Turning shallow recess

I am about to turn a recess in an aluminum plate which is mounted on a face plate. The plate is 1/4" thick. The proposed recess is 5.400" x
0.125". The diameter is critical, the depth is not as long as the floor of the recess is flat. I am not clear what is the best way to approach this.
1) Drill a center hole (the middle 2" or so of the recess do not matter). Cut the recess using an AR tool from the middle stopping at the circumference of the recess. The tool path will be 5.400" minus whatever the hole diameter is. This way I can get a nice flat bottom of the recess. The problem I see is getting the diameter accurate. I usually like to "sneak" upon the final dimension which in this case is not possible (at least I do not see how).
Theoretically also the AR cutter might rub at the start of the cut on the small diameter of the starter hole. I wonder if one should do this with a boring bar.
2) Start with a boring bar, enlarging the hole to the required depth of 1/8" in small passes. I have a depth stop for the carriage so consistency should not be a problem. This will allow for frequent checks as one approaches the diameter, reducing the depth of cut etc. OTOH one might die of old age doing this.
3) Combination of the two: Cut a smaller recess to the required depth as in (1) and then carefully enlarge it with a boring bar as in (2).
What would a real machinist do?
Michael Koblic, Campbell River, BC
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On Mar 23, 11:57 pm, snipped-for-privacy@gmail.com wrote:

That leaves me out. But anyway...
If appearance isn't important I'd cut a slightly deeper groove in the corner to separate the two cuts.
If it is I would touch the bit to the plate and set the carriage stop to cut 0.125" deeper, https://picasaweb.google.com/KB1DAL/HomeMadeMachines#5107533382447691698 then let the stop control the depth while sneaking up on the diameter.
Probably I would rough it to within 0.005" or so with a more rigid turning tool before switching to the boring bar.
jsw
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On Thu, 24 Mar 2011 04:10:13 -0700 (PDT), Jim Wilkins

OK, it sounds like you favor the third method. I was kind of thinking that if no responses were forthcoming I would have a go at that. It seems to combine speed and accuracy.
BTW appearance is not an issue and having the recess slightly deeper at the periphery sounds like a good idea.
Thanks,
Michael Koblic, Campbell River, BC
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snipped-for-privacy@gmail.com wrote:

Rotary table on the mill .
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I don't even see where the problem is.
You approach a bore size the same way you approach a spindle size: On a spindle, you cut until you're a couple of thou large, then creep up on the last two. On a bore, you cut until you're a couple-thou under the size you want, then cut swarf for the last few cuts to make sure your finished i.d. is dead-on.
The only difference is what direction you turn the cross slide crank.
I'd turn the whole recess to .125" deep, but undersized by (say) four thousanths. Then I'd cut the remaining two thou of carriage travel in half-thou increments about a couple of tenths deeper than .125", just to make sure I didn't leave a shoulder in the hole.
A screw-adjustable carriage stop makes all this a lot easier. You only have to worry about the hole diameter.
There's absolutely no reason to bore a hole in the center of the work unless you have difficulty setting up a tool to cut on-center. You sure don't need a boring bar to do this kind of work, just a straight-cut tool with the correct side rake for the material you're cutting.
LLoyd
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On Thu, 24 Mar 2011 07:12:04 -0500, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:>> The problem I see is getting the diameter accurate. I

Ah, that would be the No. 2 method then...OK.
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No clue. I am not a real machinist.
What I might do however is pocket the hole on my CNC mini mill to just under sized, and then setup a boring rig of some kind to finish to exact size.
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snipped-for-privacy@gmail.com wrote:

Ass-u-me-ing you mean something like this:
http://mysite.verizon.net/richgrise/images/recess.gif
I'll ask Joe the Real Machinist tomorrow.
Cheers! Rich
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On Thu, 24 Mar 2011 17:19:46 -0700, Rich Grise

Yes
Great.
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snipped-for-privacy@gmail.com wrote:

All he said was, "Either on the lathe or a rotary table, probably more likely the rotary table, because the material is so thin."
Dunno if this is helpful at all, especially if you don't have a rotary table, but there you are.
If it's only aluminum, I'd think that it should be fairly easy either way, but like I said, I mainly just draw the pretty pictures around here. ;-)
Another thing a real machinist would know how to do is decide which way to turn the rotary table - I don't know the exact terminology, even though somebody here mentioned it just a few days ago - what comes off the top of my headbone is "upstream" or "downstream," i.e., if you're turning the rotary table the same way the tool is turning, or the opposite way.
Good Luck! Rich
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    You mention AR -- just the shape, or are you specifying an index tool?
    How sharp does the corner need to be between the bottom and the wall? Can you live with the radius on an index AR tool?

