Denker's Mini Lathe Page

Mini Lathe Information

I purchased the old version of the HOMIER 7" x 12" mini lathe. It comes with 4mm change gear keyways and a number of other differences from most other mini lathes. I don't think they make these anymore so unless you buy one of these used, you will get 3mm gear keyways with most of the parts the same between makers. Now the main differences are color, metric or inch cross-slide screw and compound rest screw and the length of the machine. The motor has plenty of power for this machine size but the drive gearing is a bit high for most threading and large diameter machining. Also the plastic drive gears may be a little light duty. As a result, I greatly modified my lathe.

Modification Contents:

Machine Stop Addition

This addition is mainly used during threading operations to stop the machine at the end of the threads. I usually cut a groove where the threads end so there is room for some variation where the cutter stops. A set ring on a rod below the leadscrew is set so it is hit by an addition to the carriage assembly. This rod can move in ether direction and activates a switch inside the control cover to turn off the lathe. The carriage must be moved away from the stop before the motor can be turned on again. It can also be used as a safety stop. METRIC THREADING NOTE! When doing metric threads with a non-metric leadscrew, do NOT disengage the leadscrew because threading will not match again. This is a problem because when the switch is open the motor cannot be started. For metric treads I add a spacer (shown in picture) on the stop rod for each cutting pass. When the machine stops I remove it, (the switch closes) then I back off the cutter and reverse the lathe back to the start of the thread. This is quite a hassle but is the only way it can be done without changing the leadscrew to a metric one. (which I think would also be a hassle!) I don't do many metric threads so I'll keep using the inch one.

The next picture shows the switch with the controller removed.

Low Speed Addition

This addition lowers the spindle speed limit to about 600 RPM and almost doubles the torque. This is a major addition with many parts and I use it most of the time. It completely bypasses the internal plastic gears. (The speed selector must be in neutral) Low speed can be disabled to use the higher speeds when needed. The method I used reverses the direction of the spindle so a switch must be added to reverse the half speed function. This is a nice addition for the additional power needed when machining bigger parts and for the lower speeds needed when threading, grooving or cutting off parts.

Gear Plate Change

I greatly disliked the original change gear plate. It was hard to adjust and required a lot of adjustment every time a change was made. Adjustment was centered on the leadscrew shaft when it should be on the "A" shaft. So after much engineering, out with the old and in with the new! This .25" thick plate was laser cut at work and has many built in gear options. The gear plate mounting shaft and the "A" shaft mount had to be slightly modified too. With the addition of 21, 25 and 42-tooth gears, I can make just about any metric thread to within .00015" per inch. (For threads within the machine capability limits using plastic gears) For inch threads, I can get many threads by changing only the leadscrew shaft gear and adjusting the gear plate. Also this configuration gives me many more machining feed possibilities. (Down to .0018"/rev with the added 25T gear.) I use 8mm x 20mm long shoulder bolts with spacers to hold the gears to the plate. There is also a T-nut held in place with a thin spring steel bracket for gear adjustments. (No need to get a wrench behind this thing!)

Now that the gear plate does not rotate on the left leadscrew mount, I can improve wear and performance by replacing it with a ball bearing mount.

Note: Because this plate can have more gear locations, it may not maintain a direction standard. Some gear setups may require using the reverse of the normal feed selection. This setup is for a M0.7 thread. (To be more accurate: M0.70009)

Multiple Gear Plate Addition

OK - on this one I got a little carried away! With this addition I can get 3 different machining feeds by changing a gear location. The 35-tooth gear mounted on the plate of the next picture uses a spring and ball indent so it can be moved. I can get 14 different threading feeds by changing only the leadscrew gear and the position of the gear plates. I don't think it's going to get much easier on this machine. I did have to buy and modify more gears and I added a ball bearing in the "A" shaft mount. (Required modifying the "A" shaft too) Mounted to the "A" shaft is a steel 20-tooth 3 deep (.95" long) gear. The 3-gear cluster is made up of 25, 20 and 40-tooth gears with the 20 or 40-tooth used to drive the next gear. These 3 gears are connected by a key on the modified brass 25-tooth gear. It looks like a lot of gears, but everything seems to work well. I use this addition most of the time but I do remove it for threads under 14TPI and metric threads. Using other gearing possibilities, this addition gives me a very wide range of machining feeds. Note: This addition also required modifying the gear cover for gear clearance.

The selection knob below the gear plate is used to setup for different machining ranges so changes can be made easier and faster. Adjustment screws are used to preset the location of the gear plate for a 20, 25 or 30-tooth gear on the inside of the middle 80-tooth gear. This gives me 9 machining selections from .0020"/rev to .0059"/rev available. I have removed the middle 80-tooth gear on the next picture to show it better. The knob is turned to select one of the three adjustment screws or none at all. The knob position is held by a ball and spring indent.

Tailstock Change

The tailstock had 2 things that needed changing. The first thing is the nut to bolt it down. It’s a pain in the neck. There are a few kits available to fix this but I went with a lift and set adjusting lever. The inside bed surface of my machine is not very parallel with the top so some of the available methods would not work well. I couldn't find an adjustable lift handle that fit in the tailstock cavity so I made this one. It is easy to adjust and can be moved out of the way in ether direction when done.

The second change I wanted was a gauge dial on the tailstock screw shaft. This was not possible with the metric threads being used. I needed something with 20 TPI or a M1.0 thread. I drilled out the old quill thread with a .390" diameter drill and tapped it 7/16 - 20 left hand. After making a new tailstock screw shaft, buying an inch style 50-division compound rest dial, compound rest retainer and making the other necessary modifications, I was almost done. My lathe did not come with depth markings on the quill so I added them too.

Other Lathe Additions & Changes: