Thread: The Journey for a Master Square

Josh, with respect to the Sony indicator, will you really be measuring to the 1/2 micron or will you be measuring thermal effects, vibration etc? You've probably seen the variations you get with the laser.
The other thing with trying to chase things to that degree of precision is Cosine error on the stand. I think I'd be looking at some masking tape for the last digit or two...

Michael

Originally Posted by Michael G

Josh, with respect to the Sony indicator, will you really be measuring to the 1/2 micron or will you be measuring thermal effects, vibration etc? You've probably seen the variations you get with the laser.
The other thing with trying to chase things to that degree of precision is Cosine error on the stand. I think I'd be looking at some masking tape for the last digit or two...

Michael

Hi Michael,
I reckon if I was Josh I would be doing the same purely because I can, but I'm not, so, I would probably put tape over the last six digits.

Phil

Hi Josh,
If its a 0.0005mm indicator, why is the last number an 8?
How high is the stand going to be? 200mmish was it? Surely there is some sort of rule of thumb re base v height? Maybe find a cylindrical square the same height and see what diameter it is?


Hi Michael,

Given the distance over which Josh will be measuring, wont Cosine error be a couple more places the the right?
Even if its not, it should be repeatable so after the first few goes Josh should know what downfeed is needed for what error, even if the error isnt strictly an absolute measurement.


Stuart

Hi Michael,
All those things are a real pain at this level but not as much as you might think, over the short time of the measurement thermal effects are minimal as it takes quite a long time for enough heat to be transferred to something with as much mass as these to change the geometry at micron level and the change that I have modelled seems like it will be reasonably uniform as long as the temperature gradient is not too steep. Cosine error is not an issues, there is more variability in the grinder downfeed than there is cosine error. From doing the 200mm angle plate the most error comes from dust on the part, surface plate, the mag chuck and dirty hands. But I can handle that just by being very careful and clean (super clean).

Stuart, the 8 is just an artefact from the photo, it should have been a zero. The stand would be for the 200mm blocks so I guess a height about 190mm would be ok. I wonder what that relation is, I will have to look it up.


The nice thing about the indicator for this purpose is its range of measurement 0-26mm and ease of reading, the display tracks the maximum and minimum values (no chance the kind of error from miss reading the small totaliser clock complication (sorry I can't think what they are called)) , its absolute accuracy wanders a little in the 5-10mm range to a maximum absolute error of 3µm. But, as Stuart says its more about the relative measurement. The other thing to note here is that all the indicators have a degree of repeatability and hysteresis at the finer end of this level. At the fine end of the scale a comparator would be better for the job because of its high degree of repeatability and low hysteresis but its a case of using what is available, and this was essentially a freebie since Ray only wanted the pelican case the test rig came in.

As far as motivation goes, I will probably only ever make one set of master squares from scratch so to speak, so I'm pushing my boundaries as far as they can go.

-Josh

Originally Posted by Brobdingnagian

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

If it's just a few castings, all of which are going to be subsequently machined so don't need to be perfectly identical, personally I would just use sacrificial foam patterns. I don't see where you would need fine detail for this purpose, although there are foams that will allow some. They allow more flexibility in design as you don't have to consider how the pattern will draw. I'd expect the foundry would love you too; no cope and drag to contend with.

Pete

Originally Posted by Pete F

If it's just a few castings, all of which are going to be subsequently machined so don't need to be perfectly identical, personally I would just use sacrificial foam patterns. I don't see where you would need fine detail for this purpose, although there are foams that will allow some. They allow more flexibility in design as you don't have to consider how the pattern will draw. I'd expect the foundry would love you too; no cope and drag to contend with.

Pete

How well does that work with iron?

Is there going to be a group order for the castings?

Can I put my hand up for 1?

I made a little progress this afternoon with the stand for the Sony indicator.

I still need to make a clamp to hold the indicator in place and mill the slot for the "curved blade". I was hoping to pick up some 100mm or 125mm BMS bar but no one around town had any. even though it is very rigid I might have to clamp it down to the surface plate to get good readings.

