Cutter bushing length
On flexible extrudates
, it is important to minimize the length
of the cutter bushings. It is very difficult to push flexible
extrudates through since it tends to compress as it is pushed,
causing a marginal increase in the tube diameter. For this rea-
son, bushing lubrication may be necessary to minimize drag as
the length of the bushings increase. A discharge conveyor may
also be helpful in removing longer cut parts. The exit bushing
may be funneled to allow the cut part to drop out faster while
still maintaining minimal bushing length for safety.
●
For flexibles, the upstream cutter bushing should offer
total support to the extrudate as close to the nip point
of the puller as possible. In this way the part is not able to
move from side to side or bow from the weight of the
tube, which can, in turn, cause variable drag. You use the
strength of the tube to push itself.
●
The bore length of the exit bushing should not be shorter
than 1 1\2 times the diameter of the tube with the remain-
der of the bushing length being tapered. On sticky flexi-
ble extrudates, the parts will actually stick back together
if the new part has to push the cut part out very far.
For rigid extrudates,
the length of the cutter bushings can
result in a square cut or an angular cut. The cutter bushings
support the extrudate keeping it from moving from side to
side and bowing from the weight of the profile itself. Many
processors make their bushings short to minimize cost of
EDM which is determined by depth of cut.
●
For rigid extrudates, a general rule is to make the length
of the cutting bushings equal to two times the largest out-
side dimension. NOTE: In the case of full profile cutter
bushings where maximum support is offered, the bushing
length may be shortened depending on actual clearance.
●
Be sure to have a lead-in angle machined into the
entrance of the upstream cutter bushing. The transition
from the bore to the lead-in angle should not be abrupt as
it to can cause variable drag.
CAUTION: Blade hazard
In order to comply with OSHA regulations, the
distance from the sidewall of the cutter to the
blade (through the bushing) must be long
enough to prevent fingers from reaching the
blade.
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