Surface gage recommendation

[Sonic EscapeParticipant @sonicescape38234]

I found an rusty 40x60cm cast iron surface plate. I cleaned is with citric acid but unfortunately there are spots where the rust made tiny holes in the metal. But a quick test with a 1µm indicator looks promising. On short distances the error is < 8µm.

 

 

 

I was using a magnetic base to hold the dial indicator but it has two sharp edges and is not good to slide it across the plate. Where can I found a decent surface gage for the indicator? Something like this would be nice, but that model is too expensive. Most surface gage I found have some kind of marking needle  and can’t hold a dial indicator.

 

 

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Sonic Escape, I prefer these types of surface gauges, rather than a magnetic base.

Regards Nick.

[Sonic Escape]

On 14 August 2024 at 19:35 Sonic Escape Said:

I found an rusty 40x60cm cast iron surface plate. I cleaned is with citric acid but unfortunately there are spots where the rust made tiny holes in the metal. But a quick test with a 1µm indicator looks promising. On short distances the error is < 8µm.

 

…

 

 

… Where can I found a decent surface gage for the indicator? Something like this would be nice, but that model is too expensive. Most surface gage I found have some kind of marking needle  and can’t hold a dial indicator.

 

 

I’ve banged the drum on this before, but if you need a Surface Plate, that one is probably junk.  For a surface plate, 0.008mm ‘over short distances’ is poor, though that might be the result of bad measuring.  Watch this chap’s video for an better way of doing a basic sanity check.

Key features:

• The need to understand where to measure.
• His height gauge is nicer than the one Sonic and I both consider too expensive!
• The need for cleanliness
• A good Dial Indicator, not an el-cheapo with a sticky movement
• Use of a Gauge Block between the Dial Indicator and the plate.   The indicator is zeroed on the gauge block at the beginning
• All points on the surface should measure zero.

Of course most hobbyists don’t need a real surface plate.   All I require is a reasonably flat surface, sufficient to get somewhere near ±0.02mm, roughly.  I either use my mill table or a sheet of float glass.   A bit of worktop granite would do.  The limitations are open and honest with no pretensions of grandeur.  I’m not fooled into believing that a second-hand surface table is anything special!   Many of them wear a dip somewhere near the centre until the table lets the owner down and is scrapped.

Is it worth spending money on a good height gauge and other accessories, only to find the table itself is shot?

Dave

 

 

 

 

 

[Graham MeekParticipant @grahammeek88282]

My first Surface plate was a Glass Platen from a Photo-copier. This was mounted on a board with a felt, baize layer beneath it and edged with wooden narrow beading strips. When not in use it was stored up on edge next to the bench out of harms way.

As regards a Surface gauge I use mostly a Starrett Scribing block. That is until I use my 0,02 mm per division clock when this gauge struggles to give repeatable readings.

Then I use the Multi-purpose Clock stand I made some while ago.

 

This has the advantage that it can be used to check verticals as well as flat items.

 

It also doubles as a height gauge thanks to Ketan.

The handwheel provides a fine and a coarse adjustment just by pulling the handwheel out or pushing it in.

Or

Regards

Gray,

[Bo’sunParticipant @bosun58570]

Just as Graham shows, a height gauge does the job (if you have one of course).  Although on a small surface plate, things might get a little congested.  With the right accessories, my Rabone vernier height gauge works fine.

[Rod RenshawParticipant @rodrenshaw28584]

All good stuff above, but also note that most simple surface gauges supplied with a scriber can have the scriber removed and then the stem of a DTI can be inserted. The “universal joint” usually has 2 holes, one to suit the scriber and one to suit the DTI. See Nick’s second photo and Graham’s first photo.

[Robert Atkinson 2Participant @robertatkinson2]

The correct instrument for simple checks of a surface plate is a Repeat Reading Gauge A.K.A Repeatometer.
American Federal standard GGG-P-463C (google it) has details of proceedure and gauge

This alows direct comparisons between plates with different gauges.

Robert.

