squaring a block

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jonathan davies
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squaring a block

Post by jonathan davies »

Hello

I'm sorry for such a basic question but it's really frustrating me. For some reason I'm not able to perfectly square a workpiece on my mill. My procedure has been to flatten one side, then turn that face toward the fixed jaw and cut the other side. I've tried this with and without a bolster bar getting the same result, a slither of light growing wider between the workpiece and the square when I hold it up to the light. I don't think it's the tools as I've checked them against one another and everything seems square. Both sides of the block are completely flat so the square isn't rocking on the surface, I've also tried just sitting the work on a flat surface and moving the square up to it just in case I wasn't seating the square properly. The workpiece is always cleaned and corners broken. I've checked and rechecked the mills tramming and it's spot on, with the exception of the far corners of the bed showing some movement on the DI (maybe the bed is warped), front to back (directly in front of the column ) and left to right the tramming is perfect. Is there something I'm missing or am I just expecting too much? It's not a huge gap but it is noticeable, being very new to this the only point of reference I have are some ground squares and vice.

Kind regards

Jonathan
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GlennW
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Post by GlennW »

Hello Johnathan,

Perhaps tha fixed jaw on your vise is not perfectly perpendiicular to the table. You did not mention what type of vise you were using.

Try holding a DTI in the spindle and raising and lowering it (Z) against the fixed jaw for starters.

You might also run the DTI on the vise ways in X and Y to see if the ways are parallel to the table.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
toastydeath
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Post by toastydeath »

One thing that kills me occasionally is the rear jaw gets dirt behind it somehow (I have no idea how) and when it is tightened, the hard jaw itself moves.

As you tighten it, put a DTI on the BACK of the hard jaw, and torque it down. It should not move much, if at all. If it does, take the jaw off and clean it.

Probably isn't your problem, but it's just one more thing to check.

Also, when you're going for anything under .001"/6" flatness or parallelism on a bridgeport, I only use the lightest possible pressure - barely closed at all. A good pull should allow you to rip the part out of the vise. Any more, and it's too tight.

If I want the absolute limit of accuracy on a milling machine, I cut or skim a set of soft jaws on the machine, and use the same light pressure described above.
JimGlass
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Post by JimGlass »

Jonathan;

A few checks with a dial indicator will tell you what is going on.

I would start out with a piece of metal that is already square like a
1-2-3 block or a solid square. Place the 1-2-3 block in the vise then mount an indicator to the spindle and sweep the 1-2-3 block for squareness.

Take A dial indicator mounted to a surface gage and check if the vise base is parallel to the mill table.

Learn to use that dial indicator. I have shown countless people in my career the real problems using a dial indicator, a surface plate and a square.

Jim
Tool & Die Maker/Electrician, Retired 2007

So much to learn and so little time.

www.outbackmachineshop.com
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seal killer
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Post by seal killer »

Jonathan--

Your topic is very popular on this forum and I imagine it is on other machinist's forums, as well . . . or it should be!

Our forum moderator has written well concerning squaring a workpiece. I wish I could find it and post the link right here, right now. Unfortunately, my very good friend, Sailor Jerry is visiting and his constant interference with my ability to concentrate prevents me from finding Harold's writing.

Perhaps someone else will do so?

Essentially, I BELIEVE the idea is to level one side, then turn the workpiece only 90* and square the subsequent side with the previous. I have experienced the same problems as you, while executing your method. I have also had great good fortune while executing the method you describe. But, I will definitely attempt to implement Harold's method the next time I need to square a workpiece.

--Bill
You are what you write.
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GlennW
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Post by GlennW »

You may also want to make sure your square is correct!
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
schwabw
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Post by schwabw »

Jonathan,

One thing you did not mention (sorry if this is assumed) is alignment of the vise. Have you checked its alignment with the table? Mount a DTI in the spindle, and sweep the fixed jaw; the DTI should not move very much during the travel across the jaw.

Machine Shop Trade Secrets is a great book, and has some good information on squaring blocks among many other good topics. One thing that I think I picked up from it is to bump the vise in only one direction. That is vs. alternately loosening and tightening bolts on either side to be able to bump in both directions.

My procedure is to align the vise by feeling the bolt slots on the vise and the t-slots on the table. At the risk of over-congratulating myself, I am frequently surprised at how good I have gotten at using my thumbs to push the vise into near alignment. Use grade 8 bolts and washers with good t-nuts; slide them into place to hold the vise, initially finger tight on both sides. Use a wrench to gently tighten the left bolt; tighten the right bolt until it gets snug, and then back off just a little. The idea is to allow the vise to move when tapped with a rubber mallet; the left bolt is tight, the right bolt is not loose exactly, but not really tight.

Oddly, I cannot remember when I do this part, but I clamp a v-block (any bargain hardened and ground well-squared block would suffice, mine happen to have been made in India and are really nice) into the vise. I recommend tightening the vise on the block before fussing too much with its alignment or you risk disturbing same. My hunch is that I rely on the left bolt to hold the vise to the table while I tighten the jaws, and then align it, but I'm on auto pilot and won't swear that I do it the same way every time. There is probably no wrong way, other than to skip the part about knocking the vise out of alignment when tightening the jaws.

Tightening the vise appears to generally be considered a good thing, and I like having the block's surface so I can sweep on the back surface of something, not to mention that it avoids any disagreement with the moving jaw. One thing: never waste your time sweeping the moving jaw.

For each pass, get the DTI on the left side of the block. Begin (a power feed helps here) moving the table and tap the vise as the table moves. You will quickly get the idea of which direction moves the needle which way; the goal is to make the reading constant, but at first, you simply want to bump it in the correct direction. When you run out of block, use the feed to return the table to the starting position. Move the y-axis to re-zero the DTI reading, and begin another pass; again, bump as you go. With a good starting position you can get the vise into alignment with a couple of passes.

If it starts to get really strange, start over; it gets easier with practice. Also, consider that one of your bolts might be pushing against the front or back of the t-slot. You want to start out close to correct position, but that's really not hard to achieve with a little practice.

Once you have it aligned, you have to tighten the right bolt. Do it carefully to avoid moving the vise. Retighten both bolts. Now take a confirmation pass over the block; the DTI should not move very much. If you do not like what you see, loosen the bolts and start over; join the club :)

Again, sorry if this is too basic for you. To the gang, feel free to jump all over me for anything you think is bogus in the above.

Bill
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Harold_V
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Post by Harold_V »

Before making any decisions, it would be important to know the type of machine you operate. If you are running a knee mill, a serious concern is knee sag. Everything will appear to be proper, but the part won't be. I have yet to see this mentioned. You may have to look beyond the obvious to eliminate the problem. It can be rooted in the fixed jaw of the vise. That was the case with my Bridgeport vise, which was replaced with a Kurt. End of problems.

Harold
jonathan davies
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Joined: Tue May 19, 2009 11:04 am
Location: bristol

Post by jonathan davies »

Hello

thanks for everyone's ideas, especially Toastydeath, the moment I read your comments about not using too much force I thought that's probably it. I took Jim's advice and went over everything with a DTI, I found that the work piece was out of square by about 0.03mm, and when I then used the DTI on the fixed jaw of the vice I found that on tightening with the amount of pressure I've been using there was 0.03mm of flex. I've taken a few cuts and everything has been perfect.

Thanks again, this has made my day.

Jon
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