CAD for simple 3-D metal & wood projects?

Indeed. How is the government going to justify raising taxes because of global COOLING?

Fire the astronomers. They're ruining the scam!

Same folks that are running obamacare.

There's a lot of that going around. :(

Gunner Asch on Mon, 25 Nov 2013 15:35:22 -0800 typed in rec.crafts.metalworking the following:

Yep. All depends on what you are used to working with.

-- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone."

Gunner Asch on Mon, 25 Nov 2013 15:33:52 -0800 typed in rec.crafts.metalworking the following:

I have noticed, over the years, that the simplest instructions are usually the most difficult or time consumptive. Make grade 8 ball bearings. Build a wing in 3D space in CATIA. Put a canal across the Isthmus of Panama. Send men to the moon and bring them back in the next decade. Change the timing belt.

-- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone."

I'm trying to ask a more basic question: Moore tells us how to construct flats, straight edges and squares. I don't think he ever explained how to make and check a cylinder, much less a screw, given that one is starting with neither. Obviously, it was done, but I'd like to understand the sequence. Crudely put, if one wanted the reconstruct the Industrial Revolution, what is the sequence of steps, starting from the stone age, that is required? It's been a long time since I looked at Moore's book, if I'm mistaken please enlighten me.

In case the OP is still around, I'd suggest exploring Ashlar Graphite,

Thanks for reading,

bob prohaska

The new neighbors are a lot nicer tho. They don't stack their trash cans in my driveway. I appreciate that...

That is a difference in measurement techniques and machine design. Most machine tools have dials which read on 0.001" (or finer for some machines), but in decimal format anyway.

Way back when, machinists worked to 1/128" at best (the Vernier calipers would measure to that, while scales were marked to 1/64" at best. But then, to make a running fit in a bearing, they would use inside calipers and outside calipers to transfer measurements from one to the other. Bore the bearing hole, take the measurement with an inside caliper, transfer that measurement to an outside caliper (by closing one onto the other by feel -- these had and have no markings) and then machine the shaft to fit the bearing by slowly removing metal until the outside calipers just slide over it with the right "feel". (the calipers will spring a bit, so you need to learn what the right feel is.)

These days, you purchase the shaft, measure it with a micrometer to be sure that it is what it is claimed to be, (in decimal fractions of an inch), make a trial bore with the cross-feed dial on the lathe zeroed, measure the bore it produced, subtract that from the desired size, divide by two (since most machine's cross-feeds are calibrated in radius, not diameter) amd for rough work, just set it and bore. If you need more precision, you approach the final cut in finer cuts, so set that your last cut will be the same depth as the others, measure as you approach it to be sure.

And (on a regular lathe, if you want even finer precision, you set up a toolpost grinder, set the compound at an angle which gives you

And -- if you need even more precision, you bore and grind to just under size, and then use a roller burnishing tool to mash the surface down to a smoother finish at the desired measurement.

Or -- you use lapping to get that final finish and dimension.

The above is how *I* would approach greater and greater precision on my machines.

This is how it could be done on a manual machine -- especially one in a home hobby workshop (such as mine). CNC changes the game somewhat. But -- the whole time you are working with tools and instruments which read and are set in decimal factions of an inch, so there is never a need to convert something like your 144.531250" to

BTW The conversion with my scientific calculator (HP 15C) is done with no problems -- discard the integer inch part, multiply the decimal faction by the largest likely denominator (64), see that it reads an even number, so multiply by two (converting to 32nds instead of 64ths and get an odd precise integer number, so you are there. Then add back the integer part of the overall dimension once you have your fractional part right.

There are *some* digital calipers which will read in both decimal factions of an inch, and in the nearest fractional inch size -- but you are unlikely to find a machinist using one of these for the fractional readings -- which are, after all, just a "nearest fractional size", not a "true reading", or you would wind up needing it to display at least down to 1/1024th of an inch (to be close to the metalworking basic of 1/1000" -- in some fields called a "mil" -- such as in the pin layout dimensions for integrated circuits in electronics -- useful for designing printed circuit boards. Some few of us got into metalworking from the electronics field (as did I), but we seldom mention "mils" as it confuses those measuring in mm (Millimeters -- a very different unit.

I've seen these "fractional reading" digital calipers, but never been tempted to buy them. I just don't *think* in fractional inches most of the time. Some few places, it is convenient. 16 Ga steel is very close to 1/16", so I can convert that to 0.0625" and be close enough to tell 16 ga from other sizes. (And no, that does not work anywhere else, as the larger the gauge number, the thinner the metal. This is related to how it is formed, progressively rolled thinner and thinner, so it is just a lucky crossover point -- and where the limits of my sheet metal brake and shear happen to be, so it is easy to check whether I should try the sheet metal in those tools or not.

Enjoy, DoN.

P.S. Not sure why I am bothering to post in this cross-posted argument, but at least it is metalworking related, not political. :-)

Turning an *aspherical* lens does need a model, and a very precise and mathematically complex one at that, to cause it to focus where it should. And you can't check a Germanium lens by the techniques used for visible-light lenses -- they are opaque to visible light, so you want it cut right the first time. Same applies to silicon lenses. I've seen both used in various experimental Infrared cameras.

He did not say that he was watching someone else do it. He was watching the *machine* do it. No *human* does it with CNC. At best s/he feeds the data to a program which generates the motions necessary to produce the surface to feed to the CNC machine tool.

Enjoy, DoN.

The only good neighbors I've had around here have either moved away, or died.

1. Build a giant funnel

1. Attach servo motors so it can track the sun

2. Place over Congress

1. Hot air rises...

I thought $600 to change a timing belt was robbery until I did the job myself. jsw

There's no need to go back to the Stone Age, hand and eye precision was the best we had until about the mid to late 1700's.

Holtzapffel covers the original generation of screw threads and much, much more:

Lapping on a dead-center lathe can generate true cylinders with simple handmade equipment. You don't need to know their precise diameter to Babbit them into a close-fitting bearing.

In essence you bootstrap high precision by generating a master flat or cylindrical surface through geometric methods and transfer it by testing and scraping for full contact. Old gunmakers used a candle smoke film to show areas of contact.

jsw

Very good description!

I've memorized the decimals down to 16ths but the simple approach is to hang a decimal equivalents chart near the machine, as it also gives the nearest fractional or metric collet size to your workpiece diameter and shows english-metric equivalents.

No thanks, I had friends with MGs and Jags and learned my lesson to avoid them. My Honda Civic cornered tighter than my buddy's MG Midget, though he was the better and crazier racer.

A local dealer had a Lotus in his showroom. I sat in it, opened the glovebox door for a flat place to put my coffee, and watched it sag down under the weight of the cup. jsw

The machine was built by Joseph Clement, one of the founding geniuses of the Industrial Revolution, who learned his skills from the great masters Joseph Bramah and Henry Maudslay.

jsw

"Jim Wilkins" on Tue, 26 Nov 2013 07:37:57

-0500 typed in rec.crafts.metalworking the following:

Don't ask ...

The one time - I took it to a shop, left it after work (and I worked nights). Got up the next day, walked over - and was informed that it had broken just as they tried to get my truck into the shop. I'd say that was pretty much maximizing the useful life of the part.

-- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone."

Here is a naturally ocurring example:

jsw