CNC lathe conversion part 2 - X axis

So I decided to undertake a non-destructive conversion of my King 10x36 Gear head. Not replacing the acme screws with lead-screws means that the mechanical conversion is pretty easy. Backlash and precision are not going to be great, but they may be good enough for the application. Time will tell.



Here is the saddle with the compound and the cross slide removed.
The lead screw is 5/8 x 10tpi acme. This has always been the weak point of this machine. It seems impossible to torque the acme nut to the compound and have the acme nut correctly adjusted to eliminate unreasonable backlash. Fixing that would likely require replacing the bearing, mount and probably also the nut and screw. More trouble that I think it is worth going to at this stage.





A shot of the existing screw and fixed bearing assembly. The double nuts at the end of the journal bearing are a very poor solution as counter-tightening the second nut tends to dramatically alter the load on the bearing.





I'll be using 5mm HTD timing belts and pulleys from SDP/SI (who have a very useful pulley designer on their site) rather than direct drive for this build. The X axis is the tricky one as the pulley plus the belt and the cover have to fit under the cross-slide. I was trying for around 2:1 advantage, but couldn't quite get there on the X. The configuration for the X is 13 double flange : 22 no flange with a 60 tooth belt. The Z is 19 df : 38 nf with a 77 tooth belt. Three of the four hubs all had to be re-bored to the correct shaft size. The 13 tooth was a total pita. 

A 6A25M022NF1508
A 6R25M060150
A 6A25M013DF1506
A 6A25M038NF1510
A 6R25M077150

A 6A25M019DF1508






The disassembled fixed bearing and, at the bottom of the shot, the journal extension with a 0.3745" stub, a section of M10 x 1.5 thread and a 0.5000" shaft to receive the drive pulley.





Here, the existing threads have been cut off the end of the lead screw journal and I'm just about to centre drill, drill out and ream a 0.3750" hole that will receive stub of the new journal extension.





A little loctite and a coffee break later and the new journal is done. 




All finished except for a cover (which turned out to be a little hard than I thought and after a couple of false starts isn't done yet). Note the brass nut replacing the double M10 nuts. This can be tightened to put just the right load on the bearing and then locked in place with a set screw. I dropped a little brass slug into the set screw hole before torquing it down to avoid damaging the screws on the journal.






The stepper (an Oriental Motor PK296DAA I think) and the mounts just fit inside the splash guard. A couple of final thoughts... There is an alternative to this mounting position as the King has an excellent gear box on the saddle to power either the Z or the X axis. Mounting the motor on the drive shaft of the gear box instead of directly to the end of the X lead screw would be very easy. While taking the X axis fixed bearing apart and reassembling it a few times I realized that, in addition to it being the least well-built part of this machine, it also isn't really intended to handle radial loads. While the motor and timing belt aren't particularly large loads, they still shouldn't really be on this bearing. If this proves problematic, I can either attempt to replace the whole bearing assembly with something better off-the-shelf, make a housing for the existing bearing that will handle the load or move the whole shebang to the gear box drive shaft. I decided not to go this route at the start because the gear box will induce considerably more backlash.

CNC lathe conversion part 1 - research

I was not really planning on going here at the beginning of the coffee project, but the prices I'm getting back for some of the parts are making me rethink at least the initial production run. There are some things that I cannot do in the shop: castings, complex cnc parts and plating etc. Cutting tapered parts is also not possible (or at least not practical) and the time I would spend on the learning curve for manual single point metric threading on an inch lathe seems like it might be better spent on tackling the CNC. However, my lathe is manual and possibly not the best starting point for a cnc conversion. I'm also not terribly keen on no longer having any manual control. So, some things to consider. 

(Note - here is a technique for manual metric threading using the half nut to disengage the lead screw.)   https://m.youtube.com/watch?v=HXt4TWa382Q  


Useful lathe CNC conversion posts:

8x12 Harbor Freight conversion
http://plsntcov.8m.com/CNClathe/CNClathe1.html

Excellent conversion of a Jet 13x40 http://www.hobby-machinist.com/threads/converting-a-13x40-manual-lathe-to-cnc-with-servos-and-mach3.33405/

Another excellent conversion using a kit from Billy Tools
longezproject.blogspot.ca/2015/02/cnc-lathe-conversion-part-1.html Possible converts:

Busy Bee 7x12

At 75 lbs there isn't really enough meat on the bones and bore is only 20mm.

