It has been more than a year and a half since I bought my 7×12 mini-lathe and I finally decided I needed to get serious about building or buying a cam-operated tailstock lock for it. A lever-operated lock is probably one of the most popular modifications for the mini-lathe because it increases your productivity by eliminating the need to find a wrench and turn a nut every time you want to move the tailstock.
Much of my delay has been because of my indecision about which of the various designs floating around the Internet is the best. So I started sorting through my collection of bookmarks and found that I needed to compare three well-known designs I could make, plus a kit I could buy and install easily.
1) Frank Hoose’s lock is probably very well known because of the popularity of his web site mini-lathe.com. Frank’s lock is based on one by J. W. Early, who may have been the first to design and publish plans for a lever-operated lock. Frank does not provide any plans but he does have lots of pictures and instructions detailing how it is made, which should make it easy to copy. The mechanism appears to be robust, but a mill is needed to make a 14-degree wedge to provide a flat support surface on the back of the tailstock. You also need to mill a flat spot on the inside front of the tailstock.
It uses a ¾-inch bolt that has been modified and drilled lengthwise to act as a bushing to support the cam. A hole for the bolt is drilled through the back of the tailstock and the bushing is inserted through the hole and held in place with a nut. The cam is then inserted through the bushing with the actuating lever attached on the back side and the locking plate attached to the front.
The fundamental difference with this design, compared to the others I will discuss, is that a hole is drilled through that back of the tailstock which supports the cam and the forces it generates.
Most of the other designs have a hole in about the same spot so that the operating lever can be located on the back of the lathe. However, in those designs, the cam and the forces it generates are supported by the bottom of the tailstock where the locking nut on the stock lathe is located.
2) Those other designs seem to be based on Rick Kruger’s tailstock cam lock. Rick’s locking lever is located on the front of the tailstock, unlike all the other locks I’ve seen. As a result, the lock is very simple to make and does not require any milling, drilling or any other modifications to the tailstock. There are no plans available for it, but there are enough pictures and instructions on his web pages to replicate his design, although it would be easier if the pictures were a little bigger.
3) John Moran’s cam lock is based on Rick’s design but he has moved the operating lever to the rear of the lathe by drilling a hole through the tailstock. It is a simple clearance hole and the dimensions are not critical because the cam just passes through it. Again, there are no plans available for John’s design, but his web site has lots of good pictures and detailed instructions for building one. Besides looking like it is easy to make, it is also made out of cheap and easy to obtain materials, mainly a few hardware store bolts and a 1-inch length of 5/8″ (approximately) or larger round steel stock, and a small piece of flat 1/8″ steel for a new locking plate.
I am not sure if you need a mill to construct John’s design. The base of the tailstock where the lock sits is not flat. It has a small slope running from the back to the front, which if not addressed could cause the lock to bind and/or the cam to deform or wear unevenly. John flattened the area with a Dremel tool, but at some point after using the lock for a while he went back and milled it flat.
I’ve read that a penny makes a good spacer when the cutting the cam. Simply put it between the work piece and one of the jaws of your three-jaw chuck. Then cut away what will become the low point of your cam and stop before your bit starts to cut the opposite “high” side. I suspect that you could also create a cam by just filing a flat spot on the shaft and rounding the edges.
4) If you don’t want to figure out how to build your own cam lock from a bunch of pictures and descriptions you can buy a kit from Littlemachineshop.com for about $30 (Oct. 2008). Their lock also appears to be based Rick Kruger’s design and according to the instructions all you have to do to install it is disassemble the old locking mechanism on the tailstock, drill a 1/2-inch hole through back of the tailstock with a hand-held drill and reassemble it with the new parts.
The LMS kit is the easiest way to add a tailstock cam lock to the mini-mill. It appears to be much beefier than the other designs and likely to be the most durable and trouble-free. It only requires a few hand tools to install and so it may be your only option if you don’t own a mill or at least a drill press.
The Rick Kruger / John Moran designs can probably be built for almost nothing with materials you may already have in your shop. Even if you had to buy all the materials they would still probably cost less than the LMS lock and you’d have lots of leftover material to use for other projects. Building your own lock may also be a good way to develop your skills if you are a novice machinist.
After having studied pictures of the LMS lock, I keep thinking that John and Rick’s designs could be improved upon. The LMS design is obviously much bigger and more robust in almost every way. The instructions say that a 1/2-inch transfer punch is used to mark where to drill through the tailstock, so that means the cam is about .500-inches in diameter. John’s cam is less than half that, at .215 inches in diameter. As a result his cam won’t be as strong, and because the cam and lock shaft have a much smaller contact area they are likely to wear much quicker. The LMS lock also uses heat-treated 4140 steel, while John’s lock uses hardware store bolts made out of low grade steel. On the other hand, John says his lock has worked well for 2-1/2 years, so maybe it doesn’t really need to be any bigger or stronger.
Even if his lock doesn’t need to be stronger, making some of the parts bigger might make it easier for a novice machinist to build it and also maybe make some tolerances and alignment less critical. However, the bigger you make the base, the more likely it is that the slope of the tailstock’s base is going to cause problems.
So what am I going to do? I am very tempted to just buy the LMS kit. It would be the easiest way to add a lever-operated lock to my lathe, it is reasonably priced, and knowing the company’s reputation, it will probably work well and never give me any trouble. Even with John’s pictures and descriptions, building his lock is probably going to require some head scratching, some trial and error, and at least a few hours of work.
On the other hand, I would rather spend $30 on tooling that I can’t, or don’t want, to make myself. I’m also intrigued by the idea of maybe improving his lock. So I’m going to either build John’s design, or my own, which would be a combination of his and the LMS design. Only I’m going to leave the locking lever at the front of the lathe until I’m sure I am happy with the design. That’s because drilling a hole through the back of the tailstock would complicate things if I changed my mind and decided later on to buy the LMS lock.