Measuring drill rod...calipers and micrometers.

[zeeprogrammer]

I got my first ever bit of drill rod (silver steel) today.
It doesn't look like I expected. I was expecting some grundgy kind of stuff but it almost looks like finished steel rods you find in printers.

Anyway...I've had some questions about measuring for some time and thought this was a good opportunity.

One of the rods is 3/8". Supposedly 0.375.

1) How accurate should I expect this to be? That is, when ordering 3/8" drill rod...is it exactly 0.375"?

2) I used two calipers...when I close the jaws with hardly any pressure, I measure 0.374. Applying pressure can bring this down to 0.368. It raises the question of how much pressure does one apply when using calipers.

3) I used a 35 year old cheap micrometer I got in college that's been banging around a box since then. When I close the (? what do you call them?...anvil!), I measure 0.375. Usually 0.3745. No real pressure. Applying pressure might get down to 0.371. Same question as number 2.

I figure the calipers will dig in (sharp edge). I also figure the micrometer is more accurate (despite its age and abuse). I also figure there's some question about the 3rd digit of significance.

This is where having a teacher/tutor right here is helpful. How do you describe pressure?

A very newbie question...but I'm betting there's at least one other newbie out there wondering the same thing.

Thanks.

Oh...what else is drill rod good for besides reamers? ;D

 

[rake60]

First off, you need to be sure either device is zeroed.

It is easy to get a errant reading from calipers.
For me the best way to use a caliper is to bring the jaws lightly into contact
with the piece, then roll the piece in the jaws to be sure I'm not on a flaw.

Everybody's feel for mics is different. They are much more accurate than
calipers. Hold the mic in your right hand, if you are right handed. Place the
anvil of the mic on the lower side of the piece. Slowly turn the thimble in
while slightly rocking the mic back and forth over the piece to be sure your
are measuring it's highest point. When it brushes over the high spot with
just enough resistance to be felt, that is your size.

If you have mics with ratcheting thimbles you can twist as hard as you want
on the ratchet end. It won't allow you to exceed an accurate measuring pressure.

Rick

 

[doc1955]

Calipers IMHO are only good to get you close say +-.005 and only if you are careful.
And a micrometer if you are careful will get you to +-.0002
and if you set up a comparator mic it should get you to within +-.00003 if you set it up carefully.
As far as how much pressure for a mic if you close the jaws close them on a piece of paper just snug enough so you can still pull the paper out pull out the paper (this will clean out anything on the jaws) then close them snug not tight and read zero if necessary try and remember just how snug you made them and that is what you should be using. Some mics will have a friction anvil after awhile you will develop a feel at how tight is just right.

It is not uncommon to get drill rod u/s to .001 under it depends on the grade drill rod you purchased.

 

[gmac]

Zee
The drill rod spec's I've encountered depend on the diameter of the round stock, for example;

2 - 1.5 in. dia +/- .00075 in
1.5 - 0.125 in. dia +/- .0005 in
0.124 and less in dia +/- .0003 in

I think these are the common tolerance bands - more money buys you tighter. Google drill rod dimensional spec's and numerous supplier spec sheets in pdf form come up (inch and metric).

Cheers
Garry

 

[Deanofid]

Zee, the things Rick mentions about 'feel' are well said.
To get an idea of how tight is tight enough, here's an example you can try. Works for mic or
caliper;

Cut a piece of that 3/8" drill rod about 3" long. When you have the thimble on the mic 'right',
it will just hold the 3" long piece between the spindle and anvil parts. Will be almost ready to
fall out from between them, but will stay there. That is while holding the mic so that the drill
rod piece is pointing straight up and down.

My American made dial calipers measure a 1/2" gage pin at .500". With those, you can't resolve
more than about .0005" between lines, if you're honest with yourself. My American made mic
measures the same gage at .500", plus the tiniest amount more. You can't make a guess at how
much more, but you can tell that it's a tiny bit past the .500" line, and way less than the .501" line.
My China made dial calipers measure very close to this, but not quite "on". One shows up
at about half a thou under, one at about half a thou over. Okay for home shop work, mostly.
All these instruments measure the same diameter consistently, meaning, the small difference is
the same every time.

My Chinese made electronic calipers, (two of them) are so badly off at varying measurements that
I would only consider them good enough for carpentry. They will measure that same .500" gage pin
anywhere from .488" to .515", and they measure differently on a number of tries.

Over the long run, and often the short run, depending on what you buy, a mic will be, and stay, more
accurate than a caliper. The screw is enclosed, and not subject to the debris that a geared, or
electronic, calipers can suffer from.

To answer another of your questions, drill rod is ground to size, and you can expect it to be very
close to the nominal size. Usually, will not differ more than half a thou from what it's supposed to
be, and often perfectly on as measured with an instrument of .001" resolution.

