BDS A024 vs B024 Compact Datum: How to Choose a Positioning Datum for Robot-Handled Fixture Carriers

Should the robot pallet use the smaller BDS A024, or step up to B024? Both bodies list the same hold-down force. The real split is table space, robot payload, and whether a side cut can tip the pallet.

A compact positioning datum is the small receiver on the machine table. The robot carries a matching pallet, often called a fixture carrier. The pallet drops onto the receiver. The receiver holds it while the mill cuts. Shop air then opens the lock so the robot can lift the pallet out.

NEXTAS sells this stack as the BDS family. The two common bodies are A024 and B024. The selected model drawing still wins over this page.

What sits on the table?

Keep two parts distinct. The datum body stays on the machine, the trunnion, or a setup bench. The datum pallet is the part the robot moves. Vises, nests, or dovetail blocks bolt to that pallet. If you order the wrong pair, the robot cannot seat the job.

BDS is the compact family for that handoff. It is smaller than a large multi-receiver zero-point plate. Use BDS when the table, the 5-axis platter, or the gripper needs a short stack. Use a larger plate family when the fixture is wide and the cut is heavy. The BDS product page is the catalogue source for the numbers in this article.

A024 and B024 use the same spring-and-ball lock. Hardened balls, pushed by springs, pull the pallet down. Shop air at 0.5 to 0.8 MPa compresses those springs to unlock. When air vents, the springs hold again. That shared lock does not make an A024 pallet interchangeable with a B024 body. The hold is a process hold. It is not a safety-rated stop unless the full cell safety design says so.

The catalogue also lists a centre lift inside the receiver. Air extends that lift so the pallet first lands on a cushion, not on the precision locating faces. Seals and an air blast help keep chips out of the seat. An air-seat check can then watch the seat: it is a process check that can block Cycle Start when the pallet is not down, not a safety stop. Set the leak or pressure limit on the real cell.

Same listed force, two different bases

A common first question is: if A024 and B024 both list 60,000 N and seat closer than 0.003 mm, why pay for the larger body?

The listed force is the spring pull-down on the selected body. It is not the same as the side load a tall fixture can take. A side cut tries to tip the pallet around the outer edge of the seat. A wider seat gives a longer lever against that tip. The force number does not change. The support width does.

A024’s body is 320 × 240 × 50 mm. B024’s body is 330 × 267 × 50 mm. The short side grows from 240 mm to 267 mm. That extra width is the reason to step up when the part is tall or the cutter pushes hard to one side.

The catalogue reseat closeness is also the same: below 0.003 mm on both main bodies. That figure is how close the pallet sits again on the selected interface. It is not a finished-part tolerance, and it is not a coordinate measuring machine (CMM) transfer result. Prove those on the project.

Catalogue sizes and weights

Values below come from the current BDS catalogue page. Confirm the selected model drawing before you freeze a robot payload.

Keep the body and pallet in the same family. An A024 pallet is not a drop-in on a B024 body. Confirm the pair on the interface drawing before the robot program is written.

Both bodies use four Ø13 mm mounting slots. Torque the screws on a clean, flat plate. Confirm flatness on the approved drawing. Do not twist a hardened body onto a bowed subplate and then blame the seat.

Can a side cut tip the pallet?

A024 is the compact choice. It fits a small 5-axis platter and a tight enclosure. B024 adds 27 mm on the short side. Use that extra width when the fixture or part stands well above the pallet, or when a heavy side cut can pry the far edge of the 320 × 240 mm A024 seat.

This is planning talk, not a NEXTAS load test. Send part height, tool path, and fixture mass if the cut is aggressive. Do not treat 60,000 N as a licence to cantilever a tall tombstone on the small body.

Will the robot still lift it?

Every kilogram on the pallet is a kilogram the robot cannot spend on the part. The A024 pallet lists 7.5 kg. The B024 pallet lists 10 kg. That is 2.5 kg of extra empty-pallet weight on every transfer.

On a compact six-axis arm in the 12 kg to 20 kg class, 2.5 kg can be the difference between keeping the current robot and buying a heavier one. Count the pallet, the gripper fingers, the vise, and the part. Write “unknown” on any line you have not weighed.

