Matrix Plate- A2 or 4140? Newb needing help machining

[Odin]

Hi all,

I'm a young machinist working for a tungsten carbide tooling manufacturer, and I have my own small Taig mill. I'm looking to make a tooling plate/matrix plate for my mill
better than anything commercially available, of which I only have seen stuff in Mic-6.

I've done a ton of metals research in the last few weeks for my plate. I need it to be of some grade of high-wear resistant material with good dimensional stability.
See, I'd like to both spare my anodized table from wear, get all the benefits of a matrix plate, but finally- and the key reason I'm not interested in Mic-6 aluminum tables-
get an excellent, low wear surface to tram my adjustable Z axis into the tenths range. I cannot do this easily now with the table, and here's the key:

I have current access to full sized manual Bridgeports and precision surface grinding equipment in a class I'm taking at a local college.

I know Mic-6 has excellent dimensional stability and is cheap, but it cannot be precision ground into the tenths range of flatness as steels can by normal methods.
I have done lathe work on 4140, and I like the stuff. I have not worked with A2 tool steel at all. My class teacher, a very old machinist with ridiculous skills, has told me
A2 can be drilled and tapped without extraordinary difficulty, but my research leads me to believe it's difficult stuff.

I am looking right now to do 0.750" thick, 5x18" plate, with around 310 or so holes- so material and tool choice is very important. I cannot afford a scrap piece. I can do this
once. The full sized machines all have DROs available for precise positioning.

I know I will be spot drilling all the holes first, and using a collet to hold the drill for ultimate concentricity. Holes will most likely be 1/4-28. I am still deciding what
size would be most useful for tooling on a mill my size.

A2 already comes ground and in the exact size I need, but is a bit more $ and seems like it will be more difficult to machine than 4140. 4140 doesn't seem to have the hardness
and dimensional stability of A2, nor the wear resistance. I think it will have higher corrosion resistance, though, as the piece I have I have exposed to water and
could not get it to rust at all.

I wanted something rust resistant just in case. I live in a high humidity environment.

Based on all this, and assuming surface ground finish on all sides for an excellent indicating surface, which material would you suggest, and what tooling would you
use to drill the holes and especially tap them? I am assuming a good quality M42 drill for either right now, but it seems tapping in A2 is difficult according to other sources.
I have access to various tapping heads on the mills.

I originally thought of 1018, but I cannot find a source for hot rolled flats. Everything's cold rolled, which has less dimensional stability. I also wanted a very high wear
resistant steel with good corrosion resistance and excellent dimensional stabilty, in something I can find and afford! I am willing to pay ~150$ for the material, and
A2 and 4140 fit the bill.

Can anyone suggest which would be better, specific tools for each, or something else entirely if I missed something better in wear resistance, dimensional stability, and
machinability that can be precision ground by me on the steel surface grinders? I will only have access to those for about 2 more months.

Finally- I am a machinist, but I am still green and just starting out. I'm sure I've made some incorrect assumptions/comments above, as I'm machining from wake to
bed every day of the week, I'm sure I've mixed up some facts or just plain got stuff wrong. Please correct me where I was- I need to learn more than I need to feel correct.

Thanks!

[Korellibopper]

I think you'd be fine with cold rolled steel. I think that a plate that size may be kindof heavy for a taig mll but that doesnt mean im right. Under the kind of use your talking about I doubt youll wear out any of the steels your talking about.

When you grind the surfaces. make sure you shim them so that whatever warp is in the plate will be removed.

As for bold size Id go with #10x24 there mor then strong enough thats what I used when I had a sherline.

You might want to consider pocketing the back side of the plate to lighten it.

[RICHARD ZASTROW]

If you want flat, accurate surfaces, rough machine then have it stress relieved. Then finish machine, harden and finally grind.

You might even drill under-size before stress relieving, then jig borer ream to tap drill size and tap after stress relief. See if your instructor doesn't agree.

You might consider 8620. Tough inside, fairly easy to machine and good case hardening characteristics. Not too $$$$$$$

Dick Z

[H.A.S.]

"I am looking right now to do 0.750" thick, 5x18" plate, with around 310 or so holes- so material and tool choice is very important. I cannot afford a scrap piece. I can do this
once. The full sized machines all have DROs available for precise positioning."





Since it's .750 thick, you have a lot of choices. I would go with 4140 or 8620, since you have access to all the equipment you need. Good luck, and share some pics when you get it finished.

[Delw]

Just use alum, your wasting your time and your money on making a subplate of that quality for the type of mill your running.
Alum works fine I use them eveyday