Lathe Brake

Discussion in 'Machine Modifications' started by deeferdog, Oct 29, 2017.

  1. Oct 29, 2017 #1

    deeferdog

    deeferdog

    deeferdog

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    If ever you have used a lathe fitted with a brake and liked it, then using other lathes not fitted with this will leave you with the feeling that something is missing, which of course it is. My small Chinese bench lathe does not have a brake, turn off the power and it coasts to a stop as you would expect. In most cases this is not an issue but it can be an irritation if, like me, you have limited patience. At other times, such as threading up to a shoulder, a brake is a nice thing to have. I decided to see if I could fit one to my lathe. A quick Google search did not reveal much, lathe brakes seem to be one of those things that most operators can do without. I decided to use a pushbike disc brake setup as they are fairly cheap to buy. I do not have the mathematical ability to determine if the disc and pads would be capable of absorbing the energy of the rotating lathe mass so this was going to be very much a “suck it and see” exercise.
    I removed the end of the lathe, this is like a small cabinet with a lockable door that allows access to the drive belts and screwcutting gears. I mounted the disc on the end of the motor pulley via an adaptor spigoted and bolted to it. The brake callipers were attached to the bench the lathe is mounted on and then adjusted to ensure the pads did not rub on the disc, this was a bit fiddley to achieve and in the initial running some slight scraping occurred until the pads bedded in. I think this is usual on a new bike setup but I have never owned a bike with disc brakes.
    The brake pedal was a bit of messing around but in the end worked OK. I wanted to incorporate a micro switch into the design to cut the power to the motor contactor coil prior to the callipers engaging the disc, the pictures explain. The disc brake is actuated by a standard bike cable attached to the pedal. The theory is that when the pedal is depressed, firstly the power is disconnected from the drive motor via the micro switch then the brake pads engage the disc and stop the lathe.
    The system worked much better than I had hoped. Depressing the pedal brings the lathe to an instant stop, regardless of the rotational speed selected. The highest speed of my lathe is 1600 rpm but I can honestly say that I have never machined anything at that speed, certainly not cutting a thread to a shoulder! After five or six quick stops at mainly 700 rpm I felt the disc and pads and they were barely warm. This indicated to me that the setup was capable of absorbing and dissipating the energy OK. My lathe chucks bolt to the backplate so I had no qualms about operating the brake in either direction of rotation. I suppose that there will be some that will say that I am imposing a big load on the bearings etc, but I think that they will handle it OK, mainly because I don’t think the decelerational load is very much more than the accelerational, also, the brake will not be used all that much, only when the particular machining operation calls for it. I am quite prepared to stand corrected on this and invite comments. As a safety feature I personally would rather have it than not. I think I could stomp on the pedal quicker than I could reach the emergency stop button, plus it would have the added advantage of instant stop of the lathe. Just my opinion.
    Costs was pretty minimal, around A$40 from BangGood in HK. I had to modify the end of the lathe as the original end would no longer fit but it came out all right at the finish. Obviously a bigger lathe would require a bigger disc setup, possibly twin discs and use hydraulic actuation rather than cable. The application of a bit of math would help as well. Here is a link to a brief video https://youtu.be/_2dwS6Xu9A4 Hope you enjoyed this post, all comments are welcome, Cheers, Peter.

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    Blogwitch, 10K Pete, bmac2 and 3 others like this.
  2. Oct 29, 2017 #2

    DJP

    DJP

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    I have a disc from a motorcycle that needs a project. Thanks for sharing your ideas.
     
  3. Oct 29, 2017 #3

    Blogwitch

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    Lovely piece of work, simple and it does the job.

    I have an instantaneous emergency brake on my far eastern machines, but they are old school, having a brake drum rather than a disc brake that actually works on the back of the spindle, but I am sure yours is more efficient, and yes, if ever you have used a lathe or mill with a mechanical brake, you come to rely on it just like any other accessories on the machine. I would be lost without mine on the mill and lathe.

    Nice one

    John
     
  4. Oct 29, 2017 #4

    10K Pete

    10K Pete

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    I've been thinking about putting a switch/brake bar on my South Bend 10K. Back when, I worked lathes with that sort of set-up and really missed it when I left the company.

    I never once thought about a bicycle disc brake!!!!:wall::wall:

    Your post has shown me the path to happiness...:thumbup::thumbup:

    Thanks,
    Pete
     
  5. Oct 30, 2017 #5

    Wizard69

    Wizard69

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    While brakes are great for lathe you should be aware of the risk on machines with screwed on chucks. Stopping excessively fast can unscrew the chuck.
     
  6. Oct 30, 2017 #6

    perko7

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    Brilliant!! Would also save using the back gear to lock the spindle when trying to remove screw-on chucks that have become a bit tight ;)
     
  7. Oct 30, 2017 #7

    XD351

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    I was doing some machine work on a gear shaft last week and damned if i could get it to run true in the chuck - i usually et around 0.0005 run out at worst on that chuck , i had some copper shims under the jaws to stop the jaws marring the shaft and though one shim might be thicker than the others but no they were all the same .
    I ended up trying to shim the part up to get it running dead true as i didn't feel like changing to a four jaw but every time i did something the readings would go all over the place , ended up the screw on chuck was loose !
    I like the idea of having a brake on my bigger lathe as it has a bolt on chuck !
     