Old and tired gearhead on kijiji

More old and tired 36" Logan on lespac

Converting a manual lathe to CNC is quite a bit more invasive than doing a manual mill. All of the elaborate gearing for threading and power feed are dumped along with the compound and the worm screws. All that one really needs is a solid frame, a good apron and the head and tail stock. Finding one with a 3 phase 220V motor would be a bonus, but unlikely. 

...so its back to ballscrews...

For my mill conversion I bought used ground ball screws for the X & Y and a new surplus for the Z from ebay. The precision of all three was C5 if not better. However, the X axis (which is the longest, most expensive and was the hardest to find) has some issues, possible because of a crash courtesy of the previous owner. So I am somewhat ambivalent about going the used route again. However, finding surplus screws of the right dimensions with support blocks is really tough, so the only affordable and convenient options for buying new are Chinese rolled C7 precision grade that come with journals and matching supports. C7 is 0.002" in 12" (in the worst case over the length of the screw) which, given what we are proposing to manufacture here, isn't that bad.

X axis

used THK - 14x4mm 358mm with 235mm travel - with supports and stepper frame - $189

used NSK - 16x5mm 407mm with 282mm travel - with supports and stepper frame - $189

used NSK 20x5 460mm overall with supports - $250

new NSK 25x5 ~440mm overall no supports - $270

surplus THK 14x2mm 416mm overall no supports $200

new Kuroda 12x2?mm ~15.5" overall no supports $90 plus shipping from US



Z Axis - the hard one...

used THK - 20x5mm x 1385mm ROLLED with supports - $239

new C7 Chinese - 20x05 x 1352mm with supports- linearmotionbearings2008 - $105 plus shipping



Update 2016 4 27

A couple of simple conversions using the existing lead screws. The second one is particularly interesting because it doesn't require giving up manual control! 

flashcut cnc
https://www.youtube.com/watch?v=_Polq5piWhQ

optimum
https://www.youtube.com/watch?v=FWg8NzfP108

A conversion of a small grizzly using a kit from BD Tools. Excellent blog about building an airplane too.

http://longezproject.blogspot.ca/2015/02/cnc-lathe-conversion-part-1.html

For the shrink that fits - Alice's adventures in tolerance land

More thoughts about the group body casting.

Having stared at the casting after looking directly at sun for a few minutes I am now pretty sure that it is an assembly of two parts: the bulk plus a small internal sleeve that holds the dispersion screen. Putting these two parts together could be done in a number of ways, but to avoid the possible consequences of heating the casting to soldering or brazing temperatures, I think that a shrink fit is probably the best bet.

From the engineeringtoolbox:

Shrink-fits are assembled by heating them to temperatures where the expansion exceeds the interference. Required temperature heating can be calculated as

dt = δ / α d_i         (1)

where

dt = temperature heating (^oC, ^oF)

δ = diametric interference (mm, in)

α = coefficient of linear expansion (m/m^oK, in/in^oF)

d_i = initial diameter of hole before expansion (mm, in)

Diametric interference can be calculated as

δ = dt α d_i         (2)

So assuming the sleeve is at room temperature and the body is heated in boiling water:

Nominal hole diameter d_{i =} 58mm
Temperature heating dt = 80^oC
Coefficient of linear expansion α for C23000 brass = 18.7x10^-6 (°C)^-1
Coefficient of linear expansion α for C87850 brass = 18.5x10-6 PER °C (20-100 C)

Therefore:

for C23000
δ (80^oC) = 80^oC x 0.0000187 (°C)^-1 x 58mm = 0.086768mm

for C87850
δ = 0.08584mm

...or more or less the same.


So over-sizing the sleeve diameter by 0.08mm (which is pretty close to 0.003") will allow it to be shrink fit into place with minimal force.