    This is likely to work well -- and should not take as long as you think. (But your lathe does not have power cross-feed does it? So the finish of the bottom is going to be a function of how smoothly you can turn the crank.

    Take a HSS bit, grind it to the proper rake and end clearance angles, and then grind extra radiused clearance on the cutting side around to the bottom to clear at the start of the drilled hole. With the HSS bit, you can get a very sharp tip radius if that is important (and it likely is, unless what fits in the recess will be beveled first).
    This sounds as though it is to fit one of your sundial rings for boring the ID after turning the OD. If so -- it might be better done mounted on master jaws as top jaws, and cut to either three or six wedges depending on the chuck. The only one which I know you to have is the Taig 3-jaw, which is a bit small for this task. But if you are making soft jaws for a chuck, the boring of the step to size should be done after mounting to the chuck master jaws or you have another place where error can creep in.
    But it may be that you plan to clamp the workpiece into the recess using bolts with washers just outside the OD of the final workpiece (not your tooling plate described above), or perhaps using DeStaCo toggle clamps (might be difficult to work around on the size lathe you have), so yes, you only need to make the recess concentric on the faceplate -- and forever after dedicate that faceplate to that fixture -- unless you drill for and install some dowel pins to make sure that it always mounts in the same place every time.
    Good Luck,         DoN.
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On 25 Mar 2011 01:43:48 GMT, "DoN. Nichols"

=========A useful dodge is to undercut the recess [cut a groove at the edge] to eliminate any interference, even with a square edge/corner on the insert. If strength is a consideration, this will be stronger than a square corner if the bottom of the undercut is radiused as it eliminates the stress riser at the square corner. In any event it will be easier to machine and grind tools for.
Good luck and let the group know how you make out.
-- 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).
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On Thu, 24 Mar 2011 21:11:06 -0600, F. George McDuffee

OK, it`s late and I am obtuse. What you are saying is make the mouth of the recess slightly smaller than the floor of the recess (keyboard still refusing to type question marks)
Michael Koblic, Campbell River, BC
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On Thu, 24 Mar 2011 22:48:39 -0700, snipped-for-privacy@gmail.com wrote:

=========Yes
Another way to do this is use a "radius" tool bit and the lathe compound [top slide] at a 45 degree angle to slightly undercut both the side and bottom of the recess to provide clearance for sharp edge insert. Hand ground HSS tool bit, similar to a threading tool, should be adequate as long as it does not produce a sharp corner.
-- 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).
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    [ ... ]

    Depending on the size of the hole, you can grind a tool to cut either of these shapes (ASCII graphics -- use a fixed-pitch font like Courier to avoid distortion):
----+ |                    Perfect shape -- but difficult +--------------------------- .....
----+ | | Deep well -- undercut the side ++ at the bottom | +---------------------------- .....
----+ | Shallow well -- cut deeper at OD | +------------------------- ..... in the bottom. +-+
Either of the second and third allow clearing a square edge on the part to fit into the recess -- and each requires grinding an HSS tool to a different shape.
    The reason for the second being for deep wells only is that with a shallow well, it perhaps leaves too little metal for strength.
    Enjoy,         DoN.
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wrote:
(snip)

Shape. Right hand tool that cuts to shoulder. I could use an insert, HSS or brazed carbide (a pretty pointy one).

A good question. Proof of the pudding etc. I will know when I done it.

If I do it this way I will be turning the crank in small steps while I am boring each pass. I agree this will make the bottom look like a washboard if I take too deep cuts.

This is just an experiment along the lines you outline. Chucks, however, are definitely not involved.

