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Broaching units and broaching tools

Keyways, splines, squares and hexagons cut on the lathe, in the turning cycle. A broaching unit turns turret rotation into a reciprocating slide stroke, so an internal form is cut on the machine that already holds the part — no second setup, no slotting machine, no sub-contract operation. Mongtec publishes four unit sizes and a complete insert-holder and insert programme behind them. Mongtec Precision is a Taiwanese brand, designed and engineered in Taichung, Taiwan.

Send the form, size and material — we quote the unit and the tooling →

What the unit does

The slide carries a single-point tool that is pushed through the bore on every stroke, taking a small increment each pass until the form is finished. Because the ratio is 1:1 and the stroke is fixed, the cycle is programmed like any other turret operation. Both internal and external profiles can be cut with the same slotter by reversing the rotation of the unit and turning the tool to the working direction.

Unit sizes and slide travel

Broaching tool code	Max slide travel	A1	A2	A3	B1	B2	B3	L1	L2	H
MLST25	25 mm	50	27	77	46	27	73	52	63	30
MLST35	35 mm	76	35	111	76	35	111	95	100	58
MLST50	50 mm	91	50	141	76	50	126	95	110	58
MLST65	65 mm	106	65	171	76	65	141	97	125	57.5

All dimensions in millimetres. A, B, L and H refer to the dimensioned drawing in the broaching unit catalogue.

Insert holders

The insert holder is the part that reaches down the bore and presents the insert. It is chosen by the form you are cutting and by the smallest hole it has to pass through, then matched to the unit size (25, 35, 50 or 65).

Holder family	Form cut	Unit series	Holder dia. D1	Smallest hole
MLUTM	Round bore — keyway, standard length	25 / 35 / 50 / 65	6 – 25 mm	7 – 27 mm
MLUTMS	Round bore — keyway, short body	25 / 35 / 50	6.5 – 28 mm	7 – 30 mm
MLUTMSQ	Square internal form	25 / 35 / 50 / 65	7.25 – 25 mm	8 – 27 mm
MLUTMHEX	Hexagon internal form	25 / 35 / 50 / 65	8 – 28 mm	8.7 – 30 mm
MLUTMM	Blank holder for special and non-standard forms	25 / 35 / 50 / 65	made to the form	made to the form

Holder codes carry the unit series as the last digits — MLUTM0435 is the ø10 mm round holder for the 35 series. Per-code lengths (L1 to L6), diameters and weights are tabulated in the catalogue.

Inserts

This is the part most buyers do not expect: for round keyways, squares and hexagons the insert is a catalogue item, not a special. Only genuinely non-standard forms are made to the workpiece.

Insert programme	Code	Range	Classes
Round keyway, metric	MLIN02 – MLIN25	nominal 2 to 25 mm	P9, H7, D10, C11 — plus P9SM and H7SM narrow versions
Round keyway, inch	MLIN3/32" – MLIN3/4"	3/32" to 3/4"	P9, H7, D10, C11
Square	MLINSQ8/10 – MLINSQ37/50	working range 8 to 50 mm	—
Hexagon	MLINHEX9/11 – MLINHEX45/70	working range 9 to 70 mm	—

Every insert code in the catalogue names the holder (“tool”) it belongs in — UT02 to UT18/25 for round, UTSQ and UTHEX for square and hexagon — so the holder and insert pairing is fixed, not a judgement call.

Setting up and running the unit

These are the points that decide whether the first part is good. They come from the Mongtec broaching unit operation manual, which is published as a separate PDF.

Delivery condition	Units ship greased, tested and ready to run.
Ratio and stroke	Ratio 1:1. The operation manual describes fixed strokes of 35, 50 and 65 mm.
Mounting	The flange is aligned on the turret with a comparator against the flange perimeter, then the turret bolts are tightened. The unit itself locates on the aligned flange through a CamLock system and is secured with M10 grub screws.
Y-axis adjustment pin	For lathes without a Y axis. Turning the pin shifts the tool ±0.5 mm along Y — enough to correct symmetry error between the hole and the part.
Cutting angle screw	Corrects taper caused by mechanical deflection. Range about ±3°.
Gib adjustment	After long use, clearance is taken out at all four gibs: release the hexagonal nut, bring the central grub screw flush with the slide (near it, not tight), then re-tighten the nut.
Lubrication	Grease the slotter after roughly 10 continuous running hours through the two grease nipples. A GAS 3/8" threaded port feeds internal coolant — internal is recommended over external, so the fluid reaches the cutting zone.
Maintenance interval	After roughly 1,000 running hours or one year, wear parts such as bearings and seals are replaced.

Catalogue PDFs

Mongtec broaching unit toolholder catalogue

Broaching unit toolholder catalogue (PDF)

Mongtec broaching toolholder operation manual

Broaching unit operation manual (PDF)

What we need to quote. The form (keyway, square, hexagon or special), its size and tolerance class, the bore it has to pass through, the depth, the material — and the machine and turret. Send those and Mongtec engineering comes back with the unit size, the holder, the insert code and the turret interface. That check is free.

Get the unit, holder and insert codes for my part →

Frequently asked

Do I need a special tool for every keyway?

No. Round keyways from 2 to 25 mm and 3/32" to 3/4", squares from 8 to 50 mm and hexagons from 9 to 70 mm are catalogue inserts in fixed tolerance classes. Specials are built when the form itself is non-standard.

Which unit size do I need?

Start from the longest form you have to cut: the slide travel (25, 35, 50 or 65 mm) has to cover it. The bore the holder must pass through then decides the holder family and diameter.

Can it cut external profiles?

Yes. The same slotter cuts external profiles by reversing the rotation of the unit and turning the tool into the working direction.

Will it fit my turret?

The unit mounts on a flange that is aligned to your turret. Send the machine model and a photograph of the turret face and Mongtec confirms the interface against the actual drawing before quoting.

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