Dial Indicator

This is one of the best and useful mods I have done on the Mini to date. As stated on the home page I can barely read the markings on the shaft and they are very course markings. I need to be more precise especially for doing counter bores as you can see in the Micro Coil Winder project.

I designed this system based on several methods discussed on the web. (One I did like used a digital linear scale, but they are fairly pricey.) It works very well as built, however the plan is to build a new and better base point device for the shaft instead of the acrylic one shown. Again it was all built from things around the shop...except the dial gauge I picked up at HFT for $10 with a coupon. I did this project in an afternoon in the shop...maybe 3-4 hrs, and built it on the fly from the idea in my head.

Here are the basic components:

1. Dial Gauge
2. 3/4" angle aluminum
3. 4 ea. 10-32 button head machine screws about 5/16" long
4. 2 ea. 10-32 nuts
5. 1/4-28 x 1.5" cut down to about 1.25 (wanted the shank)
6. 1 ea 1/4-28 nut and 1/4" washer
7. 3 ea 1/4" I.D. Delrin bushings parted to fit

Cut the Aluminum angle to match the length of the top of the tail stock (about 4.75"). Then scribe a line .25 in from the end and sides of the angle, center punch and drill the two top holes as clearance for a #10 ( I used a #8 drill for a little play). The two other holes are .25 down from the top of the angle and .25 in from the ends. These two holes are tapped 10-32 using a #21 tap drill. These screws and nuts are to adjust the tension on the 1/4-28 bolt head against the side of the tail stock so it slides smoothly on the rough casting but gives it a rigidity when tightening the nut. I also faced off about 2/3 the thickness of the head of the 1/4-28 bolt, to achieve the desired sliding fit.

The slot is centered on the angle and a clearance width for the shank of the 1/4-28 and is about 2.50" long. This makes it possible to move the dial gauge forward or back and allow for pre-loading the 1" throw of the gauge and be able to move it back, out of the way. Each dial gauge is slightly different; the center of the slot can be located by placing the gauge on top and transferring the center of the mount to the angle. The HFT gauge has a little raised flat around the mount that works well to keep it straight and square to the angle when sliding it. Not having a mill to do the slot meant drilling a bunch of holes along the center line, then used a file and Dremel to clean up and straighten the slot. For a smooth slide, be sure and debur the slot on both sides.

Next was to mark and tap the top of the tail stock by setting the angle with the 1/4-28 and bushings in place. Adjust the side stop screws to get the smooth slide then use a transfer punch to mark the top of the tail stock. Use a #21 drill and try to control your depth to about .3125. You can put a piece of tape on your drill at .3125 from the tip for a guide. Again, I ground the end of one of my 10-32 taps to simulate a bottom tap and tapped both holes. Here is a picture of these ready to assemble and partially assembled.

The next part is to make the stop for the dial gauge which attaches to the tail stock shaft. (This was all done on the fly.) Cut a piece of Delrin to have a snug press fit over the shaft and a diameter to match the hole in the acrylic. It's about .175 wide as you can see from the picture. This is to allow the release of the MT2 taper without pushing the bushing off the end every time.

Here is the acrylic round. I had a couple extra of these ø3" x .125 thick from another project. Note that it was drilled it off-center in order to reach the dial plunger point. Using a Forstner bit on acrylic works well, but it flexed on me while boring and made a bit of ragged hole...but even so, it presses on to the Delrin nicely and I used a dab of epoxy to hold it because not much sticks to Delrin. I will be rebuilding this piece to make it more simple and elegant and post my pictures when I it's done. For now it works great and is pretty accurate. I used an end mill and cut a .016 deep counter bore on a piece of aluminum - it was perfect.

Note the live center is just released from the MT2 and the scale shows about .1 between the back of the acrylic and the front of the tail stock. This allows me to remove the chuck or live center without pushing off the base point acrylic and bushing.

As I go along, this will be improved and I will post my changes and maybe even make a drawing with actual dimensions and stuff! ~¿@ Hope that gives you enough to make one for yourself or ideas for a better one. It was a fun half day for me and it's been a wonderful and useful addition to my Mini.