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brian Rupnow
01-16-2016, 11:16 AM
My CX701 lathe by Craftex seems to be a very good working lathe, and I am quite happy with it. The only thing that concerns me is that there is no clutch on the power feed shaft where it exits the gearbox at the head of the lathe, only a brass shear pin. It is my fondest hope that I never get to see if that shear-pin really will protect the rest of the drive train in the lathe if I should do something dumb like run the tool into a shoulder on a turned shaft in power feed mode. I know that other lathes have a slip clutch on that shaft. Does anyone know if there is a slip clutch available for lathes that can be retrofitted to that shaft as an aftermarket kind of thing?---Brian

Ian B
01-16-2016, 11:28 AM
Brian,

I'm not familiar with your particular lathe, but from what I see, it has a separate leadscrew & power feed shaft.

Is there an adjustable clutch built into the saddle, that automatically drops power feed out at a certain load? Mine has this, and it allows me to power into the bedstop when machining to a shoulder.

Ian

achtanelion
01-16-2016, 12:42 PM
On my Leblond regal The lead screw and feed shaft both have ball detent clutches. I would think with a little work, You should be able to fit the same to your lathe in place of the shear pin.

brian Rupnow
01-16-2016, 01:12 PM
Mine has no clutch. period.--That's why I'm asking bout a clutch that I can retrofit.

plunger
01-16-2016, 01:23 PM
I know where this is going.lots of amazing cad drawings .There must be alot of online downloadable drawings of existing clutches. I wonder how or if my lathe has also got this .I better go look. (emco v 13)

achtanelion
01-16-2016, 02:04 PM
Well, you can buy or build. The principles seem fairly simple http://mechanical-design-handbook.blogspot.ca/2012/05/ball-detent-torque-limiter-overload.html so making your own should be quite possible. Having looked a little at prices, new would seem to almost double the cost of your lathe.

dalee100
01-16-2016, 02:08 PM
Hi,

If you need the clutch, you are doing something wrong.

The brass pin is much cheaper than a full blown dog clutch. Which was easier on your wallet. And it WILL do the job properly. Shear pins are used in many applications and from my experience are often more reliable than a clutch. So I wouldn't be concerned. You should be paying enough attention to not crash anyway. And if you should be that unfortunate, just don't use a dowel pin as a substitute.:eek::eek:

Dalee

Forestgnome
01-16-2016, 02:11 PM
Note that even lathes with clutches don't use them when threading, and the carriage is moving much faster then. May as well develop the reflexes.

Black_Moons
01-16-2016, 02:33 PM
Don't worry about the shear pin. I was being stupid one day and grabbing the handwheel on my 12x36 while the lathe was in power feed and giving it extra resistance for kicks and giggles, seeing how much torque it had... And then the shear pin broke and the whole power feed axle popped out the right side mount, freeing the carriage to move as it wished.

So yes, it will definitely shear before anything else is damaged, and does not take much torque at all to shear that little pin. A crash or feed to end will definately shear it no problem at all.

I took the shear pin out, and stuffed it back in the other side of the hole since I didn't have a spare. Still works just fine, haven't sheared it again even though its now only going through 1 of the 2 'holes'

PS: I once accidentally turned my lathe on the wrong way while threading, starting at a shoulder...
it *displaced* 0.1" of aluminum with the turning tool and seemed very happy to do it. Sorta like roll threading except the resulting thread was wayyyy too high.

Id wager if you accidentally power feed into a shoulder, that shear pin will snap or it will happily turn the shoulder off for you.

wern
01-16-2016, 02:35 PM
Eugene, our V13 has a clutch on the feed-shaft, which is adjustable and a shear pin on the lead screw.

lakeside53
01-16-2016, 03:07 PM
The Emco V10 also has a small clutch, maybe 1 inch diameter x 2 inches(?) Very nice. You can even use it to power feed to a stop, and I did! (from the manual) but I doubt it would last to long if you did a lot. Just a series of slips disks and a preload spring. Easy to make and retrofit. It goes directly inline with the power bar (not the lead screw). There are couple of v10s being parted out on ebay - contact the seller and ask if they still have the part - probably didn't occur to them to list it.

