Final Bore is under spec

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wlw-19958
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Re: Final Bore is under spec

Post by wlw-19958 » Thu Nov 16, 2017 10:58 am

Hi There,

It was my understanding that a lap uses an abrasive
compound to "charge" the lap. The laps I see are made
of brass and the abrasive is supposed to embed into
the lap. Seeing that the material being lapped is also
brass, I would be concerned the abrasive would also
embed in it too. This is why I didn't suggest a lap in
the first place.

Good Luck!
-Blue Chips-
Webb

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SteveM
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Re: Final Bore is under spec

Post by SteveM » Thu Nov 16, 2017 10:28 pm

You need to use a lap that is softer than the material being lapped.

Would aluminum work?

Steve

EOsteam
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Re: Final Bore is under spec

Post by EOsteam » Fri Nov 17, 2017 3:00 am

Edit: You made mention of using a dial bore gauge. How was it set? If you used a micrometer, you may or may not have an accurate setting. It's VERY easy to miss dead center (don't ask me how I know). A ring gauge of known (certified) size is the most reliable way to set a dial bore. Even gauge blocks leave a lot to be desired, due to the ability to miss center.
You are correct. I don't possess any ring gauges. A micrometer is what has been used. However, I have gotten pretty accurate at getting consistent results with the following technique. A micrometer stand is used to hold the micrometer. Next the non-moving part of the dial bore gauge is gently stabilized against one of the faces of the micrometer with two fingers of the left hand. Then the gauge is swept across the opposite face of the micrometer until the position is found where the dial reaches it's maximum zenith. Then the plunger is swept across the same face of the micrometer 90 degrees to the original sweep until you again find the new zenith. I have been verifying my results with a telescoping bore gauge. A dial indicator that has 0.0001 accuracy has been used which makes setting the instrument twitchy as heck but pretty consistent.
An insert tool may or may not have the degree of sharpness that is desirable. For that reason, I suggest you learn to hand grind boring tools, so you can present the exact tool geometry, as well as the desired sharpness, to the work at hand. Relying on insert tooling, especially for the novice, is asking for problems that can be difficult to overcome, and it cheats the operator from learning the fundamentals of tool geometry and sharpening.
I have gotten reasonably good at grinding HSS lathe tools but don't have any 1/2" round HSS blanks at present so I used a Criterion insert tool that was purchased before this forum became regular reading.
It's a matter of procedure. When you work to tight tolerances, you don't take irregular cuts, nor do you take a light cut after a heavy cut. Not ever. When you bore properly, you should be able to go back in the hole and remove a tenth or two, no more. You do that by taking three light cuts when you approach size, each being 1/3 of the amount of remaining stock. A good target size, before finish cuts, is generally about .030" under. By taking a third each time, the tool works under identical tool pressure and removes a predictable amount of material. If it's properly sharpened, and is NOT dragging anywhere, very little will be removed with a spring pass, as it should be.
This sounds like a great procedure to follow in the future. Previously, the final two passes were taken at 0.030 and 0.010". I think the main problem was caused by my eyesight not quite resolving the small divisions on the 2" boring head. To remedy my part, the bore was blued and then the boring head was backed off far enough to remove any backlash concerns and then advanced until the tool just made contact. One machining pass was made and 0.0006" were removed which put the results right in the middle of the tolerance range.

Thanks for all the help.

HJ

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Re: Final Bore is under spec

Post by Harold_V » Fri Nov 17, 2017 4:17 am

I'm well pleased to read of your success. I was afraid that you would attempt other methods, each of which has its own problems.

Insert tooling. It can be quite good, depending on the inserts. I should have made that clear. Some of them are diamond ground and have positive rake, which is quite desirable when boring, as it reduces cutting pressure and tends to ensure a better finish.

You can be damned proud of your accomplishment. It's not easy to do.

