Inexpensive (cheap) Surface Plate

[Silvergoose]

Although I have had a Mill and Lathe for some time only since I 've retired have I found time to use them. I have built a wobble plate engine based on Elmer's design and found that it is a lot of fun along with being a challenge. I read the forum with great interest and admire the talent that I fear the young will never know.

But to the point of the post. I needed a surface plate, the granite plates while being time tested, proved to be a bit spendy. I did not want a metal plate, living in Arkansas were the summer months bring the "air you can wear" the metal would prove to be a pain to keep clean.

While driving home one afternoon, I passed by a monument company. I turned around and went in to ask about grainite. After explaining what I was looking for I noticed a few broken headstones. I asked about the stones. Most all had highly polished surfaces, at least on one side. Found a piece, broken. I bought the stone for $20.00. The stone is a bit thick at 8 inches, but warping will not be a problem. The usable surface is about 18 X 16 inches. The surface is smooth and for the work I am doing it will be perfect.

Just thought I would pass on some information, I ran a search, but could find any post for this, forgive me if you all have done this and it is old news.

Thanks for the forum and the vast wealth of information.

 

[kquiggle]

I think you are right in saying that it will probably work for you, but I would also caution that "smooth" is not the same as flat. Unfortunately, to really test for flatness you need a surface plate, but a couple of things you might try at a bare minimum:

- test with a straight edge steel ruler, with a light shining from behind; kind of a crude test, but will certainly show any serious issues
- if you can fit the stone on your mill, test it with an indicator while running the table back and forth (you will need to shim the stone to get the top parallel to the table surface)

Just a couple of things I can think of off the top of my head.

I had some small "surface plates" made for me at the local glass shop by having them cut some rectangles of thick float glass for me (any thick plate glass you buy nowadays is likely to be float glass). This is also not a true surface plate, but also good enough for the work I do.

 

[gus]

Surface Plare.
Here's mine -----a recycled but brand new Ingersoll-Rand Model 3000 Air Compressor Valve plate which is cast iron and lapped to flatness to function as valve plate with finger valves.
For the small jobs that I scribed, it meets my requirement. Along with it ,I bought a Starrett Digital Surface Gage. Same is M.I.C. (made in china).

The Webster,Rupnow,Namett-Lynx & Howell V-2 Engines were scribed with same surface plate.

 

[Theclockworks]

Had mine from Tesco cooking department £14.00 they say it's a chopping board but it's made of granite about 14x10 inch.

 

[Silvergoose]

Kquggle, You made a very good point about shiney vs flat. I checked the surface with a straight edge, result, no light. When checked on the mill table the result was still very good. For the model steam/IC hobby I feel this is in line. With my skill and equipment dealing in more than 4 decimal places is out of my realm.

Thanks for the input

 

[barnesrickw]

I used to pick up pieces to use for sharpening my woodworking tools. I would tape fine grit automotive sandpaper over them. I found them to be very flat. Just the same checking would be a good idea.

On a side note, I used to teach Geology, briefly, but I got some of my samples from a headstone company. Some had parts of names in them. Had a great deal of fun letting the students think I was a night time sample collector before letting them know the real origin.

 

[kwoodhands]

I think you are right in saying that it will probably work for you, but I would also caution that "smooth" is not the same as flat. Unfortunately, to really test for flatness you need a surface plate, but a couple of things you might try at a bare minimum:

- test with a straight edge steel ruler, with a light shining from behind; kind of a crude test, but will certainly show any serious issues
- if you can fit the stone on your mill, test it with an indicator while running the table back and forth (you will need to shim the stone to get the top parallel to the table surface)

Just a couple of things I can think of off the top of my head.

I had some small "surface plates" made for me at the local glass shop by having them cut some rectangles of thick float glass for me (any thick plate glass you buy nowadays is likely to be float glass). This is also not a true surface plate, but also good enough for the work I do.

I installed a new bay window in my sons home a long time ago. The window I removed was a jalousie window with 1/4" plate glass 4" x 16" . I saved 10 pieces , did not have a use at the time , to good to throw away. I glued sandpaper to the glass with the adhesive used to adhere sandpaper to a sanding disk. I have glass with 120 , 180, 220,320,400,600, 1000 and 1200 grit paper. I have a granite surface plate, 9x12 x2" thick. I use the glass for lapping mostly. One piece is used to set jointer knives. The glass is placed over the cutterhead slightly more than half way. The dull knives are removed first, one new knife installed at a time. Knife locking screws are snugged , should be able to move upward . Strong magnet is place on the glass, cutterhead is rocked for& aft til the magnet pulls the knife up to the bottom of the glass. Bevel should be flat against the glass. You will hear a "click" . Then tighten the rest of the locking screws. Repeat with the other knives. There is no need to find dead center as this method does it automatically.
I can do this quickly, 20 minutes or so. Expect to spend at least an hour the first time. I've been doing this for 51 years so I got a bit of speed.
mike

 

[Lloyd-ss]

Sink cut-outs and scraps from a granite countertop fab shop.

