Review of the Knaell (Minimech) threading attachment

The Minimech threading attachment is the latest in a run of different solutions to the lack of threading capability on the Taig. The system is a fairly conventional conversion involving a leadscrew and split nut fed by a gear train from the headstock spindle. What is unconventional is the substitution of timing belt pulleys for the gears one is used to on larger lathes. Timing belt systems are as accurate as gears with several advantages: lower cost, vibration and sound compared to gear systems. All wear is usually confined to the belt, rather than the gear teeth, which is another advantage.

The unit is fairly straightforward to install, as Ken Knaell (the inventor of the system) has taken great pains to include most everything you need to complete the installation. The biggest task does not involve the system so much as remounting the lathe so that there is enough space around the headstock for all the components to fit - the lathe needs to be risen above the mounting surface by about 2" and the motor needs to be moved up a bit so that its belt will clear the system as well. He includes pictures of his solution and one could certainly come up with other options. My lathe was already on a riser so that was not a problem, although my motor did need to be moved out of the way. As I was planning on only using the unit manually (by making a hand crank for the spindle) I didn't bother on reconfiguring the motor mount on mine.

View of minimech threading attachment setup on my Taig lathe
Looking down at headstock
Back view
Another view

Once you study the pictures in the manual it is fairly clear how the leadscrew, split nuts and pulley frame mount. I had some moments of confusion while mounting the split nut, as it requires aligning with the supplied screw bearing brackets, and it can take a while to get it set up so that there is no misalignment. The whole system only requires one hole to be drilled and tapped in the carriage for mounting, using a supplied jig. There were a few questions I had during setup which were promptly answered by Ken via. email. The leadscrew brackets slide and lock into the thin dovetail that the rack protector uses, and you will need to shorten or remove the rack protector in order to use the system.

The headstock pulley is replaced by a modified Taig pulley, which has the highest speed groove removed and replaced by a timing belt pulley. This is one place where I was thankful I had filed a flat for my pulley setscrew - always do this if you can so the setscrew doesn't mar the shaft preventing the pulley from being removed. There is sadly not enough room for an index plate in this setup, but one could rig indexing from the timing belt system if that was a necessity.

Ken include instructions and parts for making the carriage handwheel snap in and out of engagement, so that the handwheel doesn't add drag to the system. I didn't choose to install this as I never bothered putting the snap ring on my handwheel and it just pulls all the way out. It is a thoughtful addition and looks fairly easy to make. All wrenches and such are included, one only needs a #21 drill bit and 10-32 tap (which you should have anyway in my opinion) and some lumber for the base risers.

Setting up to cut threads is fairly easy, you just build a train from the headstock to the leadscrew, using different combinations of timing pulleys to achieve the required threads per inch. A familiarity with gear trains is helpful in the regard, but not rocket science. Using the supplied pulleys the following pitches are possible: 24, 28, 32,40, 48, 56, 60 and 64 tpi. I was able to figure out a way to use stock pulleys to achieve 20 tpi, there's a picture of it later on. One can buy timing pulleys in with just about any number of teeth, so with a minor expenditure there are really no limits as to what pitches you can cut. The unit will cut left hand threads using an tension bracket and pulley with a double sided belt that is supplied. The pulleys mount to the various shafts with setscrews, that fit into small divots machined on the shafts so that the diameter does not become marred with repeated use.

The split nut mechanism is beautifully made and works quite well. One could make a thread dial, but when I tested the unit I simply reverse cranked the spindle after pulling the tool back, backed up the carriage a little more than necessary to take out backlash, and resumed threading. A handwheel could be fitted at the headstock end of the leadscrew for fine manual feeds. One can also convert this system to drive the leadscrew with CNC systems.

Halfnuts closed
Closeup of closed halfnuts
Halfnuts open
Closeup of clsed halfnuts

To test the system I cobbled up a handcrank and set the system up to cut a 28 pitch thread. This only took a few minutes. I needed a 1/4"-28 mandrel for a Severance deburring tool I had, so I decided that would be a good test. I chucked up a piece of 1/4" 12L14 ("ledloy" free machining steel) and proceeded to take .005" deep cuts at a time, dropping the feed to .002" as I got closer to the final diameter. The finished mandrel threaded smoothly onto the tool and seemed to have perfect threads. Some reading on thread cutting will help the novice here. I was already used to using a hand crank as I use one on my Jet 9" lathe all the time - one has better control over the length of the thread than threading under power. Tensioning the belts is important as if the belts were slack, they could jump out of the pulley teeth - I had no such problems, and tensioning is comparable to tensioning the Taig drive belt.

Beginning thread
Thread checks out fine
Completed thread with deburring tool screwed on

For a laugh I figured out how to unconventionally set the system up to cut a 20 pitch thread, and was able to do so just as easily. The belt doesn't have as much contact on the pulley teeth, but it seemed to work and I was able to cut a 1/4"-20 thread. Clever people could set up all sorts of unconventional drives like this. One could add a milling head to the crosslide and use it for milling threads in difficult materials such as wood, or even do helical milling.

20 Pitch unconventional setup

So, down to the bottom line: would I recommend this unit? I think it is great. It does exactly what is asked of it and allows the Taig to be used for a greater scope of work than the stock unit. The quality of workmanship is excellent, the split nut alone is a marvel of design. If you find yourself needing to cut custom threads and you have a Taig lathe, you may want to give it a try.

The Minimech attachment is no longer being manufactured and none are available.

Back to the Taig page