# Small Cast Iron Surface Plate



## TomKro (Jan 18, 2015)

There's been a lot of talk about surface plates lately, so I thought I'd post a pic of my latest Craigslist find.  
It's a 12 x 12 plate in pretty decent condition.  It had a couple of tapped holes, which I wasn't crazy about, but for $40 and a short Saturday drive, I couldn't resist.





The first pic has my buggered up soft jaw sitting on the plate, but that's another story.
My only real point is that there's some pretty good old stuff out there, you just have to be patient if you're on a budget. 
I'm not poo-pooing low cost alternatives.  Sometimes folks just want to get this stuff out of their basement.


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## Ulma Doctor (Jan 19, 2015)

Sweet Pick!!!
Looks like it's in pretty good shape:thumbsup2:

don't be too concerned about the holes, a light stoning of the areas surrounding the holes will show any high spots.
if you are lucky enough to have a straight edge or something really flat , you could then see if there are any defects or high/low spots near the holes or anywhere else on the plate.
a parallel, 1-2-3 block, a large tool blank or other precision ground items could be utilized as well to different degrees of accuracy.

you could, if you were so inclined, to map and sweep the surface of the plate with a test indicator.
this will give you a pretty accurate survey of condition of the plate.
if you are lucky enough to have a friend with another known good ,flat plate you could blue up your plate and use his plate as a master. then re-scrape your plate to the master's flatness.
like this video:
https://www.youtube.com/watch?v=O2nyrSq0tY4

nice find
good luck!
mike)


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## visenfile (Jan 19, 2015)

Looks like a great find.  I would have grabbed it if priced right.


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## The Liberal Arts Garage (Dec 21, 2015)

Just another " Yes, but" . A foot square plate is a good aid with sandpaper to touch 
up  small parts, it's easy to re- flatten it when necessary. Don't "poison"  a good flat
piece of granite........BLJHB


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## Wreck™Wreck (Dec 21, 2015)

Why exactly do you need a surface plate at all?


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## TomKro (Dec 21, 2015)

Wow, this is resurrecting an old thread.  Forgot I posted it.

It could be used for measuring up small items, or could be used for a lapping plate.   It's best for taking pictures of small parts to provide the illusion of technical competence.  If he has a surface plate, he must know something... 

It would be used for a lot more if I didn't have it buried on my bench.  Total disaster down in the basement - and no time to pick up until after Christmas. 

Excellent timing as a reminder.  Tomorrow at work I have to help a co-worker re-set one of those fancy laser surface measurement arms.  Maybe I'll bring it in and see just how flat it really is. 

TomKro


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## Uglydog (Dec 22, 2015)

The Liberal Arts Garage said:


> Just another " Yes, but" . A foot square plate is a good aid with sandpaper to touch up  small parts, it's easy to re- flatten it when necessary. Don't "poison"  a good flat piece of granite........BLJHB



It's your plate.
Consider a piece of plate glass or a lapping plate and some Cottons. 

Edit: not "Cottons". Should have written "Clover" lapping paste.
I really enjoy lapping, something therapeutic about the process. I am fortunate to have been given a very large unused vintage lapping plate. Note: that's different from being good at it!


Daryl
MN


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## joshua43214 (Dec 22, 2015)

Wreck™Wreck said:


> Why exactly do you need a surface plate at all?



I think a better question for most of us would be, "why exactly do you need a quality surface plate?"

I have two of them. A small cheap one from Shars that I stick sand paper to and use as a lapping plate. It also doubles as a door stop, a gluing weight, and a base for my Sartorius balance. This in my mind is a perfect use for a small cheap surface plate and is a fine tool for the hobbyist who will need to lap or polish things flat from time to time.

I also have an 18" x 24" one I got on sale with free shipping from Enco. I do quite a lot of "cut to the line" and "drill on the mark" type of work, so it gets a decent amount of use. It does nothing my mill table would not do just as well, only my mill table is usually covered in a vise and swarf...

I think many of us can find a use for one. I think very few of us can get any worth from a grade A or AA plate though.


