Author Topic: Gun metal v Phospher bronze  (Read 3241 times)

Offline Firebird

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Gun metal v Phospher bronze
« on: December 26, 2016, 08:55:28 AM »
Hi

I hope everyone had a good Christmas and looking forward to the new year  :ThumbsUp: :DrinkPint: :cheers:

A quick question.

I am embarking on my first loco build, a 3 1/2" gauge Conway. At present I am reading through the plans and gathering materials.

I know this forum isn't about loco's but if there is enough interest I'll start a topic which I can detail or just give a brief report every now and then as suits the members.

My question is this. The plans specify the use of gunmetal for the numerous bushes etc. Is phospher bronze a suitable substitute as I have a few bits in stock.

Cheers

Rich

Online Jo

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Re: Gun metal v Phospher bronze
« Reply #1 on: December 26, 2016, 09:16:58 AM »
Yes Ph Brz is good.

The reason for the plans saying gunmetal is that is what the parts would be made of if you used a casting.  :wine1:

Jo
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Offline Ramon

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Re: Gun metal v Phospher bronze
« Reply #2 on: December 26, 2016, 12:19:05 PM »
Hello Rich -

 PB (Phosphor Bronze) is a good bearing material providing it's the right one. The 'yellow' type - often referred to as 'cast' bronze is a superb bearing material in conjunction with mild steel, particularly leaded steel and is easily machined, drilled and reamed.  If it is the pinkish type however this is 'drawn' PB an is not an ideal material to use as a bearing with unhardened steel. I do use it in my I/C engines as big end bearings but it is running on EN24T pre treated toughened steel. It can (and will) easily 'pick up' and gall badly if on softer material. If it does gall it is very unlikely it will come apart without a great deal of force, usually beyond what the part can take, or more likely, will need re-machining

I took these pics quite some time ago for a similar query on here which hopefully show the differences and I guess they may be worth repeating





Note the distinct pinkish hue of the drawn bronze.  Tools should be very sharp, preferably fresh ground or a new cutter and not have been used on steel beforehand. Though that goes for both types it is particularly so for the drawn bronze and especially when drilling the latter.

Hope that's of help to you

Regards - Ramon
« Last Edit: December 26, 2016, 12:25:16 PM by Ramon »
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Offline Chipswitheverything

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Re: Gun metal v Phospher bronze
« Reply #3 on: December 26, 2016, 02:25:34 PM »
Hi Ramon, thanks for the very handy illustrations of the different bronzes, I've added that to my favorites to take a look at before I rummage in the scrap non-ferrous box.
 Just a reminder that you can have a frightening bang-up when trying to open a drilled hole in bronze ( brass too ) if the drill point hasn't been modified to take the rake off the lips of the point. Especially in a drilling m/c or mill quill where you are pushing downwards without the restraint of a tailstock feedscrew.  Generally OK I find  with smallish unmodified drills when drilling into solid metal, the chisel edge inhibits the pull of the drill flutes, it's opening out after that that creates the danger.  If the job allows, I tend to size the hole with a single point boring tool or boring head to rule out that "grabbing" possibility.   Dave

Offline Ramon

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Re: Gun metal v Phospher bronze
« Reply #4 on: December 26, 2016, 03:10:15 PM »
Dave -

I would concur with that entirely, both in brass and gunmetal and also the softer bronzes. Just taking the sharp edge off the drill with a stone at a slight negative rake is usually sufficient to prevent this often quite violent grabbing and I would certainly do as you suggest and finish by boring wherever possible.

However on no account should this backing off be done when drilling the pinkish 'drawn bronze' - this really work hardens and gets hot extremely quickly and can seize a drill to the extent it's virtually withdraw-able. Reaming can be just as fraught especially if a deep hole. Drills should be very sharp, preferably freshly ground, and the hole opened up in small stages rather than just a pilot and opening up to size with this material. If like me you have no flood coolant the action of seizing is extremely quick and even with it it can happen if a deep hole. Again, because of this characteristic rather than reaming I would finish by boring if possible.

I should say I have never tried the Colphos 90 free cutting PB so can't really comment on that other than to say it's available.

I notice now that Rich said bushes as opposed to bearings - the drawn bronze makes fine bushes for boiler fittings but the above approach is still something to be borne in mind.

