Feed Controls Explained

Reference Article

A feed control unit precisely regulates the feed rate of a self-feeding drill unit. The feed control cylinder has a single adjustable orifice through which all the hydraulic fluid must pass while the plunger rod moves smoothly at a constant rate throughout the entire stroke length.

Features

The feed controls units we have on offer are available in stroke lengths of 1″, 2″, 3″, 4″, and 6″ (See Figure 2) with a capacity of up to 1200 lbs. The feed controls are sealed so they won’t leak hydraulic fluid unless damaged. The sealed unit prevents dirt, dust or lint that can contaminate the fluid from entering, so the internal flow aperture never silts to cause variation in plunger speed. They are easily adjustable to your specific needs because the range of adjustment is over 300° with a very smooth, gradual rate of change. Each feed control unit is tested at its rated capacity to check constancy, load-holding ability and adjustability.

How It Works

The spindle of the drill unit is housed in a quill which moves out of and into the cylinder of the drill unit as it advances and retracts. The feed control unit is mounted within the stop collar, which is mounted to the end of the quill. When the spindle advances, so does the feed control unit. The feed control unit requires a surface to act against to resist the forward motion of the drill unit and provide a smooth, consistent feed rate. In some cases, customers have used the surface of the workpiece for this purpose. Unfortunately, many factors can make this impractical. Blackalloy offers a feed control stop bracket which is normally quoted with every drill unit equipped with a feed control. The feed control stop bracket is slotted and can be mounted in such a way that it provides an adjustable surface that the feed control unit can act against.

In the case where a feed control stop bracket is utilized, the bracket is adjusted to meet the plunger of the feed control just before the cutting tool enters the workpiece. This ensures that any excess stroke distance before the cut occurs as fast as possible while also preventing the shock of the cutting tool engaging the workpiece at full speed. The feed control engages just before the cutting tool enters the workpiece and provides a constant rate of forward motion through the cut. In the case where the workpiece is utilized, the feed control unit must be adjusted within the stop collar so that the plunger of the feed control contacts the workpiece just before the cutting tool.

In Figure 1 below, the drill unit will travel at maximum stroking speed (determined by air pressure, PSI supplied to the drill unit) through the first 1/2" of the stroke until the feed control unit contacts the adjustable stop. When this happens, the feed control unit reduces the stroking speed to a constant adjustable rate over the remaining 1" of stroke.

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Figure 1

Size Matters

The feed control unit should always have a stroke length that exceeds the full depth of cut for the workpiece. If the stroke length of the feed control unit is less than the full depth of cut for the workpiece, the drill unit will not reach the intended depth because the feed control unit has reached the limit of its travel and the drill unit will no longer advance to the end of the stroke. Alternatively, you would have to set the feed control to engage after the cutting tool has engaged the workpiece, which reduces considerably the benefit of using a feed control unit.

In many cases you will have some excess stroke length in the drill unit to allow clearance for loading the workpiece or make up for variability in the workpiece, among other reasons. In these cases, it is not necessary that the stroke length of your feed control unit equal or exceed the stroke length of your drill unit. Ideally your feed control stroke length will exceed the depth of cut required for the workpiece and no more. Else you will be purchasing stroke length you do not need and will not use.

For example, you have a 3" stroke drill unit and you are drilling a 1-1/4" deep hole. You would likely use a 2" stroke feed control as opposed to a 3" stroke feed control because the last 1-1/2" of stroke would never be utilized.

An exception would be a case where you have a 1-1/2" stroke drill unit and you are drilling a 1" hole. In all likelihood you would use a 2" stroke feed control unit to ensure that you have room for clearance at the beginning and the end of the 1" depth of cut.

Feed Rate Adjustment

1", 2", and 3" stroke length feed controls are adjusted by inserting a rod in the hole in the brass adjustment knob at the base of the unit and rotating the knob. The 4" & 6" feed controls are adjusted by turning the knurled brass adjustment knob with fingers. Turning adjustment knob full circle, will not harm the unit but do not adjust while under load. Adjustment is at its fastest setting when indicator slot is at #0 on the scale line and at its slowest setting at #30 on the scale line. The no scale area between #30 and #0 is a null area with no adjustment.

