Broaching a spline coupler

[moggymatt]

For all you machinest pros out there. A project i have in mind needs an acrylic coupler made to go on on a splined shaft. I have everything worked out to broach the inside with the correct number of splines.
The plan is to use the shopsmith in drill press mode, the predrilled coupler is mounted to an index wheel on the table. Using the router bit chuck to hold the cutting tool, i'll plunge around, adjust the table with the adjustable collar stop and plunge around, again and again till its done.

Question is: What is the best way to lock the Shopsmith spindle? I dont want the cutting tool to roatate any at all.

[JPG]

Turn a coupling with bore in each end that matches to od of the quill and the serrated collar. Then cut a slot in one side. Use water hose clamps to squeeze the collar onto the quill and collar.