What's new
What's new

Measuring Small Dia. Bore (~= 0.650) With +/- 0.0001 Accuracy ???

  • Thread starter C.M.
  • Start date
  • Replies 72
  • Views 9,152
C

C.M.

Guest
SOLVED: Measuring Small Dia. Bore (~= 0.650) With +/- 0.0001 Accuracy ???

I need to measure the bore of a trumpet cylinder that is about 0.665 inches. I have a set of crappy telescoping gauges and there is no way I'm trusting any sort of transfer measurement to the precision/tolerance I need, and that's +/- 0.0001 inches. I haven't seen dial bore gauges that go down that small and I don't want to break the bank. Any suggestions ?;)
 
Last edited:
At that precision you pretty much have to break the bank. The only thing I'd really trust is air gauging with a couple reference rings to compare to. You could also get close with a set of tenth increment pins covering a thou or two. You'd probably find out the bores aren't as straight, true and wonderful as you hoped. :eek:
 
At that precision you pretty much have to break the bank. The only thing I'd really trust is air gauging with a couple reference rings to compare to. You could also get close with a set of tenth increment pins covering a thou or two. You'd probably find out the bores aren't as straight, true and wonderful as you hoped. :eek:

Bummer cause straight and true are the aim. I hear you on the go/ no go gauges. I was thinking that would probably be my only hope. I can finally mount that cylindrical grinding attachment on my lathe and do some grinding between centers and do rough telescope gauge measurements until I'm really close and then switch to a few "pins" I make. The thing is too, my piston is going to be easy to measure with my high end Mit Digital micrometer and I can chase whatever dimension I have on the cylinder with my pistons. Since they will be nickle plated, KNOCK ON WOOD, I shouldn't end up going under on them. I wish I had a ring gauge to practice my telescoping skills. I got a real crappy set from China, that won't help. I guess I can just practice awhile with my micrometer.
 
Air gage or Sunnen bore gage. Not sure how you're figuring to machine your bore to +-.0001 but it better be something damn tricky since that's close tolerance. Better yet send them out to be honed.
If you finish before nickel plate your tolerance will be shot after plate. Only way to do it is finish after plate.
Work with these tight of tolerances is tricky. Only real way to do it it finish after plate, grind the pistons and hone the bores.
 
Thanks guys. I've got all the machining stuff figured out. I won't drag you all down with the details. My question was specifically how to measure a bore hole that is about 0.665 to within 1 tenth of a thou ? I have yet to find a bore gauge that goes that small and I am trying to avoid spending large amounts of money on one-off projects. So far, I've decided to just use telescoping gauges to get my measurements to within a thou and make a series of go/no go pins in 3/10's increments around that measurement. My outside micrometer is a real nice, high end digital Mitutoyo that goes down to hundredths of a thou. I haven't heard nor thought of any better ideas.
 
It might help people understand what you are doing if you put a link to your other thread.

I was trying to avoid writing an essay when it mattered not to the question I was asking, but I see your point. I'm lapping a cylinder and a piston together.The fit has become too sloppy. As the clearance will be grossly over tolerance, I will plate a few thou of nickel onto the piston as a start. Neither will be honed or ground but rather lapped. That is covered in another thread.
 
My bad !! Found lots of affordable dial bore gauges on Ebay that are in the right range. Can't recall why I never saw them earlier. Cheers.
 
My bad !! Found lots of affordable dial bore gauges on Ebay that are in the right range. Can't recall why I never saw them earlier. Cheers.

I wouldn't trust a dial bore gauge much more than a telescopic gauge, unless you have a similarly sized reference ring gauge to set it against, or a sunnen style setting fixture. Trying to qualify a dial bore gauge within a tenth with a mic is an exercise in futility.

I would trust a 1µm digital three point mic, if used in conjuction with an on-size calibrated ring gauge. I might trust the same with a next nearest calibrated ring gauge, probably 17mm, if I didn't have other options.

Nobody has mentioned temperature...
 
I suggest that you get real about what's really needed before you spend a ton of time and money chasing .0001 We machine tight tolerance fine finish bores in aluminum, stainless and brass that are liquid/pneumatic sealing surfaces for actuators used in aircraft engines. These bores and seals cannot leak and have moving elements along the bore length. We use a variety of gages from good quality I.D Micrometers, a sunnen bore gage and our CMM to check the finished size. The typical Tolerance of these bores is +/- .0005

Find out why you need to hold .0001 before you start chasing it. Did some guy who has no idea what .0001 really means to you, the shop making it just toss a number on it because he thought it would make him famous ?

Good Luck

Make Chips Boys !

Ron
 
Something else to keep in mind is the size of dirt. A piston and bore with 0.0001" clearance has a good chance of binding up forever if you get a bit of schmutz in there. I wouldn't bother with the toolpost grinder. Lathes make really poor grinders. Turn with good sharp tools and use a cast iron lap to finish. That will take care of roundness, straightness and all the rest. My hobby shop reference for everything is also the Mitutoyo digital mic. We have several at work and the agreement between all of them, and several gauge block sets is remarkable.
 
if you're really trying to inspect them within .0001 for dia, roundness, and straightness, you really need to use an air gage. Doesn't sound like you can afford one, and it doesn't sound like you'd know how to use one if you had it. My advise for just getting the job done (let's face it, it's not exactly a valve body for a jet engine, it's a trumpet) just buy yourelf the deltronic sizes you need. More than adequate.
 
The reality is that you can't make or inspect to that tolerance. The good thing is, that unlike the pros on this forum, no one is inspecting your work. Just make the parts as best you can and see if it works.
 
Does the valve bore really have to be an exact size? It would seem more practical to hone or lap the bore to a near perfect cylinder. Then measure the bore with something like this:
Tesa Brown and Sharpe .6 - .7" .2 Intrimik Inside Bore Micrometer FH59 | eBay
You will need a ring gauge to verify the hole mike is on calibration.

Once you have the bore to an acceptable condition lap the valve to bore diameter minus .0003. By doing it this way you only have to make one part to a critical dimension.
The down side is that the valve will only fit the bore it is made to fit.
 
Your point is well taken. I expected a couple of thou on a sliding fit for a trumpet. When I posted this assumption on the prestigious Trumpet Herald website, the gang jumped on it. Those who pounced included trumpet makers and repair people. They claimed the clearance of pro horns is only about 3 tenths. What do I know ??? I do hear you though. The same site had some posters claiming the holes running through the pistons have to align with the pipes, in and out of the cylinder, within a thou, which is beyond absurd; it's impossible, for reasons I won't get into.
 
You might think about a Moore & Wright small hole gauge...
My set only goes to .500.
There are 2 balls you adjust to the hole then measure with a micrometer.

View attachment 229911

Hmmmmm .... sounds interesting. The only link I come up with are those bell shaped gauges, for a search term "Small Hole" gauge. Would you happen to have a link ?
 

I did just that and the link to the product that comes up short , at 0.500 is 125 British Pounds. I found a used mic that will do the trick, on Ebay. Waiting to hear back from seller re shipping. The only issue I have with it is that it's a nominal size +/- 0.006 and although I luckily fall into the range, it would be nice to have something a little more versatile, for other projects.
 








 
Back
Top