I'm watching a YT restoration on a 1971 mower. Their using a small surface plate and some kind of compound to lap the top of the cylinder flat. Is this a typical use for a plate?
Surface plate use question
- Thread starter 930dreamer
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rlitman
Well-known member
No. That's how you ruin your plate.
There is a difference between a surface plate and a lapping plate. Are you sure that it was a surface plate? An out of spec surface plate can be used for lapping as well as a chunk of granite countertop. Can you give a link to the vid?
lg
no neat sig line
lg
no neat sig line
OP
39 minute mark, could be an older plate repurposed, no idea.
Yep, it's a lapping plate, I use mine often. Two stroke case halves, intake flanges, cylinder heads, etc.
Edit: he's using sandpaper on top of the plate, not compound. Although one could use lapping compound directly on the plate as well.
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Zeus36
Well-known member
That is a granite surface plate with sandpaper.
Here is a lapping plate:
Here is a lapping plate:
RTM
Well-known member
If you aren’t a professional machinist, tool & die Maker, patternmaker, or got the plate cheap, it is not unusual to misuse a plate like that.
I know guys bought them, put sandpaper, or lapped, directly on them, then sharpen stuff.
MacMcMacmac
Well-known member
I used a heavy granite surface plate a few years ago to lap the face of a large 8" check valve plate. I spray glued some emery sheets to it and did a figure 8 for about 20 minutes. Worked well, but a definite workout. Afterwards, I peeled the sheets off and wiped the plate clean with alcohol. The plate was unused and tagged to be surplussed. There seems to be a lot of them going out the door the last few years. Looks like quite a waste as I'm sure they aren't cheap to make.
That is a granite surface plate with sandpaper.
Here is a lapping plate:
Of course you are correct. But granite surface plates are often (mis?) used for lapping. Glass (I've never used) too.
pelletman
Well-known member
Used surface plates go pretty cheap at auctions
I got several from an industrial liquidation years ago. Paid $60 a piece, 12x18 brand new in their crates with AA certification.
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Firebrick43
Well-known member
My father rebuilt/restored half a dozen cub cadets and their K Kohlers for sale in the spring every winter. To save money we had an old surface plate that we attached sand paper to with 3M 77 adhesive, a real light mist of it.
He would then put me to work straightening out the heads.
I use a surface plate to straighten heads out still but blue the head up on a surface plate and scrape it in with the Biax.
He would then put me to work straightening out the heads.
I use a surface plate to straighten heads out still but blue the head up on a surface plate and scrape it in with the Biax.
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That doesn’t work the way people think it does. Sandpaper on glass or granite doesn’t make the surface you rub on it flat. Lapping plates are really different. It might work well enough. But rubbing something on a flat surface absolutely does not guarantee it’s flatness.
What is flat? Are you needing surfaces that will wring together or just straighten out the warp in a cylinder head. like the op's example? In the op's example the process is to make the bottom of the cylinder head flat enough that it will conform to the gasket between it and the block. The measurement of Flat to a machinist is a lot different than the measurement of flat to a concrete finisher doing a concrete floor.
lg
no neat sig line
That’s the right way to flatten with a surface plate. A biax is a little overkill for a lawn mower cylinder head. But if you’ve got one, I guess why not use it. If I were doing heads, I’d checked them on the surface plate and fly cut them on my bridgeport. Rubbing them on sandpaper can easily make them convex.
Just for kicks, if you want to use a surface plate as a lapping plate, do what you want, then blue up the plate and check. But be prepared to be disappointed.
RPH
Well-known member
Glass shelves from the fridges work great. Glass is close enough for most diy clean ups. It’s easy to find and replace when gone.
isb cornbinder
Well-known member
Good thinking.
I have used refrigerator wire shelves in a temporary disposable spray booth. I have painted hundreds of small parts this way. I found the range hood on Craigslist. I pulls the overspray down and through twin filters to outside. The spray booth is an appliance carton.
Attachments
cycle61
Well-known member
We used to resurface smoked motorcycle clutch plates on the parking lot concrete. Not ideal but it'll get you through another race or two.
slowtwitch73
Well-known member
The glass out of a printer/scanner is good as you can get. Put that on top of an actually flat surface plate and Bob is your uncle.
RTM
Well-known member
I use a 1/2” plate glass piece, about 12” x30”
isb cornbinder
Well-known member
Many years ago, I bought a ground cast iron surface plate. In the shop, it was called an assembly plate. I mounted it on a hydraulic motorcycle lift from Princess Auto.
bugnut
ALLIANCE MEMBER
For many years a piece of ceramic floor tile was used at home for resurfacing gasketing surfaces.
Firebrick43
Well-known member
For a small ope gas engine it’s probably faster than setting up in a mill, figuring out how to clamp especially with out distortion from the clamps themselves and then leveling/indicating it and shimming to get cut the minimum possible.
Multi cylinder engines I uses the superfly if the have any significant warp in them set them in my bed mill to deck.
I know it's heresy to some here, but I have a small granite surface plate that I bought from Enco decades ago for exactly this purpose. I've used it dozens of times for small parts like this and it works. A similarly sized sheet of 1/4" tempered glass that I have is ~.003" out of flat. I have a cast iron ground machinist straight edge to check with. If you don't have room for a mill, surface grinder.... it's better than anything else I could think of. While the parts may not meet aerospace flatness specs, they are greatly improved and function fine.
bpwoodworking
Well-known member
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I have a cheapo woodcraft granite surface plate that I use with sandpaper to surface small parts.
rust in the eye
Well-known member
I can recall scuffing used ones with sandpaper or sand blasting and thinking that was quite primitive. Scuffing the steels on concrete must have made them pretty grabby. "another race or two" indeed.We used to resurface smoked motorcycle clutch plates on the parking lot concrete. Not ideal but it'll get you through another race or two.
cycle61
Well-known member
rd65
Well-known member
I used an old piece of granite countertop to check/surface the head on my YT3000 Briggs mower. Those heads are always blowing gaskets. Used a felt marker for die on the head and 400 grit paper taped to the granite. I could easily see the low spot and sanded until it was gone. Used a flat bar on the cylinder. I now have a piece of 1/2" thick glass that I will use in the future. That is what we used at the bike shop years ago, with mesh sandpaper.
rust in the eye
Well-known member
I helped a friend with a street/drag bike, never owned one myself. Your photo reminds me of the natural resting position of motorcycles.I used to be cool (says everybody who's ever owned a motorcycle)
esben57
Well-known member
Decades ago I was apprentice Fitter and was tasked with a similar method facing up compressor valves. Reciprocating type probably Atlas Copco - large. May have used an old surface plate, definitely lapping compound on the valve units. This was done on a radial arm drill and re-assembled with new springs and plates, long time ago so a a bit foggy here.
Anyways. The old gent I was working with had a habit of bushwacking the young lads (he was ex WW2 Commando, yes one of those).
He'd call you to see this compressor at work then crack off a cap screw with the valve under pressure. It would go off with a loud CRRAAAACK and take 10 minutes off your lifespan.
He'd quietly chuckle to himself.
Anyways. The old gent I was working with had a habit of bushwacking the young lads (he was ex WW2 Commando, yes one of those).
He'd call you to see this compressor at work then crack off a cap screw with the valve under pressure. It would go off with a loud CRRAAAACK and take 10 minutes off your lifespan.
He'd quietly chuckle to himself.