Reamers

Hi Jim:

I have always worked on the basis that straight-fluted are for hand use, while spiral ones are for machine use.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk

snipped-for-privacy@easynet.co.ukhttp://www.oldengine.org/members/dieselhttp://www.stationary-engine.co.uk So did I. But then if you look through various mail order catalogues, the distinction becomes a bit unclear. I've seen both spiral & straight described as hand and 'chucking'. (Have a look at 'Chronos' and 'Engineers toolroom' for example.) I think reamers with a helix generally cut easier than straight ones. For Jim's info, hand reamers will have a distinct taper 'lead in', where machine reamers have very little. regards Mike

As far as I know: straight reamers are for general purpose and fine/accurate cuts. Spiral reamers are for harder materials and deep/interrupted cuts: the spiral doesn't jam so easily in a non-round or interrupted hole, and shears the swarf away so it doesn't pack in the flutes so much. Clearing swarf is important when machining, so I guess that's why the spiral/helical form is preferred.

HTH Guy

You need to understand the purpose of the flutes in any machining tool and then most of it will become apparent. Let's start with a drill bit. Drills must be able to drill into material from scratch so they are by definition creating a blind hole. They could also equally be enlarging a blind hole already made by a smaller drill. This means that the swarf must be pulled back out of the hole by the tool and therefore the flutes must operate in the same direction as the tool rotation i.e. right handed flutes.

Reamers are always enlarging an existing hole and also not removing much stock so the swarf is less of a problem. Also most reamed holes are through holes. The flute direction is therefore usually left handed to push the swarf through the hole and make sure the flutes do not clog which would abrasively create an oversized hole. The other advantage of a left handed flute is it doesn't pull the tool into the work which could lead to chatter if the tool 'overtakes' the driving force behind it. In hand reaming this could also mean the tool jams in the hole. Both of these things lead to better hole sizing and finish. They also indicate that reaming works better in the vertical direction than the horizontal so that the swarf falls away from the tool. However this should not prevent lathe reaming in the horizontal plane if the stock removal is correctly sized.

For reaming blind holes a straight flute is usually better although if the stock removal is correct the reamer should still not clog in short holes because the flutes have sufficient void volume to contain it. It does tend to indicate that you might want to drill closer to finished size with blind holes than through holes.

In no case does the flute direction indicate whether the reamer is a hand or machine (chucking) reamer. This is determined by the 'lead in' to the parallel section. Hand reamers (fixed or adjustable) have a fairly long tapered lead in (an inch or so) which self centralises the tool. Chucking reamers have a very short lead in because the tool is centralised by the machine and the action of the bevel. In both cases the tool only cuts on the bevel of the lead in and not on the flutes which are there solely to position the tool in the finished hole. Regrinding a blunt reamer therefore means that only the lead in is reground and not the full length of the tool, as with a drill bit.

In summary therefore you shouldn't be concerned with the flute direction other than sometimes for blind holes.

The most important thing to get right is speed. Traditional wisdom was to ream at half the drilling speed but IMO this is usually far too high, especially on non rigid equipment. Even with small reamers 100-200 rpm is fine for most purposes. High speeds create chatter and oversized holes.

In message , MikeH_QB writes

[snip]

At the risk of stating the obvious, a square end would seem to indicate hand use while an MT end can only be for machine use. But, of course, some are neither square ended nor MT ended.

Can I ask if there is a "rule of thumb" regarding drill size for a particular reamer size? For example, if reaming to 1/8", what should the drill size be?

Cheers, Paul

Useful chart here:

Looking at the allowances though, I'm sure that these are for machine reaming, i.e under power. For hand reaming I would allow less than these figures, perhaps by as much as 30-40%.

Peter

It depends a lot on the quality of the drilled hole. The Dormer handbook distinguishes between pre drilled holes and pre core drilled holes (a core drill is a special multi fluted drill designed for high accuracy). The handbook advises against leaving too little stock for the reamer to remove which is meant to promote rubbing and wear of the reamer.

