PDA

View Full Version : Working silicon bronze



J Harp
06-03-2014, 05:39 AM
I need tips on drilling, boring, reaming, and turning silicon bronze. What tool point angles work best with this material.

Is the chip stringy, gummy, or flaky like brass, in other words do I need a cutting, or scraping action. As you can tell I have never worked with Si bronze, I'd like to avoid spoiling two or three pieces if possible. Thanks

sandiapaul
06-03-2014, 07:42 AM
Here is some info:
http://www.practicalmachinist.com/vb/general/silicon-bronze-157685/

thread has links to more info.

Paul

cameron
06-03-2014, 08:08 AM
I've only threaded 5/8" and 1/2 " bars in the lathe. Long, stringy, very tough cuttings, definitely not "chips". Unsupported overhang from the chuck pushes away from the tool, and you can take cut after cut without advancing the tool. Also digs in badly every now and then.

I had a lot of very long threads to cut and gave up trying to cut them to finish dimension in the lathe. Even cut to about 2/3 depth, it was hard work to finish them with a 20" long die stock by hand. By comparison, cutting the same thread from the solid on a steel bar seemed like cutting cheese.

Nasty stuff to machine, in my limited experience.

J Harp
06-03-2014, 09:10 AM
Thanks Guys,

Looks as if it's a love it or hate it deal. I found this.

http://www.bladeforums.com/forums/showthread.php/716846-Drilling-bronze

Just hope I can make it work without screwing something up.

capperbar
06-03-2014, 04:38 PM
Drilling, take a diamond sharpener and put a very small flat on the on the end of the sharp edge. Hold the hone in line with the long axis of the drill.
Lathe worked well with usual geometry. No long stringy bits for me.
Milling just throws large square chunks every where but is easier than steel. Good finish
Scraping action I quess.
This is with whatever alloy that was labelled as 'Silicon bronze" by the foundry.

Another Bill
06-03-2014, 04:52 PM
There are at least two kinds of silicon bronze.
The industrial grade silicon bronze (Herculoy) has about four percent zinc content that aids machining. When welded though, the zinc can leave behind a ghostly surface trail that is not easy to remove.
Sculptors cast an artist grade bronze (Everdur) that has no zinc. This lack of zinc allows them to weld castings together without discoloring the surface or the final patina. Bill.

J Harp
06-05-2014, 11:55 PM
Thanks everyone,

I wondered about a tendency to grab when drilling, I'll give the edge a tiny flat.

Old Hat
06-06-2014, 12:17 AM
There is a family of alloys that are tuff not hard.
Much tooling is ruined by assuming that sfm can by faster.

Consider machining prehards and the limitations inherent to those alloys.
Tuffness is not hardness, picture how Rockwell hardness testing is done.
A ball is forced into the surface at a given pressure, and the distance it dents
in the surface is a measure of the molecules resitence to being compacted
and being displaced.

Now take what we call Ampco around here, a tuff@ss alloy that is highly wear resistant.
It's not hard by any means. It's tuff! It's molecules (or grains or crystalline matrix)
or what ever the trolls will correct me on, missing the point alltogether
fight like hell being separated.

A great deal of heat is released or generated by separating these molecules.
This heat distroys tooling when too high of sfm is used.

Further the effect of drills corkscrewing into these alloys is due to the fact
that they are not hard at all, and once the cutting edge finally parts the metal
under much force, the highly pliant nature of the chip lets things get out of hand quickly.

I've made tooling for the manufacture of catalytic converts from this stuff.
Using normall good quallity high speed drills, screw~machine lenght when possible,
and held firm in collet-mounted Cat 50 holders and done on full CNC machine centers.

I keep my speeds low and feeds about the same as 300 series stainless.
I get great results with holes and my method is sound, because there is no more
metal pushed out the bottom of the thru holes than with other alloys.

