Inexpensive Mill and Lathe

[JohnU]

I occasionally need to be able to make a precision metal part for my modeling work. For very small parts it's hard to keep the precision needed by the scale when doing hand work. I looked at available lathe and mill and combination machines such as the popular Sherline. This is a fine and versatile tool but the $3000 price tag is high for occasional hobby work. A cheaper alternative is the Unimat system. That's still $800 with tax and shipping. Parts and accessories are also expensive from the vendor. I did find an unused one on Ebay for $400. It was open box and who knows what might be missing. Also, while the Unimat is capable of being configured as many machine tools, it's only one at a time and needs reconfiguration to go from a mill to a lathe.

Another consideration is whether such a cheap tool is capable of the precision I would like to achieve. For my purposes a resolution of 0.1 mm(.004") is sufficient. This seems a lot to expect from a cheap machine tool.

 

I did a lot of searching online. I kept hitting upon really cheap machines that looked almost identical to the Unimat. Some were in other colors but they were all the same construction and the actual parts were identical. I also found I could purchase parts and accessories very cheaply for these. I decided to purchase a micro mill and micro lathe of this type and see what could be done to improve them. I found a lathe and a mill for $200 each. Along with accessories, tax and shipping the cost of two machines came to ~$500. The machines as delivered were actually better than expected. They were surprisingly robust and ridged for their size and cost. The brand was "First Tool".  A search for parts found most items available from GK Tool. Because these all use the same parts I was able to download manuals and parts lists from the Unimat site. Interestingly, these were labeled "Cool Tool" and said "Made in Austria". Perhaps "Assembled" in Austria is more accurate as the ones purchased are identical except for the labels and they were definitely made in China.

 

I spent considerable time adjusting the machines. In the end I was able to align them to my needed specifications. The worst part is the cross slides which use a nylon gib shim and are very difficult to adjust. The X axis slide that's on the base is much better. The design of sub parts such as the tail stock and motor carrier use dovetail clamps that do a really good job of keeping everything in alignment and make configuration easy. There are flat plates that provide additional rigidity. You can see these features in the Unimat pictures. The motor on the lathe is a bit wimpy(looks just like the Unimat one) but the mill has a robust motor. The spindle speed is ~150 rpm. That's too low for some metals and too high for other jobs. There are no speed controls or gear adjustments. Here's a picture of the mill as delivered. The vise is a separate purchase. The supplied one was complete junk. There was a plastic base plate supplied. I recommend replacing that with metal or hardwood. The supplied tool rest was simply a dovetail clamp. I replaced that with the same tool rest shown on the Unimat. The throat height of the lathe was too small for a lot of work. I added centering blocks as shown in the Unimat lathe.

I did find accessory gears and different size belts to accommodate them available. It takes a lot of searching though. These are DC motors so a variable DC supply should be able to control the speed. Remember though, these are cheap motors and they may not do well at higher voltages and currents needed to get higher speeds. It's probably better to figure out gear ratios and purchase them.

 

The first thing I did after alignment was turn the mill motor 90 degrees. As configured it extends so far over the work area that you can't see the work.

 

The cheap lead screws and indicator wheels were not consistent enough for my target resolution. The slides stayed aligned in their plane(as determined by a dial indicator) as long as too much force was not used. They will wiggle if much side pressure is applied. Probably the nylon gib shims. The backlash was pretty awful. Part of this was a size mismatch between the indicator wheels D shape and the lead screw's D shape. I applied a shim to the flat of the D which helped a great deal. The lead screw itself is slightly inconsistent. I was able to achieve good results by careful measurements while machining and sneaking up on the dimension needed. During this trial and error period I found and tightened parts to make things more ridged. 

 

The backlash could not be controlled consistently. I determined to add X-Y DRO(Digital Read Out) for the lathe and X-Y-Z DRO for the mill. While shopping for the machines I ran across very inexpensive digital calipers and dial Indicators. These all have zero setting capability and dual inch/metric readout. Some will even read out fractional inches.

