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Lathe Carriage Stop

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Justin Siemens03/04/2019 16:07:24
8 forum posts

After finally deciding to just get one done I finished a carriage stop for my main workhorse:

I didn't have to but I wanted to profile it on my bench shaper:

Any of the items that need frequent adjustment use handles so I'm not always fumbling for an allen key or screwdriver. I glued the brass ends on with loctite. Brass was done for looks.

I also did a video up if you wish to watch it.

The direct link is here if you wish:

**LINK**

I'm just finishing up some drawings of the project. I'll post them as soon as I'm done.

David George 103/04/2019 18:05:10
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815 forum posts
282 photos

Nice looking solid project.

David

jimmy b03/04/2019 18:09:16
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485 forum posts
28 photos

Nice!

Jim

David Noble03/04/2019 18:14:27
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52 forum posts
1 photos

Very nice, I've been wanting one for ages.

David

Justin Siemens05/04/2019 01:53:37
8 forum posts

Thanks everyone!

I finished up the drawings. You can find them on my blog in pdf format: **LINK**

Being a Canadian I do all my engineering work in metric, but for whatever reason I visualize in imperial. That and all my machines are imperial. So the drawings are in inches. For that I apologize.

David Davies 805/04/2019 11:10:50
10 forum posts

A nice accessory Justin and an excellent video.

Glad to see that the slitting saw incident had a happy ending!

Cheers

Dave

Mark Gould 105/04/2019 13:14:18
101 forum posts
60 photos

Nice looking stop Justin, reminds me of another project I keep putting off!

Clive Foster05/04/2019 15:32:23
1749 forum posts
56 photos

Very neat set up but as designed the only positive stop for the saddle is the dial gauge itself. Serious risk of damaging the gauge should you move things too far. Whether D'OH moment or temporary distraction.

Its worth adding a sleeve a bit longer than the full retraction point of the meter movement so that it can't be driven hard right to the end. Around 1/4 of a rev short sounds about right with a nice long travel indicator like that.

Having done more or less that with the old fashioned "make your mill a jig borer" set comprising an indicator mount and a set of length rods in a tray I have a healthy respect for how easy it is to make such errors. The indicator mounts used with rods in a tray systems are generally arranged so the rod hits the indicator carrier case before the indicator is driven right to the end stops. For which I was somewhat grateful.

Clive

Jim C05/04/2019 17:28:40
55 forum posts
1 photos

Looking at this well designed device it would appear that it does have a stop rod item 6 which presumably could be used to protect the DTI before its end of travel??

Clive Foster05/04/2019 18:55:20
1749 forum posts
56 photos
Posted by Jim C on 05/04/2019 17:28:40:

Looking at this well designed device it would appear that it does have a stop rod item 6 which presumably could be used to protect the DTI before its end of travel??

Indeed so but, if I read the way this device is intended to be used, its not a perfect protection.

Looks to me that the primary purpose of the stop rod is to set an end of saddle travel position by reference to the dial gauge before making the cut. So you don't need to watch the dial during the cut. Also a good way of ensuring that all the cuts are the same length. Which is really handy if you are making several parts.

With a long travel dial gauge you have plenty of scope for adjusting things so it is, in principle, quite easy to set it up in a vulnerable state. Obviously you could make it so the end of the stem is sunk back in the body far enough that the saddle strikes the body before pushing the gauge right up to the end stop. But that would be counter-productive as it would seriously reduce the set up range. As designed the gauge can be moved back and forth within the clamp to make best use of its reading range. Far more useful than a fixed gauge position. But it does introduce vulnerability to the 'I can't believe I did that!" error.

Clive

Jon Lawes05/04/2019 18:59:37
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308 forum posts

Our MES has a Myford with a lovely little device that clicks off the feed once its reached the desired travel. Fantastic bit of design.

You've got a lovely finish on those components, nice work.

