About 6 months ago, I became the proud and excited owner of a HiTorque Mini Mill from LittleMachineShop.com.
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| New life goals include buying more things that come on pallets |
Owning a mill has been a goal of mine since sometime in high school. Getting to work on full sized manual and CNC machine tools in college only further prioritized this goal to a need. It also revealed that while my manual milling work might be passable, the speed, precision, and geometric flexibility afforded by a CNC setup would be invaluable as my projects became more ambitious. After months of consideration, this was the route I chose to get there. There was essentially no design or analysis involved with getting this tool set up, so the following isn't much more than an annotated slideshow.
But first - the details people actually want to know about:
The Tool & Tooling
1 x Mini Mill - $895.95 (plus ~$200 or so for residential shipping!)
1 x Drill Chuck - $10.95 (I was a dummy and bought a second not realizing one came with the mill)
1 x Tooling package - $229.95
1x Dial Indicator - $24.95
1 x CNC fusion Mini Mill Kit #5 - $655 (You can pay a little extra for pre-loaded ball nuts, which I did)
3 x "Green Monster" Stepper motors -$224.85 (total)
3 x "MondoStep" 4.2 Bi-polar stepper drivers - $239.85 (total)
1 x 40V 10A Linar Power Supply - $89.95
1 x PBX-MX Parallel Isolated Breakout Board - $69.95
3 x IDC Mondo Cable Kit - $50.97 (total)
The Random Amazon/McMaster Stuff
1 x Generic Cheap Grey Enclosure - $27.43
1 x Bag of Tiny Cable Glands - $5.12
1 x Extra Clicky Limit Switches - $6.08
1 x IDC Female Sockets - $11.95 (I find myself looking for excuses to use these everywhere now)
1 x Colorful Ribbon Cable - $10.95 (Complements the IDC sockets)
1 x Uncomfortably Cheap E-Stop - $5.92
1 x Extra misc. parts and fasteners - $100
Total: ~$2,659.82 (shipping not included)
A few thoughts:
-Don't skimp on the tooling package, that was an awesome value for what you get
-CNC Fusion is run by some very nice people who produce really high quality kits. However, turn around time seems to really depend on how busy they are, so consider ordering well in advance.
-Probotix seems a little overpriced, but for peace of mind and a deadline constrained build, it worked out
-The PBX-MX board works fine, but it makes me sad that the CNC world still hasn't really advanced beyond the year 2000's communication standards. If I were to do it again, I'd pay up a little more for something USB capable.
-That linear power supply (at least at the time) was supported with absolutely no documentation, which is a shame, because it wasn't immediately obvious to me how it should get wired. Check out the images below if you're in the same boat.
-Yeah, that IDC cable kit is silly expensive...but at least it looks nice.
So were the results worth the price tag? For me, absolutely. I suspect that will also be the case for anyone else who looks forward to putting in the time to assemble a setup like this. That doesn't mean that there aren't potentially better options out there for different needs though. I spend a good deal of time looking at CNC solutions in the sub-$10k market, and for me it came down to the following highly oversimplified chart:
I don't have the time to design and built a Bridgeport conversion kit from scratch, or the money to buy an off-the-shelf solution. I definitely don't have that kind of space availability either. I've done the CNC router thing before. Although I donated my Franken-ShapeOko creation to a student team a few months ago, I wouldn't be opposed to buying/making another in the future. But those machines still lack the spindle power and rigidity to pull off more demanding machining. The Tormach machines have been documented to death on Youtube as being awesome and surprisingly capable for the price. But that price (especially with the addition of tooling and peripherals) is too high for me right now. One day I'll probably be ready to make the investment, but I feel reasonably confident that that day is far enough away that I'll have gotten my money's worth out of the mini mill by then. Of course, it could just be that my impatience is making up justifications to buy now...
(Just as a note, LittleMachineShop does also sell a Sieg prebuilt CNC option, which seems to fall into the cost and capability space between a benchtop conversion and Tormach. Unfortunately, it has a fairly limited y-axis travel distance, which was a deal breaker for me.)
The Documentation
(Please note that this is far from comprehensive. Just a quick tour of some of the highlights from the build)
It turns out that I don't have the patience to do nothing while waiting for parts to arrive. So instead, I built this big box to hold the mill. The idea was to have big sliding doors with polycarb windows to seal off the machining area. I never got around to installing the doors because....
This was a fun and informative process. I'd not seen gibs before, nor how the leadscrew nuts were retained. It turns out they're allowed to float in machined slots on the x and y axes (visible with nuts still installed above), before being tightened down with set screws once threaded and aligned with the leadscrew.
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| Slightly more detail of the x-nut slot |
Fitting in the ballscrews basically involves reversing the previous process with some new hardware, except with ball nuts.
And grinding. Somewhat excessive amounts of grinding. To be fair, the instructions note that the y ballscrew is slightly too long for this model of mill. A small relief has to be put at the back of the base for it to fit.
It doesn't hurt to grind a little more than you think is necessary. I probably stopped before I should have, and now get very occasional grinding noises from the y ballscrew if I approach the max table travel. It doesn't seem to affect performance, and it's not quite annoying enough to convince me to take the whole thing apart again.
Mounting the z-axis is probably one of the trickiest steps, as it requires somewhat precise drilling into steel that doesn't want to be drilled into. I messed up one of the holes by using a wandering dull drill bit, so had to make full use of the slotted mount points on the z-block. Getting the mill head support block aligned with the ballscrew and the z-block was also slightly time consuming, and took a little fiddling before I got clean up and down operation. Clamping the head or resting it down on a block is probably a good idea for safety.
And suddenly, a nearly complete mill appears. Installing the motors and lovejoy-couplings was fairly uneventful. A single bolt on a motor mount block was bent from shipping, but it was redundant and easy to replace.
In parallel with the machine, I was making progress on the control box.
It's not perfect, but I think I did an acceptable job at keeping things neat. I used a scrap piece of plastic to act as a back plane in the enclosure. The E-Stop and main power switch are mounted on the outside facing the operator, while the parallel port and stepper lines exit near the back.
The crucial shot. No, that's not the stock fuse...
The E-Stop really is a must. It saved me from countless crashes during the "getting to know you" stages of Mach3 wrangling.
All told, I'd guess the built took 2 days going at a slow-medium pace. True to my expectations, the debug period involved about another 3 days of playing around. As my experience grew with the software and the controller layout, it became much for convenient to use.
For my first "test" project on the machine, I machined a LED lamp casing for a friend. It involved some tricky to fixture and indicate parts, as well as gave me a change to get familiar with Fusion 360 CAM.
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| Material prepped on the lathe |
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| Temporary clamps to spot drill holes |
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| It's a good idea to protect nearby outlets from flying aluminum chips |
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| Some deep inner and outer cuts, plus fixture plate action |
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| The finished piece |
- Jogging with the mouse and keyboard is frustrating. I might invest in a peripheral for this.
- Resetting the tool height for every tool is extremely time consuming, and increases the risks of crashing because I have to stop and restart the program from a certain point. I started outfitting certain endmills with collar stops (kind of like a cheap version of the Tormach Tooling System), which should allow me to get consistent tool heights.
- Using the drawbar to swap endmills is slow. I see the appeal of power drawbar systems. I often found it faster to just do drilling tasks manually on the drill press
Unfortunately, my time with the machine was limited due to winter break. Since then I haven't had the chance to do an accuracy or precision study on the parts the machine produces. Nevertheless, I'm extremely happy with how the conversion turned out, and hope to get years of prototyping out of it. If I ever spend some time making modifications or updates to the machine, I'll be sure to document those as well.
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