater is what I’m talking about; if you lean over the workpiece your belly could get sucked into the lathe. I like to imagine I have an invisible bubble around me, or an orbit, and nothing is allowed in the bubble. It’s a 6th sense you develop over time. Just practice doing inputs with the machine off, you’ll get the hang of it in no time. 

* * *

Mounting, engineering, retrofitting, whatever. Installing a DRO onto an older machine is not an easy task. You’re dealing with so many unknown variables and curveballs that you have to adapt your system to fit your machine. Once it’s complete, you will have a fairly competitive piece of equipment. Get creative with your design too, this example isn’t church by any means.

DISCLAIMER: Using heavy equipment such as lathes and milling machines can cause injury or even death if the person is not properly trained. This guide from Acsis Systems is designed to help people who ARE trained on such equipment. Power off and lock out/tag out your equipment when installing the DRO system.