Accurate, Precise bore measurement

[steamer]

I have a planned project that I am working on that requires a 3.5" deep x 7/8 bore.

This bore size is not real critical, as the mating part can be changed, but the taper of the bore can not be more than about .0002"

I can lap that straight....but how do I measure the bore accurately?...in the home shop environment......suggestions

I'm thinking a plug gage...but what say you?

Dave

 

[vlmarshall]

Maybe not a plug gauge, or at least not a long pin, but how about a split-ball gauge, which would let you feel for the bore opening up towards the middle... and you could easily make one in the size and length you need.

 

[IanN]

Hi,

There are several ideas for measuring and checking bores in this thread:

http://www.homemodelenginemachinist.com/index.php?topic=5015.0

The later posts show a couple of designs that handle deep bores.

Ian.

P.S. Is the bore a blind hole or can you access both ends?

 

[steamer]

it's a thru bore, so it will be easy to lap, and perhaps lap feel is sufficient to detect and correct any taper. Then I can check actual size with a plug gage.......Just Thinking out loud...keep the ideas coming.....

Can you get to .000050" resolution with that bore gage?

Dave

 

[Jasonb]

Can you machine it with a between cts boring bar, that way you should not get any taper. A bit of 3/4" bar cross drilled for a 3/16 HSS bit with a grub screw to lock it should be quite rigid.

Jason

 

[abby]

Hi Steamer , I am intrigued , how are you going to measure to 0.00005" , I don't know of many gauge rooms that could do it.

 

[rake60]

For that bore size range I use telescoping gages.
My set will measure from 5/16" to 6"

You squeeze the anvils in and snug up the lock to hold them until they
are in the position where you want to take the measurement. With the
gage slightly tilted, release the lock then snug it back up. Rotate
the gage through the tight spot in it's travel and the lock will
hold that smallest diameter. Then you mic the gage with an outside mic.

That sounds like a lot...
It isn't. I decided to chuck up a clear plastic tube for a little demo.
[ame]http://www.youtube.com/watch?v=LXTOlSnIo4k[/ame]

It does take a little practice to get the correct feel on how tight to
turn the lock but it doesn't take long to pick that up.
Using these allows you mic at any depth of the bore and in different
directions to check for round. If your outside mics have a vernier scale
on them you can accurately measure to the .0001".

If your interested that tube measured .630" - 16.002mm
Must be a METRIC precision oiler.

Rick

 

[steamer]

Thanks Rick,

I have some telescoping gages also. I think that should get me close.
Was curious as to what else this fine group had in mind

The spec is no more than .0002" taper for the bore.

I'll bore first a thou under and bring to size and straightness with a lap and check with the snap gages....then check with a plug gage for actual size.

At a minimum, if your looking for certainty, you need to measure to a resolution of 1/10 your tolerance.....or .000020 ( 20 millionths)...though I would settle for .000050" ( 50 millionths).

Very easy to do with a proper comparator air gage in a temperature controlled room....but I think very optimistic with just about anything else......
It's a housing and spindle for an air spindle for a Tool and Cutter Grinder.....

I'm Trying to figure out if I can even come close with what I have.......

Thanks!,

Dave

 

[putputman]

Geeeeeeeeeez Dave, I thought you were a small engine builder. ??? ??? It is only politicians that use that many zeros or move the decimal point around like that. ;D

 

[steamer]

yeah I know, but I move the zero's the wrong way......tipacal enganeeer!


;D


Im just trying to come to grips with what's required.....It may be a bridge too far.....I'm noodling....

Dave

 

[vlmarshall]

Geez... I thought I was doing good with digital mics reading .00005" :


.00002"! Skip my split-ball gauge idea! :big:

 

[rake60]

This is becoming a very interesting thread.
The most accurate bore measuring device I have ever used
was the Bowers SuperBore System
It retails for about $4500 USD. With the head required to
measure a 7/8" bore Bowers advertises an accuracy of .00007"

Of course there ARE more accurate systyems.
They involve radioactive isotopes bouncing around inside a machine
the size of a house to measure a nanoinch.

If it were an external length to be measured, you can get much finer.
The Labconcept Universal Length Measuring Instrument
can measure a length to an accuracy of .000028"
It is only $47,750 UDS. Regrettably they are both beyond
my hobby budget.

Rick

 

[steamer]

Air gages will split tenths reliably and we used them at Milacron all the time. OD and ID Precision grinders ( Heald Machine).

A few millionths in our lapping department was everyday run of work...
Best of all we had our own metrology department, if you had a set of mic's or calipers or whatever, bring them in and they would square them, lap the contact faces to optical flats references and calibrate free of charge to all employee's

wish I knew where those guys are today..... :'(

Well....i'll let the cat out for a romp....I am considering a Wilson Tool and Cutter Grinder build this winter. It would be for end mills and lathe tools, and if I get my wish a little surface grinding of small parts.
She's a bit small, but should work out as I have NO more room...
It has an air spindle for sharpening end mill flutes. He calls for a clearance between the spindle and bore of (if memory serves) .0017 +.0002/ - 0.000. for proper operation. Phil Duclos did one very similar.
Anybody build one of these and make it work?


Oh and Rick, check out diamond turning....500 Picometer tolerances measured with white laser interferometry...50 picometers is the diameter of a hydrogen atom....

http://www.nanotechsys.com/wp-content/uploads/file/PDFs/PDFsJune272009/App Report Al - 05_01_08.pdf



But we digress....

Dave

 

[rake60]

As I said, this thread is becoming very interesting!

I have never worked on these scales before and I'm
loving the information!

Rick

 

[steamer]

Rick
Check out the positioning resolution while your at it on that machine....
34 Picometers!....... 0.000000034 meters th_confused0052


Anyway. Those of you who have made a working air spindle to either the Wilson or Duclos design...talk to me!

Dave

 

[Andrew_D]

Can you machine it with a between cts boring bar, that way you should not get any taper. A bit of 3/4" bar cross drilled for a 3/16 HSS bit with a grub screw to lock it should be quite rigid.

Jason

As soon as steamer mentioned that both ends of the hole were open, I thought...I should suggest boring it between centers...oh well...beat again.

Andrew

 

[steamer]

Saw this on Youtube.....it's also on the Quorn yahoo group...It's what I am talking about anyway.....

Dave


[ame]http://www.youtube.com/watch?v=I9YgG_soRcE[/ame]