OT? looking for input on checking a 6.816" +/-.001 hole 2.812 dp.

I'm more of an operator gone owner. My metrology background isn't the best, and I'm quoting a job. It as the title states is a bore diameter of 3.816" +/- .001 . The material is some type of casted material and appears to look like a section of tubing with a 9" o.d. and a 6-9/16" i.d. that is 4-1/2" long. It is counter bored to my dimension. I see no run out tolerance just the + or - .001 and my best guess is they press this over a bearing, because they are calling it a return roller.

I would plan to chuck it on a lathe. I'm not sure if I can use pie jaws yet to minimize distortion or if I will rough at a higher chuck pressure than finish at another pressure.

My question is how would you guys check this. At the place I used to work at they'd use or buy a pistol grip type 3 leged digital bore mic. I'm guessing that set up would be in the $2,000+ range. I'm not sure on the amount of future work and this customer is very touchy on asking too many questions. They are pretty loyal to keep their jobs at the same shops until they screw up. They have me quoting qty's of 10, 30, 60, 120, and 240. So my thought is they will order 10 or 30 occasionally. This customer would be casting the parts and giving to me to machine, then selling to their customer. I'm sure they'd throw me under the bus in half a heart beat if something wasn't well within tolerance. So I'm going to inspect and document every part, and give them a copy report of dimensions and save the original for myself. I'm just about positive they have no way to inspect the part and could care less. If I say it is a certain size, They will believe it until told differently, then they will make me prove what I did.

I think my machine with some effort could hold the dimensions, but I need a good way of checking the part, that will hold water if I need to defend the measurement here. I can't justify more than $500+ up front. Even writing that makes me nervous.

Bottom line, I need a good means of checking this part that any end customers inspection dept. would respect my method of machining/inspection. I'd like a bit of efficiency, and I don't typically run into parts that I need to use my bore gage(I'm trying to say I'm not comfortable trusting/using this type of gaging yet).

A big thanks in advance,
Rosie

From your description of all the details, I'd check it with a Sunnen bore gage. A cheaper bore gage could do just as well if you have an accurate way to set it, like gage blocks. The bore mic is overkill for ±.001, and roundness won't enter into it if they don't specify it and have no way to check it themselves, right?

If it's just this one part, I'd turn a dedicated go-no plug gage. You've got a thousandth on either side after all. OTOH, if you think there'll be more parts with similar bore ID's, then a gage with some range makes sense.

Regards.

Finegrain

I'm not sure if this link works but this is what I found on fleabay.


STARRETT TOOLS 84-111-6 DIAL BORE GAGE 5.000" to 8.125" - eBay (item 250579799849 end time Apr-13-10 19:36:46 PDT)

If the link doesn't work cut and paste this item number into the search on ebay.
250579799849

They have 3 in different ranges of decay.

Quick question on these. Do you set with a micrometer or ?????
Thanks
Rosie

An ID micrometer and a OD micrometer to measure it with would easily handle +/-0.001. If you can find one, a NSK is ideal. Avoid the Starrett rod type as they do not have a spindle lock. A dial bore gage is faster and requires less technique, the ID micrometer covers a much larger range and is just as accurate using good technique. Do not use the ID micrometer's graduations. Use an OD micrometer checked with gage blocks to measure the ID micrometer.

Bear in mind that it's possible to produce a three-lobed bore that measures exactly the same everywhere when you check it with a dial bore gage or inside micrometer.

I would do it with a bore gage and a calaibrated master (mics and Jo blocks) to set the bore gage, then turn a go and no go gage to ensure the part is round. RJT

That Starrett gage should work just fine. You can set it with a micrometer, but then your measurement is only as good as the micrometer minus any error between the two tools. I'd stack up gage blocks to the correct dimension with a pair of wear blocks overhanging the ends to set the bore gage. That will look better to the customer.

An ID mic and an OD mic in the correct hands will do an adequate job, but it's more subject to feel and easier to question if you get challenged.

