Introduction: Quick-Change Lathe Tool Post and Holder
Hello again everyone, this time I'll be showing you how to make a quick-change tool holder for your metal lathe. I've been wanting one for mine for a few years, but a good post and a matching set of tool holders costs a few hundred dollars at minimum, and I couldn't justify that kind of expense when I already owned old but perfectly functional tool holders. Well, I finally got sick of having to mess around with shims, incorrect tool alignment after locking down the tool holders, and other assorted garbage for 5 minutes every time I wanted to switch tools, so I decided to see if I could design and machine a homemade version of a quick-change tool holder which would work as well as the best ones I could buy. I ended up making it mostly out of random bits of scrap I had lying around, and ended up spending about $15 on a few set screws and a 1/2-13 tap. (I already had one somewhere, but I couldn't find it.) I have been very satisfied with the result so far.
My design is based around a hollow cylindrical central tool post which is split vertically into 4 sections, allowing it to expand and lock the tool holders in place by tightening a nut. One advantage of my design over traditional tool holders is that it has space for 2-3 tools on each tool holder block depending on which tools you put in each block, compared to one tool per block on traditional dovetailed tool posts. This allows you to put your most-used tools on the same holder, thus making switching between them even faster as all you have to do is rotate the block around the post to select one.
Let's get started!
Note: Dimensions in this instructable are for the pieces to fit on my particular lathe, an ancient (but still going strong) south bend model A 9 inch. You will probably have to adjust some of the dimensions to make the tool fit your lathe.
Step 1: Required Tooling and Materials
Here are the lists of tools and materials you will need to complete this project.
- (1) 1 1/2" diameter by 3" long round solid steel stock
- (1 for each tool holder block) 3" by 3" square by 2" high steel or aluminum stock (I used aluminum)
- (1) 1" diameter by 2" long round solid steel stock
- about 4" of 1/2"-13 threaded rod
- (2) 1/2"-13 hex nuts
- (10 for each tool holder block) 3/8"-16 by 3/4" long set screws
- (1 for each tool holder block) 3/8"-16 by 3" long hex bolt
- (1 for each tool holder block) 3/8-16 hex nut or wing nut
- milling machine
- lathe (but you already knew that didn't you)
- drill press
- band saw (optional)
- assorted files
- mill vise
- 3/8" end mill
- 3/16" end mill
- 3 jaw lathe chuck (optional)
- 4 jaw lathe chuck
- right hand turning tool
- boring bar
- live center (optional)
- center drill
- drill chuck for lathe tailstock
- parting tool (optional)
- sandpaper strips
- 1/2"-13 tap
- 3/8"-16 tap
- various drill bits ranging from 5/16" to 3/4"
- various metal shims
- precision calipers
- master square
Step 2: Part 1: Tool Post
First, we will be making the tool post itself. It consists of the post, the expanding cone, a 4" section of 1/2" threaded rod, and a 1/2" nut. It works by tightening the nut on the threaded rod, which forces the expanding cone down into the end of the tool post, spreading the 4 sections apart and locking your tool holder in place at the angle of your choice.
Step 3: The Safety Lecture
As usual, don't attempt this if you don't know anything about machining or you'll probably lose your fingers or worse. Machining tools are dangerous. Don't wear long sleeves or gloves, don't have ties dangling off your clothing, don't wear jewelry, and tie your hair back if it's long enough to get caught in the machines. Also don't be stupid, and pay attention while you're working. Don't become an OSHA statistic!
Step 4: Cut Stock
Use a band saw to cut a 3" section of 1 1/2" steel stock for the tool post, and cut a 2" section of 3" by 3" aluminum stock for each tool holder you want to make. Also cut a 2" section of 1" steel stock for the cone piece, and a 4" length of 1/2-13 threaded rod. If you don't have a band saw, you may substitute a circular saw or miter saw with a negative rake saw blade for the aluminum and a grinder cutoff blade for the steel. If you use a circular saw, give yourself a bit of extra length (1/4" should be plenty) on the pieces to compensate for the potential inaccuracy of your cuts.
Step 5: Cut Tool Post Diameter
Lock your 3" round steel stock in your lathe chuck, making sure to leave at least 2 3/8" of the length available for cutting. Face cut the exposed end of the workpiece so that it is flat using the right hand turning tool, then use a center drill to make a hole for a live center to stabilize the workpiece. Now, turn down the diameter of the workpiece until you have a cylinder that is 0.995" thick (+/- 0.005) and 2.250" long (+/- 0.025). This will be the cylinder that locks your tool holders into place.
Step 6: Drill Out Center of Cylinder
Use a 27/64" drill bit mounted in the tailstock to drill out the center of the cylinder. Drill all the way through to the other side. You will need to periodically back out the drill bit to help with chip removal. Next, enlarge the hole to a 3/4" diameter to a depth of 2.375".
Step 7: Cut 45 Degree Taper
Use a right hand turning tool with the cross slide turned to a 45 degree angle to cut a taper on the lip of the hole through the cylinder. The tapered surface should be about 1/2 of the wall thickness of the hollow section of the cylinder (about 1/16"). Use a file to round the sharp edge on the end of the cylinder.
