I want to make a plug gauge using O1 tool steel. I am going to harden, grind and lap the gauge and knurl the handle. So if I harden the entire piece, how do I get the scale out of the knurls? Or do I heat the entire piece, only quench the plug end, let the handle cool slowly keeping the handle annealed, remove the scale and knurl? Or do I not have a clue what I am talking about?
A good way to remove scale after hardening is with sand blasting. You might be able to do it chemically but that sounds dangerous (for both you and your tools).
Out of curiosity, how are you grinding and lapping the gauge? Do you have a cylindrical grinder? A lathe with a tool post grinder? Always looking for new ways to do things...
If I was making the plug gage, and I didn't have a controlled atmosphere furnace ( which I don't), I'd bead blast the entire gage after heat treat, just before grinding. I'd heat treat the entire gage, not just the plug end. Bead blasting removes all the scale and leaves a very pleasing finish. All depends on the size of the media you use, of course. Very fine sand (aluminum oxide, really) does a bang up job, too.
I found making plug gauges of smaller diameters way too much work, so I started making the handle out of 12L14 knurled to suit, drilled holes into each end, then crossdrilled and tapped for setscrews to hold appropriate flatted pieces of either drill blank, or reamer blank. One of them is supplied with plus tolerances, and the other is supplied with minus tolerances. By choosing what I need, along with metric sizes available, I have been able to all but eliminate scratch making most of the gauges we use. Depths for hole testing can be established by grinding a V ring around the blanks at the proper depth on the "go" end. It's heartbreaking to spend a lot of time on a scratch built gauge, then have someone drop it onto a concrete floor.
Thanks to Robin and Harold for the comments on sand or bead blasting. I did not realize that sand blasting could remove the scale in the knurl. I try and learn something new every day. I am off to a good start today.
I am going to use a tool post grinder on my 9 inch star lathe. I picked up a Dunmore #14 at an auction recently. It is small, but taking lite passes and grinding between centers, I think think it will be OK. This is a hobby project, time is not a major concern. For lapping, I am planning to use cast iron laps and lap on the lathe, as described in modern toolmaking methods (1915). Just seems like a neat project.
How any shop survives without at least a few sets of drill blanks is beyond me. The are so useful that I have several sets of each, numbers, letters and fractions. Drill (and reamer) blanks have to be one of the best bargains available for the shop. They can be had from eBay for prices so low that anyone can afford them. All my spare sets came from that source, often for less than $20/set.
If you set your compound rest to 6º clockwise past the z-axis (that is, almost parallel with the ways the carriage slides on), each graduation on the compound turns into a movement of 1/10 of the grad in the x-axis.
This means that if you dial in .001" on the compound rest, you will reduce the *diameter* of the work piece by .0002".
Yes, for all of you with calculators it's actually something like 5.75º but you don't need to be that picky.
I've had to turn (with a HSS cutter) 12L14 to a tolerance of +/-.008mm and this method works quite well.
I mount dial indicators to measure the actual movement of the cutter in the radial direction. Then I do not need to measure angles and backlash is much less of a problem. About a year ago I collected various Starrett .001 and .0001 reading dial indicators from EBAY. It has proven to be a great investment.
Yeah, it works quite well until you have to rely on stops or marks such as when approaching shoulders. Movement of the compound causes you to lose location. It's far better to learn to work with the cross slide instead. Yes, it is difficult, but certainly not impossible. I've done .0002" tolerance work that way for years with good results.
Stupid question: Has anyone ever tried to come up whith a more sensible set of sizes for drills than numbers and letters? If so how come it never went over? Engineman1
How about metric? I've got sets of drills in 0.1mm steps from
1mm to 10mm. I use them in addition to the fractional, number, and letter sizes to give more choices.
And I consider the number and letter drills to be intended to fill the holes in the original fractional size sets, so you can get a better size to drill holes to be tapped. The fractional sizes (in steps of 1/64") are jumping something like 0.0156" per step, so there is a need for smaller steps to fit various pitches of threads.
Because the extra sizes offered by whatever "rational" system were simply absorbed as yet another way to get finer steps.
Probably, the most rational system (but a real pain to use) would have each size 1% larger than the previous, as resistors area available (also for coarser sets, 5%, 10%, and 20%).
An example, starting with 1 ohm, and 10% steps (a common set of the carbon composition sets) would go (IIRC):
Note that the spacing in sizes grows with the size, which would work find for finding reasonable tap drills for normal pitches, which also get coarser with increasing size.
But -- it would still be a problem with extra-fine pitches.
1% increments wind up with really strange values, but they would probably work nicely. Just pick some standard as the starting point, e.g. 1.0", and use negative numbers for smaller, and positive for larger.
And then, all you have to do is convince the world to re-tool using your new system. :-)
1% resistors are the 96th root of 10 times the value before. To find the 1% resistor value nearest to the value your calculator defines (1) take the ln of the exact value (2) take the ln of the 96th root of 10 (3) divide the second number into the first. You will come out with a number and a decimal. Throw the decimal away(NOT rounding, discarding). Raise the 96th root of 10 to the whole number result of the division. This operation will give you (after rounding to three decimals) the 1% value below the exact number you sought. Multiplying by the 96th root of 10 once more gives you the 1% value above the exact number you sought.
Program this into your calculator if you work with resistors all the time.
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