Thread: The Journey for a Master Square

Thanks, Pete, Richard
I understand now - I have an old cast iron "square" that should be but I've never been able to satisfactorily check. I should be able to adapt this method to check that for squareness. I could check it with a cylindrical square but I'm wary about checking a plane with a line contact. While in theory it will work it doesn't tell you how square and it doesn't take much of a gap to show some light.

Michael

Originally Posted by Brobdingnagian

It is just a fraction to big for the little cnc.

But I also had the idea of making 2 more sets of patterns for a set of 150mm and a 100mm squares of similar design, and I could knock them out on the cnc out of machineable wax and then cast aluminium masters patterns, as the wax is not so good for multi time uses.

I don't think I should post the quotes, it does not feel ethical. I'm happy to tell you in private just not on a public space. I will say that it is much cheaper than buying new stock and machining the excess away.

-Josh

I might be able to help you out with that. Jelutong machines really nicely and my CNC cutting envelope is 450x, 250y, 350z.

Christian

Originally Posted by Michael G

While in theory it will work it doesn't tell you how square and it doesn't take much of a gap to show some light.

Hi Michael,
I'm led to believe you just need a couple of pieces of shim/feeler guage the same thickness. One at the top one at the bottom. If they "feel" the same it will be damn close.

Stuart

Not often you need very square, But for a master....

Method 1.
Normally if I'm squaring up a block on the surface grinder I will be able to get to within 0.04mm using long wide brass shims like the picture bellow.
I grind the block parallel I then measure the block, determine how much it needs to be corrected find closest shim smaller than the error and then set the block up on the surface plate and move the shim further in or further out from the centre to get a finer degree of adjustment. I mark the corners of the block on the shim and transfer everything over to the surface grinder, setting the block aligned to the markings on the shim. Grind and test. Generally it works well on parts that are rigid enough not to be distorted, and takes not much more time than it does to measure squareness.
Block with shim.JPG

The limitation with this method is I'm limited to how small the error can be corrected being a little less than the thickness of my finest shim. So if I was out by 0.02mm and that was not good enough I would have to correct another way.

Method 2. For smaller and non rigid parts that need a fine degree squareness instead of shims I use a 10" sine table with a specially ground gauge to cancel the error and with a little care on surface plate setup and measuring I can correct most squareness errors. The limitation with method 2 is that the sine table it self takes ~150mm of travel off my Z axis and adjusting a fine amount of error is a tedious endeavour. Plus the cleaning of the sine table after grinding is time very consuming.

Method 3 is one that Machtools told me about today. it involves making a fine step with the grinder parallel with the error, and the adjustment can be as fine as the down feed on the grinder in this case about 2µm. it is akin to having a set of 2µm shims. I thought it was a very neat solution and would not take long to do.

block with step.jpg

Thanks for that one, I will be putting it to use for these master squares

-Josh

Edit: Anyone got more techniques?

Originally Posted by CGroves

I might be able to help you out with that. Jelutong machines really nicely and my CNC cutting envelope is 450x, 250y, 350z.

Christian

Seriously, That would be awesome.

Originally Posted by Brobdingnagian

Seriously, That would be awesome.

Josh,

PM me with an IGES file of the square and i'll take a look to see that I can do it. Seeing the square is symmetrical its probably easiest to mill each half separately and then fix them together.

Christian

Josh your pictures are far better than I'd do, scribled out on the back of a cigerrete pack.

https://www.woodworkforums.com/attach...block-step.jpg

Just to expand. I meant to comment when R.C was knocking up blocks. If you can measure the squarness error, easy way to corect it is to step grind it out. And the accuracy is only dependant on the down feed accuracy of your grinder.

No offence Rich. Rather than hollow cut your blocks, them lap one land down, grind one off and then leave a land.

For the sake of an urgument your error was 1 thou out of square. You have to invision which way the square has to move to inprove it.

I'd take a dust cut to establish wheel to work height. Thermal stabilty and all that. Then take a thou cut from the side that needed reducing, until you leave a high land. Ie: dont complete the pass, but leave a high land. 3 -4 - 5 mm wide.

Then flip that over. Tipping it on the as Josh's renderings. Your high land will tip the part over correcting the out of squarness. Then flip flop & grind off the land and get back to parrallel.

I have trouble descibing it, it takes me seconds when I'm in front of a grinder.

If it's symmetrical do you even need to make 2 halves?

Stuart

Originally Posted by Stustoys

If it's symmetrical do you even need to make 2 halves?

Yes and no,

I was going to cast the single hand made half Pattern in Aluminium twice and then that would become the Master Pattern to be then used to make the molds for casting in iron.

And I have allowed for double shrinkage; once for the aluminium and once of the iron and there is no guarantee that the two halves would be mirror images. My thinking was that I would align the two aluminium halves as best as possible and bolt them together and then machine/clean up the Master Pattern together as one unit.

On the plus side the pattern would be extremely durable, and would be able to take very nice detail

But with the possibility of them being milled on a CNC a lot of the variability goes down between making 2 separate halves. If it was only ever just me getting it cast then a painted wooden pattern would be sufficient for the three casting I need. If other people wanted to have it cast? then I would make an aluminium master.

-Josh

Originally Posted by Machtool

Josh your pictures are far better than I'd do, scribled out on the back of a cigerrete pack.

https://www.woodworkforums.com/attach...block-step.jpg

Just to expand. I meant to comment when R.C was knocking up blocks. If you can measure the squarness error, easy way to corect it is to step grind it out. And the accuracy is only dependant on the down feed accuracy of your grinder.

No offence Rich. Rather than hollow cut your blocks, them lap one land down, grind one off and then leave a land.

For the sake of an urgument your error was 1 thou out of square. You have to invision which way the square has to move to inprove it.
1.jpg
28 somthings in this case
2.jpg

I'd take a dust cut to establish wheel to work height. Thermal stabilty and all that. Then take a thou cut from the side that needed reducing,
until you leave a high land. Ie: dont complete the pass, but leave a high land. 3 -4 - 5 mm wide.
3.jpg

Then flip that over.
4.jpg
Tipping it on the as Josh's renderings. Your high land will tip the part over correcting the out of squarness.

Then flip flop & grind off the land and get back to parrallel.
5.jpg
I have trouble descibing it, it takes me seconds when I'm in front of a grinder.

Team work

Originally Posted by Brobdingnagian

Team work

Do you think any one will believe us? Its such a good thing this isn't an international forum.

In full discloser. This method was spelt out with just the use of a beer coaster, and no available pen.

Originally Posted by Machtool

Just to expand. I meant to comment when R.C was knocking up blocks. If you can measure the squarness error, easy way to corect it is to step grind it out. And the accuracy is only dependant on the down feed accuracy of your grinder.

I did not have a clue how to square up a block to get it right and relied on information on PM to work out a way.... Did not think of step grinding like that...

Originally Posted by Machtool

Do you think any one will believe us? Its such a good thing this isn't an international forum.

In full discloser. This method was spelt out with just the use of a beer coaster, and no available pen.

Even i understood it with the beer coaster.....and i don't own a grinder and i was trying to control Mr too much energy and long car trip ahead.....

In aid of my search for a better square, Ray earlier in the day extracted a Sony 0.5 micron indicator and display from the turbine test rig he picked up a while back. see picture

DSCN2642[1].jpg

So I need to fabricate a stand to for it to as it is too large for any of the existing stands. I'm hoping someone has a bright idea for a dedicated indicator stand to suit for testing square by reversal.

Thinking about it I think I have some 3" dia mild steel bar somewhere around here, it squared off and a V cut into the top might serve that purpose. what do you guys think?