Need Help!- Reaming nickel bronze (C630)

[altaic]

Hello,

I have to ream two Kibblewhite valve guides for a motorcycle tomorrow, and I did a little reading on the 'net that scared me a little. I wasn't able to find any information on the C630 bronze alloy I have, but I found a bit on aluminum bronze... I take it that aluminum bronze is a nightmare. I hope nickel bronze is different!

Anyway, I have a brand new HSS chucking reamer, and until I read about aluminum bronze chewing carbide reamers up, I figured it would work well. Since I only have to do two valve guides it doesn't matter how long it takes to ream them. It just has to work and leave a good surface finish

I would dearly appreciate some tips before I go at it. Maybe I should hand crank my mill spindle? I plan on finish honing with a nylon brush and yellow time-saver lapping compound, BTW. I also have tapmagic, tapmagic aluminum, and tapmagic pro cutting fluids, and I'm wondering which would be best, or if paraffin or something is better.

Thanks!
Will

Edit: I just discovered C630 alloy is also called C630000 or AMS 4640, and is classified as an aluminum-nickel bronze.

[christinandavid]

Are you reaming a pre-existing hole? How much material are you reaming out?

DP

[altaic]

Not much, but it's hard to be sure since pressing the guide in causes the ID to shrink a bit... I'm thinking 0.001" - 0.002".

The bore was precision machined by Kibblewhite. I forget the tolerances, but IIRC they were relatively high.

[christinandavid]

My guess is that you would struggle to ream that small an amount out of any material with any reamer...and you would need pretty good tooling/set-up to consider boring it...is honing an option?

DP

[altaic]

I should have said this, but I'm new to reaming. I see what you mean, though. Unfortunately honing isn't an really an option since I don't have the tooling for it.

[christinandavid]

I've done plenty of reaming, but not in bronze, so I'm pissing in the wind here a bit too...

My best advice is run the reamer dead slow to stop it rubbing and reduce wear. Feed it fast to give it something to cut at. A reamer with a positive rake on the flute form is probably best for scooping the material out. Retract the reamer carefully, not rapidly.

If it were me I would do a trial run on a similar test-piece to check the size/finish/parallelism. Doing this would also eliminate any over-keen-ness on your brand-new reamer. Plenty of gunk throughout.

DP

[altaic]

I appreciate the advice. My mill has a min speed of 100rpm, which works out to ~3.8m/min surface speed. From what I've read, that's pretty low, but I'm tempted to hand crank it since I'm paranoid about the bronze swelling and seizing the reamer. Luckily I have an extra guide from a botched insertion to use as a guinea pig

I'm hoping one of the tapmagic cutting fluids will work well from bronze-- I don't want to have to buy purpose-made bronze cutting fluid since it may be a long time before I need to use it again and I'll probably never use an entire bottle. I'll check out what tapmagic recommends, though.

Will

[altaic]

In case anyone else is wondering, tapmagic recommends their aluminum cutting fluid for bronze or other "soft" metals. Additionally, Kibblewhite said that reaming C630 bronze is difficult and tends to rapidly dull reamers similarly to what I had read about aluminum bronzes. This should be interesting.

[RICHARD ZASTROW]

FYI, I just looked this stuff up. Machinability rating of 30%. Looks like fun stuff.

Dick Z

[CASTLEVILLE]

fun stuff!! when i did my guides i did just what you are suggesting. go as slow as you can. the guide wanted to grab the reamer pretty bad. when i was done all my holes were under sized and running the reamer though again didn't do anything but cause a headache. i just worked the holes with the nylon brushs with the lapping compound till the valves fit correctly.

[altaic]

Good to hear a success story anyway! I was thinking of running the reamer backwards with the time-saver yellow extra fine. Since it's the soft metal compound, I'm thinking it would not do too much to the reamer. OTOH, maybe I should just make a brass lap...

Edit: I meant to say that I was thinking of lapping after properly reaming (hopefully slightly undersize as happened with Castleville).

[kantarr]

Never never never run a Reamer backwards. I am thinking that If A carbide reamer lasts for hundreds of holes in tool steel then It should last for two in a non ferrous material.

I haven't machined this stuff but Al bronze is easy so if you think that its similar there is some hope here.

Have you considered wire cutting it? best of luck.

PS wire cut is capable of A 3 micron (metric) fit.