Tapping Phosphor Bronze balls

[Steve RowbothamParticipant @steverowbotham77083]

I’m currently building the Stuart governor and am on the final component, drilling and tapping the Phosphor Bronze balls. I made an Aluminium collet to hold the balls as advised by the very helpful Tug, and all went well in terms of drilling the 2.05m hole for tapping 7BA.

Holding the first (taper) tap in a a T handle wrench guided by a spring tapping guide in the tailstock chuck, I started cutting the thread using cutting fluid and regularly reversing the tap, and managed to tap almost to the required 3/8 depth, then disaster struck.

So now I have 2 problems, firstly sourcing another ball and secondly working out how to avoid repeating the problem.

I have struggled to find 5/8 Phosphor Bronze balls, Stuart provide them only as part of the fittings kit but that would be an expensive way to buy them. My thoughts are to use Brass balls which are readily available, and the difference in density is negligible (8.73 gm/cm3 vs 8.86 for Phosphor Bronze).

So firstly, can anyone advise where to source 5/8 PB balls at a sensible price, if not I will just go down the Brass route. Secondly, any views on what I could have differently to avoid breaking the tap would be greatly appreciated!

 

 

 

[JasonBModerator @jasonb]

On small threads like that although you were backing off to break the chips they will build up around the tap so worth withdrawing and cleaning the tap maybe half way through. Alternative is a spiral flute tap that will push the swarf up out of the hole.

[John HaineParticipant @johnhaine32865]

PB isn’t nice to tap.  I can’t see any benefit over brass, just get brass balls.

[Nigel BennettParticipant @nigelbennett69913]

I would use a larger tapping drill than 2.05mm; you could probably get away with 2.2mm, which considerably reduces the load on the tap and provided you’ve got more than 3 or 4 threads, won’t significantly reduce the strength of the assembly.

[DalboyParticipant @dalboy]

Something worth looking at when tapping any material with a T handle is the way the tap is held.

This video explains it better than I could.

https://youtu.be/C0PBPGjd0Pc?si=Lg1M7CO4v21t_ikD

 

[Peter Cook 6Participant @petercook6]

Try soaking the existing ball in a saturated solution of alum. Watchmakers use it to get broken steel screws out of brass. May discolour the ball but should turn the broken tap to mush.

[ChrisLHParticipant @chrislh]

I had such a bad time just with the drilling that I deleted the tapping and Loctited the shaft in place. This was for a “wiggler” edge finder which needed two lots of difficult drilling, one in each ball. Try Maccmodels.co.uk they sell “bronze ball bearings” which are in fact bronze balls, ball bearings being the name usually applied to the complete bearing assembly ready to use.

[Peter TuckerParticipant @petertucker86088]

Hi Steve,

Sulfuric acid should eat the tap out leaving the bronze ball relatively untouched.

Hope this helps.

Peter.

[bernard towersParticipant @bernardtowers37738]

Use Alum powder from your friendly

indian spice shop, mix up a strong solution and dunk agitate the solution down the tap flutes with a hypo and you should see black gunk which is the tap being dissolved. Use warm if you can it speeds things up (be Patient) and the alum will not damage your bronze ball. Only works on non ferrous.

[Robert Atkinson 2Participant @robertatkinson2]

+1 for Alum (Potassium Aluminium Sulphate, AKA Fatakdi, Fitkari).

I use a peristaltic pump to direct a jet of solution (under the surface of the liquid). This keeps fresh solution on the hole and flushes the debris out. I happen to have a lab pump, but you can get small ones on ebay and amazon. Sometimes called dosing pumps. They have the advantage that the liquid only touches the inside of the plastic pipe so no corrosion.

Robert.

[Nigel Graham 2Participant @nigelgraham2]

Degrease the ball and tap first, to give the alum solution chance to get at the bit of tap.

Starting with a hot solution is worthwhile, but it may still take quite a long time. I have had to use the technique once, with a tap snapped in stainless-steel, and I think it took a few days but did work.

I don’t know if your tap being in a copper alloy will accelerate the rate of dissolution compared with my case of steel and steel-alloy.

Put the ball and solution in an old jam-jar or similar, put the lid on, give the thing a gentle shake around now and then to clear the debris from the hole.

I forget where I bought the alum, but it wasn’t in an Asian food shop.

[Dalboy]

On Dalboy Said:

Something worth looking at when tapping any material with a T handle is the way the tap is held.

This video explains it better than I could.

https://youtu.be/C0PBPGjd0Pc?si=Lg1M7CO4v21t_ikD

 

Thanks for the link I have seen the video before but re  watched anyway

H

[MikeKParticipant @mikek40713]

Having recently tried alum to dissolve a tap broken in aluminum, I wish anyone good luck.  Heat helps, and may even be necessary.  Take care to not use a steel pot.  I used a Pyrex glass dish sitting on a hotplate.  Lots of bubbles, but didn’t see any progress after two [8-hour] days.

(I got my alum in the grocery store, it being a common item used for pickling food items.)

[noel shelleyParticipant @noelshelley55608]

Spark erosion is MUCH quicker if you know someone with such a machine. As has been said a slightly bigger tapping drill. Brass would be cheaper and do the same job. Noel

[Steve RowbothamParticipant @steverowbotham77083]

Thanks all for your most helpful suggestions, I will have ago at recovering the first ball and drilling & tapping the second using the above advice, and change to Brass as a fallback if needed. The video is excellent, Joe gives a very clear explanation as to the most likely cause of my tap breaking – and I had no idea the plunger in the spring loaded tap guide was reversible! Will report back in due course when the weights are fitted to this…..

