The Cummins Mini Milling Machine
I've been selling some of my engines to finance the purchase of a mini mill for some time now. Today the Cummins Tool Truck Sale came to town. I've been waiting for that! I stopped in and came home with this.
I have to say I was impressed with the packing in the crate.
The machine was well protected and showed no signs of any shipping damage. Another impressive fact, being these machines are manufactured in China. The machine sold by Cummins is the same mill sold by Harbor Freight and Grizzly. The Grizzly mill is the highest priced. It comes with a few more accessories, and their customer service can't be beat. The only drawback to the Grizzly machine is that it has a Morse MT-3 spindle taper. The Harbor Freight and Cummins have R8 taper. There are more tools available for the R8. The Harbor Freight mill is still $70 more than the Cummins but there customer service makes up for that. I knew what I was buying, so I wasn't too concerned about the issue.
With all the parts out of the crate, there was a lot of rust preventive grease to clean off the ways. It cleaned up easily, and everything was there.
It will be bolted to the bench between the drill press and the lathe in my hobby shop. After setting it on the bench I checked the spindle run out with a dial indicator. Total run out at the spindle is less than .001" I think I can live with that...
-------------------------------------------------------------------------
My First Project on the Mini Mill
Miniature machines call for miniature tools. I wanted a little fly cutter, but wasn't able to find anything small enough for the mini mill. What I did find was a drawing for such a cutter.
Being my very first part made on the mill, it was a learning process. I junked the first attempt. Attempting to cut one side via conventional milling, the end mill grabbed and gouged the piece. After a couple more little lessons taught me by the mill, the second attempt was successful.
This is the finished product. Along with the end mills I've bought one at a time for other projects, the mill is getting tooled up. I still need to find a 1/16" end mill. Well, maybe 2. I'm sure I'll be breaking that size!
---------------------------------------------------
A Few Modifications Are In Order
The weakest part of the China made Mini Mill is the nylon gear drive.
Sooner or later you will end up with a gear that looks like this one.
It took me 2-1/2 hours to get the head of the mill disassembled to the point that I could access this broken gear. A replacement gear would have been somewhere around $8 + shipping costs, but knowing that it WOULD happen again someday led me to go the route of converting the mill to a belt drive that would eliminate all the nylon gears.
The belt drive conversion kit was purchased from Little Machine Shop.com
The belt drive is much quieter and smoother cutting than the gears were.
-----------------
Another mod was to extent the Z axis travel. Little Machine Shop made that easy as well. They sell the old style Z axis rack to replace the shorter one on the newer mills.
It's a simple, inexpensive, bolt on installation that adds two inches to the vertical travel to the head.
-------------------------------------
The Air Spring Conversion Kit also from Little Machine Shop is yet another great Mod for the Mini Mill. It includes the extended Z axis rack mentioned above.
The Air Spring replaces the original torsion spring to balance the weight of the head. It's more stable and adds travel to the Z axis.
----------------------------------------
Another accessory for the mini mill was this ER 32 collet chuck set.
It was purchased through an eBay auction for $80 The set included the collet chuck with a R8 shank, 18- ER 32 spring collets from 1/8" to 3/4" and a single hook spanner wrench. That wrench looked like a knuckle buster to me so I bought a proper collet chuck wrench to replace it.
I wasn't all that sure just what I'd get for $80 but I was very pleased with the product!
The indicator run out is less than .001" The fact that it is almost 1" shorter than the drill chuck that I had been using is an added bonus.