25 March 2008

My minilathe, and several mods thereof

It's been a while. There are various excuses for that, but the main excuse is that I've been putting in long days at my new job.

Lathe has arrivedThe big news (on the diy/hacking/modding front) is the arrival of my minilathe. I had been dreaming about owning a minilathe for a long time. I had always been frustrated by the cost and accessibility of various machine parts; to me, it's torture when you have a great idea and no way to build it. I looked forward to all of the rights and responsibilities given to lathe owners.

This lathe is just one brand of a common chinese lathe, sold by Cummins, Harbor Freight, Grizzly, and others.
One benefit of this oft rebranded tool is that many online communities have sprung up about how to use or modify it, for example the right-wing 7x10 minilathe group. However, the Cummins model is in a class by itself. It is simultaneously the cheapest, and shipped with the most accessories, including a faceplate, a 3-jaw chuck with both internal and external jaws, 5 HSS tool bits, a tailstock chuck, a dead center, a set of change gears, a steady rest and a follower rest. It is a great value.

Let me first say that, despite the limitations inherent to small lathe, this lathe is quality. Every moving part has a gib or some other way to adjust it. Although each part may slowly wear out, the designers have provided the end user with a way to compensate.

Let's compare it to the famous Sherline Mini-lathes. Among hobby machinists, Sherlines have a good reputation for quality, and are comparable to my Cummins in size. However, Sherlines do not include change gears and a feed screw -- necessities for cutting internal / external threads -- nor do they include a compound slide, thus one cannot cut bevels. Oh yeah, Sherlines cost more too.

Lathe has arrivedEnough about comparisons, on to the juicy stuff. I unpacked the lathe. The first thing you need to do with a machine like this is take it apart. I took it down to it's solid pieces, cleaned off the factory grease, re-greased. re-assembled and adjusted it. These preliminaries are critical, since they give you a good understanding of how the machine all works, and yield a certain confidence toward using or modifying the machine.

Lathe Mod #1So, what modifications have I done? First the simple shit: I removed and recycled the two chip guards. Then, I removed the plastic do-hickey covering the emergency stop button. Perhaps I'm misunderstanding it, but it seems much safer to have a clear path between my left hand and the stop button. Additionally, I replaced the bolts that secured the hand wheels, since they tended to hit my knucles.

Lathe Mod #2aNext, I grabbed some strong magnets pulled from a scrap hard drive, and used them to keep track of the various chucks. I find that the use of a magnet is just slightly entertaining, perhaps only on the subconscious level, but that is enough that I never forget to replace the key. I don't imagine I'll ever accidentally leave it in the chuck.

Lathe Mod #3I don't own a grinder with which I can grind my tool bits, but I can put a small arbor-mounted grinding wheel in my lathe. The beauty of this is that I can use my lathe's compound slide to get a precise angle onto the tool bits. Similarly, I realized that I can use fragments of hackway blades to shim-up the cutting tool.

Lathe Mod #5My lathe came with a lot of accessories, and suddenly I had nowhere to keep them all, let alone work. So, I went to work building a drawer set. I collected a bunch of scrap wood and plastic from around the neighborhood (and trash day in Brooklyn contains enough wood to build a few houses, I'm sure). The drawer set is sturdy as hell. I added in a few solid brass drawer pulls that I found at the Park Slope Flea Market to finish the effect. So much of this sort of improvised building involves moments of inspiration. This simple allen wrench holder is one such example.

Most recently, I built a apron chip guard, inspired by the one that Varmint Al made. One failing of the minilathe design is that it leaves the gears behind the apron exposed, and poised to collect metal chips from the cutting action. As Jobst Brandt once said, "Commercial abrasive grinding paste is made of oil and silicon dioxide," and so I was concerned about these chips, even though the gears were otherwise greased. So, here is how I built it:

Lathe mob #7 [1/6]Cut a sheet of 1/8"-thick pastic to the rough contours of the lathe's apron. I used some plastic that used to be part of a printer's enclosure. Drill a hole large enough for the gear's shaft (I cut mine 7/8" since I had that bit available, though smaller would do). Drill and countersink five holes around the perimiter of the chip guard.

Lathe mob #7 [2/6]Transfer those holes from the plastic chip guard onto the back side of the apron using a center punch. Drill and tap those holes. I used a #36 drill, and a 6-32 tap, though anything of similar size will work. The apron is made of cast iron, which is a surpisingly soft metal. Nonetheless, proceed with caution so you don't break your tap, and use lot's of wd40.

Lathe mob #7 [3/6]This is a view of the back side of the apron after the five holes have been drilled and tapped.

Lathe mob #7 [4/6]Clean out all metal chips from the area, and re-install the gears.

Lathe mob #7 [5/6]Drench the gears in a heavy grease. I used an old hacksaw blade as a spatula to really muck it into the nooks and crannies.

Lathe mob #7 [6/6]Install the chip guard. It is secured down by five 6-32 machine screws. Re-install the apron onto the lathe, and rejoice in your apron's newfound ability to repel chips!

1 comment:

Fred said...

This is good info, but you've done one thing wrong. The red emergency stop button for your lathe is also the power button. By removing the locking cover, you can no longer shut off the power to the lathe. So even when you're not using it, the control board is still drawing power. This will waste electricity and may shorten the life of the board.