How to correctly use a height gauge

Hi guys. I just wanted to get the general opinion on the correct way to set and use a height gauge.

Lets say for example I want to scribe a line on a block at a known height.

I have put the height gauge on a surface plate, and then put a gauge block next to it. I swing the height gauge finger over the gauge block and drop the height until I can just feel it rub on the top of the gauge block as I swing the height gauge over it. I am doing this using the under face of the height gauge finger. I then adjust the vernier on the height gauge to calibrate it. Is that the right way to calibrate the height, or should I do it until the point strikes the side of the gauge block and then back off slightly.

I can then set the desired height on the height gauge and swing it across the face of my item scribing the line.

Is this the correct way?

Presumably the scribed line will be offset by half of the radius of the end of the height gauge scriber. As the height gauge was zero'd on the underneath surface of the finger but the line was scribed at the point. Does this matter, I can't gauge what the likely difference would be.

How do people care for their height gauge fingers, do people regrind the points, and if so is there a preferred method.

If doing it using my method, then the flatness of the underside of the finger, having the finger mounted horizontally, and having a point ground at the very bottom of the finger with a small radius are all key to getting an accurate measurement out of it.

Sorry if this is a dumb question, but i've searched online for help on how to use one, and they don't cover these specific questions.

Thanks

Graham

Hi Graham,

At BAe I was taught that the surface table or plate is zero height and all measurements are taken from that common plane, as you probably know already. So with your height gauge base sitting on the table and the bottom edge of your marking point also resting on the table your scales should read 0. If not then the finger needs to be adjusted.

We never had to do any adjusting as there was a calibration department to do all that with calibration testing date stickers etc. but I don't think it would be too difficult. Once you have set zero on your scales and adjusted your marking point you could then check against a gauge block to see how accurate your zero setting was. That's how I would do it (if I had a height gauge and gauge blocks - future purchases maybe).

There are many, far more experienced people on the forum who could probably offer a better description of how to do this than myself.

Ed.

The '0' reference for the scale of the Height Gauge is the surface of the table and from then on just set the moving center scale to '0' also and from then on just set the scribing bar to the height measurement you require.

The scribing point, I use a diamond plate to sharpen it ensuring the underside is flat with no burrs. Scribing the line I would accept as the height and rely on the zero reference as a start point. Always handy to have a note book by you to jot down readings where you need to go under or over another reading. Also a calculator too!

Clive

I'm guessing the actual questions, ignored by everyone so far, is what to do about the:

- radius of the edge of the surface block in terms of the initial proposed calibration method - I would suggest nothing, as the face of the gauge block is the reference height
- radius of the sharp edge of the scribing block, seeing that the reference height (block or surface plate) is set on the underside of the scribing block, but the radius is the part that scribes the work - to which, pragmatically, surely can be assumed to be zero (even if academically or from a "high precision metrology" point of view this is not true)

...especially given what the line is being scribed on the work for (some manual cut/file/etc operation with way less precision than the marking out)?

I just touch the flat underside of the scribing leg onto the surface plate, use the top adjustment screw to set zero and then lock that. From then on just raise and lower the head to read the size you want on the scale.

Do make sure that the scribing part sits flat or pointing sloghtly downwards, I bought a cheapie digital height gauge from one of out suppliers and when resting on teh surface plate teh actual scribing part of teh blade wa sabout 0.010" off the surface.

Martin not sure where any radius comes from?

Cheers guys. The finger on mine doesn't go down to the base. I'm presuming at some point it had the old cranked finger replaced with a straight one. I stick a 1 inch gauge block under it and calibrate it at the 2 inch mark.

If I use the fine adjusting knob on the height gauge to slowly drop the finger down until it touches, its quite often tricky to actually determine the point at which it touches, and I guess you could have the same effect when zeroing to the base. You could crank it a thou too far and actually have lifted the front of the height gauge up, or alternatively what you think is touching is actually slightly above base. You loose all feel for the "touch down" point when using the fine adjustment. This isn't just a calibration thing. It would be exactly the same if you were using your height gauge to measure the height of a block and needed to touch down the finger on the top of the block.

This is on a chesterman height gauge with has coarse adjustment by disengaging the head from the feedscrew and sliding the whole head up and down, or fine adjustment using a knob on the base to spin the feedscrew. If I attempt to touch down onto a gauge block using the coarse adjustment, the head drops back into the nearest thread in the feedscrew which moves the head.

If I get the height gauge close to the right height using coarse adjustment, then press down on the base and use fine adjustment to drop the finger onto the top of the item being measured, I can kindof feel it touch, but not definate enough for it to be repeatable to the thou.

