Professional Machinists... need some tips on brand names/quality...

I understand that Central Tools used to make precision measuring devices for Snap-On. Since Snap-On went in-house (or at least to a different brand I'm unaware of) Central tools has supplied for MAC Tools.

Adding Metco Tools to the list of quality tools out there, I've been cruising eBay and found that Starrett seems to be "the big dog" and coincidentally, out of my price range considerablly. With my engine build I'm looking for external micrometers in the range of 0 to 6" capabilty.

My question is this:
What brands are out there I should include? Ebay is FULL of cheap micro's I really don't feel comfortable using... and a fair number of extremely expensive sets as well.

Is Mitotoyo a decent brand? They seem cheaply priced, but the pics look good. Has anyone used this brand before, and if so, how accurate is the calibration/durability?

Any brands I should be watching for? (positive or negative)

Thanks guys... :)

some of the old Central indicators i have are not that great in quality ..but they still give accurate readings

Is Mitotoyo a decent brand? yes !! very good quality with smooth movement ..also checkout TeaLock (spelling ??)

very impressed with TeaLock dial indicator quality

things to watch out for if its a dial indicator is back lug orientation and hole diameter ..and is it 3 screws or 4 screws and can use position back lug in different planes ?(4 evenly spaced screws)

Starrett ..i have also, but way over priced

sometimes a ratchet/noise mike set are very useful until you gain ability to "feel" mike

also a 1 inch Ball Mike for rod/main bearings (curved surfaces)
that reads in ten thousandths

can checkout price differences between Mikes that read to .001 thousandths -VS- Mike that read to .0001" ten-thousandths

ratchet/noise type mikes -vs- regular feel only Mikes

might look at Manhattan Supply Company (MSC Website)
they have multiple locations in every State

also Perf Tool Sites

Originally posted by MaxRaceSoftware
some of the old Central indicators i have are not that great in quality ..but they still give accurate readings

Is Mitotoyo a decent brand? yes !! very good quality with smooth movement ..also checkout TeaLock (spelling ??)

very impressed with TeaLock dial indicator qualityawesome. there's some great deals on Mitotoyo on ebay. :)

things to watch out for if its a dial indicator is back lug orientation and hole diameter ..and is it 3 screws or 4 screws and can use position back lug in different planes ?(4 evenly spaced screws)ok... hole diameter I understand, but can you explain the back lug orientation a bit more.

Would I be better off going with a design more like this: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=43989&item=2462765042
instead of this: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2384108093&category=20766&sspagename=STRK%3AMEBWN%3AIT&rd=1

It looks to me like the second one is a simple 2-point lock gauge. I was under the impression that the 4-point gauge in the first link would be pointless in different bore ranges since it seems the 3-point arch made by each screww wouldn't be correct for anything but one specific-bore. are the screws adjustable at all?

Starrett ..i have also, but way over pricedyeah, I nearly choked on the price listed. :p (glad it just wasn't me)

sometimes a ratchet/noise mike set are very useful until you gain ability to "feel" mike understood. I've used a few small-scall micrometers in my science courses (BioChem major)... I really like a small clicking when using micros.

might look at Manhattan Supply Company (MSC Website) they have multiple locations in every State
also Perf Tool Sites Thanks! :)

It looks to me like the second one is a simple 2-point lock gauge. I was under the impression that the 4-point gauge in the first link would be pointless in different bore ranges since it seems the 3-point arch made by each screww wouldn't be correct for anything but one specific-bore. are the screws adjustable at all?
==========================================

Steve..you misunderstood me..i'm sorry i didn't explain better

i was referring only to a 1 inch dial inicator in case you were interested in purchasing one along with a set of Mikes

the 3 or 4 screws are very tiny screws that attach dial indicator backplates/covers on the dial indicator ...it has the Lug on it
the 4 evenly scpaced screw type backs allow you to orienate the lug either Vertical or Horizontal

the Dial Bore Gauge is what you were talking about
i use a high dollar Sunnen with .0001" built-in maginifying large diameter setting fixture

but have also used the Mitotoyo Dial Bore Gauge for mikeing cylinder bores , mains, rods, etc ...very accurate ..and at that time was very cheap ..if i had the extra money, right then and there would have purchased that Gauge also even though i had the Sunnen ..the quality was that great, a bargain back then

The B/FX Camaro (John Cunningham) back in 1984 we raced was co-sponsored by MSC for short term ...MSC also sponsored Ken Veney Funny Car at one time ....now days prices at MSC are kinda high ..back then had connections to get anything real cheap :)

get on MSC Flyer list and every once in awhile you get great deals

Steve, my Sunnen is 3 Centering Legs with a 4th indicator probe

the Mitotoyo was made same way back then..hadn't recently seen any newer version

the Central Dial Bore Gauge looks like Centrals come a long way ..looks like decent quality except maybe for actual dial indicator part.