My big lathe has a ratcheting overload; saved my butt a couple of times. it's not for use to a stop, but for emergencies. You can have the best reflexes in the world, but inattention will still get you. In my case it was two fold : long fine repetitive power feeds that "allowed" me to not watch every second. Bad, but... AND the other time... slamming the "wrong" lever. lol

Daveb
01-16-2016, 03:33 PM
Smart & Brown model A lathes have a trip on the feedshaft, it's built into the apron and is intended to be used when cutting to a shoulder. The feedshaft apron gears are carried on a sliding frame, when the carriage stops, the sliding frame continues moving towards the headstock, actuates a cam and disengages the feed lever. The leadscrew is protected by a shear pin located in the drive gear boss. The shear pin is hardened steel with a reduced section in the middle. My current Taiwanese lathe uses brass pins in the drive bosses for both the feedshaft and the leadscrew so power feeding to a shoulder is not an option.

Mike Burdick
01-16-2016, 03:58 PM
To me, a shear pin is the way to go, but...

is this what you have in mind?

http://www.dynatect.com/uploads/images/polyclutch/slippers_image.jpg

http://www.dynatect.com/mechanical-motion-control/slip-clutches/mechanical/slipper-clutch

One can also make slip clutch using two bearing balls, two set screws, two compression springs, and a couple of pieces of round stock.

ikdor
01-16-2016, 04:52 PM
Or you could steal the clutch from an electric screwdriver, you can even set the tripping point on those.

Igor

brian Rupnow
01-16-2016, 04:55 PM
Mike Burdick---thank you.--That is exactly what I meant. I have asked them for a quote.--Brian rupnow

Black_Moons
01-16-2016, 05:02 PM
Or you could steal the clutch from an electric screwdriver, you can even set the tripping point on those.

Igor

I *really* like this idea.

brian Rupnow
01-16-2016, 05:19 PM
I *really* like this idea.

I don't think the clutch from an electric screwdriver would have a high enough torque setting for power feed or power parting off with a lathe.

danlb
01-16-2016, 07:17 PM
You will need to pay attention to where you put that clutch.

The gear train keeps a relationship between the chuck position and the threading lead screw. A single tooth dog clutch is usually used to disengage the lead screw so that it can be re-engaged back to the same relative position. This saves you from having to manually pick up the thread again. The single tooth clutch ends up between the final change gear and the lead screw. The down side is that you end up with the threading tool cutting a groove when the leadscrew stops moving but the chuck does not.

An alternative is the clutch such as shown in post 13 and to put that between the motor and the gear that drives the chuck (and the rest of the gear train). The ball detent clutch (also mentioned in post 13) works well there too. That's what the 1995 version of the 9x20 lathes used. The down side of placing the clutch there is that the inertia of the chuck will try to keep things moving for a little after the clutch starts to slip.

Dan

plunger
01-17-2016, 03:10 AM
Eugene, our V13 has a clutch on the feed-shaft, which is adjustable and a shear pin on the lead screw.

Werner is that the thing we engage and disengage to do thread turning on the leadscrew? The push pull nut by the gearbox. Its very compact,I wonder how difficult it would be to copy?

MrSleepy
01-17-2016, 06:40 AM
Werner is that the thing we engage and disengage to do thread turning on the leadscrew? The push pull nut by the gearbox. Its very compact,I wonder how difficult it would be to copy?


Eugene ... its the black cylinder on the feed shaft..

http://i897.photobucket.com/albums/ac180/MrSleepy123/emco%20clutch_zps2axfbonc.jpg

Do you have the manuals ... I can let you have them if required.
Rob

Lew Hartswick
01-17-2016, 10:50 AM
Eugene, our V13 has a clutch on the feed-shaft, which is adjustable and a shear pin on the lead screw.

That is what our Clausing/Metosa have at school . I've had to make quite a few taper brass shear pins. :-) Fairly easy to do with the right set up.
...lew...

Don Young
01-17-2016, 10:24 PM
Later versions of the much maligned Atlas 12" lathe have an adjustable slip clutch on the leadscrew, no separate feed shaft.