That is the concept. I am not really thinking much past the recess. It took me a while to work out how to attach the aluminum plate to the face plate (do you ever drill and tap holes in your face plates-my keyboard refuses to type a question mark).
Also, you are advising a man who spent the whole of today changing a switch on his drill press - half a day running around to find one and the other half struggling to change it (Don`t ask).
Michael Koblic, Campbell River, BC
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On Mar 25, 1:45 am, snipped-for-privacy@gmail.com wrote:

An HSS boring bar can be sharpened to take a light cut outwards or backwards. The ones I have are angled inwards from the point on both the end and side cutting edges.
http://littlemachineshop.com/Products/Images/480/480.2682.jpg
You should be able to face the bottom of the hole outwards from the center and then cut the ID by withdrawing the tool to the right, assuming you have already related the dial reading to the cut diameter.
I bore nearly to size with the end and then finish with light cuts in both directions. The end holds size better but the side is still razor sharp and seems to leave a smoother finish. The boring bar deflects in if asked to cut more than about 0.005" in steel backwards.
If you don't mind rotating the compound or toolpost you could do the job with a more rigid turning bit. I can angle the tool holder on my Multifix post without losing the squareness for the parting tool or the 29 degree threading angle. If I do have to move the compound I reset it afterwards by pressing the parting tool holder against the spindle end while tightening the clamp screws.

Previous owners drilled and tapped my second-hand cast iron faceplates without hurting them. Try to avoid the stiffening ribs.

I won't ask about light bulbs either.
My mother's stove hood opened to change the bulb or filter with two quarter-turn latches right behind the front edge where she couldn't see them. She and then a neighbor nearly tore it apart trying to change the bulb. She got really mad at me when I opened it with one hand in 5 seconds.
jsw
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On Fri, 25 Mar 2011 05:13:36 -0700 (PDT), Jim Wilkins

Got them.

I can do that but I thought the AR cutter which is shaped like the boring bars in the pics would do the job lined up at right angles.

I managed to do without (just) as the slots extend to 6.5". I am thinking ahead to the next job.

1) Getting anything out of the ordinary in our town (yes, a dirt common switch comes under that category) is a sport. In fact such shopping trips are often spiced up by frequent bets between myself and my wife. However, the longer we live here the more often the response seems to be "no takers".
2) As with air (or many other) disasters the expected 10-minute job extended to 2-1/2 hours though a series of minor mishaps including crowding of the switch box with Chinese wiring which exploded out of the box at the first opportunity thus distorting the original anatomy. This lead to misdiagnosis of the connections. Coupled with a couple of terminals which I have never seen before (remember I took another Chinese drill press apart and built a lathe out of it) led to an inevitable diagnosis of motor failure. By the time I sorted what goes where and what does what and where it has to be crammed into to do it time and polite restraint run out.
Cutting a tricky recess was (wisely IMHO) postponed until such time that the temperature under my hat reached a level below that of No. 3 Fukushima reactor.
Michael Koblic, Campbell River, BC
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    [ ... ]

    O.K. So some other means of clamping the workpiece in by the edge -- perhaps as followed.

    Hmm ... first, for the keyboard -- do you have cats? Every once in a while I have to pop the keycaps off and clean out cat hair which starts cushioning the keycaps and preventing full closure. Just pop out the ? and the one next to it and see whether you can use some bent wire to drag out the cat hair.
    As for drilling and tapping holes in my faceplates -- the answer is not yet -- most have enough slots so I can make clamps work with bolts through the slots -- but for something important enough, I would certainly be willing to drill and tap at need. Mostly depends on whether I can find another way first which does not require modifying the faceplate. I've got one large faceplate, and two smaller dog drivers (one slot out to the edge for larger dog tails), and usually things fit the 3-jaw, the 6-jaw or the 4-jaw chucks in one way or another. But for a long production run of some part, the cost of modifying a faceplate (and perhaps getting a replacement later) balanced against the extra work of handling a large number of parts in the chucks might balance the other way.

    Soldered switch wires, push-on tabs, or wires under screws?
    Problems gaining physical access to the switch so you could remove it?
    Problems finding a switch which mounted in a particular snap-in way forced by the design of say a trim plate on the drill press? Perhaps making a replacement mounting plate for the switch which you did get?
    Oh yes -- don't ask he said. :-) But I can guess at (and suggest) *quite* a few things which could slow up the process -- especially if you don't have the crimping tools and crimp-on "Faston" push-on connectors in stock at home. Electrical and electronic repair work involves tools which I have *tons* of -- and still something can wind up taking a lot longer than I expect.
    Enjoy,         DoN.
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wrote:

It seems to have been Forte Agent specific and has now resolved itself without any obvious effort on my part other than rebooting.

Thankfully I was able to avoid it by a fraction of an inch. Still it would not have mattered - this plate is now committed. See part 2 and 3 - OTOH I seem to remember that you cannot see flickr posts.

All of the above, more or less.

I have accepted that things *always* take longer than planned. Thankfully, I am no longer in a position where planning is essential.
Michael Koblic, Campbell River, BC
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