Help me check this bore

Dupa3872 · Feb 23, 2015

I'm looking for ideas. I am boring a step into the face of a 5 inch round part on my HAAS SL-20 lathe, the part is aluminum 6061 and has a bore through. The Dia. is 4.3307 X .492 deep my Tolerance is +.0013 -0.0 I am making one part and my bore gages only go up to 2 inches. I have to creep up on it as the tool probe in my machine is only good for a few Thow. I don't want to take it out of the machine and go to the CMM. I plan to rough the part then finish everything but the bore and let it cool down for awhile. I will then come back with a nice finish B/B and finish the stepped bore.

I want to check it in the machine. I could make a go no go gage but I'm looking for other ideas. I could also rough it all then run the finish bore .02 to .03 under then take it out and go to the CMM get my number, make my offset and then finish turn the entire part. I still would want to check it before taking it out.

Thanks Ron

quadman2007 · Feb 23, 2015

Bore something under 2in so you can use your bore guage and set your tool offset

Fulcircleny · Feb 23, 2015

Is the OD turned as well? or is it stock? if it is turned, measure it, dead accurate. take your od reading, verify that reading. now work with wall thickness, you have .00065 per side, do the math.
5.0000 - 4.3307 = .6630 *.5 = .3315 wall thickness using your 0-1 mic or an indicating mic. measure over a gage ball ....
Not to add confusion, but are you holding in pie jaws, or regular? light clamping pressure? you may find you have an egg when you unclamp, but that's another days problem....
Best of Luck,
Chris

Derek Smalls · Feb 23, 2015

Inside mic? I actually prefer inside mics over bore gage on any diameter. Not saying they are better, just what I prefer. If no id mic available, telescope gage. Thats a bit tighter tolerance than I would usually use them on, but with a lot of care it will work. Best bet would probably be a shallow bore gage.

Matt@RFR · Feb 23, 2015

If this kind of bore gage:

Make your own anvil or something to clamp on to an existing one to extend capacity. It doesn't need to be anything special.

6061Mike · Feb 23, 2015

I would not turn it undersize and check it on cmm and use that number to make an offset! Too many variables. I think the easiest thing would be to make a go-nogo gage. If you don't want to make anything I would suggest going with Matt's idea about a modified anvil or whatnot to fit onto an existing boregage. You could bore a pin to slip over the longest anvil and use a couple small set screws to fasten it.
You could also use a telescoping gage and verify your reading using a gage block stackup and an indicator on a surface plate. Set you indicator with the gage blocks and then spin/rotate/slide the telescoping gage underneath to check size. Maybe do this method to a size that you can check with an alternate form (*cough* boregage) to verify your readings.

edit: you still have to 'make' something for the bore gage method, but could be a good exercise to extend your measuring capabilities!

6061Mike · Feb 23, 2015

Matt@RFR said:
If this kind of bore gage:

Make your own anvil or something to clamp on to an existing one to extend capacity. It doesn't need to be anything special.

I'm really thinking about this idea Matt... Have you ever done this? I have up to 6" capacity at work so I don't know that I need to go bigger... It seems too simple LoL?... Why couldn't you make basically a sleeve to fit over the longest anvil with a set screw, maybe two. They would have to be small, like 2-56 or so, but still, how much holding force do you need? The only real work I could see would be grinding the end radius so you don't have too much flat, or too much 'point'.

Heavey Metal · Feb 23, 2015

A dial bore gage is going to be iffy.

You are going to need a tri mike and a 2 point mike or gage and some trial to learn the chucking deflection.

Matt@RFR · Feb 23, 2015

No, I haven't done it but I can't see a reason it wouldn't work as long as the extension doesn't have any play. After all, a bore gauge is just a comparator, so all that really matters is repeatability. It does seem too simple though.

brian.pallas · Feb 23, 2015

At least in my experience adding extensions onto bore gages is not very accurate. It only got me within .002 in the past until I bought a bigger bore gage. I would say just get it over with and buy a bore gage or id mic. They really aren't very expensive at all for the use you get out of them, plus not dinking around on a job.

Since it sounds like your job is already in the machine - You don't have the 110mm bearing laying around to check your bore with?

Matt@RFR · Feb 23, 2015

brian.pallas said:
At least in my experience adding extensions onto bore gages is not very accurate. It only got me within .002 in the past until I bought a bigger bore gage.

Interesting. Do you know what to attribute this to?

6061Mike · Feb 23, 2015

brian.pallas said:
At least in my experience adding extensions onto bore gages is not very accurate. It only got me within .002 in the past until I bought a bigger bore gage. I would say just get it over with and buy a bore gage or id mic. They really aren't very expensive at all for the use you get out of them, plus not dinking around on a job.

