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How badly do I need a surface plate?

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andrew lyner21/07/2019 10:34:39
117 forum posts
1 photos

I have watched a number of YouTube movies showing how to improve the various 'flat' surfaces on a mini lathe. They mostly seem to involve a surface plate, which is not a cheap item.

What is the alternative? I do have a number of thick steel plates. Would that be a good place to start - or perhaps some glass? Failing that, I guess I could start with the 'best' surface that's on the lathe and use that as a reference. Is that easy to measure? I have a budget dial indicator to help me.

Many people must have improved their mini lathe performance. How have they done it?

Edited By andrew lyner on 21/07/2019 10:35:23

Michael Gilligan21/07/2019 10:54:28
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13780 forum posts
599 photos

A decent piece of 'Float Glass' is probably your best bet.

MichaelG.

Mike Poole21/07/2019 10:59:04
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2038 forum posts
47 photos

Many people have used plate glass as a surface plate, float glass is pretty flat as well but will actually have a curve of 8000 miles radius which would be near impossible to measure and certainly of no consequence to normal model engineering, for all practical purposes it is flat. Some care needs to be taken on supporting the glass as it can be distorted if heavy items are placed on it when it is poorly supported.

Mike

Bizibilder21/07/2019 10:59:33
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60 forum posts
7 photos

The old favourite is a piece of plate glass which is flat enough for amateur use as a surface plate. A modern alternative is a polished granite cutting board - under £20 from a well known auction site and many supermarkets. I checked mine with a new good quality 300mm steel ruler and feelers - I cannot get a 1.5 thou feeler between the ruler and the board in any position. More than good enough!

Nicholas Wheeler 121/07/2019 11:08:10
266 forum posts
16 photos

I didn't do a lot to my mini-lathe, but bluing the sliding surfaces and gently removing the high spots made a huge improvement. Pinning the gibs and aligning the lead screws is a good idea and takes no time.

the bearing mods for the screws are worthwhile.

A cam lock for the tailstock is necessary if the lathe is old enough not to have it already

jimmy b21/07/2019 11:11:02
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500 forum posts
28 photos

I have had a variety of granite work top off cuts over the years.

Finally treated myself to a 450mm x 450mm x100mm one a couple of years ago.

 

It appears I now use all of them to gather dust........

 

Jim

Edited By jimmy b on 21/07/2019 11:11:20

Barrie Lever21/07/2019 11:20:51
323 forum posts
1 photos

Once you own a surface plate or surface table you will wonder how you got on without one, look on Ebay for a good condition second hand item.

I purchased a second hand high quality Swedish made granite table 900x600x100 thick on a stand for £360.00 on Ebay.

B.

ChrisB21/07/2019 11:25:44
392 forum posts
162 photos
Posted by andrew lyner on 21/07/2019 10:34:39:

I have watched a number of YouTube movies showing how to improve the various 'flat' surfaces on a mini lathe. They mostly seem to involve a surface plate, which is not a cheap item.

Do you mean scraping? If so I think you would need a proper surface plate, but then again it all depends on the level of precision you're trying to achieve.

I use a piece of granite worktop, a 0.05 feeler will not slip under a straight edge - good enough for my needs, but could be way off for someone else.

Tony Pratt 121/07/2019 12:26:47
882 forum posts
2 photos

Never fancied the glass option & you can pick up decent surface plates fairly cheaply.

Tony

Pete Rimmer21/07/2019 12:38:51
395 forum posts
18 photos

Glass and granite worktops are fine for marking out, but not much good as a reference surface for scraping. The main reason is that whilst it MIGHT be flat enough it almost certainly isn't and then any bend twist or dish that's in the plate will be scraped into the part.

Edited By Pete Rimmer on 21/07/2019 12:39:06

Michael Gilligan21/07/2019 12:53:56
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13780 forum posts
599 photos
Posted by Pete Rimmer on 21/07/2019 12:38:51:

Glass and granite worktops are fine for marking out, but not much good as a reference surface for scraping. The main reason is that whilst it MIGHT be flat enough it almost certainly isn't and then any bend twist or dish that's in the plate will be scraped into the part.

.

Pete [and Tony]

Doubtless you are correct ... but Andrew was quite specific when he asked:

I have watched a number of YouTube movies showing how to improve the various 'flat' surfaces on a mini lathe. They mostly seem to involve a surface plate, which is not a cheap item.

What is the alternative?

[my emphasis]

.

Incidentally: I have three small 'proper' surface plates [all secondhand, and far from pristine] two iron and one granite ... but the flattest thing I own is an 'Optical Flat' made of [you guessed it folks] Glass.

MichaelG.

old mart21/07/2019 13:49:32
433 forum posts
42 photos

At the museum we now have two plates, the first one is a 12" square of float glass stuck onto a 14" square piece of chipboard with some 1/4 round beading glued round the edge. It does the job admirably , especially for small jobs.

The second is a 2 foot square surface table which I bought on ebay for £50, which I collected from about 30 miles away, it just fitted in the back of my Corsa. It is heavy, my left arm is still bad after four months.