Besides making D bits, you can use it for all kinds of small shafting in your small engines. It gives you
a ready size that will fit most call outs on prints without having to turn something down to fit. All
manner of other round shanked tooling, too; Counterbores, radius cutters, T-slot and keyway cutters,
and like that. Chisels, punches, scribers, etc. Other things I can't think of at the moment.

Here's something I was taught when learning this stuff. Get a gage pin, (drill rod will do), close your eyes,
and practice measuring repeatedly. Look at your measurement each time you try, and work on
the 'touch' part of it until you can hit the same mark every time. Even if the rod you have is slightly off,
it won't matter to your practice. What you are going for is consistency, and that will serve you well
when making measurements for projects. Even if your instrument is off, if you use it the same every
time, it will give you what you need to make comparative fits in the shop.

Dean

 

[mklotz]

Like Dean says, get a gage pin and practice. Keep it with the mike and calipers and check them occasionally to see if they've "gone out of calibration". The people who make gage pins pass out 0.25" ones as samples at WESTEC. Shows like that are a treasure trove for shop-useful freebies.

A good pair of calipers, used properly, can be accurate to 0.001" and, with care, 0.0005" is readable. You've got to keep the jaws parallel. After closing the calipers gently on the object, use your thumb and forefinger to gently squeeze the outside of the jaws in line with the part.

My Mitutoyos (dial and digital) will both catch the half thou in a gage block when used this way.

Accuracy aside, calipers are, IMO, not the right tool to measure on the lathe. It's just not possible to hold them the way they should be handled and get a good consistent reading. Use a mike. I like the mechanical digital mikes - the ones with an odometer like readout geared off the spindle. Easy to read and more rugged than an electronic. (I use my electronic one more as a bench comparator in a stand.)

 

[Troutsqueezer]

That's an excellent question Zee. I can measure each part I make a dozen times and there's always some ambiguity yet we plod along not thinking to ask the experts. We hope the parts come out right and then scratch our heads when they are off, despite having measured them numerous times.

Measuring on the lathe has always been a tricky deal for me. Never thought to use a micrometer. Now I have to buy one. Harbor Freight has a number of styles for not too much money. Worth trying? Don't really want to buy a mega bucks Starret.

-dennis

 

[Deanofid]

Dennis, you don't need to spend big bucks. At least, not right now. B&S make a very good mic that
goes for about $80 at Enco. That may seem like quite a bit. Mitutoyo shows up in sale catalogs now
and then for less than $60.
The 'other' kind, the $25 ones, are still worth having over depending on cheaper calipers for measuring
round stock, especially if measuring in the lathe, like Marv says. Get one you can swing, and upgrade
when the time is right.

There is a difference in the good brands, and the far east types. The good brands measure thou for thou
over the entire length of the spindle screw. The far east types I've checked on different sizes of gage
pins don't.
That won't matter as much when you are taking measurements on two mating parts in the shop,
because even most cheaper mics will be consistent (repeatable) over a short range.
If you ever get your hands on a Mit, B&S, or Starrett, and compare them to the cheap ones, the
difference is real. For home shop work, (on your own stuff), it may not matter!

Dean

 

[Tin Falcon]

Z:
As far as calipers I have found then to be accurate within .002 inches. I have a set of digitals from grizzly that I love. I also have a couple of pair of HF . for $ 16 a pair they are affordable and work great for the home shop . I wish I had gotten 3 or 4 pair of left handed ones from grizzly when I had the chance.
When I did precision work I measured with starret mics then double checked with the digital calipers. Not that the calipers are more accurate but sometimes it is easy to miss a line on mics and be off by .025. I have good mics with the traditional vernier reading. I also have a HF digital mic a bit clumsy in the hand but a nice easy to read tool for double checking or nice for learning to read a mic and no experience over the shoulder.
IMHO everyone should learn to read vernier calipers and mics . But the new digital stuff is affordable and easy on the eyes.
So calipers to get close micrometers for precision and read the tolerance on the drill rod in the catalog.
Tin

 

[kvom]

If you don't have a gauge pin handy, a 123 block can be used for practice. While they are not absolutely accurate as to dimension, you will see what it takes to get a repeatable reading.

 

[zeeprogrammer]

Thanks Rick, doc, Garry, Dean, Marv, Dennis, Tin and kvom.

This is great help and I think my measuring skills will significantly improve because of it. Thanks again.

Certainly I've been applying too much pressure when measuring. And I think it's worthwhile to practice some more on some reference material. (I think I can get a hold of a couple of pin gauges from work.)

I played around some more with the drill rod (and a 1-2-3 block per kvom) and my confidence has increased. It looks like my old mic isn't too bad!

 

[kf2qd]

Just remeber - a micrometer is not a C-Clamp. When you bring closed on a piece of stock you want it to stop when it touches the material. If you get down to the size of the material and then open and close it 3 or 4 times you should be able to feel any mis-alignment and have it measuring the true size. If your mic is properly zeroed (piece of clean paper drawn from between the spindle face and the anvil face, close the mic until it just stops, repeat this several times to verify that you get the same reading and that reading is zero each time - a tenth or 2 plus or minus is probably temperature) you should be able to get accurate readings. You cam also compare your mics to the standards that came with the mics to get comfortable with making measurements.