(I'm trying to say I'm not comfortable trusting/using this type of gaging yet).

Click to expand...

A GOOD dial bore gage takes 'feel' out of the equation, which is a plus in that case. Cheaper bore gages are like toys next to a Sunnen, Starrett, Federal, etc. and are not to be trusted for tenths. For ±.001, I want a tool that measures to tenths.

mud, thanks for taking a look at the bore gage. I hope I get the job since I just made an offer and ended up getting that gage for $250. The more I think about the job the easier I think it will be. nieve or not I don't know.

mrainey, thanks for the thought. Kind of funny how that works.

Thanks for all the thoughts/input.
Rosie

Rosie,

Your thread's subject line reads "6.816" diameter but in your first post the text reads "3.816". I hope that's a typo in your posting because the range for the gage you apparently bought is over 5".

Dial bore gage would work. You might as well by the set I'm sure you'll use it in the future. +-.001 is a lot of tolerance (depending on machine and mat'l, I guess) so you can probably set the bore gage off a OD mic.
As mentioned above go/no go plug gages would be nice, especially the Go to check for out of round. You could easily make those out of cold rolled using a mic and gage blocs to make sure they're spot on.
Though with plug gages you'll never get it to go 'net fit' so a min size plug gage won't go in a min size bore it seems like they'd go in a bore that + a couple of tenths. And they won't show you if the bore is straight, could be small in front big in back.

PixMan said:

Rosie,

Your thread's subject line reads "6.816" diameter but in your first post the text reads "3.816". I hope that's a typo in your posting because the range for the gage you apparently bought is over 5".

Click to expand...

Yep, typo. The size is 6.816, so I did buy the right size frame. Now I just hope I bought something in good condition. He had 3, this one didn't have any noted problems and it was the most expensive. Like it was noted I'll use it if I get the job, and if not I'm sure I'll use it in the future. My guess is I got it for a third of the price I'd pay if I needed it yesterday. MSC is about $800 before you wait for the optimal 40% off Friday's.

I'm leaning towards making a homade go/no go hard gage for a function check, just in case I end up with the 3 lobed hole. I'm not too worried about the hole being larger in the back. I'll be able to check enough of that with the bore gage.

I don't want to do it(ASS U ME), however do to my customers nature of business, If it presses in to the manner their customer is used to it, all will be good. I'm optimistic that if I get the job it could be a decent one once things are tweeked in. Another reason for the thread is I'm just not used to turning o.d. work much over a few inches with any mildly tight dimensions.

Rosie

P.S. Before I forget I have a mitutoyo dial bore gage set up that is metric. By the math it looks as if it is good to about 6". Can I slap on a standard dial indicator on the end of it, or does something else need to be done to do it and be used correctly. Up until now I set it with a standard mic and set the markers to high and low with the standard mic. I just ask this because I don't have a dial indicator that will fit in the end of the handle. They are either too big or small, and I don't want to dump money if I'm only going to have another indicator laying next to the other dozen I already have.

rosie said:

Quick question on these. Do you set with a micrometer or ?????

Click to expand...

You set them with a ring gage.

That device uses three measuring surfaces. Two of them are fixed; the third moves and gives the reading. So the measurement technique uses three points on an arc.

You'll notice that all three surfaces are curved. This doesn't matter for the middle (movable) one, but it certainly does matter for the two outer ones, since the exact points that bear on the surface being measured change with the diameter of the work.

You might be able to get a reference reading by pushing all three points against a surface plate. However, this would be outside of the normal measurement range (since the radius is infinite). The technique would only be acceptable for calibration if Starrett recommends it in their instructions, and provides proper correlation data.

- Leigh

I agree that a ring gage would be optimim, but you should be abe to st it with a micrometer. The outer points appear to be centralizers with the center point being the live one. The one on the far side would be the adjustable fixed point. I can not verify this as I uses Sunnen bore gages.