I have no plans to retire the glass plate because it is still very useful. If anyone gets a glass plate then I recommend not sticking it down too permanently, as it can then be turned over when the first side gets scratched. I had the cross slide of the lathe on the glass sitting on two 123 blocks. When I lifted the slide off, one of the blocks stuck to it and then fell 6" onto the glass without breaking it. It took a chip out of the glass surface, the plus side of this is there can be no burrs unlike a cast iron surface would have.

Paul Lousick21/07/2019 13:59:23
1149 forum posts
492 photos

You can make your own surface plate for little cost and a lot of elbow grease useing the 3-plate method of lapping the plates. See link below. (other examples of this method on the web)

Paul

Surface Plate

andrew lyner21/07/2019 14:08:44
117 forum posts
1 photos
Posted by Paul Lousick on 21/07/2019 13:59:23:

You can make your own surface plate for little cost and a lot of elbow grease useing the 3-plate method of lapping the plates. See link below. (other examples of this method on the web)

Paul

Surface Plate

Many thanks for all those thoughts from everyone. Much appreciated, as usual.

I did consider the Three Plate method aamof, as it was mentioned in the Optics part of my Physics degree course. The lecturer (decades ago) seemed to imply that it was done by ancient old technicians in long brown coats and that it took days and days (he was talking about optical flatness of course).

I guess it would have the advantage that I could sell one or two of the resulting plates.

A cheapish solution seems to be the way to go. After all, it I get more fussy as time goes by, I can always step up in cost and quality.

Michael Gilligan21/07/2019 14:35:36
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13780 forum posts
599 photos
Posted by andrew lyner on 21/07/2019 14:08:44:

A cheapish solution seems to be the way to go. After all, it I get more fussy as time goes by, I can always step up in cost and quality.

.

yes

SillyOldDuffer21/07/2019 15:16:53
4587 forum posts
980 photos
Posted by Barrie Lever on 21/07/2019 11:20:51:

Once you own a surface plate or surface table you will wonder how you got on without one, look on Ebay for a good condition second hand item.

I purchased a second hand high quality Swedish made granite table 900x600x100 thick on a stand for £360.00 on Ebay.

B.

Not in my workshop! I feel it would be a waste of space and £360. I'd cheerfully buy one if it was going to be used, but I rarely need such a thing. If Andrew only wants one to sort out his mini-lathe, that's big money for one job.

When I need a flat surface a lump of kitchen worktop is generally 'good enough' or a sheet of float glass when better is needed. Float glass is close to being optically flat. The main disadvantage of worktop and glass sheet is they bend when overloaded, so care is needed in use. (Bending is probably the reason why the stands used to support granite plates are 2x or 3x more expensive than the plate itself.)

For precision work a surface plate must be calibrated. Read all about it here. More expense!

My main reason for needing a flat surface is to transfer a position accurately from one object to another with a scriber block or height gauge. Doesn't happen often. I can't remember ever needing to make a flat surface flatter than can be managed by my mill or by facing-off on my lathe, so scraping is off my agenda. Ignorance is bliss - am I missing any other uses for a surface table?

Dave

pgk pgk21/07/2019 15:59:40
1425 forum posts
278 photos

I freely admit to being a 'that's good enough' hobbyist and figure if the mill table isn't flat enough for reference then I'm in trouble. I'd like a surface plate just because I like tools but it'd be second to wanting other stuff more.

Maurice21/07/2019 17:09:05
443 forum posts
50 photos

I can recommend the use of a piece of plate (or float) glass as a surface plate. To avoid the possibility of it bending under load, or indeed to make it stronger, the advice used to be to bed it on a layer of pitch. This stuff always remains a liquid, albeit a very viscous one, and will flow out to support the glass right across its surface. If buying a piece from a glass dealer, then for a modest charge they can remove the sharp corners and polish the edges.

Maurice

Barrie Lever21/07/2019 17:43:12
323 forum posts
1 photos

Dave

We have discussed before about your luddite tendencies !!laugh

I did say you would wonder how you got on without a plate or table before you had one, seeing as you don't have one then how would you know?

OK robust ribbing over !!

Granite table and plates do not suffer from bending and flexing in the same way as a cast iron plate, you can read up about that.

The problem with glass is that is way too flexible, it really conforms to what ever it is mounted or placed upon. Over a very long period of time glass also flows out, an old window is thicker at the bottom than it is at the top, maybe not too much of a problem for a plate but the flex definitely is.

I have used the granite table for a whole host of tasks that I never envisaged, the latest one being to reset the mirrors in my crappy Chinese laser cutter when the tube was replaced. Placing the laser cutter on the table is a good starting point in setting the mirrors, When not being used I have a wooden cover that enables the granite table to be used for other tasks.

I have also said to you before that because the item (granite table in this case) is good quality and well looked after I can get my £360.00 back anytime that I want or need it as someone will buy it.

So what is there to loose?

Best Regards

Barrie

mechman4821/07/2019 18:00:37
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2432 forum posts
372 photos

i have used float / plate glass & either are more than 'flat' enough for marking out. I presently have an polished marble off cut ( sink cut out ) from a kitchen fitting firm, free gratis! Just went in & asked the foreman & after a short explanation of what I wanted it for, he produced a 18" x 18" x 1" piece; ran a digital dti over it & only a .001" fall off at one corner with slight chip on same corner, does fine for me.

George.

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