If they're not familiar with grinding flexible items, they may not do the work to a standard that will satisfy you. Also, there are accounts of folks in the U.S.who took planes to job shops to find a significant amount of material milled from their planes. How many of those are direct accounts, I don't know, but worth asking if you're going to pay someone to do something that may cost more than the materials would cost to do 10 planes in your shop.why not take it to an Engineering shop and get them to precision skim it like they do with cylinder heads ?
Sorry but this is bad information, if it's from a vehicle it'll be tempered, and thus not "flat" enough for lapping a plane - there's a reason why makers like Ollie Sparks (a member here) use a certified granite surface plate and elbow grease - for some things there are just no shortcuts and a plane without a dead flat sole along most of it's length* will just give continued poor service and headaches.Hi,
Another way of flattening is to get a piece of flat glass from a car or van from scrapyard. Using carborundum paste as for grinding engine valves this will flatten the sole of your plane.
Lapping on a larger surface abrasive than an item is will make everything convex, doesn't matter how flat your lapping plate is, if your not going to use it right.Lapping a plane sole on tempered glass will result in a slightly convex sole, and a plane which is good for F ALL but as a door stop - or planing the inside circumference of REALLY REALLY REALLY big wagon wheels
In this case, the toe and heel of the plane are low and a long flat lap is exactly what's needed for a final check. I think it's more practical to have a long reference and work convexity out if that were the problem here, and then finish on the lap.I can't speak for doing so on a lathe Phil, but I will rant on for them gluttons for punishment who are going to do it by hand.
I've made huge errors in the past lapping with a surface plate,
destroyed two no.60 1/2's, a wafer thin welded Bailey no.5, thankfully I made sure I had sense to buy a thick soled n.8 which I also made convex.
I'm not talking a sheet of paper or two hollow either!
(not to mention other things not so important as a hand plane)
This needs to be understood for the folks using a lapping plate, as there is a large amount of misinformation out there.
The longer a plane is, the more material will be removed off of the toe and heel, as it will start to pivot from the point that's getting larger somewhere in the middle,
and this will lead to it going convex across the width next.
(which means possibly hindering the use of the cap iron if its bad, as it would act like a negative camber)
Having a slightly concave plane only needs to have the edges feathered off, if its only concave across the width, then it is very likely that one would need to stop removing metal from the toe/heel on a plane this long.
That means the abrasive must be shorter than the plane is.
lapping will always favor removal of the edges
For the folks still in doubt, then I suggest getting some 4 or 5mm mild steel plate and doing some experiments with a small square, scribble marker over all of a face and try and remove metal only from the middle, or try and lap flat some intentionally filed convexity , and you will see lapping will just copy the profile and polish it.
You will learn the same thing as with wood preparation that the edges are the reference and those contact points are important for the wood to sit flat and not pivot/see saw about from the middle.
See Charlesworth's video again
If you shop around for a "replacement shelf", it should just be non toughened float glass. I wouldn't get it thinner than about 9 or ten mm, but a longer shelf should be that thick, anyway, and inexpensive.Toughened glass won’t be flat (compared to non-toughened) but also remember it’s not magic, if you put a 6mm piece of glass on an uneven surface and push on it, the glass will deform.
I cannot speak for US engineering standards but here in the UK Engineers are qualified to a high standard with a BSc Degree qualification and are registered with the Chartered Institute of Engineering CEng in order to practice as an Engineer and be entitled to use the title Engineer.If they're not familiar with grinding flexible items, they may not do the work to a standard that will satisfy you. Also, there are accounts of folks in the U.S.who took planes to job shops to find a significant amount of material milled from their planes.
Different terminology here, yes. An engineer wouldn't run a machine like you're talking about here, they would determine spec and a trade-trained (associates degree, or 2 year college type) would operate the machine.I cannot speak for US engineering standards but here in the UK Engineers are qualified to a high standard with a BSc Degree qualification and are registered with the Chartered Institute of Engineering CEng in order to practice as an Engineer and be entitled to use the title Engineer.
There is not much more precise than a CNC Milling machine, they work to +/-0.1mm geometric tolerance and a surface finish of 1.6µm (micrometer) tolerances tighter than 0.01µm can be achieved where the design requires it. ( General Tolerances to DIN ISO 2768. )
I' wasn't referring to back street mechanics and 'machine shops'