Question about Bronze

[Garry Coles]

Merry Xmas to all
I've been modeling for quite awhile now and have only been working with cast iron and brass, but now with my next project, (3.5" William) I'm venturing into the bronze age! (From the iron age)
Can any one explain the difference between the bronzes, IE phos bronze, gunmetal, SAE 660 leaded gunmetal and cast gunmetal.
This would be of great assistance to me.
Cheers
Garry

[catgate]

www.matweb.com/reference/copper.asp
www.tak2000.com/data/prop1.htm

[SteveW]

Garry,

You'll find bronze a whole lot different to brass and cast iron. I have my biggest problems drilling the stuff. Everything is going fine then suddenly the drill picks up and screws everything. On the lathe it can drag the chuck out of the tailstock.

When it's going good it's great but don't underestimate the stuff.

The phosphor bronzes can also bite back maybe more so.

[catgate]

I have found that with these "other" materials it virtually imperative to use the correct cutting speed and the correct type of drill.

[SteveW]

Cat,

I go wrong because I can't sharpen a drill to save my life so the last thing I want to do is mess with the cutting angles for fear of stuffing it for drilling other materials and not being able to restore the angles.

I see a four facet sharpening engine for larger drills advised for the next copy of MEW but given the news in another thread I may never see it.

I generally find that the drills I have get me a good result until it all suddenly goes wrong. One day I'll have two sets of drills but this is still a way off.

[catgate]

I have used one of the simple swivel type for many years and find them quite satisfactory if used with care.

The main problem people have is not having any means of running the drill bit at a high enough speed. The smaller the hole, the higher the speed, and in model engineering that can lead to surprisingly high RPM, particularly in the sorts of metal to which you are referring.
I had a friend who did wonderful things with a router to get high enough speeds for some of his work.

[SteveW]

All,

Re: needing drills ground to favour bronze:

I have used the trick of drilling through a pad of folded cloth learned from my metalwork teacher years ago. This also works great for larger holes in thinish/sheet metals.

Method: Get a piece of old sheet folded to two/four layers and drill through it. It needs more pressure to get going but you get great results.

Basically the drill rides on a cloth pad just behind the cutting edges effectively reducing the amount the the edge can cut into the base metal.

Result: Five faceted holes are a thing of the past just keep the pad small enough to be safe from fingers/ other bits.

(and yes this is a repeat but it's so useful it needs sharing and it saves me having to change my drill geometry).

[jackrae]

Not exactly the subject of the topic but never the less it may be of interest to some.

There's an interesting article in today's dailt telegraph about the authenticity of the gun metal used to make the Victoria Cross war-medals.

I'd always believed that they were manufactured from part of a gun recovered from the Crimea war but this article casts that theory into some doubt.

jack

[chris vine]

Tip for drilling phosphor bronze.

This is always a bit tricky, obviously you need to use a sharp drill and lots of coolant, not just to lubricate but also to take the heat away.

If you need to drill a deep hole, say 6 mm diameter, it is best to start at perhaps 5.8mm and go in a bit, then use a 5.6 and go in a bit deeper and so on. IE use smaller drills as you go deeper. That way they don't rub on the part that isn't cutting and generate heat.

When you have the hole to full depth, run the correct size drill down fairly quickly, or bore it out to size.

It works a treat, Honest!!

chris.

[davidimurray]

The other thing to really consider is whether you really need to use PB. PB is generally specified for heavy duty bearing use whereas SAE660 is a general duty bearing material. With SAE660 being much easier to machine I tend to stay away from PB. This thread may be of interest :-

www.aimoo.com/forum/postview.cfm?id=378488&CategoryID=75747&threadid=2267871&highlight_key=y&keyword1=bearing

Cheers

Dave

[Shawki Shlemon]

Hi All
May be I am too late for this thread ,but I only joined last month and I am surfing through all threads slowly and making remarks where I feel it is necessary .
To drill in bronze or soft metals all one needs to-do is to stone the cutting edges of the drill flat and everything will be fine .
Try it on a scrap piece first .