David Powell
01-18-2016, 10:08 AM
Most, if not all, Southbend lathes and the copies thereof, have an adjustable slip clutch in the saddle for the power FEEDS. There is no such official protection for the gear train when screwcutting, though, if you do not tighten the screw clamping the banjo ( Which holds the change gears) too tightly the banjo will turn slightly and the gears will pull out of mesh before any damage is done. I have used ( abused??) the slip clutch in my Standard Modern for over 20 yrs without any problems. Hope this helps someone. David Powell.

Doozer
01-18-2016, 10:27 AM
Consider that maybe
if you think you need a safety clutch
you are not approaching
using the lathe
with a serious enough mindset.

-Doozer

brian Rupnow
01-18-2016, 11:12 AM
Consider that maybe
if you think you need a safety clutch
you are not approaching
using the lathe
with a serious enough mindset.

-Doozer

Doozer--I'm taking a VERY serious approach to using the automatic feed on my lathe. I watch that damn tool like a hawk anytime the auto-feed is engaged. It's just that I've read a couple of horror stories on line about people who didn't watch it carefully, and ended up taking out gear boxes, breaking castings, etcetera. It scares the Hell outa me, and I know that some lathes do have that clutch, and even though it doesn't as a matter of course get used, it provides a bit of insurance against disaster.---Brian

firbikrhd1
01-18-2016, 11:44 AM
If I am understand your concerns you want some sort of clutch or other system to prevent you from destroying your lead screw, carriage, apron components etc. in the event of a crash with the headstock. It seems to me that systems requiring a specified amount of force to stop drivetrain movement might allow considerable damage to occur before "clutching" or pin failure.
So, how about an electronic system that shuts off the motor as the carriage approaches a specific point? Perhaps a switch attached to the bed which would shut off power via a relay. If such a switch were designed to be movable, say on a clamp that attached to the ways I could be adjusted for other jobs as well, say stopping at a shoulder or relief cut prior to threading.

Disregard this post if I misunderstand your goals, this is just how I interpreted your concerns.

Doozer
01-18-2016, 02:34 PM
Try working in a live 480volt panel.
You guys up there have 575volt.
Brings a whole new meaning to the
word serious.

-Doozer

Black_Moons
01-18-2016, 03:30 PM
If I am understand your concerns you want some sort of clutch or other system to prevent you from destroying your lead screw, carriage, apron components etc. in the event of a crash with the headstock. It seems to me that systems requiring a specified amount of force to stop drivetrain movement might allow considerable damage to occur before "clutching" or pin failure.
So, how about an electronic system that shuts off the motor as the carriage approaches a specific point? Perhaps a switch attached to the bed which would shut off power via a relay. If such a switch were designed to be movable, say on a clamp that attached to the ways I could be adjusted for other jobs as well, say stopping at a shoulder or relief cut prior to threading.

Disregard this post if I misunderstand your goals, this is just how I interpreted your concerns.

Lathe motors/chucks take too long to spin down for that to work.

Even at my lowest speed, my lathe takes another turn or two before stopping when you disengage power to the motor.

The trick is just learn to be fast at that feed/threading handle. Or put your threading tool upside down and thread away from the shoulder.

For cutting to a shoulder, I disengage power feed for the last 1/2" or so and do it manually as only manual feed will 'stop' at my micrometer carriage stop.

Doc Nickel
01-18-2016, 04:16 PM
It's just that I've read a couple of horror stories on line about people who didn't watch it carefully, and ended up taking out gear boxes, breaking castings, etcetera.

-I've been working on a big Springfield gearhead lathe for the last couple of years. The machine's had a hard life, and I've had to do several repairs in addition to the usual cleaning and de-rusting.

It had two broken gears in the gearbox, plus one already-repaired gear, and a fourth with a sheared key.

Once I fixed those and went to reinstall the gearbox, I'm reasonably sure I discovered why: The leadscrew (as well as the feed rod) was attached to the gearbox shafts with taper pins. At some point somebody had a crash and it sheared, probably saving the gearbox.

They "fixed" it by adding a KEY to that same shaft, AND redrilling the hole out- badly- for a straight bolt.