Step 8: Sand the Cylinder
Use strips of sandpaper to smooth out any imperfections on the outer surface of the cylinder, as well as the inner taper. I went up to about 320 grit, which was enough to make it rather nice and shiny. You want it to be smooth so that your tool holders can easily slide onto the post, and to increase the amount of surface area in contact with the tool holders when they are locked in place.
Step 9: Measure Cross Slide Tool Post Mounting Slot
Accurately measure the dimensions of your tool post mounting slot with a precision caliper. Draw the profile and write the dimensions down for later.
Step 10: Cut Base Height
Flip the workpiece so that the hollow cylinder is clamped in the chuck and the thick part is sticking out. Face down the bottom of the workpiece until it is the same height as your tool holder's slot. Do a finishing cut on the outer surface of the base, and break any sharp edges with a file.
Step 11: Mill Flats
Clamp the cylinder in your milling machine so that the base is facing up. Use an end mill to cut flats on 2 sides of the base so that it is the same width as the bottom part of your tool post mounting slot.
Step 12: Mill Secondary Flats
Clamp the tool post in the vise as shown, and mill the secondary flats onto the sides of the base so that it is the same width as the top part of the tool post mounting slot. The tool post should now fit snugly into the slot on your lathe cross slide. It is important to have a tight fit on the upper section of the slot to prevent the tool post from rotating when you tighten it to lock the tool holder in place.
Step 13: Cut Expansion Slots
Use a 3/16" end mill to cut down the sides of the tool post, dividing it into 4 equal sections. The slots should be 2.000" long, although if you're a bit off it doesn't really make a difference here.
Step 14: Tap Hole
Use a 1/2-13 tap to cut threads into the hole in the base of the tool post, then insert a 4" length of 1/2" threaded rod.
Step 15: Make Cone Piece
Now it's time to make the piece that will force the 4 sections of the tool post apart. Take the 2" length of 1" diameter stock, and cut it down to 0.990" (+/- 0.005). Face cut one end flat, then drill a 1/2" hole through the center. Put a 45 degree taper on the end. Use a parting tool to cut a 1/2" deep section off the end of the cylinder, and smooth out any rough edges with a file. I forgot to take pictures of this step, but if you've made it this far, you should be able to make this part pretty easily.
Step 16: Part 2: Tool Blocks
The second part of this project consists of making tool blocks to hold all of your most-used lathe tools. Each tool block is made out of a 3" by 3" by 2" chunk of aluminum (feel free to use steel instead, I used aluminum because I already had some lying around). The tool blocks each have a hole in the center which slides onto the tool post, which then expands to lock them in place. Each tool block also has a precise height adjustment feature.
Step 17: Flatten Block Surfaces
Clamp your tool block in a 4 jaw lathe chuck and face cut all 6 sides until they are perfectly flat. Make sure that the tool holder is still square when you are finished.
Step 18: Bore Center Hole
Center the block in your 4 jaw chuck and drill out the center with progressively larger drill bits up to 3/4". Then, use a boring bar to enlarge the center hole to exactly 1.000" (+.005, -.000). It is important to be extremely precise here, as you want a very close fit on your tool post, while still being able to slide the tool block off easily.
Step 19: Cut Tool Slots
Use a 3/8" end mill in your lathe chuck to mill horizontal slots on 3 sides of the tool holder. Now is the first time you will be able to place your tool holder on the tool post. To set up the tool post, slide it into the cross slide , then tighten 2 nuts against each other on the threaded rod, and tighten the threaded rod to lock the tool post in place. Remove the nuts, add the expanding cone, and replace one of the nuts. Now place your tool holder onto the tool post, but shim it up 5/16". Use a master square to set the tool holder square with the lathe chuck, and tighten the nut to lock the tool holder in place. Cut the slot, then remove the shims and enlarge the slot. Repeat for 2 of the other sides. Leave one side with no slot. The slots should be about 0.600" deep, although if they're a little bit off it doesn't matter.
Step 20: Lay Out Hole Locations
Use a precision caliper to score light lines on the top of the tool holder to mark the locations of the holes. You want there to be 4 evenly spaced holes on each of the 3 slotted sides, and the centers of the holes should be 0.300" in from the edges. On the non-slotted side, mark a hole in the center of the side, 0.500" from the edge.
Step 21: Drill Holes
Drill holes at all of your marked locations. The holes over the slots should be drilled through only the top part of the tool holder, while the hole on the non-slotted side should go all the way through the block.
Step 22: Tap Holes
Use a 3/8-16 tap to cut threads in all 11 holes.
Step 23: Insert Set Screws and Height Adjuster
Thread a 3/8" hex nut onto your 3" hex bolt, then thread the hex bolt into the hole on the non-slotted side of your tool holder. This will be the height adjustment screw. Turn it to adjust the height, and lock it in place by tightening the hex nut against the tool holder block. Thread 10 3/8" set screws, each 3/4" long, into the remaining threaded holes.
Step 24: Finished!
Add some tools into the slots and enjoy your new quick-change tool post!