[Michael GilliganParticipant @michaelgilligan61133]

Please correct me if I am wrong, Robert

I seem to recall that American Federal standard GGG-P-463C applies specifically to Granite plates …

1. Does it really matter ?
2. Is there an alternative, for Iron Plates ?

The difference, of course, being that Granite only tends to get ‘digs and scratches’

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

DIY Repeat-O- Meter

https://youtu.be/ra727zZCMzk?feature=shared

MichaelG.

[FulmenParticipant @fulmen]

That’s awfully complicated compared to a surface gauge and a dial indicator, but I’m sure it’s all for a reason.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I can use my Chesterman height gauge with my DTI, but it’s a bit OTT for my little table.

However, my small surface gauge block, can be configured to low profile.

Regards Nick.

[PeteParticipant @pete41194]

It all depends on why your needing or wanting a surface plate. If your checking the flatness, parallelisum etc of anything, or scraping parts to a high degree of precision. Then no, that particular surface plate isn’t going to be good enough without it first being re-scraped against a known to be highly accurate master surface. Or using the very involved and labor intensive 3 plate method. https://ericweinhoffer.com/blog/2017/7/30/the-whitworth-three-plates-method Picking up and moving your magnetic indicator base for each measurement isn’t the usual recommended procedure either. Leaving out the use of that magnetic indicator base, then in general, it would be better to first ensure the plate and the base of the tool holding the indicator are almost surgically spotless, then slide the base around the plate. Checking flatness over larger areas is one of the harder things to do without the much more specialized and expensive equipment designed for the task. And that Suburban Tools video explains why quite well.

Now if your only intending on using it for marking out, it would be fine, or at least good enough. Even a thick piece of what’s known as float glass as Dave and Gray already mentioned can fill in for a surface plate for general marking out if needed. So it really depends on your level of accuracy and what your doing with it that dictates what may or may not be good enough. Highly accurate, rigid, repeatable and yet cheap usually doesn’t happen. And most items that might be used on a surface plate will have the base built from cast iron and not hardened steel. The coefficient of friction with cast iron on cast iron is far less than steel against cast iron, and it’s much less likely to scratch or damage a surface plate. For checking anything made from softer metals, aluminum, brass, or if there hardened, it’s also better to slide the gauge around the part than slide the part around and under the gauge. Personally, I don’t think a magnetic indicator base is anywhere large enough or probably even close to flat enough for use on a surface plate. The tools stability and known repeatability while rigidly holding an indicator are everything for accurate measurements or test checks.

Pre owned surface gauges such as the one’s in Nicholas’s and Grahams pictures can be picked up quite reasonably from used tool sellers or places like Ebay. It’s extremely important that the working surface of there base is still flat and does not show any evidence of rocking though. Slight rust pitting will have no real effect, flat is much important than perfect aesthetics. Commercial snugs are available that can be used to adapt most DTI’s or plunge indicators to those SG’s. Again it depends on the indicators design, and especially so for dti’s. My Mitutoyo dti’s are easiest to use with a dovetail clamp. Most of the cheapest snugs will be made using injection molded plastic and are I think a poor substitute for metal. Or shop made versions aren’t too difficult to design & machine. https://www.glue-it.com/homemade-tools/old-snug-new-snug/ Most SG’s that are similar to the Starrett, B & S or other surface gauges will also have that built in adjustment in the base that’s used to then help zero the indicator on the part. That to me is an extremely important feature to have. At one time many apprentices made there own surface gauges, so machining your own version certainly isn’t out of the question. And with a few simple additions, these SG’s can also check squareness that’s also something important. https://www.instructables.com/Modifying-a-Surface-Gauge-for-Squareness-Measuring/ But you’d still need an accurate surface plate as your first reference surface to use it properly.

 

[Nicholas Farr]

On Nicholas Farr Said:

Hi, I can use my Chesterman height gauge with my DTI, but it’s a bit OTT for my little table.

However, my small surface gauge block, can be configured to low profile.

Regards Nick.

