Multipurpose Mini-Machine for your Workshop
November 1, 2012
These days everyone is talking about how great 3D printing is but for the hobbyist this still limits you to plastic parts. Before 3D printers were around I always wanted a lathe and a milling machine, I still do!
When you want to build more than just basic robots it is sometimes necessary to make small metal parts. Maybe you need a special metal rod, mounting bracket, shaft adaptor etc.
I had this exact problem building a project for a local University. I sent drawings away to a local factory to get metal parts but after waiting a week or more the parts were often wrong or just badly made. If I asked for brass, I got copper. If I asked for steel, I got aluminium.I told the boss I need a lathe and a milling machine. Nothing big, nothing fancy.
Today we went to a factory that makes these machines. Everything from small hobbyist kits to large industrial CNC machines. While I was there we saw this:
This is the "Mini Multipurpose Machine". The kit is almost entirely aluminium parts and weighed a good 4 or 5Kg. This particular kit comes with enough parts to build 8 different machines:
- Lathe (metal or wood)
- Drill Press
- Milling Machine
- Disk Sander / Tool Sharpener
- Hand Tool (similar to a Dremel)
- Rotary Drill / Mill machine with angle selection (can make crude gears)
As you can see from the photo below, this kit did not skimp on parts, I had trouble finding a table big enough to lay them all out on! The parts include tools, safety goggles and even 4x milling tools. Two power supplies were included so you can have two different machines built and running at once. Click on the photo for a high resolution image.
What interested me the most is that they also offer stepper motors that can be fitted to the machines to make small CNC machines. my job now is to test the quality of this kit. At first glance the overall quality is very good with most parts made from anodized aluminium.
After testing I hope to upgrade any parts that did not make the grade, add stepper motors and a suitable Arduino compatible controller. The end result should be a Mini CNC kit that can be used with free software such as Sketchup to produce metal parts. If all goes well I will add 3D printer and laser cutter to the list of machines that can be made with this kit.
Time to start building, there are days when I love this job!
First on my list is the milling machine. At this point while I am testing for quality issues all the machines will be manual, not computer controlled. The milling machine, in my opinion, is the best test of overal rigidity and accuracy. The milling process puts the structure under heavy load. Click on the photo for a higher resolution image.
I tested the mill on a scrap piece of aluminium. This piece was a fairly hard alloy so it made for a good test subject. I found the chuck was the biggest problem as it can only be tightened by hand and part way into my second cut it vibrated loose. We now need to find a suitable 8mm (3/8) drill chuck. I also want to replace the plastic platform and clamps with metal.
The power of the motors is quite good, they are 12V motors and the switchmode power supplies are rated at 2A each. The housings are plastic but still quite strong and include a fan and air vents to keep the motor cool with prolonged use. The kit came with 3 high speed motors (20,000 rpm) and 1 low speed (12,000 rpm). For the milling machine I used a high speed motor and a two stage belt reduction.
The first stage provides a 6:1 reduction. The second stage provides a 2.6:1 reduction for a total of 15.6:1. The parts I am using now have plastic wheels but there is supposed to be a metal version available according to the manual. The reduction modules are ball raced with quite large sealed bearings (6000ZZ: 26mm x 10mm x 8mm).
Although this mill will not be able to cut as deeply as a purpose built machine, it still shows a lot of potential for a small hobby grade CNC machine that is small and light enough you can pick it up with one hand and put it in a cupboard when you are finished.
After building the milling machine I still had more than enough parts to build a lathe complete with tool sharpening stone. I have made the base using the longest part so that if I change it to a wood lathe later then it will be big enough to make chair legs with.
There are two ways to adjust the speed of the lathe. You can change the motor between high speed and low speed and you can also change the reduction ratio. When I did my test video I probably had the speed too high (about 3000 rpm). A lot depends on the material being machined and the size of it.
For this test I tried to machie a stainless steel screw. This machine is not recommended for stainless although I think if I had a pump dribling cutting fluid onto the screw and a slower speed then it might do a fairly good job.
The chuck performed better than expected. As it is quite small, less than 50mm (2 inch) in diameter it does not use a rotary key. Insead it is supplied with two steel rods that slot into holes in the chuck. You use the rods as levers to grip and tighten the chuck.
The chuck has a maximum gripping diameter of 20mm however you can buy a set of jaws for holding larger objects. Rods of up to 8mm diameter can pass through the hollow shaft of the reduction module. Because I added the sharpening stone on the end I would need to remove the protective cover or drill a hole in the cover if I wanted to insert a long rod.
The sliders currently used on my lathe only have a travel of about 45mm. There is a long slide but it is being used on my milling machine. I can move the slider along the length of the bed by simply loosening a screw and moving the sliders to a new position.
I went to a part of town today that specialises in CNC machinery and bought some upgrade parts. After the discussions below, I looked into some high quality collets for milling. For now I only have 3mm and 5mm. As the machine is not very powerful I think 5mm is about the limit when machining metal.
Although the collets can be used for drilling they can be a pain to change when drilling different sized holes so I also got a standard drill chuck for drilling.
Because I do want to machine metal I think cutting fluid is a good idea so I also got a pump and hose for directing cutting fluid onto the cutting tool.
Unfortunately the drill chuck and collet shaft will need to be adapted a bit to suit the kit so more work for me :(