How to ream a hole

[j45on]

I need to ream a 12 mm through hole in some brass parts I am making.
And also a 12mm blind hole in a blank MT2 arbour.
I'm looking at the "HSS Metric Parallel Hand Reamers (H8)" from Arc Euro http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/HSS-Reamers
I am presuming that the parallel part is the cutting end and not the shank is that right ?
And how close do I drill the hole to final size ?
Lube or no lube ?
Any other reaming tips would be greatly appreciated 

[kwackers]

My understanding is that parallel is the shank.
All reamers have 'lead in', I believe machine reamers have less than hand reamers though.

If you want a flat bottomed hole I suspect boring it is the best way. Making up a cutter would be fairly easy too, might be worth considering.

What works for me, is to drill a size down as close as possible (0.1mm metric or 1/64th imp) and then machine ream it fairly slowly (say 30rpm) with a bit of lube brushed in and a decent feed rate. Too much RPM and I find I end up with hexagonal holes!

[arnoldb]

Hi Jason

Parallel in the case of the hand reamers you linked to means "parallel through hole" as opposed to taper reamers which are used to ream taper holes such as for Morse tapers or taper pins.
Parallel hand reamers do have a longish tapered tip and are not suitable for reaming blind holes... - You'd have to get a machine reamer for that, or make up a d-bit.  My 12mm parallel hand reamer runs taper to about 30mm along its length before it actually becomes parallel.

I found an 11.8mm drill to be the best companion for the 12mm reamer; it leaves enough meat to prevent chatter, but easily reams out as there is not too much metal left to remove.  I ream brass dry.

As to tips... Don't force the reamer - just use a steady light positive pressure.  If it starts to feel tight to turn, remove it (turning it all the time while removing) and clean the chips off then continue.  Never ever reverse it - even when removing it from the cut.

HTH

Arnold

[jim]

i'd be inclined to bore the hole.

if you ream, i'd leave 5-10 thou, but try it on some scrap first, to make sure the ream cuts ok.

[j45on]

Cheers guys 
I shall bore the blind hole and order the reamer for the brass bits