[Ramon WilsonParticipant @ramonwilson3]

Hi Steve – as I said help is at hand but to add to the other good advice

Phosphor Bronze – as opposed to gunmetal – is probably one of the worst materials outside of some stainless that the average ME comes up against. It is very prone to work hardening and will seize and break a drill/tap quicker than you can see or feel it happening. Reaming is also fraught with difficulties rapid heat build up and seizure quite common to the uninitiated. Best advice is to avoid it when ever possible.

I have never tried it but old school advice is to use alum – whether it works efficiently I have no idea.

On something like this – or a casting for instance it is better to drill the hole over size then Loctite in a pre-tapped insert. If you are unfortunate to break a tap in the insert then at least the part is not affected.

I can’t help with a spare ball that size. If you really want non ferrous then I’m not sure where to get them but you can purchase steel ‘soft balls’ from Simply Bearings which is a more realistic alternative.

 

Be in touch later – Tug

 

[MikeK]

On MikeK Said:

Having recently tried alum to dissolve a tap broken in aluminum, I wish anyone good luck.  Heat helps, and may even be necessary.  Take care to not use a steel pot.  I used a Pyrex glass dish sitting on a hotplate.  Lots of bubbles, but didn’t see any progress after two [8-hour] days.

(I got my alum in the grocery store, it being a common item used for pickling food items.)

Chances are it’s the wrong Alum!   Our forefathers in trade called a number of different chemicals ‘Alum’, and we are still confused by their imprecise nomenclature today.

There are 3 common Alums on sale: Potassium Alum, Sodium Alum, and Ammonium Alum.   Of these, only Potassium Alum (E522), dissolves steel.  (Robert’s post identifies the correct Alum.)

What may have happened is that Ammonium Alum is a cheaper substitute for Potassium Alum, satisfactory for some purposes, but not dissolving taps.  Or Sodium Alum is also food-grade product (E521), opening the door to buying another Alum that won’t work.

What the tap is made of may be a problem too.   Carbon-steel taps are easy meat for Alum, but High-Speed Steels contain Chromium and other elements with distinct anti-corrosion properties.  Their similarity to Stainless Steel suggests an HSS tap may resist Alum for  longer than expected.   Ditto coated taps, because the likes of Titanium Nitride will make it hard for the Alum to get at the underlying steel.   It will work eventually, but may take an age…

Dave

 

[duncan webster 1Participant @duncanwebster1]

I bet the full size had cast iron balls. Not worth messing, just buy some soft steel or brass.

This reminds me of the rugby song version of ‘do ya Ken John Peel’ where the named gentleman had genitalia made from steel and brass, and a ‘cast iron **se’

[Steve Rowbotham]

On Steve Rowbotham Said:

and I had no idea the plunger in the spring loaded tap guide was reversible! Will report back in due course when the weights are fitted to this…..

 

Not all of them are reversible. There are some videos out there that show making them if that is something that you want to do

[duncan webster 1Participant @duncanwebster1]

It looks like ARC’s is from the picture, can Ketan confirm? If so I’ll buy a set, looks like a useful bit of kit

[Steve RowbothamParticipant @steverowbotham77083]

I checked last night Dalboy and mine is reversible, I tried it and what a big improvement as Joe says in the video!

[SillyOldDuffer]

On SillyOldDuffer Said:

On MikeK Said:

Having recently tried alum to dissolve a tap broken in aluminum, I wish anyone good luck.  Heat helps, and may even be necessary.  Take care to not use a steel pot.  I used a Pyrex glass dish sitting on a hotplate.  Lots of bubbles, but didn’t see any progress after two [8-hour] days.

(I got my alum in the grocery store, it being a common item used for pickling food items.)

Chances are it’s the wrong Alum!   Our forefathers in trade called a number of different chemicals ‘Alum’, and we are still confused by their imprecise nomenclature today.

There are 3 common Alums on sale: Potassium Alum, Sodium Alum, and Ammonium Alum.   Of these, only Potassium Alum (E522), dissolves steel.  (Robert’s post identifies the correct Alum.)

What may have happened is that Ammonium Alum is a cheaper substitute for Potassium Alum, satisfactory for some purposes, but not dissolving taps.  Or Sodium Alum is also food-grade product (E521), opening the door to buying another Alum that won’t work.

What the tap is made of may be a problem too.   Carbon-steel taps are easy meat for Alum, but High-Speed Steels contain Chromium and other elements with distinct anti-corrosion properties.  Their similarity to Stainless Steel suggests an HSS tap may resist Alum for  longer than expected.   Ditto coated taps, because the likes of Titanium Nitride will make it hard for the Alum to get at the underlying steel.   It will work eventually, but may take an age…

Dave

 

Mine does say “potassium aluminum sulfate” on the jar.  Tap might be HSS, but knowing how cheap I am I would have thought carbon-steel.

[mike robinson 2Participant @mikerobinson2]

Try this: instead of gripping the tap by its square end, use your (not T type) tap wrench on the plan shaft just above the threaded section. This minimises twist in the tap and you have a free friction clutch which if nipped up correctly should prevent most calamities. I do it this way all the time. Your governor is looking good !

[Steve RowbothamParticipant @steverowbotham77083]

so this is what happened…. I drilled the tap out successfully using a Carbide drill (advised by Tug) then fitted a Brass bush tapped 7BA, and also fitted a bush into the second ball. This has been a very instructive exercise in terms of working with Phosphor Bronze, tapping technique, and removing a broken tap. Also I did purchase a bag of Alum so have put the other part of the broken tap in that to see what happens! Thanks all for your very helpful advice.

[Ramon WilsonParticipant @ramonwilson3]

Nice work, nice result and a good save Steve 😊

Governor looks great 👍 👍

Tug

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