My experience with setting dial bore gauges with anything but rings wasn't always bad. It's just that you don't always get it right. I recall one instance where I was working with a diameter around 3", and missed it a couple tenths, in spite of using gauge blocks and exercising caution. Thanks to the secondary standards lab, the error was caught before any scrap was made.

A useful tip: End mill shanks are hardened, and make great cutting tools. You can also use drill blanks, or reamer blanks.
You can also silver solder HSS bits to steel shanks. Heating HSS doesn't harm it, nor does it anneal. Just allow it to air cool, as quenching pretty much guarantees micro-fracturing. Once soldered, you can then grind the desired geometry.

H
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EOsteam
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Re: Final Bore is under spec

Post by EOsteam » Fri Nov 17, 2017 12:38 pm

Harold,

I'm curious as how to the gage block setting method is performed?

HJ

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GlennW
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Re: Final Bore is under spec

Post by GlennW » Fri Nov 17, 2017 3:13 pm

I'm sure that there are other methods, but I prefer using a Gage Block Accessory set for that.
PC160727.JPG
Set up your gage blocks to the desired dimension and place them in the holder with a couple of extensions on the ends of the stack. Other gage blocks stuck up higher will work, but the ones in the accessory set are longer.
PC160726.JPG
I use Sunnen bore gauges which have a large, flat, base which makes it easier to get a decent reading. Other gauges may be a bit mere difficult to square up.
PC160725.JPG
Glenn

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Re: Final Bore is under spec

Post by Harold_V » Fri Nov 17, 2017 4:25 pm

Thanks, Glenn. We can always count on you to present good and useful information. Including those pictures really helped!

H
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ctwo
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Re: Final Bore is under spec

Post by ctwo » Fri Nov 17, 2017 9:30 pm

I'm not afraid to hand hone my insert tooling on a diamond "stone".

I was wondering about doing that, using a DTI to sweep the tool, then hone a though off, and give it a pass.

The inserts are more brittle with a fine edge though, but seem great for finish passes...

I really enjoyed the the outcome of this topic.
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Disclaimer: I'm just a guy with a few machines...

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GlennW
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Re: Final Bore is under spec

Post by GlennW » Fri Nov 17, 2017 10:05 pm

Thanks, Harold!
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

AllenH59
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Re: Final Bore is under spec

Post by AllenH59 » Thu Dec 14, 2017 1:34 am

Does that hole measure exactly round? I am no expert, but we are talking about a very small amount. if forced to do this I would turn a piece of steel to the min size and press it in... presto..the hole is the right size..it is much easier to measure od...but I am an amateur. the good thing about this for me is it could take several tries to get it to the right tenth, and it would not matter

EOsteam
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Re: Final Bore is under spec

Post by EOsteam » Thu Dec 14, 2017 8:28 pm

The original question involved a bore in a journal box that was slightly undersized after what should have been the final machining pass. An off the shelf bearing will be pressed in or the journal box may be heated enough to allow the bearing to slip in to place. The bore was true after the final pass.

HJ

Harold_V
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Re: Final Bore is under spec

Post by Harold_V » Fri Dec 15, 2017 2:43 am

AllenH59 wrote:Does that hole measure exactly round?
Having been bored, unless there's an issue with the tool, the material, or with the bearings in the head of the mill, it should be round within acceptable limits---likely less than a tenth.
I am no expert, but we are talking about a very small amount. if forced to do this I would turn a piece of steel to the min size and press it in... presto..the hole is the right size..
Not a good idea. First, if you press and don't get the parts in dead alignment, you can deform the hole. Worse yet, if you can turn the piece you'd press, it likely is soft, so you run the risk of galling. If you've never had two parts seize when you put them together, you just haven't lived! :lol:
it is much easier to measure od...but I am an amateur.
It's always easier with OD's, as they can be determined directly. Still, with just a little practice, one can get quite good with telescoping gauges. It's not unreasonable to trust them to a couple tenths. Takes practice, and the proper technique, though. The point is, it can be done, and has been done for many decades.

H
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