Chucking reamers... Are they necessary?

[Benjamin Borowsky]

I'm building a machine from a plan and it states numerous times that a hole should be drilled and then reamed out. It seems to be for two different reasons. The first is to make a snug fit for bolts. For example, a 1/4" bolt has a 1/4" hole drilled, and then a .251 hole reamed out. Another example is an injection rod having it's hole reamed out to .501, when the rod is 1/2".

A) I'm having trouble finding chucking reamers in these specific sizes.
B) The one's I've found haven't been cheap.
C) I find it hard to believe that each hole, to a thousandth of an inch, needs a seperate reamer.

Can a boring head do it? Can an adjustable reamer work (Harbor Freight has them, are they good? Do they work? Are they worth the money?)

As always, any comments appreciated. Thanks,

B2

[bdarin]

For the oversize reamers, Enco (among others) sells chucking reamer sets in the over/under size set, ie, .249, .251, .374, .376, etc. The adjustable reamers are hard to adjust...adjust, cut, measure, tweak adjustment, cut, measure, and so on till the size you want is reached. Too much hassle for me, I'll stick with the over/unders.

[Kerry.S]

Mc master car also has over and under sized reamers. but don't drill them on size or the reamer will fall right through. you need to drill atleast 1/64 to 1/32 under size depending on the material to leave enough to clean up.
Kerry

[Al Messer]

Benjamin, as a general rule, if your drill bits are not sharpened "dead on" they will drill a thou or two over-sized anyhow.

[John Garner]

Benjamin --

Can 0.251 inch or 0.501 inch holes be bored with a boring head? Sure, but the smaller or deeper the hole, the more difficult the boring becomes. The price of the reamers will probably look downright cheap after you try boring a 0.251 inch hole or two.

A second point or two: Standard 1/4 inch fasteners are always several thousandths of an inch under 0.250 inch diameter on their unthreaded shanks, and lower-grade fasteners may have very-nearly-pitch-diameter shanks that are WAY under the nominal diameter. For this reason, using fasteners to locate one part relative to another is not considered to be good design practice.

Yes, there are some SPECIALIZED fasteners with over-nominal-size shanks that are designed to be press-fitted into place, but the average person probably doesn't run into this type of fastener in a lifetime. I would guess that this type of fastener is most common in aircraft and spacecraft structural applications, and even here they're pretty rare. (Maybe I've encountered them twice since I started in the space business in 1975.)

John

[Al Messer]

I meant to ask in my first post: what sort of machine are you building? And as an after thought, by "step-drilling the holes, and using a brand new sharp bit to take out the final 1/64 th inch, many times you can get by without a reamer.

[s7hss]

Ben,

For some classes of work, reamers are necessary. Consider a twist drill a roughing tool as they usually cut a little oversize. A reamer is used to make a drilled hole round, accurately sized and to leave a good finish inside the hole.

A) Try the following places:
http://www.mscdirect.com
http://www.mcmaster.com
http://www.use-enco.com
All carry chucking reamers.

B) Nope, they're not cheap. Good incentive to treat them carefully i.e. store them so they don't get knocked around. You probably won't have to buy them twice, though.

C) Each distinct size calls for its own reamer. Way it is. A .501 reamer can't finish a hole to .251 and vice versa. If you're building a machine, taking care here is usually worthwhile in the long run.

Consider this the beginning of your tool-buying habit. Accept it now. Plan for it to exist. Your life will change in ways you can only dimly perceive. 8->

Me, I don't like adjustables. There's no way to accurately control the size and the design is prone to chattering. To offset the expense, buy the good ones as needed. Spiral flutes seem to cut with less chatter than straight flutes. You could always make a D-bit reamer from drill rod if you felt like doing some toolmaking.

A boring head can do it, but if you have to finish fifty or a hundred holes of the sizes you mentioned, you'll be wishing for the reamer. Hope some of this helps.

So what machine are you building?

Tom

[Benjamin Borowsky]

Thanks, guys. The enco over/under set wins.

I'm building Gingery's plastic injection molding machine. Since I know nothing about metalworking or plastic injection molding, expect more questions....


As always, thanks a bunch.

B2

[spope14]

I believe this was in the BEDSIDE READER. There is a way to make reamers cut OS or undersize. I have tried both, and they work.

Oversize method:
1. Put a piece of wood, say a match stick, in one flute of a reamer. Done after reaming the initial hole, or even before. best after. This will cause the reamer to cut "off kilter", not to be confused with off center, as the reamer still follows the hole. Check, maybe add a bit of wood more or make it stick out again, then cut again until desired size. The key is the wood touches the hole above the flutes, but is compressed enough to cause a bit of OS cut action.

#2. Find an old carbide insert. Run the carbide insert inside the flute along the general edge of the flutes, the full length, thus raising the edge slightly, like a burr. Not the tip, but the full length edges. This will give .0005 to .0015 OS cut. Start small and work up.

Undersize:

Use the carbide method again, but running on the outer edge, running the flute edge in.

Have tried all of these, they work well.

To return a reamer to size after the burr method, run the carbide the opposite ways OS or US, or for gawds sake, remove the piece of wood.

Just a few hints if you are in a pickle.

[Peter S]

In my experience a 'standard' size chucking reamer (ie machine reamer) will give you the oversize you seem to want, eg a 1/4" machine reamer will give you something larger than .250", possibly up to .251".

You should be able to avoid buying strange oversize or undersize reamers.

I think a 'standard' reamer will always cut over the nominal size, however a hand reamer seems to give a tighter fit, eg when you want to hammer in dowels.

However, if you just want a good fit for your bolt, then just drill 1/4".

If you really want a reamed 1/4" hole, you would drill undersize (say .010") and then ream to finish size. (A hand reamer would need less material).
Reamers need to have something to cut, otherwise they may just burnish the hole. Use speeds say 2/3rds that of drilling, higher feeds than drilling and plenty of sulphurised oil.

Without knowing more detail, hard to advise. Generally, if you want good location of parts, then dowels or machined shoulders etc. are used, not the bolts. The bolts would have clearance holes.

As for adjustable reamers, if you mean the true adjustable type (ie several blades adjustable for size) they are useful at times, but require a through hole in the workpiece. The ones I have used are hand type and prone to chatter. I certainly wouldn't normally use them for bolt holes etc. There could be other adjustable types that I haven't seen. (eg floating type)

There is another type of machine reamer sometimes called 'adjustable' but a more correct description is 're-grindable'. A capscrew in the end allows you to increase the reamer diameter by a few thou and then re-grind it to size.