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  1. #1
    Join Date
    Jan 2007
    Posts
    114

    Rotary Broaching

    I have a job I am doing and the part needs to be internally broached T60 I am interested in rotary broaching the parts in my machine I found a company that makes torx rotary broaches and when I was speaking to the salesman he thought that I might have trouble overloading my servos I found this unlikely but I have no experience with this at all so here it is

    Haas VF3SS
    T60 rotary broach
    303 Stainless Steel part

    Thanks in advance

  2. #2
    Join Date
    Jul 2007
    Posts
    52
    Max thrust for Z axis is 3923 lb, maybe compare that to a Lathe z axis thrust that is known to work with the broach.

    Andrew.
    VF3+TRT210, VF3, VF2+HRT160, VF2SS+TR160, VF2SS+TR160, VF5TR, VF5TR, VF2SS+HRT-210HSHS,VF2SS+HRT-210HSHS,VF2SS+HRT-210HSHS

  3. #3
    Join Date
    Jan 2007
    Posts
    114
    That is a good call I will look into it for sure
    The guy that makes the broaches was more concerned with the X & Y holding force
    I guess is because it creates a huge side load on the part as it works

  4. #4
    Join Date
    Nov 2007
    Posts
    1702
    I guess I don't see how rotary broaching would cause any side loads. I thought you were asking about Z axis loads as well.
    Greg

  5. #5
    Join Date
    Nov 2010
    Posts
    32
    I agree, side loads are a minor issue compared to factors like depth, material and pre-drill size.

  6. #6
    Join Date
    May 2009
    Posts
    19
    There is some side loading that goes on, but I dont think it will be a problem to you. the z-axis load is easily controlled by feed rate. How hard is the stainless? high speed steel is usually used for rotary broaches, and is about 47C. There are some carbide tipped broaches, but chipping is the real problem there. Your stainless will like to see a 3 degree hook min, and make the bore is as large as possible. If you are going to a shoulder or blind hole, do the broach in steps, for deeper holes, with chip clearing in between. and make sure you follow with an e.m to remove the last burrs. I have broached alot of aerospace parts for rosan ports. usually in 15-5 stainless. Currently working on Hy-Tuff which is the same hardness as the broach. thinking we may have to edm our own broach out of 300 m and take it to about 60C.
    good luck.

  7. #7
    Join Date
    Nov 2006
    Posts
    490
    How big is the broach being used?

  8. #8
    Join Date
    Jan 2007
    Posts
    114
    The broach is a through hole .5 deep and it is called out at Torx T60 in 303 SS
    I have not found anyone that actually makes the broach yet does anyone know of a company that makes an off the shelf cutter for this ?

  9. #9
    Join Date
    May 2009
    Posts
    19
    Well the thru hole makes it alot easier, and it's a torx shape, so there isn't a big load on the broach either.
    a search on the net will turn up different sources, Polygon solutions would be a good place to start. They have off the shelf broaches, and can do customs if necessary.

  10. #10
    Join Date
    Aug 2010
    Posts
    579
    Quote Originally Posted by inertialabs View Post
    The broach is a through hole .5 deep and it is called out at Torx T60 in 303 SS
    I have not found anyone that actually makes the broach yet does anyone know of a company that makes an off the shelf cutter for this ?
    Slater Tools Internal and External Rotary Broaches

    Slater Tools is the company I use for this type of work. They have a tool-holding system that reduces the load.

    Another solution is two broaches (rough/finish).
    Thanks,
    Ken Foulks

  11. #11
    Join Date
    Jan 2007
    Posts
    114
    Thank you for the tip I will get in touch with them

    Have you done any projects similar to this ?

    If so can you give me an idea of how many parts I could get out of a setup like this I know that there are a ton of variables but a rough guess would be appreciated

  12. #12
    Join Date
    Dec 2010
    Posts
    0
    You could also try Polygon Solutions. Their holder is better built than Slater's Holder and it is grease-free!

  13. #13
    Join Date
    Aug 2010
    Posts
    579
    Yes, a hex broach at Westec and IMTS, we ran a demo on an SL-10 with a barfeeder. It was the same tool at both shows. Probably 1000 parts and still don't plan on changing it.
    Thanks,
    Ken Foulks

  14. #14
    Join Date
    Jan 2007
    Posts
    114
    That sounds like the amount of parts I would hope to get out of one
    What size Hex was it ?

  15. #15
    Join Date
    May 2009
    Posts
    19
    haw hard is the material? that's going to be the real factor in how many parts you may get. Most demos will use a softer free machining material for effect.

  16. #16
    Join Date
    Jan 2007
    Posts
    114
    The broach is a through hole .5 deep and it is called out at Torx T60 in 303 SS

    here are the properties I get for 303

    Rockwell Hardness B83

    I was told that broaching smaller sizes give much better tool life have you found this to be true ?

  17. #17
    Join Date
    May 2009
    Posts
    19
    the smaller broaches do tend to get longer life, and use less power due mainly to the fact that less material volume is being moved. this material is malleable, so try for the largest hook clearance, or let the seller know what you are machining. the broach should last quite well in this.

  18. #18
    Join Date
    Aug 2010
    Posts
    579
    We were broaching 1/2" wide 1/2" deep in 1018 steel which is 150 brinell. Expect about 2000 pcs. 303 is listed as 228 brinell.
    Thanks,
    Ken Foulks

  19. #19
    Join Date
    Aug 2008
    Posts
    292

    Broaching Forces

    Some machinist are concerned about damaging bearings when Rotary Broaching especially a larger size broach. Especially if Broach travels too far or is jammed with chips.

    You might want to check your Servo Overload protection. Whether it is a computer controlled setting or a overload clutch, a fuse, circuit breaker, shear pin etc. And possible consider increasing protection (lower amounts of force before overload / fault is created)

    Myself I believe a CNC machine should be able to take a cutter collision with a Vise and any servo X,Y,Z etc should stop after 2 seconds of non movement and generate a fault message (and safely shut servos down) on CNC control panel without damaging any bearing even spindle bearings.

    But as many CNC machinist know even a Auto Tool Changer can break parts sometimes needing repairs. When is the last time a CNC overload protection devices have been checked / calibrated ?? There are gages that will measure force and many will record maximum force (when overload trips force may drop quickly). It might be as simple as using the CNC controller and a special command mode to type in a lower overload amount before a fault is created to stop and protect the machine.

  20. #20
    Join Date
    Oct 2007
    Posts
    45
    Here is a good video showing how chips flow and accumulate during the rotary broaching process.

    [nomedia="http://www.youtube.com/watch?v=BhvNU2E_x_Y"]YouTube - Rotary Broaching Demonstration - How It Works - GenSwiss[/nomedia]

    The larger the allowable pre-drill size, the less force is required from the machine's z-axis during the broaching process. A full form T60 in 303 stainless will be troublesome for most machines to push unless the predrill diameter is opened slightly to help alleviate chip volume. The drawback to opening the predrill more is there will be a radius on the minor diameter lobes on the Torx profile which usually is not acceptable.

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