And after drinking the potion mark "drink me" Alice can now go down the rabbit hole to tolerance land. 

Interference H7/s6 S7/h6  - Medium drive fit for ordinary steel parts or shrink fits on light sections, the tightest fit usable with cast iron. 

The tolerance for the sleeve and the hole diameters is important as the two add together. So a symmetrical tolerance of +/- t will possibly result in a total tolerance of 2t.

So allowing for a minimum of 0.05 interference which should still provide a 'medium drive' shrink fit, the diameter of the hole should be 58 +0.015/-0 and the sleeve diameter should be 58.08 +0/-0.015

So in the worst case scenario, the hole is 58.015 and the sleeve is 58.065 which still results in 0.05 interference.

Brazing

From copper.org

http://www.copper.org/applications/plumbing/techcorner/soldering_brazing_explained.html

A major difference between brazed and soldered joints is in the amount of joint overlap or fill necessary to develop full strength of the joint. In a brazed joint, full insertion of the tube to the back of the fitting cup is still highly recommended; however, complete fill of this joint space throughout this entire length is not necessary to achieve full joint strength. According to the American Welding Society (AWS), it is suggested that the brazing filler metal penetrate the capillary space at least three times the thickness of the thinnest component being joined, which is usually the tube. This is known in the industry as the AWS 3-T Rule.

Because of the increased strength of brazing alloys, even this rather small amount of fill penetration will result in a properly fabricated brazed joint stronger than the tube and or fitting themselves. However, unlike a solder joint, where the cap or fillet provides minimal additional strength, a brazed joint should be fabricated so that a well-developed fillet or "cap" of filler metal is provided between the tube and fitting on the face of the fitting. This fillet, or cap as it is often referred to in the trade, permits the stresses developed within the joint (by thermal expansion, pressure or other cyclic reactions such as vibration or thermal fatigue) to be distributed along the face of the fillet. In a brazed joint fabricated without the well-developed concave fillet, all stress would be concentrated at the sharp point of contact between the tube, braze alloy (filler metal), and the fitting, possibly leading to development of a stress fracture in the tube at that point. Creation of the fillet when fabricating the brazed joint greatly minimizes this possibility.

______________

Besides the strength of the filler metal in the joint, the overall strength of the joint or assembly (tube, fitting and joint) following the joining operation must also be considered when choosing whether to use soldered or brazed joints. As discussed, by definition the temperature that defines the difference between soldering and brazing of copper is approximately 840°F/449°C. This temperature is much more important than just an arbitrary definitional threshold. It is important because 700°F/371°C is the temperature at which copper begins to anneal, or be changed from hard temper (rigid) to annealed temper (soft). With this change in temper comes an inherent loss in strength - hard temper copper is stronger than annealed temper copper. The overall amount of annealing that occurs, and thus strength that is lost, is determined by the temperature and the time the material spends at that temperature. The higher the temperature, the less time it takes to change from hard temper to soft temper.

Since brazing temperatures must exceed the melting point of the brazing alloys, between 1,150°F/621°C and 1,550°F/843°C, the process of making a brazed joint causes the base metals to anneal or soften, resulting in a reduction in the overall strength of the assembly. While a brazed joint is demonstrably stronger than a solder joint, the Rated Internal Working Pressure, that is the 24/7 allowable working pressure of the system, is lower for annealed tube (see Copper Tube Handbook, Tables 3a through 3e).

Boiler research

The following is based on two avenues of research, one from the model steam boiler community, the other from the copper industry - the latter is perhaps more pertinent finally. 


The massively skilled Don R. Giandomenico, aka rcdon, built a model steam boiler based on instructions from "Model Boilers & Boilermaking” by K.N. Harris (1967). 