Starret all the way, price be damned! I have some Starret tools that are 75+ years old and still work fine.

Rich Krause

I agree with MaxRaceSoftware (Larry).
Mitutoyo measuring instruments are top notch. Buy .0001 reading mics instead of .001 reading.

Mitutoyo digital calipers are also well done.

I also like Sunnen bore gages.

My opinion, and it's just an opinion, is that gages sold by "Tool Suppliers" are rugged first, of good quality, but not what is used in precision machine shops. No flames intended, as we have close personal ties with one company representative.

One caveat: buying used measuring tools is like buying used engine rotating parts; you never know what abuse thy have endured. If you buy off the internet, assure that you can return them for credit if they aren't as represented.

There are some bargains in tools on eBay, and some junk. Some of the stuff sells at a fraction of new and some sells at or above new! Just saw an example of that recently: a $250 new honing accessory tool sold for about $230 or so, and an $850 version sold for about $150. Go figure. Some of the best buys are in the larger size gages, too. many of them haven't been used anywhere near as much as 0-1" or 1"-2" tools.

If you want to check new prices (or buy new) try www.mscdirect.com

Check the accuracy, alignment, etc. against gage blocks. If you know someone who operates a precision machine shop, ask if they will check the gages for you. I like to check a micrometer in at least its smallest and largest measurement against gage blocks. This will tell you if it is linear. Note that if the measurement is off the same amount, the barrel can be adjusted for alignment. If the mics come with a case, there shuld be a little stamped metal spanner with it for adjustment.

My $.02

Also look for mics with a solid beam it will provide accurate measurements over a longer period. Brown and Sharpe are also very good but quite expensive. The hollow beams work well but can bend, flex or dent.

Just my .02

P.S. I worked at a machine/hydraulic shop for two years

I would go with the mitutoyo on just about everything unless you are planning to use them every day day in and day out.As for the mics go I woud get the rachet feature and get the .0001 increments.I would also go with the mitutoyo bore gauge and get it with the .0001 increments.The sunnen bore gauges are good but they are over priced.Another good bore gauge would be from federal they seem to be pretty good.As for every day use I would go with something like the Starret or Brown&Sharp.

As an unintended tesimonial....

I had no idea Starrett was still making tools. I have my GRANDAFTHER'S STARRETT mics from freaking WORLD WAR II. No joke. I try my best to keep surface rust off of them. Cosmetically, they have seen better days. Buy if you want to nail a measurement dead-on +- .0001" these are the only tools I use. When I use them it's almost like a religious expereince. I take them out of their tonge-and-groove wooden box with sliding wooden lid, unwrap the cotten gauze protective wrapper from around them and generally treat them like they were the original 10 Commandments handed down from off the mountain.

Do I know how to actually USE a tool of that quality correctly? You damned right I do. My grandfatther who left them to me used to calibrate bombsites on B-17 and B-29 bombers. He taught me my mechanical "touch" for things like this. I LEARNED on these tools. I had no idea what I actually had in my hand back then.

This is a tool that is literally TWICE as old as I am and it'll still dead-zero like the day it was made. Spin the piston in your hand and it moves like silk. No oil, no nothing, just dead-perfect machining. Mic something at .3875 and then do it again. And again. And again. Always nails .3875. Time and time gain- as many times as you want to measure it- no variation. I am really blown away that Starrett is still in business. I figured they were dead and gone decades ago. I had no idea.

When I started my apprentiship as a machinist many years ago, Starrett was the flagship for pricision measuring tools. If you want quality and your livelyhood depends on precision, you went Starrett. Like mentioned above, Mitotoyo makes some pretty nice "stuff". It was hard at the time to "sell" the old-timers on anything but Starrett...almost blasphemous...but Mitotoyo became a second favorite...mostly b/c of the competitive price and quality. I owned both, but presently own none. I left the business 15 years ago, and never looked back. I even left around $8 g's of tools and toolbox right where it sat when I left the trade. Go figure!....

starett is indead the one to get if you can. if not look into brown and sharp's they are also excellent.

mitsi's are good for cheap digital stuff but i would stick to the above mentioned for 0-6 mic's. i'm been a machinists for 7 yrs, if you want something realiable your gonna have to pay unless you can find someone getting out of the trade and selling their whole tool box for a decent price.

side note, things like this shouldn't be left in a garage unless it's heated, moisture and temp changes will ruin presion instruments.