Others have heavy bulged rings pushed out the bottom.
I find higher failure of spiral fluted taps than with even prehards.
So I opt for gun-taps, (spiral~point taps).
Naturally this requires consideration in blind holes but the chip-wad
is pretty fluid, and I remove some of the end of the tap for chip-wad clearence.
Especialy with the taps with the male or cone-point on them.

Jaakko Fagerlund
06-06-2014, 03:55 AM
Find the manufacturer and check their site. They usually have very good PDF's about how the stuff machines with different speeds and tools, weldability info, hardening & tempering etc.

boslab
06-06-2014, 04:25 AM
I agree with old hat about ampco, i disagree with the trolls comment, not nessicary to call anyone who knows more a troll, you wont get far with that attitude, if you comment on toolmaking then im going to listen, try to understand and question, it seems you dont like being questioned much?, only a fool wont suffer fools gladly, disslocation theory is quite useful too.
Please try to tone it down a bit, others have an opinion too, if correcting somone makes you a troll then what are you?, same as me, a troll i suppose.
Btw ampco bronze will happily cut steel, non spark chisels are made from it, as well as wrenches, hammers, even die nuts and taps!
The most expensive shovel i own is ampco bronze, its very good too
Mark

Old Hat
06-06-2014, 07:09 AM
You're right, I've retained bad habits from years and years in a very fast paced very agressive R&D wing
of a very fast paced very agressive motion controll company in the 80's.

The montra was "get the thing out of burn-in and shipped! You ladies can banter later
about symantics and puncuation." That was the Boss's dictum.

A few of the engineers had a propencity for picking flys out of pig s**t.
I see that tendency on forums too often.
Actually I would much prefer to be using corrected terminollogy
and to be able to provide more accurate details but not at the cost
of derailing the train of thought.

My Bad.

Willy
06-06-2014, 07:37 AM
OLD Hat, good info on the machining of Ampco alloys, I'm sure you have more experience than I do with it but your words echo my limited experiences.
I've used Ampco 45 aluminum bronze quite a bit and have had excellent results following the guidelines set forth on the Ampco website.

Ampco's homepage.
(http://www.ampcometal.com/en/index.php?page=home)Didn't realize it but they list over 30 different alloys. Lots of data sheets and info there.

Also a link to a 9 page PDF of their machining guidelines.

http://www.ampcometal.com/common/datasheets/ampco_machining_recommendations.pdf




The most expensive shovel i own is ampco bronze, its very good too
Mark

I'd love to see that Mark, and yes I'll bet it would be bloody expensive. :)

Old Hat
06-06-2014, 10:31 AM
Before there was PDFs or homepages I saw an apprentice on an engine lathe
madder than an (explative of choice). He had allready destroyed several inserts
trying to ruff down some awfull variety of Ampco tube for large bushings.

An old lathe-hand finally came over and said "don't waste any more inserts".
He put the best of the injured ones back in, and said "gimmy about a third of the RPM
you have going on there". He doubled the feed, left cut depth alone and went to it.

He told the lad to put in a good insert with just enough stock left for three = passes.
went even slower and cut the feed down too. "He said two passes proof out your cut,
so that your final pass can be relyed on to hit size". "No sanding these in! Got it!"

boslab
06-06-2014, 11:58 AM
Funny you should say that, i tend to work better with heavy cuts, the finish is better, part dosent get so hot so its easier to get to size, and the inserts perform better, they like to be worked, rubbing them destroys them quick, most of the heat leaves with the swarf
Mark

Jaakko Fagerlund
06-06-2014, 05:57 PM
Funny you should say that, i tend to work better with heavy cuts, the finish is better, part dosent get so hot so its easier to get to size, and the inserts perform better, they like to be worked, rubbing them destroys them quick, most of the heat leaves with the swarf
Mark
Depends very much on the insert, chip breaker, material, nose radius, feed rate, surface speed etc. Some inserts I use like to only have 4 mm DOC or larger, some fine finish inserts can easily shave off 0.01 mm DOC or smaller. And all this without dulling or rubbing.