I suppose I could try getting it to what I think is touching, then if I can slide the gauge block in and out from under the finger, but not feel any noticeable up and down play when I try and rattle the gauge block, that would probably work.

I guess its all in the technique.

Do i have a 40 year old gummed up height gauge that has "lost its feel".

My height gauge has been at the back of my tool cupboard since I acquired it. And Ive only just tried to start using it. Can you tell

Graham

<<Martin not sure where any radius comes from?>>

..ask the OP...

Presumably the scribed line will be offset by half of the radius of the end of the height gauge scriber. As the height gauge was zero'd on the underneath surface of the finger but the line was scribed at the point. Does this matter, I can't gauge what the likely difference would be.

I was just thinking aloud. I haven't ever tried sharpening the end of my scriber in the height gauge. It had occurred to be if the end was dull, or badly radiused, or not ground correctly, I could actually be scribing a line somewhat above my zero reference.

i.e if there was a 5 thou radius on the end of my scriber, all, all my scribed lines would be 5 thou greater than any height measurements made using the under side of the scriber.

This is how I did the dodgy one, spray fix some wet and dry to the surface plate or float glass, with the head free to move apply finger pressure ontop of the scriber and move back & forth. This sets the bottom flat, any subsequent sharpening is done on the angled face.

To set the height I use the adjusters at the top of the gauge which move the scale until it is reading zero.

If you are trying to use it with a round scriber then its not much more than a glorified scribing block and very hard to set a point to zero. New cranked scribers are quite cheap from ARC so worth getting one so you can easily zero it to the surface plate.

Edited By JasonB on 08/01/2015 16:20:00

Hi Graham

I battled with a similar problem for quite a while, a height guage with a missing cranked scriber, tried hard but coudl not find a similar one to buy...

I made a new one by brazing together a small stack of pieces of 1/8" HSS (as 1/8 was the width of the previous one and easy to get in Sw HSS).This got me to within .002", Most of this I ground away on my tool cutter/grinder, then did the last piece on a piece of 600grit wet and dry on the surface plate, until the vernier showed Zero...

HSS brazed just about OK, but needed Deep V's where the pieces touched.There is probably a special flux but I had none.... It does not move very fast!

It wont be as good as the orginal, but it cost me £3 and a couple of hours. Certainly zeroed to .0001 (by the vernier on the height guage)

Hope it helps

Edited By jason udall on 08/01/2015 18:10:50

Thanks for everyones suggestions. They've been really useful.

Ive actually just been out and had a look at the height gauge again, with the intention of measuring it up for a new cranked scriber however as you can see from the photos, its designed to have a straight scriber and by the looks of it, designed not to measure anything below about 40mm. I guess I would place small items on a 1-2-3 block to raise their height.

You can see here on a 2" block, its reading 2", so no need to manually add numbers as I originally thought.

Calibrating the metric side with a 50mm slip.

Calibration is done by loosening the screws on the vernier plates, which are slotted and adjusting them to suit.

I have a digital height gauge supplied by Machine-DRO which I set zero when scribe blade is set on a polished marble plate, after all is cleaned, press 'zero' button on readout & set to req'd height...voila!

**LINK**

George

Graham, from your picture of the height gauge you have the scriber fixed to the top of the clamp bar, it should be underneath the clamp bar! No wonder you cannot zero the scriber to the table surface.Also it looks as if you have a round nose turning tool in the clamp when you want a 30 deg. wedge shape with a flat bottom. You need a chisel edge on it.

Clive

Jason,

A massively exagerated illustration, but if the scriber is blunt, you will scribe a line higher than you wanted to.

Maybe on a blunt scriber it equates to a tenth, a thou, maybe 10 thou I have no idea.

Graham

Clive,

It is a wedge type scribe point, not a round one. It doesnt come out well in the pictures. Heres a closer view.

If I mount the scriber below the clamp bar it still does not reach the table. If it was designed to reach the table, the scale on the height gauge would start from 0. As it is the scale starts at 1.5 inches. If I put the height gauge to 1.5 inches, the top of the clamp bar is 1.5 inches from the table. There is only approximately +/- 1mm adjustment in position of the scale, so theres no way it can work any other way, than with the scriber mounted in the top of the clamp bar.

Graham

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Nice sketch, Graham ... It shows exactly your 'feared' problem.

The fact is though ... The blade should be sharp, and "single sided" ... if it looks anything like your lower image then you need to grind the angled top face.

Assuming good material, you should be able to feel it "dig-in" if you drag it over your thumbnail. [same test as joiners use for chisels]

MichaelG.

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Edit: Having just seen your photo ... You need a new blade.

Edited By Michael Gilligan on 08/01/2015 21:40:34