Clearly, I’m not the only one with a VHG that can be too large for a small plate.  The small surface gauge here looks similar to one I bought from Tracy Tools for around £12.00.  Maybe not a Starrett, but excellent for the price (or was I just lucky?).  Some fettling with a stone to smooth the sharp edges and it works as expected.

[Michael GilliganParticipant @michaelgilligan61133]

Best summary I have seen, Pete !

Thanks for sharing your wisdom so concisely.

MichaelG.

[Michael Gilligan]

On Michael Gilligan Said:

Please correct me if I am wrong, Robert

I seem to recall that American Federal standard GGG-P-463C applies specifically to Granite plates …

1. Does it really matter ?
2. Is there an alternative, for Iron Plates ?

The difference, of course, being that Granite only tends to get ‘digs and scratches’

MichaelG.

That standard was used because it has details of the measurement device which is the same for all plate types.
The standard for cast iron plates, GGG-P-453A does not include details of the gauge.

Robert.

[Robert Atkinson 2Participant @robertatkinson2]

The key difference between a repeat-o-meter and a marking out base or height indicator is that it has 3 defined points of contact rather than a flat base. Tne classic amicrian design is 3/8″ diamleter “feet with the single being spaced 5″ from the pair. The moving measurement contact is also 3/8″ and spaced 5” from the single foot.

[Neil LickfoldParticipant @neillickfold44316]

I went and radius the edges of the magnetic base, and then lapped it flat on some glass and lapping paste. Then blued it against a granite plate. I carefully went over a piece of 2000 grit wet dry paper sitting on the surface plate. It works very well. I use the now nicely finished mag base more than I use the marking out gauge. I did pick up a damaged Mitutoyo height gauge for a price I could not turn it down. Repainted it and repaired the housing. It is a lot taller than what I actually need, its 600 mm high. I finished the base of that the same way. I found that if it is too smooth, it is actually quite draggy on the surface plate. So I wiped it on  the 2000 paper at 45 degrees cross hatch and made it really nice. It takes time to make things right. Another option is to scrap away some of the area in the centre of the rail and making it being firm of the outer edges. I also have a round block of cast iron that was faced and flattened. I use the small Noga stand on that piece and works really well. It only runs of the outer 10mm or so with the centre being relieved.

Granite reference plates are at a very reasonable price for something around 300mm X 450mm and around 82mm thick. Mine is to the American A grade standard with the max error of 2.5um between the 2 planes. It is flat enough for my home shop and was around 230NZD or about 115 pound. You pay about 4x the price for an AA reference plate of the same size. The workshop B grade plates are not that much cheaper than a A grade granite plate out here. I am sure that these cheaper granite plates are all in from China.  I have not priced a Rahn AA surface plate like at work. I expect it to be at least 2x that of the far east stuff maybe more.

Keeping the plate very clean is essential and there are many types of granite cleaners out there.  I use a waterless cleaner. You can use naphtha and acetone mixture, but don’t like the fumes of the acetone.

Sometimes I use a piece of rice tissue paper between the gauge and the plate, especially when moving it around a part for checking. If I am marking out, I put the part on the tissue paper, so that it keeps the plate clean. Also allows the part to slide easier, like if its mounted in a toolmakers vice or mounted on an angle plate etc.

Keeping the over hang or over reach to a minimum is very important when trying to get the best from what you have. Using low pressure measuring gear really helps if you are looking for small amounts. Get an indicator on the end of a bar and have it out 100mm. then put a 40 gram magnet on the bar . It is surprising how much things move/deflect with not much weight on them.

Neil

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Bo’sun, I got my small one at an auction, which was bundled together with what was termed a miniature engineer’s vice, which was a cheap small die cast thing, although has come in handy a few times, and they cost me £10.00, but at the same time I got two solid angle plates with just one rib, one being 3″ x 3″ x 3″ and the other 2″ x 2″ x 2″ which cost£15.00, also a small bench mounted hand drill for £15.00, with an inclusive premium of £2.40 for the lot. There is no name on my surface gauge, but it has the same specs as the Eclipse model 100B with a 4″ and 7″ long spindles. That was back in 2004.

Regards Nick.

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