To make the boiler shell (outer cylinder of the pressure vessel) I am using a piece of solid drawn (seamless) type “L” copper tubing (seen below). This tubing is 6.125” in OD and has a wall thickness of .140”. According to the Harris book (page 31) it is satisfactory to have a seamless boiler shell at 5.845” ID x 0.094” wall operating at a working pressure of 100 PSI. This is calculated by multiplying the the working pressure (P) by the internal diameter of the shell in inches (D). You then divide this value by two times the derated tensile strength of the material being used (t). T is equal to the thickness of the boiler shell in inches:

                                      (P X D) ÷ (2t)= T

       The normal tensile strength of copper is around 25,000 pounds per square inch which in this case is derated by the factor of 8 times for a safety margin (3,125 X 8 = 25,000 PSI). This means that the boiler can handle 8 times the stress that would be applied to it under normal operating conditions. Knowing these values I can then plug them into the equation:

     (100 x 5.845) ÷ (2 X 3125) = T ................... 584.5 ÷ 6250 = 0.094” thick

       The boiler shell I am going to use would effectively handle a working pressure of 150 PSI. In fact, the manufacturers listed burst pressure of this type of tubing is at around 2,690 PSI !!!! I will have no trouble trusting this tubing at 80 PSI. Of course copper starts to lose it’s strength at elevated temperatures so it is important to keep it within it’s operating temperature.

The Aurora is rated to 1.5 atmospheres (or 1.5 bar) with an operating pressure of between 0.8 and 1 atmosphere. 

From Harris p.28:

In all boilers it is usual to allow a comparatively high factor of safety, that is to say that if a boiler is required to work at 100 lb. per sq. in., its plates, stays, etc., are calculated on a basis of its bursting at anything from six to ten times this pressure. A good all round factor for model work is eight and that will be the one adopted in what follows.

p.31

This brings us to the strength of boiler shells. In calculations relating to the strength of a boiler shell; so far as the plate is concerned it makes no difference whether it is a rolled plate with a longitudinal joint or a solid drawn tube, that is to say so far as the stressing of the shell is concerned. What does have to be taken into account, however, is the strength of the longitudinal joint, a solid drawn tube having no joint is the strongest form.

The next best arrangement (model practice) is probably one with an inside butt strap riveted and hard soldered, the rivets being only to hold the whole issue together during the brazing or silver soldering operation. If all the contacting surfaces of butt -strap and boiler shell are clean and well fluxed and a proper job is made of the soldering, which entails on the one Land plenty of heat and on the other the avoidance of over-heating, the value of the joint should be about 95 per cent. of that of a solid drawn tube. A joint made with a double butt -strap, see sketches of of joints and double or treble riveted, which means either two or three rows of rivets each side of the joint, should have a strength equal to about 80 per cent. of that of a solid tube.

A double riveted lap joint will have around 75 per cent. and a single riveted lap joint 55 per cent of the strength of a solid drawn tube, so that it is very obvious that it pays handsomely to use the butt-strap plus brazing technique in making longitudinal joints. Best of all, of course, is
to use a solid drawn tube.

As I am not interested in riveting, the approximately 7" diameter boiler must be butt-strap and (hard) brazed construction as 7" nominal tube is not to be had. t, the derated tensile strength for copper is 25,000psi / 8 = 3125psi. The construction technique further derates the thickness by a factor of 100/95%.

T = (P x D)/2t x 100/95

T - thickness of the shell
P - working pressure in psi
D - internal diameter of the shell in inches 
t - derated tensile strength of the material

The working pressure is 1 bar or 14.7 psi so:

T = (14.7psi  x 7")/(2 x 3125psi) x 100/95

T = 0.017in which is around 26 gauge or not very thick at all...

Too thin in fact to make it easy to braze the fittings in place.


_______

The Copper tube handbook contains all the tables, formulas and recommendations discussed here.

Further reading on the copper.org site suggests that brazing or welding will anneal the copper considerably lowering its tensile strength. The brazing temperature threshold is 840F (450C) with most brazing alloys considerably higher than that (~1200F (650C)). Copper begins to anneal  at 700F (370C). The hotter temperature and the longer the heat is applied, the quicker the annealing takes place.

Since brazing temperatures must exceed the melting point of the brazing alloys, between 1,150°F/621°C and 1,550°F/843°C, the process of making a brazed joint causes the base metals to anneal or soften, resulting in a reduction in the overall strength of the assembly. 

Consequently, copper.org offers tables of the maximum safe working temperatures and pressures for various diameters of annealed tube.