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## Wreck™Wreck (Dec 23, 2015)

joshua43214 said:


> I think many of us can find a use for one. I think very few of us can get any worth from a grade A or AA plate though.



Well said. during all of the years that I have worked in this business I have found that having gauge blocks in order to check your tools to be more beneficial in the long run. This may cost a bit more then a small surface plate

If ones hobby is throwing every part on a surface plate and painstakingly measuring it, then enjoy.

What is the point of having a high end  plate without the ability to set the tools, even if you own the most expensive Starrett height gauge available one would still stack the blocks at the desired dimension, remember that setting the tool to 0.000 at the base and then measuring a part 3.000" along the scale would impart some error. In order to measure such a part check it with a gauge block first, then measure the parts

Gauge blocks first, surface plates second otherwise an accurate surface plate is silly.


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## Andre (Dec 23, 2015)

Wreck, I'm not an admin, but please keep in mind very few of us here are doing aerospace work. If a guy wants a surface plate, let him have one. I have three, and a fancy Starrett height gauge to boot. Why? Because I got a Starrett 255 and a medium size plate (at one time) certified to 15 millionths for $50.

Lets say I'm making a ball bearing spindle, which I am in the process of doing now, and I want to make sure the spindle I just turned hasn't bent when my butter fingers dropped it. I'll use V-blocks and an indicator on a known precision surface plate. Sometimes you just need, or want one.


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## TomKro (Dec 24, 2015)

Hi Guys:   I think there's a real opportunity for sharing some knowledge here. 

  I'm a complete novice and figured I'd use my little $50 surface plate to check some measurements with a height gage, or scratch a few layout lines prior to putting in punch marks and drilling holes.   Wishful thinking on my part, as I don't have a real height gage yet. 

  When I think of lapping, I know one uses various compounds/pastes, but the only thing I've done is set fine emery cloth face up to clean up flat faces  (maybe just "precision sanding"?).   If using "paste" directly on an iron plate, how does one properly clean off the paste if you needed different grades of paste?  How do you prevent/minimize wear on the plate?  Also, aside from having the surface reground or hand scraped, how would an iron plate be "fixed"?  

  As to "setting tools",  I'm guessing this refers to using gage blocks for setting precise gaps from the table or some other part on a mill.  I don't have a working mill yet, but the only way I've seen anyone set heights closely was to slip a piece of thin paper between a part and the tool to grab the paper and zero a digital readout.   If someone were doing really precision work, do you actually set each tool from the bed of the mill to hold tolerances?   I'd like to understand the process, but best to use "little words", as I'm quite the novice. 

I hope you folks are better prepared for Christmas than I am. 
Time to get wrapping. 
TomKro


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## Wreck™Wreck (Dec 24, 2015)

Andre said:


> Wreck, I'm not an admin, but please keep in mind very few of us here are doing aerospace work. If a guy wants a surface plate, let him have one. I have three, and a fancy Starrett height gauge to boot. Why? Because I got a Starrett 255 and a medium size plate (at one time) certified to 15 millionths for $50.
> 
> Lets say I'm making a ball bearing spindle, which I am in the process of doing now, and I want to make sure the spindle I just turned hasn't bent when my butter fingers dropped it. I'll use V-blocks and an indicator on a known precision surface plate. Sometimes you just need, or want one.



I do not discourage the use of precision tools. I do not wish to see people spending money on equipment that they can not effectively use however.
Indeed, this is a hobby machinist forum for people that are looking for information or advice, purchasing an accurate reference surface before having the tools that would be used with such a device is putting the cart before the horse so to speak. You may have a "Certified" tool that will resolve to 15 millionths yet without a gauge of same or higher accuracy to check it against you really have no idea how accurate it is.
I was merely pointing out that a less expensive array of gauge blocks should be purchased before a surface plate.


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## joshua43214 (Dec 24, 2015)

TomKro said:


> Hi Guys:   I think there's a real opportunity for sharing some knowledge here.
> 
> I'm a complete novice and figured I'd use my little $50 surface plate to check some measurements with a height gage, or scratch a few layout lines prior to putting in punch marks and drilling holes.   Wishful thinking on my part, as I don't have a real height gage yet.


