LIFE WITH A HARBOR FREIGHT

7" X 10" MINILATHE

2ND INSTALLMENT

 

When we last left each other, I was commenting on my first experiences with a pretty nice but much underrated little lathe. Maybe someday if I have opportunity to either own or work on larger, much more expensive, so called professional equipment of American lineage, I'll be able to give some opinions on them. Up to now I can only comment on the lower cost, more affordable Asian makes of machine tools.

It's been two years since I acquired my little 7" x 10" lathe and so far so good. But since then, I've been able to design and make a myriad of gadgets and model steam engines as well as making a few pretty cool physical modifications to the lathe itself to improve on its performance even more.

One of the very first things I did after unpacking it was to degrease the entire gear train and apply some nice viscous silicone grease. This proved to be a great choice for the Delrin like gears on the lead screw / spindle gear train. I really have to try hard to hear the gears running when the auto feed is engaged. The head stock portion of the gear train is all metal and that called for the typical Moly type grease treatment. For the sliding surfaces of the carriage, cross and compound slides I applied a mixture of 30w non detergent motor oil and STP oil treatment at a ratio of about 20 to 1, wiping it onto all the dovetail slides and gibs. Very slippery, almost frictionless stuff. The tail stock's Morse tapered bore is not drilled all the way through like that on the spindle so the centers, arbors and other attachments can be popped out when the ram is retracted beyond a certain point. The overall capacity of the tail stock is rather small so full length Morse taper arbors with tangs cannot be used. You must either get short shank units or cut the tangs off. I've cut them and just grind the ends until smooth and chamfered. The head spindle will accept regular length arbors and centers so not much problem there. The compound slide has to be retracted about two inches before the two loosening screws that allow it to be rotated to other angles can be reached. That can be sort of a pain but I have a lot of patience and I'm able to tolerate such small irritations. There is no protractor on the compound slide pivot so once again you have to rely on a good, adjustable protractor with its base bearing against the side of the cross slide body in order to set the compound to a specific angle. Once I got it set to 29.5 degrees for single point threading, I scribed a witness mark directly on the cross slide surface so the compound body could be returned to that setting instantly. I continued scribing and marking several other important angles with 1/16" number punches. I also filled the scribe marks with black enamel for better visibility. This made things a lot less aggravating during regular use. One of the many angles I specifically set up for was the exact angle for cutting a morse taper and a setting parallel to the lathe bed so I could turn perfect short cylinders with the compound alone rather than relying on the carriage movement. This can be pretty handy as you can use the micrometer dial on the compound to measure the exact length of such cylinders.

