Redneck Lathe DRO

Having digital read outs (DROs) on my mill has spoiled me, so I've been wanting to add them to my lathe. One idea I've seen has been to adapt inexpensive digital tire depth gauges bought on eBay for under $10. I tried this out tonight. Here's my proof of concept redneck lathe DRO:

I setup the lathe with a 3/4" diameter aluminum rod in the chuck and the DRO affixed to the saddle and cross slide with magnets. My goal was to turn the rod down to 1/2", which would require advancing the tool 1/8". (When turning down stock in lathe, since you're cutting a rotating piece, you divide the amount you want to remove in half, then move the cutting tool that amount. E.g., 0.75" - 0.5" = 0.25" to remove, thus you move the cutter in 0.125", or 1/8".)

Unfortunately, it's not going to work, as it's not accurate enough. I turned the stock down until the DRO read that I'd moved the cutter in 0.125", but when I measured the rod, I got 0.490". It was off by 1/1000" over such a small distance, which in metalworking terms is too coarse.

I'm going to go ahead and try the iGaging DROs, which a lot of mini mill and mini lathe owners have had good results with. I'm planning to install one for the cross slide and another for the compound.

Cut My First Single Point Threads

I'll be adding info about this to my machining site, but thought it was worth posting here as well.

Tonight I cut my first single point threads on my mini lathe. One of the advantages that the Chinese-made mini lathes have over the American-made Sherlines and Taigs is that they can be used for thread cutting without any additional attachments. To setup the lathe to cut threads at the desired pitch, you change gears in the headstock. A good explanation of the procedure can be found in the Little Machine Shop Mini Lathe User's Guide (PDF).

After finding my change gears and the reading the threading section of the LMS guide, I was able to cut 1/2x28 threads on the end of this 1/2" 6061 aluminum rod:

1/2x28 is of course the standard thread used for muzzle devices on .22s and 5.56mm firearms. E.g., my Ruger 22/45 Lite's barrel is threaded 1/2x28.

The cutting tool I used was from a set that I got at Harbor Freight shortly after I bought the lathe, with 1/4" shanks. I used some Tap Magic as cutting fluid but I probably could have cut these threads dry. (I've used a lot of WD-40 as cutting fluid when working with aluminum since I got my lathe and mill in 2013.)

Since I'm just learning how to thread on the lathe and wanted to reduce the risk of crashing the tool into the chuck, I got a spindle hand crank from Little Machine Shop. It fits into the spindle the same way a bicycle handlebar stem goes into the head tube.

Aside from safety, the spindle hand crank gives you lots of low speed torque. However, if I ever want to thread a barrel I'll have to do it under power, because the hand crank blocks the spindle bore.

Also shown in the above pics is a chip tray that I fashioned from some sheet steel and attached to the cross slide using a couple existing holes. I ran across this mod on the web somewhere and thought it was a good idea. It should keep the ways a bit cleaner. Here's a better view:

If the chip tray gets in the way of a job it can be easily removed.