Walter
Fellow
When I am working with acrylics I normally leave the blanks over length, drill just short of breaking through and saw to length to avoid breakout or splitting.
With this 5" (125mm) blank there was no scope for cutting over length.
IMG_8437 by walter.hall, on Flickr
Here is how I got around the problem. I began by mounting the whole blank in my pillar drill and drilling the smaller diameter hole (in this case 10.5mm) to a depth of about 5mm more than the brass tube.
IMG_8440 by walter.hall, on Flickr
I checked (by inserting the tube)to see that the hole was longer than the tube:
IMG_8443 by walter.hall, on Flickr
I then marked the exact length of the tube and cut this length off on the bandsaw
IMG_8444 by walter.hall, on Flickr
This left the remainder of the blank with a 10.5mm hole in one end. I mounted this, hole end down, in the pillar drill and drilled through from the other end with the larger 12.5mm drill. Result, minimal breakout (just one shallow chip) and plenty of "meat" on the end to trim it back square.
IMG_8445 by walter.hall, on Flickr
I wouldn't recommend this as a normal method of drilling, but if you have a short blank and long tubes it may just save the day as it did for me.
Wasn't sure whether to put this here or in tips and jigs. Feel free to move it Jim.
Walter
With this 5" (125mm) blank there was no scope for cutting over length.
IMG_8437 by walter.hall, on Flickr
Here is how I got around the problem. I began by mounting the whole blank in my pillar drill and drilling the smaller diameter hole (in this case 10.5mm) to a depth of about 5mm more than the brass tube.
IMG_8440 by walter.hall, on Flickr
I checked (by inserting the tube)to see that the hole was longer than the tube:
IMG_8443 by walter.hall, on Flickr
I then marked the exact length of the tube and cut this length off on the bandsaw
IMG_8444 by walter.hall, on Flickr
This left the remainder of the blank with a 10.5mm hole in one end. I mounted this, hole end down, in the pillar drill and drilled through from the other end with the larger 12.5mm drill. Result, minimal breakout (just one shallow chip) and plenty of "meat" on the end to trim it back square.
IMG_8445 by walter.hall, on Flickr
I wouldn't recommend this as a normal method of drilling, but if you have a short blank and long tubes it may just save the day as it did for me.
Wasn't sure whether to put this here or in tips and jigs. Feel free to move it Jim.
Walter