This is no doubt an emotional subject for us machinst.:)

Myself being an aussie and considering that there are NO precision tool manufacturers to speak of from my home I hold no loyalty per se. I've bought from the americans, the japanese, the germans and even the polish! Believe it or not, they make a nice economy micrometer.

I don't see the real issue with price. As I see it each manufacturer offers "models" in competetive price ranges.

I don't believe there is one "Big Dawg" in precision instruments either. Look at any precision manufacturer, wether it be medical, automotive, aerospace and you'll likely see a QC department that uses an abundance of instrumentation from Starrett, Fowler, Brown & Sharpe, Mitutoya and Mahr. I personally have favorites for each type of measuring tool just based on my experience in this trade for the last 30+ years.

You ask about mics. Let's go back to this price discrepency....

Starrett, for instance, has a 0-1" with .0001 res. and carbide faces (carbide faces & .0001 resolution recommended) for around $85 USD. Brown and Sharpe has a model about the exact same price. Mitu has a mic that sells for a smidge better than $90 and another model that goes for about $75. Then they have an economy model that looks like the $75 model but sells for about $20 less. I'd pass on those and only mention them because you need to check the model you're buying! Someone (perhaps ebay?) may very well attempt to pass the cheapie off as the $75 model.

So where's that big price difference in Starrett vs everyone else?

If you look at flatness and parallelism specs for Mitu mics they are one of the best in the industry. You don't need me to tell you that though, Mitu displays their specs openly.

Friction vs ratchet is a matter of preference. I personally prefer friction but the ratchet may be better suited to greenies. Slant-line vs straight-line is another matter of preference. You'd have to be in contact with either enough to develop a favorite.

The overall feel of a micrometer is my biggest concern and certain brands like a few of B & Sharpe's models just feel bulky to me. Again, this comes with working with a tool every day and probably won't mean much to you.

For a ball mic, you'll want Mitu or Brown & Sharpe in .0001 resolution. Starrett doesn't make a .0001 res. ball mic.. at least they didn't the last time I checked. Price difference within $10.

I agree with Larry on the Teclock dial indicators. They are good quality general use indicators. If you're going to buy one I'd go with Teclock or B & Sharpe. For a precision model, Starrett or Mitutoya. A magnetic base is also a good thing to have in any toolbox.

Bore gages.... I'd find a friend and borrow. Either that or take the "whatever-it-is-your-checking" to a shop and watch them check it out. Good bore gages aren't cheap and would likely be a waste of money for you.

Reading through your original post, it doesn't look like you're going to be building turbine engines. You just need some good quality tools that you can get a lifetime of use out of. I believe in buying the right tool for the job and obviously your needs are a little different than mine or any other person who makes a living off of precise measurements.

You should be careful though. Buying used precision tools is risky. It only takes one drop to ruin a micrometer, I don't care what brand it is. I would buy new.:)

Good day!

Originally posted by rskrause
Starret all the way, price be damned! I have some Starret tools that are 75+ years old and still work fine.

Rich Krause

Easy for you to say, you're in a position to save on shipping. :p

Didn't ever buy Starret new, but first mic I owned, was a used 1", bought for a buck, from a guy ready to retire, back in the 60s, and he had it for decades. Still have, and use it, and still accurate. Course, I don't use any of my mics as C clamps. :)

The new 'stuff' I bought, (from early on) was almost exclusively Mitotoyo. As an apprectice, it was cheap, but over decades of time, the quality has proved itself.

Originally posted by Chads71camaro
I would go with the mitutoyo on just about everything unless you are planning to use them every day day in and day out. As for the mics go I woud get the rachet feature...

Well, I do use them every day! See note above. As for the rachet...not here. In retrospect, with experience , glad I didn't. I much prefer micing by feel, with any mic.

I came by some Starret stuff the easy way. My father-in-law is an EE who started his working career after high school at Starret. He worked his way up to a machinist/quality control position and then got drafted. After WWII he went to college and so on. He accumulated a lot of Starret stuff when he worked there and after graduation started a business that involved a lot of precision machining. So, more measuring tools which he got from Starret. He has since retired and some of the excess tools have found their way to my box. He still has a full set of tools, even though he doesn't use them, which I completely understand.

