Surface Plate & Height Gauge recommendations

Seems a bit much to spend up big on a precision surface table to use it to run a digital height gauge over to scribe lines on jobs. The lines themselves are at least two thou wide and are generally just a rough guide. Final machining for anything precision is done by measurement during the machining process, not by machining to the line. If you are just machining to the scribed line, then you might as well just use a piece of glass or a bit of granite worktop or whatever as it will be close enough for that type of work.

As far as setting your sine bar or sine table goes, that is only as accurate as the milling table it is then sat on. So you might as well just use the mill table for the original set up.

And if you want to use a 10th of a thou dial indicator for measuring bearing roller diameters etc sat on a flat surface, you might as well use a much handier proper comparator stand with its own mini-surface table incorporated below the dial gauge holder.

But if you just want to buy a surface plate, rule of thumb is buy the most expensive one you can afford. Cheap will be cheap. Used will be used and possibly abused. Quality new will be quality new.

For the 8 clocks that I have made and the number of small steam engines. I have managed with a 6inch rule, a pair of dividers, a good loupe. and the dials on my Myford. ( My mothers dressmakers tape for pendulum lengths )

When I was an apprentice the use of the ratchet on a mike was frowned upon as well.

Roy

I spend my money on good Irish Whiskey, can,t do much better than that !

Now I know you're fibbing.

*Good* Irish Whiskey indeed. ​​​​​​

Whatever next? Quality import tooling?

I bought a few years ago a digital height gauge. One of the cheaper ones. About 1 weekend after using it a lot that weekend, wish that I bought the type with a hand wheel like Mitutoyo make. Did not need to be Mitutoyo but that type. My friend did pick up a brand new Mitutoyo for a rediculously cheap price, because they were no longer going to be stocking that model any more. Ahhhh

Sometimes you can spend more time getting what you want from inferior gear, and the right gear allows you to have Sunday free to enjoy a nice meal and glass of wine.

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If there's enough money left for a nice meal with wine, you haven't spent enough!

A proper Coordinate Measuring Machine is essential, not that old-fashioned Surface Table and Height Gauge rubbish. Golly, it's impossible these days for a Model Engineer to make anything without a Point Cloud.

Not your ordinary Cast-iron and Granite table CMMs mind, they're yesterday's carp. No, decent CMMs are made of Silicon Carbide and Ceramics. Put daughter on the game, sell drugs, mortgage the house and rob a bank. Only the best tools are good enough...

Dave

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SoD - I installed the mini-computer that ran an early 'CCM' at the Jaguar plant many years ago. It replaced a team of men with large (manual) height gauges and other devices who QA'd body shells taken off the line. The problem with the old system was that it took nearly a week to do the work and by that time a week of 'duff' body shells could have been produced (and possibly were occasionally).

The new system had a single multi-axis probe and the body shell was placed on a very (very) large slab of granite and the probe just moved manually about touching key reference points. It could be done in two hours in theory - at least when it was working. The system suffered from an unusually high number of failures, which didn't seem to upset everyone at Jaguar, as a 'downtime' rate had been negotiated for the operators before the table was installed.

The other service engineers where I worked all hated going there and I (being the Newbie at that time) often go the short straw. It wasn't possible to drive my Ford estate into the plant (well you could - but you might not be able to drive it out again) which meant dragging toolboxes and scopes from outside, right across the factory floor - which was some way. You then waited an hour or two for the electrician and his apprentice to arrive and change your 13A plugs over to factory 'standard' plugs so you could start work (I was not allowed to do this myself). When finished it was about another hour for them to come back and replace your 13A plugs before you could leave. When the manufacturer of the CMM system approached me to ask if I'd like to work directly for them - I declined!

Hopper - I think the Rotagrip plates are perfectly good enough for the majority of Hobbyist users and when/if they need to start making sure things are 'flat' (enough) - then they will already have the right tool available to check against. It's certainly not essential - but then many things available to us these days fall into that category...

Regards,

IanT

how about Welsh Whisky **LINK**

or even English **LINK**

There are quite a few English whisky makers, unfortunatley all rather expensive, so I'll stick to Scotch, preferably Islay

Work threw one in the skip last year - literally The Rennishaw touch probe was still attached but smashed up aginst the edge of the skip.

I splashed out on a granite worktop protector from Dunelm, 400 x 300 x 15mm cost £10 and for a tenner it is easily good enough for what I will be using it for, some occasional marking out and measuring and parts assembly that need a flat surface.

I havnt got a height gauge at the moment, currently looking for one and will probably go with a digital but I would be ok with a vernier type. Not having a height gauge yet I used the Mitutoyo Digimatic as accurately as I could to check out the plate. I placed a bar of silver steel across a pair of V blocks and measured the height at each end, I then moved the blocks and bar around to numerous positions on the plate checking against the original measurement. I was pleasantly surprised at how good it was, 80% of the plate was within 0.001" a couple of places towards the edges and corners 0.002" and one corner was 0.003".