Working pressure for the machine is 1 bar gauge (which is 2 bar absolute pressure i.e. 1 atmosphere above atmospheric pressure). At 2 bar, water boils at 120C (250F). So from tables 14.3 A, B and C:

Calculated Rated Internal Working Pressures for Annealed Copper Tube

Nominal Tube type and diameter inches	S = 4800psi 250F	Wall thickness inches	Inside diameter inches
6 K	277	0.192	5.741
8 K	295	0.271	7.583
6 L	201	0.14	5.845
8 L	216	0.2	7.725
6 M	175	0.122	5.881
8 M	183	0.17	7.785

Based on maximum allowable stress in tension (psi) for the indicated temperatures (°F).

Raising the temperature to 300F results in a lowering the safe working pressures by around 6psi.

An explanation of the formula used to calculate these values is here. 

Furthermore:

In designing a system, joint ratings must also be considered, because the lower of the two ratings (tube or joint) will govern the installation. Most tubing systems are joined by soldering or brazing. Rated internal working pressures for such joints are shown in Table 14.4a. These ratings are for all types of tube with standard solder joint pressure fittings and DWV fittings. In soldered tubing systems, the rated strength of the joint often governs design.

From table 14.4a - the working pressure rating for brazed joints on all diameters of tube for use with saturated steam is 120psi gauge. Soldered joints, with all alloys and for all diameters and for use with saturated steam are limited to 15psi gauge.

The very conservative working pressure ratings give added assurance that pressurized systems will operate successfully for long periods of time. The much higher burst pressures measured in tests indicate that tubes are well able to withstand unpredictable pressure surges that may occur during the long service life of the system. Similar conservative principles were applied in arriving at the working pressures for brazed and soldered joints. The allowable stresses for the soldered joints assure joint integrity under full rated load for extended periods of time. Short-term strength and burst pressures for soldered joints are many times higher. In addition, safety margins were factored into calculating the joint strengths.

So what are the conclusions to be drawn from this? The numbers from copper.org are far more conservative than those from Harris. However, the desired working pressure of 1 bar (14.7 psi) is exactly on the money for soldered systems! My guess, given that espresso machines are low-pressure steam systems, is that the boiler is soft soldered!

Once again copper.org gets the last word:

Temperature and pressure are directly proportional for steam. As the pressure in the system is increased, the temperature increases accordingly. Saturated steam, a condition where steam contains as much water as it can and still be a vapor, at 15 psig has an absolute pressure at sea level of 29.7 psia (pounds per square inch absolute). At this pressure it would have a corresponding temperature of approximately 250°F which is the maximum recommended temperature for soldered joints as shown in Table 4 of the Copper Tube Handbook. Therefore, rather than the allowable pressure of the soldered joints controlling the rating, the allowable temperature is the controlling factor, leading to the rating of 15 psig regardless of the solder alloy used.

...

As with any piping system, the pressure rating of the system is controlled by the lowest allowable pressure of the tube, fitting, joint or joining material. For steam systems constructed using copper tube of Types K or L, the maximum allowable pressure at which the system could be designed would be 120 psig. As shown in Tables 3a and 3b of the Copper Tube Handbook, the lowest maximum operating pressure for Type L copper tube is 127 psig (corresponds to 12-inch nominal Type L tube in annealed form). Since this is more than the allowable pressure for the brazed joint, the 120 psig allowable for the joint is the controlling factor, regardless of the fact that smaller diameter tubes have higher allowable pressures. However, to use copper tube and fittings in a steam system at this pressure the joints must be brazed.


As long as these temperature and pressure limits are met, copper tube and fittings can be used in both high- and low-pressure steam systems. The system must still be designed and installed to meet the requirements of all applicable local, state and federal construction and safety codes for steam applications.

Grouphead materials - lead in your morning coffee?

