View Full Version : Cable Diven PR to Rack and Pinion

10-07-2006, 12:28 PM
I want to update my cable driven PR to rack and pinion.
Could someone give me the gear rack and matching pinion gear specs so I can order the proper materials.

My machine is as follows:
1996 cable driven PR
72" by 120" 3 axis with Vexta PK266-02A 2 phase 1.8 degree 2A stepper motors with 1/4" shaft.

Thank you,

10-07-2006, 01:28 PM
You can buy the spur gears and racks from McMaster-Carr. The 20-degree pressure angle, 20-pitch gears and racks are found on page 985 of their on-line catalog. I use the 20-tooth spur gear, but others find that the 25-tooth or the 30-tooth spur gears work better.

I would re-consider using the PK266-02A stepper motors. The 23-frame size is awfully small. Although I've used dozens of PK268-02A motors on non-CNC projects, I wouldn't consider using them on anything larger than a micro/mini mill or lathe. The 34-frame size PK299-02AA stepper from Oriental Motor is about $200 each, and much better suited to handle the torque of a large CNC machine. Of course that would also mean that you would have to update your controller to the Agek or G4 - but it's do-able, and, if the cost of about $2,500 - $3,000 is within your budget, you'd be on your way.

10-07-2006, 01:37 PM
A 1/4" shaft won't do for springloading the pinion against the rack.

10-07-2006, 02:02 PM
Thank you for the info and quick response. The main reason for the upgrade is that I have already upgraded my controller to the Ascension 1000 and due to the speed increase have found that the cable drive and my current motors are not allowing me to take full advantage of my current setup.

Even with my current motor configuration, if I try to run my machine at two thirds of the new controllers full potential I feel it would literally tear it apart over time.
I am hoping that with some beefing up that the machine will be able to run close to its potential.

I have no problem upgrading the motors during this conversion if you feel that a slightly modified original PR frame could handle it.

Thank you,

10-07-2006, 02:10 PM

I wish that I had information concerning the frame, but my only real experience is with my Alpha. I've worked with one PRT but never a PR. However, I can't imagine why any machine couldn't be beefed up.

You might try searching this forum for threads about tables, etc. Be sure to look at Gerald's Mechmate website for lots of information and photos.