I dont know if I have been lucky with a good one or if they are all fairly close.

Unless I've misunderstood what was measured I don't see that it tells you anything about how flat the plate is? If you put the rod and V-blocks on a large sphere and move it around the ends of the rod will stay at the same height relative to the surface.

Andrew

Thats not how I saw it Andrew, if I move the two blocks to a different position and one of the blocks climbs or lowers surely that would raise or lower the bar at the opposite end wouldnt it..?

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They're made on a surface grinder and as these out-perform milling machines by a considerable margin, there's a good chance ordinary products will be impressively flat. Grinding wheels are composed of millions of tiny cutting points, often artificial diamonds, embedded in a matrix. As grinding wheels can be dressed very accurately, and wear corrected with optical guidance, a typical modern CNC grinder can work down to about 0.5μm. A precision grinder does considerably better, achieving accuracy expressed in nanometres.

Although CNC surface grinders are widely used to make granite worktops I doubt operators pay enormous attention to getting best possible results out of their machines, and some might be using older/cheaper kit that doesn't correct automatically for wear. Nonetheless, output is going to be fairly good because the product has to have a high polish for cosmetic reasons.

It's another gamble. Potentially good, but no guarantee. Worktops and tiles haven't gone through the next stage of surface table production, which is accurately assessing and correcting flatness to a specification. Nor are they concerned with temperature stability or rigidity. Plate glass is in the same boat; it's made by floating hot liquid glass across a bed of molten Tin. As liuid Tin is naturally flat there's a good chance the resulting glass plate will be excellent. Unfortunately, as the production process isn't deliberately going for flatness, random glass as used in a workshop might not be the best. Most of the glass in my double glazing is optically impressive but I can find a few panes with small imperfections if I look hard enough.

I reckon Granite and Plate Glass are both fully capable of meeting my flatness needs, but I'm very much in the 'good enough' camp, with no need - so far - for accuracy better than ±0.01mm.

Grinding in industry is extremely common. I guess more metal is cut with grinders than any other sort of tool. Pity we don't have high-end grinders in our home workshops because the results are fast and accurate with excellent finish. Unfortunately the machines are big, expensive, take a lot of setting up and several might be needed in a line. Brilliant for mass-production, rarely sensible for us ordinary Joes.

Dave

Thanks Barrie for the video I will give that a try, I do have a test indicator not a tenths one but it is 0.01mm and I have some slip gauges so it should give some idea.

I had the bar over hang at around 20mm but the test indicator is a better way of measuring than the caliper I was using.

Thanks again

Ron

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Yes it would, if the two planes on which the V-blocks sit are parallel. One issue is that the movement of the end of the rod compared to the movement of the V-block is reduced by roughly the ratio of the length of the V-block compared to the rod. Which is rather unhelpful.

If the two planes on which the V-blocks sit are not parallel (quite likely if the plate isn't flat) then all bets are off, as the movement of one end of the rod will be influenced not only by the vertical movement of the V-block at the other end but also by it's tilt. Without other measurements it would be difficult to determine which effect was the cause of any movement of the rod end.

No idea where SoD got the statistic that grinding moves more metal in industry than anything else. Most of the machine shops I've used professionally over the years didn't have any grinding machines. Grinding is good for precision and high quality surface finishes, but it's a relatively slow process. As such it's to be avoided unless absolutely necessary. One of the factors driving the development of inserts that will turn or mill hardened steel was to avoid having to use grinders for finishing operations.

Andrew

I saw that video a while ago and used the same method to check out my piece of black granite worktop, hoping I could use it for scraping in some parts of a surface grinder.
Unfortunately it has dips of about 5 and 10 thou as well as ripples, and drops off at some sides, though it looks OK at first glance.

I did try a sheet of 6mm float glass on top to even out the dips, but found that heavy objects just bent the glass.
Next try was to make layered shims out of baco foil, but that didn't really work either.
I've now kept that for use as a clean surface on the bench and picked up a used 24" square cast iron plate locally.
This has a minor bit of rust staining, but for the most part, the original scraping marks are present.

Had I not found an affordable plate locally, the next plan was to use a different piece of unpolished quarztite worktop, and add some plaster to the top surface of it; whilst still wet, top it off with the piece of float glass, which would then be substantially supported and pretty flat. The trouble was, that I think the piece of new glass was actually warped by several thou because of the way it had been stored at the window shop prior to delivery.

The first job for the proper cast iron one was to scrape in the top surface of the main table, so I can use that as a portable surface plate to scrape in the main column.

Never really tried scraping before, and I'm very slow and not exactly good at it, but getting there eventually.

Stuart's Blue is the new woad for 2020.

Bill