The first tool I made for it was a two function tool holder for a 3/32" thick x 1/2" parting tool with the opposite side of the block accepting 3/8" shank boring tools. A very simple project taking only a single evening. Materials were a 2" cube of aluminum from my local scrap yard and a 2" x 2" square of 1/4" thick aluminum plate that was/is screwed to the side of the tool holder housing the cutoff tool itself. This acts as a very efficient tool clamp. The cutoff tool sits and slides in a very snug fitting 1/2" wide groove that is a bit shallower than the full 3/32" thickness of the tool. The opposite side has a 3/8" reamed, lathe center horizontal hole with two vertical set screw holes to lock the shank of boring tools in position. The vertical center of the tool holder block is drilled to 3/8" to slip over the threaded tool post stud on the compound slide. It works great and I get no chatter even when parting off steel. Following that I made a die holder for the tail stock. A 2" diameter length of scrap aluminum was drilled and reamed to 1/2" through its center and the opposite end was then opened up by boring to accept my 1" diameter round button dies as a slip fit. A set of four locking set screw holes were drilled along the periphery of the larger bored end. I also drilled a set of six 1/4" by 1/2" deep holes around the body of the die holder, about mid way down its length to act as "Tommy bar" holes. To use, I chuck a short length of 1/2" drill rod on the tail stock chuck and slip the die holder through the drill rod. To cut some threads you just slide the tail stock toward the work and rotate the die holder plus die onto the workpiece with a tommy bar made out of steel rod. The holder will be guided by the 1/2" piece of drill rod and the perfect running fit of the die holder's reamed hole. A variation for some of the smaller machine screw threads is to chuck a hexagonal die for say, a 5-40 thread and take the corresponding workpiece ( 1/8" diameter common hobby brass rod ) and chuck it to a tail stock chuck. You can then thread it using power by just loosening the tailstock lock while guiding the work into the spinning die. I use this method for making up to 8" long 5-40 threaded rod. This is my standard size for all my steam engine push rods and connecting link rods. I could have chosen to use 4-40 or 6-32 but I would then have to prepare material to the correct diameter for those odd thread diameters and such small diameter material would be very difficult to turn down evenly, since I need at least 6"to 8" at a time. Just like on some other small hobby lathes, I wanted to be able to turn the lead screw with the half nuts engaged to advance or retract the carriage specific amounts. I could also disconnect the power advance gears and advance the carriage by hand thereby being able to achieve a super fine feed which would be fully independent of the spindle speed. As it was, I had a auto fine feed of about 250 to 1. That is, the spindle turns about 250 times per inch of advance. Still pretty fine but no matter what spindle speed you use the actual carriage feed rate would also remain the same, 250 to 1. Of course, I could just disconnect the half nuts and feed the carriage with the carriage handle but by turning the lead screw itself I could increase the fineness of the feed rate since the lead screw pitch is 16 tpi. That means I advance only 1/16" per every full turn of the screw. With high spindle speeds of around 2900 rpm, I could take a super fine cut that would leave an almost mirror finish on my work. The problem was how to turn the screw by hand. The answer would be a handle! I drilled the tail stock end of the lead screw with a hand drill to a 1/4 - 20 tap size as the screw turned under power. This more or less self centered the drill bit as it drilled the hole which was then tapped. I recycled the shaft and ball handle from a damaged drill press vice and turned a matching thread and shoulder on the business end of the handle shaft. Installation was simply screwing it into the end of the lead screw after first coating the threads with two part epoxy. Overnight curing yielded a super strong connection to it. Now I could use it whenever I needed a very fine feed rate as well as acting as a warning, letting me know that the half nuts are engaged. You wouldn't want that during a facing operation. It works like a charm and cost only pennies to produce. I also made a small face plate that directly mounts like the chuck does to the spindle mounting flange. Since I cut the face plate mounting recess on the same lathe, I made a matching dummy flange that perfectly seated on the lathe chuck. I used this "gauge" to check the progress of my machining. The center hole was bored large enough to allow a #3 MT dead center to be inserted into the spindle with the face plate still mounted. A simple double clamping "Dog" was made to drive the work held between centers. So far I had produced a specialty tool holder for cut off and boring work, a face plate and drive dog clamps, a die holder for threading rod material and the ends of engine links and other components, but I had to come up with a way to mill on the lathe. Not presently owning a milling machine, I had been forced to utilize the poor man's version of a mill in the use of a drill press and a 12" x 5" X & Y milling slide. This had provided me with the capability to perform just about any kind of milling cuts I have needed on any of my tool making or modeling projects. Though I've always known that a drill press spindle assembly cannot compare with that on a lathe or milling machine, I still decided to use a drill press. The only feasible alternative at this time was to get a vertical slide / vice for the Minilathe but they can run you a bunch of bucks even for a "universal" one such as those made by Palmgreen. Having already used the equivalent unit for the Taig lathe ( $50.00 ), I thought about making one from scratch or simply adapting the Taig unit to the Minilathe's cross slide. Since the Taig unit already had two vertical mounting holes through the housing I just aligned the unit so the bottom surface of the vertical slide would run flush with the edge side surface of the cross slide. That would serve to square the unit up to the head spindle axis. I then transferred the two hole positions with transfer punches, drilled and tapped them for a 10-32 thread. To use I just bring the compound to the Zero position ( parallel to the bed and to get it out of the way ) and screw the unit to the cross slide top surface. Alignment to the spindle is at this time within 5 to 10 thou off. A few minutes with a magnet mounted indicator and a small brass hammer is all that's needed to bring it to perfect squareness. This set up allows me to take 1/8" deep cuts in aluminum or brass with a 1/4" diameter two to four flute end mill. Somewhat less on steel. Depth adjustments are measured with a dial indicator attached to the tail side of the lathe bed to take readings directly against the right side edge of the cross slide or carriage. This is where the lead screw handle can come handy. You can easily advance the carriage in single thousands or any amount within the reading capacity of the indicator. I use #3 MT draw bar type end mill holders directly in the head spindle. End mills as well as flycutters can be used with these holders. The only disadvantage is the limited amount of travel offered by any vertical slide and my cross slide but you can still produce some very good results rivaling those of a real milling machine. For larger work pieces requiring several inches or more of machining, I still go back to the drill press & machining slide combo.

As far as single point threading on this lathe is concerned, I have done projects with 16 - 20 - 24 - 32 - 40 & 52 TPI and produced perfectly clean, accurate threads. The lathe will cut 7 other odd, in between thread pitches but these are the ones I use the most. This was done after my re-setting of the electronic speed controller to effectively reduce the lowest speed on the low speed setting of the gear box to around 30-40 rpm. This I cannot fully endorse as I did it with full knowledge and assumption of the risks involved. So far so good and it's been well over a year. I have to admit that I have not yet mastered the use of the threading dial and so most of my thread cutting has been done by retracting the cutter with the cross slide to clear the just cut thread and without disengaging the half nuts, reversing the lathe to place the carriage back to the starting position. That's where the reversing switch really earns its keep. Once the carriage has moved beyond the beginning of the thread, I return the cross slide to its previous reading which I had set at ZERO and advance the cutter another few thousands further into the cut with the compound set at 29.5 degrees. This technique will fully insure that the new cut will perfectly match or mesh with the preceding cut. This is continued until the full thread is cut and has been fitted to its mating part.

As you can detect from my writings, I am very satisfied with this small lathe as well as with the Taig lathe. With it I have been able to build a ton of tooling not readily available or costing a bunch of bucks. I've also built over a dozen fully working steam engines some of which are double cylinder, dual acting designs. The level of fit of the running parts is so good that even though the total displacements range in the way of one to two inches, they will readily run on breath power, though compressed air or steam is always best.

Visual speaking, this tool definitely won't even place in a lathe beauty contest but I've never been one to buy tools for their "good looks", I prefer they just do their intended job and that is to accurately cut metal!