In my experience - most drill rod has been a half a thou under.

If the mic will stay on the workpiece in the lathe while you roll the spindle over the mic is way too tight...

 

[RonGinger]

You will also find drill rod is not round, but rather lobed. This is most apparent if you try to lap a piece. You will see the lap first cleans off 3 lobes or ridges.

Non-digital calipers are called vernier calipers- a friend of mine refers to them as 'very nears'. I dont think of them as really accurate measuring instruments. I would never trust a caliper for a diameter measurement on a lathe, particularly if you are doing as bearing fit.

 

[mklotz]

This is what I use for my everyday mike work...

http://www.use-enco.com/CGI/INSRIT?PMAKA=600-2311

along with some non-digital Mitutoyos and an electronic Mitutoyo for the really prissy stuff (which comes along only rarely).

I've checked the inexpensive ENCO mikes against gage blocks and they were all spot-on out of the box. At that price they're cheap enough to have one on the bench, one on the mill and one on the lathe. Easy to read and you'll never have a missed 0.025". The digits on the mechanical readout are white on black and about 3/16" high so even us old guys can read them comfortably from a distance.

Incidentally, if you check your mike with gage blocks, there is a preferred series of blocks to use so you can catch drunken thread errors. The sequence is:

0.105, 0.210, 0.315, 0.420, 0.500, 0.605, 0.710, 0.815, 0.920, 1.000

 

[Tin Falcon]

while measuring 123 blocks is fine measuring a round pin s a different animal . you kind of need to feel for the high spot. you want to be able to slide the pin or part in an out of the mic with the slightest drag and no play. definitely not clamped down.
Tin

 

[zeeprogrammer]

Thanks kf2qd, RonGinger, Marv, and Tin.

Many good points again.

 

[Maryak]

2) I used two calipers...when I close the jaws with hardly any pressure, I measure 0.374. Applying pressure can bring this down to 0.368. It raises the question of how much pressure does one apply when using calipers.

OK, if you take an ordinary pair of 6" spring loaded outside calipers and offer it to the rod, the caliper should just slip over the diameter under its' own weight. try this a few times over and back until you get a feel for how much pressure this is to you. Apply the same pressure/feel to your digital, vernier, inside, outside and in my ladies chamber measuring device.

3) I used a 35 year old cheap micrometer I got in college that's been banging around a box since then. When I close the (? what do you call them?...anvil!), I measure 0.375. Usually 0.3745. No real pressure. Applying pressure might get down to 0.371. Same question as number 2.

Same answer ;D

Oh...what else is drill rod good for besides reamers? ;D

DRILL ROD e.g. rock drills for rock. :

Best Regards
Bob

 

[Rockytime]

Calipers IMHO are only good to get you close say +-.005 and only if you are careful.
And a micrometer if you are careful will get you to +-.0002
and if you set up a comparator mic it should get you to within +-.00003 if you set it up carefully.
As far as how much pressure for a mic if you close the jaws close them on a piece of paper just snug enough so you can still pull the paper out pull out the paper (this will clean out anything on the jaws) then close them snug not tight and read zero if necessary try and remember just how snug you made them and that is what you should be using. Some mics will have a friction anvil after awhile you will develop a feel at how tight is just right.

It is not uncommon to get drill rod u/s to .001 under it depends on the grade drill rod you purchased.

Hi Doc1955,
This is a little off topic but I'm responding to doc1955 because I grew up just a few miles from Jamestown. OK, back to topic. Quite a few years ago MSC had bargain tables for return items or overstock things. Their salesman had Chinese mikes in the trunk of his car. The were in wood cases and wrapped in oiled paper. The mike cases got soaked when his trunk leaked. I purchased six for sis dollars each. They were in perfect condition. I have them all over the shop. They work very well for the work (play) I do For critical work I use a B&S and a very old Scherr-Tumico, a very nice instrument. Never heard of that brand but was given to me by a retired instrument maker.

(Back off topic) How are things in Jamestown these days? Miss that town.
Les

 

[Tin Falcon]

old Scherr-Tumico

It is not a brand I have seen for sale except on flea bay. I have seen them in military tool boxes along with Strarrett.
Tin

 

[Twmaster]

The Scherr-Tumico are mostly Chinese.

Good info here on mics:

http://www.longislandindicator.com/p29.html

Calipers:

http://www.longislandindicator.com/p11.html

My eyes are to the point where I need digital readout devices. I have an SPI mechanical digitial like Marv mentioned. It's been a saviour...

Also, buying good measurement tools need not be spendy. eBay is a good source for top names at reasonable pricing.

I've got three Starrett mics (0-1", 1-2", 2-3") that I do not have more than $25 in total with shipping.