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| The Basics of Rotary Broaching & Technical Support | ||||||
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Rotating Broach – Rotary Broaching can be performed on turned parts as well as CNC machining centers or transfer-machine. The only difference being that the broach holder is rotated in the machine spindle and the part is stationary instead of the reverse condition on a lathe. Orientation of a profile and part can be accomplished with a drive on the spindle nose which maintains the exact angular position required. In order to produce parts successfully there are some basic rules that must be followed. |
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Cutting Principle - The tool is held at a 1° angle relative to the part centerline and has a 1° 30'' clearance angle built in. The face of the broach tool is the pivot of the 1° angle and is placed on centerline with the part. As the tool comes in contact with the part, friction drives the broach to rotate synchronously. The cutting edge is kept on center and the rest of the tool oscillates around the part centerline with a wobble effect. With the faces of the tool and part at a relative 1° angle, only the leading point of the tool is cutting and not the entire profile. The wobble effect moves the leading edge to rotate in and out of the cut like a cam. It shears the shape into the part with a scalloping effect as it advances forward. This reduces the required thrust force up to 80% when it is at the optimum feed. |
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Coolant - Usual coolant or cutting oil |
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Broach Preparation - A 60° or 90° chamfer, slightly bigger than the largest dimension of the broach, is essential for and easy start of the broach. When exact concentricity is required, counter bore the hole at the same size as the measured profile across corners, boring approximately .020” deep will provide the best results. |
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| Drilling The Hole - For internal broaching, the hole should be drilled approx. 1 % bigger than the diameter across the flats of a hex shape. This percentage can be reduced in free cutting material and increased as machinability decreases. In mild steel we recommend the following tolerances: | ||||||
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Drill the hole as deep as possible to leave room for chip accumulation. We recommend a depth of 1.3 to 1.5 times the length of the profile. |
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When a drill radius is not allowed along the broached walls of the part, tool life and bearing life will be reduced. When exact concentricity is required, c'bore, drill and pre-bore the hole which will keep the broach concentric when it enters the hole. With such a tight fit push back may result as the broach becomes a hydraulic ram. This pressure can be relieved with a vent hole supplied in the broach tool. |
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Centering The Broach - Nothing is more important than having the cutter centered as close as possible to the center of the work piece. Improper center setting will cause an uneven hole configuration, oversize holes and spiraling. The maximum eccentricity should not exceed .0008” To simplify setup on more accurate Swiss Type and Gang Machines, use our (on-center) 2100 Series holders. For easier setting on conventional CNC and other machines, use our gages 6189 or 6199 with the adjustable type broaching heads. |
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Broaching Rotation Speed - The basic principle of the 1° offset allows high speed application from 1500 up to 3000 rpm. Rotational speed has very little effect on cutting action or tool life. The cutting edges of the broach tend to dig in to the face of the part as the tool comes in to contact with the rotating material. When there is full contact they are in synchronous rotation. At higher speeds this dig mark will become more pronounced and tool life will suffer. For Best results start the broach operation at a slow rotation and then increase the speed when it is in full contact. Reversing the spindle rotation half way into the part can reduce spiraling. |
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Feed Rate - The feed choice mainly depends on the material characteristics. In a mild-steel, we recommend .0012 -.0024 per revolution. If the machine thrust force is sufficient, the feed can be doubled even tripled as machinability increases. In most cases the maximum feed rate should not exceed .03 x the profile diameter. A slower feed rate will produce an improved finish with finer lines along the sidewalls of the broached hole. By increasing the feed rate the cutting cycle will be faster but the broaching lines will be more pronounced leaving a coarse finish. |
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| An excellent place to start with speeds & feeds is by using the following formula; .016 x h = Inches / Revolution, where 'h' is equal to the size of the hex you are attempting to broach. | ||||||
Broach Sharpening – An external or internal broach tool can usually be sharpened one or two times if the tools are in reasonable condition. Only the front face will be re-sharpened with a cutting angle from 4 to 8°. |
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| Broach Setup For 2100, 2102, 2104 & 2160 series Swiss Type Broach Holders | ||||||
Setup of Swiss Type broach holders: The 2100 Series holders, 2100 line, 2150 line, and 2160 line do not require centering with an indicator. These heads are designed for machines with more accurate centering built into the machine. This would include Swiss Type, Gang type, and small precision lathes, all of which are designed for small diameter precision turning. It is not generally recommended to use the 2100 series broach head on conventional CNC turret type lathes due to the centering inaccuracy associated with these lathes. With the 2100 series broach head it is essential to use the correct length broach . The overall length of the broaching bit is 28mm +0,30 -0,0 and the shank diameter is 8mm with an h5 tolerance. Failure to use the correct length or to bottom out the broach will result in poor broach size, & quality. |
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| Broach Setup for 6180, 6190 26200 & 26300 series Adjustable Center | ||||||
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Setup of Conventional Style broach Holders: PCM broaching holders series 6180, 6190, 26200 and 26300 are delivered adjusted within .0006” for our standard tools with a 55mm +0.3 length. When tools with different length are used, it is essential to re-adjust the exact centering position. Experience has proven that turret bores are not in perfect alignment with the machine spindle after a certain working time. When misalignment is over .002 of an inch it is necessary to re-adjust the turret positioning to avoid broaching difficulties especially on small sizes. |
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| | Rotary Broaching.net Homepage | Swiss-Type Broaching | Adjustable Broach Holders | Rotary Broach Tools | | External Broaching Tools | Rotary/Wobble Broaching Support | Rotary Broaching 101 | |
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Thank you for taking the time to visit our site. Please do not hesitate to call or email with rotary broaching application questions or if you need help deciding which tools are right for your job. Hours of Operation: Mon - Fri 8:00AM - 5:00PM Eastern Time Genevieve Swiss Industries, Inc. |
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