I just love the concept of the AccuScribePro -- except that with those beautiful little brass thumb nuts, I find that I must use vise-grips to get it tight enough to not slip -- and slipping is the death of a scribe. Although because the bolt was metric, I had to tap a metric thread in the only wing nuts I could find, it is now a great device with wing nuts in the place of the knurled nuts. See photo. May I recommend a nut change so I could rate this tool as perfect?
You could try to take some blue painters tape and wrap the pencil to increase its diameter. Or see if you replace the pencil if you have the same issue. Anyhow hope that helps
After I received your message I tested it and it worked just fine. We sell tens of thousands of them and I maybe heard this three times in 15 years. I'm happy to send you another one to try. Just send your information to Sandi (firstname.lastname@example.org).