Most of the heat usually doesn't come from the cutting/shearing action but from the chip breaker folding the chip.

Old Hat
06-07-2014, 06:21 AM
Funny you should say that, i tend to work better with heavy cuts, the finish is better, part dosent get so hot so its easier to get to size, and the inserts perform better, they like to be worked, rubbing them destroys them quick, most of the heat leaves with the swarf
Mark


Depends very much on the insert, chip breaker, material, nose radius, feed rate, surface speed etc. Some inserts I use like to only have 4 mm DOC or larger, some fine finish inserts can easily shave off 0.01 mm DOC or smaller. And all this without dulling or rubbing.

Most of the heat usually doesn't come from the cutting/shearing action but from the chip breaker folding the chip.

Up to a point in time I would have agreed with both the statements in bold.
In my early years I had to put 7/16" & 9/16" water lines in small injection mold cores & cavities.
This work being done entirely on Bridgeports and radial drills. I got to the point I could drill thru holes
in 2" thick anything (any tool-steel alloy or mild steel) all in one shot dry, and no pecking. . .
with a standard 7/16" h.s. jobbers drill. I used quite slow rpm. and very heavy hand-feed.
I could feel the point max chip delivery was reached and not rub on the back-off (lip relief).
This I did for easy $5 bets about the role cutting fluids play.

The appearence of, and terrificly broken up nature of the chips, allong with no coolant or cutting oil
would support both statements in bold.

Then came our Gun-Drill !! Tailor ground single-flute carbide spoon bits. 5 attributes could be tuned
to needs on the tip-grinding fixture. At least 1000 psi. coolant thru (sulfur oil was best) the black stuff.
Ideal chips were ribbons all riddled with brittle folding in them which would brake up in to lenghts about
1 3/4" to 2 1/4".

In the chip box the oil that came out with the chips was just beyond a heat you could keep your hand in.
water passages were one thing, but bubblers or up-lines were quite another. These molds were BIG !
Garden tractor hoods and the like. I don't think the bubbler depths were calculated off a cad solid.
The designers would warn me that they had regions where depth was a challenge to get correct.
Basicly say on a large cavity, we wanted about 7/16" of steel left between the end of the hole
and the molding surface in the cavity. My predicessor showed me to place my palm on the molding
as the drill reached the end of it's programed depth. I was to make circles of about a hand width
to keep from getting acklamated to the temporature rise. With about 1 1/2" to go in P20
I could feel the heat building rapidly. On big molds I had a helper stay at the abbort botton.

He (my predicessor) told me when you have to take your hand off the molding, SING OUT!
And he was right! Any hole programmed too deep I abborted, and always the web remaining was
estimated to be about 3/8".

SO, I now have to beleive that at least in drilling opps, as much heat is released in the actual parting of the metal
as is developed by the deformation of the chips.

Jaakko Fagerlund
06-07-2014, 07:18 AM
Old Hat, sounds very familiar operation, been doing those pesky 8 and 10 mm gun drill holes for a few years now :)

But drilling is another matter opposed to turning, as in drilling a large portion of the heat comes from displacing metal in the center of the drill tip, as it is non-cutting and only pushes or shoves the metal away.

Old Hat
06-07-2014, 09:07 AM
Good point! When ya stop to think about it, I spose it's remarkable that drilling & ball-contour
surfacing even work at all. Especially in tuffer stuff, like Ramax & CPM 10 V.

I gotta try one of those "0 mm holes" you mentioned . . . sounds tricky.!;)

Jaakko Fagerlund
06-07-2014, 10:36 AM
Good point! When ya stop to think about it, I spose it's remarkable that drilling & ball-contour
surfacing even work at all. Especially in tuffer stuff, like Ramax & CPM 10 V.

I gotta try one of those "0 mm holes" you mentioned . . . sounds tricky.!;)
The same with facing when you approach the center. Really shows when the surface speed drops too low and tearing starts.

Woops, edited that to 10 mm :D Yeah, as I was saying, very pesky those 0 mm holes ;)