-Josh

DSCN2645.jpg

DSCN2651.jpg

Hi Josh,
Could you bolt the radius piece to the bottom?
I have a 12ishmm thick piece of 120mm cast bar in the shed if that would work for you.

Stuart

p.s. When I said one half pattern I was thinking they would just mount it to a flat plate. Cant remember what thats called. Two halves might be easier for them for all I know??

Originally Posted by .RC.

Is there going to be a group order for the castings?

Can I put my hand up for 1?

No group purchase yet.

When I put in a request for quotes, I asked about any volume discounts, there was none. So there is no real incentive to get a whole bunch made.

I'm getting 3 cast for myself so that I can scrape the last few microns in and make a true and square set of masters. But that's just me.

If think you might want a casting let me know via a PM and we will sort something out. Maybe direct payment to the foundry or something like that.

-Josh

Originally Posted by Brobdingnagian

How well does that work with iron?

Don't know as I've never had any done. But my mother's side of the family are 4+ generations of pattern makers and I've spoken with my uncle in the past about sacrificial foam patterns, how they're affecting the pattern making business etc and he's never said they don't work with iron. I personally can't see why it should make a difference what metal is being cast, I think the flasks and sand are the same right? If it were me I'd certainly be asking the foundry, as making a decent pattern is a job in itself.

Edit: Here's a bit more information on the process, I'm sure a bit of further research would provide more specifics on preparing the pattern
Lost-foam casting - Wikipedia, the free encyclopedia

BTW Josh, I know you are going to stress relieve this, but I keep meaning to mention that you may want to run that render/design past a pattern maker or foundry and specify precisely what its intended purpose is. To my eyes the design appears to be very highly stressed as cast. But what would I know.

Got a couple of more things done on the sony indicator stand.

Just the indicator clamp to go, but that will have to wait till tomorrow now.

DSCN2657.jpg

The blade is a close fit and I have made it to suit 8.5mm thick parallels if i ever need to swap it out for some reason also added 3 cup grub screw to keep every thing snug.

-Josh

Originally Posted by Pete F

Don't know as I've never had any done. But my mother's side of the family are 4+ generations of pattern makers and I've spoken with my uncle in the past about sacrificial foam patterns, how they're affecting the pattern making business etc and he's never said they don't work with iron. I personally can't see why it should make a difference what metal is being cast, I think the flasks and sand are the same right? If it were me I'd certainly be asking the foundry, as making a decent pattern is a job in itself.

Edit: Here's a bit more information on the process, I'm sure a bit of further research would provide more specifics on preparing the pattern
Lost-foam casting - Wikipedia, the free encyclopedia

BTW Josh, I know you are going to stress relieve this, but I keep meaning to mention that you may want to run that render/design past a pattern maker or foundry and specify precisely what its intended purpose is. To my eyes the design appears to be very highly stressed as cast. But what would I know.

It is an interesting process I'd admit and have been interested in trying it in my own foundry with bronze. But I still need to make the patterns and at the end of the day I am more familiar and articulate with making shapes out of wood and metal than polystyrene.

I have sent it to the pattern design to the foundries and what its intended purpose is and asked them to quote accordingly on the moulding and casting.

You will have to clarify as to what you think exactly would be the problem, as I can't see it.

-Josh

What you have is essentially a square and wide wheel. In CI I believe the narrower "spokes" of the design will cool before the "hub" and "rim", the stresses thus produced can be very high, and is the reason many wheel castings fail at this point.

I'm not entirely certain what the purpose of the hub actually is? It seems to me to be redundant and would add considerably to the cost. I would personally be more inclined to look at a design that was basically a circle sitting inside a square (obviously extruded) if that makes sense? The hollow circle would make the design significantly lighter, yet form a web to resist racking forces. It would also largely avoid many of the casting stresses I alluded to above. Even after heat treatment, any unequal residual stresses in your design will be trying to distort the overall shape. Obviously bad. However in the design as mentioned, the nature of the design maintains the stress to a localised area, which would have little to no real effect on the overall shape ie squareness.

My 2 cents for what it's worth