Modification of vintage emco unimat 3 lathe/Milling Machine
This project started from the need to produce small yet detailed parts for various photographic lens modification projects I've been making. I acquired this vintage lathe and went about adding digital read outs and threading capabilities in order to make my lens components.
The detailed design features which I'm working with require strict tolerances of 0.05mm or better so machining is the ideal manufacturing technique. Having small batches or prototypes made by a fabrication workshop proved far expensive due to the low numbers required. I came to the conclusion that I needed my own equipment so I purchased an Emco Unimat 3 lathe, a small Austrian lathe introduced in 1976. I chose this model because it is very well made, compact and most importantly has the option of adding a milling attachment. This means I could get an excellent lathe/mill setup for under £500 after some searching on eBay.
The machine is several decades old and hadn't been used for some time so I immediately stripped the entire thing down, cleaned everything well, lubricated and reassembled. The machine worked very well and so I went about adding the modifications. The hand wheels which control the x and y axis have markings down to 0.05mm, this combined with the irremovable backlash made for pretty poor accuracy. I had seen online people use vernier callipers to add digital-read-outs (DRO) to some machines, this is an excellent idea since they are accurate to 0.01mm and can be found extremely cheap.
I bought 2 vernier callipers for around £10 each and started chopping them up to fit to the lathe. Above is the calliper before and after removing most of the unwanted material, I made sure to remove the electronics for this stage so the cutting and grinding vibrations wouldn't ruin anything. The jaws of the calliper are extremely useful since they protrude to give 2 excellent mounting surfaces, I drilled holes in these and made a small corner bracket to fit the lathe.
Excuse the mess, this was taken during a project. Here is the calliper from the previous photos mounted on the cross slide via 2 M5 holes which I tapped. One thing I noticed when I first mounted the calliper was how exposed the electronics were, so to keep chips and oil out away form the sensor I glued 2 small blocks of foam to each edge of the display where it slides over the beam.
And for the x axis I did the same thing, this time mounting it to the lathe bed and the base of the cross slide, being sure to it's parallel to the lathe bed. Note that since the mill uses the lathe bed to move the work during cutting, the DROs can also be used for milling in the x and y axis. The rightmost image shows the mill cutting out a window for a lens component.
After adding the DROs I wanted to make a thread cutting attachment for the lathe. I decided to use custom spur gears that rotate the x-axis lead screw in the opposite direction to the spindle. I chose to make gears with ratios to give 1mm and 10mm pitch options (1mm for m39x1 lens mounts and 10mm for lens focussing helicoids). I used a high density polyethylene to make the gears, since it would speed up the process.
idAfter cutting the sheet to rough size with a small hacksaw, I turned them to the max diameter of the gears needed. I drew the gears up in soldiworks, after taking measurements of the lathe, and then decided on a profile I could use for all of the gears. I then ground a small shank to the shape of this profile and cut 45 teeth in the 1mm pitch gears, using the milling attachment that came with the lathe (2nd image).
In the end it turned out the milling attachment could not be setup to cut the much larger 90 tooth gear, so I 3D printed them from the files I had made previously. To mount he gears to the lathe I made 2 small fixtures, one mounting to the lead screw (left) and one sliding over the spindle (right).
Here is the finished setup for cutting 1mm threads. The image on the right shows a m39x1 (Leica camera screw mount) thread being machined into plastic.
Finally, heres an example part machined from aluminum, made possible by the DROs and threading attachment.