Rich Krause

I still have the 1 in Brown & Sharpe mics my dad gave me 40+ years ago. They are in my desk. Slant line .0001.

However we use mostly Mitutoyo equipment in our CNC and grinding business. My grinders like friction thimbles a lot better than ratchet. Me, too.

FWIW, Etalon and Mahr stuff is also excellent. B&S hasn't made instruments in the USA for a long time. I'm not sure about Starrett.

Just something I'd like to add in talking "guaging". If your measuring to [.xx] you need to use a tool that is good to [.xxx] .
[.xxx] needs to be measured with a tool that can measure to [.xxxx]. MY stuff is Starret

Originally posted by Hot Rod Hawk
Just something I'd like to add in talking "guaging". If your measuring to [.xx] you need to use a tool that is good to [.xxx] .
[.xxx] needs to be measured with a tool that can measure to [.xxxx]. MY stuff is Starret

Yes, that's the party line for metrology. That's not always practical when you are measuring to .0001 like piston pins or pin bores. Very few engine builders have gages with a least count of .000010 (10 millionths or a tenth of a "tenth").

.000050 (50 millionths or half a "tenth") least count on some measuring equipment can be used if you set the exact size to a master gage block or pin. You are then doing comparative not absolute measurements.

Of course anytime you are talking absolute measurement in "tenths" (.0001) you need to specify a gaging temperature. That's one of the things that makes hot honing so interesting. A 4.03 inch bore grows about .000024 per degree F, or about .0036 from 70 F to 220F.

Originally posted by OldSStroker
A 4.03 inch bore grows about .000024 per degree F, or about .0036 from 70 F to 220F. Holy crap! I knew it was there, and I've read a bunch about getting block honed with torqueplates and recently at operating temps... but I never really did the math on heat expansion for this situation.

3.6 thousandths is nearly the clearance I need for my pistons! (in the opposite direction of course) Go figure. Guess I'll look for a machine shop that bores at temperture if I can. Granted the bore expansion may not be too "uneven" expansion, but damn that's scarry to think I'm gonna bore it in "contracted" form and hope it expands evenly (like I'd hope the piston will :)).

Almost makes me want to call Weisco and ask for install clearance TEMPERTURES, and piston expansion specs.

I always figured it was an issue with SMALL changes relative to honing finish and such...0.0036" just sounds a lot more than I expected. :o

Thanks for the scale-insight. :)

Originally posted by OldSStroker
Yes, that's the party line for metrology. That's not always practical when you are measuring to .0001 like piston pins or pin bores. Very few engine builders have gages with a least count of .000010 (10 millionths or a tenth of a "tenth"). Yeah, as a Biochem major I have to admit I've messed with more micrometers, micropipets, and specialized equipement to occationally hitting a wall of accuracy from time to time.

Many times the reason you see the accepted accuracy (reading's correctness to the object's physical atribute) being 1 magnitude greater than the precision (the tool's relative scale correctness regardless of calibration)... it's mostly due to two things:
- calibration abilities
- industry standard

If calibrated correctly, there's no reason your mic couldn't be +/- 0.0002 (instead of +/-0.0005 as implied by 1-magnitude accuracy rules-of-thumb). Obviously this is stuff that really gets to some people, but in a lab sometimes you just have no other option (accuracy limits are always included in calculations and can sometimes be a substancial amount of values produced).

Even if someone rated their mic to 0.0001" (with 0.00001" precision), I doubt it would be much off of the accuracy for a 0.001" mic (with 0.0001" precision), especially if they're competators in the same market/target.

I havn't seen a 6" mic that claims 0.00001" precision, but I'd have to be a bit sceptical after looking at all the quality mics out there that only run to 0.0001".

Originally posted by Steve in Seattle
Guess I'll look for a machine shop that bores at temperture if I can.

Me too!!! Good luck finding one, hot honing is very rare and expensive. Considering the add ons for a Sunnen CK-10 are $25,000, and it's a new technology for the average guy don't expect to find too many units out there

Originally posted by Steve in Seattle
Granted the bore expansion may not be too "uneven" expansion, but damn that's scarry to think I'm gonna bore it in "contracted" form and hope it expands evenly (like I'd hope the piston will :)).

Almost makes me want to call Weisco and ask for install clearance TEMPERTURES, and piston expansion specs.

