Tools - Tailstock DRO
Tailstock Digital Read-Out
[March 10, 2014]
[March 23, 2014 - note]
[April 5, 2014 - addendum]
[May 12, 2014 - note]
[Aug. 24, 2014 - Model 2]
This project is not original with me, and is in fact based on a very similar project by George Race. For a link to that project and other related projects look here (scroll down to Tailstock > Depth Gage).
Revised Model 2
This revised Model 2 was made because the original Model 1 was interfering too much with the compound rest. This is in part due to the fact that my compound rest was modified by a previous owner with a cam-lock handle.
This new design moves the DRO to the top of the tailstock. A bracket is made from a small piece of aluminum flat stock, bent into shape, and secured to the DRO with two screws in the back. Some parts of the original version were re-purposed for this new version - see the Model 1 write up for more relevant details.
A measured drawing is available for Model 2 at the links below:
Aluminum flat stock - before cutting.
The stock was bent first, then cut to length.
The holes drilled for the Model 1 were re-used.
To make it easier to bend, the aluminum flat stuck was held in a vise and bent before it was cut to length. As the dimensions of the bracket are not critical, the ends were simply dressed with a file and then de-burred with a "scotch-brite" type abrasive wheel. Two holes were drilled in the piece to match the threaded holes already drilled in the tailstock for the Model 1; these holes were countersunk for flat head socket screws.
The back of the DRO was removed, and two mounting holes were drilled and tapped for socket cap button head screws. The back was mounted on the bracket and clamped in a vise, and the protruding ends of the screws were ground off with a Dremel tool (see picture to the left).
The clamp to hold the end of the DRO was made by re-using the clamp from the Model 1; this required the clamp to be milled down to fit the revised application.
In the new location, the DRO is just high enough to interfere with the quill clamp. To address this issue, a short brass spacer (essentially a washer 0.170" thick) was made to raise the quill handle slightly (see pictures below). The washer was made from 0.75" diameter brass rod, drilled in the center to 5/16" and cut to length. See picture below right.
Quill clamp interference.
Brass spacer.
Original Model 1
Note added Aug. 24, 2014: Because this version was interfering too much with the compound rest, I decided to make the revised Model 2 above. As of this writing, I have not yet had time to use the revised model; however, I can say that the revised model is simpler and easier to make, although it does require taking apart the DRO.
A measured drawing is available for Model 1 at the links below:
Note added March 23, 2014: After using the new set-up for short while, I have noticed issue that gives me some concern, which is that the caliper mount on the quill does not have much clearance with the tool holder on the cross slide. I haven't decided yet whether to change this or not, but I thought I would add this note for the benefit of anyone thinking of copying this design. Also, there is not as much clearance between the tailstock handwheel and the end of the caliper as I would like, so I may cut an inch or two off the end of the caliper. If and when I make a change, I will update this page. [April 5, 2014] After using the DRO a bit more, I have decided that the cross slide clearance issue is not as bad as I thought. However, I did address the handwheel clearance concern (see below).
Note added May 12, 2014: Now that I have had a chance to use this DRO a bit more, I thought I would add this note. The DRO has proven to be very useful. It does make things a bit "crowded" around the tool post, but so far I have not run in to any limitations I could not work around. This has been a very worthwhile addition to my lathe. However, I think if I had it to do over, I would place the caliper above the tailstock; although this would make it a bit more difficult to read, it would likely reduce or eliminate the clearance issue. It also occurs to me that the best location for the DRO, in terms of clearance, would actually be behind the tailstock, if a way can be found to do this and still enable readability.
The project is based on a 4" digital caliper purchased from Harbor Freight (Pittsburgh - item#47256) as shown below. The caliper has some nice features which make it ideal for this project:
- The short length fits the mini-lathe tailstock nicely
- When the caliper display shuts off automatically, it "remembers" its last reading when turned back on again (instead of resetting to zero as some calipers do)
- When the caliper rule is moved, if the display is off it automatically comes back on again
Modifying the Digital Caliper
The first step in the project is to remove the caliper jaws. I did this using a cutting wheel on a Dremel tool. While this could probably be done with disassembling the caliper, I thought there would be less risk of damage to the electronics if I did so.
Removing the electronics (see note below).
Removing the end piece.
Removing the depth probe (see note below)
Removing the electronics : The electronics section is held on by four screws, note that there are three "plastics screws" and one machine screw. Caution - while you can't really see them in the picture above, there are also two very small plastic "wipers" fitted into slots on the bottom of the plastic case - remove these wipers and store them for safekeeping until you are ready to reassemble the caliper, or you may lose one like I did! (I made a replacement from card stock - seems to work OK).
Removing the depth probe : The depth probe is welded onto the main metal piece - a little gentle bending back and forth will break it off. Note that in the section shown on the above right, there is a small flat spring (not shown in the photo) and two very tiny adjustment screws. It is recommended that these three pieces be removed and stored for safekeeping until you are ready to reassemble the caliper.
Cutting off the jaws with a Dremel tool.
Jaws removed.
After cutting off all four jaws with a Dremel tool, I cleaned up the cuts a bit with a small grinder. Cutting off the jaws created quite a bit of dust - a mixture of metal and abrasive from the cut off wheel; I'm glad none of this dust ended up in the electronics or inside the mechanism.
Making the Brackets
The mounting hardware for this project consists of two main components:
- Tailstock Bracket : This bracket attaches to the body of the tailstock and holds the main body of the digital caliper. There are two pieces to this component - the bracket itself and a clamping piece.
- Quill Bracket : This bracket attaches to the tailstock quill and to the scale section of the digital caliper. There are two pieces to this component - the bracket itself and a clamping piece.
