Learning to scrape - with help from Richard King

[p3bhambama]

Ooooh, they're only PFG stones if they come from Kinetic Precision. But yeah, the real ones aren't cheap, flatness has a price (and so does the Okamoto he grinds them on.)

Yeah I will probably get some from him when I get tired of these but they behave properly and weren’t exactly cheap - just not as much as the kinetic ones or the ones from Lance Balsey.

 

[p3bhambama]

Anybody with a clue what this is? It was advertised in the auction as “dovetail measuring device”. It’s very well made with ground and lapped surfaces but idk what it actually is. I paid $10 so no loss either way.

 

[TGTool]

Yeah, it looks like it could be good for measuring dovetails. The rolls are nested into male of female dovetails and you mic over them. Then a little trigonometry will tell you where the slanted surfaces are. On female dovetails I'll often put rolls (dowels) in the corner and then expand an adjustable parallel so it's snug between them and measure the parallel. Male dovetails you can usually just mic over the rolls.

There's a specific case where that device could be more useful. Most often the working surfaces of a male dovetail are the slanted surface and the horizontal surfaces just outside them. The top surface is just clearance. That's the case you'd find on most mill tables and saddles since it gives the widest geometry for stability. However, if the male dovetail uses the top and two adjacent slanted surfaces and you measure over rolls as before, you're measuring to a clearance face which isn't guaranteed. Your device has flats that would contact the top and sides of a dovetail if required.

 

[p3bhambama]

Yeah, it looks like it could be good for measuring dovetails. The rolls are nested into male of female dovetails and you mic over them. Then a little trigonometry will tell you where the slanted surfaces are. On female dovetails I'll often put rolls (dowels) in the corner and then expand an adjustable parallel so it's snug between them and measure the parallel. Male dovetails you can usually just mic over the rolls.

There's a specific case where that device could be more useful. Most often the working surfaces of a male dovetail are the slanted surface and the horizontal surfaces just outside them. The top surface is just clearance. That's the case you'd find on most mill tables and saddles since it gives the widest geometry for stability. However, if the male dovetail uses the top and two adjacent slanted surfaces and you measure over rolls as before, you're measuring to a clearance face which isn't guaranteed. Your device has flats that would contact the top and sides of a dovetail if required.

Thanks for the detailed explanation TG. Makes sense.

 

[Mark Rand]

I made a very similar device when I was rebuilding my Hardinge HLV lathe. I used it when measuring and grinding the dovetail surfaces on the bed (flat top, sides angled, with the widest part at the top of the bed plate).