Mike Goetzke
02-13-2019, 9:37 AM
I've really never used bench dogs much so unfamiliar with fit required. I'm having an MFT style MDF slab CNC'd to use with my track saw system. This is known as a 20mm system. What should be the fit between the bench dogs and top holes?
From my investigation I found many use 20mm drill bits, 20mm router bits, 20mm hinge boring bit, and 20.01mm for CNC. I had a test hole bored and the 20.10mm hole size that is recommended by some seemed too loose using my bench dog as a plug gauge (my bench dogs are 19.89mm to 19.90mm). The CNC guy was nice enough to bore six more holes at 0.001" smaller increments (I know metric/English). So I had holes at 0.791", 0.790", 0.789", 0.788", 0.787", 0.786", and 0.785" (note: these were sizes he punched into his CNC, no measurement made to verify their exactness). At 0.788" the dog did not drop right in under it's own weight but still had noticeable side-side motion. At 0.787" with slight force it slid in the hole, no side-side motion, and pulled out without much effort.
I choose this hole but in hind site is this too tight? The tables haven't been machined yet.
Thanks for your input,
Mike
From my investigation I found many use 20mm drill bits, 20mm router bits, 20mm hinge boring bit, and 20.01mm for CNC. I had a test hole bored and the 20.10mm hole size that is recommended by some seemed too loose using my bench dog as a plug gauge (my bench dogs are 19.89mm to 19.90mm). The CNC guy was nice enough to bore six more holes at 0.001" smaller increments (I know metric/English). So I had holes at 0.791", 0.790", 0.789", 0.788", 0.787", 0.786", and 0.785" (note: these were sizes he punched into his CNC, no measurement made to verify their exactness). At 0.788" the dog did not drop right in under it's own weight but still had noticeable side-side motion. At 0.787" with slight force it slid in the hole, no side-side motion, and pulled out without much effort.
I choose this hole but in hind site is this too tight? The tables haven't been machined yet.
Thanks for your input,
Mike