Reaming Brass

Am making 4 x cranks with a 12mm hole in one end. OK, bored to within about .05mm and then put a good 12mm reamer through but they chatter, the holes come to size OK.

Any comments, apart from doing it slowly and lubricate etc?

Clive

I'd leave a bit more meat for the reamer to bite into.

I usually ream brass dry, but sometimes use paraffin if needed.

Martin.

Classic problem with Brass

Clockmakers use 5-sided Broaches for that very reason. [The resulting negative rake angle works a treat] ... unfortunately these are usually slightly tapered over the whole length; but I guess you could make something with a parallel section.

MichaelG.

I bought some strange reamers some time ago, they have 3 or 4 flutes machined on a quadrant of about about 100degrees and on the rest of the diameter (260 deg) there are NO flutes.. I was told that they may be for thin sheet. This probably doesn't hep you, but another trick was to put some rag around the reamer to 'fill' the flutes and reduce chatter. Use talow or lard as cutting lubricant.

try some matches in the flutes

\hi \live,

Use an accurate D bit. Can be made easily at home using silver steel. Inexpensive, very accurate and no chance of chatter. G H Thomas gives a good account of how to make one in his book 'The Model Engineers Workshop Manual',

Regards

Terry

How many 'blades' do your reamers have/ I was always taught that whilst you cannot 'mike' a 5 bladed reamer it cuts better and gives a better finish.

I have some 6 bladed reamers but you have to use them at the right speed to get them not to chatter.

To clean up a 0.05 mm hole I would use a tool makers broach. This is a bit of bar of the right size which has been slash cut across irs end at about 10 degrees. If it is well polishes with sharp edges it leaves a beautiful finish, but take it slowly with lots of oil.

Rgds

Dick

Hi,

Speedy Builder,

This type of reamer are called "alesoir facon paris"

http://magafor.net/article.php?grp=822&famille=675

very good finish

brgds

pierre

Hi there, Clive,

Please check your PMs (different subject).

Best regards,

Swarf, Mostly!

I'd go with Dick's tool makers reamer, I often use these, usually un hardened for one off jobs. If you use an ordenary reamer on brass, it should be one that is reserved for brass only, just as with files. Use it with steel, and it looses its edge. Ian S C

Pierre,

That's very useful, thanks

A clever design, which should have "self-aligning" properties because of the full radius "plain bearing"

... I would expect them to be good for deep holes.

MichaelG.

Yes I often use tool maker's broaches unhardened. I also hone the small ones in a clock makers screwdrivers honing jig I can get them razor sharp that way.

a 4mm hole 12 mm deep is a doodle. But go slow and use only a light pressure they can be greedy things.

Rdgs

Dick

A slight clearance can be gained by leaving a slight bit of a burr on the edge after sharpening, or possibly on resharpening after reaming the hole to dead size. Ian S C