Crappy Shahe DTI vs Mitutoyo, Baty and "Kurt"

Some time back I bought a couple of digital micrometers from Shahe (say "Sha huh"), which is a Chinese manufacturer of measurement equipment. One was 0-25mm and the other 25-50mm, both with resolution of 1um (0.001mm). From what I can tell, they seem to be reasonably well made and they appear to be deadly accurate. I have a set of spotless Class II carbide gauge blocks and the tests I did appear to confirm that the readings are within the 1um resolution of the display, measured at various points within the measurement range.

At the same time, I also bought a 0.8mm range DTI with a claimed resolution of 1um. I already had 3 DTIs, all of which are 10um (0.01mm) resolution. But when I was investigating the backlash and runout of The Shiz, I felt I should really get something with better resolution at some stage.

Having just perpetrated a heinous bodge on a BT40 toolholder (to convert it to ISO40 by welding a threaded extension piece on the end), it seemed sensible to check if the result was remotely fit for use. Sure enough, the runout of the chuck itself is pretty damned good (certainly less than 10um and probably around 6-7um from what I can tell). The fact that the only ER32 collets I have might as well have fallen out of a Xmas cracker is beside the point - let's just pretend I knew what I was doing when I bought them - something in the interests of science perhaps.

One thing I discovered fairly quickly is that the Shahe DTI doesn't manage to register any actual movement (runout), despite there evidently being plenty to look at (this with about 6-7um runout). On the exact same tool, measuring side by side, the Mitutoyo DTI shows a definite runout, while the Shahe remains almost stationary. That's basically shit. What's going on? I suppose this would be a great tool for showing allegedly stupendous accuracy of your machine on one of those willy waving videos...

As mentioned, I have 3 other DTIs:

• A "Kurt" branded chinesium 0-1" thing that actually seems to work quite consistently, even though it is a bit on the large size. This has a resolution of 0.001" (25um) per division.
• A 0-0.8mm Baty (Swiss, badged as RS) DTI with ball-ended lever (the others all have linear plungers). This has a resolution of 10um.
• A genuine 0-1mm Mitutoyo with a resolution of 10um.

I also have 2 magnetic stands:

• A generic "simple" mag base that I've possessed for my years, rather like this.
• A recent "universal" stand ("Insize" brand) - this one in fact.

The latter is a bit more convenient to use, as you can pretty much position the arms and the DTI in almost any way you choose when the knob is loosened. 

Anyway, here's the Shahe jobby:

Looks the part but clearly something doesn't work quite as hoped. Time to take the back off:

I've seen these before somewhere, where somebody was comparing a Chinesium DTI against the likes of Mitutoyo etc. It's largely what you'd expect to see:

• Some sort of "jewel" bearings for the spindles. Of course, they may simply be ruby coloured plastic....
• The return spring acts on the actual dial spindle. One large pinion drives the spindle from the plunger (through 2 step-up gear stages) and the other provides the preload and return movement. 
• Nothing obviously "bear's arse rough" to snigger at.
• No thick grease - or light oil evident.
• No obvious rubbing of the mechanism that might cause sticking.
• About the only thing I could do was put a few drops of light oil (oh alright - WD40 in fact) on the various spindle bearings that I could access by dipping a watchmaker's screwdriver in the stuff and then touching it onto the "jewels". That clearly wasn't going to magically fix anything but it seemed rude not to, given that I had the back off and it was sort of sticking.

Not surprisingly, this didn't bring about the slightest improvement.

Bottom line is to do some side by side testing. And as well as seeing how the various DTIs compare, it would be informative to measure runout of some of my tooling. I've checked a couple of them during setup in preparation for jobs but I'm interested to see how they compare:

• End mill holders (hopefully fairly accurate)
• Collet chucks (ER40, should be fairly good)
• Keyless chucks (not holding my breath but they aren't so critical anyway.

Couldn't be arsed to get all anal about writing stuff down, not least because many of the measurements will change when I swap cutters etc. This is for indication purposes only. So I simply made a few short videos instead. They are on my Pootube channel for reference.

Here are some indicative numbers:

• End mill holder - 10mm carbide tool - 10-15um
• End mill holder - 16mm indexable tool - 20um
• ER32 collet chuck - taper bore - 1-2um (I clearly just got lucky). Note that my original measurement showed an estimated 6-7um, so clearly it varies a little each time you mount the toolholder etc:

• ER40 collet chuck - 16mm carbide chamfer tool - 15um
• Keyless chuck - 10mm carbide tool - 50-80um:

Some of the videos wouldn't upload - I guess it's an Apple thing.

Conclusion:

• The Shahe DTI suffers from stiction and isn't much good for small movements (<10um). Which is ironic for a "1um" indicator...
• The other DTIs seem to be pretty consistent and usable, although they only resolve 10um per division. But I reckon you can reasonably discern a few microns.
• The various toolholders seem to be in the 5-16um runout range in practice. Where it's critical, I could probably spend a little more time in setup to reduce that.

Yes, the focus sort of changed a little from a direct comparison of the DTIs to asseement of the toolholder and cutter runout. But having found that the Shahe isn't much use beloew 10um of movement, I concluded that I actually possess four DTIs, all with 10um resolution. If I want a proper 1um DTI, I'm going to have to cough up for  genuine Mitutoyo one.