 

[Ghosty]

I went to a tile place and picked up a granite tile, good enough for what I need, not building rocket engines.
Cheers
Andrew

 

[TonyM]

I use a granite tile too. In fact I have two which I lapped together to make sure they were good.

 

[Mike Ginn]

I have a 24inch cast iron surface plate which is great but heavy and not easy to move. I mainly use a discarded 18 x 12 inch bathroom mirror 3/8 thick as my working surface plate. Easy to move around, very flat and has the added advantage that it lets me (often) see under the object I am marking.
I recommend a mirror - cheap and easy to replace. So far it has lasted 20 years with only a few scratches but take care not to drop it!

 

[metalmangler]

I use a granite tile too. In fact I have two which I lapped together to make sure they were good.

I thought you had to lap three things together in order to ensure they were truly flat ?

 

[Mike Ginn]

You do need to lap 3 surfaces but what does "truly flat" mean? Everything has a tolerance or error bound, the key is to decide where you want to be in the flatness arena. I would suggest that float glass such as used for mirrors is good enough for model engineering work. In the same vane I use cheap ER collets and not those costing 10 times more. Model engineers have the benefit on not producing to manufacturing standards and have the luxury of making parts fit by being careful of the order of machining.

 

[Lloyd-ss]

edit ........................... Model engineers have the benefit on not producing to manufacturing standards and have the luxury of making parts fit by being careful of the order of machining.

Exactly !

For example: 2 parts don't fit properly. One part is easier to chuck up more accurately, so that is the one that gets machined. Easy choice. Now, just revise the cadd model.

 

[TonyM]

I thought you had to lap three things together in order to ensure they were truly flat ?

Thats true but it just depends on how far you are prepared to go to get something fit for purpose. I started out using a piece of thick glass until I broke it. I found some cheap granite tiles so I bought two. It took hours to get them to a stage where I was happy with them. I was not looking for perfection.

 

[Mike Ginn]

For me glass is a good way forward - but don't drop it! I have a wooden frame and backing on a 18x12inch mirror which I have used for many years without breakage. If you break it buy another!

 

[Steamchick]

I do not have a surface plate (yet) but often use the lathe bed or miller bed instead. - Adequately flat for my purposes.
I had an old flat mirror - but it broke when something fell onto it accidentally. It was in a frame with a thin sheet of wood behind it. I always stored it facing down so anything falling on it would not chip it... but what fell on it broke it completely...
I have used a piece of glass on a Formica work-top, with 600 ~ 1200 wet-and dry paper on top for lapping a 3 in. dia. motorcycle cylinder head and results were adequate. No obvious high spots seen on the abrasive paper. Marking blue from the glass transferred nicely to show the lapped surface on the aluminium head face....
Adequate for marking small model parts of an inch or 2 as well.
Check glass flatness with a rule and reflection... which should not be curved or have gaps. The eye is a pretty good judge.
K2

 

[Mike Ginn]

K2 Much easier to check for flatness if it is a mirror. The eye is a super sensor for flatness of a mirror!
Mike

 

[Lloyd-ss]

I was able to watch as an outside specialty house came in to update the calibration of all of our granite surface plates, including one monster that was 3 feet x 14 feet x 2 ft thick. It actually rested on 3 granite pillars on the concrete floor. (We had some big forklifts, but had to rent a bigger one to get that plate off the truck and into place.) The calibration process was pretty straight forward but it was also something where you could ruin a $30,000 plate in an instant.
They used an optical collimator to check the overall flatness of the plates,to make sure there wasn't any twist or dips, from end to end, etc. Then they had a device that looked similar to a height gauge base, about 2" x 6", with an arm sticking out of one end to make the total device be about 2" x 12". This was to check the local flatness. The arm had a stylus and gauge on the end of it so that as the entire device was moved around on the table, the stylus would indicate any dips or humps. Of course there never were any real "humps". And here is where the real skill came in. They had what appeared to be just a cast iron lapping plate about 18" square with 2 handles on it. They put a little diamond lapping paste in the appropriate place and pushed the lapping plate back and forth and around in some sort of pattern. They then cleaned it up with solvent and rechecked the spot with the small device again. Check...OK! New calibration certification applied and put on file. The process seemed quick and efficient, but not for a novice to even think about.
Lloyd

 

[jirvin_4505]

Usefull video describing how a plate was made diy