Turning shallow recess - part 3

========== Very nice work -- thanks for closing the loop.

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

Thanks.

However, the loop will be closed when I have done a *second* piece in this contraption. I don't know about you but I find that the dear Lord gives me a pass with the first attempt at anything and screws me on the next one :-)

It is amazing how often this holds true. To the point where I now tend to do two of everything if possible.

Michael Koblic, Campbell River, BC

Very nice setup, Michael.

There are some workholding clamps that grip laterally as the fastener is tightened, which may work well for holding the rings by their edges.. while allowing you to make light facing cuts. Since the rings are captively held by the undercut, I wouldn't expect there to be much likelyhood of clamping devices distorting the rings (WAG, mostly).

There seems to be enough surface area around the threaded holes in the plate to support those kinds of clamps, although the jaws of the clamps could leave marks unless the tips of them were biting into brass shims (definite maybe). Grinding an appropriate radius into the clamp "jaws" could be worthwhile.

The types of clamps I'm thinking of (but can't remember the notable brand name) could turn your workholding plate into a 3 or 4-jaw chuck, for that specific size of rings.

Some metal blocks with screws in them (located around the ring area) could potentially work about the same as those clamps, but screws perpendicular to the lathe spindle's axis won't also push the workpieces into the workholding plate.. which is what those clamps do.

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

I caught a young hobbiest purchasing *one* op-amp at an electronics shop. I opined that she should buy five. Two to lose, One to burn up, one to use and one backup. Luckily she laughed. :)

--Winston

OMG, Win. "Hobbyist", please.

Five sounds about right.

-- Most people assume the fights are going to be the right versus the left, but it always is the reasonable versus the jerks. -- Jimmy Wales

I had a look at some of them. Firstly, only the smallest ones would hold the ring without sticking up above the surface of the ring and interfering with facing. Secondly, the smallest ones have only very limited range of gripping. Thirdly, there is the issue of centering the workpiece accurately.

In the end I was not sure that they would not do the job any differently than a 4-jaw chuck. Plus they would add complexity and cost to the existing project (e.g. I doubt that I could get away with just a 1/4" aluminum plate).

I am keeping them in mind for a similar project in the future, though.

Michael Koblic, Campbell River, BC

You nailed it again, George.. Toe clamp, and Mitee-Bite were the words I wasn't remembering.

There are other manufacturers of toe clamps which work very well for a wide variety of workholding tasks.

The add-on fixturing plate gives you lots of options that a bare faceplate doesn't offer (without more drilling of the faceplate, anyway). A thicker fixturing plate would provide more workholding alternatives without extending the workpiece as far from the spindle bearing that a full-sized chuck would likely cause. I think the faceplate solution saved you a lot of grief as far as minimizing the potential for chatter, by keeping the workpieces close to the headstock bearing (especially since the lathe doesn't have variable speed).

Complexity and expense nearly always enter into the equation for convenience, it seems.. but hey, it's for the enjoyment of metalworking.

I haven't used double-sided tape for workholding, although I've seen that it's a fairly common method.. but I think I'd feel more confident with mechanical fasteners retaining the workpiece. For the ultimate in precision (typically not my goal), having the workpiece securely seated on a (clean) metal surface would insure that the workpiece is precisely flat against the fixture plate/reference surface.

I did notice your excellent safety bar approach.. inexpensive and practical. A soft tip on the end would ensure that the bar doesn't affect the spindle's internal taper, in the unlikely event of an Oh S*it incident.

With other workholding methods, centering shouldn't be an issue with the shoulder of the fixture plate recess to accurately center the rings, otherwise, adding a disk/ring in the ring I.D. area for other fixture plates may work well.

I don't recall at which stage of the process you're finishing the I.D. of the rings.

========= Thanks for the kind words.

Here are some URLs that may give you some additional ideas. [All it takes is money]

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

Today I did the crucial second piece and learned more about the process. As far as chatter goes there is a trade-off: Not getting close enough to the work-piece makes the *tool* chatter. I could not understand why I did not have chatter problems doing the ID on the previous piece and could not get rid of it this time. Then I shortened the (identical)_ boring bar as much as I could, running the plate really close to the carriage, and voila! All was well.

Road with many curves leads to sheep losses (don't ask! :-)

Second piece held fine even as I got bolder with the depth of cut. I did not even clamp this piece like the first one (the strength of the adhesion of a double-sided sticky tape is given by the pressure applied to the bond). I still had to heat it up with a heat gun to get it off.

The tape is about 0.003" thick. Well beyond my requirements for accuracy.

The end goes nowhere near the spindle - just inside the opening. Like yourself I did not want to risk spindle damage.

AT this point it goes like this:

Michael Koblic, Campbell River, BC

Thes appeal to me in their simplicity. Sadly, all sizes are on back order and hence no pricing info.

Bookmarked for future reference. Thanks.

Michael Koblic, Campbell River, BC