In practice however for low volume and home shop applications none of this is likely to be relevant. As long as there is some stock left and the hole is straight enough to clean up I find any reamer works just fine. The less stock removal the better IMO. For small sizes (up to 10mm) I always double drill and finish off at about 0.1mm below finished size at a slow drilling speed, say 200 rpm. The key to accuracy with a drill bit is slow speed for the final cut so it doesn't chatter and cut oversize. If the drilled hole is not dead straight you might need a tad more than this but careful double drilling usually works well enough. For larger holes, up to say 25mm I'll leave about 0.2mm in.

Recently I had to enlarge some existing cast iron valve guides from 8.0mm to

8.04mm for use with different valves and had no trouble reaming them out and the cut was clean and sharp.

As for speeds the handbook suggests half the drilling speed but even so says "in fact present ideas tend to reduce this even further." Well they certainly do and IME if you use anything like half the suggested high volume drilling speeds you'll run into a lot of trouble on light equipment with chatter and oversized holes. I find 200 rpm to be fine at 8mm for example and half that maybe for much larger reamers. Basically it's whatever works best for you and your equipment but start slow and work up to higher speeds if the equipment and material will take it.

Remember that most advice you'll see on speeds and feeds for anything are biased to high volume production work on rigid machines to get the job out as fast as possible with 'acceptable' tool wear. For shop use if you go slower you won't be wasting much time anyway and the tooling will work better and last much longer.

Gentlemen, thank you for this info. In my ignorance, I've been reaming small diameter holes in stainless and aluminium for years at the same speed used for drilling (on the lathe).

However, I've yet to wear out a reamer, despite this unintentional "abuse" (broken a couple mind :D ).

Apologies for hijacking the thread.

On or around Thu, 17 Jan 2008 09:02:26 +0000, Peter Neill enlightened us thusly:

reaming under power, I have no hassles with taking a 3/4" drilled hole out to 20mm.

On or around Thu, 17 Jan 2008 10:28:06 -0600, Mr Crane enlightened us thusly:

I tend to run drills on the lathe not that fast, anyway. Quite apart from anything else, the lathe is flat out at about 1200, which is slow for any drill under about 8mm.

You've got it good. Just think how us poor sods with Myfords have to cope....

Peter

Actually, don't tell anybody, but Myfords can be run noticeably faster than the manual says without the world coming to an end. Properly adjusted and oiled, the headstock bearings can run barely warm to the touch at 1500rpm. The countershaft bearings are a bit more marginal, though. One day, I see a pair of needle roller bearings creeping into that location :-)

Mark Rand RTFM

I can't pedal mine that fast

Peter

Inverters are nice. So are home made motor pulleys :-)

Mark Rand RTFM

So my variable speed chinese lathe spinning my asian ER32 collet chuck at

3000rpm (3/10s TIR repeatable) is better than a Myford? ;-)))

Steve

On or around Sun, 20 Jan 2008 11:31:55 -0000, "Steve" enlightened us thusly:

I could in theory get the Student to run at 2400 by fitting a fast motor, but I think it'd need the gearbox bearings upgrading. The spindle is in rollers and would probably manage OK.

However, that would lose the low (about 54, I think) speed, which I also use.

The other possibility would be to change the belt drive for a V belt one and install 2 different pulley ratios, which could, done right, double the number of gears, give a wider range and more intermediate speeds.

Or, of course, fit a variable speed motor.

When do you use 3000rpm? And how much torque is available at very low speeds? I have fitted a VFD to my Viceroy, now up and running. I can take it down to about10 rpm with reasonable torque. At 1300 rpm it happily today turned some freecutting steel from 6mm od down to 1mm. A lot noisier than your chinky though.

On or around Sun, 20 Jan 2008 15:24:25 +0000, Richard Edwards enlightened us thusly:

The student is a bit noisy, too. partly that's gear-driven lathes for you. It's also a 1960 machine and looks not to have had too much TLC for at least half its life. Still prettty good, mind - the worst issue (yet to be addressed properly) is play in the crossfeed. I'm inclined to get a spare nut and screw and then try to convert it, using either one nut cut in half or 2 nuts, to the same kind of adjustment that the Mk 2 has.