How to square a 1/8” plate on the mill?

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Harrzack
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How to square a 1/8” plate on the mill?

Post by Harrzack »

I have learned how to square a BLOCK on the mill from the great video by Tom Grifen. Now I have a 10” x 10” x 1/8” AL plate I’ve sawn out of a larger plate. I’d like to square all 4 edges but not sure how to line it up with the table. I know I can mill any of the 4 edges to start, but not sure how to set the other 3 edges to be square with the “reference” edge. I’m working with a small mill - LMS 5550 and have the capacity on the x-axis. I’m setting the plate on parallels and can do the “ref” edge but how do I then turn each edge and ensure the previous edge is 90 deg to the next one to finish?

Regards - Alan R.
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Bill Shields
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Re: How to square a 1/8” plate on the mill?

Post by Bill Shields »

put it down with multiple clamps and just move one clamp at a time to get at each side -> this assumes that your mill has a 10" travel on the short axis.
Too many things going on to bother listing them.
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GlennW
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Re: How to square a 1/8” plate on the mill?

Post by GlennW »

Machine the first edge using the X axis.

Turn the plate ninety degrees and then indicate the machined edge using the Y axis so the edge is parallel with the Y movement of the table. Then use the X axis to machine the edge parallel to that axis.

Now flip the plate to the left or right and indicate the first cut edge again using the Y axis.

Now use the indicator along the X axis and see what the reading is. Your machine error will be 1/2 the indicated error and you can now compensate for it and mill the remaining edges to square the plate.

Easier done than explained...
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
pete
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Re: How to square a 1/8” plate on the mill?

Post by pete »

Few mills would be orthographicaly square to high limits and how well or accurately you want to do this would define the exact methods. But one trick I use is an already known to be square object to align the first machined surface with the next. Machine one edge using the X axis, turn 90 degrees, then set a 123 block or better a 246 block against the first machined surface with the blocks long edge running parallel to the X axis. I used a soft faced wood working clamp to hold the block against the first machined edge. Align the block with an indicator true to the X axis. Machine the second edge, turn, repeat for all edges. That way your always using the same axis to do the machining and your not locked into what the machines alignments are. If your block is good and you do your part you should get as square as possible even with a less than perfect machine, or the short travel on your Y axis that mill has. I squared up four 1" thick 8" x 8" plates using this method but with all 4 plates held with a couple of C clamps and then holding all 4 plates in a 6" mill vise and fly cutting the edges. The C clamps were rotated one at a time as the plates were rotated in the mill vise to the next edge to maintain the alignment and so all would be to the same size. You can do the same with one plate held to the table. It's not a fast method but it's quite accurate. It still depends on how good the part needs to be for squareness. A carpenters square can be enough sometimes. A known to be good square from a machinist's combination set could be substituted for the 123 blocks, but the blocks make it a bit easier.

Cheap off shore 123, 246 blocks can be a whole lot less accurate than there "supposed" to be, or pretty good sometimes. I don't blindly trust anything and the cheaper it is the more likely I'd check the blocks first using one of the methods shown on Youtube for checking squareness. Because of the multiplication factor 3/10ths out on a 2" long 123 block edge works out to at least .0015" on the parts 10" long edge.
Magicniner
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Re: How to square a 1/8” plate on the mill?

Post by Magicniner »

pete wrote: Thu Jun 07, 2018 11:09 am Few mills would be orthographicaly square to high limits and how well or accurately you want to do this would define the exact methods.
That means that milling small square parts just became a lot more complex ;-)
John Hasler
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Re: How to square a 1/8” plate on the mill?

Post by John Hasler »

pete writes:
Machine one edge using the X axis, turn 90 degrees, then set a 123 block or better a 246 block
against the first machined surface with the blocks long edge running parallel to the X axis.
I used a soft faced wood working clamp to hold the block against the first machined edge.
Align the block with an indicator true to the X axis.

I'd set the long edge of the block parallel to the Y axis, clamp my Starrett square against it, and dial in the X axis of the square by adjusting the block. That gives me both a longer edge to dial in against and a longer edge to align the part against.

That is, if I had any 246 (or 123) blocks. I don't, so I'd use two cylinders secured to the T-slots or a piece of 1/8" scrap no longer than the side of the square.
pete
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Re: How to square a 1/8” plate on the mill?

Post by pete »

A bit off the OT so I hope Harrzack doesn't mind.
Using Youtube and these forums as my demographics for how many actualy check there tables X,Y alignment Magic my guess is not very many do. Atman Unlimited on YT did a great series of videos showing how to check a cnc bed mill and almost all of it could be used on about any manual mill. I'd agree with his point about tramming the head is pretty much the last step until you know the rest checks out for any new or used mill. A hardened and ground 12" cylindrical square would be a big help, but a shop made lathe turned one would do just about as well and there easy to check for accuracy using a good micrometer.

With a good square and an indicator you can check a mill for it's spindle travel, knee movement and the X,Y. What I did was remove my mill vises moving jaw, square the rear fixed jaw as accurately as possible to the tables X axis and use that as my fixed reference. Then butt the cylindrical square against that jaw surface with it being horizontal. You can then indicate the side of the square in the Y axis to see how square that is to the X axis. If the table is known to be flat in both directions then standing the square upright on it and then indicating the Z travel for both the spindle and knee is easy. Checking needs to be done on one side of the squares X axis and either the front or back of the square in the Y axis since there's more than one direction the spindle and knee could be misaligned. Our mills sure aren't built to jig borer specifications and using past experience, then depending on how you want the rest of the day go and exactly what you find? It might be worthwhile to already be in a great or lousy mood :-) There's other methods of course, but using a cylindrical square is about the easiest I've found since I had one.

If the table isn't in great shape as far as being flat? I think it was Glenn who did a post on here some years ago showing boring a 1"- 2" hole in plate in the mill vise and zeroing an indicator true to the hole with the indicator spun using the spindle rotation. Then moving the knee or spindle down and reindicating it again using the same spindle rotation. That will also show any misalignment and I thought it was more than a bit clever and certainly not a method I've seen anywhere else.
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