I had a set of relatively cheap calipers that read to 0.0001" but never took them seriously.My second measurement peeve is when someone calls out a print to 0.001mm, then tells me they measured parts with calipers
Just how many of you folks are even trained to read measuring tools that read in .0001”? I have overhauled many large diesel engines and large transmissions during my working career and got along fine with measuring tools that read to.001”. These machines have operated for thousands of hours without any problems. Maybe precision machine shops need that kind of accuracy but in the real world.001” is fine
Reading the number is fine, any idiot can do that...being able to work to and hold that number is the problem.
What makes an oil film "strong" enough to support bearing loads is its rate of shear. The greater the difference in velocity between journal and bearing shell the higher the actual viscosity. That is why small, higher revving engines can use much "lighter" lubricating oils. BUT: since lower RPM works for less frictional losses it backs the designer into a corner where more shear would be better. Just going up in oil viscosity doesn't actually do much except increase pumping losses, so about all that's left is to make the clearance less so the rate of shear goes up between the moving surfaces (think of the film as a lot of layers moving in opposite direction meeting in the middle at zero. Cut the number of "layers" and the differential in velocity between each goes up). To make a no-so-simple thing even more interesting: the shaft does not site in the middle of the journal hole, it is offset jaming the oil into a "hydrodynamic wedge" where the shear rate, thus the actual viscosity and resultant film pressure is extremely high - high enough to float the rod brg on the crank journal.Things are different now. The crankshaft to engine bearing specs and the connecting rod to rod journal specs are now below 0.002 on a modern Toyota engine making tenths measurement sort of a necessity. My Toyota for example uses 0W-16 motor oil which is thinner than water so these clearances need to be really tight to maintain an oil film. There is a reason Sunnen Dial Bore Gauges go down to tents. In the old days with 10W-40 oil looser( .003-.004) was acceptable. Not really the case with these modern engines from which they're trying to squeeze out every MPG.
You make a good point, but as I had mentioned most machinists read not only the number but where the thimble stops between one and the next. Personally, I use digital calipers for rough work but for anything requiring precision I use strictly mechanical micrometers with gauge blocks in each box to check. Reading the location of mechanical mic indication between 0.001" increments of a decent tool with a careful hand is as accurate as having a 0.0001" readout display. Not a fan of electronics on micrometers, but if doing so then you are correct - you should have the higher resolution to know what a machinist easily sees on his (or her) 0.001" resolving mechanical tool.Keep in mind that what ever decimal place you are measuring to, in theory the tool you use needs 10x the resolution in order to have confidence in the measurement.
So if you are measuring to the 0.001" your tool needs to be able to measure to the 0.0001". In that case a micrometer would be needed, the most accurate caliper is only good to about 0.001" and that's even a bit of a stretch.
And how are you going to read any of the measurements you talked about with a dial indicator? That is the instrument we are talking about.Things are different now. The crankshaft to engine bearing specs and the connecting rod to rod journal specs are now below 0.002 on a modern Toyota engine making tenths measurement sort of a necessity. My Toyota for example uses 0W-16 motor oil which is thinner than water so these clearances need to be really tight to maintain an oil film. There is a reason Sunnen Dial Bore Gauges go down to tents. In the old days with 10W-40 oil looser( .003-.004) was acceptable. Not really the case with these modern engines from which they're trying to squeeze out every MPG.
Again, we are talking about a home shop assembling an engine.I worked in an automotive machine shop as a yoot. The crank grinding operation (performed solely by the shop owner) was measured in tenths. We worked on a fair number of imports in addition to the typical small block/big block Chevy/ford stuff.
We used a bore gauge for the housing and a micrometer for the journal, never once used plastigauge.
Again, we are talking about a home shop assembling an engine.
We used dial bore gauges all the time at cat but final checks were air gauges, marposs, and CMM. None of those are in home shops either?
Agree 110%Having worked at a well known ship engine motor manufacturer, I'll second itsNemo and alfadan.
Keep in mind you'll also need machinery that can consistently achieve 0.0001 in both accuracy and precision.
Which is not your typical home lathe or second hand mill.
How else do you measure bores, or what your machining.it’s a rare home shop that has dial bore gauges and the setting rings for them
Duh! Inside micrometers are what I have always used. Most bore dials are mounted on a skid to measure bore taper, not absolute diameter.How else do you measure bores, or what your machining.
I'd assume most building engines "at home" also have a Mill and a lathe.
Maybe not.
Most modern engines are not going to be rebuilt with a mill and a lathe. They are just assembling the engine. You still need some measuring tools for assembly however.How else do you measure bores, or what your machining.
I'd assume most building engines "at home" also have a Mill and a lathe.
Maybe not.