The soft taper pin was the manufacturer's "clutch". It would shear to save the rest of the geartrain. Once they reinforced it, then then next weaker component gave way, which considering the size and bulk of everything on this monster, was the gear teeth.

I've removed the key, and will be refitting a proper pin. In fact, for the first little while, I'm considering making up an aluminum pin, 'til I'm better acquainted with the machine.

Doc.

firbikrhd1
01-18-2016, 04:32 PM
Lathe motors/chucks take too long to spin down for that to work.

Even at my lowest speed, my lathe takes another turn or two before stopping when you disengage power to the motor.

The trick is just learn to be fast at that feed/threading handle. Or put your threading tool upside down and thread away from the shoulder.

For cutting to a shoulder, I disengage power feed for the last 1/2" or so and do it manually as only manual feed will 'stop' at my micrometer carriage stop.

My old Logan has neither a clutch, plastic gear, pin, nor an electrical "stop" and I still manage to thread toward the headstock without issues. Some later Logans did offer a ratcheting clutch. Of course, I'm in no hurry and not in production of anything and I am very cautious even stopping well ahead of the shoulder and turning the headstock by hand if necessary, and I have back gears so my lowest RPM is around 30 leaving me plenty of reaction time. I have not tried the threading away for the headstock method as yet as there has been no need although at some point I may use that method for internal bores where it's difficult to see where the thread ends and crashes are likely. Until now I've used the manual method for the last few threads by marking the bed in a previously determined place and shutting the motor off at that mark then manually continuing the thread to it's end. Slow? Yes, but crashes are eliminated, and as I say, it's a hobby and speed isn't an issue.

I understand that the spindle may take a turn or three to stop if an electronic "stop" was used, however it seems that the stop could be placed far enough away from the headstock to compensate for those additional turns. The distance covered by the carriage during those last rotations is determined by whether the thread is coarse or fine. In fine thread situations it would be easier to predict where the carriage would stop if the motor were switched off, coarse threads would likely present a greater problem.

To each his own, I was just attempting to give another option if it suited your needs.

lakeside53
01-18-2016, 06:24 PM
Mine has an electric brake. I will stop on a dime (few turns) but you will snap of most carbide tooling tips if they are materially in the work. Done a few of those in but the rest of the machine/work.

Nothing wrong with safety devices for the oh crap times.... If we were all perfect, wouldn't need any of them in life, even condoms . ;)

dalee100
01-18-2016, 11:14 PM
Hi,

In your first post you state the gear train has a shear pin to protect it. I really am interested in why you don't think that shear pin won't do the job it was designed to do? Or do I misunderstand your first post?

Dalee

J Tiers
01-19-2016, 12:10 AM
Some DC injected into the motor after power is removed will definitely stop it quite fast. No two turns of the spindle, I'd bet, it will be faster than that.

I think I'd be a little more worried about the clutch etc releasing when I want it to hold..... The shear pin ought to be good enough to prevent damage.

Hopefuldave
01-19-2016, 04:49 AM
I sometimes think it's unfair that lathes in the "affordable" range don't have as many safety / ease-of-use features as many industrial machines...

A shear pin is, however, RELIABLE, possibly more reliable than a slipping clutch assembled by a Chinese child on a dirt floor, so I think the shear pin's probably a safer bet - as long as nobody fits a dowel instead.

The ultimate is probably what Holbrook fitted, the feedshaft drives a two-piece worm with cam ramps between the halves (separately for each cross and carriage feeds which can be used independently and simultaneously), when it hits the stop (and really does STOP) the ramps push the halves apart (against adjustable spring pressure) which trips the feed. Reliably and accurately as in within a few tenths every time. It would be horrendously expensive to build though, much like everything Holbrook, and may explain why there are so few about...