You should be able to wring a stack of gage blocks to the proper dimension, clamp a micrometer to it, lock the spindle while it is clamped on the blocks to eliminate any wear related error, and carefully slide the blocks out. Set the bore gage to the micrometer. Stand up a wear block on each end of the gage blocks and set the bore gage to that, which can be a bit tricky. If you can cross check the micrometer on the gage blocks, the bore gage on the gage blocks, and the bore gage in the micrometer and everything agrees, you are good. It takes a bit of time and care to get it right, but it will work, especially for your needed tolerance.

The key is to not handle anything any more than absolutely necessary so warmth does not affect the outcome. Use a micrometer stand to hold the micrometer when setting the bore gage. Set the gage block stack on the surface plate while setting the micrometer, etc.

I agree that ring gauges are best, but in between rings and micrometers is the option that I'm going to add, since I already own the Digi Chek height gauge. Check out this nifty little way of doing it:

http://www.starrett.com/download/253_p129_130.pdf

rosie said:

P.S. Before I forget I have a mitutoyo dial bore gage set up that is metric. By the math it looks as if it is good to about 6". Can I slap on a standard dial indicator on the end of it, or does something else need to be done to do it and be used correctly. Up until now I set it with a standard mic and set the markers to high and low with the standard mic. I just ask this because I don't have a dial indicator that will fit in the end of the handle. They are either too big or small, and I don't want to dump money if I'm only going to have another indicator laying next to the other dozen I already have.

Click to expand...

Rosie,

I believe the indicators used for those have only a .050" to .100" (1mm to 3mm?) range and there's lots of indicators like that on Ebay. I think they've all got 3/8" shanks. If you measure the bore in the end of the handle on that Mitutoyo, I bet you'd be able to get an indicator for under $50 and have another very useful tool. If not, I'll buy the Mit from you and do it up myself.

+1 on the ring gage, and a XX master within .002 of desired size, at that. I've set my larger Standard bore gages with either Standard's fixture or jo blocks and fingers in a cage, though I won't trust the last two methods as much as the ring.
While plate checking with an indicator and cadillac height gage makes for a nice backup, for inprocess, I'll take the bore gage.
You might try your customer on paying for the ring, it may give you a better feel for the quantities you'll see.

I've looked on ebay for a ring gage. I sincerely agree that that is the way to go. I've not yet had a ring gage quoted from a manufacturer, but my guess would be $500+. The size is really close to 6-13/16, and I'm sure a bearing size, so I'm nievely hopefull to find one. If I can't get a ring gage for the right price I'll buy a good set of I'd mics, I'll check the 1st part a few different ways and use it for my standard. A bit hooky but I think it will be acceptable.

If I were to ask the customer to pay for the ring gage, I think they'd say here's a nice kite do what you want with it. They are a bit abrasive, and pay a bit late. However they are my first customer and I'm getting more work from them as time goes on. They are starting to give me more shots new work and stuff that other suppliers aren't up to snuff on. The nicest thing with this customer is they supply material. For the 12 years I've known of the them, they are loyal to good shops. I've been trying for 3 years to get parts I used to run at my old employer, but no luck yet.

Rambling over
Rosie

I'll check the 1st part a few different ways and use it for my standard.

Click to expand...

Maybe have another shop check it with a CMM, and give you a size and roundness number. A CMM can check it in 20 locations faster than you can check it in 2 with an inside mic, and be more accurate. Since I bought one used last year, it's been an eye opener.

PS - allow your part to age at least 24 hours before checking/using it as a standard. You are not removing much material here, which is a plus, but I've bored parts and had them move quite a bit in a short period of time before settling down.

Asking how THEY plan on inspecting the parts may help make the decision on how YOU are going to measure them...

If you want to see something move after being machined, try some AMPCO!

When you are documenting your measurements make note of the temperature. 68 degrees F is standard measuring temperature. If the parts are near the tolerance limits and they are measuring at 100 F it could be important.