Materials - Alternatives to leaded brass used in the Aurora grouphead

The body of the Aurora grouphead is made from cast brass. Lead is added to brass to improve machinability. It acts as a lubricant and causes the chips to break into small pieces while it is being cut. Worse still, because of the way the lead crystals form as the liquid metal solidifies in the mold, the concentration of lead is highest at the inside surface - i.e. where the water comes into contact with the group body. C84400, traditionally the most popular alloy for faucets and plumbing fixtures, contains 7% lead, so it is highly likely that all vintage espresso machines help you meet your recommended daily dose of lead in the morning. This was just the way things were was until California passed its law in the early 90s. Since then, considerable effort has been made to find alternatives to leaded brass. 

Excellent guide to copper casting alloys from copper.org


From: http://www.copper.org/applications/industrial/lowlead.html

Sand-cast faucets and other plumbing components have traditionally been made from leaded red, semi-red and yellow brasses. The most common plumbing brass, C84400 (also known as 81 Metal or 81-3-7-9) contains nominally 7% lead. The most popular red brass, C83600 (85 Metal, 85-5-5-5), contains nominally 5% lead. Permanent mold and pressure die castings of plumbing components are also commonly made of the leaded yellow brass alloy C85800, which contains nominally 1.5% lead. In contrast to the red brasses, which are moderate-strength, single-phase alpha alloys, alloy C85800 is stronger at both room temperature and at elevated temperatures approaching the solidus, because of the presence of the beta phase in the alpha matrix. These improved mechanical properties are an advantage not only during casting and machining, but also in service. Alloy C85800 has a pleasant light yellow color and can be buffed to a high polish.

EnviroBrass (SeBiLOY) http://www.copper.org/environment/water/NACE02122/nace02122b.html

The idea of using a combination of bismuth and selenium as a substitute for lead was originally conceived by the ASARCO Technical Center, Salt Lake City, Utah. This was pursued by several years of research by an industry consortium which included the Copper Development Association Inc. (CDA), the American Foundrymen's Society (AFS), the Brass and Bronze Ingot Manufacturers (BBIM), the Materials Technology Laboratory of CANMET, other foundries and water product producers. The research shows that a combination of bismuth and selenium provides the same beneficial effect on machinability as does lead. In addition, pressure tightness and other casting characteristics of bismuth/selenium brasses were found to be virtually identical to those in conventional leaded alloys.

Three alloys have been developed, EnviroBrass® I, II and III, which are Alloys C89510, C89520 and C89550

Elements	Range or Max%
	EnviroBrass I C89510	EnviroBrass II C89520	EnviroBrass III C89550
Copper	86.0-88.0	85.0-87.0	58.0-64.0
Tin	4.0-6.0	5.0-6.0	0.1-1.2
Lead	0.25	0.25	0.1
Zinc	4.0-6.0	4.0-6.0	32.0-38.0
Bismuth	0.5-1.5**	1.6-2.2***	0.6-1.2
Selenium	0.35-0.75**	0.8-1.1***	0.01-0.1
Nickel (incl. Cobalt)	1	1	1.0.
Iron	0.2	0.2	0.5
Antimony	0.25	0.25	0.05
Sulphur	0.08	0.08	0.05
Phosphorus	0.05	0.05	0.01
Aluminum	0.005	0.005	0.1-0.6
Silicon	0.005	0.005	0.25

Sum of named elements 99.5

* Cu + sum of named elements, 99.5% min. 

** Experience favors Bi:Se ≥ 2:1. 

*** Bi:Se ratio ≥ 2:1.


Federalloy - http://www.concast.com/green-alloys.php

Federalloy is a patented alloy in which lead is replaced with bismuth to create pressure-tight plumbing fittings and fixtures. It has excellent machinability. Concast has been the only foundry in the nation licensed to produce the Federalloy series of lead-free copper alloys. We joined forces with Federal Metal Company, who developed the Federalloy group of alloys, such as C89831 and C89835.

C89831 is a replacement for C84400

Chemical Composition
Alloy	Cu%	Sn%	Pb%	Zn%	Fe%	Ni%1	Sb%	P%	S%	Al%	Si%	Bi%
C89831
	91-87	3.7-2.7	0.1	4	0.3	1	0.25	0.05	0.08	0.005	0.005	3.7-2.7
1Ni value includes Co.
Note: Cu + Sum of Named Elements, 99.0% min. Single values represent maximums.

