BBQ cast iron plate for sharpening?

[Dengue]

hi, I am looking at getting an old cast iron BBQ plate 10mm thick and cutting it into rectangles 8" x 3" to use as a sharpening plate with diamond paste after getting them machined and flattened

Can anyone please advise on whethere a plate like this would be suitable for this purpose, considering the annealing, whatever, that could come from exposure to a flame on the one side?

[Michael G]

You're effectively making up a lapping plate (or a hone). They are normally much thicker for dimensional stability - the amount you would be removing is from the tool is very slight so with a thin plate deflections from being on an uneven surface or poorly supported start to become important.

Michael

[RayG]

Hi Dengue,

Depends how flat you want it. This discussion comes up from time to time, If the cast iron is rigid enough to stay flat then you could surface grind it, and then scrape it flat against a surface plate.. but if it's just 1/4" thick then it's going to warp and flex all over the place.

If you want to make a cast iron lapping plate, ( the type with grooves ) and it was fairly small, (say less than 6 inches or so) I think it would be ok.

Mill the grooves first, then surface grind it.

Ray

EDIT... I got interrupted while typing a reply, so I crossposted... but I see Michael is saying pretty much the same thing. :)

[derekcohen]

Hi Dengue

You could use the soles of old/broken cast iron hand planes ...

http://www.inthewoodshop.com/WoodworkTechniques/Castironhoningplatesfordiamondpaste_html_m3e1b511a.jpg

Link: http://www.inthewoodshop.com/WoodworkTechniques/Castironhoningplatesfordiamondpaste.html

Regards from Perth

Derek

[Brobdingnagian]

Dengue, The BBQ does not get hot enough to do anything interesting to the metallurgy of the iron. if you want fully annealed cast iron you need to get it hotter much hotter, glowing bright yellow hot, and hold it there for a good few minutes and then letting it cool very very slowly. If you think you are up for that I'll post the full process specs.but..... that being said...As long as it is flat and is softer than what you are trying to hone and will hold the diamond particles you are good to go, the rest is mostly preference and refinements. The hardest part is getting it flat and keeping it flat (not distorting on you), and by flat I mean proper flat.Cast Iron is a great materiel, annealed grey cast iron would be at the top of my list, due to is slipperiness with steel, nice and soft to ready take the diamond particles, dimensionally stable and easy to work. small Thin circular groves help to keep the removed materiel for clogging up your plate and let you work in any direction. I would go a thick as you can get as it helps stop distortions and keeps the plate from moving around while you are working your edges. A cheap supply thick slabs 45mm+ of cast iron can be tractor weights, but they will need to be de skinned to get into its soft core. -Lates