The fractional capability is impressive in such an inexpensive tool, but I'd be happy if I never see another fraction.

 

I found a DRO specific indicator with mounts in stainless steel that was the right size for my machines. Amazingly, 0.01 mm resolution and +/-  0.02 mm accuracy for $15! Mounting was simply a matter of using the dovetail in the side of the X axis slide to mount the brackets. I then made a small block to connect the moving part to the X slide. My first precision part! It was necessary to drill and tap a hole in the slide to mount the connector.

That worked for the X axis but the Y axis is much smaller with limited space for mounting. I bought a plastic digital caliper for $2 to cut down for the Y axis. The plastic was easy to machine but the accuracy was only 0.1 mm. This turned out to not work well. To get 0.1 mm on my work I really need to read 0.01. Otherwise the reading is +/- 0.09 and you don't know how close you are to 0.1 mm. I went back to shopping and found calipers with 0.01 mm resolution and 0.02 mm accuracy for $11 in stainless steel. Unfortunately there are none available in plastic with that resolution. That made for great difficulty in machining. Here's the plastic part mounted:

Here's the stainless replacement I bought for $11 with the required accuracy:

 

Here it's disassembled and marked for grinding. Grinding because it's hardened stainless and my little machine can't handle that.

 

Note the hole. That's for the mounting. That hole was the most difficult part. I had to use a carbide PC board drill to start the hole and then use successive drills to ream it out in increments of a couple tenths of a mm. Ordinary drill bits just go dull on this stuff. Same with the 3mm hole in the other part. Matching holes were made and tapped into the slides. Here it is ready for installation:

It discolored a bit on the scale due to the heat from grinding. That's not important though as the scale is not going to be used. The silver part is simply a tape that's applied over the etched pattern the readout unit uses. Here's a picture of what that looks like where I had a misalignment that scraped part of the silver tape off:

The Z axis for the milling machine is simply mounting a dial indicator at the top:

 

Future improvements might be upgrading the motor or changing gear ratios, sturdy base plate, change the existing gib shims to copper.

 

Some useful accessories:

 

Micro square, drill chuck for tail stock, 4 jaw chuck(Comes with auto centering 3 Jaw), rotation adapter, face plate, centering blocks, mills, tool bits, Collets in various sizes, brass or wood rod for taping out collets, center drills, etc.

 

There are good machining tutorials on YouTube. I particularly like Blondihacks. You can find books on machining at your hobby store and the library.

 

Here's some pictures of the finished product:

 

 

[wefalck]

Replacing some dodgy materials, such as plastic gib-strips can take you a long way indeed. And proper adjusting ...

 

I went down a different route many years ago, but always found these modular system an interesting proposition, though 'combination' machines are not terribly useful, if you have the space and the money for a separate lathe and mill - very often you need to transfer parts from one or the other. However, you can create set-ups for specific machining operations that may not be possible or convenient with a standard lathe or mill.

 

There are way of compensating back-lash, such as split leadscrew-nuts. The good thing is that once you have the machines, they can also make parts to improve themselves.

 

The Austrian company behind these machines went through a lot of changes over the past few decades. Originally, they made the Unimat lathes. At a time they made the Unimat 4, they started to develop this modular lathe, which originally was called Unimat 1, but then changed the name to CoolTool, presumably to avoid confusion with the 'real' Unimat. The same company also served as an importer for Sherline machines and I think they were also branded CoolTool, at least for some time. Some 20 years ago I had conversations with them to buy some Sherline parts, but they had a quite high mark-up compared to buying directly in the USA.

 

I think the trade law says, when something is assembled in country X, it become 'Made in X'. So legally it would be correct to claim 'Made in Austria', although the parts came from China. It's the assembler, who determines what quality is required from the supplier of parts and that is the key point.