From: Dave Baker
Subject: Re: reaming holes in brass
Date: 04 Feb 1999
Newsgroups: rec.crafts.metalworking

>From: dcbrouse@yahoo.com
>
>I am having trouble getting a good finish when reaming a 7/16" hole in CA360
>brass.  I drilled the hole to 27/64 first and ran the reamer at about 300rpm.
>This is a thru hole 1.75" long.  The drilled hole was smoother than the
>reamed
>hole.  Does anyone have a suggestion?  I am new to machining, am I missing
>something obvious?


You are running the reamer too fast for one thing. Reamers are designed to run
slow and brass and bronze especially have a tendency to chatter if reamed too
fast. Try 80 rpm and get the reamer in and out fast. Don't let it dwell in the
hole or you'll cut oversize. Also try leaving a bit more to ream out. If your
drill ends up drilling a tad oversize then you are reaming less than 15 thou.
Try it at a true 20 thou if necessary but the speed alone should solve your
problems.

I presume of course that the reamer is new, sharp, held properly and running on
the same centre as the drill. (and with some lubricant needless to say).


Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work. .

From: Dave Baker
Subject: Re: reaming holes in brass
Date: 04 Feb 1999
Newsgroups: rec.crafts.metalworking

>From: untmaintco@aol.com (UntMaintco)
>
>Sounds good so far Just had to add make sure the reamer is not filing with
>chips. The hole is quite deep the chips might pack up in the reamer then it
>will leave a oversize hole and a poor finsh.

You are absolutely right and my fault for not mentioning it. Even more so as I
was reaming out valve guides on the lathe today and taking care to ensure that
I didn't get caught out by that too.

It raises another couple of points about reaming though. I was reaming
horizontally of course and over about 1.5 inches also. Much more chance of
swarf not coming out during horizontal reaming than vertical. Also I was using
a taper start hand reamer in a drill chuck rather than a machine reamer. I was
only taking out about 2 thou thou and there was enough room in the flutes for
the swarf to collect but I needed to brush them clean before each new guide.
With the first inch of reamer being tapered and blocking inside the workpiece
there is not much room for swarf to get out.

On the brass job in the original post I would suggest a machine reamer that
cuts on the front bevel lead rather than a taper hand reamer that cuts on the
taper lead. Machine reamers push the swarf ahead of them more than taper
reamers. If swarf causes a problem then drill tighter to size and ensure that
plenty of coolant is going down the flutes. A reamer will work happily enough
on small cuts but will tend to rub and blunt the edges. The Dormer reaming
handbook suggests 15 thou for a 7/16 reamer or 10 thou if core drilled prior to
reaming. I should have looked it up before my first post as my suggestion of 20
thou was a bit too much. Given that the job is probably vertical on a mill and
the cut was about the suggested 15 thou then I still think speed is the main
problem. Let us know how you get on though please.


Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work. .

From: Dave Baker
Subject: Re: reaming holes in brass
Date: 05 Feb 1999
Newsgroups: rec.crafts.metalworking

>From: dcbrouse@yahoo.com
>
>I should have mentioned that I was using a machine reamer and that the part
>was on a lathe, so the hole was horizontal.  The reamer must have become
>packed with chips.

Ah - now you tell us :)

>  I will try this again with the part mounted vertically in
>my mill.

Not necessary - see below.

> I should also mention that I wasn't using any lubricant.  I was
>under the impression that it wasn't needed when machining brass.

Eeeek - cast iron is the main material that is machined dry. Brass and bronze
should be machined with lubricant ideally but your main problem is swarf
clearance in reaming not the lubrication aspect.


>  The mill I
>am using is a Sherline and I don't have any way of lubricating the reamer
>other than brushing it on.  Will this suffice?

No


To ream 15 thou over 1.5 inches in one pass is way too much swarf for the
flutes on a reamer to cope with horizontally. You should have been able to
"feel" the reamer picking up and binding even winding through on a tailstock.
The first half inch would have cut fairly easy then it would have got all stiff
and icky probably. I bet you didn't drill straight through without frequently
pulling the drill out and clearing the swarf !!

If you have a boring bar then drill to 1/64 under and bore to within a thou or
2 - then ream. Or ream a quarter inch at a time and pull back to clear the
flutes. You'll soon get a feel for the length you can ream on each pass before
the flutes clog. If you have to keep pulling back the reamer then ream really
slow. This will help offset the tendency of the reamer to cut oversize on
repeated passes.

A good tip for lubricant when reaming is not to direct the nozzle at the start
of the job but to let the coolant flow down the length of the reamer. By the
time the coolant gets to the start of the job the flutes will be full of
coolant in a nice laminar flow which will help evacuate the swarf at the tip.

If you don't have a suds pump on the lathe or mill then use a washing up liquid
squeezy bottle. A mix of 3 or 4 parts paraffin to 1 part engine oil will do a
decent job on brass (and most other stuff) if you don't have cutting oil.

Final tip for reaming on a lathe - if you are taking small cuts of a few thou
then no need to wind through on the tailstock. Just leave the clamp off and
push the whole tailstock through by hand. This will help you feel the pressure
needed and if the reamer binds up you'll know straight away. Also it's far
quicker and as soon as you feel the pressure slacken off you know you are
through the job and can pull straight back out and get on with the next one. It
also helps the reamer self centralise if the tailstock is not set up dead true
to centreline.

Like anything in life, machining is not about charts of feeds and speeds and
angles of cutting tips etc etc - it's a matter of feel and experience and what
you know works for you on a particular material and a particular machine.
There's an old saying that a good machinist on a bad lathe is better than a bad
machinist on a good lathe.


Dave Baker at Puma Race Engines (London - England)  - specialist flow
development and engine work. .