The Tailstock Bracket
An aluminum block is first milled to the correct size, and mounting holes are drilled and counterbored. One side of the piece is then coated with layout dye, and a height gauge is used to layout the required dimensions for the finished piece.
Mounting holes are drilled and counterbored.
Pattern is laid out with a height gauge.
The photos below show the milling of the tailstock bracket. I was a bit concerned that the small area clamped might not hold firmly enough, but by taking cautious cuts (0.040 maximum depth of cut) all went well. Once the milling is completed, the screw holes for the clamping piece can be drilled and tapped.
Milling the tailstock bracket begins.
Test fitting the caliper main body.
Tailstock bracket - milling completed.
With the main section of the tailstock clamp completed, I could now drill the mounting holes in the tailstock. As a precaution, I removed the quill from the tailstock first to make sure I did not accidentally drill into it (the mounting holes should be blind holes that do not penetrate to the quill, but better safe than sorry). I was able to mount the tailstock in my mill vise for drilling and tapping, but with care this could also be done with a hand drill. After reassembling the tailstock, I screwed the bracket to the tailstock, using a bit of thread lock to make sure it stayed secure.
Next, the clamping piece is milled from a piece of 0.260" thick aluminum plate. Once the milling is complete, the piece is flipped over and holes are drilled and countersunk (not shown) for the clamp screws. At this time, another test fit is advised to ensure that the clamp is holding securely.
Clamping piece - milling started.
Clamping piece - milling complete.
Quill Bracket
The quill bracket is made by affixing a printed template to 0.260" aluminum plate. I attached the template to the aluminum plate by coating both the plate and the back of the template with rubber cement - a allowed the rubber cement to dry a minute or two and then pressed the template to the plate. This did a very nice job of holding the template on and left almost no residue when it was removed; anyrubber cement remaining on the plate was easily rubbed off.
I actually made two versions of the the template - the first version was made based on careful measurements, and was then test fitted to the tailstock. Based on this test fitting I made further modifications to create the final template.
After attaching the template to the raw stock, I rough cut it to shape using my portable bandsaw on my portable bandsaw stand.
Version 1 of the template is test fitted.
The template and raw stock prior to rough sawing.
The piece after rough cutting.
After rough cutting I milled all the "flats" on the piece, in preparation for milling the rounded sections. Next, I drilled the center hole diameter to match a "pivot rod" (made from a short section of drill rod); the pivot rod is held in the milling vise with the aid of a small V-block. Using the pivot rod to hold the piece, the rounded sections are carefully milled to match the template. CAUTION: when milling the rounded sections be sure to use very light cuts, and always conventional mill, do NOT do any climb milling or the piece will almost certainly be pulled out of your hand with risk of injury.
Milling the "flats"
Drilled for the pivot rod
Milling the rounded sections
Once the circumference is milled to shape, the hole is enlarged to fit the quill. I did this by mounting the piece on a faceplate and boring it out on my lathe; initially I used a live center to make sure the piece was centered before clamping it to the faceplate, after which the tailstock was withdrawn and a boring bar was used. The piece should be bored out to make a close fit to the quill, so that only a small amount of clamping force is needed to secure it in place on the quill. I used the lathe to bore out the hole as I thought it would be faster, but I suppose this could also have been done on the mill using a boring head.
Once the hole is bored to the proper diameter (verified by test fitting), the hole for the clamping screw is drilled, counterbored, and threaded. The final step is to open up the clamp section with a slitting saw.
Boring out the central hole in the quill clamp
After boring to size, the hole is drilled for the clamp screw.
Final step: Open the clamp section with a slitting saw.
At this point I reassembled the caliper and mounted it in the tailstock bracket. I attached the main piece of the quill clamp, and verified that everything was fitting together properly.
The clamping piece to hold the caliper rule is made from the same 0.260" aluminum plate as the quill clamp. After milling to size, the holes for the clamping screws are drilled and countersunk. The cutout for the caliper rule is then milled out to a depth 0.010" less than the thickness of the rule (to ensure ti will apply clamping pressure to the rule).
The rule clamp is milled out.
The only thing left is to do is to attach the rule clamp, tighten down the quill clamp, and verify that everything is working.
Job done!
Here are some more views of the completed tailstock DRO:
Addendum
[April 5, 2014]
As noted earlier in this write-up, the clearance between the end of the DRO and the tailstock handwheel is a bit tight (see photo to the left). I therefore decided to cut about 1-1/2" off the end of the DRO.
As before, I used a Dremel tool to make the cut. To the left, you see the DRO held in the vise prior to the cut. I did not remove the electronics, but I did wrap them in a shop rag and some tape to keep abrasive dust out of the mechanism. I had to cut at a slight angle to get the Dremel cutting wheel to fit. After the cut, I dressed up the cut end on a small grinding wheel.
After the cut was made, the digital indicator part of the DRO was still working, but on occasion it would give an erratic reading. I believe this was because there was metal dust in the end of the cut (see photo to the left). I carefully cleaned out the end of the cut, and then for good measure I cut about 1/16" off the end of the circuit board at the end (the circuit board in this case is the black strip with numbers on it laying along the top of the DRO. To be on the safe side, I did the same for the other end, anf then selaed both ends with some quick-setting epoxy.
To the left is a photo of the cut down DRO. I should note that this does not impact the measuring range of the DRO in this application, as it still covers the full range of quill travel.
Now that I have had a chance to use this DRO a bit, I thought I would add this note. The DRO has proven to be very useful. It does make things a bit "crowded" around the tool post, but so far I have not run in to any limitations I could not work around. However