This is the typical way of using a surface plate. You can do work of near identical quality with nothing more than a mill table and a caliper. If you watch some videos of people on YouTube, you will very commonly see them using a dial caliper for scribing lines. Purists will balk at such mis-use of a caliper because it will eventually ruin the tools ability to measure accurately. I use a cheap dial caliper for this purpose myself, and it is the same caliper I keep at my mill or lathe for making rough size checks. It has fallen to the floor countless times, and no long is trustworthy for measurements under 0.003". The old school method that is probably the most accurate method for scribing lines is to use a flat bottomed scriber on top of a set of gauge blocks on a surface plate. In this era, scribed lines are mostly a sanity check to make sure we are not milling past the line, and we use a DRO or the handwheels for actual positioning of the cutter.
BTW, center punching by hand has it's own set of problems. It is almost impossible to hold and strike the punch vertically, and you end up with a dimple around the punch mark that is taller on one side than the other. This little dimple will flex a small drill and cause the hole to start in the wrong place, drill off at an angle, and often break the drill. There are ways around it, but do not assume that center punching will always give you good results, usually you will get results just as good by using a spotting drill and hitting scribed lines by eye.



TomKro said:


> When I think of lapping, I know one uses various compounds/pastes, but the only thing I've done is set fine emery cloth face up to clean up flat faces  (maybe just "precision sanding"?).   If using "paste" directly on an iron plate, how does one properly clean off the paste if you needed different grades of paste?  How do you prevent/minimize wear on the plate?  Also, aside from having the surface reground or hand scraped, how would an iron plate be "fixed"?


Properly, lapping is done as you describe with lapping compound on a lapping plate. Lapping compound should not be used on a surface plate, and never should be allowed near a cast iron surface plate. The compound embeds in the iron and can only be removed by surfacing the plate. Lapping plates have groove cut in them and wear over time. Dressing the plate is part of maintenance, and done by grinding/scraping. If you have three plates of equal size, they can be lapped to each other until all three plates are flat. Many of us use small granite surface plates with sand paper as "lapping" plates, and call it lapping even though properly it is just flat sanding.



TomKro said:


> As to "setting tools",  I'm guessing this refers to using gage blocks for setting precise gaps from the table or some other part on a mill.  I don't have a working mill yet, but the only way I've seen anyone set heights closely was to slip a piece of thin paper between a part and the tool to grab the paper and zero a digital readout.   If someone were doing really precision work, do you actually set each tool from the bed of the mill to hold tolerances?   I'd like to understand the process, but best to use "little words", as I'm quite the novice.
> 
> I hope you folks are better prepared for Christmas than I am.
> Time to get wrapping.
> TomKro


Short answer - it depends...
Generally, the way we work is to make a test cut and measure, then adjust. For instance, to mill a part exactly 1.000" thick, I would mill it slightly over sized, measure, then adjust the cutter down to reach the final dimension. This is much more reliable that trying to set a reference from the table top, and takes into account things like expansion from heat. I was milling a piece of aluminum the other day. I milled it to near finished height and took a break for the night. When I returned the next day, I found the cutter was slightly too high to scratch the work even though I had left it all set up from the night before. When my mill head cooled down, the quill actually got shorter by just enough to raise the tool away from the work. The work itself might have contracted a bit over niht as well, but it was very cool to the touch when I quit for the night.

