ADAPTING A FOUR JAW CHUCK TO A
HARBOR FREIGHT "MINI LATHE " SPINDLE
The Asian built 7x10 inch electronic variable speed bench top lathe known as a the "Mini lathe" is presently being sold through several tool houses at prices ranging from as low as $349 including shipping, and up although not so long ago it was being offered at a whooping $1000 by a large discount tool mail order company and just a few days ago I read that somewhere in Canada it was being sold for over $1,200. Though typically not very refined cosmetically, as many Asian tools tend to be, it is however a very good small, basic portable ( 89 pounds, shipping weight ) versatile little machine that can perform just about anything asked of it.
The standard issue chuck is a three inch three jaw chuck of unknown Japanese lineage and seems very good in quality as well as being pretty accurate. It is offered with both inside and outside set of steel jaws. But what about when you need to hold square, odd shaped stock or those instances when you need to either center something close to perfection or purposely shift a workpiece off center a certain amount. You need a four jaw independent chuck for that kind of work. Well, one is not available for this lathe and any queries to any of the importers will be returned to you with the same negative answer. After carefully examining the chuck mount of the lathe, I realized that there was nothing really exotic about it and being fairly naive myself, I thought I should be able to very easily adapt another company's chuck to the mini lathe's somewhat strange spindle backplate. The lathe spindle has a solid 1/4" thick (approx) plate that fits into a matching recess in the back of the chuck. Three equidistant threaded studs on the back of the chuck slide through the back plate's holes and are secured with nuts behind the back plate. This is a little tricky to do without constantly dropping the nuts. Not enough clearance back there for normal human size fingers.
For this particular conversion I chose the Taig brand four jaw chuck because it is very good and the price is ridiculously low at only around $50-$60 direct from Taig tools. It is about 3-1/2" in diameter, about 1-1/2" thick and it is solid steel. I removed all of the jaws and the screws and reversed chucked it on another lathe so I could machine a snug fitting recess on the back face of the chuck that was a perfect match for the back plate of the mini lathe spindle chuck mount. You could also machine the recess on your Minilathe if you use the outside steps on the jaws to hold the four jaw body and you first make a matching flange to use as a fitting gauge. Check out our video on just that very subject. You see, you can't otherwise tell when you have reached the correct dimensions on the recess as you would have to constantly remove the three jaws just to check for fit. I made sure that the chuck back face was perfectly square to the rotation axis before I began removing any metal. As I neared the correct diameter I began to use the gauge so I could check the progress of the recess on the chuck. I stopped when the gauge had to be wiggled, but not forced into place. The fit was so good the friction alone held it in place even without the studs or nuts to hold it in. Now the three 1/4-20 mounting holes needed to be transferred, drilled and tapped. That was a relatively simple job that I did on my drill press and small rotary table. The holes only need to roughly line up with the ones on the back plate since their job is only to hold the chuck, not actually center or locate it to the spindle axis. After drilling and tapping the holes I screwed and epoxied three equal length threaded studs of the same length as those on the original chuck and gave everything a good coating of oil to preserve the newly machined surfaces. I also made three brass nuts out of _ hex bar by drilling and tapping about an inch of stock and parting off each nut. By making the nuts a little bit thinner in cross section, they are easier to screw on the studs in the limited room behind the spindle backplate. During use, you can hold a test dial indicator on the tool holder to center work using a wiggler.
A second mounting possibility is the use of a #3 morse sleeve with a #1 morse center hole. These are available from any tool supplier. Into this sleeve you insert a #1 morse with 3/4-16 end adapter, available from American Tool Co for about $19.95. You can coat the inner surfaces of the adapter with low viscosity CA glue and allow to cure. This whole set up then inserts into the #3 morse spindle on the Minilathe and cinched up with a draw bar ( construction of which to be described in a later installment ). The registration flange of the adapter is faced off to true it up perfectly square to the lathe spindle. The Taig chuck or any other 3/4-16 threaded chuck can now be screwed to the spindle. I have also made a flanged and threaded adapter to accept threaded tooling. I have also made a lot of 3 MT tooling to fit the spindle with a draw bar. All of these projects were prompted by the multitude of statements made by many about the lack of four jaw chucks and other tooling for this lathe. Yes, it was true that a ready to use factory chuck or other accessories are not readily available but I would have thought that this rather minor hurdle would have been an easy one to conquer. It turned out that it was!