  8. Oct 30, 2017 #8

    Blogwitch

    Blogwitch

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    I run my lathe as either a D1-4 or a Myford nose, and despite using the drum brake harshly, I have never had the Myford chucks come unscrewed.

    John
     
  9. Oct 31, 2017 #9

    john_reese

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    I used to have a Pratt & Whitney lathe with a brake. If I hit the brake hard it would open the Hardinge Sjogren collet chuck.

    In the machine shop at college a guy showed me how to plug reverse to stop the spindle. The first time I did it I spun off the chuck and sent it spinning across the room.
     
  10. Oct 31, 2017 #10

    john_reese

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    Some industrial equipment used DC injection on the motor as a braking device. I suppose it could be adapted to a lathe.
     
  11. Nov 4, 2017 #11

    Wizard69

    Wizard69

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    I wouldn't even bother unless I had a very secure method of securing the chuck to the lathe. One option that might be OK is a ramp down via a VFD or some other smart motor drive. Believe me you only need to see a chuck unscrewing once to realize crap is about to happen. Even on a small lathe there is a lot of energy in that spinning chuck.

    Of course this didn't register on me until after buying my 9x20 lathe. If people ask, I always suggest going with some sort of bolted on chuck or something keyed to the spindle.
     
  12. Nov 5, 2017 #12

    Hopper

    Hopper

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    If you are worried about Myford etc chuck unscrewing it is easy enough to put a grub screw and copper insert in the chuck or backplate to lock it onto the spindle thread.
     
  13. Nov 5, 2017 #13

    DJP

    DJP

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    With my spare motorcycle brake disk I was thinking of attaching it to the back plate of the chuck. The caliper would need to be easily removed and replaced when changing chucks but that should solve the unscrewing danger. I got spooked once when the chuck backed out a couple of threads so the risk is real.

    A chuck brake would be useful but it's a project idea for my files. I'm OK with the lathe as is.
     
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  14. Nov 9, 2017 #14

    mattty

    mattty

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    I love the Brake, do you have a link for the brake you bought, I want to put one on my HAFCO lathe.
    Thanks Matt
     
  15. Nov 9, 2017 #15

    goldstar31

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    I've experienced this many times and on several Myfords.
    It is difficult to pin point the cause but one reason is wear and the possible use of the wrong tap or die as it closely approximates a standard tap but with a 60 degree thread rather than the normal 55 one.

    I also experienced a jammed catch plate which came with a ML10 and was put on my S7B.

    The removal involved converting a bit of square tubing and welding an extension. And 'No' I know all about belting bits of wood etc which other workers have recommended:wall:

    And yes, I know ALL about risks of damage to 60 and 55 tooth bull wheels- thank you:hDe:

    N
     
  16. Nov 9, 2017 #16

    Blogwitch

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    Norm,

    I had the same question asked about the Myford nose adapter on my powered RT, why it never came undone when I was machining using it.

    The only reason is the way I made both the noses and the way I do fit the chucks and the speed I run them at.

    The first thing is that I made both to very high tolerances after measuring up a few screw on fittings (you wouldn't believe how much difference there is between commercially made items, sometimes as much as 0.003" between threads and registers on individual backplates, that is why I like to make my own)

    I don't use threadlock or anything on the threads or register, just coming in at speed when fitting the chucks and finishing off with a solid 'thud', this sort of locks them in position.I suppose I could easily design something to lock the plates into position, but that would most probably destroy the register and runout I so carefully machined.

    The other thing is speed. I have two ranges on my lathe, changed over by moving belts on the motor, a thing I have never done, the high range can stay hidden forever as far as I am concerned, I have never needed it before now and don't need to contemplate it for future use. It seems some people can't live without speed, coming from old school where fast wasn't an option, you learn to do things at a more modest pace.and despite using all the latest tungsten tooling, I can get surface finishes far exceeding what people who have the need for speed crave for, it is just a matter of working with what you have got. If it is that critical, just run your machine in reverse, so it tightens up the chuck as you machine.

    So, why don't they come undone when I slam on the brake? No idea, maybe just the way I operate my machines when I am using threaded noses, slowly and carefully does it.


    John
     
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  17. Nov 9, 2017 #17

    goldstar31

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    Thanks John

    An awfully long time ago, I was making the Alan Timmins Dividing Head from a bought out part finished spindle and casting- ex Engineering in Miniature and a 'thinned' worm a la Martin Cleeve. Quite!!!!!

    And NONE of my Myford chucks and faceplates and whatever would fit. Somebody else's wrong tap!

    I wasn't a happy bunny

    Norm
     
  18. Nov 9, 2017 #18

    deeferdog

    deeferdog

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  19. Nov 9, 2017 #19

    deeferdog

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  20. Nov 10, 2017 #20

    Canobi

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    I know that one all too well, happened a couple weeks ago. A combination of absentmidedness, a new motor and a VFD was all it took to create the scariest experience I've had with my lathe to date, she was at full tilt when I tested the brake too.

    I hadn't tightened the chuck after swapping over from the four jaw and the dog clutch wasn't engaged properly, the result being that the chuck was able to spin once freely until the clutch pin caught, which dislodged the chuck with enough force to remove it and throw it directly at me when it dropped and caught the lathe. *club* Luckily there was a small piece of ply to hand which I used as a shield and to stop it from flying around my tiny workshop.

    The experience certainly left it's scar in more ways than one and those two factors are now top of my pre operations checklist. With them in place it's been behaving so far and I've eased back a tad on ramp and stop times as an extra precaution.
     

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