Paul Jones (04-11-2017)
To make the height gauge hold a dial indicator, I used some 7/16" square brass stock I had. I made one for 3/8" stems, and another for 8mm stem.
The screw on the end is 10-32. So to finish this, I need to make some brass thumb screws. These fit in place of the carbide tipped scribe.
I didn't see this posted by anyone, which I was hoping to see for a better design.
One of the most useful height gauge accessories I've made is the skinny probe...
for measuring down in holes where the supplied gauge probe won't fit.
It would be a simple addition to either of the holders described above. Simply drill a hole and thread it for a rod or fit a setscrew to secure an unthreaded rod.
Thanks, that exactly what I was hoping for was different ideas on modifications to a surface plate height gage. I didn't think of the lug mount. I've been machining for 40+ years, but only recently have gotten into surface plate usage and measurements. My metrology tools are still limited. I don't have a cylindrical square, or precision compound angle plate yet. I'm thinking at $180 for a 3x6 inch cylindrical, I would attempt to make one on the lathe, and tool post grind the final surface cut. So far the measurement needs were for a tapered sleeve, so a sine plate, Jo blocks, and bench center were the first surface plate "furniture" I purchased.
Thanks, that is another tool to make for the height gage. "Playing" on the surface plate is a new hobby direction. So I'm still in learn mode with using it to make parts measurements. Up till now, the only 'tenths' measurements were for ball bearing press fits. I let the machine (and my setup) do it's best for square and parallel. Which has not been a problem until I ran into one on the lathe. Namely the sleeve in the headstock that reduces what was thought to be a 6MT (per the manual), to the 4MT center. Pretty sure it's a DIN 90mm gauge line 20:1 metric taper. 6MT is about 1" smaller diameter (7MT is too small as well), so I have no idea what the China manufacture draftsman was trying to describe. I recently purchased a Federal dial indicator ADG1 size that is small enough to fit inside the spindle bore. I verified the 20:1 taper (off by 0.01mm per 40mm, and I need to cross check with another indicator to validate it does not have error). I also learned the import indicator mag holders I had were horrible at dealing with the small spring forces of the indicator (when cantilevered out 6 inches). So I just got a Noga, WOW. Again, my dial indicator measurements were really only runout on the lathe, I think this was the first time I've used one for absolute measurement for a taper angle. The bottom zero adjust is a must from here on out. I thought my mag bases were OK, till I put them on the surface plate and they all rock. I guess $15-$25 is not enough for the manufacture to grind them flat. The stiffness of the Noga is really impressive.
In addition to a DI holder you'll want to provide for a way to mount a DTI, preferably one that reads to tenths. I simply tapped a hole into the side of my holder and mounted a cross-drilled rod that accepts the DTI stem.
My main use for the DTI is to provide repeatable measuring pressure. For example, comparing a workpiece height to a reference Jo block height... Touch off on the Jo block with the DTI tip and note the dial reading. Now touch the work in such a way as to repeat that dial reading. Then the height difference measured on the height gauge is not influenced by human ability to reproduce touch pressure accurately.
When touching down on something it's all too easy to lift the height gauge foot slightly and thus create an erroneous reference. Using the DTI approach helps solve that problem.
It would only be in exceptional cases that I would ever use a screw to clamp the barrel in a hole as you have done. There are 2 reasons for this.
1. It is the least kind method for the instrument, if tightened too much it will distort the barrel.
2. It is the least secure method. Unless the hole is a very good fit and reasonably long the gauge is likely to wobble about destroying accuracy. This imprecise fitting encourages over-tightening of the screw.
There are those who worry about the lack of precise vertical alignment, when using the lug, but these concerns are over exaggerated. Without much care it is easy to align the plunger to within say 0.5deg as a worst case. The effect of such misalignment is proportional to the cosine of the angular error. To put numbers to that, it means that over a movement range of 25mm the total error would be less than 1 micron for a 0.5 deg setup error. Or in other words 0.04 microns per 1mm. Way, way less than the resolution and accuracy of most any dial gauge, and also way less than the effect of minor temperature changes.
On the left the encoder is clamped for use on a surface plate. On the right it is mounted in place of a lathe toolpost for measuring camshaft profiles. The large hole in the block is a legacy of the block's previous use. just a nice heavy piece out of the scrap box, hardened and ground on the bottom and sides so ideal for its new use.
Here is another example of clamping on the shank that I posted a while back.
The next tool is a height gauge holder for the DTI. As it's apparent I need this for the stiffness when above the surface plate 12 or so inches. I recently purchase a surface gauge (used), which has a sloppy zero adjust. Seeing the 'buggered' screw head (for the hinge of the rocker), this was a problem to the previous owner. I don't know if there is a shim missing, but the rocker plate has much clearance to the machined slot this fits. It's an 'antique' of unknown maker (it does appear manufactured, with old chipped black paint on the sides). I'm of the belief now that the previous owner disassembled this and lost some shim. I Probably should buy a used Starrett. The seem to be pricey if they are complete and not rusty (eBay).
I'll make another holder for the DTI, as I've got many feet of this square brass stock. I assume I don't need to use tool steel for this as it's a holder and not relying on a machined surface for accuracy. The main effort was to 'whittle' the end down to fit the existing clamp of the scriber, as I'm mimicking this geometry. The DTI I have, came with 2 different dovetail mounts. Seems the large one would be the one that would be held with the least compliance from 'my' machining tolerance. I'm thinking the end mount dovetail would be the best general purpose mount to accommodate. Seems this would give the best reach on a larger part.
For lathe 'dialing in' the lug mount is how my current setup is.
I'm new to surface plate work, so still in learning mode. I've not machined many split clamps (the lathe tails stock quill, and drill press spindle both for depth measurement tooling are the only ones I can think of). So small thin slits I've not done, (and I don't think I have a thin saw in my tooling). Time for eBay search.
How accurate is the linear encoder? I'm looking for something to use on the surface grinder, as I can't trust the down feed dial.
From looking at your piston crown thickness gauge, and your camshaft lobe metrology, you must do custom engine work needing such measurements. Is this for hobby or 'prostitution'?
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