Expensive Inside Calipers Worth the $$? Plus Die Grinders

[SteveHGraham]

Right, but as I said, the other calipers would be easier to use on the mill.

[mklotz]

Examine the inside jaws of your calipers under magnification. Note that they are not knife-edged but have very small flats on the measuring edges. That means that, when measuring a hole, you will always be measuring the distance between two very small chords. As a result the measurement will be very slightly less than the actual diameter of the hole.

[BadDog]

Right, but as I said, the other calipers would be easier to use on the mill.

I'm not sure that it would, at least not to my way of thinking. Those require the wiggle-woggle searching for minimum that t-gages find by tracing through and remembering. But you've got to find it and recognize it. Also, because of the point made by marv, you will generally want it straight up so that the center of the leg hinge is on bore axis. Tilting off axis will change the measurement, more so on a small bore than a large bore. However, though even casual application of these may be slightly more accurate, the inside jaws of a common caliper naturally aid in getting it reasonably aligned for a measurement that will be within that expected of ID measurements using calipers, AND it does not require the rather large z-space to use. To figure out where I am on the way to a size that may require better means to measure (or not), the common ID/OD calipers win every time for me.

That's just my general arm-chair machinist thought process. But for real world anecdote, I've owned a set for quite a while and don't remember the last time I used them since I "played around with them" to try them out when first brought home. Which can be interpreted to indicate quite clearly that I in no way found them better or more convenient to use in applications where such devices would be appropriate. Your usage and expectations may yield a different result, but that's the experience of someone who has had them in their box for a while. This may be sort of like the sometimes evident fixation on things like "tramming" widget (or on-center widgets) or "coaxial indicators" when I find a few DTIs in appropriate range and selection of fingers is FAR more versatile and no harder to use. I absolutely LOVE metrology gear seemingly in the same way women love jewelry. It fascinates me, and the amazing quality and mechanical creativity that created them just gives me a warm fuzzy as I fondle them (TMI?). But in the end, I have a relatively small selection (honestly, its like 3% of the total hoard... er... collection) that I actually use regularly.

[Harold_V]

This may be sort of like the sometimes evident fixation on things like "tramming" widget (or on-center widgets) or "coaxial indicators" when I find a few DTIs in appropriate range and selection of fingers is FAR more versatile and no harder to use.

I consider that there are those who assume that if they load up on all of the less than necessary trick tools that they will become proficient, perhaps the equal of those who have years of experience. As if to suggest that if one stands in the garage, he becomes a car.

Funny.

There is no substitute for experience. All the trick tools in existence won't make a guy a machinist, and the majority of those who are (machinists) don't own unneeded tools. What one owns often makes little difference in that department. It's knowing how to (properly) use that which you own that spells the difference.

I absolutely LOVE metrology gear seemingly in the same way women love jewelry. It fascinates me, and the amazing quality and mechanical creativity that created them just gives me a warm fuzzy as I fondle them (TMI?). But in the end, I have a relatively small selection (honestly, its like 3% of the total hoard... er... collection) that I actually use regularly.

See what I mean?

Harold

[SteveHGraham]

Examine the inside jaws of your calipers under magnification. Note that they are not knife-edged but have very small flats on the measuring edges. That means that, when measuring a hole, you will always be measuring the distance between two very small chords. As a result the measurement will be very slightly less than the actual diameter of the hole.

This relates to another reason I don't like using them on the mill. You have to lean the calipers over, spanning even bigger chords. I was hoping the other calipers had ball ends on them to reduce the inaccuracy. I am not looking for great accuracy here, but I would like to be within a few thousandths.

The main reason I don't like using regular calipers on the mill is that the spindle and end mill get in the way.

[Inspector]

In Mitutoyo's catalogue their version of those gauges has a statement telling you that they are for comparison measurement only and are to be used in association with ring gauges. They have better ones but the external ones in the same family cost $600+ with the digital being even more, so I don't think the internal will be any less. The external ones I use regularly for thickness measurements are graduated to 0.0005 and I always compare them to a gauge block at the size I need to check because they deviate from the closed zero point to their maximum of 0.8000 to 1.0000 when fully open. The ones you are looking at will get you in the ballpark but at least set them to a micrometer at the dimension you want or you will find you could be out 0.005 or more when done.
Just to clarify all the above is in inches.

Pete

[SteveHGraham]

That sounds about like what I was hoping. A tool for quick measurements to help me avoid overshooting.

Getting back to die grinders, I wonder if anyone can recommend a decent one for a decent price. It seems like it goes: $25 Chinese, $50 Chinese, $100 Chinese, $400-$1000 American.

I thought Ingersoll-Rand might be okay, but if what I'm reading is right, they're Chinese, so they would be in the $50 Chinese bracket. If that's true, then there may be a better Chinese tool in the same range. I have seen people saying nice things about Sioux and Florida Pneumatics.

Obviously I would not expect to run one all day, so I don't need Dynabrade quality, but it would be nice if it didn't blow up in a year.

[Russ Hanscom]

There also electric die grinders; the two 1/4" that I have access to are pretty decent; not sure how they compare to the air ones.

[redneckalbertan]

I prefer air to electric but I have an electric Dewalt. Not real happy with it but not displeased with it, you turn it on and it spins around. There is flex in the body of the Dewalt that i don't like. If i had to get another electric I would look for a steel body Makita. From what I have seen they are the best. I don't know a price on them. For pnumatic I have used older Chicago Pnumatic die grinders and I was happy with the prefomance.

[revrnd]

I think die grinders have become a disposable item. I don't ever recall anyone @ work having anything more than whatever the company supplied. I had the same grinder for years (I don't recall the brand). Unfortunately I dropped it & broke the shaft by the wrench flats.

Looking in the various tool catalogs, the 1/4" grinder that they sell looks identical except for the round sticker affixed inside the circular boss.