thread lead-in/ measuring chamfer

I've tried to look this up and found no real answers so far.
Is there any sort of standard for cutting the chamfer on a thread lead-in?
Say I'm just threading the end of a 1/2" Al rod. The start of the thread at the end will be jagged and weak. Cutting a 45 (I found 60 does nothing useful) degree chamfer helps and makes thing far prettier, and for anything I've done you can just eye-ball this and it really doesn't matter too much how you do it for my uses.
What's done in the production world for stuff like this where looking pretty is key? Is there a special angle and distance to cut this chamfer?
Would it be measured as distance into the thread, or the diameter of the end of the fastner once cut?
Last question- how does one really measure a chamfer anyways? There's no real surfaces to measure off.
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On Wed, 22 Jan 2014 21:26:06 +0000 (UTC), Cydrome Leader

Typically on a 60 degree thread a 45 degree chamfer will be cut just beyond the major or minor diameter. Major for internal threads, minor for external. So, for example, a 1/4-20 tapped hole will be countersunk 90 degrees included angle to .265 diameter. But on work that has a large tolerance the countersink may be much larger. When measuring a chamfer it is fairly easy measure the diameter where the chamfered surface intersects either the O.D. or I.D. There several ways. One is to use a magnifier and calipers. This method is good enough for +or- .003 for someone competent at inspecting machined parts. Then there are magnifiers with built in reticles with scales for measuring angles and distances. An optical comparator can be used as well and then measurements to .001 are easy. Gauges are also available that have a plunger ground for the specific angle of a countersink, 100, 90, and 82 degree being the most common ones, that have a dial indicator that shows either the depth or the diameter of the countersink. These gauges are used by pressing them into the countersink until the flat surface that the plunger protrudes from contacts the work. If you are doing work for yourself then do just what looks good. I like to finish screws with a rounded end. The radius used on the end of the screw is much larger than the radius of the screw, so the end of the screw isn't quite flat. This type of finishing of screws is common on screws used in high quality inspection equipment. ERic
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wrote:

The rounded form tool can be a quarter-round concave end mill, or custom ground on a lathe bit with a conical stone in a die grinder. The conical stone leaves a smooth and circular (or elliptical) edge that is relieved all around for cutting clearance. You can measure and mark the desired finish diameter on the stone. jsw
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What about for cutting the parts?
I use a sherline, so the compound slide cuts from the "back" of the lathe with upside down toolbits. I've just been touching the end of the work with the cutter tip and then doing the math and making the cuts. I touch off on the end of the work piece as if I prick it and mess up the surface, it doesn't matter as that side gets cut off anyways. I can't think if any tricks to make this easier, but I'm all ears if there are tips for this.
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Your question is unclear. Are you asking how to cut-off to a specific length?
I normally measure from the cutoff blade to the end of the work with a ruler, which is good to about 0.01". For closer accuracy the end rod on a 4" dial caliper serves well.
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I mean to cut a chamfer, where the size matters, say for a 45 degree compression fitting.
I had to make a few of these, and in theory the distance from the OD or the end of the rod to where the cut starts is the same for 45 degrees.
The parts I made will work fine, but I noticed there's not a really good way to measure them just to be sure. There's nothing for calipers to catch on so it's an issue of make the cuts and just hope it's right.
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On Mon, 27 Jan 2014 22:50:53 +0000 (UTC), Cydrome Leader

If you have a good loupe, at least 7x, then you can indeed use calipers to measure the chamfer. You just compare the chamfer to the open calipers. If you open the calipers .003" at a time it will be easy to see the difference. You can also grind a tool to the correct angle and just plunge cut the chamfer. Eric
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wrote:

I use one of these, bought used for much less, to measure features where calipers have nothing to catch on: http://www.2spi.com/catalog/magnifiers/mag8.php
The smallest division is 0.0025" which is fine for my home projects.
You could make a gauge from a solid rod and a sleeve that fits over it, hobby brass tubing works well, and calculate the distance the sleeve should slide over the rod onto the chamfer, at the sleeve's inner diameter.
For example if the flat on the end of the chamfer is 0.3" in diameter and the ID of the tube is 0.5" it should slide in 0.1".
If you clamp the sleeve and rod together and machine their ends flush (actual length doesn't matter) you can measure the offset directly with the step on a caliper. jsw
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Interesting tool there, I'll have to pick one up.

good idea. As much as folks complain about off topic stuff, there's lots of good answers around here.
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On Wednesday, January 22, 2014 1:26:06 PM UTC-8, Cydrome Leader wrote:

Cut lead in chamfers slighty smaller than the tap size diameter.
IE 1/2-13 = .421 tap dia. .5-.421= .079 / 2 = .0395 chamfer so .04 - .045 X 45 chamfer cut on before the threads will be fine.
Same kind of deal for taping. C-sink slighty larger than major thread diameter.

either way .040 X 45deg chamfer or .42 dia. plus 45 deg.

chamfers are one time everybody can: scale & eyeball vernier tips
The real c-sink question is : Why are Flat Head Screws c-sink at 82 deg? (41 deg / side) The heads of FHS are 45 deg.?
any takers?
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On Wed, 22 Jan 2014 15:47:49 -0800 (PST), snipped-for-privacy@gmail.com wrote:

I'd recommend against using calipers as chamfer cutters, myself.

When I was in QA in the '70s, I inspected some FHSs which were 82, while others were cut at 100 degs. I guess the former were US standards while the latter was aviation.
Oops, these guys show a larger array of angles for countersinks. http://en.wikipedia.org/wiki/Countersink
Are you in MetricLand? 90 would be the norm, giving you your fave 45 number.
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On Wed, 22 Jan 2014 21:26:06 +0000 (UTC), Cydrome Leader

I just had a look at a number of Grade 8 bolts - all from Caterpillar Tractor it happens - and none of them has a noticeable chamfer on the beginning of the threads. Perhaps in the industrial world "pretty" is not a common requirement.

Most drawings I've seen call out a chamfer by the angle and the width of the chamfer
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wrote:

Those probably are rolled threads.

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On Wed, 22 Jan 2014 20:06:01 -0800, "PrecisionmachinisT"

If it was it was pretty sneaky as the o.d. of the threads and the bolt was identical :-)

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wrote:

Even micrometer threads are rolled. Look closely at how the metal extruded at the end, amd measure the ODs of the threads and the unthreaded shank. jsw
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On Thu, 23 Jan 2014 09:15:14 -0500, "Jim Wilkins"

I did, and I just said that the O.D. of both the unthreaded shank and the threads was identical.
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Greetings Miguel, I just measured the threads on several grade 8 capscrews. All the screws have rolled threads. I was surprised to find the the O.D. of the threads and the shanks were the same diameter within .001". This implies some pretty tight tolerances on the screw shanks before the threads were rolled. But why not? It really makes sense. Thread rolling requires accurate sizing, too big and the rolls can break or chip, too small and the thread comes out way undersize. A rolled thread screw is easy to identify with just a casual inspection. Between where the thread stops and the shank begins is a taper that goes from the shank O.D. to the diameter of the screw before rolling. You can aslo plainly see that the thread diminishes to nothing on this taper. A cut thread will have 4 terminations where the 4 dies in the die head stop cutting when they pull away from the work. I haven't seen a cut thread machine screw in some time. Cheers, Eric
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No reason to chamfer beyond the root diameter.

Diameter after cut, or depth below theoretical major, take your pick...

Optical comparators work really well for this.
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