When using a feed control unit, the feed rate is constant through the stroke length of the feed control unit. However, the feed rate is affected by load. If you adjust the cylinder to your desired feed rate while running the drill unit at 80 PSI, then you adjust the air pressure to the drill unit to 100 PSI, your feed rate will likely increase because the load on the feed control has increased. You will want to control and monitor these and other factors if you need to maintain a precise feed rate over time.

Positioning Considerations

Feed control units are mounted on the drill unit stop collar and clamped in place in a split mounting configuration. The position of the feed control unit can be adjusted within the stop collar by loosening the clamping screw and moving the feed control forward or back within the mounting hole. The feed control unit must be clamped within the safe clamping zone to avoid crushing the cylinder and voiding the warranty. The safe clamping zone for each feed control unit is within the first 3.25", 4.25", and 5.25" for the 1", 2", & 3" feed controls respectively. For 4" and 6" feed control units, the safe clamping zone is within the reduced diameter at the front of the cylinder.

Do not twist the plunger rod within the body of the feed control unit or allow load to slide across end of plunger causing the plunger to twist during its stroke, otherwise the plunger seal and bushing life will be shortened.

Feed Control reference dimensions illustration.
Figure 2

Service & Maintenance Considerations

If necessary, readjust after the feed control has reached its highest operating temperature. The maximum recommended operating temperature is 135° F. We do not recommend operation in ambient temperatures below +40° F or above +120° F.

The feed control units are designed to operate without external lubrication. The plunger bushing and seal are permanently lubricated with a special lubricant and protected by a rod wiper. Additional lubrication of the plunger is not recommended because ordinary oil will displace the special lubricant and may shorten the long wearing life of the
unit.

Remove feed control units from service immediately if the plunger hesitates or fails to travel all the way out on its return stroke. Keep a spare unit on hand if a breakdown would be costly. Life expectancy is millions of cycles, but any hydraulic unit will eventually wear out. When repair service is required, the unit may be returned to factory for fast, expert work at reasonable rates. The feed control units are light weight and inexpensive to ship.

Technical Specifications

Feed Control
P/N
DescriptionStrokeMinimum Full
Stroke Force
Return
Spring
Force
Plunger
Return
Time
1" per
Second
Load
4" per
Second
Load
1000
lb.
Load
500
lb.
Load
100
lb.
Load
K10Slow Speed1"5 lbs.4 lbs..378 sec.30 lbs.90 lbs.75 sec.180 sec.25 min.
K20Slow Speed2"5 lbs.4 lbs..730 sec.30 lbs.90 lbs.150 sec.6 min.50 min.
K30Slow Speed3"5 lbs.4 lbs..1.62 sec.30 lbs.90 lbs.225 sec.9 min.75 min.
K40Slow Speed4"5 lbs.4 lbs.1.87 sec.30 lbs.90 lbs.5 min.12 min.100 min.
K60Slow Speed6"8 lbs.7 lbs.2.39 sec.30 lbs.90 lbs.7.5 min.18 min.150 min.

Capacity: 1200 lbs. Maximum – Including Impact When Load Strikes Plunger.
135˚F Maximum Continuous Operating Temperature

  • Minimum Full Stroke Force - Minimum force that will operate plunger full stroke. (lbs.)
  • Return Spring Force - Plunger return spring force. (lbs.)
  • Plunger Return Time - Time required for plunger to return outward if released suddenly.
  • 1" per Second Load - Load that will push plunger 1 inch per second at fastest adjustment.
  • 4" per Second Load - Load that will push plunger 4 inches per second at fastest adjustment.
  • 1000 lb., 500 lb., 100 lb. Load - Time for full stroke of plunger at slowest adjustment at 1000 lb. load, 500 lb. load, and 100 lb. load.
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