Shallow Disk Grinder for a 7" Lathe
Using the Electronic Lead Screw (ELS) to grind tool bits by mounting a shallow dish grinding stone onto an arbour which is threaded onto the spindle. The X axis is used to move a tool bit, mounted in an angled holder, back and forth across the stone while the Z axis is feeds the tool bit further into the stone every few passes.
First I needed something to hold the standard 1.25" cup or dished wheel grind stone. I used Alibre to create a 3D parametric drawing of each of the parts and then drawings of those parts.
The Adobe Acrobat Link has an animation that lets you rotate and look at the drawing from all sides. (1.7Mbytes)
I found a pulley pattern that would serve as the arbour but I had to make a pattern for the clamping plate. The arbour is designed to screw onto the 3/4"x16 spindle and has a 3" diameter stepped flange with a 1.25" diameter arbour to hold the grinding disk. The grinding disk is held against the flange with a clamping flange held in place with a 1.2"x20 one inch long bolt.
Here are the Patterns.
Here are the castings.
Now the machined castings:
The hole for the 3/4"-16 thread has been bored and then threaded. After the relief and threads for the spindle were cut, the plate was threaded onto the spindle and the rest of the machining was done so that the grinding disk arbour and flange will be concentric and the mounting stay repeatable between mounts within the tolerance of the lathe. In retrospect, I'd make a new pattern for the arbour so that I'd have to do less machining afterwards.
Mounted with the stone on the lathe.
Finally, the metal shield completely around the stone except for area where the tool bit contacts the stone. (Still needs to be made)
The video shows the Cross Slide moving in and out past the spinning stone. After each pass the carriage is moved 0.002" closer to the stone. The spindle is running 1180 RPM. The ELS software is really just a kludge at the moment just to make things work. I haven't integrated it into the ELS main code although now that it's done and working that wouldn't be really hard.
Ideally, a separate spindle/mandrel that clamps onto the ways using ball bearings and a higher speed would be more ideal. Similar to mounting a tool post grinder onto the bed rather than the cross slide and letting automation like the ELS or MACH do the movements. Or dedicate a small 7x10 lathe specifically to this and just set it up to run the spindle at higher speeds. The loading is really minimal.
Video of tool bit grinding : ELS Grinding a tool bit on the Gingery Lathe (1.55MBytes)