Pure unadulterated plug

Got a job on doing some small gear selectors in aluminium bronze, the drawn variety. The job calls for two M3 tapped holes 10mm deep into a bore.

Now for anyone not familiar with this material it's horrible. It heats up at the drop of a hat and then cools down gripping whatever it is you are trying to cut it with. It's also very abrasive and needs very sharp tools. Reaming this stuff shags reamers faster than rubbing them on the hard shoulder between junctions 15 to 17 on the M25 [ clockwise ]

Well tapping these is getting thru taps like one O unless you go over size on the tapping drill and finish up with a less percentage thread. Only broke one tap but it's costly as the component has a lot of work in it.

I picked some fluteless forming taps from Ketan at Arc Euro the other week and although they are fine in soft metals I have never tried them in ali bronze.

Delight of delights they go straight thru, and felt a lot better. With having no flutes they feel and are stronger, no heart in mouth feeling and I finished up power tapping these with the reversible air drill set to flat out.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

formatting link

Reply to
John Stevenson
Loading thread data ...

That is a horror.

Oh my god!

I didn't think that this will even work. Thanks.

Nick

Reply to
Nick Mueller

oooh!!!

I got some ali-bronze bar given me to play with... Had no idea it played that rough. I thank you for the insight, I will choose carefully which tools to feed it on.

Joules

Reply to
Joules Beech

They seem to work in most materials. You are right in that they are much stronger. I had a jobe recently that called for a fairly deep M3 blind hole in 316 St-St, worked like a charm. Have also used them in Titanium, Pure Ally Heatsinks and various other materials.

Tapping drill is quite critical though ;)

Wayne...

Reply to
Wayne Weedon

Do you use the same size tapping drill as for a fluted tap or larger?

Alan

Reply to
Alan Marshall

John, I've looked on the Arc Euro site but can only find the serial taps,Ar the forming taps under a different heading as I can't find them and search doesn't show any.

Alla

-- Allan Waterfal

----------------------------------------------------------------------- Allan Waterfall's Profile:

formatting link
this thread:
formatting link

Reply to
Allan Waterfall

Can't find them either. They are in the new catalogue, 4 sizes 3.0, 3.5, 4.0, and 5.0mm Not got the book in front of me but I think they are £4.75 each.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

formatting link

Reply to
John Stevenson

Thanks John,I'll give Ketan a ring this next week and get a couple.

Alla

-- Allan Waterfal

----------------------------------------------------------------------- Allan Waterfall's Profile:

formatting link
this thread:
formatting link

Reply to
Allan Waterfall

Ah, so that'll be the stuff I made a bush for a small boiler I was building a while ago with. Had to sharpen what I thought was already a sharp drill to drill a hole in it, got very hot, very quick. Cooled down and trapped drill. Was a right b****r to tap.

It came in some bar oddments I bought off a model engineer (I think

-it was in my "stock" pile anyway). Thats the problem with material that you don't buy from a stockholder, you never know quite what it is. I can usually make a fair guess between copper. brass & bronze

-but hadn't come across this stuff before. I presume it is extremely good for bearings in tough conditions?

Regards Kevin

Reply to
Kevin Steele

Larger. Using the normal tapping size you wont have a forming tap for long ;)

There are charts somewhere.

Wayne...

Reply to
Wayne Weedon

Alan

Been a while since I thought about this but if my memory still works I think we used to aim for about 65% thread rather than the 75-80% ish for cut threads, so as Wayne says the drill needs to be slightly larger. As always depend on material as well. There are plenty of cold forming tap drill size calculators on line but charts seem a bit more scarce, there is one of sorts here:

formatting link
Hope this helps a little

Regards

Keith

Reply to
jontom_1uk

from Wayne Weedon

The tolerance on the tapping drill size for 'rolled' threads is much more critical than cut threads. The potential to produce badly formed creasts is very high. This is one reason that they are (were?) not allowed in the aircraft industry - (they wern't when I was an apprentice anyway, 1957-62).

If the hole is fractionally too large there is insufficent material available to completely fill the creast so there is a hole formed along the thread leaving it liable to break away. Slightly larger still and there will be a ridge along the creast with even more chance of metalic slivers coming loose.

JG

Reply to
JG

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.