EcoBrass - C69300 (wrought) / C87850 (cast)


http://en.coppercanada.ca/pdfs/CCMagazinePDFs/E157b.pdf

The two most common types of lead-free alloys in commercial use today are the silicon brasses (of which ECO BRASS®
 is one) and the bismuth containing bronze alloys. It is noteworthy that ECO BRASS® melts at temperatures about 150°C
(300°F) lower than the bismuth alloys, and it is 7% less dense. This means that for the same size component, the manufacturer can reduce the casting weight by 7%.

ECO BRASS® can be used in all potable water applications incorporating extruded rod, forgings and castings. Some examples are faucets, fire protection devices, ball valves, shower valves and water meter bodies.

Element
	Cu(1,2)	Pb	Sn	Zn	Fe	P	Ni(3)	Mn	Si
Min (%)	73					0.04			2.7
Max (%)	77	0.09	0.2	Rem	0.1	0.15	0.1	0.1	3.4
(1) Cu value includes Ag.
(2) Cu + Sum of Named Elements 99.5% min.
(3) Ni value includes Co.

C89833 Copper Bismuth Alloy - source lbfoundry.com

Alloy C89833
Cu%	Sn%	Pb%	Zn%	Fe%	Ni%	Sb%
86.00-91.00	4.00-6.00	0.09	2.00-6.00	0.3	1	0.25
P%	S%	Al%	Mn%	Si%	Bi%
0.05	0.08	0.005	N/A	0.005	1.70-2.70

Update 2016 3 2

Excellent database of properties of copper alloys.
http://www.copper.org/resources/properties/db/basic-search.php

_________

First quote back from a foundry in China. They seem to be suggesting casting in CuZn40 alloy which is C28000 aka Muntz Metal. C85800

This is both odd and not desirable as:

The UNS designations for wrought brasses includes C20500 through C28580, and C83300 through C85800 for cast brasses.


Certain brasses can corrode in various environments. Dezincification can be a problem in alloys containing more than 15% zinc in stagnant, acidic aqueous environments. Dezincification begins as the removal of zinc from the surface of the brass, leaving a relatively porous and weak layer of copper and copper oxide. The dezincification can progress through the brass and weaken the entire component

http://www.copper.org/resources/properties/microstructure/brasses.html _________

LEAD FREE COMPLIANCE

With the legislation passed in California (AB1953) and Vermont S152) serving as a catalyst for a national interest in the lead free regulations for potable water, a National Lead Free Bill was signed by President Obama in January 2011. This Senate Bill S.3874 (aka: Reduction in Lead in Drinking Water Act) that was signed will reduce the lead content in faucets, fittings and valves from 8% to no more than a weighted average of 0.25% maximum lead when used with respect to the wetted surface of pipes, plumbing fittings and fixtures or other potable water applications. This law will go into effect nationally January 1, 2014.

__________

Interesting reading:

Metal Casting: A Sand Casting Manual for the Small Foundry, Volume 2
By Steve Chastain


____________________

Update 2016 3 3

Excellent site and white paper on the comparison of lead-free copper alloys.

__________________


Update 2016 3 20 - Dezincification - slay the beast you cannot see

Finding an appropriate brass alloy in China is proving to be complicated. Further reading is required.

General discussion of brass types 

http://admin.copperalliance.eu/docs/librariesprovider5/publication-117/117-section-6-types-of-brass.pdf

A note on the dezincification of brass and the inhibiting effect of elemental additions - 1993 

http://www.copper.org/applications/rodbar/pdf/7013.pdf

Excellent explanation and analysis of dezincification 

https://cdn.chasebrass.com/wp-content/uploads/2016/11/Dezincification-Web-Class-ver-5-11-17.pdf

Some Conclusions

15% is the limit for zinc content to avoid the problem (mostly).

Arsenic, phosphorus, antimony, aluminum, silicon are used to inhibit corrosion in brasses of up to 35% zinc composition. 

Annealing redistributes the vulnerable beta phase in duplex brasses into localized pockets as opposed to strings thus reducing the effects of dezincification.