I use gauge blocks constantly, far more than I ever expected to when I purchased them. I find them invaluable for setting stops and for making quick go/no-go measurements.
I am in agreement with wrecks on this topic. gauge blocks are far more useful and valuable than surface plates, and a surface plate and height gauge are wasted with out blocks to set the gauge. I do suggest getting a cheap class B 9"x12" plate for "lapping" and the like. If you wait for an Enco 20% off and free shipping coupon, it will run you about $35.00 to your door. If you find you are using it a lot for measurement, then get a bigger one. If you are not using it much you have not lost out very much cash, and it will eventually find some other use. No need to buy a height gage, just get blocks and grind a 1/4" HSS tool blank into a scribe. You won't be able to fit a height gauge on a small plate easily anyway. Get economy blocks to start with, you can always verify the set up with a micrometer and if you end up to a lot of very precise work, they can be put to use for machine set up and a nicer set purchased for metrology. They should be considered consumable tools in any case.
I found I was using my plate a great deal, so I purchased an 18"x24" Class B plate. My work is just fine enough that I could probably use a class A plate, but it is not worth the added cost, and I doubt even my nice Taiwan machines would hold those tolerances anyway.


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## T Bredehoft (Dec 24, 2015)

I know my cast iron table saw table is not FLAT, but it's good enough for any layout work I want to do. I can mount an indicator on a (what do you call the thing with the movable arm and four pins that holds a scribe or an indicator) that thing and compare a dimension to a stack of Jo Blocks.  I have two laps, both about 3 inches across, which I use to  make a flatish surface a bit flatter, but only for appearance sake.  I spent 28 years as a tool and die maker and have no expectations that I need to work in tenths (.0001's) I can hit ±.0005 on any of my machines, and that 's good enough for me. No surface plate, no granite, not even a piece of plate glass. Don't need 'em. My opinion, you may need a surface plate.


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## Wreck™Wreck (Dec 24, 2015)

T Bredehoft said:


> I know my cast iron table saw table is not FLAT, but it's good enough for any layout work I want to do. I can mount an indicator on a (what do you call the thing with the movable arm and four pins that holds a scribe or an indicator) that thing and compare a dimension to a stack of Jo Blocks.  I have two laps, both about 3 inches across, which I use to  make a flatish surface a bit flatter, but only for appearance sake.  I spent 28 years as a tool and die maker and have no expectations that I need to work in tenths (.0001's) I can hit ±.0005 on any of my machines, and that 's good enough for me. No surface plate, no granite, not even a piece of plate glass. Don't need 'em. My opinion, you may need a surface plate.



Exactly, one may do perfectly awesome work without a surface plate, gauge blocks are inexpensive and far more useful when actually making parts.

A hobbyist would be well served purchasing blocks before buying a surface plate.


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## JimDawson (Dec 24, 2015)

For most layout work I just use my mill table rather than digging out my surface plate, which hides under my toolbox in a protective box.  Rarely do I actually use the surface plate.  The only reason I even have one is because it was a good deal, nearby, and I didn't have one.  Another Craigslist find.


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## Ulma Doctor (Dec 24, 2015)

My plates are used for scraping references and inspection 

I didn't spend a lot of money on them, but it did take some time to find nice ones, all craigslist deals.
They get used very frequently.


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## TomKro (Dec 26, 2015)

Thanks to all for the lessons in proper use and care of these tools.  

Dumb luck on my part, but I haven't done anything to the 12 inch cast iron plate to cause any damage.  I'm still interested in trying to determine if it's reasonably flat (primarily just curiosity), so I think I'll use a ground flat bar and feel my way around the top of the plate to get an idea if it has any problem areas.  For me, it's just an itty-bitty layout table, so it should work for anything I might do in the near future.   I am truly amazed at the accuracy in measuring that can be performed with these simple tools - in the proper hands.     

Thanks also for the guidance on the proper order of purchases.   Good guidance as to getting an inexpensive set of gage blocks for layout tools.   I think I'll also look for an intermediate size "sanding base" - something a little bigger than the back of the vise, but handier for moving around than a heavy plate.  

I hope everyone had an enjoyable Christmas.

TomKro


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## Wreck™Wreck (Dec 26, 2015)

Uglydog said:


> It's your plate.
> Consider a piece of plate glass or a lapping plate and some Cottons.
> 
> Edit: not "Cottons". Should have written "Clover" lapping paste.
> ...


Have you ever used a round lap when making bored holes to .0005 diameter or better?  If not be assured that it is one of the most tedious chores that you will ever do in life. The Clover brand lapping compound is excellent however, well controlled grain size from batch to batch.


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