Regards - Ramon
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Offline Firebird

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Re: Gun metal v Phospher bronze
« Reply #5 on: December 26, 2016, 04:45:32 PM »
Hi

Thanks for the info guys.

I should have stated the bushes are boiler fittings.

cheers

Rich

Offline kvom

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Re: Gun metal v Phospher bronze
« Reply #6 on: December 26, 2016, 03:19:15 PM »
I assume it's a copper boiler.  Bushes for a steel boiler can be steel welded to the boiler tube.  Kozo's copper  boilers specify phosphor bronze for bushings.

Offline Firebird

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Re: Gun metal v Phospher bronze
« Reply #7 on: December 26, 2016, 05:49:48 PM »
Hi Kvom

Yes its a copper boiler as per the original plans

Cheers

Rich

Offline Admiral_dk

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Re: Gun metal v Phospher bronze
« Reply #8 on: December 26, 2016, 09:03:00 PM »
Sorry Rich for the interruption, but I have to ask Ramon why you shouldn't use a tool that has been used on steel on the bronze ?

I'm adware that tools need to be ground differently for bronze (and other materials) to the ones used on steel (drill bits and cutters for the lathe / mill) - but I'm not adware off different reamers for different materials ....  :noidea:

Offline Ramon

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Re: Gun metal v Phospher bronze
« Reply #9 on: December 26, 2016, 11:01:28 PM »
Hi Per - apologies to Rich's thread but in answer to your question -

A carbon or HSS tool - any tool, lathe, milling cutter, drill or even a file will not cut brass/bronze cleanly if having been used on steel but tend to 'push' the material ahead of itself generating considerable heat. The more it's been used the greater this effect manifests itself. Yes, such a cutter will cut to a degree but nowhere near as clean as a fresh one. That very sharp edge left from grinding will be taken off immediately if used on steel. A new cutter will out perform one for some time on brass against one that has only taken just the finest cut on steel.

It was good practice at work for new files to be marked as such for brass and only get used on steel once the keenness on brass has gone.  I still do that and with new milling cutters too but often forget to rub the marking off and then find out the hard way  ::) Reaming is one area were this tends to get overlooked due to usually only having one tool available but the older/more used the reamer the harder it is to ream especially in the drawn bronze - hence the preference to finish bore - with a freshly ground tool  ;)

I admit I don't pay much attention to the 'precision' of grinding of HSS lathe tools - just tweaking the tip if it's not performing as hoped for (and it is only the tip that's doing the work for most of the time) but keeping it sharp on brasses of all types is a priority

Hope that helps Per - Ramon
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Offline petertha

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Re: Gun metal v Phospher bronze
« Reply #10 on: December 26, 2017, 05:45:35 AM »
Reviving old thread (coincidentally almost one exact year)

I made some bronze bushings. Turning was straightforward enough, it came off not as curly swarf but cast of cast iron looking shavings. But because this part was a larger bore than I had made previously, I unfortunately also experienced 'the grab' once I progressed up to ~5/8" diameter. It took some persuasion to back the drill out but fortunately that was the last drill size so I could carry on with boring bar which went very well.

I wasn't expecting this drilling issue so want to learn from this experience. I would say it was about the same problem I recall of drilling brass. I now have re-dressed some drills in this diameter range with appropriate reduced rake angle & set these drills aside for brass - and maybe now also bronze use.

But I'm trying to correlate the materials referenced in this post to what I have been using or other possible N-Am offerings.
OLM lists these common bronze's in round. I used from (USA terminology) Bearing Bronze C932, aka SAE 660 which they list as "comparably easy to machine"
http://www.onlinemetals.com/productguides/bronzeguide.cfm

Of the 3, only the C932 has phosphorus content & its only <0.15% according to specs. C655 (silicon) bronze is indicated as "more difficult to machine". I usually take this to mean surface finish as opposed to problems, but its partially what directed me to C932. So is problem more related to C932 being softer than the others & phosphorus just so happens to be a constituent related to this alloy? Strangely, it has a high % of lead which usually makes for a good 'free machining' constituent.