Since it sounds like your job is already in the machine - You don't have the 110mm bearing laying around to check your bore with?

Doesn't the 2-6" Mitutoyo use an extension? I think the accuracy would be directly related to how good/accurate the extension was. I guess if the extension fits over a rod with .002-.004" clearance and then the set screw pushes it off center it would certainly be less accurate the longer the extension is...

Heavy Metal, yea that is true checking the part in the chuck (because of the 3 points of contact), especially if the bore is 'inside' the jaws. But, fwiw, I have had my bores checked on a cmm (that I checked with bore gages and rings) to within .0001" of what I got on size, but not on a lathe.

Brian · Feb 23, 2015

You loose accuracy when you oversize the capacity of the bore gage because the centralizers are not effective. That's the two round discs on either side of the moving anvil. I have used extensions on the very style of bore gage shown above, but I don't know if I'd feel warm and fuzzy trying to hit .0013" tolerance.

We used to have a Mueller gage for shallow but large bores, like these: Mueller Gages Company - 77 Series You could probably find on on ebay for peanuts....

6061Mike · Feb 23, 2015

Brian said:
You loose accuracy when you oversize the capacity of the bore gage because the centralizers are not effective. That's the two round discs on either side of the moving anvil. I have used extensions on the very style of bore gage shown above, but I don't know if I'd feel warm and fuzzy trying to hit .0013" tolerance.

We used to have a Mueller gage for shallow but large bores, like these: Mueller Gages Company - 77 Series You could probably find on on ebay for peanuts....

Good point. I think the OP was however trying to "get the job done" and not buy special tooling.... I revert to my original suggestion in this case, make a go-nogo gage.

brian.pallas · Feb 23, 2015

Yes, the 2"-6" uses an extension. I tried using two extensions from two different sets to measure 7.500" bores, and even though the gage would zero on the gage block stack, and measure the bore as right on, the cmm, calipers and id mic all measured it as .002 over. Maybe I was doing something else wrong with the bore gage, definitely possible. But I think the issue is how far apart the little centering wheels on the gage are for different size bores.

allloutmx · Feb 23, 2015

INDI-CAL INTERNAL GROOVE GAGE

or some gage blocks and some pins?

aerodark · Feb 23, 2015

.0013 is easily held with careful use of an inside micrometer. I always check the ID mic with an OD mic to be sure.

Some here claim they can check size within .0001 using telescoping gages. I wouldn't trust them to less than .002 total tolerance.

Get a Mahr bore gage in that range if you want to be absolutely sure. Use a set ring.

scadvice · Feb 23, 2015

I would check the roundness of your bore also, because this figures in. Finally don't forget temperature. What? .00004" per degree (F) per inch I believe in aluminum should be close enough. ( Someone correct me if I've recalled wrong.) :scratchchin:

litlerob1 · Feb 23, 2015

aerodark said:
.0013 is easily held with careful use of an inside micrometer. I always check the ID mic with an OD mic to be sure.

Some here claim they can check size within .0001 using telescoping gages. I wouldn't trust them to less than .002 total tolerance.

Get a Mahr bore gage in that range if you want to be absolutely sure. Use a set ring.

AHH someone thinks they can reasonably measure a bore with telescoping bore gages, those are a reference tool only as far as I am concerned. :willy_nilly:

6061Mike said:
Good point. I think the OP was however trying to "get the job done" and not buy special tooling.... I revert to my original suggestion in this case, make a go-nogo gage.

The problem with go no/go is that it only tells you if you have scrapped the part or not, it isn't a measurement.

Robert

pmtool · Feb 23, 2015

litlerob1 said:
AHH someone thinks they can reasonably measure a bore with telescoping bore gages, those are a reference tool only as far as I am concerned.

The problem with go no/go is that it only tells you if you have scrapped the part or not, it isn't a measurement.

Robert

I don't pretend I can measure a bore to a tenth with telescoping bore gage but I think that with a tolerance of .0013 is doable and would be the cheapest route if you were willing to buy tools. I think they get a bad wrap because they are highly dependent of the operator and their feel but I they will repeat well if you use them correctly. The better the finish the better the result.

Of course a proper bore gauge will tell you a lot more about the hole. I hate to say it but the best way is to suck it up and by a 2-6 inch bore gauge. Something like a Mitutoyo is cheap for what you get and good enough to work to tolerances much smaller than this. Of course you need to set these properly too.

Buying the correct tool always hurts, but just once. Coming up with time consuming and sometimes marginal work arounds is a pain everytime!

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