Foot Brake For The Pm 1340gt

[Randbo]

I'm so used to a foot brake on lathes, that I decided to see what I could come up with for the 1340GT. I had a couple of foot switches laying around work so I incorporated it into my lathe. I just rewired the microswitch inside the foot petal to NC. Then I just wired it in series with my E-stop. Now I can just rest my foot on the petal and stop the lathe at a moments notice, freeing up my hands. I'm curious has anyone else tried or done this? I'm sure some of you have. Thought I'd post it for anyone who was looking for something like this.

 

[tweinke]

Good idea!

 

[mksj]

Nice solution and added safety feature, probably better than trying to hit the E-Stop. On machines that have had mechanical brakes and were converted to a VFD system, I have rewired the foot brake switch into the VFD for electronic braking. Also have done this on some machines that have a trip wire type system. I had thought of using something like a dead man switch that would require it to be depressed to operate, but one tends to move around a machine a bit so probably would not be too good. On the PM1340GT I had thought of adding an electronic foot brake between the cabinets, but I am fine without it. Having an electronic stop that reverts the system to 1 second braking also helps.

 

[Randbo]

Nice solution and added safety feature, probably better than trying to hit the E-Stop. On machines that have had mechanical brakes and were converted to a VFD system, I have rewired the foot brake switch into the VFD for electronic braking. Also have done this on some machines that have a trip wire type system. I had thought of using something like a dead man switch that would require it to be depressed to operate, but one tends to move around a machine a bit so probably would not be too good. On the PM1340GT I had thought of adding an electronic foot brake between the cabinets, but I am fine without it. Having an electronic stop that reverts the system to 1 second braking also helps.

At this point I've kept it simple. My VFD is set up on a .5 sec decel for all stops (e-stop, foot brake, fwd/rev switch) and I'm using an overkill 1000 watt, 75 ohm braking resistor that came my way for free. The thing never even gets warm. I've considered setting up various decel rates, on multiple inputs, based on various situations. At this point I've decided that is unnecessary for my use.

 

[diamond]

At this point I've kept it simple. My VFD is set up on a .5 sec decel for all stops (e-stop, foot brake, fwd/rev switch) and I'm using an overkill 1000 watt, 75 ohm braking resistor that came my way for free. The thing never even gets warm. I've considered setting up various decel rates, on multiple inputs, based on various situations. At this point I've decided that is unnecessary for my use.

I apologize for the 2 year old necro post. I have a 1340gt on order and just wondering how this has worked for you after a couple years with it set up this way. Have you found the .5 sec stop to be rough at all on the gears, bearings etc? What size chuck are you running with that half second stop?

 

[Randbo]

So far it has been working absolutely flawlessly. The chuck stops faster then any manual brake I’ve used, but isn’t jerky and extremely smooth. There isn’t any signs of excessive load on the gears or power train. Starting the lathe probably puts just as much load on the system as braking for the way I have it set.
I’m running multiple chucks with this set up. 6 inch 3 jaw, 8 inch 4 jaw and 8 inch 3 jaw. I haven’t had any problems with any of them at the current settings. I have had some pretty large chunks of material in the chucks with no problems. I did have to play with the VFD settings to find the sweet spot for my liking. I can post them if you are interested.

Randy

 

[diamond]

Thanks a lot for the reply Randy. I just placed my 1340gt order and its end of July before I get to start putting her in the shop and working on the VFD conversion. I will do nearly all my work with the 8" 4 jaw (about 35 lbs) and the work itself is rifle barrel chambering, threading etc. So mostly lowish speeds and not a ton of stress. I'm planning on Mark Jakobs proximity stop and wondering about the .5 second stop when threading. Though he says a 1 second stop is still plenty. Once I get it all installed and get into programming I may take you up on the parameters. I'm at least a couple months out from that though.

-dave

 

[Randbo]

Thanks a lot for the reply Randy. I just placed my 1340gt order and its end of July before I get to start putting her in the shop and working on the VFD conversion. I will do nearly all my work with the 8" 4 jaw (about 35 lbs) and the work itself is rifle barrel chambering, threading etc. So mostly lowish speeds and not a ton of stress. I'm planning on Mark Jakobs proximity stop and wondering about the .5 second stop when threading. Though he says a 1 second stop is still plenty. Once I get it all installed and get into programming I may take you up on the parameters. I'm at least a couple months out from that though.

-dave

 

[Randbo]

Congrats on the new purchase.
It’s been a decent lathe for me. Honestly I wish I’d have gone with a larger lathe (casting) but I’m able to do most of what I need.
I’ve done a few modifications to the lathe but honestly have never seen a need for a prox. stop. I can machine or thread right up to the chuck or end of the tool without any issues or concern. I don’t want to criticize anyone who finds this function handy but I’ve just never seen the need for it. Keep me posted on your new lathe and modifications!

