Appropriate size surface plate to buy?

G'day guys, I guess this is stupid question of the day time

I'm about to buy a surface plate and am not sure what size to get. Obviously "bigger is better" but it could come at a price. The size options I'm looking at are (in metric) 400 x 300 x 70 mm at 46 kg or 630 x 400 x 100 at 93 kg. Both are specced 00. At first I was just going to get the larger one, however once I actually saw the area it would take up on the bench I started to wonder about the amount of real estate it was going to take up! The weight is also a significant point as I would like to keep it as level as possible for balancing things in addition to spotting/measuring and it sits on an MDF bench that may sag slightly with sustained weight (I've had that happen before and that was just a 25 kg vice!). Installing and moving anything over about 40-50 kg just becomes a bit of a PIA by myself in my book, getting a 93 kg into my little Alfa sedan, home, and installed by myself could be interesting just in itself ... the joys of being a scrawny weakling

The purpose at the moment for it is in renovating/restoring a SB 9" lathe. I've heard some say even a 9 x 12" plate is enough, others say no you will need a larger one to construct/maintain straight edges to do the bed. Once the lathe is finished I will be installing a (small for you guys) Sieg X3 mill and will probably go over that also when I get it. Other than that, these would be the largest machines I could imagine working on and the parts I make and measure are generally quite small.

I'm starting to lean towards the smaller plate if it will do the job, and figure I can always sell it on ebay if it turns out to be just too small but thought I'd ask you guys for some expert opinions.

Thanks for the help.

Pete

Figure the diagonal, the longer the better for checking long straight edges.
Harry

You are correct in your own assessment -- larger is certainly better in this choice, if you can make the initial sacrifices to get the larger size. I find that there are always additional things to use the surface plate for, such as keeping important papers off the floor, making sure that every measuring tool that you own ends up on the plate simultaneously, and functioning as a tramp oil magnet for most of the activity in the shop. :-)
All kidding aside, buy the largest one you can deal with. You will find many additional ways to use it. If you are not overly concerned about never doing anything that carries any risk to the surface, a granite plate is a marvelous assembly table for precision mechanisms that need to be aligned well.
If you buy the small one, you'll end up buying the larger one anyway and keeping the small one as well...

Ok thanks guys, I appreciate your input. Based on what you've said, a possibility I'm now considering is to weld up a dedicated stand for it with castors and also 3 leveling feet, the idea being that it will sit over against the wall leveled for incidental jobs but can be dropped down onto the castors and wheeled out and leveled free of obstructions when I have bigger projects. Indeed if I enclose and put drawers in the frame it would probably make a logical place to store the associated measuring gear.

Now just to con my ever-loving wife and unsuspecting niece into giving me a hand to get it out the car

Just to clarify then, a 630x400 is roughly 750 diagonal and as I understand it you can check straight edges slightly longer than the plate and still be valid? Up to 1000mm? BTW sorry this is all metric. A straight edge that length would be long enough to do a SB 9" lathe bed?

OT, but at the moment I'm away for work but FINALLY managed to find what I think is a "proper" scraper. I know that probably sounds like no big deal for you guys up in the US who can basically wander into the local 7 Eleven and buy them by the dozen, but down here in Oz they certainly seem to be difficult to get! The brand is Elora eg http://www.bloomertool.com/BearingScrapers.html 200mm Blunt Bearing Scraper, is that likely to be ok?

Thanks again for helping out. Guess now nothing for it but to get home and practice.

Cheers,
Pete

I'm not going to comment on the surface plate size, however I wish to point out that you can make your own scraper pretty easily. Just buy some carbide blanks (or scrap), and either braze or bolt them to a piece of flat steel stock. An old file would work for that. Add a nice handle, and sharpen away.

Allied carbide spade drill inserts can easily be converted into dirt cheap scraper blades with a green wheel and some patience. You can get assorted packs of 30 of them used for $9USD on ebay. That comes out to like $0.30 per blade.

That one probbably is not carbide
Best choise is a carbide tipped one And I like mine a bit longer
It is easy to make your own by brazing a piece of carbide on some piece of flat. I think a piece of a springleave would do for that
But then you have to grind it into shape and keep it sharp
So you also need a diamond grinding wheel and for best also a daimond lapping wheel

Good luck

Peter from Holland

keeping important papers off the floor, making sure that every measuring tool that you own ends up on the plate simultaneously, and functioning as a tramp oil magnet for most of the activity in the shop. :-)

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ROFL

What ever you get make or buy a good strong cover 'cos that's what it'll spend most of the time doing

Everything specfab said is absolutely true... in my case anyway. It is also why I now have two surface plates, the second one larger than the other. You may find that the clutter will migrate to the larger plate which will leave the smaller one free for actual work

BTW sorry this is all metric

Click to expand...

Then why not call it an "SB 228.6 lathe" then to be consistent?

I would go with the larger plate (roughly 24" X 16" X 4"). My smaller plate is 24" X 18" X 4" and I have found that to be a very handy size. It is the same size we used in one of Forrest Addy's scraping classes a couple of years ago and was adequate for ten of us to do our work on.

The mass you give works out to a density of about 3.7 g/cm³ which is a bit high for granite. It should be closer to 69 kg bare. Granite averages 2.75 g/cm³.

A very handy accessory for your plate is a granite "knee" or right angle for spotting right angled surfaces.

-DU-

David Utidjian said:

Then why not call it an "SB 228.6 lathe" then to be consistent?

-DU-

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The lathe is stuck in 1969 when it was named and made, I, and most of the rest of the world, have moved on. :P

The stand you build would be better with four feet if you use it for storage. What should be on 3 points is the plate itself.