Dave H. (the other one)

Baz
01-19-2016, 09:17 AM
Don't rely on the existing factory fitted shear pin. Plenty of tales of broken gears from people relying on that. It was not designed by careful calculation and test but by what hole was easy to drill and fill. Make a new brass shear pin thinner than you think may work. If it breaks under load examine your operation and make it thicker only if justified.
I've never used my shear pin like I've never used my fire insurance but only a dummy wouldn't make the payment just because of 30 years of no claim.
Tip: the friction clutches on eg SB and Boxford, unlike the trips mentioned above are not meant to be used to let you whack the micrometer bed stop with the full weight of the saddle if you want accurate work - when within 20 thou of the stop retard the saddle by grasping the handwheel and take it in slow by power assisted hand feed.

brian Rupnow
01-19-2016, 09:49 AM
Hi,

In your first post you state the gear train has a shear pin to protect it. I really am interested in why you don't think that shear pin won't do the job it was designed to do? Or do I misunderstand your first post?

Dalee

Dalee--Before I bought this lathe, I did a lot of internet research on it. There were two or three stories about people who had crashed the carriage into the chuck, or shoulders on shafts, etcetera, and severely damaged their lathes. Their shear pins apparently didn't shear. I have checked on my lathe, and it does have a brass shear pin in it.

JCHannum
01-19-2016, 11:09 AM
Shear pins are designed to shear. It is simple enough to reduce the force required to shear them if it is felt that it might be excessive. Note where the shear occurs, and undercut the pin in that or those locations. (Reducing the diameter by a half will greatly reduce the forces and will probably be too much.)

This procedure will have two benefits, one reducing force to shear and two, creating a clean shear, not one with smeared ends, making removal of the sheared pin easier.

Toolguy
01-19-2016, 12:59 PM
One could drill a hole in the middle of a shear pin to make it shear easier.

Willy
01-19-2016, 01:37 PM
Shear pins are designed to shear. It is simple enough to reduce the force required to shear them if it is felt that it might be excessive. Note where the shear occurs, and undercut the pin in that or those locations. (Reducing the diameter by a half will greatly reduce the forces and will probably be too much.)

This procedure will have two benefits, one reducing force to shear and two, creating a clean shear, not one with smeared ends, making removal of the sheared pin easier.

I know I've suggested this before in another thread about Brian's lathe, but the use of a shear pin like that used in snow throwers would be ideal.
Make it as weak as you like, barely adequate for normal use if you like. Also test it to gain confidence in the pin's ability to sacrifice itself in order to save the lathe's expensive bits.
I believe this last step is important in order to trust the insurance the pin will offer.

http://images.prod.meredith.com/product/f3d6cd7dd8db93300f7285a31819b12c/2e97ad550e82ea72b8faaf453a89396855df7c11312bdb9aef 973f82cf3d7dcc/m/oregon-80-749-snow-thrower-shear-bolt-for-mtd-738-04124-and1-1-2-inch-length

Richard P Wilson
01-19-2016, 02:18 PM
My Raglan lathe had a very simple shear pin - the gear driving the feedshaft had a brass grubscrew fitted with a 1/16"dia stub on the end, about 1/8" long. This fitted into a corresponding 1/16" dia hole drilled through the shaft. On the one occasion that I had a crash it was easy to slide the gear to one side, punch the remains of the pin out of the hole in the shaft, then fit a new grubscrew. I made 6 of them and only ever used the one. The grubscrew method has a shearing load about half of that for a through pin, because it only shears in one place. Downside is that I came across several other Raglans which had obviously sheared the pin, and the owners had just fitted a steel grubscrew and tightened it down hard - safety mechanism gone.

brian Rupnow
01-19-2016, 04:22 PM
To me, a shear pin is the way to go, but...

is this what you have in mind?

http://www.dynatect.com/uploads/images/polyclutch/slippers_image.jpg

http://www.dynatect.com/mechanical-motion-control/slip-clutches/mechanical/slipper-clutch

One can also make slip clutch using two bearing balls, two set screws, two compression springs, and a couple of pieces of round stock.

I just received a quote for one of these clutches, in a size that will fit my lathe. The price is $368.40 American dollars, so that is about $500.00 Canadian dollars. That'ts about $400 Canadian dollars than I would be willing to pay.---brian

danlb
01-19-2016, 05:31 PM
Brian, it seems that you could use the drawing at http://www.dynatect.com/uploads/files/slippersdiagnew.PNG to figure out how to make your own for a reasonable investment in materials and time.

Dan