ian maybury
02-05-2015, 7:07 PM
This to see what comes up - it's mostly idle curiosity/playing with methods so don't go to a lot of trouble.
The job is cutting the keyhole slots in the 18mm (we're metric this side of the Atlantic) ply shelves for a wall mounted tool cabinet to hold chisels - each chisel location is the fairly classic conical hole with 15 deg (a bit less angle might suit some chisels) off vertical sloped sides reducing to 13mm (roughly 1/2in) dia by the bottom/lower surface of the shelf. Then a 13mm wide slot cut in at right angles in from the front edge of the shelf lined up exactly with the conical hole, and just breaking through into the hole.
The narrow/circular part of the shank of the (mostly Japanese) chisels slides in through the slot, it's dropped when the conical hole is reached so that the steel male conical socket for the chisel handle drops nicely into the hole and locates in it - very similar to the arrangement in the photos here by David and especially Derek C: http://www.sawmillcreek.org/showthread.php?222017-All-purpose-nest-socket-design-for-chisel-rack
The question isn't about finding a method to cut the keyhole slots - it's just to explore whether or not there may be a straightfoward way to speed the job up a bit. It's proven possible to do it nice and cleanly by first drilling a 13mm through hole in the shelf using a very sharp Famag HSS brad point that has really sharp nickers, then plunging a conical/bevel/chamfer router cutter in the hole to a depth stop to create the taper hole. (one like the T1943-1/2 here: http://www.wealdentool.com/acatalog/Online_Catalogue_Chamfer_Bevel_79.html ) The bit has a 13mm dia guide bearing fitted which is a nice sliding fit in the drilled hole, which means that the bit is guided and can't damage the sides of the hole as the plunge is retracted. The edge to hole slot is then cut on the router table to break into the conical hole and top on its centre with the using a 13mm straight bit with the shelf clamped (bottom face down on the table) to a cross cut fence guided by a mitre bar in the mitre table slot.
It's worked fine for a run of trial slots, and cutting the 35 this way is perfectly do-able - but a faster set up would be nice. Especially given the need to accurately align the 13mm slot/router cutter and conical hole for every cut - it's slow. CNC would be the business, but isn't an option. It'd be easy to cut accurately spaced edge to hole slots first using a dado cutter or with the shelf vertical on the router table using a locating pin (like for a finger joint), but then the problem becomes how to bore the conical hole accurately located over it, and with part of one wall missing as a result of the slot… (could be done against the fence on a drill press, but the router cutter would need more rpm than the available 2,800 rpm to cut cleanly i think?)
Thoughts anybody? It's maybe worth saying that neither a shaped spade bit nor a conical reamer proved able to cut the conical hole without causing a lot of tear out in the ply. The conical router cutter also has the advantage of being carbide so it won't blunt so easily cutting ply.
The job is cutting the keyhole slots in the 18mm (we're metric this side of the Atlantic) ply shelves for a wall mounted tool cabinet to hold chisels - each chisel location is the fairly classic conical hole with 15 deg (a bit less angle might suit some chisels) off vertical sloped sides reducing to 13mm (roughly 1/2in) dia by the bottom/lower surface of the shelf. Then a 13mm wide slot cut in at right angles in from the front edge of the shelf lined up exactly with the conical hole, and just breaking through into the hole.
The narrow/circular part of the shank of the (mostly Japanese) chisels slides in through the slot, it's dropped when the conical hole is reached so that the steel male conical socket for the chisel handle drops nicely into the hole and locates in it - very similar to the arrangement in the photos here by David and especially Derek C: http://www.sawmillcreek.org/showthread.php?222017-All-purpose-nest-socket-design-for-chisel-rack
The question isn't about finding a method to cut the keyhole slots - it's just to explore whether or not there may be a straightfoward way to speed the job up a bit. It's proven possible to do it nice and cleanly by first drilling a 13mm through hole in the shelf using a very sharp Famag HSS brad point that has really sharp nickers, then plunging a conical/bevel/chamfer router cutter in the hole to a depth stop to create the taper hole. (one like the T1943-1/2 here: http://www.wealdentool.com/acatalog/Online_Catalogue_Chamfer_Bevel_79.html ) The bit has a 13mm dia guide bearing fitted which is a nice sliding fit in the drilled hole, which means that the bit is guided and can't damage the sides of the hole as the plunge is retracted. The edge to hole slot is then cut on the router table to break into the conical hole and top on its centre with the using a 13mm straight bit with the shelf clamped (bottom face down on the table) to a cross cut fence guided by a mitre bar in the mitre table slot.
It's worked fine for a run of trial slots, and cutting the 35 this way is perfectly do-able - but a faster set up would be nice. Especially given the need to accurately align the 13mm slot/router cutter and conical hole for every cut - it's slow. CNC would be the business, but isn't an option. It'd be easy to cut accurately spaced edge to hole slots first using a dado cutter or with the shelf vertical on the router table using a locating pin (like for a finger joint), but then the problem becomes how to bore the conical hole accurately located over it, and with part of one wall missing as a result of the slot… (could be done against the fence on a drill press, but the router cutter would need more rpm than the available 2,800 rpm to cut cleanly i think?)
Thoughts anybody? It's maybe worth saying that neither a shaped spade bit nor a conical reamer proved able to cut the conical hole without causing a lot of tear out in the ply. The conical router cutter also has the advantage of being carbide so it won't blunt so easily cutting ply.