Reducing thickness of .187 plate to .177

I have two plates (2"X7") that I need reduced in thickness from .187 to .177. I placed one on a surface grinder and in reducing it just .001, the plate sprung into a shallow 'C', coming up almost .010 on the extreme ends! This is a simple structural plate but I need it to be flat when I'm done.

So, how do you guys do this and end up with nice, flat plates? What would be a good process between cutting, stress relieving (not sure how to do this), bending to pretty straight and finally surface grinding to final thicknes.

Your guidance would be appreciated!
Thanks,
Joe

Sounds like a job for a Blanchard grinder..

Are you using coolant??

The small hot spot while grinding, can cool faster at edges of a thin plate then middle, causing bowing.. The material will move as it attempts to relieve the stresses..

Hi, get them lapped, I am in the the Uk and have a sub contract lapping company and we do this sort of thing all the time. Lapmaster are an American company but I dont know is they have a sub contract department , But I am sur they could suugest someone to help. If you need anymore info please just ask.

Paul

If possible, start with hot rolled material. If not, send them out for stress relief. (I realize its not practical in small lots)

If 3/16 hot rolled won't clean up, you may need to start with 1/4 HR.

That should be grind able with out much effort. Just need to select the right wheel - aproach and flip the part a few times as you go so it ends up flat. The heat from grinding can be a major source of distortion - stress. The right wheel and feed choices can get over that. The wrong ones and you make some truly curly shapes!

The fact that you only took 1 thou off to me says you were using a wide traverse shallow depth of cut approach. Try it again with a 46 grit j ish hardness alox oxide wheel, seeded gel - blue style if you have it with a nice coarse dress. Take a 1-3 thou depth of cut (you are using a fine pole magnet i hope?) and step over only 5-10 thou per pass. Plate should show no signs of heat at all if the wheels cutting freely. Ground surface should look dull, not shiny, if its shiny the wheels rubbing and thats your problem. A nicely cut ground surface on mild steel should have more of a dull brushed look than a shiny polished one. Flip it and grind the other side, repeat till your at the thickness you want. Distortion should be minimal. Might still want a final straightening if its cold rolled material but straightening something like that is pretty easy for a structural application, presuming you only need flat to be flat within 5 thou tops over the whole part?

the post suggests only one pass on one side

You do have to take the skin off BOTH sides if you want the part to lay flat.

For that size part, a surface coat of soluble oil will suffice to lube and COOL. If the lube evaporates, it's too warm. (just spray on some more)

Find your local double disc grinding shop.

You don't say what the material is. If it is springing that much it may be difficult to manage the stress.

You may want to lap it by hand as a test. If it laps fine, then your grinding technique is at fault. If it still springs, you have a problematic material.

Without seeing the parts first, but from the description, my guess is you started with sheared cold rolled steel. Two problems. Cold rolled, also called crs, has surface stresses that when relieved on one side will cause the plate to bow, typically up at the ends because the surfaces are in compression and want to stretch the part. Second is the shearing leaves burrs on one side and broadly radiused curve on the side opposite the burr. The plate probably did not seat flat on the magnet and without cooling, got hot quickly from the grinding.

Been there, done it.

Tom

Lot of good suggestions and procedures. One more. If it's already warped, shim it with appropriate feeler guage thickness. If it's sucked down to the mag. warped, it won't change when released. I have a DoAll with "through the wheel coolant". The coolant is forced through the stone's center hitting the exact point of contact. Really helps. CRS usually stinks for true flatness. You'll definitely be better off with hot rolled.

Sheet Inch Vs metric

3/16th Sheet (.1875) is 4,76mm

.177 is 4,5mm

4,5mm is a standard metric sheet size.

Problem solved. (Unless one is in the USA....)

regards, Doc AV

4.5mm might be a standard sheet size in oz, but good luck finding it over here in Europe! 4 or 5mm take your pick. That said there often under size by anything upto 0.4mm. Hence its a intresting game!

There's probably not one chance in 5000 that the pieces were cut from cold rolled sheet since CR sheet that heavy is near impossible to find. In grinding a fair bit of stuff in the past, I sorta think the thinner range of hot rolled sheet and plate has some residual stress similar to what's seen in cold finished stock. 3/16 and 1/4 stuff seems to always want to move around. I assume the processing speed employed in today's mills ends up with a product that's cool enough by the time it gets to the final rolling passes that its no longer hot enough to be self annealling. Just a guess based on what I've seen though.

If the pieces were plasma cut from HR sheet then you'd need to get rid of the nitride hardened edges because they'll make the metal do all kinds of unpredictable and crazy stuff that you don't expect because the edge is highly stressed.

Simplest solution might be a 2 ft piece of 3/16 x 2 low carbon ground stock for about 30 bucks. It will be stable and easy to grind to the proper thickness.

Thank you!

Thanks to all of you for your guidance. My friend and I will be tackling this with your input. As it is, I received the plate in a parts kit and don't know the steel type. It was laser cut and that seems to be an additional factor to consider. My next attempt is going to be making the plate from scratch and applying some of your tips.

I will post a follow-up when this is done. Most likely that will be after the holidays.

Thanks and regards,
Joe