How do I set and turn very small internal taper (ER11)

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djc:

--- Quote from: PekkaNF on May 11, 2011, 02:41:35 PM ---...How about miniscule ER collet with 8 degree taper?
--- End quote ---

Hope I'm not telling you something you already know, but all ER collets have the same taper. Hence, you could set up on a bigger series collet or on the female cavity of a bigger series chuck. It's not as if you are setting up on something X mm long and then trying to turn a taper 10X mm long - what you set up on and what you turn are in the same field lengthwise.

BillTodd:
You could always set your top-slide to 8° with a sinebar.

Here's Frank Ford's method : http://www.frets.com/HomeShopTech/Tooling/LatheSineFixture/sinefixture.html

If your top-slide does not have nice reliable parallel sides, then you'll need to drop a gauge pin (or similar) into the top-slide dovetail to get reference edge to work from. (The picture shows the top-slide at 10° BTW 'cos that's my 10° block)

PekkaNF:
Thank you all.

I have to read Lew_Merrick_PE:s message couple of times more, I think I got it. Sort of like MT gauge made out of individual flat parallels idea.

After Bogstandards post and ref.link:
http://madmodder.net/index.php?topic=2249.msg23587#msg23587

I went to garage and come out with a cunning plan:
I'll fit over 6mm silver steel rod (center holes both ends) ER11 AND ER25 collets, then I'll adjust their relative position until their flanks will line up with a parallel. This will allow me a reference of more than twice the length of a ER25 collet.

I noticed that someone else come out with more or less same plan (djc:Hope I'm not telling you something you already know, but all ER collets have the same taper. Hence, you could set up on a bigger series collet or on the female cavity of a bigger series chuck. It's not as if you are setting up on something X mm long and then trying to turn a taper 10X mm long - what you set up on and what you turn are in the same field lengthwise.)

While toying with collets and silver steel, I remember Bogstandard mentioning of using two ER32 collets to check the fit with engnineering blue. I noticed that the collet is much more rigid with a nominal size silver steel rod inside of it. I'm pretty confident that if I manage drill/turn the collet cavity close to correct taper, I can check the fit now. The smaller collets seem to have fair amount of flex and I was really concerned about getting the angle as close as possible. I believe that the collet could fit into firly bad taper, but it would not grip the tool shank parallel, unless the taper is exact.

BillTodds sine bar method is something I have to investigate as a back up, and I'm going to need this method soon. Better toy with it before I really need it.

Thank you all, you have been most helpfull,
PekkaNF

Bogstandard:
I did a little job for Dave Bluechip a couple of weeks ago, attempting to straighten out an ER collet fitting. I set the topslide to the normal rough 8 degrees and after grinding, it was found to be spot on, no further tweaking of the topslide required.

So really, all you do is set the topslide with the rough angle markings, and when checked out with engineers (prussian) blue after the first few shallow cuts, it is only just a tiny tweak either way to get it spot on.
I honestly think you are maybe clouding the issue by attempting to get it spot on first time and turning it into a major machining exercise rather than just a normal turning job.

Once set up for cutting at 8 degs, the whole process only takes 10 to 15 minutes, and that is with fine adjusting as well, maybe a little longer because you are not used to doing such things.

Just relax, don't panic, think about what you are doing and take your time. You will kick yourself when you find out just how easy it is to do when you do everything in logical steps.

So basically, measure the small end of the collet, and with a drill just a tiny bit under or even spot on that size, drill down the part as deep as you want to go.

Find the largest boring bar that you have that will go down the drilled hole, and set it up and take a few very light skims down the hole, to make sure it is cutting OK.

Swing your topslide to 8 degs.

Wind your topslide fully back, and bring the tool tip to within about 5mm of entering the hole using the saddle and crosslide. Lock up the saddle.

Using the topslide start to take the cuts, using the crosslide to put the cut on.

Once you are about 2/3rds to depth with the cut, blue up and check your angle. Slacken off the topslide clamp screws so that they still grip a little, then tap the topslide very gently in the correct angular direction, using say the plastic handle of a screwdriver, then tighten up the nuts. Usually, if you see it move, you have gone too far, it really is only a tiny amount each time.

Take a skimming cut until all the blue has gone from the tapered hole, recheck for angle. Adjust if necessary.

Once you reach a full covering of blue, then you can gently open out until the collet sits perfectly at the correct depth in the hole.

Job done.

If you go a bit too deep, skim a couple of mm off the front of the job (you can use the set up boring bar), and then carry on taking material out of the hole, but more gently this time.

This is a longer posting than I really wanted to do, but by explaining it this way does show that there is no black magic or super critical measurements involved to turning an inside taper.

By all means go ahead and try to get things spot on first time, but it could cost you a lot more money in time, effort and tooling costs than the tool you are making is worth. The way I have explained is how a jobbing machinist gets it done in less time than it takes the average home machinist to even think about doing it.

All that is required is a tin or tube of Engineers Blue (NOT marking out blue) and a bit of logical thinking, plus of course, common sense.

ALWAYS TRY TO GO FOR THE EASY OPTION.

Bogs

Lew_Merrick_PE:

--- Quote from: PekkaNF on May 13, 2011, 03:01:17 AM ---I have to read Lew_Merrick_PE:s message couple of times more, I think I got it. Sort of like MT gauge made out of individual flat parallels idea.
--- End quote ---

Pekka, The thing about the angle plate method is that you can, if your mill is set-up for it, get sine bar/plate accuracy fairly easily. I most often use this approach when I need a surface at some bizarre angle and may need to repeat it again in the future. I make the angle plates in pairs and use the "high-end index hole" to line them up in my mill vise such that I can set my part on them (angled "parallels," if you will). I use them (singly) with centers in my lathe when I have to create stupidly accurate tapers.

I tend to go with set-up goodies that make reproducing one result easier when an additional set-up may be required as one successful project usually (in my world) ends up needing additional "units" being made. I make them up as needed, steel stamp the angle information on them, and store them in a box. I don't use them that often in the lathe, but when I need to, I take out all the angle plates made since the last such exercise and centerdrill the whole lot. That way they are "lathe ready" if I need them.

Prussian blue (also called: engineer's blue or high-spot blue) works well when you have a one-off project. It certainly proves out a fit like nothing else. Chalk-line powder (dyed chalk powder) can be used in a pinch -- as can solvent thinned lipstick. (Chalk-line powder works very well when you need a "blue fit" for wood.)

.

Lew

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