Best Way to Make Identical 2.125" Rods?

[SteveHGraham]

I always feel like I already know how to do the simple stuff, but I just cut four identical pieces of round rod, and I am wondering if I did it the right way.

I needed four 2.125" pieces of 1/2" rod for a CNC motor mount. I did it in the way that seemed obvious to me. I parted them off to around 2.5", I faced one end of each one, and then I turned each one around, trimmed it to nearly the right size, and then did the final cuts using a caliper and the DRO. I chucked the rods so I could get one jaw of the caliper behind them in the chuck. That way I could measure them from one end to the other.

The lengths of the finished rods vary within a range of maybe .005", which is not a problem, but .001" would have been more satisfying. Is there a better way to do this? I think that if I did this a few more times, I would hit .002", but I don't think anyone would give me a prize for that.

It seemed like the results were always .002" longer than the pre-cutting measurements indicated, so I had to compensate for that.

Also wondering if there is a method better than air for getting chips out of tapped holes. I had to make 10-32 threads in the ends of these things, and the chips don't seem impressed by air. I have only gotten one of them cleaned out completely, and I had to run the tap in there two more times to do it.

[hammermill]

use a chuck face spider as a stop now they can't move back into the chuck as you machine them.


http://www.neme-s.org/Spider.htm

to get the electrons in the cranium moving

[BadDog]

Depending on machine and setup, desired tolerance at or below a thou requires a bit of planning. It is near impossible to determine the flex of your setup due to too many variables. So you can't just touch off and crank 0.030 and expect to remove 0.030. In order to hit a dimension, I like to step in with 3 identical cuts to final, each one attempts to take exactly 1/3 the remaining material. The first cut deviation is noted, and I use that information to take off exactly 1/2 of what remains. That deviation (hopefully substantially smaller) is also noted and applied to the final cut depth, hopefully hitting in range.

[SteveHGraham]

Lathes are so crazy. If I adjust the mill to take off .134", that's what it takes off. I should just do the final cut on the mill!

I do like the spider, though.

I guess being .002" off one way or the other is not that terrible.

[SteveM]

When I need to do that, I put a collet in the spindle (with the chuck in place) with a piece of rod sticking out just enough that I can still get a proper grip on the work piece.

Each time you chuck up a new piece, you just push it up against the rod as you chuck it up.

Steve

[SteveHGraham]

It sounds like people think there is flex in the jaws.

[hammermill]

Flex is everywhere,it's all in how you understand and use it. Depending on how you do it softjaws would also work




Sorry I had to suggest them

edited to correct auto correct errors

[BadDog]

Yes, flex is everywhere, including the jaws, but the jaws are not your problem. Same thing happens on a mill, but in a different way and to direct less impact, partly due to the nature of the way it cuts. But even on a mill with a brand new sharp EM, I still step to final if it really matters to me that it be "dead on" (or as possible).

[spro]

It has already occurred but the "follower rest" is good for this. The entire quad is sized at once and then parted off.

[Harold_V]

I always feel like I already know how to do the simple stuff, but I just cut four identical pieces of round rod, and I am wondering if I did it the right way.

Right way?

Many would argue that there is such a thing.

then did the final cuts using a caliper and the DRO. I chucked the rods so I could get one jaw of the caliper behind them in the chuck. That way I could measure them from one end to the other.

Caliper?

Thought you said you wanted to do them right?

I've commented endlessly on a caliper being used for close tolerance work. It's not suited to the task. It is suited to holding ± .005", assuming you don't care where the measurement falls, as there is nothing that will ensure that what you read is the true size, at least within a couple thou.

Sure, there's exceptions. Some guys insist they can trust them to a couple tenths, but that's absurd.

The lengths of the finished rods vary within a range of maybe .005", which is not a problem, but .001" would have been more satisfying. Is there a better way to do this? I think that if I did this a few more times, I would hit .002", but I don't think anyone would give me a prize for that.

I've heard soft jaws lend themselves quite nicely to this concept. Could be wrong, but my many years of using them tend to reinforce the idea that I'm not.

If you bore a shoulder in soft jaws, it can be used reliably to stop the shaft at the same location each time it, or its brother, is installed. Couple that with a preset on the DRO or a dial indicator and you can rapidly duplicate lengths within ± .001" without effort. Don't make your measurements with a caliper if you really want to know the length. You're kidding yourself if you do.

Also wondering if there is a method better than air for getting chips out of tapped holes.

I've never discovered a better way, but then I'm wise enough to use a needle, so the air is applied where it's needed. If you're blowing across the hole, trying to dislodge chips that are seated (by using a gun tap in a blind hole), you're wasting your time, although you can expect the limited success you achieved.

Harold

[BadDog]

I missed the point about chips in tapped holes. I recall another method of packing the hole with soft wax (or perhaps clay, or ???) before tapping. The tap displace the media, and that carries the chips out. If using an oily wax, say tapping wax, it provides multiple benefits. Saving the excess and melting would allow reclaiming much of it sans chips.

That said, like Harold, I use air. I have 3 air nozzles setup. One has a convenient replaceable nozzle tip from before those ridiculous annoying "safety nozzles" became the OSHA mandated norm. It normally has a ~1/8" tube attached. Very little flow, but clears holes well. And I have other tips over a range that can be attached, including some with soft rubber hoses that can seal relatively well as needed. Comes in handy, though for clearing chips in most holes, a standard nozzle of most any sort close at hand works just fine...

[Harold_V]

I missed the point about chips in tapped holes. I recall another method of packing the hole with soft wax (or perhaps clay, or ???) before tapping. The tap displace the media, and that carries the chips out.

While I've never given that method a go, I expect it won't serve well if guns taps are in use, as they drive the chip forward, generally intertwined with one another. It's not at all uncommon to retrieve the chips as a unit, assuming they don't get compressed in the bottom of the hole.

The subject about wax was discussed a while ago. There used to be what was called Johnson's wax, which was used for tapping aluminum. It resembled beeswax in color, but was very thin, almost a gel. It was easily applied with an acid brush. A dab on the end of a tap would permit tapping a few holes before it had to be refreshed. In my opinion, and, keep in mind, all tapped holes were inspected for fit, it was far superior to the fluids that were available at the time.

I haven't seen the product in many years. Don't have a clue if it might still be available, but I'd recommend it highly if it is.

Harold