Cutting threads

[Paul Paukstelis]

Things are pretty quiet around here, so I thought I would show something that I have been playing with recently. Using my bolt-on CNC for the lathe I wrote a little script with a few parameters that spits out gcode that lets me cut internal or external threads for boxes, etc. Suffice it to say 0.7 mm pitch isn't going to be useful (but can be done!) and the 2 mm pitch either needs multiple passes or CA glue to prevent some of the chip out. The router with the collet adapter also has way more runout than I would like.

 

[robo hippy]

Hmm, well, for sure, some woods are far better for cutting threads than others. Soft maples are very difficult to cut threads in. Dogwood is okay, Osage is very difficult. Boxwood, of course, is ideal!

robo hippy

 

[Monte Richard]

How do you feed the cutter to determine the threads per inch?

 

[Paul Paukstelis]

How do you feed the cutter to determine the threads per inch?

I just tell the motor to move a certain distance (pitch) every time it rotates the piece 360 degrees. It is all computer controlled.

 

[colinsp]

Impressive use of technology but it may be quicker to use conventional thread cutting chasers 😉

 

[Paul Paukstelis]

Impressive use of technology but it may be quicker to use conventional thread cutting chasers 😉

It maybe slightly faster, but certainly not as versatile. With this you can easily cut threads in side grain bowls/boxes, something that you would very hard to do well with conventional thread chasers.

 

[Darryl Fective]

I keep wondering if stepper motors and arduino couldn't be used to create a master/slave function to cut threads and spriral flutes, etc. I don't know where to start with it though. 😕

 

[Paul Paukstelis]

I keep wondering if stepper motors and arduino couldn't be used to create a master/slave function to cut threads and spriral flutes, etc. I don't know where to start with it though. 😕

Certainly. The machine I've created does that and a whole lot more. It There are a lot more powerful microcontrollers than Arduinos these days and it is much cheaper to buy a motor control board for a 3D printer rather than trying to wire everything up to run steppers off of Arduino.

 

[Jeff Hankinson]

Are you using Grblgru to cut the threads? I’ve been using it to single point cut threads on metal rods driven by a 3A closed loop Nema23 stepper.
Although I have thread cutters similar to yours at 60 and 90 degrees, I haven’t tried that in wood yet = real soon now 😉

 

[Paul Paukstelis]

Are you using Grblgru to cut the threads? I’ve been using it to single point cut threads on metal rods driven by a 3A closed loop Nema23 stepper.
Although I have thread cutters similar to yours at 60 and 90 degrees, I haven’t tried that in wood yet = real soon now 😉

No, I wrote my own setup for doing this. I use OctoPrint as my Gcode sender, so it is a plugin I wrote that you can specify pitch, length, etc. and it spits out the gcode. I love GrblGru, but for sort of "single" applications, it is much more complicated than the workflow I have developed for these simple tasks. I mostly use it for cases where I want to wrap a design over a large portion of a bowl.

 

[Jeff Hankinson]

Sometimes I forget I am using both a CNC and a small, stepper adapted metal lathe with Grblgru. The lathe works with Grblgru Lathe of course. The threading routine Grblgru has built into that is as straightforward as his wrapping macros = set length, thread diameter, pitch and away you go. I’ll try threading with Grblgru Lathe on wood soon using a cutter like yours. I don’t anticipate any issues.

 

[Paul Paukstelis]

I've added a few things specifically with cutting threads in wood. For example, in my work flow, I have an option for putting in a "pause" step before the last cutting pass that will move the cutter away, then slowly rotate the piece 720 degrees to allow applying CA glue. I'm not sure there is something similar with GrblGru. Interface needs some cleanup, but it is nice having it all in same program (web interface) that is doing gcode sending.

 

[Jeff Hankinson]

Very handy app you’ve made. I mainly use Grblgru but I have also played with CNCL. That required programming his firmware on to a Mega 2560 board (= very easy) but other than being a fully featured app for a CNC controlled metal lathe, it allowed adding Hal effect sensors to the spindle to register rpm and a sync signal. This allows either powered thread cutting or stepper controlled C axis threading for example.