User guide

Appendix l C-4
All About Cutter Bushings
Cutter bushing length
On flexible extrudates, it is important to minimize the length of the cutter bush-
ings. It is very difficult to push flexible extrudates through since it tends to com-
press 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 remainder of the bushing length being
tapered. On sticky flexible 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 outside 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 blades.
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