Usable Interface for CNC Turntable on Manual Mill

Greetings, all. I am currently helping a relative with a small project. He is a machinist, and has a manual horizontal mill. For this mill, he has a small manual turntable, which he is hoping to be able to automate to some degree.

The stepper motor that has been purchased to drive the turntable does not have enough torque to machine with, even at a 40:1 reduction. However, it should be able to turn the turntable a given number of degrees in a given direction, and then the turntable can be locked down before proceeding with the machining process.

I have the official LinuxCNC Debian image installed on a Pi4 (and have fixed the GPIO permissions issue), and have configured the X axis as angular, with no other axis in the configuration. I can put in the 40:1 gearing.

My problem is that I haven't the foggiest idea what interface to use. I need something that can order a rotation of a certain amount of degrees and then a stop, as well as switching between clockwise and counterclockwise. However, all the interfaces I've seen are specifically designed to run Gcode from CAM software. Is there an interface that supports these needs, or do I need to code something myself? 

Linuxcnc is probably overkill for this situation.
If you look around YouTube you'll find plenty of projects addressing this idea.
Myfordboy has done such a project but using a spin indexer.

Its not very hard to do this with an Arduino (even for me) and there are several such indexers available. Sorry but I don't think I have the code anymore.

The interface has a manual mode where you can jog to an angle.
Or enter G0 X-40 in the MDI for it to go to -40 degrees.

Hello,

we had a longish discussion about using an arduino for this task; here:

www.homemodelenginemachinist.com/threads...rduino-idexer.35108/

and here:

www.homemodelenginemachinist.com/threads...e-for-dummies.26744/

Be careful with rounding errors and backlash, but for simple indexing this does work fine.

With an Arduino and stepper that is rel. slow, but I would prefer it over a linux CNC system, because it "stand alone" and cheap and easy to build.
The second link is good for the basic setup and wiring description. 
The first link dives into the rounding error explanation. 

Good luck. 

Wow! Lots of replies that I was hoping to receive an email about. >.> 

I'll admit, Arduino would absolutely be a better platform for this, considering the timing overhead of running the entire Linux kernal for the sake of a single stepper motor. That being said, (and at the risk of falling prey to sunk cost) I'd really like to use this as a jumping off point to using LinuxCNC for other stuff down the line. Also, I've got the Pi in hand, whereas I'll have to order an Uno clone to pivot on hardware. 

I'm also hoping to make the solution a black box that presents a web interface advertised to `turntable.local`, so that my uncle can control the thing from any device on the LAN. I'm pivoting from using the desktop interface because he's hoping to use a tablet to control the turntable. (Personally I think a touchscreen would be KISS, but I'm not going to argue with the 'customer'.)

Or enter G0 X-40 in the MDI for it to go to -40 degrees.

G0, huh? I think that might be my ticket in under the hood, assuming I can get the HAL config all figured out. I'm going to give that a go before I make another topic asking for help adapting a `STEPCONF` output.