Bazyle05/04/2019 20:36:13
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4590 forum posts
185 photos

Just to clarify. You are never meant to power feed up to a stop even with a feed clutch like the Boxfords.. 3/4 HP motor with gearing isn't going to stop for a pesky little stop. If it were a firm stop it would break something instead. If you need a smooth finish from power feed right to a shoulder start there and run left to right.

not done it yet05/04/2019 20:49:45
3028 forum posts
11 photos

I’m off to see if my carriage stop is good enough to cut to a shoulder. I’ll only try it on aluminium and will report back later how I got on. It’s an auto stop. Good lathes were made lik that, way back when....

Clive Foster05/04/2019 21:49:42
1749 forum posts
56 photos

The only machines that can reliably and indiscriminately power feed up against a stop are those fitted with a proper fast actuating, usually spring assisted, drive disengagement device. An example is the single tooth dog clutch on my big Pratt & Whitney, also used by Holbrook, Hardinge et al and described by Graham Meek and Martin Cleeves for Model Engineer types. Various slide-bar trip devices, both factory and home made, exist to disengage the clutch in the saddle.

If you don't have such a device the usual, reliable, method is to track the last part of the feed by resting your hand on the saddle traverse wheel so you can seamlessly take over the last half mm or so of travel after dropping the clutch. Its what I do with my Smart & Brown 1024 which is quite capable of shifting the standard, two bolt clamping micrometer stop down the bed unless its done up silly tight. This technique would work just fine with Justins carriage stop.

It is said that machines with rising ball and similar overload clutches in the drive line, as used on some Harrisons and Colchesters, can safely be power fed up to a stop if the overload clutch is appropriately adjusted. The action can be imprecise as disengagement is not only quite slow but also dependent on the actual clutch setting and feed rate. Maximum depth of cut is compromised. Similar imprecision due to slow disengagement rates afflicts the simple trip driven dog clutch device used on early Drummonds et al. As disengagement approaches the drive is taken by an ever smaller section of the dog clutch teeth which is less than ideal and promotes wear of the tips. Which doesn't stop the device working quite well if you aren't too demanding.

Machines with the old style star-wheel on a screw clutch engagement can safely feed up to a stop if the clutch is only lightly engaged. Such setting will seriously reduce maximum cut and, being by open ended personal judgement, is awfully variable. Not a nice method if an (expensive) dial gauge is at risk.

If you have a DRO system the ideal would be an electrically operated disengagement device linked into the DRO so that when a certain reading is reached the drive would be thrown out or the lathe motor stopped and a brake applied. I'm surprised that none of the usual, affordable, offer such a system. ES-i do supply DRO readout boxes with an external trigger output which could well do the deed but the implementation isn't ideal if you want to use more than one stop position. Can be done but its a bit clunky and clearly not what its intended to do.

Clive

Edited By Clive Foster on 05/04/2019 21:53:14

not done it yet05/04/2019 22:03:25
3028 forum posts
11 photos

Did several cuts on a 29mm ally round. All to the carriage stop. First 3 or 4 cuts were 10 thous (lathe is imperial) and then I increased the depth of cut to 15, 20, 30, 40 thous and the last was about 55 thous (cutter was close to the revolving centre).

Every cut stopped at the same reading on the dial gauge, after the gauge had been driven 3.00mm + or - 0.01, as far as I could tell - the gauge fell back about 3 divisions after the trips. The final shoulder was 6mm and all the cuts were done on the same feed and speed. I would not, of course, rely on the shoulder being perfectly formed, but certainly good enough for just needing a small finishing cut.

I have never tried it before (only left the trip positioned such that it would trip before a crash - just in case), so easily good enough for threading, good on aluminium and likely no problem with steel. Clearly needs winding back from the shoulder after tripping, to avoid leaving the cutter rubbing, but I am pleased with that first try with it.

Will I use it regularly? I very much doubt it - I don’t do much repetitive work - but I could, if I needed to remove a lot of material from a piece, I suppose.

I’m now wondering how many lathes have this feature.

Howard Lewis06/04/2019 11:52:22
2048 forum posts
2 photos

A nice piece of work!

My carriage stop was made to carry a Micrometer barrel. From the way that the barrel is graduated, it was meant for this use. But,to prevent it being moved under power, I disengage the feed about 0.025" (Luddite! ) before it, and use the handwheel to "feel" up to the stop.

Howard

Edited By Howard Lewis on 06/04/2019 11:53:01

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