 

[mksj]

A lot of different factors and depends on the relief groove when threading and the speed that you thread. Typically I thread at around 250 RPM which is too quick for one to consistently disengage the half-nut on every pass. My relief grooves are the thickness of the thread cutting insert, so I can thread up to a shoulder or internally to a blind cap. I also do not disengage the half-nut for threading so doing metric threads is easily done. Being a bit older and not using the lathe daily, my hand eye reflexes got it down to 9 out of every 10 threading passes I got right, and then I would break my insert. Internal threading to a shoulder was not as successful.

On braking, you can dial down the braking time to whatever you want but the electronic braking only has so much ability to generate a given stopping force. On the smaller lathes the 1.0 second stopping time is about as low as you can go without risking a VFD fault (over voltage on the buss), but this is a factor of speed and chuck weight. The size of the braking resistor has no bearing on braking time so you get the same braking times whether you have a 250W or 1000W braking resistor, I use a 500W but never had it even get warm. Braking your lathe at 1 second or under all the time I think is a bad idea, why put undue stress on the lathe and gear sets, something is going to break or wear out sooner. The VFD has programming for two different acceleration and braking rates (1 stage or 2 stage), I set up all my VFD systems to allow the user to choose the rate (typically 1.0 and 2.5 seconds), but also that any trigger/fault overrides the braking rate switch to the shortest possible time. Some of us run heavier (80lb) 8" chucks and at speed these will trip a VFD error when run at speed, 1 second is about the max. and on a few systems (and larger lathes/chucks) we have setup slightly longer braking times when running above 1000 RPM. So YMMV.

In the video below threading at ~250 RPM into a blind cap the chuck will stop in the same exact position on every pass (typically 0.0002") using a proximity stop trigger.

 

[diamond]

Thanks Mark. Since I'm going to be using your control board I'll be using the 2 stage braking for sure. If with the proximity stop I can get that kind of repeatability I'll be ecstatic. Especially being a noob at machining. I don't have the experience of many folks here. The idea of the foot brake switch just intrigues me as an additional safety feature when for whatever reason both hands are occupied and everything goes sideways somehow.

 

[qualitymachinetools]

That stop is the best setup for threading on a manual machine that I have ever seen. I must have watched those videos 100 times over the last few years

 

[Bob Korves]

I have a mechanical foot brake on my Kent 13x40 and it stops the spindle seemingly instantaneously, even at high speeds. Seems like less than one revolution, but not sure of the reality of it. I have used it for stopping internal threading and boring, and it works great for that, but I finally smartened up and now cut outward rather than inward. Stops that nervous tic...

 

[Randbo]

I knew people would chime in on the stop feature. Like I said I'm not criticizing anyone for using it, I just don't need it. I always thread to a relief and have enough experience to do so at any reasonable speed. I do believe this would be a good system for someone just learning the single point threading process. Also when I'm threading I use a magnetic dial indicator on the ways and can stop the carriage easily within a thou or two. So I know right when I'm at the end of my thread. With lots of practice you'd be surprised how fluid the treading process can become. 250 rpm threading is really no trouble at all. Of course it depends on TPI as much as RPM. 32 tpi @250 rpm is quite a bit different than 4 tpi@250 RPM. If you are threading 13tpi @250 rpm the carriage is moving roughly 5/16 per second. Super easy to disengage the half nuts at that speed. Yes metric can be a little more of a challenge with a standard thread dial but it is possible. And besides you will never see a master machinist stopping the lathe during the threading process except when measuring with thread wires. Sorry have to poke a little fun! Of course almost everything is CNC now anyway

As far as braking I honestly can't remember the exact amount of time mine is set to. I'd have to look to be sure but it's somewhere between .6 to 1 second. I agree that anything under 1 second is probably overkill and there aren't any advantages. I installed a foot brake on mine simply because I'm so used to having that option. It's literally muscle memory at this point for me and when it's not there it throws me off my game.
The braking resistor I happen to be using is 1000 watt which has nothing to do with braking performance, it just has to be large enough to dissipate the energy of the dynamic braking process. 1000 watt is insane overkill for my application, I just happen to get it for free. What matters is the "resistance" of the resistor. Mine happens to be 75 Ohms which is in the acceptable range of my VFD. (really should be 70) every VFD will have a specific resistance required. Can't just throw any resistor you want in there. Too high and it won't brake as effectively. Too low and you'll start smoking things like your IGBT's.

