Dial bore gauge feedback

[hardtail]

I'm looking for a DBG in the 2-6" range with .0001" accuracy and was wondering if any of you had purchased this Shars unit or any recent Shars tools lately and had any comments to share. I'm sure for this price it's offshore and I would probably be better off buying a good brand name but likely wouldn't use it much, however accuracy doesn't care about that........LOL

http://www.shars.com/products/view/8..._Gage_0001quot

I see MSC has a similar Mitutoyo for $319, that was more than I was wanting to spend but still not outrageous.......now how much are they're coupons worth off?

[oldtiffie]

I bought this one from Littlemachineshop.com:
http://www.littlemachineshop.com/pro...ory=1310310429

It cost US$70 as apposed to Shars US$145:
http://www.shars.com/products/view/8..._Gage_0001quot

While mine calibrated to 0.0005" - and not to 0.0001" as the Shars tool is.

I am quite happy with mine and would have no problem measuring to 0.0002" at least.

There is a lot of skill required to both set up and to measure with those units. I use slip guages to set mine up in preference to using a micrometer. In the case I use, the bore guage becomes a comparator instead of a measuring device or tool.

There are not a lot of bores that need to be closer than 0.01mm (0.0004").

I reserve the bore guage for deep bores as I prefer to use a "stick" or an inside micrometer as I get a better "feel" than with a bore guage.



http://www.cdcotools.com/item.php?itemid=453





These digital calipers are accurate to 0.01mm (0.0004") but are complicated to set up - but work well:


I can easily hold 0.0004" (0.01mm) with a micrometer and spring calipers and ball and telescopic guages - and I can hold 0.0002" (0.005mm) with a bit more effort and concentration.

Job, shop and measuring tool ambient temperature differences become crucial at this level of accuracy. A job in a lathe that has heated up can take quite a while to cool down to ambient (shop) temperature. There has been many a job that was "spot on" when measured on the machine but which "shrank" or "moved" as it cooled afterwards.

[ptjw7uk]

Seems to me that the ability to display 0.0001" resolution is a bit academic without some way of knowing if you are in the centre of the bore and at right angles to the sides.
I expect the measurements get more consistant with use.
I have also seen bore measuring gauges that have 2 'skids' at 120 degree separation which I assume will give an average measurement(cylinder boring).

Peter

[oldtiffie]

Peter,

the rollers are the two of the "120* skids" - the top anvil/spindle is the other. There is a second anvil/spindle at the top:


It does work - and works quite well, but a lot of care and skill is needed.

The two "rollers" centralise it pretty well as regards "left-right" but having achieved that, the diameter is the least reading on the dial during the "rocking/forward-back" motion. It is essential that inadvertent hand/other pressures do not interfere with the measuring and positioning processes.

I am quite happy with mine to 0.0002" (0.005mm).

A "ring" is the best guage to set up to, but in the absence of a precision test ring (source of more errors if "shop-made") a micrometer or slip guages work well enough.

[JCHannum]

Any of the indicator type dial bore gages are no better then the means used to calibrate them. While the gage might have a 0.0001" resolution, it is the standard used to set the gage that determines the accuracy of the reading.

If ultimate accuracy is required, a standard in the range of the desired reading is needed. These standards can cost more than the bore gage in some cases.

In general, the gage heads do a good job of centering, but the quality of the components is likely to go downhill as the price declines, making the action sticky and readings not as repeatable in the lower priced instruments.

[oldtiffie]

Jim.

I agree with you 100% (I really don't which us is going to be the most surprised with that statement - I think I feel a dizzy fit coming on!!).

At best, and as you've said before, when using guages or references to set the bore guage, it is really not measuring anything as it is a comparator that compares the job to the reference. That might be a fine point but while an inside micrometer may well be a measuring device in its own right, the bore guage is not and cannot be.

Just holding the fairly long bore guage tube incorrectly can cause it to expand quite significantly. The outer tube holds the dial indicator body and the indicator plunger is inside and pretty well thermally insulated from the outer tube and relative thermally-induced significant movement is quite possible.

"Stickiness" can be a problem and needs to be guarded against. Like most (95%+ minimum) of the stuff I've bought from LMS, it works really well.

I set mine with slip guages on my surface plate (black granite or float glass - all depends!!). I have the upper slip set as a cantilever and use that or alternatively, bring the arm of the height guage down onto the stack of slips and use the underside of the height guage arm as my reference.

I did have a problem with the two roller/supports not contacting the table so I packed them evenly and that solved it.

One of the big problems with dial bore guages and inside micrometers is that they don't work too well on hole/bores that are less than about 3/4">1" deep as they need to "rock" forward and back to get the reading. Its very easy to get a false reading in a shallow hole/bore. That is where old-fashioned calipers as well as telescopic bore guages work well.

The degree of accuracy assumed in the OP is fine - but it should be accompanied by a very high level of surface finish.

If I have to bore a hole with limits less than 0.025mm (~0.001"), I really do ask myself if it is really necessary, and if it is, why it is, and if it isn't, why the hell am I doing it.

[Scishopguy]

Hardtail...The April MSC flier has dial bore gages on sale. The 2"-6" range unit is $62.99 with indicator, case, and interchangeable tips. The order number is: UC06451744

It is an import but what isn't these days?!

[philbur]

The photo of the Shars dial shows 0.0005" graduations.

Of course resolution, precision and repeatability are all different things. Increasing the gearing of an instrument doesn't increase the precision. Ask for the test certificate. If it doesn't have one then don't buy it.

Phil

Hardtail...The April MSC flier has dial bore gages on sale. The 2"-6" range unit is $62.99 with indicator, case, and interchangeable tips. The order number is: UC06451744

It is an import but what isn't these days?!

[Dr Stan]

I just arranged the purchase of a Scheer-Tumico Dial Bore gage off Craig's List for $25. I'll need to buy the tips to get the full range, but I'm getting a quality US tool with a Japanese made indicator for about 10 cents on the dollar.

If you know how to perform a nation wide search on CL you can locate some good deals. I have also bought a US made 6" bench vice made of high strength cast steel, a Baldor 8" pedestal grinder and a Baldor 6" carbide tool grinder off CL. Shipping was a bit high on the grinders and the vice, but I ended up with new (the vice) or virtually new tools for less than half price including shipping.

[JCHannum]

The photo of the Shars dial shows 0.0005" graduations.

Of course resolution, precision and repeatability are all different things. Increasing the gearing of an instrument doesn't increase the precision. Ask for the test certificate. If it doesn't have one then don't buy it.

Phil

The test certificates for most chicom instruments are printed in bulk at some location other than where the instrument was manufactured. Most consist of an ornate piece of paper with a couple of unreadable signatures stating that the instrument is certified to be whatever it happens to be.