If the robot payload is tight and the fixture is tall or the cutter pushes sideways, do not freeze A024 from payload alone. Send height, tool path, fixture mass, and the arm chart at the real centre of gravity. You may need B024 for seat width, or a larger plate if neither compact body covers the job.

If the arm is in the 25 kg class or above, and the table can take 330 × 267 mm, B024 is often the better first pick because the seat is wider against tip. Extra pallet mass is a second, weaker reason. Those robot classes are planning ranges, not a NEXTAS robot spec. Use the arm maker’s payload chart at your real centre of gravity. A pallet that is legal at rest can still over-torque the wrist in a fast flip.

How the robot should set the pallet down

A typical load is slow and boring. That is the point. Rushing the last 20 mm is how the precision locating faces get scarred.

1. Bring the pallet to about ±0.5 mm of the seat. That is a rough window, not a precision claim.
2. Turn on unlock air at 0.5 to 0.8 MPa. The lock balls retract. The centre lift rises.
3. Lower the pallet onto that lift, not onto the precision locating tapers.
4. Let the air blast clear chips from the seat.
5. Release the gripper. Vent the air. The springs pull the pallet down.
6. Read the air-seat check. Only then allow Cycle Start.

If unlock pressure is low, the balls may not clear. The robot then drags the pallet. If the air is wet or oily, the springs get sluggish over months. Use clean, dry air. Confirm pressure at the receiver, not only at the compressor.

The air-seat check should block Cycle Start when the pallet is not down. It is not proof of a safety-rated function. Four 90° landing rotations let the robot set the pallet down in four square angles. That helps when the enclosure is not square to the load aisle. Confirm the home angle on the drawing. Do not assume every station uses the same one.

One datum from the bench to inspection (CMM)

A frequent loss is to reclamp the part between roughing, wash, and inspection. Each reclamp adds stack. If the same BDS pair sits on the setup bench, the mill, and the coordinate measuring machine (CMM), the part keeps one origin.

That only holds if every station uses a matching body and a matching pallet. Mix families and the origin drifts. Mix a BDS pallet with a large zero-point receiver and you have two interfaces, not one.

If the fixture is already a full-size zero-point plate, do not force BDS into that job. Size the receivers from the 85 / 120 / 160 / 195 mm receiver guide. BDS is the compact fork, not a substitute for a four-receiver plate on a wide tombstone.

Which model should you shortlist?

Lean toward A024 when:

• The table or 5-axis platter cannot take a 330 × 267 mm body.
• The robot payload is tight, and 7.5 kg of pallet mass matters.
• The cut is light to medium: aluminium, drilling, or finish work.
• You want more than one compact datum on one subplate.

Lean toward B024 when:

• The fixture or part hangs past the A024 seat (320 × 240 mm).
• The table can take the 330 × 267 mm body.
• The robot can carry a 10 kg pallet plus the vise and the part.
• You need the extra seat width against tip first; extra pallet mass is only a second reason.

If neither body covers the table, stop. You may need a larger zero-point plate, not a bigger BDS. Say that in the quote pack. Do not stretch a compact datum across a job it cannot support.

What to put in the BDS quote pack

NEXTAS can review the BDS body, the matching pallet, and open questions on the stack. We cannot sign off a robot brand, a cell safety plan, or a coordinate measuring machine (CMM) program from this page. Send this brief so the quote talks about the same machine.

• Table: machine model, platter or tombstone size, leftover tool length, and a photo of the current plate. Write “unknown” if a field is open.
• Robot: maker and model, listed payload, and the true centre of gravity with gripper plus pallet.
• Job: part size, material, fixture height, and whether the cutter takes a heavy side cut.
• Flow: setup bench, mill, wash, and inspection (CMM). Note which stations need a matching receiver.
• Air: pressure you can hold at the receiver, not only at the compressor.

Ask for the body and pallet pair, the index home, and the open questions. The cell builder still owns reach, guarding, and recovery. The process owner still has to prove chips, probes, and first-part checks on the mix.