Squaring up raw stock

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KellyJones
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Squaring up raw stock

Post by KellyJones » Wed Apr 15, 2020 5:31 pm

Ok, time for an education (mine, I mean).
I started to square up some stock on the milling machine today and started thinking about whether there was a better proceed. I started with a block of aluminum which was saw cut on all 6 sides. I set a couple of parallels in the vise, set my stock up on the parallels to machine one of the two largest faces first, and went to work with the fly cutter.
When I completed that side, I rotated the block 90 degrees to cut one of the two next largest faces. I set the freshly machined surface against the fixed jaw and used a small piece of round stock between the moving jaw and the sawn face of the block opposite the one i had just machined. Then I fly cut the second face.
I then rotated the block 90 degrees again so that the first fly cut face was on the parallels and the second fly cut face was against the fixed jaw. I also used the small piece of round stock next to the moving jaw. About half way though this cut I noticed that the block was not sitting perfectly flat on both parallels.
What did I do wrong? It occurs to me that I should have fly cut the two largest faces first, so that subsequent cuts would be "square" without the small pieces of round stock.
What do you guys do?
thanks
Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
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Harold_V
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Re: Squaring up raw stock

Post by Harold_V » Wed Apr 15, 2020 5:47 pm

I do precisely what you did, but I make sure that the part is held firmly against the fixed jaw. I do NOT recommend you cut opposing faces, as there's no guarantee that they will be parallel. Be certain that the round piece you use is well centered on the fixed jaw, so it can't influence how the part mates with the jaw. I use a drill blank, but what you use isn't critical so long as it keeps pressure on the center of the jaw.

You didn't make mention of the vise you're using, and that may well be your problem. It's hard for the average guy to understand that most mill vises are simply not up to the task of squaring material. They tend to lean, albeit very little, and that yields no end to squareness problems, a lesson I learned the hard way many years ago. A Kurt vise is usually well within one's needs, however.

No, I do not own stock in Kurt. I speak from the perspective of one who has faced problems with squareness, and how I resolved the issue.

If squareness is critical, you might try using an angle plate in lieu of your vise. That's quite important if you are preparing edges on plates to be mounted vertically, as in tooling assemblies. C clamp the part to the angle plate, using a parallel stack to establish the horizontal plane. Repeat the cuts on four sides, using the last machined face as the next surface to clamp to the angle plate. When square on four sides, then use a square off the table to establish a square end. With care, your machined part will be at least as good as the angle plate, assuming you read your square properly. Simply looking at the square offers risk of error, so try to read light between the square and the part. When you see none, you know the part is parallel to the square.

H
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BadDog
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Re: Squaring up raw stock

Post by BadDog » Wed Apr 15, 2020 6:23 pm

Yeah, that was a learning phase for me. Somewhere long ago I saw a reference in an old machining text book on how to do that. Basically, pick the largest convenient side and make it flat, I often use a fly cutter. Put that against the fixed jaw, and keep working from that reference as you develop perpendicular sides, ultimately working to opposing sides, always working with minimal moves from the first side so you don't compound errors. In other words, don't do side 1, use that to do 2, then use 2 to do 3, then 3 to do 4. You will have to use a secondary surface to reference #3, but otherwise you'll always reference from the original reference. You'll want to get a reference surface (side 2) on the bottom right away too so that you don't have the block tipping, but everything else goes from there.

If it's a long part, you'll likely need to use your second axis. And if it's particularly rough (casting, saw or flame cut), you'll likely want to average. All sorts of gizmos have been used to prevent accidental intrusion of referencing an undesired surface. One option I've seen is a big ball bearing with a flat ground on one side used between part and movable jaw so it doesn't interfere with registration on the back jaw.

Obviously requires confidence in your vise, which you'll want to verify relative to your way travel within your desired tolerance (sometimes generally considered 10x the final allowed tolerance).

In general use, I find I often don't fully square stock when starting. I just prepare and use that initial reference surface, then work from there. But that depends on if I'm doing a full layout, or have features that require a lot of flipping.
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SteveM
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Re: Squaring up raw stock

Post by SteveM » Wed Apr 15, 2020 9:13 pm

Tom Lipton did a video on squaring up a block:
https://www.youtube.com/watch?v=-lgMcDOkeg8

You have most of your process, but he has a few tricks.

Oh, and what Harold said about the vise.

If you want to quantify your vise, put the block in, clamp it lightly, put an indicator on the side of the block with the movable jaw, zero it out and tighten the vise.

You will be surprised at how much your part will lift.

Steve

earlgo
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Re: Squaring up raw stock

Post by earlgo » Thu Apr 16, 2020 9:16 am

Open your textbook, "Machine Tool Operation, Part II" by Henry D Burkhardt, McGraw Hill Book Co, Inc Copyright 1922, 1937 and turn to the Chapter on Shaper Work, Section 107, where it explains this in only 3 pages.
But the essence is in these 4 steps as shown in the picture.
block squaring.jpg
block squaring
If you have a KURT vise the babbit hammer is optional.
Wish I had a shaper.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

Glenn Brooks
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Re: Squaring up raw stock

Post by Glenn Brooks » Fri Apr 17, 2020 2:27 pm

I like the ball bearing idea. Less pressure on the edges of the movable jaw side of the work. Now, where to find a 2” ball bearing. (That doesn’t cost $9 for shipping!) :)
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SteveM
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Re: Squaring up raw stock

Post by SteveM » Fri Apr 17, 2020 2:51 pm

Can't remember the name of them, but someone is making balls with a flat side specifically for such clamping in a vise.

The advantage is that they don't put so much force (as pounds per square inch) on your vise jaws.

You could make them by grinding a flat on a large ball bearing.

Steve

earlgo
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Re: Squaring up raw stock

Post by earlgo » Fri Apr 17, 2020 3:02 pm

When i was a kid we lived in a small town with dirt roads and the township garage was just down the road in the 'center' of town. They replaced the wheel bearings in the road grader and I think they were 1" diameter or thereabouts. Best of all the one I got was free.
I'd bet one could use your ball turning device on a piece of 4140PHT and have it work for the short time needed to square a block.
When I have squared a block using this method, I use a drill blank instead of a ball, and it has worked ok so far.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

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NP317
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Re: Squaring up raw stock

Post by NP317 » Fri Apr 17, 2020 7:38 pm

I have used half-round metal pieces with success.
RussN

KellyJones
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Re: Squaring up raw stock

Post by KellyJones » Thu Apr 23, 2020 4:26 pm

Thanks for the responses. The page from the text was particularly helpful.
Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
George Bernard Shaw
(1856-1950)

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