C932  http://www.matweb.com/search/DataSheet.aspx?MatGUID=b673f55f412f40ae9ee03e9986747016
C954  http://www.matweb.com/search/DataSheet.aspx?MatGUID=b950d0d72b5b467689f2d9c5d9030ae8
C655 http://www.matweb.com/search/DataSheet.aspx?MatGUID=97fc9cb4ed1f45319793fb018b38e645


« Last Edit: December 26, 2017, 06:11:52 AM by petertha »

Offline Ramon

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Re: Gun metal v Phospher bronze
« Reply #11 on: February 10, 2018, 09:57:47 PM »
However on no account should this backing off be done when drilling the pinkish 'drawn bronze' - this really work hardens and gets hot extremely quickly and can seize a drill to the extent it's virtually withdraw-able. Reaming can be just as fraught especially if a deep hole. Drills should be very sharp, preferably freshly ground, and the hole opened up in small stages rather than just a pilot and opening up to size with this material. If like me you have no flood coolant the action of seizing is extremely quick and even with it it can happen if a deep hole. Again, because of this characteristic rather than reaming I would finish by boring if possible.
Regards - Ramon

Hi guys - I don't usually quote myself but in this case I think you'll see the logic.

I had need yesterday to drill a piece of the drawn Phosphor Bronze as described above. I decided to use a 3mm pilot drill, open to 4.8 and bore to 5mm. Despite freshly grinding slightly off centre (freehand) a 3mm drill and being ready for it to get hot I wasn't ready enough as within about 8-9 mm deep of the required 22 mm depth the heat build up was extremely rapid and the drill seized.




What I really wasn't ready for was the drill to shatter which was almost instantly it seized. I felt the the shards of HSS distinctly striking my right cheek just below my glasses leaving a noticeable stinging feeling for quite a few minutes. Though totally superficial it did pierce the skin at one tiny point - I was very glad I had glasses on for sure! The gap between drill and work is not from the drill being withdrawn but the missing bit of HSS  :o

So, one lucky moment but reinforces the comment above about drawn Phosphor Bronze and just how quickly the heat and seizing occurs.

Hope that's of concern without being overly safety conscious - hate to think what one of those shards would have made of my eye

Regards - Ramon (aka 'Tug')
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Online b.lindsey

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Re: Gun metal v Phospher bronze
« Reply #12 on: February 10, 2018, 11:15:03 PM »
Reading this, I went back and looked up the bronze I had purchased for the "Little Pearl" engine as I have no problems at all. It was in fact C932 but the difference looking at Ramon's pictures at the beginning of this thread is that this is cast bronze rather than drawn bronze. Guess that makes a huge difference regarding the grabbing issues.

Bill

Offline Ramon

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Re: Gun metal v Phospher bronze
« Reply #13 on: February 11, 2018, 09:43:40 AM »
Hi Bill - just like to clarify a little more here .

It is the yellow bronzes and brasses that have the propensity to 'grab' - that is for a drill to pull itself rapidly forwards into a previously drilled (pilot or stepped) hole. This is where the stoning of the drill cutting edge helps prevent this happening and it's always best to drill as much of the material in one go as possible rather than a series of steps.

The Phosphor Bronze described above on the other hand does not 'grab' but heats very rapidly and, as it heats up, it grips the drill (or reamer) with considerable force. Getting the drill out of the holes is of paramount importance as soon as any 'drag' is felt. This material work hardens very quickly producing a very quick rise in temperature. If as on my lathe/mill there is no flood coolant then allowing it to cool, opening the previously drilled hole a small amount to provide some clearance then going back in with the first drill to drill a bit more and so on helps keep the gripping to a minimum. It is always best to drill this material in a series of steps but there's always that first hole to be aware of.

Drawn Phosphor Bronze is a lovely material to turn or mill but its a real pig to drill/ream, fraught with the conditions described and sharp cutting edges are really important.

Hope that helps a little more.

Tug
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(a very apt phrase - thanks to a well meaning MEM friend)

Offline steam guy willy

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Re: Gun metal v Phospher bronze
« Reply #14 on: February 11, 2018, 01:28:45 PM »
Hi,  I have sometimes found drilling various "brasses' difficult with grabbing etc etc but put it down to " a bad workman blames his tools" !! Now i can say " A good workman blames his tool suppliers for not making the correct type of drills for specifically drilling various type of brasses without mishap" !!!! ;D So how does the Industry cope ??  !!