I bought this poor thing at the flea market for $10. It's American made so in its original condition it was worth about $350. It was pretty dinged up and it was out 0.003" from top to bottom. Tons of gouges and wear. The faces were not flat.



Unfortunately my surface grinder is nowhere near big enough to grind this plate.

I bought a smaller angle plate with the intention of trying to fix this plate myself. I really wasn't sure how it would really come out.  

I dialed the faces in before I milled them.... I decided against a fly cutter because accuracy is paramount. I used a 3/4" endmill overlapping 0.5". This means that any possible tram deviation or head flex will be averaged over a smaller area rather than one huge ass cut. I took 0.003" off each face. The ends seem to be nearly perfect so far.



After I milled it I checked it in the setup and then I clamped it down on the table and indicated it with both the knee travel and spindle travel and both agreed I got it within 0.0005" of perpendicular. I'm extremely pleased.  Now I have two sizes of plates too.

I watched the indicator as I loosened the clamps and the plate didn't move so I got this puppy dead flat on the bottom too. No twist or bow.

That's a nice setup.  Machinist jacks and all.  Well done.  

I might have gone the fly cutter route or roughed with the E/M and finished with the fly cutter, but it's tough to argue with success.

Any inaccuracies in my tram would have pushed the accuracy off. With narrow passes I average out any issues and end up very flat.  Even head flex would come into play.

Now finish the job by scraping using your surface plate as a reference flat. You may need to make a cylinder square to help check your work on squareness.

O.K. I'm just being super picky for most people don't need an angle plate to sub tenths tolerances.  But, that is a challenge if you want to take it on.

I'm ordering a surface plate next pay. I really don't need tenths on this plate but you never know!

It's a Taft Pierce angle plate 6x6x8

But even if you don't NEED it scraped surfaces are so beautiful!

FYI, if you don't have a known good master (flat, right-angle, etc) you can create one using 3 of them, progressively scraping them each in. The process is more tedious than using a master but it's how the ancients did it and it's routinely used in machine tool rebuilding as a verification method. The premise is (assuming a flat surface is desired in this example) that with 2 plates they can print to one another without the promise of flatness. But if you add a 3rd the only way it will print true to both of the first 2 plates is if all 3 are flat.

I totally understand the  concepts behind scraping and flatness. I just don't need that level of perfection and I don't have materials to make the plates which would cost hundreds of dollars and dozens of hours.

Instead I bought an angle plate for $10 and now after a couple hours work it's within acceptable tolerance.

@batmanacw can you tell me about your mill?

Looks like a Precision Matthew. Do you like it? Any short comings that would make you look at other options?

I bought the 835S, which is the smallest knee model. It turned out to be very accurate. Much more accurate than I expected honestly.

It could be more rigid but I am told that none of the knee type Bridgeport style machines are substantially better. It will run a 1.5" indexible shell mill just fine but I don't want to run bigger. I don't need to push that hard.

I wouldn't mind more table but I just couldn't afford it.

Tramming in the head is a challenge. It seems to hold more accurately when you take the tension off the worms before you tighten things up.

The table and knee are damn smooth. I keep them pretty tight but not hard to move. I'm very generous with the oil. Lol! I don't want wear to set it. The knee gib wasn't tight enough when I got it and it threw me a few weird challenges but it really behaves well snugged up right.

If I had to do it again knowing what I know now I'd buy it again. Get the DRO and Align power feed on the X.....

Thanks for the feedback!

I’ve just started looking at the options for a hobby mill.  The Precision Matthews line looks like a great alternative to picking up a used unit.