The larger of your sizes does seam to be a pritty std size. Whilst biggers always better some thing in the 24" * 16-18" does seam common. A cover being the std method to return it back to bench space tool.

If you can find a good deal on an even larger surface plate, I'd recommend you consider it. I have a 24x18 plate, which I was always struggling with. i.e. when you fill up the diagonal, you will have a hard time measuring the top surface for parallel with an indicator. My last scraping project was the headstock for a Deckel fp2 mill, which has ways that are about 28" long. However, the reference for horizontal was the quill, which extended another 10-12". I wanted the ways to end up parallel with the quill within reasonable limits (.0002" over the length of the ways), and it was a measuring nightmare. I bought a larger surface plate (24x36) and resolved the problem easily to my satisfaction, but lots of time was wasted working at or beyond the limits of the small plate. The large plate was a bargain (surface plates aren't exactly hot sellers, so it can work to your advantage), had a recent certification as an AA grade plate, and came with a large steel cabinet to store metrology tools.

Pete, three things:

1. I picked up my plate yesterday, its 500 X 400. It's already too small, but I was able to lift it out of the car and onto it's stand easily, and I am no hercules. 4" thick, to mix dimensional metaphors.

2. Make a wood cover for it to regain bench space. There was a thread about this a couple of months ago. (One of the covers prompted feelings of inadequacy about my own woodworking skills)

3. I will send you a carbide scraper...Forrest is sending me enough carbide to braze up a couple extras for fellow travelers on this almost forgotten path. You'll need to organise some kind of diamond sharpening wheel and also a lapping wheel.

Greg

Pete:

This does not answer your question about size of a surface plate. But if space is a serious issue like it is with me here is an idea.



I bought a 9 x 12 surface plate, cut a hole in the workbench and "inlaid" the surface plate.
It is always there but never in the way. I use it all the time.

I also have a larger surface plate that is stored away. I get it out about one time a year.

Hey...John welden: I should have posted a better pic of my inlaid surface plate.
It does rest about a 1/4" above the bench surface and cleans easily. The gap between the surface plate and the bench is sealed with silicon calking to keep small tools and dirt from falling between the gap. Thanks for pointing that out.

Jim

JimGlass said:

Pete:

This does not answer your question about size of a surface plate. But if space is a serious issue like it is with me here is an idea.

I bought a 9 x 12 surface plate, cut a hole in the workbench and "inlaid" the surface plate.
It is always there but never in the way. I use it all the time.

I also have a larger surface plate that is stored away. I get it out about one time a year.

Jim

Click to expand...

I feel that your surface plate should be above the work surface of the bench to make cleaning easy. I've never seen a kitchen counter top with a lip on it, same idea for the surface plate.

Hey thanks for the help guys, and the carbide Greg!

I'm still away with work so "mentally organising" the workshop is all I can do from here. However I think the stand should work best all things considered. Unfortunately it will be next to the mill, not ideal but it will be well covered. Incidentally the larger one is the largest I can find locally at half reasonable prices.

Pete

Plate Size

Where I am working now we just recieced a 24x24 plate with a ledge ~3" thick making the total plate thickness 6" pink granite AA Lab grade lapped to .oooo36" tol. by starret. The plate has four rubber o ring like feet in a triangular pattern two at each corner on each of two sides and the other two opposite but right next to each other opposite the other two (imagine a triangle placed on a square. The manufacturer says this is the optimum set up to keep it level but the metal stand has levelers on each leg as well. Back to the size issue: This plate should be large enough for two people based the size the things we do (Boss wanted that size, maybe we needed to dump some cash). I did however make an MDF cover with 1/4 round on the bottom to keep it in place and some wheels and new levelers. It is a comfortable size with little fear of somthing being slid off inadvertantly.

Doug

...while Pete has all you surface plate guru's assembled....

I recently acquired a 24 X 18, iron surface plate, a bit weathered and have a granite plate of the same size. The idea of having a magnet-compatible plate interests me.

I'd like to try my hand at "smooth" scraping, (as little "pattern" as possible) the iron plate and will be making some scrapers. In the spirit of smooth scraping, will be starting with one of the up-to-shoulder, long sort, with carbide tip.

What is bothering me, is the notion of the mass of a big scraper, carbide brazed on and attempting to delicately work the cutting edge on my carbide tool grinder. Not only concerned about the quality of the grind but more importantly, fear for the life of my diamond wheel as I joust at it from afar.

This has me thinking that a clamp-on TC insert might be best. Then I consider accurately presenting this small piece to the wheel and realize that a compact insert grinding holder is probably called for. Any thoughts on any of the above?

Another bit of concern, I bought the granite plate for metrology, does using it for highlighting iron with dye, put undo wear on it and shortly ruin it for metrology? It's an out of inspection date AA but it's all I've got.

Oh, and Halcohead, thanks for the spade drill insert tip! Nice to be pointed toward an affordable and readily available source of scraping inserts. Great size range, found up to 2", probably even wider. The two-hole variety looks to be a good candidate.

Bob

If I were planning to do what you are planning, I would probably buy an inexpensive Chinese black granite plate for the face-to-face bluing work. I would save the AA grade for its intended purpose, speaking as a metrologist. The out-of-date doesn't matter at all compared to using it as a burnishing tool.
I also picked up a big cast iron (or maybe cast steel) platen some years ago with the same purpose in mind, but I found when I got it home from the outdoor surplus yard that it had a good .06" of crown in one dimension. It's larger than my 36" table Bridgeport, so I am using it for a nice solid tabletop currently.