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12th Dec 2020, 02:35 PM #1
Disc brake for lathe - best location?
I own a Metalmaster 12 x 36 circa 2007 - same as an AL 335 - you know, same lathe different brand and had a rush of excrement to the brain about fitting a disc brake.
In terms of efficiency, where is the best location to fit such a disc brake?
The disc is about 150 mm diameter and originates from a step through cycle. I also have the hand brake master cylinder assembly from the same cycle.Those parts gave been sitting around for 7 or 8 years.
I am favoring the pulley off the motor location as I think that may be the easiest to mount. The question in my mind is how efficient is that location?
I have heard of locations behind the chuck and also at the change gear box. Can anyone speak to the advantages and disadvantages of mounting in these places?
If members have some experience and insight over such a project on their lathe I would lathe to hear about it.
I have the lathe and drill press to do this work with ,but don't own a mill but can get access to one with some difficulty.
Any advice ,opinion and relative information is most welcome.
Thanks
Grahame
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12th Dec 2020, 05:16 PM #2Most Valued Member
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Grahame the motor would be a good spot, motor braking with a vfd works well. A mounting bracket for the caliper should be pretty straight forward and bolted to the motor mounting bolts
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12th Dec 2020, 05:17 PM #3Most Valued Member
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Motor pulley is where I put mine.
On a AL 335 that's the shaft that's spinning fastest.
Behind the chuck would mean no "worry" about the load on the gears. But you will need more brake pressure as the chuck is always at a lower rpm.
I had wondered about belt slip but I haven't had an issue. Though mine setup is a cable operated brake off a monkey bike. You might have more stopping power.
It might come down to just how fast you want the brake to stop the lathe. Mine as currently setup stop so the lathe a lot faster, but if you are after "almost instantaneous"
Can't see how you would easily fit a rotor on a camloc spindle. Unless you really do mean "chuck" which would mean a rotor on each chuck??
QCGB never entered my mind. I would be worried about the gears in that case. Besides, there is a lever on the front of the headstock that would make your brake ineffective.
Had to cut a slot in the cover for the rotor and a hole in the side for the caliper.
Pretty sure I did a thread. I will have a look.
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12th Dec 2020, 05:18 PM #4Philomath in training
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I guess the short answer is that you can mount it anywhere you like. However, as the idea is to stop the chuck quickly, ideally it will be on the spindle. Any further along the power train and there is the added inertia of the train to consider.
The other thing is that if it is the other side of say a V belt. If the belt breaks then the brake is useless, so preferably there are only rigid couplings between the brake and the chuck.
Michael
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12th Dec 2020, 05:40 PM #5Most Valued Member
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Found the thread but the pictures are gone.
Here is a video, stopping without and with brake.
https://www.youtube.com/watch?v=CmTeDUAPceg
You sure? brake has to stop all inertia where ever you put it.
With a AL335 the motor is doing 1440rpm, the chuck might only be spinning at 75rpm, so you'd need 20ish times the braking force(yeah the total energy is the same)to stop in the same time.
AL335 has twin belts. So I put it down to "damn you have to be unlucky to lose a belt the time you really needed it. How unlucky would you have to be to lose them both? and even then it will coast to a stop like 99% of the lathes out there, so no worse off"
Now there are some threading practices where that might not fly.
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12th Dec 2020, 05:44 PM #6
Me,being old and lazy ,the motor end is where it looks to be the easiest point of attachment. I have never broken a belts to date, but having said that , fresh belts will be on the agenda along with the mod.
You responded to my same inquiry in 2011 on the WW side but no pics from then . Sorry, I had forgotten completely.
Still I do need to find out as much as I can before starting.
Thanks for the replies so far.
Grahame
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12th Dec 2020, 05:56 PM #7
Fellas ,
Agree to disagree , by all means, but please do have a barney over it on my account.
OK?
What instigated this whole thing is that we are having a cleaning up of shed and garage. I blame you racingtadpole.
She who must be obeyed surely has noticed your post about the tidy up of your place, (but I still want the gooseneck please). Now I have to justify each piece my treasury of carefully collected and curated engineering items, lest they be consigned to the tip.
I am not allowed to go to the tip unaccompanied as I tend bring stuff back from the recycle shop
Grahame
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12th Dec 2020, 07:05 PM #8Most Valued Member
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You say that like I don't have stuff on my "todo" list from back then lol
Me? I hope it didn't come across as a barney. Sorry if it did. Was asking a question and or explaining why I made the decisions I made. I think on the spindle is the place for it, if 1. you want instantaneous stop. 2. you can find somewhere to mount it. 3. you supply the force required(which is no real issue if you have room for a car rotor and caliper. I see I only posted half my thought earlier "It might come down to just how fast you want the brake to stop the lathe. Mine as currently setup stop so the lathe a lot faster, but if you are after "almost instantaneous" " (I had meant to add something like) " you might have to come up with something else" ).
The date of the thread lets me find the pictures. Here it is almost finished.
If any other pictures sound like they are worth seeing let me know and I will dig them out.
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12th Dec 2020, 11:06 PM #9Most Valued Member
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13th Dec 2020, 06:37 PM #10Most Valued Member
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I'd have to agree with Stu. Braking systems remove energy from a system. This is done by generating heat. The spindle, gearbox, motor system is a coupled system and can be approximated by a single moving mass. Different parts of that mass may be moving at different speeds but the overall energy of the system is the same. Identical braking systems placed either at the spindle or the motor would absorb the same energy from the system and therefore heat up the same amount in order to bring the system to rest. From this POV there is nothing to be lost or gained in choosing one location over the other.
Gear backlash, breaking belts, ease of mounting the parts etc. are another argument all together and may perswade you to choose one location over the other.
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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13th Dec 2020, 07:43 PM #11Most Valued Member
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14th Dec 2020, 06:25 AM #12
DC Injection !
Hi Guys,
A guy that I used to know, used a rectifier and a big capacitor, of about 350 Mf charged from the mains and a two pole relay to disconnect the supply voltage and dump the capacitor charge into the motor windings. The motor didn't stop instantly but did within a couple of revolutions. I have the circuit details somewhere.
Unfortunately he is not around any more having got wasted and wrecking his bike. He did like his beer though !
His workshop was disposed of via his local MES members auction.Best Regards:
Baron J.
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14th Dec 2020, 08:13 AM #13Mechanical Butcher
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Just to mention, the brake on a Harrison M300 lathe is a V-shaped block that acts upon a pulley.
It is all mechanical, rod-operated from a foot pedal.
The lathe is still in production.
That's how brakes were on old motorbikes.
I installed such a device on a 1924 motorcycle with belt transmission, making the block out of hardwood - good enough for around the paddock.
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14th Dec 2020, 10:26 PM #14Golden Member
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The brake on my Harrison M250 is a disk, spring applied with electro-release, on the outboard side of the motor.
Removed as I do not like putting a strain on all the headstock gearing when an emergency stop is initiated.
The lathe has a VFD, and will get a braking resistor sized to reduce deceleration time as much as practicable.
Note that the electro-release was wired directly across the motor terminals when the lathe acquired.
This meant the spindle was locked whenever the motor was not energized.
Must have been a real pain to operate.
If I do re-commission, I would add an independent on/off switch to enable spindle rotation by hand when needed.
Keep well,
John.
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