What size do i drill a brass cylinder in order to ream it 5/16 “

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What size do i drill a brass cylinder in order to ream it 5/16 “

This topic has 11 replies, 9 voices, and was last updated 12 February 2012 at 02:26 by David Littlewood.

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10 February 2012 at 20:36 #5938
Chris machin
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@chrismachin
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10 February 2012 at 20:36 #84330
Chris machin
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@chrismachin
Can someone tell me what size drill do i need if i am to finish up using a 5/16″ reamer ? (its in brass)

Also any good links to tables / charts for cutting speeds / tapping sizes / thread info e.t.c.

Thanks in advance

Chris.
10 February 2012 at 21:34 #84337
Martin Walsh 1
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@martinwalsh1
I would use a 7.8mm Drill

Best Wishes Martin
10 February 2012 at 21:36 #84339
Martin Walsh 1
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@martinwalsh1
I always use a zeus chart you can get them on ebay

IMHO a absolute must have

Best Wishes Martin
10 February 2012 at 21:37 #84340
Terry Lane
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@terrylane
19/64″ if you can rely on your drilling being straight. I think I would drill it 9/32″ tho, and true it up with a little boring bar until the 5/16″ reamer ‘just won’t fit’ and then have at it.

Alan Stepney’s pages are a good place to start for data.

Alan Stepney’s pages
10 February 2012 at 21:56 #84345
Sub Mandrel
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@submandrel
I’m with Tel. After years of angst, I eventually decided to trust the manufacturer’s advice to give the reamer work to do. For my shunter I have reamed some dozen holes 5/16″ in cast iron, steel and phosphor bronze. I drilled 19/64″ for each one and they all cam out dead to size – so dead to size that dead on 5/16″ bar is a stiff push fit.

I use a hand reamer in tailstock, mill or drill press at a slowish speed (but not to slow) and it goes through like a dream.

Neil
11 February 2012 at 13:00 #84397
MadMike
Participant
@madmike
Neil, if you mean that your bar dia is exactly .3125. Plus 0, minu 0 then it follows that it will not enter a .3125 hole, drilled, reamed or bored unless the hole is oversize.

A “stiff push fit” would indicate a hole that may actually be .005 larger than the bar. Remember a 1″ peg will not go into a 1″ hole as it is technically an interference fit.

Having said that your advice on sizes etc is very good advice…..however remember again that you may need to adjust for different metals and the condition of your reamers.
11 February 2012 at 13:11 #84398
David Littlewood
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@davidlittlewood51847
Mike,

As I understand it, the standard tolerance for reamers is to cut very slightly oversize – probably a few tenths for a 5/16″ reamer. This is because reamers are intended to give a good quality finish for a good bearing surface; thus it follows that you don’t want a hole dead on size, for the reason you mentioned. Drill bits, by contrast, are toleranced slightly undersize to give force fits (though in amateur use are likely to cut over nominal size).

David
11 February 2012 at 13:27 #84402
mgj
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@mgj
Depends on the reamer tolerance, but the standard H5 should cut about .0005 oversize. Nominal bar should be a touch undersize.

As for getting reamers to cut to size, I always understood it depended a bit on the reamer. A machine reamer tends to be more tolerant of being asked to take a bit of chunk.

The problem is howerver, less one of cutting to size, but if any length is involved, cutting straight. Where that is important, I’d be inclined to bore to within about .005 of finished diameter, and then I know that either kind of reamer will cut both straight and to size – because by the nature of the beast, its difficult to guarantee that a drill will do either.

OTOH, if its not critical, then I’d drill 1/64 or so undersize and put a reamer though.
11 February 2012 at 13:38 #84403
chris stephens
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@chrisstephens63393
Hi Guys,

For those who like to give the reamer something to do (an admirable sentiment), as opposed to just rubbing, do make sure that you clear the flutes often, for failing to do this the reamer will surely cut oversize and badly.

chriStephens
11 February 2012 at 16:25 #84431
colin hawes
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@colinhawes85982
The amount a reamer should take out varies wih its diameter, about 5 thou for small ones eg. 1/8″dia , 8 thou up to 3/8″ and 8 to 12 thou above that .The drilled hole has to be a reasonable finish and should be done with an undersized drill first then opened up with the reaming size drill.Reamers over 5/8″ dia should be o.k. at 1/64″ undersize hole.As with all cutting tools, the reamer needs to be sharp.

Colin
12 February 2012 at 02:26 #84492
David Littlewood
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@davidlittlewood51847
Also, remember to keep the reamer turning in the cutting direction even when backing it out; reversing the rotation is said by the makers to blunt the edge.

David
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