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Cotters up close and personal

Ever look inside a cotter?

A cotter is a mechanism like the quill lock on a bridgeport. Guy Lautard describes them and how they work in one of his "Machinist's Bedside Reader" books and I borrow the term "cotter" from him.

I've made and used them in a number of metal projects but I'd never taken a close look inside. Now that I'm learning to use 3D modelling I did that --and found it interesting. Perhaps a few readers here will also, No news to many readers but it was interesting to me.

I've posted screenshots in the dropbox as cotter*.jpg. I was contemplating making a cotter clamp for the LED ringlight I'm building for my microscope. The mount for the ringlight to the scope is made using PVC plumbing parts from Home Depot as raw material costing less than 2 bux.

In the model, the large part is a (nominal) 2" PVC collar, cotter barrel is (nominal) 1/2" PVC pipe, the slugs in the cotter would be turned from delryn to slide easily in a .625 hole reamed into the small pipe, the pinch screw would be 1/4-20 brass. The cotter barrel is 2" long. PVC is neat stuff because it's cheap and because glue works well.

I think I'll try a simple setscrew first, but if that isn't satisfactory I'll have this as a fallback. I do like making cotters!

The thing that struck me in looking at the model was the double mechanical advantage at work to pinch tight: screw plus wedge. No wonder these things work so well!

Reply to
Don Foreman
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Thanks for mentioning these. I want to make a really nice boring bar holder for my lathe's toolpost (which I'm making) and have been considering different bar clamping methods. I'm using 1/2" shank boring bars. I wonder if a cotter clamp would be rigid enough.

Reply to
Artemia Salina

The import quick-change toolposts come with a boring bar holder that uses two screw activated wedges to lock the bar in the bore. They look sort of like half cotters, if you will. The screws are on the top and pull the wedges up from the bottom. I would expect that a full cotter (or two) would work even better. On my 200 series post, this fits a 1" boring bar.

HTH, --Glenn Lyford

Reply to
Glenn Lyford

That's the way my Phase II boring bar holder works.

Reply to
Bob Engelhardt

I made just such a boring bar holder and I found that it really works well. Have a look at the following photos:

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HTH Rick Renner

Reply to
Rick Renner

Very nice!

Reply to
Don Foreman

Nice job Rick. One thing that concerns me is the possibility of the boring bar wanting to roll a bit as the cotter clamp is tightened. Have you experienced anything like that in your holder? Anything you would have done differently after using it for a while?

Thanks

Reply to
Artemia Salina

A'int CAD cool?!

Actually, I'd be interested in details on your ringlight. I've been considering exactly this project for a while. How many LED's did you use? How are you powering them? How much light do you get compared to a fiber optic ringlight (with e.g. a 150W EKE bulb)? Other construction details?

Reply to
Greg Dermer

Hey Rick.

I like it !!

Take care.

Brian Laws>>

Reply to
Brian Lawson

Thanks for the kind words. Regarding the issue of boring bar rotation, I haven't detected any in the dozens of job set ups I've done with this holder. I can't think of anything I'd change about this holder.

Rick Renner

Reply to
Rick Renner

I don't know how much light a 150W fiberoptic ringlight throws, but I'd expect it to be a lot brighter than 10 LEDs running about 0.2 to

0.4 watts each. Experiments lead me to believe that I'll have ample light for the low (3.5x to 22.5x) magnifications I use, but 150 watts it emphatically is not.

I'm using 10 large (10mm) white LED's, arrayed in a circular array about 5" in dia. Each LED is in a little "projector" about 1.5" long and 0.5 dia with a ball nose set in a round hole to facilitate aiming. There's a little 0.5"dia lens in each projector that images the glowing phosphor surface inside the LED onto the worksurface. The result is a very well-defined and evenly-illuminated disc of light about 2.5" dia with no rings or dark spots like you get from an incandescant flashlight. It looks almost like a white disc cut out of paper. LED flashlights spray light all over the place so they're less efficient. Light not illuminating the microscope's limited field of view is wasted.

All 10 "projectors" will be aimed at the same spot, Because they all impinge at an 18 degree angle from vertical but from various directions, I'm expecting very shadow-free but high-contrast lighting, and little problem with specular reflections because no specular reflection would glint from more than one or maybe 2 of the10 projectors. It's high-contrast because the light from each projector is well-collimated, not diffuse as from a fluorescent ringlight and possibly from a fiberoptic ringlight. (I've never used a f.o. ringlight) .

Power supply will be a 45 or 50 volt DC supply current-regulated to

50 to 100 mA. (adjustable) to run all 10 LED's in series. That'll ensure that they're all running the same current so should be about the same brightness. No dropping resistors. The LED's are rated at 30 mA but they'll take considerably more, though with consequent degradation in lifetime. I may only get 5000 hours out of them. I'll "relamp" with the much better LED's available then, if I should live so long.

Other construction details (including a cad model and photos) available, just send me an email. Warning, though: I made no attempt to be "practical" or even "sensible" on this project, though I was "cheap". I'm retired, can spend my time any way I want, and that's often in the shop. It was fun just seeing if I could build this somewhat fanciful design. The 10-facet conical metal ring was an interesting challenge.

Reply to
Don Foreman

OK, see

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Reply to
Don Foreman

Boy Don, that's cool. I like the way you did the balls. I have tools and cnc to do this easily but your method is a good one to know. Especially if the lathes are full and you just gotta have that part. And all the detail on that page. gives me something to strive for if I ever manage to get mine up and running. Cheers, Eric R Snow

Reply to
Eric R Snow

Don,

Thanks for the response and for the writeup. Of course it's not 150W, but on the other hand I expect that the efficiencies of the LED's are higher than the incandescent bulb, and then there is a little loss in the fiber... So the disparity might not be as much as one might guess. Who knows?

It looks like a great project. Congrats!

-- Greg

Reply to
Greg Dermer

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