On my system I happen to be using a combination of dynamic braking and DC injection braking (DCIB). I work in the Automation Industry and we use this combination at the plant all day long. It really is the best of both worlds. I use DB to get 85-90% of the kinetic energy out of the system and then kick a little DCIB in to finish it off. It gives you really smooth braking performance. Especially when you have those heavy chucks you're trying to stop.

lathes with a mechanical brake do so with the brake mechanical setup on the motor itself which can stop the chuck quite quickly. I would argue this puts every bit as much of a strain on the system as any dynamic braking system. Lathes have had mechanical brakes on them forever so I'm not worried about any negative effects from this. I have never done the calculations but I wouldn't be surprised if the lathe operating at full load puts far more stresses on the gear train then braking at almost any level.

But like everything else in life what works best for you is what you should do. I'm only sharing my experiences of what works for me.

Hope I haven't offended anyone here.

Randy~

 

[Randbo]

I have a mechanical foot brake on my Kent 13x40 and it stops the spindle seemingly instantaneously, even at high speeds. Seems like less than one revolution, but not sure of the reality of it. I have used it for stopping internal threading and boring, and it works great for that, but I finally smartened up and now cut outward rather than inward. Stops that nervous tic...

Bob,

Where in Sacramento do you live? I lived there for 31 years and grew up in the Greenhaven/Pocket area.

Randy

 

[diamond]

As a complete new guy, I appreciate you sharing your experience Randy. And everyone else sharing their experience too!

FWIW I have several precision rifle gunsmith buddies that run their lathes in different ways. Doesn't make any one of them more right than the other. They've got it worked out their way and it works for them. They all put out stellar rifles at a level I can only aspire to. lol

 

[Randbo]

I understand what it’s like to start out. There are a lot of good sources out there and no one has all the answers. There is great information on this site and people who are willing to share it. I would humbly suggest to learn everything you can from everyone you can.
YouTube is also an excellent source for learning machining on lathes and mills. I regularly watch some guys on there that have taught me some very valuable skills. Some of those guys have tremendous talent and are willing to share their "trade secrets" with us.

 

[Downunder Bob]

Braking on a lathe. I've used a few in the past that had mechanical brakes, foot and hand operated, I've never operated lathe with electronic speed control, including braking.

My lathe is 240v single phase and single speed. 1.5 h.p. I have no desire to go to 3 ph. and VFD. By the time I put in 3 ph power, a new motor , plus VFD, it's all too much. I have enough power as it is.

However I've been thinking. Of using the electric clutch of an automotive air conditioner fitted to the belt pulley so when the clutch is activated it acts as a brake. I already have a12v dc supply near the lathe as my lathe lighting and coolant pump, plus a few other things, are 12v. A simple kill switch or even a foot pedal to activate the clutch and shut off power to the motor, should stop it pretty quick.

It has even occured to me that using a couple of these clutches I could get a two speed drive, just by having different sized pulleys on each one.

 

[Randbo]

Braking on a lathe. I've used a few in the past that had mechanical brakes, foot and hand operated, I've never operated lathe with electronic speed control, including braking.

My lathe is 240v single phase and single speed. 1.5 h.p. I have no desire to go to 3 ph. and VFD. By the time I put in 3 ph power, a new motor , plus VFD, it's all too much. I have enough power as it is.

However I've been thinking. Of using the electric clutch of an automotive air conditioner fitted to the belt pulley so when the clutch is activated it acts as a brake. I already have a12v dc supply near the lathe as my lathe lighting and coolant pump, plus a few other things, are 12v. A simple kill switch or even a foot pedal to activate the clutch and shut off power to the motor, should stop it pretty quick.

It has even occured to me that using a couple of these clutches I could get a two speed drive, just by having different sized pulleys on each one.

That's one way of braking but I think you will find the longevity of that design will be an issue. A/C clutches are not designed to be used as a brake. The friction material on the mating surfaces is insufficient for that, unlike a brake pad for instance that is designed to continuously wear against a rotor during braking. Clutches on the other hand are designed to engage as quickly as possible with as little slipping as possible. I think you would find an extremely high wear rate on the clutch faces and it wouldn't hold up for long.
Now if you were to provide some type of load that the clutch engaged that would be more desirable. ( Like having the clutch turn a hydraulic pump or power steering pump with a fixed orifice tube in the high pressure outlet returning back to the reservoir ) This would in a sense be the load that would provide the resistance needed to stop the lathe. And this is assuming the A/C compressor clutch could even hold such a load. Now if you wanted to get really crazy you run the clutch through a hysteresis magnetic brake! Way too expensive of an option obviously.
Another option might be to consider an electric brake, and there are many different designs out there. (think electric trailer brakes)
You also want to have some control over how fast the braking happens. You obviously don't want the lathe to stop instantly. You really need some method of dissipating all that kinetic energy.
But if you do opt to try the clutch I'd be curious to know how it works and holds up.

Also if you went the 3 phase motor/VFD option you don't need to have 3phase power. There are VFD's that will take single phase in and convert that to 3 phase out for the motor.