I always figured it was an issue with SMALL changes relative to honing finish and such...0.0036" just sounds a lot more than I expected. :o

Thanks for the scale-insight. :)

The reason for the piston to wall clearances being what they are is because the piston and block expand and that's all taken into account. Make sure you just follow the specs and doing it the old fashoned TQ plate way will work.

The specs that most companies give are for the parts to be at 68-70 deg F and take the measurement there.

Bret

Originally posted by SStrokerAce
The reason for the piston to wall clearances being what they are is because the piston and block expand and that's all taken into account. Make sure you just follow the specs and doing it the old fashoned TQ plate way will work.

The specs that most companies give are for the parts to be at 68-70 deg F and take the measurement there. Good to know, thanks Bret :) (I assumed that was the idea, but the difference between iron / aluminum blocks expansion rate made me a little nervous when the same clearances are used for spec'ing a piston).

Here's a strange one for you guys:

0-6" micrometer set, or a 0-6" interchangeable micrometer kit?

My gut feeling is that a 6" micrometer with a 5" bar on one end just can't possibly be as reliable as a 1" micrometer... but I found a Mitutoyo kit that does just that, with supposedly 0.0001" precision.

Is this for real? Anyone used one of these interchangeable micrometers with success? Anyone with experience think these are a bad idea to invest in?

Originally posted by Steve in Seattle
Here's a strange one for you guys:

0-6" micrometer set, or a 0-6" interchangeable micrometer kit?

My gut feeling is that a 6" micrometer with a 5" bar on one end just can't possibly be as reliable as a 1" micrometer... but I found a Mitutoyo kit that does just that, with supposedly 0.0001" precision.

Is this for real? Anyone used one of these interchangeable micrometers with success? Anyone with experience think these are a bad idea to invest in?

You have to zero it on a "standard" or gage block when you change anvils. It's much like setting the zero. I agree that using a 6 inch capacity mic to measure 0-1 wouldn't be as good as using a 0-1 but mainly because it's so big and bulky. It's a two-handed job for me. It's probably a ratchet thimble, and I'm more comfortable with a friction in the lower sizes.

We use fixed mics up to 3 inches then iterchangable from there on.

I've been in the tool and die making industry for about 7 years now and work as a transfer and progressive die builder. Of the shops I've worked at Mitutoyo mics were the most common. They're very accurate (get the .0001 version) and reasonably priced, I'd put them side to side with a Starrett set any day. As for dial indicators, there's only one company; Interapid. That's the only indicator I'd ever consider buying. Pricey but you get what you pay for w/ precision measuring tools. Compare using an Interapid w/ a B&S or Starrett and you'll see what I mean. And as for measuring to .0001, as stated before, you need to be in a temperature/humidity controlled environment and the part being machined/measured needs to be at that temperature as well. I'd say .0005 is reasonable out in the shop, but anything closer than that you need to be in a controlled environment, which is why our jig grinders and wire edms are in special rooms. Anyways, I'm a big fan of Mitutoyo, even though they're "imports."
Greg

Originally posted by Steve in Seattle
Good to know, thanks Bret :) (I assumed that was the idea, but the difference between iron / aluminum blocks expansion rate made me a little nervous when the same clearances are used for spec'ing a piston).

Most aluminum blocks have iron sleeves. There are a few that run aluminum on aluminum but not without interesting bore prep, or coatings or interesting aluminum alloys.

Thought question: why does a hole get bigger when it gets hotter if the metal is expanding? Doesn't it expand into the hole and make it smaller?

A beer to the best answer. I'll pay off at PRI Show in December!

The piston grows about 2.5-3 times as fast as the iron bore, depending on the alloy. Remember that piston skirts are not round, they are oval and some are also barrel shaped or smaller at top and bottom of the skirt than in the middle. This is on purpose to get the correct clearances when at operating temps. Cold engine piston slap usually goes away when things heat up because the clearances tighten.

Use your piston mfgr's piston-to-wall clearance specs, as Bret said.

With hot honing, they do compensate for expansion. The operator might have two bore gages: one set for hot measuring and one for room temp. measuring. It's still not pleasant work. 200F+ honing oil smarts when you get into it.

Originally posted by OldSStroker
Thought question: why does a hole get bigger when it gets hotter if the metal is expanding? Doesn't it expand into the hole and make it smaller?

AFAIC, the operating temp of coolant has a bearing on the optimum clearance to strive for, in the bore. IOW, if you plan on 210* normal operating temp, as compared to 180*, (F of course) I'd expect the bore to actually collapse a little, requiring an increase in assembly clearance. Piston mfr/engrg. conversations collaborate on this.

