CAD for simple 3-D metal & wood projects?

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On Sat, 23 Nov 2013 14:00:44 -0600, "Lloyd E. Sponenburgh"

Well, Lloyd, it appears Leon showed you his. How about you showing yours... to Leon.
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"Gordon Shumway" wrote:

-------------------------------------------- Most difficult when operating from a foot in mouth position.
Lew
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On Sat, 23 Nov 2013 12:54:21 -0500, snipped-for-privacy@attt.bizz wrote:

Im posting from rec.crafts.metalworking.
Gunner
__ "A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects." - Heinlein
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typed in rec.crafts.metalworking the following:

    half a ten thousandths of an inch?
    Yoicks, you're starting to get into the area where you can tell where it was, or how big it was, but not both. -- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone."
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On Sat, 23 Nov 2013 12:08:25 -0800, pyotr filipivich

Ayup...aerospace requires 50 millions or half 10ths all the time.
Which is damned hard to do with machines that hold +/- 2 tenths
Gunner
__ "A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects." - Heinlein
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On Sat, 23 Nov 2013 23:33:15 -0500, "Mike Marlow"

Knowing nothing about aerospace I am willing to hazard a guess. I presume the space shuttle does not require tolerances anywhere near MILLIONTHS of an inch but I presume the shuttle's trajectory calculations would. I imagine that a rounding error would be the difference between a successful orbit or crashing into Homer Simpson's house in Springfield.
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On Sat, 23 Nov 2013 23:01:06 -0600, Gordon Shumway

A lot of it has to do with rates of expansion and contraction between different metals. If a part that has a hard alloy piston contracts more than the piston does when its -250F (outer space)....its nice to know that the critter isnt going to bind up after its in orbit...so fits are carefully calculated.
Notice the old SR-71 leaked fuel like a freaking sieve when it was on the ground..but after the fuselage heated up in flight..all the cracks closed up nicely and the fuel leaks stopped. Hence the SR-71 needed to be refueled after takeoff run..then it would go like a sombitch around the planet before needing another refueling.
Gunner
__ "A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects." - Heinlein
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On Sat, 23 Nov 2013 23:01:06 -0600, Gordon Shumway

Likely jet engine parts but certainly not the galley cabinets.

Perhaps if the shuttle couldn't alter its trajectory (but orbital mechanics aren't known to that precision, anyway - three body problem). However, it does (did) have engines intended to make such corrections.
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Not for nothin', but precision bearings are machined to 10 microinches all the time -- and they're CHEAP!
Lloyd
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"Lloyd E. Sponenburgh" wrote:

How many people reading this have ever done any sort of work close to that precision?
This is what you claimed. "We work to tenths of thou"
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With a short, stiff cutter and slow feeds, I can work to half a tenth all day. Certainly, that's not 10 micro-inches, but I can buy $7.00 bearings from McMaster that meet that spec.
I can't, because of the age and condition of my machines. But my CAD and CAM work to those tolerances and below.
Somebody said in this thread that some CAD worked to an internal precision of 0.0001"... hell... my cheapest CAM software works to seven digits! <G>
Ten micro-inches is not an amazing feat with new (but fairly specialized) equipment.
Lloyd
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"Lloyd E. Sponenburgh" wrote:

I can work to a tenth with floppy piece of sandpaper, but that is a little different than creating a CAD model and then manufacturing the part to within a tenth of the model dimensions.

And how many of the 'we who work to a tenth' could make that bearing?

So can Sketchup. It uses floating point data which means it can describe geometry about 1 million times more precise than anything you could make.

One would hope so for most calculations. However it is kind of pointless to pump out G-code that is lot more precise than the machine tool positioning capability.

People have been making things flat or round to that level of precision for ages.

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Yup... I can make a piece of glass flat to about three angstroms by hand.
But your comments to the negative don't bear on the discussion. The discussion never was "how many of 'us' could do it"; But is it a realizable and realistic degree of precision?
Yes, it is... even with the sort of equipment I use (albeit newer and in better condition).
I'm not working with a table-top Tormach, and do this professionally. But even a lot of amateurs have older high-end industrial equipment. It sells for scrap value, if one is willing to do the work to rescue it and upgrade the electronics.
I just had an 'amateur/recreational' machinist friend buy a full-up Fanuc slant-bed turning center with 4th axis, 12' bar feeder, and live tooling (+ATC)... With a little TLC and good insert tooling, that machine will do sub-tenths work -- in his garage!
Lloyd
Lloyd
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On Sun, 24 Nov 2013 15:34:13 -0600, "Lloyd E. Sponenburgh"

Ayup...lots of guys have retired from companies that were closing down due to the Obama Great Depression Part 2..and have bought for pennies the very machines they were running. Doing some small machining in their garages..usually medical parts (big money). We have seen Cottage Industry come back in a big way across the US. Its not talked about very much...shrug..but its quite fascinating how many "pro shops' are in your neighbors garages.
Gunner
__ "A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects." - Heinlein
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wrote:

Flat and round (spherical) are trivial problems and as you note it's been done for ages, at least since the middle ages. Other shapes are more difficult, as is size.
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snipped-for-privacy@attt.bizz wrote:

And there isn't much advantage in having a CAD model for those shapes.

And it is doubtful there is anyone reading this who is cutting complex shapes from CAD models with precision held to tenths.
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wrote:

There isn't much reason to have a CAD model for a board, either, but when you want to put a few dozen of them together, having a CAD model gets rather interesting.

Huh??? Have you ever heard of a mirror, or lens, system? Please explain your statement?
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snipped-for-privacy@attt.bizz wrote:

How many have you modeled in CAD and then manufactured to within tenth of the designed part?
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wrote:

You still make no sense. Are you saying that precision machining doesn't require the same level of modeling that sloppier work does? Really?
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snipped-for-privacy@attt.bizz wrote:

First of all most of the examples of precision that have been given involve no 3d modeling at all. And the rest appear to be at best 2d modeling (e.g.. a lathe profile).
I'm saying that any CAD system can produce geometry that is far more accurate than any manufacturing process. If a 3d computer model has dimensions that are different than what you like them to be, it is because of the input the software was given, not because the software is sloppy.
A program like Sketchup caters to people who want to model something that looks good without paying much attention precise numbers. But that doesn't mean it is sloppy. It just means it is not as easy to hit the exact numbers you may want as in other programs that cater to people who want models driven by precise numerical inputs instead of mouse actions.
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