Carriage Stop

[hman]

A couple of recent projects on my lathe made me aware that really I needed a carriage stop of some kind. I had an old one made for another lathe (no idea where or when I got it), but it wouldn't fit my 12x24.

I measured the lathe ways and designed a new stop body that would re-use the already engraved dial and 7/16-20 rod from the existing stop. Trouble is, I just don't have a decent supply of larger "chunks" of steel or cast iron. Matter of fact, the only things I could find were a couple of very rusty 4" long pieces of 2" steel rod, pedigree unknown. IIRC, I'd used these on an outdoor gadget for a number of years. I could carve the body of the stop out of one of these, though the corners would be lopped off by the 2" circle ... OK, pretend these are chamfered edges!

After giving the steel a good soak in Evaporust and a good scrub to remove what little paint was left, I got out my new Shars face mill and started to go for it. The mill did a very nice job, and I was getting tan-to-blue chips. Whatever this steel is, it was very easy to machine. Here's the completed first face, plus some of the swarf.


Here's the completed body of the stop, along with a second chunk of raw material. Though I'd made a couple of setup/machining errors in the process, I was able to correct them successfully, and had a whale of a good time doing it!


... and the completed stop, ready to go to work ...

 

[mikey]

Great job, John! I like the graduated dial a lot.

 

[ELHEAD]

Ain't nuthin wrong with that. Great job.

 

[dieselshadow]

That is definitely nice work.

Can I ask a dumb question? Doesn't a carriage stop ask for a crash? How does a stop become accurate if you run the carriage into it with the feed engaged? If you manually stop the carriage, how is it accurate? I've obviously never used a stop. Please explain for the ignorant folks like me. Heck, maybe it's only me that's ignorant.

 

[hman]

That is definitely nice work.

Can I ask a dumb question? Doesn't a carriage stop ask for a crash? How does a stop become accurate if you run the carriage into it with the feed engaged? If you manually stop the carriage, how is it accurate? I've obviously never used a stop. Please explain for the ignorant folks like me. Heck, maybe it's only me that's ignorant.

No such thing as a dumb question! And relief of ignorance is a large part of what this forum is all about.

The answer to your question is that you don't want to use the stop to halt the power feed. You can use it when manually cranking the carriage, so it always stops at the same place (without having to keep an eagle eye on the DRO or the dial). If you do use the stop with the power feed set to move the carriage toward the stop, you must be careful to disengage the feed well before it hits, then move the rest of the way manually.

Or you can use the stop to move the carriage to a reproducible starting point, then either crank it away by hand or engage the power feed to move it away. Setting a starting point is especially useful if you're working close to the chuck and want to avoid a collision caused by a slightly less than careful move back toward the chuck for the next pass. It's this application that I was most in need of on the projects I'd mentioned in my first post.

PS - there have been other posts and threads that mention things like proximity sensing stops, which can be interfaced with machine stops, etc. A recent example is post #8107 by mksj on http://www.hobby-machinist.com/thre...in-your-shop-today.14637/page-271#post-422364

And thanks to all for the kind words!

 

[mksj]

Very nice adaptation/modification of the carriage stop, and nice machining. One small addition to consider is to machine a locking screw post with a small lever handle, makes locking it quick and you are not always looking for the Allen wrench.

On the use of the carriage stop, some machines do have a clutch on the power feed rod, so one could use it as a hard stop. The clutch tension on the feed rod can be adjusted on some lathes. It is also a good idea to put the carriage stop at some point, where it will stop the carriage before the cutter hits something you do not want it to hit. On the other hand, the lead screw used for threading does not have a clutch (usually just a shear pin) and you cannot use a carriage stop when it is engaged. So for cutting threads you need to disengage the half-nut before you crash the cutter into something. A few high end machines do have mechanical stop systems that disengage the carriage feed system. You also have the issue of the system freewheeling after the motor is stopped unless you have some form of braking. So there is a certain amount of coordination required to get it right all the time. When I was learning to thread, I would get right about 90% of the time, but just when I thought I got it my timing would screw up. Thankfully I only broke the cutter tip and nothing else.

A proximity stop is an electronic switch which can be used to detect an object (like the carriage) at a specific distance (usually 1/4-1/2"), so it can switch a relay or a control system. They are usually low voltage and can only switch around 200mA. They work well with VFD systems, because they can trigger the VFD stop command at a specific point, and the VFD can usually brake the system to a halt in around 1 second. The reproducibility of the stopping position is better than 0.001", usually the difference is not measurable. When threading, you do not need to disengage the half-nut, so no tense times when machining to a fixed point. Some of the systems I have built use two proximity sensors, so one could machine quickly between two specific points, or one could use the other sensor for the cross slide or tool post. This is similar to the electronic limit stops used on mill power feeds. Example below on its use for threading.
http://www.hobby-machinist.com/threads/pm1340gt-lathe-threading-with-a-proximity-stop.45977/

 

[mikey]

My Emco Super 11 CD has a clutch on the leadscrew that will slip if the carriage stop is hit during a moment of inattention when threading. Someday it might come in handy but I'm usually pretty focused when threading. I do agree that a carriage stop is not generally used as a hard stop other than as an end point. It is very useful to keep the cutter from running into the chuck when working up close and is a critical fixture when boring to a precision depth. I wouldn't want to be without one.

Hman, I meant it - you did a nice job!

 

[hman]

Very nice adaptation/modification of the carriage stop, and nice machining. One small addition to consider is to machine a locking screw post with a small lever handle, makes locking it quick and you are not always looking for the Allen wrench.

I was considering adding some kind of locking lever. But I already keep a special set of metric Allen wrenches handy at the lathe (5mm for setscrews on the QCTP holders, 8mm for the carriage lock, etc.) So I went with a 10mm socket head bolt. It uses the same 8mm Allen I already have close by.

I always try to keep a set of specific tools (box, open end, Allen wrenches, screwdrivers, etc.) at each tool, because I hate having to hunt something down for a routine task. Whenever I buy a new tool, I try to list what I'll need frequently, then go to a couple pawn shops I know of to find the tools. Not many of them have random bins of "junk" tools nowadays, but I keep track of those that do.

Thanks for the amplification about carriage stops and the use of prox sensors. My lathe does have an "oops" clutch on the power feed, and it did save me once. But I just don't want to be using it on a frequent basis.

And thanks to both you and Mikey for the kind words. (plus a small confession - the photos do look a bit better than the actual part. Ah, well ...)

 

[DeanDK]

That's a really nice carriage stop you made. This one is definitely going in the ever growing to-do projects! Thansk