Carbon/carbon composite bore sleeves and pistons (compliments of NASA):http://www.nasatech.com/Briefs/Aug02/LAR15094.html

zero expansion
high heat efficiency
and ELLIMINATION of ring packages

crazy eh?

Originally posted by OldSStroker

Thought question: why does a hole get bigger when it gets hotter if the metal is expanding? Doesn't it expand into the hole and make it smaller?

I don't have time to put out the equations but it's understandable this way:
If you think of a solid cylinder, you will be able to predict the expansion when you heat it. Now, if you take out a cylinder from the center of the original cylinder, leaving a donut-shaped disk, both the smaller cylinder and the new disk will also expand with heat. They expand in exactly the same manner whether they are in one piece or two. Another way to look at it is if you were to scribe a circle of some diameter on a block of steel, measure it , heat it, and measure it again, the diameters would be different (heated metal expands, so the hot circle would be larger). The behavior of the metal doesn't change whether there is metal on the inside of the circle (solid) or not (donut). The hole expands outward instead of inward.

Originally posted by nateh
I don't have time to put out the equations but it's understandable this way:
If you think of a solid cylinder, you will be able to predict the expansion when you heat it. Now, if you take out a cylinder from the center of the original cylinder, leaving a donut-shaped disk, both the smaller cylinder and the new disk will also expand with heat. They expand in exactly the same manner whether they are in one piece or two. Another way to look at it is if you were to scribe a circle of some diameter on a block of steel, measure it , heat it, and measure it again, the diameters would be different (heated metal expands, so the hot circle would be larger). The behavior of the metal doesn't change whether there is metal on the inside of the circle (solid) or not (donut). The hole expands outward instead of inward.

Good explanation. Thanks. I'm glad you skipped the math. :) Yeah, all those little molecules get farther and farther apart as they get more excited (heated).

The classic demonstration uses a metal ball and a metal ring. Welding a thin rod to them makes handling easier. At room temp the ball is too big to pass thru the ring. Heating the ring in a flame (Bunsen burner) expands it and the ball slips thru.

A further demo is to again start at room temp with a no-go condition, then cool the ball with dry ice and shrink it enough to go thru the ring.

Of couse some smarta$$ heats the ring and slips the ball into, but not thru it, and cools it to shrink fit the ring onto the ball! Anticipating this behavior, what could you do tho make this a recoverable situation for the teacher/demonstrator?

OldSStroker...

from automotive machinists point of view :)

Example=> Sunnen Rod Heater

heat connecting rod's small-end to install rods on pistons in pressed-pin situations :)

another way to look at molecular expansion due to heat

Originally posted by OldSStroker Of couse some smarta$$ heats the ring and slips the ball into, but not thru it, and cools it to shrink fit the ring onto the ball! Anticipating this behavior, what could you do tho make this a recoverable situation for the teacher/demonstrator?

If I were just demonstrating the principle and the materials were irrelevant, I'd make the ring out of material with a higher rate of thermal expansion. Then when the stuck assembly is heated as a unit, the ring would get "more bigger" than the ball. Depending on how tight the interference fit was, it would come apart that way.

If you have to keep them made of the same materials, dry ice on the ball and heat on the ring is the only thing that comes to mind, and hope that the heat transfer between the two isn't ideal.

Just a thought...

Originally posted by nateh
If I were just demonstrating the principle and the materials were irrelevant, I'd make the ring out of material with a higher rate of thermal expansion. Then when the stuck assembly is heated as a unit, the ring would get "more bigger" than the ball. Depending on how tight the interference fit was, it would come apart that way.

Just a thought...

Same thought.

We make the "balls" (pistons) out of higher expansion aluminum and the "rings" (cylinders) out of iron. We then worry about piston slap when the engine is cold. In most OEM situations we DO have it both ways: almost no slap when cold and no scuffing when very hot.

We also do the opposite with pistons and pins where we use a very close fit, a fraction of a .001. At least we're using the dissimilar materials to an advantage here.

Originally posted by OldSStroker
Of couse some smarta$$ heats the ring and slips the ball into, but not thru it, and cools it to shrink fit the ring onto the ball! Anticipating this behavior, what could you do tho make this a recoverable situation for the teacher/demonstrator?

Heh, I can be fairly scary in person… I'm pretty sure if I put it on the board that anyone that tries it will automatically fail my course… (and yes, I have taught classes before and have tried similar things and never had a problem).

Otherwise, bludgeon the student repeatedly over the head until the ball comes loose?